CAESAR II® Online Video Training Series
CAESAR II®
Statics One
Written by David Diehl
Director of Training, Intergraph® ICAS Division
Training when you need it - anywhere in the world
SM
CAESAR II® Statics One
David Diehl, Course Author
Produced and Edited by Anthony W. Horn
First Edition - February 2015
©2015 CAD Training Technologies, LLC Houston, TX USA
http://www.pipingdesignonline.com
No duplication permitted without express written consent
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Welcome to these Special Videos for Learning
CAESAR II® Statics!
These CAESAR II Statics One training videos are the second in our video
training series for CAESAR II software. These lessons were developed by David
Diehl, the Director of Training at the Intergraph® Corporation, and are designed
to teach you CAESAR II in the easiest, fastest way possible. As you watch the
videos and follow along doing the exercises you'll learn many of the commands,
features, and techniques that will make you more productive and accurate in your
work. It won't take long before using CAESAR II becomes automatic and you'll
master its intricacies as you explore the world's leading pipe stress analysis
system!
So thank you for your commitment to training, and let's get started!
Anthony W. Horn, Editor
2015
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Trademark Information
The material, applications, and routines presented in this book have been
included for their instructional value. They have been tested for accuracy, but
are not guaranteed for any particular purpose. The author and copyright holders
do not offer any representations or warranties, nor do they accept any liabilities
with respect to this video and written material, instructions, software applications,
or routines. This material in these documents and accompanying videos is solely
owned and copyrighted ©2015 by CAD Training Technologies, LLC, Houston,
Texas, USA. Duplication in any manner is strictly prohibited without express
written consent. All pipe stress analysis should be done according to the
appropriate piping codes and under the direct supervision of a professional
engineer.
Trademarks
Intergraph®, the Intergraph logo®, PDS®, SmartPlant®, SmartMarine,
FrameWorks®, SmartSketch®, I-Route, I-Export, ISOGEN®, SPOOLGEN,
SupportManager®, SupportModeler®, TANK, PV-Elite, CADWorx®, CADWorx
DraftPro®, GT STRUDL® and CAESAR II® are trademarks or registered
trademarks of Intergraph Corporation or its subsidiaries in the United States and
other countries. Microsoft® and Windows® are registered trademarks of
Microsoft Corporation. MicroStation® is a registered trademark of Bentley
Systems, Inc. AutoCAD® is registered in the U.S. Patent and Trademark office
by Autodesk, Inc. Other brands and product names are trademarks of their
respective
owners.
Intergraph® provides the programs, CAESAR II®, PV Elite, GT STRUDL and
CADWorx® Plant Professional, “as is” and with all fault. Intergraph® specifically
disclaims any implied warranty of merchantability or fitness for a particular use.
Intergraph® Corporation does not warrant that the operation of the program will
be uninterrupted or error free.
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About the Author and Editor
Drawing from over 30 years of engineering, technical
support, and training experience, David Diehl has created
an outstanding course in CAESAR II Statics One. Serving
as the Director of Training at the Intergraph® Corporation,
Mr. Diehl is recognized as one of the top CAESAR II trainers
in the world. Now you can benefit from his experience as he
shares with you his knowledge of using CAESAR II software
in a powerful, yet easy to understand course.
Anthony Horn, the Editor of this video training series and
author of the CAESAR II Fundamentals Course is the owner
and creator of PipingDesignOnline.com. Launched in 2011,
PipingDesignOnline.com has issued over 1700 certificates
in CADWorx and CAESAR II software in more than 40
countries, and is the largest Intergraph CADWorx and
Analysis Solutions software training organization in the
world.
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CAESAR II Statics One
Table of Contents
LESSON 1
Video 1
Starting the "Simple" model ...........................................................................
1
Video 2
Using the Interface, Adding Restraints and Tees, Viewing the Model ...........
6
Video 3
Using the List Feature, Analyzing and Viewing Results.................................
9
LESSON 2
Video 1
Using the Simple Model, Viewing Deflected Shape, Modifying Display ......... 18
Video 2
Expansion Stress Formula, Types of Stresses Considered ........................... 31
Video 3
Stress Cube, Morh's Circle, Expansion Stress Formula Examined ............... 36
Video 4
Axial Stress, Stress Intensification Factors .................................................... 41
Video 5
Torsional Stress, Flexibility and Stress Intensification Factors ...................... 44
Video 6
Calculating Expansion Stresses using Mathcad, Comparing to CAESAR II .. 49
Video 7
Calculating other Stresses using Mathcad, Comparing to CAESAR II .......... 57
Video 8
Operating Load Case and Stresses, Code Stresses ..................................... 65
LESSON 3
Video 1
When Spring Supports are Needed ............................................................... 72
Video 2
Calculating Dead Weight in the Hot Position, Load Variation ........................ 77
Video 3
How the Anvil® Catalog Works ...................................................................... 81
Video 4
Hanger Load Cases ....................................................................................... 85
Video 5
Example Selection, the CAESAR II Hanger Report ...................................... 88
Video 6
Hanger Report, Hanger Design Data, Actual Installed Load ......................... 93
Video 7
Hanger Selection Problem ............................................................................. 97
Video 8
Evaluating the Hanger Selection.................................................................... 103
Video 9
Modifying the Design to Improve Results ...................................................... 109
LESSON 4
Video 1
Review of Hanger Design ............................................................................. 114
Video 2
Hanger Control Settings in the Configuration and Piping Input Areas ........... 117
Video 3
3
Hanger Control Settings in the Input Spreadsheet .................................. 126
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Video 4
Additional Hanger Control Settings in the Input Spreadsheet........................ 131
Video 5
Hanger Control Settings in the Load Case Editor .......................................... 135
Video 6
A Detailed Review of the Hanger Reports ..................................................... 138
Video 7
Verifying and Modifying Hanger Selections ................................................... 143
Video 8
Things to Watch For in Hanger Selection ..................................................... 149
Video 9
When to Design Using Actual Cold Loads ..................................................... 154
LESSON 5
Video 1
Starting the Turbine Model............................................................................. 158
Video 2
Completing the Model, Including the Intake Section of the Model ................. 167
Video 3
Analyzing and Viewing the Deflected Shape ................................................. 174
Video 4
Adding CNodes, Filtering Results for Viewing ............................................... 184
Video 5
Analyzing the Turbine using NEMA SM23 ..................................................... 192
Video 6
Adding a +Y Support to Improve the Results ................................................. 203
Video 7
Changing the +Y Support to a Spring Can to Improve Results...................... 209
Video 8
Modifying the Piping Geometry to Increase Flexibility ................................... 217
Video 9
Verifying the Turbine Design Results............................................................. 228
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PipingDesignOnline Video Training
CAESAR II Statics - Building the "Simple" Model
CAESAR II Statics - Building the Simple Model, Video One
(Reference Video: C2_S_L1_V1A)
1. Here's the system that we're going to build for our exercises in the beginning of this section.
It's a very simple system going from an anchor, a horizontal run, and to an elbow. It's 8-inch
pipe. From the elbow it travels down to another anchor. The line has a reduced tee in it. The
outlet will be a 6-inch branch coming off of an 8-inch header.
We see the symbol for the CAESAR II coordinate system in the lower right area of the screen.
This model will give us all the basic components we need to talk about stress. We'll have an
elbow and a tee with their stress intensification factors. We'll heat the line up to get some load
in the system and, from that load, we can calculate stress. So this is the model we're going to
build right now.
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CAESAR II Statics - Building the "Simple" Model
2. The basis of this model is to develop the terms involved in calculating code-defined stresses
and then, evaluating those stresses. It's a very simple model. So we'll start a brand a job.
3. Click New.
For the file name, enter "Simple."
Place it in the CAESAR II Models folder (located in
the files you downloaded for you course files).
\CAESAR_II_Statics_Support_Files\CAESAR II
Models
We’ll use this same folder for the models we build in
this course.
This folder has a configuration file in it which it will use for jobs in this folder, and it sets our
units.
4. Yes, we are running metric units here in this course. The temperatures are in centigrade. The
length, OD and wall thickness of a pipe will be in millimeters.
Note that we'll have the Nominals setting turned ON. This will let us call out 8-inch pipe by
name (8), and it will put in the proper actual OD. We can enter S for standard wall, and the
system will give us true wall thickness at that condition.
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CAESAR II Statics - Building the "Simple" Model
5. Click OK and the system start the input processor.
6. The display shows the first element, 10 to 20.
Now we'll model the line.
7. In the DX field,
Type: 3000 <Enter>.
In the Diameter field,
Type: 8 <Enter>.
Notice the system puts in 219 in the diameter field (219
mm).
Also the system sends a message in the Status field that it
converted the nominal size (8") to the size in millimeters
(219.0750).
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CAESAR II Statics - Building the "Simple" Model
8. If you hover the pointer over the Wt/Sch field you'll see the
system shows mm for the units.
Type: S <Enter> (for a Standard Schedule).
The system will enter in the proper wall thickness.
If you have any question on what value to put in
there, Click in the field and press the Function 1,
or question mark key, and it will open up the help
file. It shows help on entering wall thickness, and
it gives examples. There's the S that was just
entered, standard wall.
9. Corrosion-- we don't have any corrosion here, leave this field blank.
10. Pipe density will come in when I've specified the material.
11. Fluid density-- This line will be filled with water.
Type: 1sg <Enter> in the Fluid Density field.
Make sure to enter the sg (for Specific Gravity) or your values will be much too large.
12. In the Temp 1 field,
Type: 250 <Enter> (for 250 degrees centigrade).
13. In the Temp 2 field,
Type: 21 <Enter> (for 21 degrees centigrade,
our ambient temperature).
You can find the ambient temperature used in this configuration by
clicking the Special execution options button. The system defaults to 70
degrees Fahrenheit, and when using metric units converts that to 21.114
degrees centigrade.
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CAESAR II Statics - Building the "Simple" Model
14. In the Pressure 1 field,
Type: 25 <Enter>.
15. Double click the Bend check box.
You'll see Long in the field under Radius (you may have to expand your input screen to the
right to see this field).
The system puts in a Long Radius by default.
The system displays nodes 18 and 19.
Node 18 will be on the weld line for the elbow on the horizontal run.
Node 19 is at the midpoint of the elbow.
Node 20 is at the weld line for the elbow at the end (in the vertical leg down).
The system will calculate stress at three points around the bend.
16. Double click the Restraints check box.
Click Anchor and verify it is on node 10.
17. In the Material field,
Click in the field and
Type: a106 <Enter>.
The system displays several choices (grades) for A106.
Double click on the row - Grade B.
This material has an index value of 106. So if you type 106 in the Materials field in the future
the system will use this material.
You can see the system fills out other fields it can derive from the material selection.
18. The system has now filled out the values for Pipe Density, Young's modulus, and Poisson
ratio.
19. To see the strain associated with this pipe,
Double-click on the Chevron by the Temp1 field.
The system displays the value for the thermal expansion rate, 0.002877 millimeters per
millimeter.
20. We see also that the system has displayed values for the allowable stress.
We have B31.3 selected for the default piping code.
CAESAR II has many piping codes in the program, but we'll use 31.3 for this example.
The Cold Allowable Stress (SC), or basic design stress ambient condition is 138 MPa.
When the system is at 250 centigrade, it drops down to 132 MPa (SH). That came all in with
the selection of material.
Get you model to this point and we'll continue after that!
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CAESAR II Statics - Building the "Simple" Model
CAESAR II Statics - Building the Simple Model, Video Two
(Reference Video: C2_S_L1_V1B)
1. Continuing on, you'll notice that in almost every job, this first element usually takes more
time than any others because that's where a lot of these items are initialized. Most of this
information will be carried on throughout the rest of the model, and we won't have to spend
too much time resetting many of these values.
2. Click the Continue
button.
The next element will be from 20 to 30.
In the DY field,
Type: -2000 <Enter>. (You don't have to type mm)
Note that the program automatically is incrementing the node numbers by 10.
Because the program's doing that, I'm assuming that as well. You have a choice in any kind of
increment on these node numbers that you wish.
3. To display the node numbers,
Click the Node Numbers button on the toolbar.
4. Now why did we stop at node 30? That's where our welding tee is.
5. Double click the SIFs & Tees button.
6. Verify node 30 is displayed in the field.
For Type, select Welding.
This sets a welding tee at node 30.
7. Click Continue.
In the DY field,
Type: -2000 <Enter>.
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CAESAR II Statics - Building the "Simple" Model
8. Double click Restraints.
Select Anchor (for node 40).
9. The program assumes that once you start a model, that you're specifying a restraint at the
end node (the to node). So that's why node 40 was displayed in the field automatically
when you were ready to select an Anchor. If you recall in the very first element, the
system displayed node 10 in the field. That's because with the first element, the system
figures you're starting from a boundary condition like an anchor.
10. All right, now we're going to put our branch in from node 30 to node 50 in the Z direction.
11. Click Continue.
In the From field, where it says 40, delete that value and put in 30.
In the DZ field,
Type: 1500 <Enter>.
If I had the wrong direction-- I don't, but if I had the wrong direction-- I could type a negative
here and the model would display the branch going in the negative Z direction. We won't do
that. We'll have it modeling in the positive Z direction.
12. The branch off the tee we just modeled will be a 6-inch pipe (it will be a reducing tee).
In the Diameter field,
Type: 6 <Enter>. The system converts the nominal 6" size to
millimeters (168.2750 mm).
In the Wt/Sch field,
Type: s <Enter>. This resets the wall thickness for the 6" line (7.1120 mm).
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CAESAR II Statics - Building the "Simple" Model
13. Our last component is our anchor at
the end.
Double click the Restraints check box.
The system displays node 50 in the field.
Select Anchor.
14. So we've completed the model. That's what we're going to be running in CAESAR II
today.
It's a very simple model, but again, we do have an elbow in play and also a welding tee.
The temperature in the line will give us thermal strain. We also have dead weight which
will put its own stress on the line as well.
15. Click the Orbit button to view the line from different
angles.
16. There are several tools in the program that allow you to manipulate the plot so you can
see the important data in the model, which we'll use as we progress through the course.
OK, so we have our model complete now.
You duplicate these steps yourself and build this model. Then we'll take some time to
follow on through the process of running CAESAR II, building our Load Cases, and then
viewing our results.
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CAESAR II Statics - Building the Simple Model, Video Three
(Reference Video: C2_S_L1_V1C)
1. OK, we're going to analyze this model now. We'll review it, analyze it, and then start taking a
look at some of the results and try to get a sense for the type of numbers that we're calculating
out of CAESAR II and how they're presented to you. Before I actually do the error check, I'm
going to take a look at a few items here.
We see the OD of the line is 8-inch and 6-inch pipe.
Click the Diameters button.
This displays the pipe diameters in the model.
That's confirmed.
Click the Show Temperatures button.
The system is at 250 degrees centigrade.
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CAESAR II Statics - Lesson One Video One (C)
Click the Show Pressures button.
The system shows the pressure is at 25 bars of
pressure.
Click the Show Pressures button again to turn off
this view.
We can see the anchors are displayed, showing our boundary conditions
2. If I wanted to check the lengths of my pipe, I could go to the Element list and review them.
Click on the List button.
Select Elements.
This gives us a list of information about each element in the model.
This is a simple system, but when I view the list I see 3 meters, 2 meters, 2,
meters, 1 and 1/2 meters. This looks fine. I'm ready to do my error check
on this model.
Close the Element List.
3. Click the Start Run button to run the Error Check.
The program reviews the data.
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CAESAR II Statics - Lesson One Video One (C)
There are no errors in this model. There are no
warnings from reviewing the data. But there is one
note.
In any model we run, this note will be the center of gravity report.
4. The system shows the total dead weight of this system is 5,700 N. The center of gravity report
is based on the origin being at node 10. It shows me where the center of gravity is located.
5. Click the Load Case Editor button.
There are other, faster ways to the analysis, but I believe that on the first run of any model, you
should review all the Load Cases, all the data. So let's go look at those Load Cases.
6. Here's what the program recommends that we run. The program will recommend Load Cases
to do hanger sizing, which we don't have here. It will also recommend Load Cases to do
sustained and expansion stress calculations, according with the piping code. You might have
other Load Cases to run as well, but as far as recommended cases, these are recommended
cases here.
7. Here we see the operating Load Case (OPE). That will be analyzing the system when it's in
operation. It's got dead weight, the thermal properties and also pressure terms.
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CAESAR II Statics - Lesson One Video One (C)
8. The second Load Case is for the installed position and includes weight plus pressure. I say
installed, here it says sustained (SUS). That is a collapse check performed by the piping
codes.
9. The third Load Case (highlighted above) is the fatigue check-- Load Case 1 minus Load Case
2-- that's the expansion stress range between installation and operation expansion (EXP). So
the stress type will tell us how to calculate the stress using the code equations and also what
the limit for that stress is, and compare the calculated stress to that code limit.
10. Highlight the L3 Load Case (as shown in the previous figure).
11. Click the Run the Analysis button.
12. The next stop will be the output processor. We see there are basically three columns of data
here, or three columns to my menu.
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CAESAR II Statics - Lesson One Video One (C)
13. The three columns include the Load Cases that were analyzed, different reports for these Load
Cases, and then some general data belonging to the entire model, not associated with any
specific Load Case-- our Input Echo, our intermediate results like stress intensification factors
and flexibility factors, coefficient of expansion, dead weight of pipe-- are all in these
miscellaneous data reports.
14. Normally, the first thing I would do in looking at an output is to confirm that the model is more
correct. You might notice that Load Case 3 is in red. That's an indicator that the program has
calculated an overstress in the expansion case.
15. OK, so we have three different Load Cases that were analyzed, and we have these different
reports for those three Load Cases. We're going to bring these reports to the screen for these
exercises.
16. Click Load Case One to highlight it.
17. Click Displacements for the report type we wish to display.
18. Click the View Reports button to display the report on the screen.
19. We could also send it out to a file.
We could send it out to Microsoft Word.
We could send it out to Microsoft Excel.
We could send it out directly to the printer as well, or build up a booklet. We'll leave that for a
later assignment.
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20. This report shows where the system moves to when it goes into operation.
So the anchors at 10, 40, and 50 do not move at all. They're anchors. But the piping in
between those anchors, does move around-- and quite a bit, as we see here.
At node 19, the system moves almost 12 millimeters in the Y direction.
21. So each report that we see here is associated with a Load Case. I selected the operating
case, Displacements.
Close this report.
22. I could look at the installed, Displacements.
Click the Sustained Load Case (SUS).
Click View Reports.
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In this report we see much smaller numbers; there's no thermal strain in here.
Close this report.
23. We could also look at the operating Restraint report. This is how the piping system talks to the
outside world in the operating case.
Click the Operating Load Case (OPE).
Click Restraints report.
Here are the loads on these restraints, in N and Nm. We see some rather large loads here.
Close this report.
24. The way the program works is we find the position of each node in space for each Load Case.
Then we calculate the internal forces and moments, which then can be oriented with respect to
the pipe. From there, we can calculate stress. That's going to be our first focus when we look
at where these numbers come from. How is that stress calculated in accordance with the
piping code in play?
25. Let's take a quick look at the sustained stresses.
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26. Click the Sustained Load Case (SUS).
Click Stresses (for the stresses report).
Click View Reports.
27. We see in the report, it says "CODE STRESS CHECK PASSED."
We'll take a look at all the numbers later.
Close this report.
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28. Click the Expansion Load Case (EXP). It is displayed in red.
Click Stresses.
Click View Reports.
We see in this report that the system failed since the stresses in this Load Case exceed the
allowable values in the piping code. It looks like we're 30% over the allowable stress at a node
30.
29. Now you build your model to this point, do the error check and run the analysis of your model.
Verify you have similar results to what we show here. Your numbers may vary because of the
version of the program that you're using or maybe some small difference in the input, but you
should be pretty close to these numbers when done. Then we'll continue on from there.
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CAESAR II Statics - Calculating Stresses
CAESAR II Statics - Lesson One Video One
1. Welcome to the CAESAR II training classes video courses online. This is the second in the
CAESAR II Video Training Series. The first one was on the fundamental operation of the
program. Now we're going to talk about static analysis of piping systems using CAESAR II.
Our first focus will be on the stresses that we calculate in the program. Many people call
CAESAR II a pipe stress analysis program. CAESAR II does more than just calculating stress,
but as the major portion of the program, we'll take a close look in this set of videos on the
stresses that we calculate.
2. The stresses are a measure of the mechanical demand on the piping material, and a safe
piping system is one where the calculated stresses throughout the system are kept
below the code defined allowable limit. Now, when we say code, we mean the piping code.
In the United States, for example, that is ASME B31.3, the process piping code.
There are over 30 different piping codes in CAESAR II, and they all have their own specific
rules for evaluating stress in the piping system. We'll be looking at things such as what is that
stress that we're calculating? What is its limit? How do you design the piping system to meet
those limits?
3. When the program displays its results, it will indicate a failure in the stress calculation by the
red line in the Load Case. In this example, I'm in the static output processor and Load Case 3,
and the expansion stress range case is in red. This indicates to me that if I look at that report,
the stress report, the stresses will exceed the allowable stresses at one or more points in the
piping system.
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4. Let's take a look at the model. I'm in the CAESAR II input processor now and we're using the
model we built previously, called SIMPLE. I will go into the input processor and we're going
to review it.
5. We can see that the element from 10 to 20 was the
horizontal run, with an elbow at 20. The next element, 20
to 30, is the riser. The tee is at 30. Nodes 30 to 40 ends
the vertical run at the anchor and the reduced pipe size is
on the branch off the tee from node 30 to node 50. This is
the model that we built earlier.
6. We are now going to error check this model by clicking
on the Start Run button.
7. We see we have no errors; we can run this
model. There are no warnings issued by the
program.
8. The only item we have here is the note,
which is our standard Center of Gravity
Report. It tells us the center of gravity of
just the pipe or the whole system
together, the total dead weight. After that
the report will show the position of that
center of gravity.
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9. Usually when I run a job for the first time, I always click on each of these independently:
Start Run, then the Load Cases, and then the Batch Run.
Many users, when they build their model, will click on the Batch Run. Using this procedure
causes the system to do this error check and use the default Load Cases. This might cause
you to overlook some warning from the program. So I suggest for the first pass, you always
click on the Start Run button first and look at the messages.
10. Let's take a look at our Load Cases for this model.
And yes, this is what we expect, the operating state of the system, the installed state (OPE),
the sustained stress calculations, code stress calculations (SUS), and then the range
calculation, the displacement range between the operating and installed positions (EXP). That
is useful for the expansion stress calculations.
11. Those are the recommended Load Cases. I will click the Batch Run
button now. This is that same Running Man, at this point, that we saw
earlier. This will run the analysis.
12. The next stop will be the output processor. So here we are with the output processor of
CAESAR II. Again, this is the job Simple. We see that we had three Load Cases defined,
operating, installed or sustained, and expansion stress range. We have these different
reports available for those three Load Cases.
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13. We're going to first focus on just the overstressed case (Load Case 3, EXP). When we see a
Load Case that is in red, that indicates to me that the program has calculated stress above the
allowable in that Load Case.
14. I'll select Load Case 3, EXP, then I'll click on Stresses. Next, I want to generate a report, so
we'll click on View Reports. This will display the report on the screen. I can also send it out
to a file, send it out to a printer, or send it to Microsoft Word or Microsoft Excel. We'll display it
on the screen.
15. So here I am in the output processor. This is the stress report, Load Case 3 stresses. This is
the expansion case, Load Case 3. So we are, again, repeating the Load Case that we were
looking at. Now I have a series of disconnected column headings.
Column Headings
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16. As I mentioned before, the columns are disconnected by this stress summary. Below the
summary are the node numbers. If I scroll down, the rows in the table shift up and the table
looks complete. There's a column for node, bending stress, torsion stress, code stress, and so
on.
17. Let's take another look at the summary section of the report. The summary begins by
showing us what piping code we're using, ASME B31.3 - 2012. Again, we see the message
that the code stress check failed for the expansion Load Case.
Now, the highest stress in the system, and maybe not the only overstressed point, is listed in
this summary. Code stress at node 30 is 423.6 MPa. The allowable stress is 324 MPa. It is
30% over the allowable limit defined by B31.3 - 2012.
There are some other stresses listed as well, axial stress, bending stress, torsion, hoop,
maximum stress intensity. We'll talk about those later.
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18. If we look at the list of numbers below, we see every node in the system, 10, 20, 30, 40, 50, is
shown here. We also see some other nodes here, 18, 19. These are for the elbows.
st
1 Element
nd
2 Element
rd
3 Element
We have one elbow in the system. This is the beginning of the elbow (node 18), midpoint of
the elbow (node 19), and end of the elbow (node 20). The beginning and end could be the
same as our weld points on that elbow, and we also see they are in pairs. These are element
by element pairs.
Scanning through the numbers, here is that node 30 (near the bottom in the figure above).
Again, the summary said this node was stressed 30% over the allowable. The Ratio column
here shows it at 130 (130% of the allowable). So the row displayed in red-- and if you can't
see red, perhaps you'll notice the * star shown-- is the overstressed point. Any stress that
exceeds 100% of the allowed value from the piping code will also be displayed in red and with
an asterisk.
So our code stress is calculated as 423 MPa, and our limit was 324 MPa. We'll talk more
about these numbers later.
19. If we look back at the summary section again, these are the different types of stresses that we
didn't talk about earlier. The report columns only list values for the bending stress, torsion
stress, and the code stress. However, the summary includes axial stress, hoop stress, max
stress intensity.
Those numbers are available as well, but not through this report. Let's look for more
information on those stresses.
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20. Go back to the Output menu, and instead of selecting Stresses, I will click on the Stresses
Extended report.
This will give me an extended width of the display and put in more columns in our table. View
that report.
21. This is Stresses Extended report, stresses on each element and, yes, axial stress, bending,
torsion, hoop, maximum stress intensity are displayed in this report. As I scroll down the
columns now line up with data, and if I was interested in any of these, I would have values to
use.
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22. Now the piping code does not offer an allowable stress for these columns. Frankly I'm only
interested in the code stress and its allowable. But if you do have an interest in other
calculations or, if you want, you could use these to diagnose problems elsewhere.
For example here, our code stress is 423 MPa. It's almost all bending stress (396.09), so we
can relate it like that. Now we'll move onto a graphic representation of this data. We'll start by
closing out this report.
23. From the toolbar, I can see this elbow here.
This is the 3D Plot display button. I can click
on this 3D Plot display button and it will
open up the plot processor.
24. Along the top is the same toolbar that we saw earlier in the Input Processor, but there's
another toolbar here as well for the Output Processor. We are looking at the expansion case
here. Usually when I look at the model for the first time, I'll go to the operating case, when
it's hot and in operation, with all the weight on it.
25. Then I'll click on this first button here, Deflected
Shape.
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The system displays the deflected pipe in a bronze color, which shows the deflected shape.
The display is not to
scale, but it does give
us an idea of where
the system is moving
to when it goes into
operation.
26. If we click the Orbit button we can start to view the system.
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I can see how the branch pipe
pushes out to the riser, and I can
see how the elbow grows away,
and the bending on these legs.
This is probably what we would
expect to see. The anchors are
acting like anchors. So this visual
check is a good way to confirm
your boundary conditions, and see
if they're working properly.
27. Now let's take a look at some other things
here as well. I'm going to go back to our
expansion case, because that's what we
were looking at in terms of stress. The
change in position is now shown.
This is not a true state of the piping system, because it's the change in the piping system, but
we can display numbers on the screen as well.
28. We have this Show Element Grid
button, or we can just click on a
piece of pipe to do the same thing.
Let's click on this piece of pipe,
and now we have this grid.
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29. Hold down the mouse button in the orange header area of the grid window. Drag it up
and over to the left and snap it to the side. The grid contains all the numbers for this model.
30. Click on Stresses for the Expansion case. We can see on the element 30 to 50 the code
stress, which is 30% over the allowable. So we can easily review numbers while looking at the
plot at the same time. This is a very good way to diagnose problems in your piping system.
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31. We also have another way we can review this data graphically. Instead of looking at the
deflected shape, look at the overstressed points. We can use Stress colors by percent,
Overstress, Maximum Stress, Stress by colors by value. I want to look at Stress colors by
percent.
32. Click on the Stress colors by percent button.
Reset the plot to the Southeast view.
33. If we see red, that is greater than 100%. If the pipe is burgundy, it is between 80 and 100%.
So we see some burgundy colored pipe in this display.
34. The pipe displayed in red near the branch. To make it a little easier to see, let's get rid of
these other colors, and change them to white.
35. When the colors are set to white, and when we exit the job, these settings will be stored on the
machine. So the next time we come into this file, our updated colors will appear. Changing
the colors like this makes it easier to see that the branch off of the tee is what is overstressed.
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36. To change the colors click on one of the colors you want to change. Click the button with
the dots (browse button), select the color white, and then click OK.
Do this for each color except red.
37. Now you can see the overstressed areas of the line more easily.
OK, get your model to this point. Review what we've covered and repeat these steps. Make
sure you can do this much and that you understand what's been covered to now.
We will pick up on the stress analysis after that.
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CAESAR II Statics - Lesson One Video Two
1. We're back in our model and now we'll go to the report and review the data on that report.
This report is the stress report and includes the name of the job, and to whom the software is
licensed to. It's best to take a look at the header bar to see what the report is that you're
looking at, and it will define the load case that comes out of CAESAR II.
2. We see here many different columns. Fortunately for us, we're viewing the entire model's
report (minus the stress summary which we'll talk about later). This is the entire model from 10
to 40 and 30 to 50.
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3. The report is listed by elements. So we see here focusing first on the node numbers, each
element is listed in this report as basically the free body diagram of the element.
The forces and moments to keep that free body in equilibrium are then used to calculate
stresses on the elements. We see a number of stresses listed. We have Bending Stress,
Torsion Stress, Code Stress, and Allowable Stress. Which is the stress we have to look at?
Which one's important to us?
4. Well, in my opinion, the code stress is the money stress as far as I would call it. We want to
compare the calculated code stress to the allowable stress defined by the piping code. The
line in red indicates that the branch at node 30 exceeds the allowable. The calculated stress is
423 MPa, and the allowable stress is calculated as 324 MPa. We are 30% over the allowable
stress.
5. So the system is overstressed in accordance with B31.3. Now, what does this actually mean
that we are overstressed in the expansion case? Well, according to code, we may fail this Tee
over time through fatigue. A through the wall crack might develop at that point. We really can't
say when, but assuming a certain number of cycles for this plant, it is not an initial failure, but a
failure that will happen sometime in the future.
6. In order to assure a safe design, we'll have to redesign the system in order to drop that code
stress below the code defined allowable stress. Now, what is that code stress equation? The
following figure shows what B31.3 gives us in paragraph 319.4.4(a).
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7. It says the expansion stress range equals the square root of the absolute value of the axial
stress due to displace strains (that's our thermal strain), plus the bending stress at that point,
also due to displacement strains
That squared plus two times the shear stress squared to that. So we need the square root of
the sum of the squares.
What can we learn from this formula? Well, let's talk about evaluating stress.
8. Basically, if node 10 and node 20 are on each end of the pipe element below, we're going to
calculate stress on each end. We need some kind of accounting system for all the terms that
we have to consider. We're going to relate our stresses to a local coordinate system. The
local coordinate system being the longitudinal stress term (stress along the pipe), the hoop
stress (or circumferential stress around the circumference), and the radial stress through the
wall of the pipe.
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9. If I would create a little stress element on the wall of
the pipe here, it would look like the stress cube
shown here. We have the longitudinal stress (shown
pointing to the right), and a shear stress (normal to
the tail of the longitudinal stress vector). The shear
stress is caused by torsion on the line. On the near
surface we have hoop stress, in the hoop direction,
and the shear stress. On the outside wall, we have
the radial stress.
Hoop Stress
Shear Stress Longitudinal Stress
10. We will use this stress cube to get back to that equation we saw earlier. Here are all the terms
that we're going to work with.
What we're going to do is ask, are longitudinal stress caused by thermal strain? We're looking
at expansion stress calculation. We'll have the axial term; the axial force due to stress.
Axial Term
Bending Term
The axial force is divided by the cross section of the metal, and the bending moment will be
divided by the section modulus of the pipe. Now, this will be changing through the wall of the
pipe, so we want the maximum longitudinal bending stress, and that would be at the outside of
the wall, the surface of the pipe.
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11. We have very low stress in the hoop direction caused by thermal strain. Typically, hoop stress
is considered when we're talking about pressure stress. We'll talk about that later. But right
now we've basically got what's required as far as the code is concerned. We're heating up this
piping system without any regard for pressure or dead weight. It's like we're in outer space
and we're heating up this piping system. There's no dead weight here. Radial stress is also
zero.
12. So we have a longitudinal stress. We have no hoop stress caused by thermal strain, and no
radial stress caused by thermal strain. Shear stress is caused by the torsion. So the base
equation, torsion divided by two times that same section modulus is the shear stress on the
stress element. We might have a direct shear as well, but on the outside wall, where we have
our maximum bending stress that would be zero. So we're going to exclude that from our
calculation.
So we only have the axial load, the bending term, and the torsion term remaining in our
calculation, by code.
13. If I go back to my cube, the radial term is zero, the hoop term is zero,
and I have just the shear term, and the longitudinal stress term, how
does that look?
If I look down from the top of that cube, I have a longitudinal
stress and the shear terms. Do I have a limit for longitudinal? Do
I have a limit for shear? No.
What the codes do is they take this stress element, and rotate it
in the space, to get a maximum principle stress or a maximum
shearing stress.
In our next video, we'll explore how we can convert this combination of stresses into a
simplified evaluation of the total stress on the stress element.
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CAESAR II Statics - Lesson One Video Three
1. OK, now let's convert these general stresses into
stresses that are used by the piping code.
Remember that if I have a stress cube, and we are
looking at a static analysis, that system is in
equilibrium. It's not moving. It's stable. All the
forces and moments are balanced.
So if I look at my stress cube, this surface back
here has a shear term on it. Shear times area is a load.
Here's a direct stress. Direct stress times area is a load.
So I've got loads in the vertical and horizontal directions shown here on the illustration.
2. Let's cut a new surface here. The force on this new
surface must balance out the remaining forces on the other
surfaces. So if I have forces I can calculate stress. I have
a direct stress and a shear stress on this new diagonal
face. We have an existing shear stress on the horizontal
face, and both shear and direct stresses on the vertical
face.
3. I can, with some work, calculate the stress on this new (diagonal) face. A convenient tool that
we have to do this transformation for the stresses on the new face is Mohr's Circle. Given the
stress, direct stress and shear stress, on the original faces, I can develop a new set of
numbers for the new face based on the angle and those loads.
So let's look at Mohr's Circle. Here's an example.
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On the horizontal axis, we have our direct term. On the vertical axis, we have our shear stress
term.
On this face we have SL and -τ. I'm going to say shear is positive clockwise.
So there's SL negative tau (-τ).
The other face has only shear stress and no direct stress, so direct stress
is zero, shear stress is tau. Here's the other point.
4. These two points now establish this circle called Mohr's Circle. This is a locus of points that
will have the direct stress and shear stress on the new face.
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If I plot it this way, then I rotate for the new face in this direction, angle phi, then based on this
rotation, here are my new stresses on that new face. Given the two points I can develop the
circle, and that will allow me to calculate the stresses on any angle phi. So here's my new
stress on that face.
5. Now I don't really care about any general angle; I'm most interested in the limits of this circle.
Generally speaking, in Mohr's Circle, we will have, on a 3-D surface, three principals stresses.
A principal stress is a stress where there is no shear term. It's the orientation of that face of
that cube where there is no shear.
We have that at three places here. We have the S1
defined as the largest principal stress. S3 is the
smallest principal stress. Remember that we had a 0
term in the radial direction, that 0 stress, which will be
S2. So we have the tension stress S1, compression
stress S3, and then the radial term, the third surface
which will be 0.
6. We have three stresses on our stress cube, and we've
rotated in space. We have three surfaces here. If I use Mohr's
circle, I can rotate this cube in space to a position where I get purely
normal stresses on those three faces.
Where does that happen? It happens at these three points. So S1, reorient the cube to get
the maximum principal stress, principal stress is normal to the face and no shear exists. The
minimum here is out here at S3 by definition, which is in compression. It's on the negative
side. Then again, S2, our radial term, is 0.
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7. The piping code theory of failure is maximum
sheer stress. If the sheer stress exceeds a
certain value, we assume that causes the failure
of the material. There are many different
theories of failure. Maximum shearing stress is a
quite useful one for us. The maximum shearing
stress is this value here.
We're also going to be able to relate that to the radius of Mohr's Circle, which is also then
related to the diameter Mohr's Circle. We could also talk about S1 minus S3, the diameter of
Mohr's Circle. This is twice the maximum shearing stress.
8. So we're going to use the maximum shearing stress theory of failure. We want to know what
the maximum shearing stress on this piece of pipe is. So I have a complex state of stress; I
have longitudinal stress and shear stress. How does that relate to this maximum shearing
term?
Well the nice thing about it is that now I don't have to worry about what is the magnitude of SL
and what is two times the shear term. Instead I'll just get you one number, maximum shearing
stress, and use that to compare with the failure.
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What is the maximum shearing stress here? Well I'll draw this triangle. There's my vertical run
(that's two times tau): positive tau and negative tau. The horizontal run here is SL minus 0, or
the longitudinal stress or bending term. So with those two sides of the right triangle given, I
can calculate the diameter of Mohr's Circle here. For this calculation, just take the hypotenuse
and divide by 2.
So this is our equation for the calculated stress in our
expansion case.
9. Of course we're interested in the maximum
shearing stress, but what the code will do in terms of
simplification is basically get rid of that 2 that we're
dividing by. So instead of dividing by 2 here, multiply
both sides by 2. So 2 times the maximum shearing
stress equals this equation.
10. Compare that now to the code equation. Well it has
the same format exactly. Here's a longitudinal term,
which is a direct axial load. There's our bending term. Square it. That's SL2, and here's our 2
times the shear term.
So we have bending stress and shear stress caused by torsion on the element and also any
direct axial load. The direct axial load is taken absolutely. T he code simplifies and gets rid of
the sign. We want to acknowledge that there might be some additional direct axial stress on
the line as well.
11. Like most piping codes, B31.3
will use this maximum shearing
stress theory of failure to
evaluate the strength of the
piping system. So this is our
equation from the code for the
expansion stress range
calculation, and what we'll do in
our next video is go from that
equation, to the output report in
CAESAR II.
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CAESAR II Statics - Lesson One Video Four
1. Now we're going to see how we can tie this calculated stress into an overstress at node 30 in
our piping system. We're going to be reviewing the expansion stress range, the code defines
the case that we're looking at (see the following figure) as the expansion stress calculation,
and the code says, here's our equation for the expansion stress range, and that's the equation
we just developed. This is equation 17 in the B31.3, 2012 Edition. It is found in paragraph
319.4.4 Flexibility Stresses in the code. They define these terms, SE is the computed
displacement stress range.
2. There is no dead weight in this; there is no pressure. It's just displacement stress range. Sa is
the axial stress range due to displacement strains. Sb is the resultant bending stress, again,
due to displacement strains, and St is torsional stresses, due to displacement strains. The
code goes on the state, in paragraph 302.3.5(d) that this calculated stress shall not exceed SA.
So all the piping codes that we use in CAESAR II have a similar type of calculation. A
calculated stress must be less than some allowable stress.
In doing this evaluation, if every point is below that allowable stress, the system is considered
reliable for operation. So here's our equation again, SE equals the absolute value of the axial
stress, plus the bending stress, that quantity squared, plus two times the torsion stress, that
quantity squared, square root. Sa is the axial stressed range of displacement.
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3. The code defines the axial stress range as an intensification factor times a direct axial load
caused by displacement strains divided by the area of the pipe (the cross section area of the
pipe).
4. This is a rather new equation for B31.3, the expansion stress range, and in fact, this term ia
appears for the first time in the 2012 Edition. This intensification factor changes our calculation
from a true calculated stress to an effective stress. It's an adjustment factor. This i is an
adjustment factor, to relate the relative weakness of a component. You will see that elbows
and tees have higher values of ia, and for all the intensification factors. Straight pipe does not
have a value; it's just equal to one.
5. So the piping codes use this intensification factor to adjust the stress calculation to reflect the
weakness of the component under evaluation. An elbow is weaker than a butt weld in a
straight pipe. This would mean that the elbow has a higher stress intensification factor than a
butt weld. A welding tee, or an unreinforced fabricated tee, also has its own stress
intensification factor reflecting the weakness of that component compared to a butt weld.
If I have, for example, a girth butt weld and expose it to cyclic stresses, let's say a range of
stress of 200 MPa that fails after 5,000 cycles. But an elbow, being a weaker component,
would fail at 5,000 cycles with only 100 MPa. So the elbow it has less stress level to reach the
same failure point.
The piping codes generally calculate a nominal stress, force over area, or moment divided by
section modulus, and then increases that nominal stress to account for the weakness of the
component being evaluated. This increase in the calculated stress is the stress
intensification factor. In the program you'll see it termed as SIF, for stress intensification
factor, or italic lowercase i, stress intensification factor.
6. So a larger SIF indicates a weaker component; weakness in terms of the fatigue strength that
we're talking about here in the expansion stress range, or weakness in terms of collapse,
which we'll talk about later. By increasing the calculated stress, the stress limit is now
independent of component shape. I don't care if you're talking about a tee, or an elbow, or a
butt weld, or a socket weld. If I assign the right stress intensification factor, my measure of
failure is based on the piping material itself, and not on the component shape.
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7. Here's an example, so let's have a girth butt weld on a cantilevered piece of pipe and I cycle
that cantilever up and down until it fails.
Let's say I can get the failure exactly at 10,000 cycles with a stress range (fatigue calculations),
a stress range of 260 MPa. I pull it up, get a positive 130 MPa, then I push it down to get
negative 130 MPa, and it fails after 10,000 cycles. Now let's say I set up an elbow in the same
test stand, and I miraculously have it fail at the same 10,000 cycles. But I can get the elbow to
fail at 10,000 cycles, not with 260 MPa stress range, but instead let's say it is 130 MPa instead;
it has half the stress range allowable. Well, instead of using a lower allowable stress for the
elbow, what the piping codes do is they increase the calculated stress.
8. So if the elbow fails at the same time but with half the stress, its stress intensification factor
then will be two. So we'll calculate the same stress level, we'll double to calculated stress from
130 to 260, and then I can base my allowable stress on the piping material itself, low carbon
steel, for example. It has a certain stress allowable and we compare to that allowable stress.
This was looking at one stress intensification factor for the axial term. There are intensification
factors for most terms of load in the piping codes.
We'll pick up in the next session looking at some of those other terms.
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CAESAR II Statics - Lesson One Video Five
1. Now let's take a look at some of these other terms that we have in our expansion stress range
calculations. Here's the bending term. Sb is the resultant bending stress range due to
displacement strains. B31.3 provides equation 18 to define Sb, the bending stress range.
There is our intensification factor, i but its ii. That's the in-plane stress intensification factor.
There is also an in-plane bending moment and out-plane bending moment, and it's associated
out-plane stress intensification factors. That is all divided by the section modulus for the pipe.
2. Section modulus is a common piping term. It is basically the moment of inertia, I, divided by
the radius of the pipe. Of course in bending stress calculation, the bending stress is Mc/I
where c is the point through the cross section where we wish to calculate the stress. Our
highest stress is on the outer wall, so c equals the outer wall or the radius of the pipe.
3. So the Z term is just I/r. So instead of talking about Mc/I like other mechanical engineers might
use it, we're going to say for pipers, it's M/Z. The same term.
We can see that we might have a different stress intensification factor for an in-plane bending
moment than we would for an out-plane bending; whether it's a tee or an elbow or any other
planar component in a piping system.
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4. Let's define in-plane and out-of-plane bending. If I have an elbow and I throw it on the floor, it
lies in the plane of the floor. Suppose I put a bending moment on one end or the other end of
that elbow, and that bending moment is not torsion. If I pull the elbow out of the floor plane,
that's an out-plane bending moment. If I put a bending moment on the elbow and it remains in
the plane to the floor, that's an in-plane bending moment. So the vector for this bending term
for in-plane bending is perpendicular to the plane of the component. The same is true with a
tee. If I have a tee and I put it on the floor, the bending moment that pulls it off the floor, one
end or any of the three elements framing the tee - that would be an out-of-plane bending.
5. Let's go back to our elbow stress intensification factors. There are different stress levels
required to develop a through the wall crack for in-plane and out-of-plane bending. Stress
intensification factors are different for different directions. We already saw one for the axial
term. Here we see two common terms for elbows and tees, for in-plane bending. We have a
certain level where we reach failure for this, versus an out-plane bending, which will be at a
different level. So the piping codes have defined different terms for in and out-of-plane
bending.
6. The last component of our calculated stress is our torsion stress. B31.3 gives us an equation
for that. Torsion stress is an intensification factor, but this for the torque term, times the torsion
in the line (the torsion bending moment) divided by 2 times the section modulus. Again, these
terms are defined in the piping code.
7. Where do we get the stress intensification factors? We've seen several of them. We saw an
it , an ii , and an io. Where do those values come from?
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8. If we take a look at appendix D of B31.3 entitled Flexibility and Stress Intensification Factors,
we can see they have values defined for stress intensification factors, both out-plane and inplane. We have illustrations shown for an elbow, a closely mitered joint, a widely spaced joint,
a welding tee, and reinforced fabricated tee. These values are based on the geometry of the
component.
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9. On this page, we also wee the unreinforced fabricated tee, the extruded welding tee, the
welded in contour insert (Sweep-o-let), and the branch welded on fitting (Weld-o-let). There
also SIF's for other joints in a piping system. The other piping codes have similar tables. The
tables may not be exactly the same, but they will also be used to define the intensification
factor for these piping components in those respective codes.
10. These SIFs, or stress intensification factors, are based on testing done back in the late 1940s
by A. R. C. Markl, who was the chief engineer at Tube Turns, a piping component
manufacturing company. He and his team developed these stress specification factors based
on testing.
If you wish to reference these papers, they are still very good documents in terms of pipe
stress. The ASME papers that Markl developed are still available from the company Tube
Turns in the US.
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11. So what are the stress intensification factors in and out-of-plane for a welding tee? Well, first
we see a calculation in Appendix D will be for a flexibility character h. It defines h as 3.1 times
the nominal thickness of the matching pipe for the tee divided by the mean radius of the
matching pipe for the tee. So it uses the size the pipe that is connected to the tee.
12. Basically it's the nominal thickness divided by the radius of the pipe times 3.1. This came from
testing. The out-plane SIF defined in the piping code is 0.9 divided by h to the 2/3. The inplane is 3/4 of the out-plane plus a quarter. What the program will do for you is based on your
geometry, calculate ii and io and the other terms ia and it, and apply them to your piping system
calculations.
OK, let's put these terms back into our example models in our next presentation!
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CAESAR II Statics - Lesson One Video Six
1. So let's put these back into our example. In the figure below, we can see the pipe data for our
system and below that is the stress intensification factor calculations.
The pipe data contains information on the OD, wall thickness, OD and wall thickness with a
header pipe, or the run pipe-- this is our branch pipe. Radius of the branch pipe, ID of the
branch pipe, area of the branch pipe, moment of inertia and section modulus of the branch.
And then again, the SIF's for the intersection itself. These are ii and io. We also will develop
from there some other terms before we can do our calculation.
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2. We also have some additional terms, shown in the figure which follows.
3. One comment in B31.3 is that when you have a reduced branch on a tee, you will adjust the
strength of the intersection by not changing the SIF. The way B 31.3 developed this was to
reduce the section modulus calculation to increase the calculated stress for the branch.
So we will need that term as well. Again, the program takes care of all these calculations.
For the axial term's intensification factor, the code says it equals the outplane SIF for a tee. The torsion term's intensification factor is equal to 1; in
other words, there's no value to increase the calculated stress.
4. In the following figure are the loads on our tee. We will use these loads with these terms, and
also the terms on the previous page in order to calculate the code defined stress for the branch
pipe on our tee. Where do these numbers come from? Well, they're developed by CAESAR
II. It's a preliminary calculation before we get the stress.
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5. So what are these terms?
Well, the first one listed is the axial load on the branch. It's the load pulling this branch off
the tee.
Next is the torsion term twisting this run
of pipe, twisting the branch. Following
that is in-plane bending—this is the
bending moment that keeps the tee in its
existing plane. If this anchor was not at
node 50, I could pull this free end up and
down in the plane of the tee. That means in this case, in-plane bending is about the X axis.
The last one is out-plane bending will occur if I take node 50 and pull it towards me; I'm
pulling the branch out of its plane. That would be bending about the Y axis, globally. That's
my out of plane bending moment. CAESAR II produces these numbers for us as well in
reports as part of the output. Let's look at them.
6. Here's my report from CAESAR II. I'm looking at node 30 going to node 50. The axial term is
in the Z direction. So let’s look at the global force in the Z direction.
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Here's a little free-body diagram of 30 to 50. It shows it's in the positive Z direction. Well,
positive Z is to the left; it's an axial term here. That is actually considered compression in
CAESAR II, which is why we have a negative sign in the computed value. So the program is
keeping track of the orientation locally of the element with the loads on that element. The red
arrows indicate the local forces and moments on node 30, and the magnitudes come from the
results in the next table below.
7. So we have our axial term in the Z direction. MZ is a torsion term. Next is the in-plane
bending again, which would be a vector bending about the X axis pointing out to us. This
would mean bending node 50 straight up and down. That would be the in-plane bending. Inplane bending is the MX term, the moment around X.
8. The out-plane bending is the bending moment on the branch that pulls the branch out of the
plane of the tee. That's bending about the Y axis. So if node 50 was not anchored, it would be
the bending moment associated with bringing node 50 towards us or pushing it away from us,
pulling it out of the plane. This is how we'll determine in- and out-of-plane bending of that tee.
With these loads in the system geometry, CAESAR II will proceed to calculate the code
stresses we reviewed earlier.
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9. Here's an illustration of these calculations using the MathCAD application. We can use this
program to manually calculate, by equation, those same stresses.
10. We see in the following figure the pipe OD and wall thickness, both for the branch and the
header pipe. The derived values, the radius of the pipe, the value h is a flexibility characteristic
defined in Appendix D of the B31.3 piping code. We also see values for the in- and out-ofplane stress intensification factors from the appendix. Also shown is the moment of inertia
section modulus and so on.
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11. Scrolling down through this report we see the same forces and moments for our stress
calculations as shown as calculated using MathCAD. In this analysis for the expansion case,
pressure is set to 0 because we're not looking at pressure in this analysis.
If I look at the calculations performed by MathCAD, here they are: axial stress, bending stress,
torsion stress, and the expansion stress range.
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12. Now let's look at the CAESAR report.
Here we see in the extended report the list for Axial Stress, Bending Stress, Torsion Stress,
Hoop Stress, Max Stress Intensity, and finally, Code Stress. Our focus here is on the Code
Stress calculation.
13. So here's the expansion stress
range, MathCAD calculated 423.59
and CAESAR II calculated showing
423.60. That's a match.
That's the value for stress, and it's made up of these
three components.
14. An interesting thing with CAESAR II is that we list Axial Stress, Bending Stress, Torsion
Stress, but these are basic textbook calculations that may not vary between piping codes. The
stresses shown in the previous figure (Sa, Sb, and St) are quite specific for B31.3.
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15. If I look at my axial stress that I calculate for my expansion stress range, I get minus 26.79
MPa. What does CAESAR II show? It shows 11.51 MPa. So CAESAR II is returning the pure
structural load, axial load, divided by the area of the pipe, giving me 11.5. So this is a generic
axial stress without regard for this new stress intensification factor we have in B31.3.
16. The bending term does match up. I got 396, and there's my 396. So in this column of
CAESAR II we do use SIF's, or stress intensification factors, for the bending term.
17. In the torsion column, my calculation from the code appears to be minus 12 MPa. If I look at
my listing here, it says minus 10.
This difference is from a note in the code which states that if I have a
reduced outlet on the branch connection at a tee, I shall use an effective section modulus
calculation. So here in this column, the torsion stress, it is the effective section modulus
calculation. When I add up all these terms together, I get my calculated stress of 423.59 MPa.
So now you can see how detailed some of these calculations are. These decisions made by
the software in using SIF's, in using effective section modulus versus actual section modulus
are illustrated in this section of the course.
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CAESAR II Statics - Lesson One Video Seven
1. OK, in our previous video we were reviewing the expansion stress calculations. Let's move on
and look at a few more calculations in the output report.
2. Sustained calculations will be reviewed next.
Before we start looking at the stress report, let's
collect our terms that we need to work with. First,
here is a listing of the sustained stress indices, the
capital I. We also call it the SSI, or Sustained
Stress Index. This is new to 31.3, and the SSI for
sustained stresses is a function of the stress
intensification factor that we had from the
expansion case.
3. Our in-plane SSI is 1.5, out-plane is 1.75, torsion and axial are set at 1 flat. Again, we're
looking at the outlet on the tee, node 30. So we also collect-- these are the SSIs for the
branch.
Here are the local forces and moments for our stress calculations, the axial load, in-plane
bending moment, out-plane bending moment, and torsion.
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4. So we assign those values. We also have the pressure term as well. These
will all be used to calculate the sustained stress in accordance with B 31.3.
5. Here's our calculation. We have our axial stress calculation, our bending stress and our
torsion stress. These terms are combined in order to calculate the longitudinal stress due to
sustained loads.
Our calculated value using MathCAD is 13.33, and yes, we have 13.33 in our CAESAR II
output report. The allowable stress for those collapse loads or the collapse stresses are
132.12 MPa. That's the hot allowable stress for this node in the piping system.
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6. Other stresses that we have
in the program are the calculations
for the Axial, Bending, Torsion and
Hoop stress that we see in extended
report. Again this is for node 30.
There are 12.93, and you can then
review all the rest of these. And yes,
we're calculating these stresses in
CAESAR II using these equations.
7. Note here that on the
bending stress, it is not the capital I
that we saw in the stress calculation.
Again, we consider these more the
textbook calculations of stress, and
our interest is mainly on the code
stress calculation.
8. Now what of this other calculation, Maximum Stress Intensity that appears in the CAESAR II
output report shown earlier? Well, there's a little more to talk about in that one. This is a
stress that is calculated at four points across the cross section.
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If I take my resultant bending moment and lay it on the pipe, I
have, and using the right-hand rule, the side of this pipe at
points 1 and 2 is in tension, due to this bending moment, and
the side at points 3 and 4 is in compression. We're pulling out
towards us, in 1 and 2. We're pushing in, in 3 and 4.
9. We're
going to calculate stresses on the outside
surface, inside surface, on both the tension
and compression side. Also, it's not just with
the bending term, but with all three directionsaxial, hoop, and the radial term.
10. So here are the terms, these four points. Each row represents a point. The first point is the
first row in this vector. The second point is the second row, and so forth. We're calculating
longitudinal stress at point one, two, three, four. Hoop stress is calculated at one, two, three,
four. The hoop stress calculation is the Lamē equation for hoop stress, based on the inside
and outside radius of the pipe.
11. Longitudinal stress should be familiar. It's the axial term, and the bending term, outside radius,
inside radius. Radial stress is 0 on the outside surfaces, but negative P (it's the compressive
radial stress on the inside surface of the pipe). The shear stresses are the basic shear term,
outside radius, inside radius based on torsion.
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12. We're going to calculate these four stresses at these four points through the cross section. We
will then take them to Mohr's Circle, and then calculate the three principle stresses based on
these four terms.
13. This will give us the center of Mohr's Circle, in longitudinal hoop's term.
This is the radius of Mohr's Circle.
So when I add the radius to the center, I
get one of the three principal stresses.
I subtract the radius from Mohr's Circle,
and I get the second of the principal
stresses.
The third term will just be the radial term. So these are our three stresses
on Mohr's Circle, where there is no shear term.
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14. Well, I can't tell you which one is the maximum in order to get S1 minus S3.
Again, stress intensity is the diameter of the largest Mohr's Circle, S1 minus S3. But I don't
know which one's which. So I can sort these three different stresses at the four points, and
here they are. Here's the Sa at 1, Sa at 2, and Sa at 3.
15. This is on the outside surface in the tension side (1), inside surface tension (2), inside surface
compression (3), outside surface compression (4). Then we sort these terms so that we get
them in order, and then calculate the largest difference between 1 and 3.
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Then we sort them again, and our maximum stress intensity, which comes out to 30.88 when
calculated using MathCAD.
Looking again at our CAESAR II report we see we get the same value.
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16. There is another switch you can set in the program, in the configuration file to use either the
octahedral shearing stress calculation, or the equivalent stress calculation.
In CAESAR II, what we do is run the octahedral shearing stress calculation to calculate this
octahedral stress calculation. S1 minus S2, the quantity squared; S2 minus S3, the quantity
squared; S3 minus S1, the quantity squared. We then take the square root of that, multiplied
by one third, and that's going to be our octahedral shearing stress.
17. So that value is 12.61. Again, we don't offer any allowable limits for that; it's more of a textbook
calculation.
That pretty much covers the stress calculations in CAESAR II. We'll move onto one final
section in the next video to conclude this discussion.
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CAESAR II Statics - Lesson One Video Eight
1. All right, we're about ready to wrap up the discussion on stress calculations in CAESAR II. If
you recall, I made several comments on code stresses or textbook stresses. I want to go back
to one more point on this code stress.
2. Again, in CAESAR II, we calculate code-defined stresses and we compare them to the codedefined limits. If you have an overstress, the stress case is shown in red in the output
processor that clearly indicates that the code stress check failed. But what about the operating
case?
3. If I look at the operating case in the output section of CAESAR II for 31.3 or 31.1, I'm going to
get to a report like this. Here's the stress report, and it says, NO CODE STRESS CHECK
PROCESSED for the operating case, B31.3. If I look at the allowable stress, it says 0.
4. Again, the way that the 31.3 and 31.1 piping codes, and many other piping codes, establish
criteria for safe design is not based on the state of stress in the piping system, but on two
specific modes of failure-- collapse and fatigue. They have their own stress calculations and
their own limits. However, in these piping codes, we do not combine them to calculate the
stress. So this state of stress, we still list it as a code stress in the column here, but this is not
a code-defined stress calculation here. So if you see no allowable stress and you have
allowable stresses specified, it's probably in this type of situation where the code does not
provide a calculation or an evaluation of a stress in such a state.
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5. Now, if you're not running 31.3 or you're not familiar with the terms that are used in the piping
code, you could go back to our Quick Reference Guide from the Main Menu. It's here, in the
Main Menu of CAESAR II, on the ribbon, Help, Quick Reference Guide.
6. Here's the Quick Reference Guide, right from the program.
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7. I'm going to go to Code Stresses. Here is a quick review of all the code-defined stresses that
are found in CAESAR II.
Here are some of the terms used in this section of the reference guide.
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Here are some general terms used in the US codes: Longitudinal Pressure Stress, and the
Operating Stress equation.
Here's a section for B31.1. You can see that it's broken down into the equation for stress that
we calculate, the limit that we establish for that stress case, and the stress category. Again,
when you define a stress category, you're defining the equation used to calculate the stress
and the limit for that stress. So this is how we set up our evaluation for 31.1, Sustained (SUS),
Expansion (EXP), and Occasional (OCC).
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In 31.3 it's also Sustained, Expansion, and Occasional.
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8. Here are some other codes: nuclear code, older power codes, here's the transportation code
31.4, liquids transmission code.
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Here are 31.4, chapter IX (that's the offshore code); we see different calculations are used.
We see there is hoop stress, longitudinal stress, and equivalent stress, which is von Mises
stress. These results are compared to yield limits, percentages of yield.
9. Other codes are included as well: 31.5, 31.8, and so on. So here's all the US codes.
10. Then we get involved with the international codes. The Dutch Stoomwezen code, the French
power code, Canadian transmission codes, and so on.
So review this document if you have any questions about the calculated stresses that we have
in CAESAR II, and make sure these conform to your understanding of what the program
should be doing.
So there you have it. We've completed our review of the stress calculations in CAESAR II!
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CAESAR II Statics - Selecting Hangers
CAESAR II Statics - Selecting Hangers Video One
(Reference Video: C2_S_H_V1)
1. In this series of discussions, we'll talk about the hanger selection procedure in CAESAR II.
There will be a second set of videos on manipulating the CAESAR II selection, so at this level,
we're just concerned about how the program selects springs and installs them with your piping
system.
2. Designers can locate dead weight supports quite easily. There are a number of tables and
charts for that. So it's easy to locate hard supports for carrying dead weight. Unfortunately,
because of the vertical growth of the piping system, that differential thermal growth between
the support structure and the piping complicates the actual support that is installed in the
system. The choice must be made between a rigid support (or a resting support) -- or a rod
hanger-- a variable load hanger, or what we'll call a spring hanger, or can, and also, finally, the
constant effort restraint.
3. The choice here is quite important in several respects, not just in engineering, but also in cost.
A typical support for an 8-inch pipeline at high temperature, a simple rod hanger including all
the hardware might right up to $600.00. A spring hanger might be almost twice that, over
$1,000.00. A constant effort, over $3,500.00, so yes, there is a cost associated with these
supports, as well.
4. Now if I have a piping system that only has to
support dead weight, I could easily put a +Y
support in the CAESAR II, where we see the
simple support location right here, and I could
run a dead weight analysis, and the program will
show a load on that support. I'll call that load
dead weight-- whenever that value might be. I
will take that number, go to a catalog, and select
the proper rod size, and install it in the piping
system.
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5. Now this rod is stiff enough so that it can support the
dead weight without any deflection. So in CAESAR II,
it's a rigid support. Now initially, I had it as a +Y, this
illustration would be a double-acting Y support.
Unfortunately, if this vertical riser gets hot, the piping
system will grow vertically, and we will have some
issues with what is the load on that support.
6. There could be other issues as well. Number one
might be the pipe might lift off the support, and dead
weight travels elsewhere. Or the support could
actually hold down the pipe, as shown here, in which
case, we'll end up getting more bending in this
elbow, and we might overstress that elbow. Also,
this load down at the bottom of the pipe is going to
be quite different, as well. It could be larger than the
dead weight, because now we have the thermal load
pushing down, as well. So this hard support, while
the cheapest of the three selections that I mentioned
earlier, will not be a proper selection for a thermal
analysis.
7. Now if I could possibly replace that hard
support, which can carry dead weight on its
own, with some kind of force-- so that when
the piping system is cold, it's carrying dead
weight, and when it moves to its hot
position, it is again carrying dead weight-that would be a perfect support, if you've
got the load right. So that no matter where
the pipe moves to, the support is always
giving the same load, and it can carry the
dead weight.
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8. Can you do that? Well, yes. Here's a device that can do
that, a counterweight. In fact the piping code 31.3 talks
about counterbalance supports. Now theirs are basically
levers, but this pulley system would do the same thing, so
that no matter where the pipe wants to move vertically,
the system will always supply the proper dead weight load
to that node.
9. However, that might not be practical, because the structure above the
system now has to carry two times the dead weight-- the dead weight of
the connection to the pipe, and the dead weight from the connection to
the counter balance itself. Also pulleys like this might be trouble in terms
of maintenance over the years.
10. Here's another choice. This is a very
compact choice, which is a constant
effort hanger-- you can actually read
Grinnell® on this support, but these would
be ANVIL® springs now. This is a typical
layout (there are several other layouts).
The support connection is on top, and the
piping system is down below, and the
pipe moves up and down.
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11. Now we see a spring in the hanger. So if the piping connection point moves up and down, it
will pivot about a point in the hanger, which will pull the spring in and out.
So how can we call this a constant effort support, if this spring is moving, which is changing
load? Well, that's why "Constant" is in quotes. It is effectively constant. A typical constant
effort support has a load variation-- we'll describe the term later-- of no more than 6%. That
means that the load change on this spring changes no more than 6% from its minimum to its
maximum position.
12. So if the minimum load is 1,000 pounds, the maximum load would be 1,060 pounds. Let me
note that in this presentation, I will be using US units rather than metric units. However, when
we run the actual model in CAESAR II, we'll be using metric units.
13. The reason why this is called a constant effort hanger is that the spring itself compresses a
short amount, and that because of the pivot and the links, we will get a lot larger deflection on
the free end. So a short deflection in the spring causes a much larger deflection at the free
end on our hanger. That softens the entire set-up, and gives it more travel for the same load
range. So this is a simple way to get more flexibility out of this connection.
14. What's wrong with that constant effort hanger? Well primarily, they're not cheap. We saw that
in the initial overview. This type of hanger costs three or four times the cost of a rod hanger,
and they can also allow position drift.
15. When these sorts of supports are used in high temperature systems, or piping systems in the
creep range, if you don't get the load correct, the piping system will carry some of the load
away from the spring, and as it goes into the creep mode. It will start to drop, and you could
bottom out all these constant effort hangers. So you have to get the load right.
16. Finally, internal friction in these components, at the pivot points, could cause some stickiness
when it starts to move it. If its load changes, it'll have to change more than the required load in
order to pop that free. So there is a matter of maintenance.
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17. Is there a compromise between that rigid restraint, that rod we had earlier, and that simple
applied force that we talked about earlier to carry that dead weight through a thermal travel?
Well, think of it this way. The rigid support has a very high stiffness. A constant force has no
stiffness at all. Is there anything in between these two ranges?
18. Yes there is. A regular spring can hanger, with its
finite stiffness, might serve the purpose, and that's
what CAESAR II does when we do hanger sizing.
We'll select a spring from the catalog that can handle
the load range that's required for that node in the
piping system.
So here's a simple spring can. When we start our
next session, we'll talk about the contents of the
spring catalogs that we are using in CAESAR II.
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CAESAR II Statics - Selecting Hangers Video Two
(Reference Video: C2_S_H_V2)
1. So here we have the insides of a spring hanger.
We have the connection to earth on the top side
of the hanger, and the pipe is down below,
represented by the circle. As the pipe wants to
move up or down, it pulls the rod, which then
compresses or un-compresses the spring. So
the load path is from the pipe, through the rod, to
the plate, through the spring, to the can, and then
up to the support. So as the pipe moves up and
down, it's just basically working against the
stiffness of the spring.
2. On the outside of the can, there is some sort of
marker, shown by the arrow on the face that is
tied to the plate. As the spring moves up and down, it will display, or point to, the current load
of that spring. When they build these spring cans, they set the plate here marked with these
loads on it, based on the actual load in the spring. So there will be a minimum load in the
spring and a maximum load in the spring. The loads don't start at zero-- there is some preload
on the spring, even at its top-most position.
3. Let me add to that that these springs can move up or down, the spring could be underneath
the pipe or above the pipe. There are a lot of different arrangements for this spring to work
properly.
4. When we look at this spring, it can only be balanced at one point. Because there's a spring
involved, the load changes as the pipe moves up or down. So we're going to say that we wish
to balance that dead weight term that I calculated earlier-- the dead weight of the piping
system at a point. Let's say the load type is for the cold piping system. The amount of load on
that hard support, where we pick the rod, will be the load that we want to carry with this spring
as well. Again, it can only be balanced at one position.
5. Every other position-- as it grows vertically, as temperature changes, or valves open or close-will have a different position on this spring, and the load will be a little different on the piping
system. This imbalance is usually acceptable.
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Now if we take a look at a piping system,
the same piping system we were looking
at earlier, and we install the spring so
that it is preset to carry dead weight in
the cold position, this point's not going to
sag at all, it's got the right load on it. But
then, when we heat up the piping
system, the piping will move up this
capital ∆. And now the load is going to
change on the spring, the load will now
be dead weight, minus K∆. The question
is, is that close enough?
6. Wouldn't it be nicer, or more appropriate, to get the target load in the operating position?
That's the position where the piping system is hot and active, providing the service it's
supposed to supply. Since we're interested in the loads on equipment, loads on flange pairs
and the like, we probably want to balance it out in the operating position, rather than in the
installed position.
To do that, we would have to increase (in this situation) the spring load in the cold position to
anticipate the vertical growth, so that when it gets to the hot position, it's carrying the dead
weight. And that's what we're normally going to do in hanger sizing in CAESAR II. We balance
the calculated dead weight in the hot position.
7. While we're talking about changing loads-- and we're going to talk about hot load and cold load
in the piping system, let me add that a more correct terminology would be operating load and
installed load. If we think of a regular piping system that gets hot when it goes into operation,
then saying cold load (installed) and hot load (operating) is appropriate. However, in cryogenic
lines, or when you have lines that are growing down from an anchor above, they're going to
move in the negative Y direction as they go into operation.
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8. For these examples, I'm going to say that the hot load is the target load. We're going to size
this spring to carry that hot load, in the operating position. We use the cold position to start our
calculations for the hot load, and we're going to apply it in the operating position.
9. The cold load is a calculated value that will be intentionally incorrect in order to account for the
travel to get to the hot position. So that cold load will be the calculated hot load, plus the
calculated displacement times the selected spring rate. So what we're going to do is find a
spring can from a catalog that can carry both the hot load and the cold load. If that spring
handles both of those, then we know we have the proper spring rate.
10. A term that we have to discuss also with these springs, in terms of how far out of balance they
are in other positions-- is this term called load variation. It is the change in a load between the
hot load and cold load, divided by the design load (or the hot load, in our case). If we go back
to our mathematics here, we could replace cold load with this term here.
When we subtract this out, we end up with the spring rate times the deflection (thermal
deflection at that point), divided by the design load (hot load). This is shown circled in the
figure below.
11. Oftentimes it's limited by specification to about 10% to 25%. Certain manufacturers will say
the spring load variation should be less than 25%. If the hot load is 1,000 N, the change in the
load between hot and cold should be 250, 750 to 1,000, or 1,250 to 1,000, and it will still be
within the 25% variation.
12. When you get close to equipment like pumps, that are very sensitive to loads, you will
probably reduce the load variation to make sure that there isn't too much change to keep that
variation below, let's say, 10%. But now we're getting close to the constant effort hanger range
of no more than 6%. So load variation is another item that we will be concerned about when
we select springs in CAESAR II.
13. Now how do we select the right spring? Well there are basically two terms that we were
working with-- the dead weight load, and the ∆ (movement from cold to hot). If we have an
idea of what we expect from our piping system (our demand on our spring), we can go into the
catalog with these two terms, and select a spring that can satisfy those two criteria. In the
ANVIL® catalog, the catalog we'll use today, they talk about spring size.
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14. Spring size indicates the range of loads that can be carried by a specific spring. The higher
the size number, the more load it can carry. The spring figure number (as ANVIL calls it),
relates to the amount of travel for that specific spring.
So we'll look at both size and figure number when we order it from the catalog. In the next
session, we'll talk about the data that we get from the catalog.
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CAESAR II Statics - Selecting Hangers Video Three
(Reference Video: C2_S_H_V3)
1. Let's take a look at the ANVIL® catalog. Here's the ANVIL Spring Table.
It's an unusual but very useful format, a throwback to using your finger as a computer where
you can just point to different values on this table and select your support. You just need to
know what the load is that you have to carry and also the travel, then you can make the spring
selection. For this table here, we see that there is a varying capacity.
2. We see there's a size 0 spring on the left and on the right is a size 22 spring. Different
manufacturers have different ranges, but basically they try to cover all that an engineer needs.
If I look at this number here, it says 43. That's 43 pounds.
This one carries 2,500 pounds. So the minimum load of the size zero spring is 43 pounds.
The minimum load of a size 22 is 25,000 pounds. That quite a variety of capacity; you have to
pick the right one.
3. If I go from top to bottom, that size zero spring has a range of 43 to 95 pounds, which is quite a
load variation. You could say the load variation is 100% or over that.
4. So we're not going to be able to use the entire range of any spring, but just a little segment of
that range. We can see the size 22 spring goes from 25,000 to 54,000 pounds. So hopefully
you can find a spring somewhere in this table that suits your requirements.
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5. Now if I lay the spring can on top of this table, and let's say I'm using this size 18 spring, this
point right here would be labeled 8,000 pounds. Then, if I pull this rod all the way down to the
bottom where the indicator is pointing down here, it would then be carrying about 17,000
pounds. So the range is about 8,000 pounds to 17,000 pounds.
6. Manufacturers, for the most part, do not wish that we work in the range above or below the
range marked "Recommended Travel" in the previous figure. Most manufacturers give a
recommended minimum load and a recommended maximum load on the spring. These
recommended limits are shown with solid lines on the chart.
7. If I'm off of my load calculation, perhaps a little lighter than calculated, I might start to drift up in
the range above the recommended value. So we should consider the recommended travel
and load limits to be more like a safety factor, to avoid unloading the spring completely or
bottoming out the spring. While there is a maximum travel range, by default CAESAR II sets it
to use the recommended travel range.
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8. Now, this spring table has three different size springs on it, the short range spring, the midrange spring, and the long range spring. The term short, middle, long deal with the amount of
travel, or the slot length that is actually in the spring can. We see here that if I use my
recommended minimum line here, they all start at zero. And at the other end, at the high end, it
says 1.25, 2.5, and 5.
9. So the short range spring recommended travel is 1.25 inches, mid-range is double that, 2.5,
and the long range recommended travel is double that again, or 5 inches. So that's why we
show the ratio of 1:2:4. On the overall travel, note that the short range goes from zero to 1.75.
10. So if I recommend using only 1.25 of a total of 1.75, I have a quarter inch unused at the top
and bottom of the short range spring. That increases by the time you to get to the long range
spring. On the long range spring I'm surrendering a full inch on the low end and a full inch on
the high again. Again, that's the difference between recommended travel, shown as the
"Working Range" on the left of the chart and the maximum travel on the right of the chart.
11. So those are the three types of springs that I can select. Some manufacturers have a fourth
spring, in fact, ANVIL has an extra long spring available. CAESAR II has some of these
catalogs that have that fourth category ring in the selection procedure.
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12. The three sizes short, middle, long have different spring rates. We see down at the bottom of
the screen, it says spring rate and shows the short range spring rate, mid-range, and long.
13. The size zero spring has a spring rate of 30 pounds per inch for the short range, 15 pounds
per inch for the mid-range, and 7 pounds per inch for the long range. As we go further down
the table, these springs get very, very stiff. The size 22 spring has a spring rage of 16,000
pounds per inch on the size 22 short. The way this table is built then is that the short range
spring wraps down and around as shown in the previous figure. Mid-range springs wrap
around matching travel with spring rate in a similar fashion, and the long does as well.
14. Now, how can different travel limits provide the same load limits? We
just change the spring rate.
15. Whether I'm a short, mid, or long range spring, I get the same working
range. How can I do that with different spring rates
and different travels? Well, they balance each other,
F=kx.
As the spring rate increases, the travel decreases.
16. If I look at my lengths or travels, I get the 4:2:1 (long, mid, short). If I
look at my spring rates from long, mid to short, it goes 1:2:4. Since they
get multiplied by one another, they give you the exact same range. So
we have the exact same load data for three different types of springs:
short, mid, and long. Now, how do I select the proper spring among
these many choices?
We'll pick that up in our next session.
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CAESAR II Statics - Selecting Hangers Video Four
(Reference Video: C2_S_H_V4)
1. So how do we select the proper spring, or proper support, for a piping system that grows
thermally in the vertical direction? Or maybe better asked, "How does CAESAR II select the
proper spring?" Well, it's a matter of load and deflection. Those are the two terms that
are in play here. How much load you want to carry in the operating position, and then,
what is the travel from the installed position to the operating position? Two basic input
pieces, the load, and the vertical travel. CAESAR II will run load cases to collect that
information, and then go to the catalog and find a spring that can carry the load in the
operating position, and then still carry the installed load for that same spring, by testing
different spring rates.
2. When you locate a spring to be sized by the program in your model, the program will have to
calculate the dead weight to be carried by that location. So here we see, in the load case
editor, that load case number one is weight alone and there is a stress type called hanger
(HGR).
What the program will do is put a +Y support in the model at your hanger point, and run this
weight case. That's going to be the load case that calculates the dead weight to be carried by
that point in the piping system. It will estimate the natural load carried by the support for each
selected location. We can adjust that number to suit the design, and we'll come back to that
later, but we're going to call that our hot load. So the first load case that the program runs for
hanger sizing will be to calculate the hot load of that future spring.
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3. The program then has to calculate how much travel is expected at that point, going between
cold and hot. So the program will run load case number two, which is now an operating load
case, but it will remove that +Y restraint that was used at the hanger points, and replace it with
a vertical force equal to that dead weight load, and run that operating case.
This will then simulate the action of an ideal spring, by carrying that dead weight load through
that travel. So now, if I then look at the results for deflection from load case two, that vertical
deflection must be less than what is allowed by that spring-- whether long, mid, or short. So if
a pipe moves more than two inches, and the short range spring can only move one and a
quarter inches, well, you can't install a short range spring at that point.
4. The program will then use the weight that was calculated in load case number one with the
deflection from load case number two, and then take that to the hanger table to select a spring
rate, and then back calculate what the proposed cold level will be. So it tests different spring
rates until they fit the load limits for a specific spring.
5. The program will go to the hanger table. It knows what the load is that has to be carried in the
hot position, and it knows the distance between hot and cold. It will locate the first spring-- the
smallest spring-- that can carry that operating load.
Once the spring load is set-- the hot load-- there is a set of spring stiffness values associated
with that spring size. It will test the spring rate for the short range spring by estimating what
the cold load in the spring is. Again, it's estimating that k. The dead weight is defined. The
travel is defined, and we're just going to test different spring stiffness values to see if this
installed load is also in the range for the spring that we're looking at.
6. Now, if both the operating load (dead weight) and the installed load (dead weight plus k∆) are
within the recommended range, that workable spring is identified and that spring is selected.
If, however, the cold load does not sit within that range, it will move from the short range spring
to the mid-range spring. Basically, all we're doing is dividing our spring rate by two, and then
test to see if the cold load fits. If that doesn't fit, then we go to a long range spring internally.
The long range spring is, again, the stiffness divided by two, and the procedure will continue.
In certain catalogs, we also then go to the extended range spring. This would be the fourth
set. The program could also, if it doesn't work, go to two springs at the same point, making a
trapeze out of it.
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7. If the first spring size doesn't fit, it moves up the next larger figure to see if that one works.
Again, if it can't find a single spring, it will then try to size two springs at that same point. If the
whole procedure fails to find a spring that suits, the program will recommend a constant
support hanger, where you can dial in the load. CAESAR II doesn't select one from the
catalog. You will take that load to be carried directly to the catalog, and select your constant
effort spring by hand.
8. Now, this works whether the pipe grows up or down.
In our example, we're growing up. In this case here,
we're showing where the pipe grows negative-where the install load is above. The math works the
same; it's just that now the ∆ is a negative number,
and the cold load is now less than the hot load.
It also works when you use cold load design. Typically, we want the
operating position to carry just dead weight, but you can have CAESAR
II say, well, I want to balance it in the cold position, and let it go out of
balance in the hot position. People working around rotating equipment
sometimes want to get it balanced in the cold case first, and then reset
the springs. Once the equipment is all lined up, they can reset them so
that they will get the operating position carrying just the dead weight. So it's a way that you
can manipulate the springs to work-- and again, the math works whether you move up or
down.
9. Let's take a look at an example. Let's use the ANVIL table and select a spring that will carry
the balancing load in the operating position. That's typical work with CAESAR II. I'm going to
say that we will run a weight analysis, and the program will automatically put a rigid plus Y
restraint at the hanger point. Once the weight analysis has been run we see that the load in
that hard support is 900 pounds. We then take that number, and we remove the vertical
restraint and replace it with that support load, 900 pounds, and we run an operating case to
see how much that point moves between cold and hot. We record that thermal growth-- in our
case it is 1.2 inches. So now we have the two numbers that are required to go to the table.
We know how much load we have to carry in the hot position-- or the operating position-- and
we know the travel from installed to operation. We take those two numbers to the catalog.
Here's an illustration of the catalog. In the next session we'll select a spring for this example.
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CAESAR II Statics - Selecting Hangers Video Five
(Reference Video: C2_S_H_V5)
1. So, here we are viewing our catalog to select a spring. We have two numbers we are taking to
this table with, the load we have to carry in the operating position, 900 pounds, and the travel
upwards from installed to operation, a positive 1.2 inches.
2. If I look at this table, the first spring that can carry 900 pounds. I'm going to go from solid line
to solid line here (circled in the figure below), a size 8 spring. I see 900 pounds but it is at the
limit of its load.
Now, that's going to be the hot load, 900 pounds, and will grow back down to the cold load, a
bigger number. We see that we can't use a size 8 spring because there's not enough room
below that. So, it will need to go to size 9.
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3. This is how it would work by hand. In this
figure, in the right column we see 900
pounds. It's listed in the size nine column.
I start on 900 and move across the row to
the left. In the column for the short range
spring, I'm already down one half inch
through the allowed travel for that spring.
The spring we end up choosing will have to
compress 1.2" as it goes down to the cold
position, 1.2 inches lower. As I move down
from 0.5" I can go down to 0.75", 1", then
1.25" and that's it (a movement of 3/4"). I
can't use the short-range spring, because
there is not enough room for the spring to
to move 1.2 inches down from the starting
position at 0.5".
4. Next let's try the midrange spring. The total
slot length available on
the mid-range spring
useful is 2 and 1/2
inches.
When we're at 900
pounds we're already
down one inch, so I go
down further from here
a half inch, full inch,
1.2, then I come back
to the right under the 9
column. Somewhere
in this part of the table
would be my cold load.
So, it looks to me like a size nine spring might work well for us here going from 900 pounds,
our design load, back to the cold load of about 1,130 pounds or so. There are other checks as
well, but again, we're using a computer to do this work, so there are no fingers to drag across a
catalog page like we just did in this example.
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5. Let's go through it with CAESAR II. The program knows
the minimum and maximum load for each spring size, and
I'm going to bypass trying the size eight. We'll go right into
size nine, which can carry 900 pounds. What's important
here are the spring rates associated with size nine springs.
What the program will do is say, OK, test, first, 400 pounds
per inch; that's the short-range spring size nine.
6. We'll replace these terms. The operating load is the
dead weight; that's our 900 pounds. The installed is
dead weight plus k delta, so we're testing a k here;
we're testing 400. If I substitute the other numbers, the
900 and the 1.2 inches, it will give us a cold load or,
installed load, of 1,380 pounds. Again, this is a shortrange spring.
7. The program records what the minimum
and maximum recommended loads are for
these springs, and it will fail this test, because
the maximum recommend load on a shortrange spring is 1,200 pounds. So, 1,380
exceeds 1,200. We cannot select a shortrange, size nine, spring. Also, there's only 3/4
of an inch of travel remaining in that can once
we get our operating load set.
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8. So, short-range didn't work. The program
then moves on to the mid-range spring and
the test goes on with that one. Again, we're
going to now use the same dead weight and
delta and replace it with a different stiffness.
This time, the stiffness is not 400, but 200
pounds per inch. As we go from short to mid
to long, we keep on dividing our spring rates by two.
9. As we do that math, now it's 900 plus 200 times 1.2, and our installed load, is estimated at
1,140 pounds. Well, according to our check so far, that would work, because that is less than
the 1,200 pound limit that we are using as the maximum load recommended for a size nine
spring. But we still have to check that load variation; that's also another important qualification
of the spring that we select.
10. So, we'll check the load variation. Again, the load
variation is the change in the load divided by the hot
load, or the k delta divided by the dead weight.
So, once again, the deflection is set and the load is set.
The only thing we're qualifying is that stiffness that we
just selected, 200 pounds per inch. Acceptable.
Plug in the numbers and we'll see that when we
put in the 200 here, we're excessive. We get a
change of 27%. Our limit, by default in CAESAR
II, is 25%.
11. If I know that the only thing
I'm changing is my stiffness
and I'm currently looking at a
mid-range spring, if I move
from a mid-range to a longrange spring, it'll automatically cut my load variation in half. So, right away I know if my midrange spring is 27%, my long-range spring is going to be 13 and 1/2%. So yes, the program
will select a long-range spring for this point in the piping system.
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12. The program will select a long-range spring which Anvil calls Fig. 98, size nine spring. The
operating load will be 900 pounds and the installed load will be 1,020. That's just a simple
calculation of the hot load plus k times delta. As we see, the load variation here, if you do the
math, is 13-1/2%. What CAESAR II will show in the output processor is this table.
13. The table first lists the node number, where the spring will be installed. Next is the number
required-- we only require one in this case, the figure number, 98, which is the Anvil term for a
long-range spring. It's also a size nine long-range spring with a spring rate of 100 pounds per
inch.
14. The two numbers that were used to select this spring are the numbers listed as the Vertical
Movement (travel) at that point, positive or negative, and the load that we wish to carry in the
operating position. The load next to it is that other cold load. We call it the theoretical installed
load, because it's a simple, mathematical formula, dead weight plus k delta.
We also see another term is labeled zero. That means we did not do that calculation. We'll talk
about that a little more later. Also we can see that our load variation, 13%.
Another nice thing in our report here is that we show the minimum and maximum
recommended load for that spring. Comparing these numbers, 700 to 1,200, that's the working
range of that spring, and we're going between 900 and 1,000. So, we're sitting pretty much
right in the middle of that recommended range, and that's what you wish to have. You don't
want to be near the top or the bottom of the range of the spring you select; it's best to be in the
middle, so it's easily adjusted and changed.
We'll continue on with a few more screens in our next session regarding actual installed load,
and then we'll run an example.
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CAESAR II Statics - Selecting Hangers Video Six
(Reference Video: C2_S_H_V6)
1. When you have the program select a spring for you, it is wise to check the working range of
the spring compared to what the demand on the spring is. We see in this example that the
available range is about 500 pounds, starting from 712 pounds.
We're running at 900 to 1,000 pounds, so we're sitting right in the middle of that table. That's a
good spring.
2. Now what about that actual installed load? Well remember that the spring is designed to
balance the operating load? We're calling it the hot load. When we look at the installed load,
that dead weight plus K delta may pull the system out of balance. This extra load at the point
in the cold position may cause the pipe to move.
3. If that's the case, and if you're using the pipe position to set or adjust the spring so it is properly
aligned in the cold position, we might have to accommodate that variation in position, in the
cold position. The actual install load case will do that for you. It's another analysis performed
by CAESAR II in order to count for the flexibility of the piping system and the stiffness and
preload on the spring.
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4. Now many springs that you size will have very little difference between the theoretical installed
load, the hard number we calculate, and the true actual install load, which accounts for system
flexibility. Where will these be different? Well if your piping system is very flexible in the
vertical direction compared to the spring rate of the spring itself, you could get some differential
between the theoretical the actual install load. Or if you're using a very large load variation in
spring, that means there's a large change in load at that point, the extra load in the cold
position could misalign the indicator on the spring can. So you're not sure what load is actually
in the system in the operating position because you can't line up the marker in the cold
position.
Also, if you are unblocking and aligning your springs without a fluid in the line (in a fluid filled
line), then that lack of dead weight will pull the cold load out of alignment. When I say
Alignment I'm talking about the vertical position, the spring with respect to the pipe.
5. If you wish to examine the effect of this difference you can always look at the output of
CEASAR II. Look at the installed load and any deflection in the installed position. You could
actually have the program calculate that installed load as part of the hangars design.
To do that, you would activate the hanger design control
criteria. I'm showing you the menu item. Here is a
toolbar icon that you would click to get this.
That will open up the hanger design control data, and
this check box is usually empty. Check this check box
and it will create another analysis in order to calculate
the installed position.
6. Finally, when you have that check box indicated here, you will have an additional hanger
design load case developed. In this case it is weight, no content, plus hangers. This is also a
hanger load case.
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So then if I have the box checked, I would have another number in this field right here.
7. In the input screen I'll just check the hanger box and the
system will open up this auxiliary data.
There are three areas here. The node
and Cnode pair for that node is where
you have to identify where you want
the springs to be installed. CAESAR II
does not select the best place to install
a spring or support; it only selects the
proper spring for the location you
choose.
8. The mid-part of the screen here is
used to design the spring itself.
9. We also have another area at the
bottom of the screen for predefined
hangar data. Here you are asked to
specify your spring rate and you're
theoretical cold load. Not the actual
load, but the theoretical cold load. That's what's loading the system and the system moves
from that point. If I specify these two terms, then the program will not do any design for us; it
will use the spring that we installed.
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10. A nice little item here is that if you specify just the
spring rate, and you don't specify an installation
load, the program will try to size your spring rate in
the system by changing the preload so it works
properly.
Only if this spring rate does not serve its purpose in your new design, it well then override it
with the one that it will pick from the table. So, you have a nice little design criteria here where
you can try to use existing springs. Let's say you're updating your existing line and you have a
spring out there now, maybe that old spring will still work. Just specify the K and the problem
will calculate the preload for you.
11. Finally, we offer another choice here. If you leave
these two blank, and you just specify the load, this
is the constant effort support. There is no spring
rate associated with it; it's all just load.
You might say, well I could specify this load as a
positive Y-force in my input. This is a better way do it, though. Call it a hangar and put it here,
and now this will appear as a restraint in your model. Then, when you look at your restraint
report, you'll see your constant effort hangers in the restraint report.
If you specify this load as a external force, a +Y force, the program will not put it in the restraint
table. So it's a good way to associate constant effort hangers with you our piping system.
On our next video we'll take a look at this simple model. We
would have to design springs at these three points here, and the
purpose of these springs is to unload these pump nozzles below
them. So we're going to run CAESAR II to size these three
springs. We'll start that on our next video.
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CAESAR II Statics - Selecting Hangers Video Seven
(Reference Video: C2_S_H_V7)
1. This is the model we're going to run to demonstrate some of the capabilities of hanger sizing in
CAESAR II. You will have this model on your machine almost complete. You'll be at the same
state that I have here.
2. Here is my model. We have piping system node 10 up here, coming around, coming down to
three anchors or three displacement sets. A, B, and C, these are those three nozzle
connections. We see the symbol for the hangers at these elbows, node 270 and node 170, but
there's none yet at node 70. We're going to place this hanger on that elbow at node 70.
3. This model is four-inch pipe, standard wall, A106. We're not that hot, 120 degrees centigrade.
Let's go to one of those pump nozzles at the bottom. We see that we end at node 300, which
is also called node A.
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4. The nozzle has this displacement set. It moves
up 3/4 of a millimeter going from cold to hot. So
this pump connection is growing thermally and
then the risers also growing.
Our task is to support the piping system at the
elbow at the top. The spring has to carry that load
through some vertical travel. We'll have the
program select that spring.
5. Let's take a look at the hanger on the end. Here's the hanger, check box for hangers, and
here's the hanger display data. Notice it's at node 268, not at 270. We're coding down the
riser, so node 270 is the far end of that elbow and node 268 is the near end of the elbow.
That's where I'm sizing the spring. There's no connecting node (CNode) specified.
6. We will select a spring from the ANVIL catalog, and CAESAR II has quite a few catalogs in it
available for use.
We see here several different items and we can define. The following lesson on Hanger
Controls will discuss controlling this analysis. Right now I just want to talk about standard
sizing in CAESAR II.
7. The only other items that are checked here, short range springs will be used. If you unselect
this, it will pick a mid-range instead first. We have a 25% load variation defined by default for
this spring. These are also controlled in the configuration file or in the hangar control data over
here. So a very simple spring.
8. Now I want to go to my point my piping system over at node 68.
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9. Click on that piece of pipe to select it.
Double Click Hangers.
Change the node 68.
10. It is set to ANVIL, 25% variation, short range spring.
That's my data for this model.
11. The program will size a spring, or three springs for this model. It will run a weight analysis
with +Y supports at these three locations, and determine how much weight will be carried by
those three points. Then it will remove those +Y restraints and replace them with a positive Y
force equal to the load that it just calculated. Then the program will run an operating case to
see how much these three points move as the system changes from cold to hot.
12. With that load and that travel, then the program can go into the ANVIL catalog and select
springs and install them. After that, the program will go on and complete the other analyses
requested by the user. That's our model.
13. Click the error check.
Start run.
14. The program has two messages tied directly to hanger sizing. The first note says there are
three hangars in the job and all of them have to be designed by the program. No spring is
defined completely in this model.
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It goes on to say in note two, that if you wish to size springs, you must do these load cases: a
weight alone analysis with the +Y supports, and operating case with the forces.
After case number two, then the program will select the springs and then install them in the
model for any other analyses that you request.
I'm going to look at the load cases that the program has set for me.
15. Click on Load case editor button.
Here are the load cases.
Click Recommend.
Here are the recommended load cases by the program. The first two cases are for hanger
sizing, stress type hanger.
After load case number two, the hangers have been installed in the model. So load case three
includes the stiffness of the springs. Also the pre load is included. It is called H. H stands for
hanger pre loads.
16. Then load case four, which would be the sustained stress case for the installed position. All
the force based loads are here, weight, pressure, and the hanger pre loads. Load case five is
the standard expansion stress range between three and four.
17. Click Yes.
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18. These are the load cases I'm going to run.
Click the Load Case Options tab.
Here we see that load case one is weight for hangar loads, and load case two is operating for
hanger travel.
19. Note that in both cases it says suppress. The program doesn't list by default the output for
these load cases other than the load in travel, because these two locations are not configured
with the proper supports at this time. Only load case three and on have the springs installed in
system, so there's really no data for you to review in the output processor for these two load
cases.
20. Also note that under hanger stiffness, if there were any hangers in the job, they would all be
made rigid to get the proper load distribution. If you're looking at the hanger travel, the hanger
stiffness would be ignored completely. This is an ideal travel case, so we don't see other
spring rates playing a role in here.
After that, it's all as designed. So they're your designed springs.
21. Click the Run the Analysis button (running man).
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The output screen will show up and show us the standard reports that you might expect.
22. Note how the first two load cases are grayed out; I can't access any of this data. If I try, let's
say, show me the restraints from load case one, there is no response from the machine.
There is no data, so we're not going to do that.
Turn those off if you've selected them (Do a Control-Click to de-select them).
At this point, get your model to this state, and then we'll take a look at the output for the model
in the next session.
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CAESAR II Statics - Selecting Hangers Video Eight
(Reference Video: C2_S_H_V8)
1. If your model's at this state too, then we can review our results together. We are going to take
a look at the hangers that were selected. Hangers aren't associated with any specific Load
Cases, so they're going to be over here in the column called General Computer Results.
2. We see that we have two hanger-related reports. One is Hanger Table and the other, Hanger
Table with Text; the difference is the text, of course.
3. Select them both.
We'll review the differences between these two reports.
Click the View Reports button.
4. We have two reports: Hanger Table and Hanger Table with Text.
You can tear these apart
by just dragging the tab
away, and I can have
them side-by-side.
5. Here is the simple Hanger
Table, and here's the
Hanger Table with Text.
This data here is the text.
So we can view the output
with just the two lines
(Hanger Table) or this sixline approach (Hanger
Table with Text).
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6. Close out the Hanger Table.
I prefer the Hanger Table with Text because there's more information. The machine says that
we have these three springs selected.
At node 68 is the one that I put in, that is on the far right side of the model.
It's a size 5 spring. At the midpoint of the model the system has selected a size 4 spring, and
the spring on the left side of the model is a size 4 spring.
7. That system looked symmetric and I'm kind of surprised that it's picking different-sized springs.
Let's look at the basic data we started with.
8. First of all, vertical movement, about 3 millimeters, 3.2 millimeters. Yes, we get the same
motion from each of these three springs.
9. But notice that the load is changing a little bit. We see 1,200 N. 1,100 N. 1,150 N.
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I can see that when we get over approximately 1,250 N, the size 4 spring no longer works. I
have to go to a size 5.
10. We see that the size 4 goes up to 1,254. On node 68, when you go to the cold position the
load gets higher, and that's 1,275.
11. So even here I could say, yes, 1,254 N was my maximum load on a size 4, and if we get
higher than that we need the size 5. Of course, the spring rates are changing as well, but this
is looking at why this one's different.
12. But still, I'm kind of concerned why this one has come out different from these other two. Well,
simply because CAESAR II selected it, doesn't necessarily mean it is the best spring for the
job. Let's take a quick look at the data, then we'll look at how these springs work with the rest
of the system.
13. Again at node 68, we have one spring required. It's a figure 82, which is ANVIL's short-range
spring, a size 5 spring.
14. This theoretical installed load is a calculated value, which is using this spring rate (221 N per
cm), times the vertical motion (3.2 mm), plus the hot load. This totals out to 1,275 N.
The program also lists the horizontal motion at that point. If you have a lot of horizontal
motion, you might have to put a longer rod on the spring so the horizontal travel doesn't cause
a large angle of rotation for the hanger rod.
15. Several catalogs say the angle in rods should change less than 4 degrees between installed
and operation. So if your rod is swinging too far, you have to use a longer rod to reduce the
effect of that lateral deflection of that node.
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16. Load variations are small. 6%. Again, that's the difference between these two loads divided by
the hot load. We have 6%, 5%, and 4%.
The added data shows you what type of spring it is, short, mid, or long, and then we see the
min and max loads. So, yes, we're going from 1,000 to 1,700. This is 1,200, and we're sitting
on the high side, but it doesn't change much. That's a fine spring.
17. As you look at the other two, though, we are getting close to our limit of 1254. One is 1,135
and here's 1,206. So at 1,206, we've got about 50 N, and the spring rate is 165 N per
centimeter.
So we're about one third of a centimeter away from the maximum recommended load on that
spring. These are kind of at the high side, but they work mathematically.
18. Those are the three springs that were selected by the program. Are they appropriate for our
system? We don't know that yet.
Close this report.
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19. Now let's take a look at another report.
Select Operating and Installed positions of this piping system,
Select Restraint Summary.
Select View this report.
(Note: You can use Control-Click to de-select the previous reports.)
20. This will show us all the boundary
conditions of our system. We have
several in our model. We have the
existing supports, and now the three
springs that we designed.
21. Node 10 is the anchor at the top of the
model. Node 40 is supporting the main
run of pipe.
We see these pairs of numbers, the spring
at node 68 above the anchor at node 100.
This is the right-side pair. Spring and
anchor, or spring and pump nozzle.
Then we have node 168 and node 200.
That's the middle pair. Spring, programdesigned variable support hanger and
there's our pump nozzle B.
Then finally, at node 268 and node 300,
will be the left-hand pair, spring and
anchor (pump nozzle A).
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22. Now, what we want to focus your
attention on are the anchor (pump
nozzle) loads. Let's just use this
pair right here, nodes 268 and
300. We have a spring above the
anchor at node 300, and the
purpose of that spring is to unload
the pump.
If we look at the loads in the pump, though, we see what the pump is carrying-- it's a negative
number. The system is pushing down on the pump nozzle about 700 N cold. Then, when we
go into operation, it increases the pushing down to over 1,000 N.
23. So we are pushing down cold, and pushing down even more as it gets hot. What's
happening? As the spring grows vertically, its load-carrying capability is reduced because you
are allowing the spring to relax a little. So cold, it's 1,200. Hot, it's 1,154. That accounts for
the difference down here, at least a lot of it, anyway.
24. However, the big problem for me with this system is that, when the pipe is sitting there cold, it's
already carrying 700 N. If I could pick a bigger spring up above it (carrying more weight), I
could get this number to zero, or even maybe a positive number. This is not a good spring to
work with that support.
So the program picks springs, but not necessarily the best springs. We're going to have to
modify this model a little, or modify our selection criteria in order to drop the load on the anchor
at the bottom and allow it to be carried by the spring up above.
We'll do that in the next session.
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CAESAR II Statics - Selecting Hangers Video Nine
(Reference Video: C2_S_H_V9)
1. Our issue with the selection, at this
point, is that the hanger is not
interacting well with the pump
below it. We want the hanger to
carry the load. If I pick up a bigger
spring (a heavier spring), it will
reduce the load on the pump
nozzle, and which will increase the
life of that pump.
2. Let's go back to our model and take a look at what
the program is doing for hanger sizing.
Remember that the program does two load cases
initially, in order to size the springs. First, we
calculate the dead weight.
Let's say we're doing a weight analysis. What
does the program do? First it puts a +Y support at
each one of these three points. It then does a
weight analysis using these 3 new supports plus
all the other supports in the system. These
supports include the pump nozzles as well, which
are also supporting the piping system. So some
weight is going to be resting here, at each one of
these three new support points, and then the
numbers that we saw in CAESAR II output for the
hangers is the load that we read from these three
points.
3. But you must remember that some of the dead
weight is also being supported by these points
down here at the bottom. The distribution of dead
weight between the hanger point and the anchors
(pump nozzles) is a function of the stiffness of the piping, and the dead weight of the piping.
So our problem is that these anchors are taking up too much load in this initial weight
analysis.
4. We have a way of fixing, or changing that. What we can do in CAESAR II is tell the program
that we don't want to treat these nodes at the bottom as anchors. Instead, allow them to drop
vertically if they want.
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So for this case only, in this initial dead weight analysis, we're
going to disconnect the vertical direction on these three points.
That will then drive a lot more dead weight up to these three
points (hangers). That will results in a better operation of the
system.
5. One piece of advice, though, is that if you're going to release
an anchor, be sure you have a hanger above the anchor
below. It should be close - no more than three (some say five)
pipe diameters away from the riser. We are at the near end of
these elbows, about 1-1/2 ODs away from the end of these
weld points on these elbows. Let's do that in CAESAR II. I
want to release these three anchors, only for this first dead
weight analysis, so that the hangers will carry more load.
6. Going back to my CAESAR II output, I'm just going to keep an eye on this pair on the left side.
The hangers carrying installed 1,200 N, while the pump is carrying 700 N. You add those two
numbers and you've got 1,900 N. I want to see almost all that 1,900 come up here to the
support at the top, while the nozzles carry less. Let's have the program do that.
7. Close the report.
Go back to the Input Processor.
Select that piece of pipe, which contains node 268.
Use the cell, Free the restraint or the displacement at node blank.
Enter 300 for the node to free.
That's the pump nozzle below this
hangar.
8. This piece of data alone is
insufficient to activate this
command. We also have to
specify a free code. If you recall
the way I drew it, I said I only want
to release it in the Y direction-that's typical for these types of
supports.
Click Free in the Y direction
only.
You have several choices here. If you free it in other directions, you will get shear or bending
moment terms playing a role as well. Personally, I almost always use just the Y direction only.
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9. We have to do that for all three of these hangers.
Repeat for the hanger at node 200, also in the Y direction.
Again, repeat for the hanger at node 100 in the Y direction.
Click the running man button again (Batch Run button).
This set of changes only frees these nodes
in the initial dead weight analysis.
10. We see the output results.
Select the Hanger Table with Text.
View the report.
11. We see now that the program is picking a size six spring at all three locations, which I believe
is a better solution. We have similar translations, vertical motion of 3.2 millimeters, which is
what we saw before.
12. Look at the loads on our hangers-- operating loads (hot loads): 1,953, 1,952, and 1,948.
These are all about the same spring; they're essentially identical springs which do reflect the
layout of the piping system.
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Checking the maximum and minimum: 1,307 to 2,241, 1953 to 2,050.
We're still on the high side of the ranges, but not so close to the limit. We're still about a
centimeter away.
These look like three good springs to install in the piping system.
13. How did I confirm them before? Well I went to the restraint report.
Control-click (hold down the Control key and click) on the Hanger Table with Text report
to de-select it.
Click the Operating and Sustained load case.
Click the Restraint Summary.
Click View the report.
Now let's take a look at the pair, the hanger on node 68, with the anchor at node 100.
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14. In the installed case, the pump is positive, so I'm actually pulling up a little on that nozzle in the
cold position. Then it goes negative when it goes in the hot position. You recall before that the
maximum load on the nozzle in the hot case was well over 1,000N. We have now reduced the
maximum load on the pump accordingly. We start with a little positive, cold, and then go
negative, hot.
15. I think this is a better designed pump nozzle anyway. We put the load up on the hanger
instead, and we have a similar pattern at the other two hanger points as well.
So this is important. You don't want to say "CAESAR II told me to buy this spring." You, as
the engineer, are responsible for the piping system. So the tool gives us a way to quickly
select a spring from the catalog, but you should be confirming all the selections in a manner
similar to this one here.
16. What we did is modified the load on the spring
by shifting it to existing supports. Another way
that you can do that is to type in by hand the
number that you want to see on the hanger.
This will override the calculation of the
program.
If you want to do some further manipulation of
the pump load, now that you have some idea
of what the load on that hanger is, you can
modify the hanger load right here, and re-run
this model until you get the pump's loads
proper, and the spring selections proper as
well.
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CAESAR II Statics - Hanger Controls Video One
(Reference Video: C2_S_H2_V1)
1. This set of presentations will further develop the hanger-sizing capabilities of CAESAR II by
describing the other controls we have over hanger-sizing and hanger-selection in the program.
CAESAR II will select springs from a catalog. It also can in some cases select rigid rods or
constant effort hangers.
2. But why are variable supports required in piping systems?
Well, a spring support can carry the dead weight at a node in a piping system through a range
of travel, and that's unique to that sort of a spring support. Now before we get into these other
controls, let's review some of the requirements for hanger selection. The program must
contain two components before it can select a spring from the catalog. It has to know how
much dead weight has to be carried at that point, and that could be then used as the operating
load on the support. As an option, you could also call it the installed load.
3. We also must have the travel of that node as it moves from its cold to its hot position. We will
use the operating travel to do that and we will exclude any dead weight sag when we calculate
that travel. What is the actual procedure we use in CAESAR II? Well, first we have to collect
those loads. We will run an analysis that will calculate what we're calling here the balancing
load at each hanger location. We do that by putting a +Y support at every hanger location and
running a weight analysis.
4. Whatever load we have on that +Y support will be considered the balancing load for hanger
selection. Then we remove those +Y supports that we put at every hanger point and replace
them with the load that we calculated from the first load case-- an upwards load to simulate the
effect of that spring can. Then we run an operating analysis. The change in position from 0 to
that operating position will be the vertical travel, which will then also be used along with the
dead weight to select the spring from a catalog.
5. Then those forces that we added are removed from the analysis, the springs are selected, they
are installed with preloads, and then any additional load cases are analyzed. So now we have
two numbers to work with in the catalog. In my example here (in US units) I'm going to say we
want to carry 600 pounds of force after the pipe moves up to its operating position, and it's
moving up 1/3 of an inch.
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6. So if I go to the ANVIL® catalog, I would first locate that load-- 600 pounds-- in the catalog,
and then find the relative position for, let's say, the short range spring. In the picture here it
says 1/4 of an inch. Then move it back down to the installed position. So again, when the
pipe is hot, it is moved up to within 1/4 inch of the top of the range of the short range spring.
Now we are basically cooling the pipe down back to the cold position, and the pipe is now
dropping down 1/3 of an inch. So we now are 1/3 plus 1/4 of an inch from the minimum load
on that spring.
7. Then we can read back into the table and find out what is the load on that spring in the cold
position. These two numbers then will be used to select a spring, and we're going to say the
change in the load is about 100 pounds. It is around 694, maybe 700 pounds, then back to
600 pounds. The operating load is 600, so 100 divided by 600 is 16% variation. So that would
be an acceptable spring if the maximum load variation was set to 25%.
8. So which spring is that? Well, we'd go back to the catalog and say, this is a size 8 spring. It is
a short range spring with a spring rate of 300 pounds per inch. The operating load in that
spring is 600 pounds and the change in the load is 300 pounds per inch times the 1/3 of an
inch, or 100 pounds. That means the installed load is 600 plus 100, or 700 pounds, and that's
how we would select the spring.
You could then order that spring from the manufacturer with that data. The program goes on
after that and installs that spring into the model; it will insert the stiffness. In my example, it
was a spring support. If the program picks a rigid restraint or constant effort support, it will
have different impact on the model, but in every case, the program will install the appropriate
restraint into the model, and if necessary, a preload.
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9. If it's a rigid, it's just a stiff restraint in the vertical direction. If it's a spring can, it is the spring
stiffness in the vertical direction, and a preload (the installed load). If it's a constant effort
support, it will just be a force, but a force that would also be listed in the restraint report. So it's
pretty simple.
But how do we make CAESAR II do that? That's all the controls that we have that we will
discuss in this presentation. So here are several illustrations of similar manufacturers that we
have in CAESAR II. How do we pick the right spring? That's going to be the purpose of this
session.
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CAESAR II Statics - Hanger Controls Video Two
(Reference Video: C2_S_H2_V2)
1. CAESAR II provides four different locations where you can control your hangar design
procedure; one is in the configuration file, two is in the hangar design control data, three is on
the input screen itself, and finally, in the load case processor. We're going to review each of
these four different steps.
2. Follow along with each step as we go through these options.
3. Now for the first one in the
configuration file, we will look at
several sections in this configuration
file. Just to show you where I am
right now, if I go to the main menu of
the program, I can click on
Configuration File. It's also available
in input processor. It'll bring up this
processor here, where I can set
general options for this folder while we're running CAESAR II. Several of these branches on
this tree will be directly related to hangar sizing.
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On this screen, we will be able to change the default hangar stiffness. Our current default
setting is 1E to the 12th pounds per inch as the default, just like any other restraint stiffness. I
see no reason to modify this, but it is another switch you have available to you.
4. We have 33 different hangar tables included in the CAESAR II hangar database, so if you wish
to use any one of these springs here, you could set it globally in the configuration file. Then,
whenever you open up a new spring in the program to size by the program, it will use your
table selected here by default. You can also change different colors for your hangars and
restraints.
5. Here's the default hanger restraint stiffness, 1.75E 12th. It's bolded here because I'm now in
metric units in this model.
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On the other items, spring hangar table, that's in our database definitions. Here by default is
the ANVIL® table. I could have selected any one of these tables as the default selection
table.
6. In terms of colors, that will be under Graphic settings and here we see hangars, and also
hangers with CNodes. We'll talk more about CNodes later, but that's the other end of the
hangar, (the connecting end). The hangar node is the pipe node, the hangar CNode is the
other end of that restraint. We would suggest that for CNodes you would give it a separate
color so you can see if it is connected to what I would call earth or connected to some other
point in the system.
7. There are a couple of
other switches that are
available. One is Ignore
Spring Hangar Stiffness
in the Analysis. This is
usually used only if you
wish to match hand
calculations or older
programs which did not
put stiffness into the thermal analyses. For purposes of simplicity, those stiffness’s were
ignored.
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I would not recommend that you reset that switch, but it is available in Computational Control,
Ignore Spring Hangar Stiffness.
8. Another setting is Include Spring Hangar Stiffness in the Hangar Operating Travel Case. This
is useful at times. It can reduce the travel demand on the hangar. What it will do in the
analysis is change the system stiffness when it is calculating the operating load for hangar
travel.
So the program would propose a spring and include the spring stiffness in this hangar travel
calculation. This could reduce the overall travel and maybe select for you a shorter spring.
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If you do so, you'll note that in the output it's going to change the listing from “Theoretical Cold
Load” to “Field Installed Load”. Also, be careful when you use this to confirm the data. We
have this note at the end of our hangar table saying that verify the as-assigned stiffness’s
when you start up your piping system.
So that was the Control File settings. Now we're going to talk about the Hangar Input Data.
9. To do that, I'll return to CAESAR II and we will take a look at the input for a model piping input.
And there's two ways to get to this switch. One is to click on the toolbar button Hangar Design
Criteria or in the menu from Model Hangar Design Control Data. These are the switches we're
talking about here, and here they are on the screen.
10. Again – follow along on your system as we go through these settings.
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From this switch, we can set general control and initial settings for the current job. Here is
where we can select it from the toolbar, and here's our view.
The things that are only found here on this screen are the number of design operating load
cases, and many times you're using just a single operating case to size all the springs.
However, if you have hot pump cold pump operations or other situations where the travel at
any one spring could change between load cases, you might want to use more than one load
case to select a spring. By default, it is set to one.
If you do have more than one operating case to size supports for, you will then also specify the
default design option. This would then set the default for every spring used in this model.
And finally, the other general control on this screen is calculating actual cold loads. In the
previous session, we talked about calculating cold loads to get a better setting for your springs
or better way to check the installed loads on your spring, so we can be more certain that
they're going to operate properly. It is this switch here that does the analysis after the springs
are installed and before any other load cases that you wish to have run are analyzed.
11. On the number of hangar design operating load cases, you can specify any one of up to nine
different operating load cases to select a spring by default. We also have other choices here:
maximum load at that point or average load at that point, maximum travel at that point,
average travel at that point.
This entry will determine how many different load cases are used to select a spring. Where
there is more than one operating case for the piping system, this will allow you to set the
default load case used to set each spring in the analysis.
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12. We have several switches here, and we can use any one of up to nine operating load cases to
set that travel. We could (on all the load cases used) use the maximum operating load,
maximum travel, average load average travel, or maximum load and maximum travel.
13. Here's a good example. We have a two pump system where the red line is cold and the purple
line is hot. So we see here for the system Operating Case One, the left leg is hot, and
Operating Case 2, the right leg is hot.
So I would want to design the spring on the left using Load Case 1, but when I'm designing the
spring for the right side, I'll be using Load Case Number 2. You can set the program to use
that.
So if I'm designing the piping system, I would say number of hangar design operating load
cases equals two and I will set the multiple load case design option to Load Case Number
One.
Then when I enter these springs in my model, they'll both be set to using Number One, but I
would then change the right spring to using Load Case Number Two. So Load Case Number
One or Operating Case One sets the left spring and Operating Case Number Two sets the
right spring.
14. The other switch on this general control for hangar sizing is Calculate Actual Cold Loads. This
was, again, discussed in the last session, and is a good way to verify that the cold position is
accurate in the analysis. The program will then include the analysis of the cold position. So if
the system is very flexible with respect to the spring rate or if there's a large travel or a large
load variation of the node, the pipe might spring up a little with the unbalanced cold load and it
may affect the adjustment of the spring can.
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15. Also, if you are unblocking your springs in the cold position with no fluid in the line, you would
run a weight no content analysis in order to see how much that changes the spring load in the
cold position.
16. There are other items on this control data screen, and we talked about three of them: Number
of Hangar Design Operating Load Cases, how many operating cases you have in the
analysis, and the Multiple Load Case Design Options. That selects which travel to use, and
the actual cold loads.
17. The other items that we have
on this screen are Allow
Short range springs. By
default, it's checked. This
can be useful to turn off if
you're short range springs are
more difficult to acquire or if
they might be more
expensive than the mid-range
springs.
18. Allowable load variation is
another term we have here.
By default it's 25%., by
specification B31.1 and MSS
SB-69. However, you could
change that to a smaller
number if you're very close to sensitive equipment. Also remember that the program will use
this as a limit check in the selection of the spring. If you have too much load variation for a
short range spring, the program would automatically shift to a mid range spring of that same
size to cut the load variation in half and so on.
19. We also have on this screen a few other items that were not mentioned in the initial hangar
presentation. Here’s the Rigid Support Displacement Criteria. This is a value in length
units, let's say a tenth of an inch if I'm in US units. If the pipe thermal travel is less than this
value that you enter here, the program will pick a rigid rod.
The item right below it, Maximum Allowed Travel Limit, is similar. If the pipe travels more
than the value specified here, the program will not pick a spring. It will instead take a constant
effort support.
This would happen automatically as you extend beyond the travel limits of the hangar table
that you select. So you can force the program to pick a constant support, let's say close the
rotating equipment, if you specify a low number at this point. The numbers that we're
specifying here, act for every new spring you enter into the model. These settings here, do not
affect existing springs.
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20. Here you can also specify the Hangar Table. Now again, the hangar table is specified in the
configuration file. What we're talking about here is a local change to the specific input file. So
you could re-specify it here.
21. There are also three checkboxes in this screen. Let me open that screen again here. We see
check boxes for Extended Range, Cold Load, and Hot Load Centered. One, two, or all
three could be checked at the same time.
Again, these would be useful if I'm entering a new spring. The current settings at these three
locations would also then be used on any new spring that you define, but they're also available
on the individual spring definitions.
The extended range will go beyond the recommended range defined by the manufacturer.
Cold load design will balance the supports in the cold position, not the hot position. This might
be useful in aligning your equipment. For the last item here, cold load centered, the program
will attempt to move to the next largest spring, even though a smaller spring would work. This
is to center the hot and cold loads. We'll talk about that again later when we talk about the
individual spring selections.
We'll go on to the other places where you can control hangar sizing in the next session.
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CAESAR II Statics - Hanger Controls Video Three
(Reference Video: C2_S_H2_V3)
1. The third area where you can specify or control your hanger sizing is in the actual input
spreadsheet. I'm going to pull up the CAESAR II input spreadsheet here, and we see at node
268, we have a spring to be sized. So we will review now the settings for this spring selection.
2. When you double-click the check box for hangers, the system displays the auxiliary area on
the right. Here is where you will define the controls for the hanger selection at this specific
node. Note: This illustration is for an example using Node 30 for the spring location.
Once again, we see there's the node number (Node 30 in this illustration) that we're sizing the
spring at, with a Cnode (Connecting node); general data to select a spring; and finally, at the
bottom of the page, an area where, if filled out, the program will not select a spring for you. It
will instead, use an existing support.
3. What's the difference between a restraint and a hanger? While a restraint is pure stiffness, a
hanger allows you to define stiffness and a preload, or just a constant effort hanger by itself.
The first specification for the hanger data would be the node number for the hanger.
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4. You also have, as an option, the ability to define a connecting node. Normally, this is left
blank, meaning you're connected to earth, an immovable object.
A Cnode can be used if the
connecting point of the hanger
is to a structure which also
moves vertically.
5. In this example here, we have
a vessel, a hot vessel that
grows vertically.
The pipe is supported using a
spring with this moving end,
and then I could specify a
Cnode on the connecting end.
Let's call it node 31, for
example, and I could specify a
vertical deflection of node 31. Then, when the spring is to be selected, it will be based on the
relative thermal growth, not the absolute thermal growth of just this node alone.
6. In the hanger design data area, we have many options. We see some that we've already seen
before, certainly the hanger table itself. We have, again, in CAESAR II, 33 different hanger
tables, and I expect the list of available tables will continue to grow.
7. Each one of these tables has three different sizes: short, mid, and long. Several of them also
have a fourth size as well; we'll call it extra long. So it depends on which table you use,
whether you have this extra spring can size to work with.
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We also have those three check boxes we saw
earlier, for the Extended Range, Cold Load, and
Hot Load Centered.
8. The extended range again will use the entire
range, rather than eliminating the high and low end
to allow you adjustment in the field. The cold load
will set the spring to be balanced in the cold
position rather than the hot position. This is useful
in the aligning equipment, and then changing load
after the equipment is lined up. The hot load
centered, again, will check the next size higher. If
the design load on the spring is very close to a
limit, the program will go to the next size.
9. Available Space is another item here. We
mentioned this before. If you specify a number
here, the program will use this number against the
length of the spring can itself. If the spring can is
too big to fit in the available space, the program
will not be able to select that spring.
CAESARII does not specify any length for hardware. The program has in its database the
lengths for a spring can above the pipe or a spring can below the pipe.
The program has these two lengths shown in the following figure. We do not have all the
leftover hardware length like these nuts, connecting rods, and the like. So while CAESAR II
would be watching this spring can length as the available space, in many cases, your
requirement in the field is much greater, because of all the extra hardware.
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10. One minor point about that is if you actually put a
negative number in your input in the Available
Space field, the program will show you a picture of
the support underneath the pipe, rather above the
pipe.
11. A few other items here-- Allowed Load Variation.
We saw that earlier under hanger control data
usually set to 25%. You could reduce it to a
smaller number to reduce load variation around
rotating equipment, for example, or make it even
larger if you don't want to buy springs and get
away with perhaps stiffer springs rather than more
flexible springs.
12. Rigid Support Displacement Criteria-- we saw
that also in the hanger control data. If you are out
in the middle of a run of pipe where there's really
no reason to put a spring-- if it's a very rugged
system-- you could have this setting to select a
rigid rod if the vertical growth is less than the
entered value, let's say less than a tenth of an
inch. In the middle of a pipe rack, a tenth of an inch is certainly not excessive when we talk
about using a hard support, not allowing it to move at all.
But when you're close to rotating equipment, there a tenth of an inch means a lot, so you want
to pick a spring in that case. So this setting is going to allow you to decide which type of
support to use around sensitive areas.
13. Maximum Allowed Travel Limit-- we saw in the control data, if you exceed this limit, the
program will automatically select a constant effort support.
14. Some of the other items on this screen, the Number of Hangers at Location, Hanger
Hardware Weight, and so on are also useful in that they allow you to select two springs or
have the program select two springs. Let's say you're on a riser where you really can't use just
one spring. You'd have to probably trapeze two springs on either side of the clamp that is
holding up the piping system.
And each spring would then be sized for half the load. So it's important to get this number
right. When you say you have two springs at a location, the program will divide the total
design load by half, and design two springs, each carrying half the load.
15. Allow Short Range Springs-- we saw that check earlier as well. By default the system is set
to allow short range springs. If you don't have access to short range springs, you can turn that
off.
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16. Operating Load-- this is a very good tool in fine-tuning your springs. Once you have an
analysis done, if you wanted to tweak that spring, increase a load or decrease a load, you
could use a number here to override the calculated dead weight at that point. This is a way to
do some more precise work around rotating equipment where you want to tune up your piping
system.
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CAESAR II Statics - Hanger Controls Video Four
(Reference Video: C2_S_H2_V4)
1. So, continuing on with the hanger control data on
the input spreadsheet, we also have Hanger
Hardware Weight. This is kind of interesting-- the
program will allow you to specify additional weight.
Now this would be the weight that is added into the
piping system, between the spring and the pipe
itself.
You recall earlier, in
this illustration (left),
where the program will
have the shorter
length here in its
analysis, but the true
length is a little bit
longer.
2. If this is a very light spring, and there's a lot of hardware weight, this hardware weight will also
affect the spring settings. So if it is appreciable, you might want to turn on or add this
additional weight to your hanger selection. The entered value will be added to the design load,
but it will not be shown in the restraint reports, because we're showing the load on the restraint
from the piping, and not with this added hardware weight.
3. We looked at the Multiple Load Case Design Option earlier in the general control settings for
hanger sizing, but this allows you to change it for each individual spring. You can choose
whether you want to use operating load case one, two, or the maximum travel or the average
travel for that point.
4. The final items on this screen, the Free Restraint at Node listed twice and a Free Code is
useful in sizing the spring as we saw in the previous sessions. The ability that we get here is
that dead weight can be removed from these anchors, and pushed up to a nearby spring, so
that the anchor doesn't carry the load, like at the pump nozzle. It says free restraint at node
blank, where you type in the node number. It is not limited only to restraints-- displacement
sets are also considered part of these boundary conditions. So if I have an anchor that grows
thermally, I can define it as a set of displacements, and I could also use that as a node to free
up for the dead weight distribution.
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5. Along with the setting of the node number, you also have to specify a direction (Free Code)
which you are freeing the support. We have several choices. If up is Y, you can release it in
the Y direction, Y and X, or Y and Z-- or X, Y, and Z all together and finally all six degrees of
freedom.
We suggest that you only release these anchors if the hanger that you wish to size is
above that restraint, or nearly vertical in line with that restraint. That way there's no
bending moment that gets built up as you button up this bigger spring. The bottom of the input
screen for hangers, again, allows you to define existing springs, or existing constant effort
supports.
6. You can specify the Spring Rate, and the
Theoretical Cold (Installation) Load (the
expected cold load) at that point. Or, if it's a
constant effort hanger, you can specify the
Constant Effort Support Load that the support
provides the piping system.
If you specify both a spring rate and a theoretical
installation load, the program will use that one
directly. You could also just specify the spring rate
by itself, and the program will use the hanger
design algorithm to estimate that installed load, and
perhaps reuse an existing spring that has to just be
reset for the new piping system layout.
7. One other item here-- the hanger display, how we
display it on the plot. In CAESAR II, you can turn
on or off items on the plot. Here we see three
springs at these three locations.
I'm going to turn off the display of those, and now they're gone.
I unselected, or deselected the display for the hangers.
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8. We also have the ability to increase their size, so you we
can really see them, or reduce the size. So there are
certain things you can do in here to get more information
into the plot about our springs.
9. If you put a negative value in the Available Space
field for the spring, the program will show it as a
support underneath the pipe, rather than above.
One caution on using this, if you want to see that kind
of interesting display of a can support, be sure that
you provide a large enough negative length here, so
that it does not impact the selection of the spring itself.
So don't type minus 1, to get this symbol, but type in
perhaps minus 1,000 to make sure that any can that is
less than 1,000 millimeters, or 1,000 inches, will be
still selected.
10. Now, once your data is complete in a model that has hangers to be sized, and you select error
check in the CAESAR II program, you'll see some extra notes in the error check processor that
will indicate how many springs are to be sized in the model, and also recommend load cases,
that should be analyzed. Now, what we see here is load case number one, to calculate the
dead load that will be carried by the spring, and load case number two will calculate the
thermal travel, or the strained travel expected out of that spring.
11. After those two load cases, the program will select a spring from the catalog that you specify,
install it in the model with preload, and then do any other additional load cases that you
request.
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12. Now, if you ask the program to calculate the actual cold loads in the system, you will see,
instead, a third load case, which will install the spring in the model, and preload it, and then run
a weight case-- as you define it, weight, or weight, no content-- in order to find out what the
actual installed load is, as opposed to that theoretical installed load.
So that wraps up the Piping Input options for the spring selection. In the next video, we will
talk about load case modifications that you can make for hanger sizing.
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CAESAR II Statics - Hanger Controls Video Five
(Reference Video: C2_S_H2_V5)
1. There's one more area where you can specify data for your hangers, and that is in the load
case processor. Here we see the load cases that are used for a hanger selection in this
model. We have three extra load cases that are labeled hanger for stress type. These are not
used to evaluate the piping system, but instead collect the data required to properly select a
spring and install it in the piping system.
2. The first case is the weight analysis. And by the way, this is the only case where we say we
release an anchor. It will be only in this weight case where we release the anchor to size a
spring. We'll talk more of that later. This weight case is used to calculate the design load for
the spring.
3. Then case number two is pretty much an operating analysis. Here we remove that rigid
restraint we put in the first case, the collected dead load at the point, and replace it with a force
that we calculated to replicate the action of the spring, pull out the dead weight sag, and see
how much the pipe wants to move up going in the operation or down.
4. Then, the third case we show here in this analysis is used for calculating the actual installed
load on the spring. This is the optional case that you can turn on or turn off. Then after that
we have all the regular load cases you would expect out of CAESAR II.
Also note that in this model here, we have another load case component called H. That's the
hanger preload. That will appear if you have existing springs that are preloaded in the model
or if you are using the hanger sizing procedures that we're talking about here.
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5. When you go to load case options for these same set of load cases, you're going to see there
are two areas where you can affect the results out of CAESAR II. One of them is in the output
status.
6. Now by default, we do not show you any output for-- in this case-- the two load cases that were
built to size the spring. The dead weight analysis, what we'll call the restraint weight case, and
the free thermal growth case. This says suppress here. These are not final analyses of your
piping system. We suggest you do not turn these to keep because the restraints that are used
in the output processor may not match the same restraint organizations that you had for these
two load cases.
7. You can also adjust the stiffness’s that are used in the analysis for different load cases with
these springs. We see three different choices for hanger stiffness, Rigid, Ignore, and As
Designed. Of course, once we get past the initial spring selection, you should be using the As
Designed springs in the model.
8. In the very first case, where there will be springs selected, we have it set to Rigid. So every
spring is going to be replaced with basically a rigid rod or a +Y restraint to calculate the dead
weight at all these points. In the second load case where we want to have the spring travel
calculation, we have to allow it to move, so we switch it to Ignore.
So there are three switches again. Rigid, Ignore, and As Designed.
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9. Now what would happen if you had a system that has more than one operating load case?
You're going to find that if you specify multiple load case design options, the program will have- as you see here-- more than one operating case.
So in this example, operating case one would be the left leg is in operation while the right leg is
on standby. And operating case two is the opposite, where the right leg is hot and the left leg
is cold. So the error check will show you have more than one thermal load case designed for
it, and also in the Load Case Editor you will see the same replication of the free thermal load
case.
That wraps up the hanger input and control. In the next video, we'll talk about looking at the
results from the hanger's design algorithm.
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CAESAR II Statics - Hanger Controls Video Six
(Reference Video: C2_S_H2_V6)
1. So let's take a look at the output that we get from CAESAR II when you have hangers selected
in your CAESAR II analysis. The output processor will have two items in the right column, in
the menu discussing hanger data-- what is hanger table and hanger table with text, the
difference being the text. We see here in this screen, this is the general hanger data.
If I would select instead hanger table with text, I would see this data.
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2. So what is different between hanger data and hanger your data with text? Well, here they are
side by side. We see there's a lot of common information, like through the name of the spring.
But the actual text that we're talking about here is this additional data down at the bottom.
This is quite useful, and in fact I would always recommend selecting hanger table with text,
rather than hanger table when I'm confirming the springs that were selected. If you just wanted
a list of all the springs once you have verified all of them, then hanger table would be fine.
3. Now, whether it's hanger table or hanger table with text, we have this common information.
First, again, the program will calculate the dead load at that hanger. That's listed under the hot
load. Now really, I should say operating load, because I shouldn't say hot or cold, but just the
operating load. This is the design load for the spring, by default. That comes from load case
number one.
4. The second item on the screen that is initial input for hanger selection is the vertical movement
at that spring location. That's from load case number two.
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When I say load case two, I'm talking about only one operating load case. If I had more than
one operating load case to size a spring for, I could have more than two load cases to select
this value. But these are the two numbers, the load and the travel to get to that hot position
that are used by CAESAR II to select the spring and install it in the system.
5. The spring that is selected is listed here as a spring rate. So this is how the stiffness matrix
gets updated. The program will put this spring rate in the model at that hanger point. The
other item that is calculated based on the travel and the load is this theoretical installed load.
6. Again, in the hanger selection, you know what the hot load is, or the desired hot load for the
hanger is. You will then test different spring rates to make sure you can carry the proper cold
load on that same spring. So again, this theoretical cold load equals the hot load plus the
travel times of spring rate.
7. Cold load equals hot load plus travel time spring rate. That spring corresponding to this 224
pounds per inch is an ANVIL® spring, because we used the ANVIL catalog. It is a Figure 82,
which indicates the size of the spring-- short, middle, long-- and it's a size number seven
spring.
8. This will be installed at node 68. So I have the node number, the figure number, and the size
of the spring. Here, it says we need a single Anvil spring. Be sensitive to that number.
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9. The other items that we see on this hanger table or hanger table with text is a load
variation. Again, one of the criteria for selecting the spring is to maintain a load variation
perhaps below 25%. That's the default in CAESAR II. In other words, the difference between
these two numbers is less than 25%. Well, the program displays what the load variation is,
and we have a 9% load variation, 9% is the change between 498 and 543.
10. Now in this analysis, there was no load case setup for calculating the actual installed load. If I
did throw that switch in the input processor to calculate actual cold loads, I would have another
number here, but the program would have performed an additional analysis to calculate that
load.
11. If the system is relatively stiff, this actual installed load is usually very similar to the theoretical
installed load. Or if you have a low load variation, these two numbers would be the same.
There are certain circumstances where it might be wise to calculate the actual installed load,
rather than using the theoretical installed load.
12. We also show how much lateral motion is at that spring location. So node 68, when it goes
into operation, might move up 2/10 of an inch, but it also slides over-- I'm not sure how much in
what direction, but the total lateral deflection is less than a tenth of an inch.
Keep an eye on this number. If this gets to be a large number, you might have to be
concerned about how much angulation you get on the rod. Some would say that the rod
should not swing more than four degrees. So if this starts to get large, you might need a larger
rod length in order to make sure that the angulation stays low.
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13. Now if you select hanger table with text, rather than hanger table, you get this extra text. What
do we see here? Well, here it'll say that this is a short range spring, as opposed to a mid or a
long range spring. So a Figure 82 is ANVIL nomenclature for short range spring.
14. We also show the maximum and minimum recommended load or maximum load, depending
on your selection in the input for this spring. This is a very good set of numbers to examine to
qualify the spring that was selected. Here, this size seven spring’s recommended load ranges
between 392 pounds and 672 pounds.
So that's the recommended load range for that spring, and we're going between 500 and 540.
So we're sitting right in the middle of that table, and this is a very good selection. Recall that
we are calculating a load based on your input. If you have valves, for example, in your piping
system that was selected from the CAESAR II valve flange database, those valve weights
might be off.
15. They probably are not exactly the same weights as you have in your built system. So if you
would be wrong in these loads here, you might get too close to these limits. You want to have
your spring to be in the middle of this range, and we have a good selection right here.
16. Finally, this spring can, the size seven spring is about nine and a quarter inches long, just the
can itself. Of course, there's other hardware included with this spring. But if I only have, let's
say, 12 inches of clearance between the top of the pipe and the support above the spring, I
might have difficulty. Check this number. Of course, this was also some input that was used
for selecting the spring in the first place, the clearance space or allowed space to install the
spring.
So that's the spring that was selected in this situation, but we should examine the output to
make sure this is a proper spring to be used for this application. So in our next video, we'll talk
about verifying that spring selection.
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CAESAR II Statics - Hanger Controls Video Seven
(Reference Video: C2_S_H2_V7)
1. So now we have a spring selected by CAESAR II and it's installed in the system for use in any
other analysis required for this piping system. It is up to you to verify that that spring is proper,
not only initially in the design condition, but also for any load case that you are using with this
spring in the system.
2. So again. In the Hangar Report, you can verify whether or not the spring is close to its
minimum or maximum load. Also, when you look at the output for other load cases, you can
also check to see that the spring is carrying proper load near equipment. We'll take a closer
look at that later.
3. The spring is there not just to carry load of the pipe, but also to perhaps change the load
throughout the system. You can unbalance the spring to carry more load or less load to
unload equipment nearby this spring selection. Also, in these other load cases that you may
analyze, those load cases should be checked as well to make sure that you are within the
working range for the spring.
4. Also, be concerned about horizontal deflection at these hangar locations. The B31.1 Piping
Code says the change in angle of a rod hanger shall not exceed four degrees, for example. In
your hangar supports, you do not want so excessive angulations at these hanger points. So
you could check your horizontal deflection and compare that to the rod length associated with
your hangers and make sure they are within their required values.
5. Perhaps you can do better. Don't restrict yourself to work only with the program selection. I
wouldn't want to hear anybody say “CAESAR II told me to buy that spring.” You are the
engineer, and it is your responsibility to ensure that the spring is correct.
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6. So let's take a look at a piping system. Here's a simple layout where we have a spring
selection above a pump anchor, and I'm showing the input for the hangar design criteria for the
spring. So at node 68 we have the hangar location. We’re using default data here: spring
table, allowable load variation, and if a short range spring works we're going to use it. I
highlight here that we are not specifying any node release for the dead weight distribution.
Well, let's take a look at the output.
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7. Here's the restraint report for the Hangar Point Node 68 and the anchor below Node 100.
We're looking at the operating case and installed cases three and four. In the operating case in
the Y direction, the hangar has been designed to carry 390 pounds and in installed case, 423
pounds.
8. So it goes from 423 cold to 390 hot. That's the spring that was selected by the program. I
have no complaint with that, but when I looked down at my anchor at 100, I notice that the
anchor is carrying, in the hot case, minus 282 pounds and, in the cold case, minus 127
pounds. So again, we designed this spring to carry the dead weight load in the hot case, but
that was ignoring the dead weight load in the hot case on the pump below it.
9. So the low distribution is basically shared on the riser between the hangar above and the
pump below: 390 and 282. Well, I'm buying a spring here to reduce the load and the load
change on the pump below. Now, a spring will reduce the load change, but I should take a
closer look at the balance load on the pump. Maybe I should have that be lower so that I don't
have such a large load on the pump, and I can do that with CAESAR II.
10. Is this a good spring? I'll say no. If I get a bigger spring, I could take more of the load off of
the pump, and that's what we're going to do.
We have a size 6 Figure 82 ANVIL® spring, which is a short range spring. The hot load is 390,
and the spring rate chosen for the spring is 168 pounds per inch. We can back calculate what
the installed load will be.
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11. Well, because I reviewed the output, I realized that maybe I
should carry more load on the spring, and one way you can do
that in CAESAR II is to release this anchor in the Y direction.
We’ll release the anchor at 100 in the Y direction only when you
do the dead weight distribution for the spring selection only for
that dead weight distribution.
12. So in Load Case One of CAESAR II for this hangar design case,
we'll have an anchor up at the top end of the line. I'm going to talk
just about the Y direction. The Y support at the start of the line,
the Y support near the middle of the line, and the Y support
simulating this hangar.
13. The lower end (connected to the pump) will be dangling free.
That will then drive a lot of the dead weight load up to the point at
our hanger connection on top. One caution though is that if your
hangar point is not close to the center line of the released anchor,
you're going to develop a bending moment as well and it won't
work as well. So we would suggest that you get off the riser by
no more than three ODs of the pipe to release this and have the
load come up directly.
14. Is that a better one? Well, here are the results for that analysis. That was the only change
between the two. We see that now the pump is now carrying only 124 pounds downward and
the cold load is positive 41. This is a much better balanced pump. Recall previously they were
larger numbers.
To get this to happen this way, we had to have more load on the hangar. So we see this is a
much better report in that all the load is coming up onto the hangar and not down to the pump.
So now instead of having a size 6 spring, we have a size 7 spring. It's still a short range
spring; it's just a stiffer spring.
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15. Now we could even tune this further. If I know that right now my pump is going between 41
pounds up-- we're pulling up on the pump in the cold position and pushing down 124 pounds
hot-- I can work off of that change and split the difference. So instead of going between 41
and negative 124, if that spring carried an additional 42 pounds above, I could split this pretty
much evenly between 83 and 82 pounds.
Now, I'm not going to say that's a better design; I'm just illustrating how you could fine tune the
hangar selection. Let's do that now in CAESAR II.
16. So I want my hot load in the spring, instead of being 558 which we saw before, I'm going to
add that additional 42 pounds. That will make the cold load and hot load on the pump nozzles
more balanced.
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17. What we do in CAESAR II to do that is type in the actual operating load. This will control what
load will be used at that spring point. When I run that analysis, I told the machine make it 601.
That's the spring load, and we see that the pump below is now carrying this balanced load.
Again, I'm not saying that this is a better design than the previous, but you can see that you
can fine tune the hangar selection and use that information from the pump to pick a, perhaps
better, spring. It ended up being the same spring, but with just a different load set.
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CAESAR II Statics - Hanger Controls Video Eight
(Reference Video: C2_S_H2_V8)
1. Let's take a look at a few other hanger control features we have in CAESAR II, or items that
should be of concern to you in using hanger sizing. One is CAESAR II will, at times, say there
is zero load being carried by one of your hanger selection points. You'll encounter that at two
times.
2. One is during solution. The program will say, during the solver, Mode (1) is the dead weight
calculation for every hanger.
It will say some designed hangers
may be supporting zero weight
loads. That indicates that perhaps
that hanger point should be located
somewhere else, because in the
operating case, it wouldn't be
carrying any load.
3. Also in the hanger table output, the program will say, yes, constant effort spring selected
operating load did not fall within the allowed working range. And what is the load on that
constant? It's zero. So when I would see that in my output, I will say, maybe I shouldn't have
put a spring at 20, or a support at 20, and maybe it should be located elsewhere.
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4. Now what does that really mean? One way you could investigate that problem, since the
program just ignored that weight there, is to build a model by hand. So here's that model that
we were looking at just a minute ago.
I have a hangar at 20 and 30, and I want to size the spring.
5. Now we have a valve on the end, which is a dead weight. When the dead weight sags on the
end, it's going to rest on this +Y support at node 30, and lift off the support at node 20. This is
why the program said node 20 is not carrying the proper load; it's not carrying any load.
6. Looking at the results for the operating load case, yes, node 20 is not carrying any load on the
+Y support. Again, I'm replicating what we call the restraint weight case for hanger sizing. On
Node 20, the +Y is not carrying any load.
7. It's moving up a very little bit, about one hundredth of an inch. We probably couldn't even see
it, but all the load that doesn't go to the anchor goes out to node 30. So this would be an
indication that maybe you should remove that restraint, or maybe move it somewhere else
along the line.
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8. Now, one other point is that we have a check box in the hanger selection procedure is to
center the hot load. Now, I said earlier that a better spring is one that sits in the middle of its
table. You want to be close to the upper limit of that table, so the program would normally just
stop as soon as it finds a good spring. However, you can push the program to look at the next
higher spring selection, to see if it fits better in the range.
9. Now, in order for the program to go to Hot Load Centered, the calculated hot load must be
within 10% of the maximum range for that spring. If it is within 10%, and you select hot load
centered, it well then try the next spring, as well. Here's a CAESAR II output report for the
spring, without considering centering the hot load. The hot load in this model shows 653
pounds, and the maximum allowed single spring load is 672 pounds.
10. These two numbers are within 10% of one another, so this is a candidate for that hot load
centered switch. Right now we have a size seven spring.
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11. If I go to the table, I can see that the design spring has a hot load of 653, and it goes back to
its installed position, back to 574 pounds.
12. Now, again, the vertical growth is negative. If I look at my next spring, I can see that I can
carry my 653 pounds, and unload it down to 548 pounds-- again, the same minus one third of
an inch. This might be a more useful spring in this selection.
13. So, for hot load centered to work, we have to have an operating load within 10% of the limit. If
so then the program would go on and look at the next size spring.
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14. Now, running the model again with the check box hot load centered, I see the program selects
a size eight spring. It still moves 1/3" down, going from installed to operating.
The hot load is still 653 pounds, but it picked a size eight spring, and we are farther away from
the maximum load of 653 to 900-- lots of room. This would be a better spring; it’s a size eight,
rather than size nine.
15. A few other items, be aware that the program will at times select two springs, rather than one
spring, in your system.
If you get through the table and one spring doesn't work, the program will cut the load in half,
and then select two springs, certainly by two springs. Be aware of that number (NO. REQD).
Also, in your input, you have the option to say, I want two or three springs; an example might
be in a riser situation.
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CAESAR II Statics - Hanger Controls Video Nine
(Reference Video: C2_S_H2_V9)
1. One final issue here in hanger selection is the term "Actual Cold Loads." You will see in
CAESAR II a check box that you can say "Provide Actual Cold Loads." This will have
CAESAR II calculate one more load case where the springs are installed in the system and
loaded with weight, or maybe weight no content depending on when you set your springs.
This will then be the load on that spring when you are putting it into service-- cutting the straps
off and letting it carry load on its own.
2. Now remember that we are balancing our piping system for the operating load, so at any other
position-- up or down, let's say in the installed position-- there will be either more or less load
on that spring. If you used a theoretical cold load, it may actually put more load on the piping
system in the installed position than is required because the pipe itself might deflect when you
put the unbalanced load in. It might be better if you use the hot load and the actual cold load
when ordering a spring, rather than the hot load and the theoretical cold load.
3. Again, it's one more analysis. The difference between the theoretical cold load and the actual
cold load is caused by the relative stiffness to the piping system with respect to the spring. If
you have a very, very flexible line and a large load variation on the line-- again, the load
variation is the difference between this theoretical cold load and the designed hot load-- you
will have a large imbalance. With a flexible piping system, it might actually pull the piping
system up rather than pulling the spring down.
4. One way of further adjusting the load on the spring-- related to this actual cold load-- is to have
the program include the spring stiffness in the operating load and calculate the operating
travel. If you throw this switch in the configuration file, the program then will change the status
of the hanger stiffness in the load case used to select the spring travel.
Here it says "As Designed." Usually it is free. Free thermal growth would be used to set the
travel of the spring. Here though the spring stiffness may reduce the travel of the spring going
from cold to hot.
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5. Here is an example of that. We have a rather large motion of one inch at a hanger, and we're
to carry 629 pounds in the hot case.
Well, the system picks a spring that is almost 24% load variation. The difference between
these two numbers (629 and 779) is 24% of 629. The load variation is the difference between
installed load and hot load divided by the hot load. Here the actual spring installation load
(710) was shown. So here is our regular spring selection, and the actual load was calculated.
It's only 710 pounds. The theoretical load is 779 pounds.
6. So there's a drop of 10% for the actual load. Well, some would say that this spring will never
get compressed to this load, so we are basically wasting some travel here in selecting a spring
that can move a full inch. If I throw that switch in the program-- this one we saw earlier-- to
say, yes, include spring hanger stiffness in the operating case, then I get the result shown in
the lower half of the previous figure. Note that we still have the same hot load, but the vertical
movement has been cut almost in half. This was a very flexible system, so this imbalance
caused a lot of deflection.
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7. But since we said include the proposed hanger stiffness in the vertical travel, it reduces that
travel, and our field installation load matches the actual installed load. We do make a note
when you throw the switch in the program-- the title of this column changes from "Theoretical
Installed Load" to "Field Installed Load." We also add a note at the bottom of the hanger report
to be sure to walk down these lines and check all these springs when you put them in
operation.
8. Here's another example of using that kind of a switch. Here is a very, very long run of pipe-- a
very flexible run. The user has selected springs at every location. Well, this system, because
of all the differences between the installed and operating loads, the preloads and the spring
are going to pull up the system even more. So this would be a poor selection. One way you
could fix that is to include spring hanger stiffness in the operating case.
9. We could also ask, why put a spring in the middle of this run? Call that a rigid restraint; the
system is flexible enough. That will drive down the travel of all these other springs.
10. Here's the model, again, and here's the default selection where you do not include the stiffness
of the springs in that vertical motion. In both cases, we have the exact same dead weight at
every spring, but notice the difference in the travels. For example, at node 150, all that extra
pull from the load being greater than the balance load-- we got a two inch pull on this line
vertically.
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11. However, the actual thermal growth is much less. When we include the spring stiffness, it
moves a little over 1/500 of an inch. That has a great impact on the springs that are actually
selected. Here, we're picking two triple springs-- that's the pretty expensive stuff-- when in
fact one short range spring will do the job. So if you see this kind of action in CAESAR II,
you might want to throw that switch to include the hanger stiffness in the operating travel case.
So again, when you size springs in CAESAR II, there's only one balanced position for that
spring, and typically, we're going to call that a "Design Load," and that's going to be the "Hot
Load."
12. But you can also change it to use that as the installed cold load design. Since we designed it
for the hot position, any other position will be out of balance. However, based on your
operating travel, we will limit that by the load variation setting that you have in CAESAR II. By
default, it's 25%, which limits the amount of out of balance, and that will usually make it
acceptable. However, other load cases that you might want to run in CAESAR II after the
hangers are selected might cause a greater imbalance in the system. But back to the hanger
sizing-- this imbalance will cause a spring deflection in the installed position in order to balance
the right load in the hot position.
So there you have the video series on controlling the hanger design algorithm in CAESAR II.
It's easy to just select a few spring points, but it comes down to you reviewing your work and
assuring that's a proper spring for the job. So when it comes down to it, you buy the spring,
and you design the spring. CAESAR II is just a tool that helps you select a good spring in your
analysis.
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CAESAR II Statics - Turbine Design Problem
CAESAR II Statics - Turbine Design Video One
(Reference Video: C2_S_Turbo_V1)
1. In this session we're going to gain a little more experience in using CAESAR II in working a
problem that has a turbine it. We will build a model in CAESAR II, and then evaluate the
nozzle loads and, if necessary, redesign the piping system to satisfy those load limits on that
turbine. Here's a picture of the system we're going to run. We have a 12-inch header (the
large line on the right) supplying steam to this turbine, and then an exhaust line (on the left)
taking exhaust away.
2. So we have a 12-inch header with the four-inch branch to the turbine, six-inch nozzle on the
exhaust-- reducing out to an eight-inch line, back to an 8-inch header. Now, if you look at our
boundary conditions for this model, we have the 12-inch header on the inlet side with an
anchor on one side (the left end). We do not have to code beyond that anchor to have a good
model on our side of the anchor, because no information goes through the anchor. On the
other side, there is a Y support and a guide at the end of the line (shown at the far right end of
the figure). This is controlling the displacement of the 12-inch line.
3. Now, the 12-inch line might sag a little more than normal, because we don't have the
connected pipe beyond the ends, but I doubt that pipe is going to move much. Our main
interest is in the inlet and exhaust lines, not the header in that sense, so I think we have a
pretty good boundary condition here at the branch connection. I'm going to ignore any
numbers we get of this support.
4. Likewise, on the exhaust line, one end is anchored, and that's driving the position of our
exhaust tee. At the other end, again, there is a Y support and a guide on that line. So we get
a pretty well controlled system here.
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5. The issue also then is to model this turbine.
The turbine has got an anchor at the base of
it, and we have our two nozzles-- the fourinch suction and the six-inch discharge.
There are some limits to that load, and these
equipment loads are a lot lower than the
allowable stress in the piping system. So in
many cases, it's the rotating equipment that
will control the final design of the piping
system.
6. Here's a closer look at that turbine. We can
see we have the valve coming into the line
with a flange connection to the turbine. Exiting the turbine is a six-inch flange, a six by eight
reducer, right to an elbow, right into a flange gate valve assembly-- then up to the rest of the
system.
7. Now, fortunately for us, we don't have to build the entire system. The inlet part of the system
(on the right) is saved as a model on the computer. It's called TURBO_IN.
Again, there's an anchor at the base of our turbine, so this inlet system is independent (as far
as structural response) from our system that we're going to model.
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8. But I want to evaluate that turbine, and in evaluating the turbine, you must evaluate all the
loads on the turbine assembly. So we will need both the inlet and outlet, or inlet and exhaust
piping together. In this exercise we're going to build the exhaust side, and then we're going to
bring in the inlet side so we won't have to model it.
9. Our sequence of node numbers that we're going to use, starting with the anchor, will be node
number 10. Node 20 will be the face of the flange on the turbine. Node 30 will be the end of
the flange and the beginning of the reducer, and node 40 will be the end of the reducer.
50 will be the elbow node; 60 will be the end of the elbow. 70 and then node 80 will take us to
the elbow-- then 90, 100, 110, and 120. That's all we're going to have to model here today.
The rest will come in when we bring in the rest of the model, called TURBO_IN.
10. Start up CAESAR II. All right, so we have CAESAR II open. Let's build a brand new file.
Click New.
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Type: Turbo for the file name.
It will be located in the Turbo folder, in your
course files.
The program displays the units.
These are the units that are in the Turbo folder we supplied with this course, called Training
Units. You will use these units for this model.
Our pressure is in Bars, and the stresses will be in MPa.
Click OK.
That opens up the Input Processor.
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11. The first element is from 10 to 20. This is the body of
the turbine. We're going to go from the anchor point in
the turbine to the nozzle of the turbine.
The dimensions are shown in the drawing.
12. Since we're going from the base to the nozzle,
For the DX field,
Type: -100
For the DY field,
Type: 300.
For the DZ field,
Type: 450.
Note: When you enter data into a CAESAR II data field you
must press <Enter> or click in another field to complete the entry.
For the Diameter field,
Type: 6 (for 6" diameter). The system will convert it to millimeters.
For the Wt/Sch field,
Type: 40.
We will not specify any corrosion for this model.
The fluid density is steam. I'll ignore it.
13. For the Temp1 field,
Type: 150.
For the Pressure 1 field,
Type: 5 (it is 5 bars).
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14. This element, from node 10 to node 20 will be a rigid element. This is a construction element.
Click Node Numbers (to display the node numbers).
Double Click Rigid.
This will make it a rigid, construction element; we want it to be very stiff. This will allow the
rigid element to grow thermally, but not allow the casing to deflect at all.
Double Click Anchor, to put an anchor at node 10.
15. What else do we have to specify here? Material.
In the Material field,
Type: 106 <Enter>.
The system sets the material to (106)A106 B.
16. The Code field defaults to B31.3.
If you want to be complete here, you can specify
cyclic factor F of one in the F1 field.
You can also leave it blank, it defaults to one
anyway.
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17. In the Insulation field,
Type: 50 <Enter>.
In the Insulation Density field,
Select Calcium Silicate.
If you didn't define a density, but you had a thickness, it
would default to Calcium Silicate anyway.
In the Line Number field (in the lower right area of the screen),
Type: Exhaust <Enter>.
That completes the first element.
18. We'll go on to the next element.
Click Continue.
The next element, 20 to 30.
This is the flange of the exhaust piping.
Click on the Valve flange Database.
Select the Single Flange, 150 pound class.
Click OK.
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19. The program continues the same vector as the previous
element when you use the valve flange database.
20. In this model, the flange is in the true z direction, not on
this skewed angle like the construction element for the
body of the turbine. How can I quickly change it?
In this model, the flange is in the true
z direction, not on
this skewed angle like the
construction element for the
body of the turbine. How can I
quickly change it?
Click on this chevron.
It will open up the entire field for the
delta dimensions.
Be sure to pull it open so you can
see the entire screen if it's partially
hidden. We see the length of the
flange is displayed (92.075 mm).
All we need to do here is just change the Direction Cosines.
Set the three fields to 0, 0, 1.
Click in one of the other fields (the DX, DY, or DZ). When that is done, the flange will reorient to that new vector.
We see the entire length, 92, is in the right direction.
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21. Click Continue.
22. This next element is going to be the reducer. On the drawing, it says its 152 millimeters long.
In the DZ field,
Type: 152 <Enter>.
23. Double Click Reducer.
In the Diameter 2 field (the exiting diameter),
Type: 8 <Enter>.
In the Wall Thickness field,
Type: 40 <Enter>.
As you type Enter, the system converts the diameter and wall thickness to millimeters.
24. We can see that the plot displays the conic shape for
the reducer.
25. Save your work at this point.
We'll continue on with this model in our next video.
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CAESAR II Statics - Turbine Design Video Two
(Reference Video: C2_S_Turbo_V2)
1. OK, we have our model built through the reducer. Let's continue on.
Click Continue.
In the DZ field,
Type: 305 <Enter>. This is the length of the elbow (from end to corner).
Double-click Bend.
By entering in the virtually exact length of the elbow from endpoint to corner the system does
add the midpoint node, but it does not add the value for Angle 2 (the zero angle node number).
It always puts in this value if you don't put in the "fitting to fitting" types of measurements. The
system doesn't call it out as nodes 48, 49, and 50. Node 40 is the near weld point of the
elbow.
Click Continue.
In the DY field,
Type: 305 <Enter>.
Since we may not be precise on the elbow length, the system
could have a tiny length of pipe at the end of the elbow. We're
basically connecting the next component (a flange) to the end
of the elbow, fitting-to-fitting.
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2. Click Continue.
This is the gate valve assembly.
Click the Valve flange database button.
Select a Gate valve, with the mating
flanges attached, 150-pound class.
Click OK.
3. Click Continue.
This will be from node 70 to node 80.
In the DY field,
Type: 2500 <Enter>.
Double-click Bend.
4. Click Continue.
In the DX field,
Type: -1500 <Enter>.
Double-click Bend
5. Click Continue
In the DZ field,
Type: 2500 <Enter>.
Double-click SIF's & Tees
Select a Welding Tee.
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Now we'll continue the model from node 100 to node 110.
6. Click Continue
In the DX field,
Type: -4000 <Enter>.
Double-click Restraints
At node 110,
Select a +Y restraint.
Add a second restraint at node 110
Select a Guide.
We will not fill in a value for a Gap on this guide.
7. Click the Last Element button (to go to the end of the model).
Click Continue.
Change the From node to 100. You'll be modeling from node 100 to node 120.
In the DX field,
Type: 2000 <Enter>.
Double-click Restraints.
Select an Anchor for node 120.
This completes the model for the exhaust side of the turbine.
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8. Let's take a closer look at the model. We have an anchor down there at 10, the construction
element to get the thermal growth of our turbine, through our assembly to a tee, and an anchor
on one end of the header. So we've got clean boundaries at the first node and on one end of
the header. The questionable boundary condition is the one is where we have the +Y and the
Guide, but as far as our connection point here at the tee, it's probably going to be fine.
OK, that's the model. Let's bring in the rest of the model. To bring in the rest of the model,
we're going to use a feature that has not been discussed before in this series.
It's the Include File button.
The button illustration is a folder with a piece of pipe by it. Next to it is another button showing
a folder with a piece of steel by it. These buttons allow us to include piping files and structural
steel files.
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Another option to use this command is under the Environment drop-down list, Include Piping
Input Files. So we'll use this one here.
9. Click Environment
Click Include Piping Input files.
This brings up a dialog box.
The first field is for the name of the file we wish to bring in. Next is an option to link it or embed
it (we'll talk more about this later). Next is an option to rotate that model about the Y-axis. For
example, if my orientation of my other model was different, I could realign them here. The last
field allows us to add an increment to all the node numbers for the model that we're bringing in.
This is used to avoid having a mismatch with my existing node numbers. For example, if this
old job that I'm going to bring in also started at node 10 and used 10/20/30, I would need to
increment these so they don't sit on top of each other.
10. Click the Browse button.
The system looks initially in the same folder as your current model.
Select TURBO_IN.C2.
Click Open.
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TURBO_IN_C2 is the model that we will ship with this training series. Once we click Open, the
model drops it into the data set automatically.
For this example, we're going to link the model now, rather than embedding it.
For the field Readnow?,
Leave that set to N (no).
This doesn't make it part of the model file.
We're not going to rotate it, and we're not going to change any node numbers.
Click OK.
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The system displays our model (TURBO), plus the model we just linked (TURBO_IN).
So we can save some time in building our models. If I have common subsets, I can build them
once, and then use them in several models. Since both models had a common node 10, they
both ended up with the same connection point.
11. It's kind of interesting that we see two anchors at 10. We'll
talk about that more later on.
So get your model to this point. Then we'll talk more about it in the next video.
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CAESAR II Statics - Turbine Design Video Three
(Reference Video: C2_S_Turbo_V3)
1. OK, I believe we're ready to run this model now. We have our inlet side from the other file on
the right, and we built the exhaust side, that is the portion of the model on the left.
2. What happens if I select (click on) the element from 1010 to
1020? Here's the input for it. However, it's all grayed out; I
can't edit it.
3. This is the difference between linking a file and embedding it. When we link a file, it is not part
of this model. It shows up in the model and it shows up in the analysis. It also shows up in the
output. But we can't modify it.
4. Let's fix our model here so that we can modify it.
Click Environment.
Click Include Piping Input Files.
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We see the same data in the dialog box as before.
5. Click on TURBO_IN.
The system displays a line above the current line where we can make changes to our settings.
6. In the ReadNow? field,
Highlight the N and
Type: Y <Enter>.
Click the Replace button.
This updates the settings for this file we're including in our model.
Click OK.
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7. Now nothing changed as far as appearance; it still looks the same.
8. Click on a couple of elements in the file we
included in our model. We can see that now
they are part of the model, and we can edit
them.
9. Click on Environment, Include Piping Input Files again.
The dialog box is now empty. That's because what we brought
in before is now part of the model. It's no longer itemized in
this list anymore.
10. Let's run this model.
Click on the Start Run button.
This will run the Error Checker.
11. Since this is the first time we're going to run this model, we should look at all the warnings that
come out of the program; we might want to heed them.
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12. I have two weightless rigid elements. Those are the two elements that are modeling the body
of the turbine, starting from node 10. We have a reducer in the model, and there was not a
specification of the slope of the reducer (that's the alpha value). For this piping code we don't
have to worry about it. It tells us its 15 degrees, and that's fine.
The system says we have one hanger already in the model. We didn't look
at, but on the inlet side, there's a hanger or base support (a can
underneath the pipe).
Then we see the Center of Gravity report.
They look fine. Let's look at our static load cases.
13. Click the Edit Static Load Cases button.
The program is recommending that we look at the Operating case, the Installed or Sustained
case, and the Expansion Stress Range case.
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14. Click the Run the Analysis button (the Running Man
button).
15. Here's the output menu with the three load case we analyzed, the different reports for those
load cases, and then some general data.
16. The hangar in this model was already completely defined;
there was no reason to size it.
Click on the Operating Load Case to highlight it.
Click on the 3D plot button.
Click on the Deflected Shape button.
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17. We can see how the line expands out from the Anchors. It slides out axially from the guides
on both headers. So we have pretty good results for our two tee connections.
18. Our main point of interest in the turbine.
As we zoom in, we can see that it expands from the
anchor located at node 10.
19. Let's take a look at some of the output for
this model.
Close the 3D Plot.
Click on the Sustained and Expansion
Load Cases.
Click Stresses.
Click View Reports.
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20. I selected two reports, so I have two tabs along the bottom. The Sustained Stresses (2) and
the Expansion Stress Range (3).
In the Sustained case, our highest stress ratio is 15% of the allowable and it's on the inlet side,
not the exhaust side. So I'm not going to worry about that.
On the expansion stress range case, we're using 8% of the allowable stress at node 100.
That's on our side; it's the tee connection on the exhaust header.
The stress is quite low, and that sounds good for our turbine. Usually, when you get near
equipment, you have to have low stresses in the line in order to save the equipment. I'm really
not interested in reviewing other results here now; we just needed that overview.
Close this report.
21. Our main focus in this example is working on the loads on the turbine.
So I'll look at the Operating and Sustained, Restraint Summary report.
Click on the Operating and Sustained Load Cases.
Click Restraint Summary
Click View Reports.
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22. Node 10 is on the base of the turbine. It says the load is 477 in the X direction.
But really the two nozzles are our main point of interest.
If we scroll down, we can see node 190 that is on the inlet side. But where is node 20? Node
20 is where I have my nozzle connection. It is not in the restraint report; there is no restraint at
node 20.
23. Let's look at just the Operating Load case.
Close this report.
Click the Operating Load Case.
Click the Restraints report.
Click View Reports.
We don't see node 20, but we do see node 10 twice. If your recall before, the load at node 10
in the restraint summary was two times 238. Actually, we have two anchors at 10.
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It's structurally correct. But I think we'd all rather see just one node 10 here. So I'm going to go
to tune up my model a little bit to show these data correctly.
24. Close the report.
We'll go back to the input processor.
Click the
Back to Input button.
25. Verify you're at node 10.
When we looked at it earlier, we had two anchors in the plot.
Double click Restraints.
Click OK to delete the anchor in our model at node 10.
We'll leave the anchor in the inlet side in the file we imported.
But that node 10-- there's still an anchor. Run this batch. This is just cleaning up.
26. Click the Batch Run button to re-run the analysis.
Click on the Operating Load Case.
Click on the Restraints report.
Click View Reports.
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27. Now when we look at Load Case One, restraints, there's online one node 10 and it shows 477
N under the FX column. The model didn't change at all; it's just the way it's reporting these
values.
28. Our focus from now on will be on the turbine. Let's look in the Global Element Forces report.
Close this report.
Select the Global Element Forces report.
Click View Reports.
The element 10 to 20 is the body of the turbine on the exhaust side. These numbers shown on
that row represent the load on the turbine. That's what I'm interested in.
Now, I could write these numbers down and work with them, but we're going to do a little trick
with the program in order to get these numbers here to show up in the restraint report.
So get your model to here, and in the next session we'll tune up or model a little bit more to
make it ready for load checking.
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CAESAR II Statics - Turbine Design Video Four
(Reference Video: C2_S_Turbo_V4)
1. I'd like to point out one more thing in the analysis before we go back to the input. Let's take a
look at the restraints report.
Select the Operating Load Case.
Select the Restraints report, View Reports.
Many times when I look at the model for the first time, I try to make sure the numbers make
sense.
One of things that we have in the static analysis of this operating load case is that the system
must be the equilibrium. In other words, all the internal loads are balanced by external loads.
We have dead weight, that's an external load, but everything else is internal to the system. So
if I add up my FY column, gravity is a negative Y, and this should add up to be the dead weight
of the system. If I add up all the loads of the X direction, I should see zero sum, and in the Z
direction as well.
2. Well, I don't know what the dead weight is, but if I look at the X column-- it's the simpler column
here, and this system doesn't look like it's in equilibrium. One of these anchors (the one at
node 1090) is not an absolute anchor. It's not connected to earth; it's connected to another
node.
We have a Node/CNode pair in this model.
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3. Let's take a look at that in the plot.
Close this report.
Click the 3D Plot button.
The anchor here is not an absolute anchor. You notice it's a
different color. The anchors that are absolute-- or as I'm
calling absolute, are the anchors that are connected to earth.
They are displayed in red. This gold color means that this is a
relative anchor. It's a Node/CNode pair. It's a nice trick to get
the flange loads showing up in the output restraint report.
That's a nice feature that we're going to replicate in our inlet
side.
4. I said we have to be in equilibrium. We have a filter in the program.
Let's go back to that report.
Select the Operating Case.
Select the Restraints report.
Click on the View Reports button.
Again, I'm claiming that 1090 is a relative anchor. If I pull this restraint at node 1090 from this
list (it has a value in X of -434), all the others do add up to zero.
We have a filter in our output processor, it can be quite useful.
Close this report.
Click on Filters.
Click on the Restraints tab.
Click the button for None
w/CNODEs.
Click Apply.
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5. View the same report (OPE, Restraints).
Node 1090 is not displayed in this report.
Only the absolute anchors are included, and the FX column now adds up to zero.
If we add up the column under FZ it will equal zero as well.
If we add up the column under FY that equals the dead weight of the piping system.
We're going to leave that filter on for now, and later we'll change it. There are other filters that
are quite useful as well.
Let's go create that relative anchor at node 20, now.
6. Close this report.
Go the Back to Input button.
7. Here's that node pair 1090 and 1091. Remember
that we had node 1090 in our output report. Node
1090 is the node that has the restraint on it. The
connecting node (CNode) is 1091, and that's why we
have that anchor symbol at that point.
We're going to do the same thing on the exhaust side.
We will have a node pair 20 and 21. Node 20 is the
turbine node. Right now we have 10 to 20 in our
model. We're going to change this element (this is
currently 20 to 30). We're going to make it 21 to 30,
and we're going to put the anchor between them. Let's do that.
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8. Click on the element 20 to 30.
Change it to be 21 to 30.
When you press <Enter> or click in another field the model
breaks apart.
Since node 21 was not defined previously, the system puts it
at the origin.
9. To correct this,
Double click Restraints.
Set the restraint node to be node 21.
Select Anchor.
We don't want this to be an absolute anchor, connected to "earth". We want it to be connected
to another part of the piping system.
We'll add a connecting node (a CNode).
In the CNode field,
Type: 30 <Enter>.
So we are saying node 21 is connected to node 20. Instead of being connected to earth, it's
connected to turbine. So when I look at the restraint report for the restraint at node 21, it will
give me the loads, with the proper signs, on the turbine. Just like our restraint report shows
forces and moments on the anchors and restraints, we'll see node 21 acting on node 20.
It's important that you get the sense right. We didn't want to say 20 is connected to 21,
because that would mean you'd be looking at turbine loads on the pipe.
Now that we done this, the color of the anchor changes and matches the one of the inlet side.
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We're going to also, at node 21, give that node a name.
10. Double click Name.
In the From node field,
Type: Exhaust <Enter>.
We didn't change the model; the system is still going to move at the same place, and we'll get
the same load, and the same stresses. But we are going to have the information in a format
that will be quite useful later on.
11. Click the Start Run button.
We see the same messages as before.
Click on the Batch button to start the analysis.
12. Select the Operating Case.
Select the Restraints report.
Click on the View Reports button.
Node 21 does not appear in the report (remember we have the CNodes filter on).
Close this report.
Click on Filters.
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Click on the Restraints tab.
Click the button for All w/CNODEs.
Click Apply.
This will isolate the items I wish to see.
13. Rerun the report.
If you recall, we put a label called Exhaust on node 21.
Let's turn that feature on.
Close this report.
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14. Click the Options tab.
Select Node Name.
Let's have the system display the node name, with the node number in parentheses behind it.
In the dialog box,
Click the Name button.
Click OK.
15. Rerun the report.
We now have the nozzles labeled on the report.
Close this report.
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16. Close this report.
Click on Filters.
Click the button for Reset all Filters.
Click Apply.
17. Rerun the report.
Now I know that these two named nodes are my restraints with CNodes. I can easily isolate
those from the rest of the numbers, and now I've got a good report. We'll use this format
throughout the rest of this analysis.
All right, you get your numbers looking like this, and we're ready to go on to the next video.
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CAESAR II Statics - Turbine Design Video Five
(Reference Video: C2_S_Turbo_V5)
1. You might be familiar with some of the equipment checks that we have in CAESAR II. We
have the inline checks that we can use for API 610 pumps, or different vessel connections.
In this problem we have a turbine here, and the turbine is not that simple. There are individual
checks on each individual nozzle connection, but a big part of the turbine evaluation is based
on the resolution of all the forces and moments about a single point in the turbine.
For that, we will have to go to the Outboard Processor, or the standalone equipment checks
that we have in CAESAR II. I want to evaluate those two loads on the turbine. I will leave
CAESAR II output processor, and get back to the main menu.
2. Click the Analysis tab.
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The National Equipment Manufacturing Association sets the standards for turbines, including
the maximum loads on individual turbine nozzles. Checking turbines requires that all the loads
must be resolved about a resolution point in the turbine. You can read this document to learn
more about it.
3. Click on NEMA SM23.
In the File name field,
Type: Turbo_Demo.
Click Open.
Click Yes, to create a new file.
In the Equipment Description field,
Type: Example.
4. Click on the NEMA Input Data tab.
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5. Our turbine has some specific data requirements. If I
go back to my illustration, here's the definition of the
dimensions of the inlet and exhaust with respect to
that base point.
If I look at it here, I'm saying that shaft is in the X direction. In the following figure, the upper
drawing represents a view looking into the turbine from the front. The lower view represents
the plan view (top view) of the turbine.
The shaft is in the global X direction. That's an important criteria for the definition of the
resolution point.
Eventually, all the forces and moments will be defined at the inlet and exhaust node numbers.
We will also then relate them to this resolution point. Now, the resolution point is the
intersection of the exhaust nozzle with the shaft, or equipment center line. It is indicated with
the figure showing two concentric circles.
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6. I'm going to have to then relate both my nozzles to that resolution point.
The shaft is in the X
direction.
In the Cos X field,
Type: 1 <Enter>.
Click the Add Nozzle button.
7. We will have two nozzles: the inlet and exhaust.
For the Nozzle Type field,
Select INLET.
In the Node Number field,
Type: 1090 <Enter>. That's the node number that's appearing in the restraint report.
The key here-- and this is why I put those nodes and CNODEs in the model-- so I can pull the
numbers directly from the CAESAR II output file with a button on this form (we'll do that soon),
but we do have to have the correct node numbers here.
So the pipe node is 1090, the CNODE is
1091. It's this 1090 loading up the
turbine.
In the Nominal Diameter field,
Select 4".
Now we'll fill out the area for specifying
the location of the Resolution point.
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8. We'll use this figure to get the distances from the turbine nozzles to the resolution point.
Looking at the inlet side, in the X
direction-- this is from the resolution
point to the nozzle-- I'm going in the
negative X direction. Each one of
the marks in the figure is 50mm, so
that's going to be minus 50 in the
X. (Enter this value in the form).
In the Y direction, 250 above
(positive 250). In the Z direction,
from the resolution point to the
nozzle, it is minus 250. So we
have minus 50, positive 250, and
minus 250.
In the Factor for Allowable Increase
field, Type: 1 <Enter>.
If you're doing API 617 compressors
it's basically some factor of the NEMA report, you can put that factor in here. But I'm not
allowing an increase.
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9. Now we'll do the the last item needed in this dialog box.
Click the Select Loads by Job/Load Case button.
Click on the TURBO._P
Click Open.
This is the output file for the model we've
run so far.
The system
recognizes that we have three load cases there. I want to evaluate
the turbine when it's in operation, that's when it's got load, and it's
when it's spinning.
Click CASE I (OPE).
Click OK.
10. CAESAR II displays
the numbers from the
output file.
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11. Let's add the other nozzle.
Click Add Nozzle.
In the Nozzle Type field,
Select Exhaust.
In the Node Number field,
Type: 21 <Enter>.
In the Nozzle Diameter field,
Select 6".
12. Now for the resolution point, we enter the distances from the resolution point to the nozzle.
In the DX field,
Type: 0 <Enter>.
You will always have a 0 here.
The help files kind of interesting
here, it says that there's some
kind of ambiguity in this definition,
so we give you a couple choices
here.
In the DY field,
Type: 50 <Enter>.
In the DZ field,
Type: 250 <Enter>.
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13. Click Refresh Loads from Current Job.
The system displays the loads on this second nozzle.
We have other nozzles you can add, extraction nozzles and the like, but basically, one and
one out, this will be all we need.
14. Click the Analyze button.
15. We'll review the report.
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We have a third tab here called Equipment Report
The report starts out with our input data.
Here's my inlet nozzle, and loads, exhaust nozzle and loads.
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16. Next we see the report for the inlet nozzle alone.
The system collects individual loads, and then it converts the resultant force into US units,
forces and moments. This is because the allowable limit is three times the force, plus the
moment must be less than 500 times the diameter used (3F + M < 500*D), where D is the
exhaust diameter. This has to be in US units, so we convert our metric units into English units
and then use that to satisfy this equation.
Well 3F + M = 1,253, and 500 * D = 2,000. Therefore, it says, we're only at 60% of the
allowable, which is great. That's on the inlet side alone; it's based on the inlet nozzle here-four inch.
Next we'll review the results for the exhaust nozzle.
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We see some red ink here-- we are almost two times the allowable on the exhaust nozzle.
When we go through our equation (3F + M = 5909) we're almost to 6,000, and the limit is
3,000. That's the exhaust nozzle.
Then we will look at it resolution about the center point, or the resolution point of this turbine,
and that fails as well.
All right, when we start our next session, we will diagnose this problem, and attempt to fix it.
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CAESAR II Statics - Turbine Design Video Six
(Reference Video: C2_S_Turbo_V6)
1. OK, let's work on getting the turbine loads within acceptable limits. We know we fail on the
exhaust nozzle and on the total evaluation of the turbine. Let's look at just the exhaust nozzle
right now. Knowing more about what NEMA is requesting, we're taking three times the
resultant force plus the moment, and that must be less than 3,000. Well at this point we're
almost twice that.
Since we're multiplying the forces by three, I think we should look first at lowering the forces.
In looking at the forces, the force in the global Y direction is -7,000. If we could drop that
number down, we might be able to get this to pass. Well, now we have something to look at.
We are going to focus our attention on 7213, which is in metric units, in the Y direction at node
21.
2. Let's go back to CAESAR II.
Click on the Home tab
Click on the Static button to open the Output Processor.
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3. I'm going to look at the Operating and Sustain. I don't want to look at just the Operating
because I want to be able to determine whether the load is caused by dead weight or caused
by thermal strain. If the load is caused by dead weight, I'll probably want to add some kind of
support to carry that dead weight. However, if it's caused by thermal strain, I'll want to add
flexibility, rather than stiffness. So it's important to be able to identify the cause of our big
number.
Click on Load Case 1 and Load Case 2.
Click on Select the Restraint Summary.
Click on the Filters tab.
4. We want to see only the two
nozzles. These are connected
with CNodes.
Click the Restraints tab.
Click the Only w/CNODEs
button.
Click Apply.
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5. Click View Reports.
Here is the report. If it doesn't fit your screen you
can zoom in or zoom out using this toolbar.
Here's the information for node, 21, and there is that number 7,213 that we would like to
reduce.
That's the number that's way too big. Of course, Z is pretty big also, but this is much bigger.
Now, if I look at the installed load, it's 4,500. The forces gets larger when the system goes into
operation, but the majority of the load is associated with dead weight in the sustained case.
So before the system heats up, it's already got 4,500 pounds pushing down. It is negative Y
on the turbine, so I want to add a restraint to carry off that load.
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6. Let's take a look at the plot.
Close the report.
Select only Load Case 1.
Click 3D Plot.
7. Here's our overloaded nozzle. Why don't we put a +Y support at the junction of the elbow and
reducer? This might be a quick fix to take the load off of the turbine.
Close out the Output Processor completely and
Go back to the Input Processor.
8. Click on the reducer to select it.
Double click Restraints.
On node 40,
Select a +Y restraint.
9. Click the Batch Run button.
It's a simple change. I expect no errors from the program-- running man.
10. Select the same two load cases, Operating and Sustained.
Select the Restraint Summary.
Click the View Reports button.
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11. Well, it's not what was expected, is it?
If we look at the operating case, it's still 7,213 N. The sustained load has changed, but what
happened here?
One way we could see a little more information here is look at the Restraint Summary
Extended. These extended reports give us a little more information. There are more columns
of data.
Close this report.
Select the Restraint Summary Extended report.
Click View Reports.
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We see we not only have the forces and moments, but also the position, the translation, of those
nodes. Let's go down to our node 21. There's a 7,000. We have a +Y support there at node 40.
Look what happens at 40; it lifts off the support! When it's sitting there cold, it's carrying 6,000 N, so
we actually have a positive load on our exhaust flange. Then when it heats up, it lifts off that support.
It actually moves up almost a half a millimeter at that point, and it's basically just the thermal growth of
the casing itself.
So we lift off the support when it goes into operation. Therefore a hard support will not do here, and
that's often the case when you get around equipment connections. Even though it might not move
that much, you have to be able to support the hot load more so than the cold load. That's the
important load case to consider when it's hot. So this +Y support is not going to work for us.
In the next session, we'll replace it with a spring, so get your model to this point and we'll continue on.
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CAESAR II Statics - Turbine Design Video Seven
(Reference Video: C2_S_Turbo_V7)
1. OK, so we know that the +Y alone, the resting support, will not be sufficient in carrying the
load of that nozzle as the casing grows vertically. So what we're going to do is we're going
to go ahead and replace that +Y support with a spring.
In the output menu, I'm going to go right back to the input processor.
Click the Back to Input button.
2. Select the reducer.
The +Y is defined on this element.
Double click Restraints to delete it (Click OK when prompted).
Double click Hangers.
Notice that the program shows a spring above the pipe.
The program does have a different set of data for base supports. The actual spring coil can
itself is different for a hanger and a can. If we enter a negative number in this field,
Allowable Space, the system will convert the symbol to a can symbol (underneath the pipe).
In the Allowable Space (neg. for can) field,
Type: -1000 <Enter>.
Note: You have to enter enough room in this field for the system
install the support. Entering -1 will change the symbol, but not
enough room for the can installation.
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3. Click the Batch Run button to start the analysis.
The program will try to use the existing load cases to
run the analysis, but the existing load cases are
insufficient.
Here's the message that comes up on the screen-insufficient hanger cases. So what do we do?
Click OK to return to load case definitions.
4. The system displays the load cases. We need some additional load cases to design the
new spring hanger.
Click Recommend.
5. The system recommends load cases based on the current conditions in this model. Here
are two Load Cases for Hanger sizing, and after that, then we can do the Operating,
Sustained, and Expansion Stress Load Cases.
Another load case component here we haven't seen is H, for hangers. That represents the
preload on the spring.
Click Yes to use these recommended load cases.
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6. Click the Batch Run button to start the analysis.
We're now at the output menu.
The first two Hanger Load Cases aren't available to look at. The data from those locations
are found in the Hanger Table With Text.
Select Hanger Table W/Text.
Here's information on our springs.
The spring listed at node 1065 (at the bottom of the report) is in the inlet side that was
defined by the user. The spring for node 40 is he one that the program picked for us. It's an
ANVIL Size 10, Figure 82, that's a short range spring. The reports show the load and
vertical movement. We see it's only moving at a half a millimeter, but it is carrying some
load.
So now we can carry about 6,000 N in both the hot and cold position, which is what we're
after. Let's see how that affects our numbers.
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7. Close this report.
Deselect the report (do a control-click on it to deselect it).
Select the Operating and Sustained Load Cases.
Select Restraint Summary.
Click on View Reports.
We have the filter turned on
in this report and we're only
showing nodes 21 and
1090, or the exhaust and
inlet nozzles.
Now, remember that we
had about 7,000 N before,
when it's in operation. Now
it's down to 900 N. We
might have some
complaints about the load
in the cold case; that's
when they're going to align
that piece of equipment.
Well let's not worry about
that right now; let's see if
we can get this to pass.
So we dropped this from about 7,000. We see the Z load is still pretty high, but let's see if
this will pass the turbine checks. This is a nice illustration of how CAESAR II can use the
node numbers and share data between the NEMA SM23 and CAESAR II calculations.
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8. Close this report.
Close the Output processor and return to the Main Menu.
Click on the Analysis tab.
Click on NEMA SM23.
Since we have a job already established in this folder, it's going to open that one up again.
Click on the NEMA Input Data tab.
The Inlet nozzle didn't
change; we didn't
change any of that piping
on that side. So we
don't even have to
modify these numbers.
If we just click on
Refresh Loads from the
current job, it's going to
stay with Load Case 1.
However, remember we
now have hanger sizing
in this model, so I now
want to point to Load
Case 3. So I can't use
the existing,
9. Click Select Loads by
Job/Load Case.
The system opens up a dialog box for you to select
the model again.
Click on TURBO_P.
Click Open.
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Select CASE 3.
Click OK.
But the numbers didn't change. Let's go to the second nozzle, nozzle number 2. It's the
exhaust nozzle.
10. Click the Up Arrow by the Nozzle field.
It sets the Nozzle to 2.
Now this one did change and it's set for Load Case 3, as well.
Click the Refresh Loads button.
We see 900 (approx) in the FY field.
That's what we want.
Click the Analyze button.
The input echo data for the inlet nozzle didn't change; it looks good. Reviewing the output
for the exhaust nozzle, it looks good as well.
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On the individual exhaust nozzle, that was sufficient to bring down the total. When we take
three times the force in the US units, plus the moment in US units, we get about 2,500.
Since the limit for this nozzle alone is 3,000, we are within the allowable.
11. We have one more report to check.
Scrolling down, when we resolve everything about that resolution point, we fail.
It's a different set of calculations, but we will get all the forces have almost resolved about
the resolution point, and we see that the equation we're running now (the last equation
listed) is two times the resultant in forces, plus the resultant moments, equals (in US units)
2,000. Based on our allowables, we're only allowed 1,800, so we fail here.
So the individual nozzle is OK, but we can't continue with this in this fashion, because we
still have too much load. Now once again, we're just going to work with the numbers here.
It's 2 times the force plus the moment. Well the resultant forces is 431, resultant moment is
1,100. If I reduce these forces, I'm going to have twice the effect as the change in the
bending moment. So I need to drop it by about 200.
Looking at the forces in the model we see that the force in the Z direction is the biggest
force, 1,500.
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12. Looking again at the Exhaust Nozzle, that force in the Z direction is 2,000 from the exhaust
nozzle.
And that get summed with the inlet nozzle, a positive number. So if I can get this number
smaller, this force in the Z direction, I'll drop the load on the nozzle. That might be one way
to get this to get pass.
All right, where we are right now is we will have to examine how we can possibly reduce the
Z load, that's the largest number that we see up here, to get this turbine to pass.
Verify these results in your system.
We'll continue to work on this in the next session.
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CAESAR II Statics - Turbine Design Video Eight
(Reference Video: C2_S_Turbo_V8)
1. OK. Our goal now is to reduce the force in the Z direction (FZ). That's the biggest number we
see anywhere on the exhaust nozzle and that's what we're going to try to change now.
The suction nozzle looks pretty good, so my attention will be on the force in the Z.
2. Close this report (if it's open).
Return back to CAESAR II.
Click the Home tab.
Click Static.
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3. Select the Operating and Sustained Load Cases.
Select the Restraints Summary.
Click on View Reports.
4. The program still have the filters are turned on and we see only the restraints with CNodes.
There system displays nodes 21 and 1090. This is the number that we're after. 2,000. We
have to get that lower.
Well, look at the load in the installed position, it's only minus 142. So if that 2,000 Newton load
is a sum of sustained effects and expansion effects, the greatest share is handled by the
expansion affects, because the sustained effects are only 142. So, we now can say that this is
an expansion issue; thermal strain is causing that force in the Z direction.
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5. Let's look at the plot for that.
Close this report.
Select the Operating Case.
Select the 3D Plot button.
6. Click the Deflected Shape button.
We see the plot in the operating condition.
Expanding
Absorbing and
Loading the Nozzle
We have an excessive load (in the negative Z direction) on the nozzle.
Well, there's only two pieces of pipes that are actually growing in the Z direction. We have the
short segment at the bottom, connecting to the nozzle. We also have one branching out of the
exhaust header at the top. It's a longer segment and has more thermal growth.
So this thermal strain has to be absorbed by the pipe and transmitted into that nozzle.
The leg that can flex in order to absorb that thermal growth is labeled in the previous figure. If
this horizontal leg was longer, it would make it a lot more flexible. It could then accept the
more deflection up on top and cause less response down below it. Our goal is going to be to
add flexibility by adding length to this leg, which is absorbing the load.
If we can connect into the header line with the tee moved further away from the anchor (for
instance one meter further down), leaving everything else the same, that might be the best
way to satisfy this issue.
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7. Let's go back to the input processor now, and modify the model.
Close the 3D Plot view. This returns you to the Output Processor.
Click on Back to Input.
Reduce the Input Spreadsheet Screen by clicking on
the pin in the upper right corner.
This maximizes the plot view of the model.
I reduced the input screen, so all I have is the plot.
So anything I type in, will be acting on the plot.
Type: Y <Enter>.
This causes the system to view the plot from the top.
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8. The exhaust side of our model is at the bottom of the display, and the inlet side is displayed at
the top portion of the plot.
I want to make this leg and segment of the exhaust header longer.
Shorter
Longer
9. The Distance command has been updated in the recent version of CAESAR II to work with
graphics. Before, you had to key in node numbers into a dialog box.
Note: If your system does not support these new features you can just view the videos.
Click Distance.
We'll use the Snap feature of the program.
Check the box as shown if needed.
As you move the mouse around the model, Snap points (circles)
appear.
If we click my mouse button now, it will snap a point in the piping
system (indicated by a circle).
However, the Snap symbols are big, so we're going to change the size.
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10. Right click on the plot, Select Properties, then Display
Options.
And you note there's a symbol there. You can also find that
symbol on one of the tool bars.
Scroll down to the bottom of the list.
For Symbol Information,
Click in the Type field.
Click Circle (filled center).
Set the Size to Smallest.
Click Apply.
Click the X in the corner of the Plot Settings dialog box to close it.
Now, we have a more compact symbol to work with.
11. Also - let's change the font size too.
Right click on the screen, Properties, Display Options.
Under the Fonts section,
Click Annotations.
Change the font size to 20.
Change the font color to Black.
Leave the font type as Arial.
Click OK.
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12. We should recall that the length of the line we want to lengthen is 1,500 mm and I want to
make it 2,500. This tee in the exhaust header will also be repositioned 1000 mm further down
the line.
Now, if your version of CAESAR II does not support the new Distance command features we
are about to us, you can go into the input processor and change the lengths of the piping
elements as needed.
13. Zoom in to the lower area of the model if needed.
Click Distance (if it's not already open).
We'll click some points to check our distances.
The pipe we want to change is 1500 mm.
Click the Select Element button.
This will turn off the Distance command.
Click the Move Geometry button.
This activates the other 3 buttons.
Click Move Geometry (X-Axis).
The system displays red circles at the nodes.
Using the mouse,
Click two points to
window the line you
want to move.
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14. Click on the top snap point.
Let go of the mouse button.
Drag the mouse to the left and
Type: -1000 <Enter>.
The system changes the geometry of the model.
15. To verify it's correct,
Click Distance.
Click the 2 nodes on the line to measure between them.
The distance has been increased by 1000mm.
The lower elements updated as well.
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16. Click SE Isometric to reset the view of our plot.
Click File.
Click Save As.
Type: Rerun <Enter> for the file name.
17. Click the Batch Run button to start the analysis.
The system takes us to the Output Processor.
Click the Operating and Sustained Load Cases.
Click the Restraint Summary report.
Click View Reports.
We're trying to see a smaller FZ. It was about 2,000 before; now, it's about 1,000.
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18. Let's check the turbine again and see if this has improved the analysis results.
Close this report.
Close the Output Processor.
We're back to the main menu of CAESAR II.
Click the Analysis tab.
Click NEMA SM23.
Click on the NEMA Input Data tab.
19. We saved our model under a new name (Rerun) so we need to use that file in this analysis.
Click Select Loads by Job/Load Case.
Select RERUN_P.
Click OK.
Select the Operating Load Case.
Click OK.
Click the up arrow by the Nozzle field to go to the 2nd nozzle.
Click Refresh
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The system displays the new loads.
Click the Analyze button.
Let's review the results.
Well, we're not done yet, but we are meeting the standard values for turbine nozzle loads for
our size range.
We're going to look at one more analysis after this, and then we'll be done with this model.
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CAESAR II Statics - Turbine Design Video Nine
(Reference Video: C2_S_Turbo_V9)
1. OK. Our turbine is in good shape now from the standard point of view. Let's review some of
our other output for this model.
Close the NEMA report.
We're back at the CAESAR II main menu.
Click the Output tab.
Click Static.
Our focus is going to be on that spring that we selected.
Select the Operating and Sustained Load
Cases.
Select View Reports.
2. We've been modifying piping around node 21, and we put the spring. Let's take another look
at that node.
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3. You recall that we used to have a very, very large load here in the vertical direction. That's
why we had to put the spring in there, to carry load in a hot position. But look at the load in the
cold position; it's a very large load in a cold case. This load might be difficult to carry when
you're trying to align this equipment, so I would like to have a lower load here.
What's kind of interesting too, it's a big positive number. If we would disconnect this flange, it
would drift up away from the turbine nozzle. We can readjust the spring load automatically in
the program, and that's what we're going to do here. You can do a lot of fine tuning in
CAESAR II, and let's just take a look at making that number smaller.
4. Close this report.
Click Back to Input.
We have two different ways you can change the spring selection procedure.
Click in the "To" field.
Roll your mouse wheel until you to node 40. That's where the hanger is.
We can specify our own operating load by hand, and that will override what the program
calculates. Another option is to free up one of the connections when it calculates the hot load
at that point.
Let me rephrase that. We can have the program reallocate dead weight to other supports by
releasing an anchor or two in our model. Now what anchor would I want to release? Well, if
when I'm sizing the spring at node 40, if I disconnect the nozzle close by (node 21), then all of
the load will come back onto the hanger, and I might have a better load distribution between
the hangar and nozzle.
5. So we're going to give that a try. Let's tell the system to free the restraint at node 21-- that's
where the restraint is defined-- in the Y direction.
In the Free Restraint at Node field,
Type: 21 <Enter>.
In the Free Code field,
Select 1-Y.
These two cells work together. I usually release it only in the Y direction. The system releases
it only for that very first weight load case; everything else is buttoned up properly.
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6. Click the Batch Run button.
We want to see if the installed (Sustained) load is reduced without getting an excessively large
operating load.
Select Load Case 3 (OPE) and Load Case 4 (SUS).
Select Restraint Summary.
Click View Reports.
Let's review the report.
Now, this looks a lot nicer to
me. The installed load is only
34, which is very low.
We see it goes negative in the
Operating case. The value
earlier was about 2,000, and
now it's around 1,100 positive.
This is a much better installed
load.
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7. Let's run this through NEMA SM23 again and see how this change affects it.
Close this report.
Close the Output Processor.
We're back to the CAESAR II main menu.
Click on the Analysis tab.
Click on NEMA SM23.
Click the NEMA Input Data tab.
Click Refresh Loads from Current Job.
Set the Nozzle to 2.
Click Refresh Loads from Current Job.
Click the Analyze button.
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Our exhaust nozzle comes in at 67% of the allowable, and this is better. This is a better spring
overall in its installation and also in the resulting load on the turbine.
Let's go look at that spring directly.
8. Close this report.
Click the Output tab.
Click Static.
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Click Hanger Table W/Text.
Click View Reports.
We're now using an ANVIL size nine spring. If I recall, the other spring was a size 10; so it
went to a lighter spring, and it suits this installation much better.
So there you go. We've used the program to model part of the system, and used the Include
feature to bring in other subsets of our model. Most of our attention was on the turbine, but we
worked on both satisfying sustained load problems and expansion load problems to meet the
NEMA allowable load requirements for this turbine.
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