Technical Report
Example
(1)
Chartered (CEng)
Membership
A TECHNICAL REPORT IN SUPPORT OF APPLICATION FOR CHARTERED
MEMBERSHIP OF IGEM
DESIGN OF 600 (103 BAR) 820MM SELF SEALING REPAIR CLAMP AND
VERIFICATION USING LIMIT-LOAD ANALYSIS METHOD
DECEMBER 2011
1
Table of Contents
1. DECLARATION OF AUTHENTICITY .................................................................................... 3
2. INTRODUCTION ........................................................................................................................ 3
3. REVIEW OF DESIGN SPECIFICATION ................................................................................. 4
3.1
3.2
3.3
3.4
3.5
Review Customer Specification .............................................................................................. 5
Develop table of key design/service criteria .................................................................... 5
Determine Appropriate Standards to Apply to Design .............. Error! Bookmark not
defined.
Initial Decision on Manufacturing Process & Suitable Materials for Clamp Body
....................................................................................................... Error! Bookmark not defined.
Suitable Seal Materials .......................................................... Error! Bookmark not defined.
4. DEVELOPMENT OF DESIGN BY FORMULA CALCULATIONS TO DETERMINE
BASIC STRUCTURAL GEOMETRY PRIOR TO MODELLING FOR ANALYSIS
PURPOSES................................................................................................................................... 6
4.1
4.2
4.3
Determine Minimum Shell Thickness (see Appendix v, Section A) ........................... 6
Determine Clamp Body Thickness. Minimum Shell Wall Thickness ........................ 6
Determine Number, Dia., Grade of Bolts Using ASME VIII, Division2, Appendix 3320 (see appendix v, Section C) ......................................... Error! Bookmark not defined.
4.4
Determine Clamp Side Bar Dimensions (see appendix v, Section D) .............. Error!
Bookmark not defined.
4.4.1 Minimum Lug Height for Stress Limit - (see appendix v, Section D.1)............................. 7
4.4.2 Bolt Prising - (see appendix v, Section D.2).................. Error! Bookmark not defined.
4.4.3 Minimum Lug Height for Deflection Limit - (see Appendix v, Section D.3) ....... Error!
Bookmark not defined.
4.4.4 Test Pressure (see Appendix v, Section D.4) .............................................................................. 8
5. PRODUCTION OF SOLID MODEL OF PROPOSED GEOMETRY .................................... 8
6. SIMPLIFICATION OF MODEL FOR ANALYSIS PURPOSES ............................................ 9
7. IMPORTING MODEL INTO FINITE ELEMENT SOFTWARE .......................................... 9
8. MESH MODEL, APPLY CONSTRAINTS & LOADINGS .................................................... 10
9. SOLVE ANALYSIS .................................................................................................................... 13
9.1
9.2
9.3
Limit Load Analysis (Protection against plastic collapse) .........................................14
Elastic Analysis (Protection against local failure) .........................................................14
Ratcheting Assessment-Elastic Stress Analysis (Protection against cyclic loading
(not fatigue) ................................................................................................................................14
10. INTERPRETATION OF RESULTS ........................................................................................ 15
10.1
10.2
10.3
10.4
10.5
10.6
Limit Load Analysis................................................................. Error! Bookmark not defined.
Elastic Analysis ......................................................................... Error! Bookmark not defined.
Ratcheting Assessment – Elastic Stress Analysis ......... Error! Bookmark not defined.
Bolt Areas ................................................................................... Error! Bookmark not defined.
Deformation on Joint Plane ................................................. Error! Bookmark not defined.
Conclusion ....................................................................................................................................15
11. COMPILATION OF REPORT SUMMARISING APPROACH & RESULTS .................... 16
2
12. REVIEW BENEFITS/LIMITATIONS OF USING FINITE ELEMENT ANALYSIS FOR
PRESSURE SYSTEM COMPONENTS................................................................................... 16
3
1. DECLARATION OF AUTHENTICITY
I declare that this Technical Report represents an original piece of work by Antony
Nicholls and that the statements made herein are true to the best of my knowledge.
Signature:
----------------------------------------------
Name: Adam Thistlethwaite BEng MSc CEng MIGEM
Membership No. 800117
Engineering Manager – Furmanite EMEA
Offshore Panel Chairman – Pipeline Industries Guild
2. INTRODUCTION
I will demonstrate my knowledge and understanding of engineering principles to M
Eng. Level by undertaking the design process for a high pressure self sealing repair
clamp.
My previous employer, Furmanite, kindly offered to provide me with a project
placement during November 2011 so that I could design a clamp as the subject
matter of my Technical Report.
The clamp will be designed in accordance with API Specification 6H, which requires
design to be in accordance with the methodology set out in ASME Boiler and
Pressure Vessel Code design Based on Stress Analysis.
4
I will develop the basic design using formula calculations to determine basic
structural geometry (bolt sizes etc) and carry out stress analysis using finite element
analysis of a solid model of the clamp.
The design will demonstrate conformance to the requirements of the referenced
standards for gross plastic deformation, progressive plastic deformation, bolt areas
and service stresses and deflection on the joint faces.
My role in the project will be as Design Engineer with responsibility for the product
design.
Drawing number UKE06163-DWG-03 (see Appendix i) refers to a self sealing clamp
suitable for an 820mm pipe which was originally designed to ASME VIII Division1.
My project will use the same customer specification and drawing as the basis for a
design to ASME VIII Division 2.
Division 1 is based on design by rule (code
specified Formulae) and Division 2 is design by analysis (more rigorous calculations
involved). There are also numerous differences regarding material testing, NDE
requirements and low temperature impact testing that should be reviewed prior to
selecting a design approach. In short: Division 2 provides an engineered vessel with
calculated stresses closer to real stresses, combined with more rigorous testing,
allowing for savings in material costs (thinner parts may be used).
3. REVIEW OF DESIGN SPECIFICATION
5
3.1
Review Customer Specification
The
customer
specification
details
are
recorded
using
a
Furmanite
Specification Sheet (see Appendix ii) which utilises drop down boxes to limit the
range of options and to guide the sales department. This information was used
to define the specification of the clamp designed.
3.2
Develop table of key design/service criteria
Furmanite uses a Design Specification Review process (see Appendix iii) which
set out the design requirements in a standard tabular manner which aides the
review process and contributes to the design of a fit for purpose product.
Furmanite’s offers self seal clamps that conform to API 6H.
requirements for the project are:
Feature
Requirement
Design Pressure
Design
Temperature
Nominal Pipe
Dimensions
103.42 Bar (1500 Psi)
-29°C to 40°C
Defect Envelope
Materials
Corrosion
Allowance
Design
Calculations
Content
Nominal pipe O/D 820.00mm
Pipe tolerance as per API 5L will
be apply (+ 0.75%, -0.25%) Ovality
limits will be assumed to be within
the envelope defined above.
Max –826.15mm Min –817.95mm
152mm Between Seals
Shell Material - ASTM SA 516 Gr
60
Bolted Lugs – ASTM SA 516 Gr 60
Bolts – ASTM A193 B7
Nuts – ASTM A194 2H
3.2mm corrosion allowance
Generally in accordance with the
requirements of ASME VIII Div. 2
Methane
6
The key
Sections redacted.
4.
4.1
DEVELOPMENT OF DESIGN BY FORMULA CALCULATIONS TO
DETERMINE BASIC STRUCTURAL GEOMETRY PRIOR TO
MODELLING FOR ANALYSIS PURPOSES
Determine Minimum Shell Thickness (see Appendix v, Section A)
The determination of the shell thickness is derived from the basic formula for
hoop stress:
H 
PD
2t
Where
 H = hoop stress (MPa)
P = internal pressure (MPa)
D = Inside diameter (mm)
t = thickness of wall (mm)
I have calculated the minimum wall thickness in accordance with ASME VIII
Division 2, 2007 Part 4.
Main Shell thickness tD. min  33.729mm
Actual corroded shell thickness tDa  39.000mm
The final shell wall thickness of 42.5mm exceeds the minimum
requirements.
4.2
Determine Clamp Body Thickness. Minimum Shell Wall Thickness
Requirements & General Membrane Stress Intensity Limits (at design &
test conditions) Based on Formula for Cylindrical Shells Given in ASME
VIII 2, Appendix 4-222. (see Appendix v, Section B).
7
API 6H requires a check using a calculation for general membrane stress at
test pressure. The maximum membrane stress ( Pmfact ) must not exceed 83% (
Pm ) of the yield stress ( S yplate ) for the plate material
It can be seen that:
Pmfact  81.888% and is less than Pm
Sections redacted
4.4.1
Minimum Lug Height for Stress Limit - (see appendix v, Section D.1)
The maximum bending stress occurs in the plane of the bolt
centrelines. The effective length of the lug in this plane is reduced by
the bolt holes and is calculated as follows:
LLe  LL  i 1 N Bi  DBCi
i n
Where the index i is used to identify each of the n different stud/bolt
sizes used in the sector.
The minimum allowable height for the bolting lug H L min1 , to meet the
stress limit, is given by:
H L min 1 
   2  4 
2
HL min 1  81.54mm
Sections redacted
8
4.4.4
Test Pressure (see Appendix v, Section D.4)
The clamp will be tested in excess of the design pressure (a proof test)
and so the lug and bolt arrangement needs to be designed to prevent
excessive lug separation in the seal region at the test pressure.
The deflection due to bending and possible prising of the lugs should
be within the recommended allowable limit, YSa :
It can be seen from Appendix V section D.4 that the actial prising is
YSt  0.0898mm
5.
PRODUCTION OF SOLID MODEL OF PROPOSED GEOMETRY
A 3D Computer Aided Design (CAD) package was used and I worked with the
Furmanite design engineer who developed the 2D design into a 3D solid model
which was then imported into the Finite Element Analysis (FEA) software.
The creation of a 3D model creates geometry that the FEA software can interpret
and use to mesh the structure (see Figure 1).
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Figure 1 - Featured 3D solid Model:
6.
SIMPLIFICATION OF MODEL FOR ANALYSIS PURPOSES
Sections redacted
7.
IMPORTING MODEL INTO FINITE ELEMENT SOFTWARE
I imported the de-featured 3D model (volume), which was now 1/8th of the final
product into ANSYS FEA software as Parasolid file (this is in binary format and can
communicate and migrate 3D solids which are understood by the FEA software)
which defines volumes, areas, lines and points.
Orientation of the clamp was important as Furmanite use standard macro’s in
ANSYS and manipulation and analysis are easier if conventional axis orientation is
observed. For a straight clamp the X axis lies across the half joint plane, Y axis is
normal to the half joint face and Z axis along the main centreline.
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8.
MESH MODEL, APPLY CONSTRAINTS & LOADINGS
The meshing process required the volume to be divided into shell and lug
components in order to develop regular elements with minimum distortion to make
the analysis as accurate as possible. In the meshing process, I utilised 20 node
bricks for the shell and 10 node tetrahedrons for the lugs. The shell/lug interface
was meshed using 13 node pyramids, which provide a good transition between the
20 node bricks and 10 node tetrahedrons (see Figure 5).
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Figure 5 - Finite Element Mesh
Once the meshing was completed, I used a macro to define the bolting constraints
using real constant sets (see table 1), the key steps being:- create lines representing
the bolt centres (red line in Figure 5), create pre tension sections at the mid-length
point of the bolt line (green point in Figure 5) and link bolts to clamp volumes using
constraint equations which defined a rigid region.
Table 1 Real Constant Set
Real
Constant
Set
Minor Thread Minor Section
Dia.
Area
Representing
TKY and TKZ
AREA
inch
mm
mm2
Full Bolt 2.25 UN8 5.3254E+01 2.2274E+03
Area Moment of
Inertia
IYY and IZZ
mm4
3.9479E+05
A contact surface was then defined at the half joint faces (where opposing lugs
contact one another). As only one lug was being modelled, the contact surface was
defined as being rigid and fully constrained.
12
It was necessary to ensure that the model had sufficient constraints to prevent rigid
body motion, whilst at the same time not over constraining the model and inducing
unrealistic stresses and strains. As the clamp has three planes of symmetry, there
was no requirement for additional constraints.
The model therefore had 6º of
freedom, that is, the model was fixed from moving in the X, Y and Z axis and rotating
(ROT) in the X, Y and Z axis. The model was then saved to the database.
The following material properties were used for the analyses; Yield Stress, Tangent
Modulus, Young’s modulus and poisons ratio(yield stress only applies to the elasticplastic (limit) analysis).
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Table 2 Material Properties
Material ID1
Young’s Modulus (E) MPa
205000
(Solid Structure)
Poisson’s Ratio
0.3
Yield Stress MPa
207
Tangent (Plastic) Modulus
0
Plasticity Model
Bilinear Kinematic
Hardening
Material ID2
Young’s Modulus (E) MPa
205000
(Bolts)
Poisson’s Ratio
0.3
Yield Stress MPa
723
Tangent (Plastic) Modulus
0
Plasticity Model
Bilinear Kinematic
Hardening
Coefficient of Friction
0
Material ID3
(Joint Contact)
9.
SOLVE ANALYSIS
ASME VIII, Division 2, Part 5 design-by-analysis, requires that four potential failure
modes be considered:
a. Protection against plastic collapse
b. Protection against local failure
c. Protection against collapse from buckling
d. Protection against failure from cyclic loading
Failure modes a), b) and d), are all applicable to the clamp and conditions being
analysed, as the material thickness and configuration are established through
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design-by-analysis rules. The clamp will not be subjected to loads that will induce a
compressive stress field and so mode c) is not applicable in this case.
Each of the analysis runs were performed on an ANSYS model. The primary
pressure loading was applied to a set of areas called “AP_1” which represents the
pressure area of the sectioned clamp (see Figure 6).
Figure 6 - Areas on which internal pressure was imposed
9.1
Limit Load Analysis (Protection against plastic collapse)
Sections redacted
9.3
Ratcheting Assessment-Elastic Stress Analysis (Protection against cyclic
loading (not fatigue)
Sections redacted
15
10. INTERPRETATION OF RESULTS
Sections redacted
Figure 7 – Deflection of Half Joint Face at Test Condition
10.6 Conclusion
The design was shown to meet the requirements of the referenced standards
for gross plastic deformation, progressive plastic deformation, bolt areas and
service stresses.
Deflection on the joint faces was also within acceptable
limits. The design was therefore considered to be acceptable.
16
11. COMPILATION OF REPORT SUMMARISING APPROACH &
RESULTS
The results of the analysis were compiled into a standard design validation report
(see appendix IX) that sets out the design specification and performance of the
clamp.
12. REVIEW BENEFITS/LIMITATIONS OF USING FINITE ELEMENT
ANALYSIS FOR PRESSURE SYSTEM COMPONENTS
Sections redacted
17