Chapter 11
PIPING
Section 1.0 Scope
This chapter provides general and specific requirements not only for plant or building piping but also for
general piping installations. It includes Power Piping System Design and pipe color coding for safety and
proper fluid identification in the system.
Section 2.0 Definitions
Pipe and Tube – the fundamental difference between pipe and tube is the dimensional standard to which
each is manufactured. A pipe is a tube with a round cross section conforming to the international
requirements for nominal pipe size as tabulated in the table for pipe schedules.
A tube is a hollow product of round or any other cross section having a continuous periphery. Round tube
size maybe specified with respect to any two, but not all three of the following: outside diameter or bell at
one end into which the plain or spigot and of another piece is inserted when laying. The joint is then made
tight by cement, oakum, lead, or rubber caulked into the bell around the spigot.
Black Pipe – steel pipe that has not been galvanized.
Bell and Spigot Joint – the most commonly used joint in cast-iron pipe. Each piece is made with an
enlarged diameter or bell at one end, into which the plain or spigot end of another piece is inserted when
laying. The joint is then made tight by cement, oakum, lead, or rubber caulked into the bell around the
spigot.
Bull Head Tee – A tee the branch of which is larger than the run.
Butt Weld Joint – A welded pipe joint made with the ends of the two pipes butting each other, the weld
being around the periphery.
Carbon Steel Pipe – Steel pipe which owes these properties chiefly on the carbon which it contains.
Check Valve – A valve designed to allow a fluid to pass through in one direction only. A common type has
a plate so suspended that the reverse flow aids gravity in forcing the plate against a seat, shutting off
reverse flow.
Compression joint – a multi-piece joint with cup shape threaded nuts which, when tightened, compress
tapered sleeves so that they form a tight joints on the periphery of the tubing they connect.
Cross-Over – a small fitting with a double offset, or shaped like the letter U with the ends turned out. It is
only made in small sizes and used to pass the flow of one pipe past another when the pipes are in the same
plane.
Expansion Loop – a large bend in pipe line to absorb longitudinal expansion in the pipe line due to heat.
Galvanized pipe – steel pipe coated with zinc to resist corrosion.
Gate Valve – A valve employing a gate, often wedge-shaped, allowing fluid to flow when the gate is lifted
from the seat. Such valves have less resistance to flow than globe valves.
Globe valve – one with a somewhat globe shaped body with a manually raised or lower disc which when
closed rests on a seat so as to prevent passage of a fluid.
Header - a large pipe or drum into which each of a group of pipe is connected. Also used for a large pipe
from which a number of smaller ones are connected in line and from the side of the large pipe.
Malleable Iron – Cast iron head-treated to reduce its brittleness. The process enables the materials to
stretch to some extent and to stand greater shock.
Manifold – a fitting with a number of branches in line connecting to smaller pipes. Used largely as an
interchangeable term with header.
Medium pressure – when applied to valves and fittings, implies they are suitable for the working pressure
of from 862 to 1207 kPa (125 to 175 psi).
Mill Length – also known as random lengt. Run-of-mill pipe is 4880 mm to 6000 mm in length. Some pipes
are made in double lengths 9150 to 10675 mm.
Relief Valve – Designed to open automatically to relieve excess pressure.
Run - a length of pipe made of more than on piece of pipe; a portion of a fitting having its end in line or
nearly so, in contradistinction to the branch or side opening, as of a tee.
Saddle Flange – A flange curved to fit a boiler or tank and to be attached to a threaded pipe. The flange is
riveted or welded to the boiler or tank.
Screwed Flange – a flange screwed on the pipe which is connected to an adjoining pipe.
Socket weld – A joint made by use of a socket weld fitting which has a prepared female end or socket for
insertion of the pipe to which it is welded.
Standard Pressure – Formerly used to designate cast-iron flanges, fittings, valves, etc. , suitable for a
maximum working steam pressure of 862 kPa.
Street elbow – an elbow with a male thread on one end, and female thread on the other end.
Stress-Relieving – uniform heating of a structure or portion thereof to a sufficient temperature to relieve
the major portion of the residual stresses, followed by uniform cooling.
Wrought Iron – iron refined to a plastic state in a pudding furnace. It is characterized by the presence of
about 3 percent slag irregularly mixed with pure iron and about 0.5 percent carbon.
Wrought Pipe – this term refers to the both wrought steel and iron. Wrought in this sense means worked,
as in the process of forming furnace-welded pipe from skelp, or seamless pipe from the plates or billets.
The expression wrought pipe is thus used as a distinction from cast pipe. When wrought-iron pipe is referred
to, it should be designated by its complete name.
Section 3.0 General Requirement
3.1. All piping should run parallel to building walls.
3.2. Grouped piping shall be supported on racks either on horizontal or vertical planes.
3.3. All piping to headers shall come from below rack.
3.4. All piping from the header shall go up above the rack.
3.5. All piping below or above racks shall be supported on separate racks.
3.6. All piping should run with slight inclination for drainage of main header.
3.7. All piping on racks shall have a sufficient spacing for pipe or chain wrenches so that any single line can
be altered without disturbing the rest of the piping rack.
3.8. All piping 63.5 mm and above shall be flanged while smaller sizes can be screwed.
3.9. On long headers, a pair of flanges shall be provided for every three lengths of 6000 mm of pipes smaller
than 63.5 mm.
3.10. On long headers, a pair of unions shall be provided for every three length of 6000 mm of pipes smaller
than 63.5 mm.
3.11. All piping subject to varying temperatures shall be provided with expansion joints or expansion loops
to take care of expansion.
3.12. No galvanized piping shall be used for steam.
3.13. No piping material shall be used that is easily corroded by the material passing thru.
3.14. All piping shall be clamped by “U” bolts or clamps to supporting racks except steam piping. All steam
piping shall be supported on rollers or sliding support for expansion.
3.15. Piping support shall be placed on a 3000 mm interval or less.
3.16. All steam piping shall be supported on rollers or sliding support for expansion.
3.17. All piping carrying pressure shall be of sufficient bursting strength for the pressure applied. A minimum
factor of safety of 4 for working pressure applied shall be used.
3.18. A minimum factor of safety of 4 for working pressure shall be used.
3.19. For conveying liquid subjects to water hammer, additional safety factor of a minimum of 100% of
working pressure shall be used.
3.20. Piping support shall be placed on a 3000 mm interval or less.
3.21. All piping carrying steam, hot water or hot liquids shall be properly insulated to prevent accidental
contact and loss of heat.
3.22. Drains from the steam piping shall be provided with steam straps.
3.23. On all screwed joints, the threaded portion shall enter fittings with three threads by hand before a pipe
wrench is applied.
3.24. Pipe wrench shall be lubricated by white lead, red lead, graphite and oil or other approved thread
lubricants before tightening.
3.25. No rubber or rubberized gasket shall be used for steam or hot liquids.
3.26. A shut off valve shall be installed on every branch from the header.
3.27. All piping shall be reasonably cleaned before installation.
3.28. All piping shall be free from burrs or protruding metals inside.
3.29. No piping carrying steam or hot liquids shall be embedded on concrete walls or floors.
3.30. Where piping has to be located in trenches the pipe shall be supported on steel branches on floor of
trench.
3.31. Where piping has to be located in trenches a suitable drainage or sump for removal of liquid
accumulations shall be provided for trench.
3.32. Where piping carrying steam or hot liquids have to pass walls of concrete suitable sleeves made of
pipes ones size bigger shall be imbedded in concrete before piping is laid.
3.33. Piping to all equipment shall not be subjected to any stress on equipment being connected.
3.34. Pipe carrying liquids with solid shall use long radius elbows or tees with plugs in the direction of flow.
Section 4.0. Identification colors for pipes
4.1. Identification of piping by color, or color bands at convenient locations shall be as follows:
Material Piped
Pipe color
Pipe identification
Acetylene
Orange
Acetylene
Acid
Yellow
Acid
Air-high pressure
Yellow
H.P. air
Air-low pressure
Green
L.P. air
Ammonia
Yellow
Ammonia
Argon-low pressure
Green
L.P. argon
Blast furnace gas
Orange
B.F. gas
Carbon dioxide
Green
Carbon dioxide
Gasoline
Orange
Gasoline
Grease
Orange
Grease
Helium-low pressure
Green
L.P. Helium
Hydrogen
Orange
Hydrogen
Nitrogen-low pressure
Green
L.P. Nitrogen
Oxygen
Orange
Oxygen
Oil
Orange
Oil
Steam-high pressure
Yellow
H.P. Steam
Steam-low pressure
Yellow
L.P. Steam
Tar
Orange
Tar
Producer gas
Orange
Producer gas
Liquid petroleum gas
Orange
L.P.G.
Vacuum-high
Orange
High vacuum
Water-boiler feed
Yellow
Boiler feed Water
Water-cold
Green
Cold Water
Water-distilled
Green
Distilled Water
Water (fire service)
Red
Fire Service Water
Water-hot
Yellow
Hot Water
Water-low pressure
Green
L.P. Water
Water-high pressure
Yellow
H.P. Water
Water-treated
Green
Treated water
Oil and water (for hydraulic Green
Oil and water
system)
Oil and water (for hydraulic Orange
Oil and water
system)
In addition to color coding, the specific content of piping must be identified by sticker, stencil, tag, etc.
4.2. Color bands and pipes flow identifications shall be as specific and installed as shown in page 192.
Section 5.0 Fluid Flow Velocities
5.1. In practice, the average fluid flow velocities maybe shown as follows:
A. Water
…….
1.5-3.0 meter/second
B. High pressure saturated steam
…….
25-50 meter/second
C. High pressure superheated steam
…….
50-77 meter/second
D. Atmospheric Exhaust steam
…….
40-60 meter/second
E. Low pressure exhausted steam
…….
100-120 meter/second
Section 6.0 Power piping system design
6.1. Scope. Power piping system include all steam, water and oil piping and the component parts such as
the pipe, flanges, bolting, gaskets, valves and fittings for steam generating plants, central heating plants
and industrial plants.
6.2. Materials. Material used shall conform to table 11.6.2, any material other than those specified should
meet the physical and chemical requirements and, test of the latest revision of the respective specifications
in the table 11.6.2.
6.3. Valves. It is mandatory that valves be (a) of the design or equal to the design which the manufacturer
thereof recommends for the service, and (b) of materials allowed by the code for the pressure and
temperature.
6.4. Wall thickness. The following formula shall be used to determine the pipe wall thickness:
𝑡𝑚 =
𝑃𝐷
+𝐶
2𝑆 + 𝑌𝑃
Where:
𝑡𝑚 =minimum pipe wall thickness in mm
P= maximum internal service pressure in kPa
t = nominal pipe wall thickness in mm
D = outside diameter of the pipe in mm
S= Allowable stress in materials in kPa
C= allowance for threading, mechanical strength and/or corrosion in mm
Y= coefficient for values
6.5. Variation in pressure and temperature. Either pressure or temperature, or both, may exceed the
nominal design values if the computed stress in the pipe wall calculated for the pressure doesn’t exceed
the allowable S value in table 11.6.5 and 11.6.5a for the expected temperature by more than the following
allowances for the period of duration indicated.
A. Up to 15 percent increase above the S value during 10 percent of the operating period.
6.6. Pressure reducing and relief valves
A. Where pressure reducing valves are used, one or more relief or safety valves shall be provided on the
low pressure side of the reducing valve in case the piping or equipment on the low pressure side does not
met the requirement for full initial pressure. The relief of safety valve shall be located adjoining or as close
as possible to the reducing valve. Proper protection shall be provided to prevent injury or damage caused
by escaping fluids from relief or safety valves in vented to the atmosphere. The vents shall be of ample size
and as short and direct as possible. The combined discharge capacity of the relief valves shall be such that
the pressure rating of the lower pressure piping and equipment will not be exceed if the reducing valves
sticks open.
B. It is mandatory that the pressure gauge be installed on the low pressure side of the reducing valve.
6.7. Pipe
A. For pressure above 4137 kPa, the pipe shall be:
1. seamless steel meeting ASTM specifications A-106, A-312, A-335 or A-378; or
2. forged or bored steel meeting A-380; or
3. Automatic welded steel meeting A-312.
4. electric-fusion welded steel pipe meeting with ASTM specifications A-155…
B. For pressure above 1724 kPa, but not above 4137 kPa, shall be:
1. Seamless steel in accordance with ASTM specification A-106
2. Electric-fusion welded steel pipe in accordance with ASTM specification A-155.
3. Electric resistance welded steel pipe of ASTM specification of A-135 or
4. Seamless or electric resistance welded steel pipe of ASTM specification of a-53
C. For service up to 400oC and pressure of not over 1724 kPa, any of the following classes of pipe may be
used:
1. Electric fusion welded steel of ASTM specification A-134 or A-139
2. Electric resistance welded steel pipe of ASTM specification A-135, or
3. Wrought iron pipe of ASTM specification A-72.
D. Grade A seamless steel pipe of ASTM specification A-106, wrought iron pipe of ASTM specification A72, Grade A seamless steel pipe of ASTM A-53, A-135 or A-139 shall be used for close coiling, cold bending
or other uses.
E. Pipe permissible for the service specified in Sec. 11.6.7.3 may be used for temperature higher than 400
C unless otherwise prohibited, if the S value in accordance with Sec. 11.6.4 is used when calculating the
pipe wall thickness.
F. Pipe meeting API Specification 5L may also be used.
6.8. Boltings
A. The following standards shall apply to bolting:
1. For steam service pressure in access of 1724 kPa or for steam or water service temperature
exceeding 232 C, the bolting material shall conform to ASTM specification A-193. For temperature
exceeding 400 C, only bolt studs are recommended. When sast iron flanges are used, bolting material shall
be of carbon steel conforming to ASTM specification A- 307, Grade B, or A-107, Grade 1120.
B. Flange bolts or bolt-studs shall be of the dimension and material specified for the purpose in the
corresponding American flange standards. Bolts or bolt-studs shall extend completely through the nuts and
if desired, may have reduced shanks of a diameter not less than the diameter at root of threads.
C. Nuts shall conform to ASTM specification A-194.
6.9. Flanges
A. Flanges shall conform to the American standard B 16.5 for respective pressures and temperature or to
the specifications set by the manufacturer.
B. 172 kPa and class 862 kPa cast iron integral or screwed companion flanges maybe used with a full
gasket or with a ring gasket extending to the inner edge of the bolt holes. When using a full face gasket,
the bolting maybe of heat treated carbon steel, or alloy steel. When using a ring gasket, the bolting shall be
of carbon steel equivalent to ASTM A-307, Grade B, without heat treatment other than stress relief.
C. When bolting together two class 1724 kPa integral or screwed companions cast iron flanges, having 1.6
mm raised steel equivalent to ASTM A-307, Grade B. without heat treatment other than the stress relief.
D. 1034 kPa steel flanges maybe bolted to cast iron valves, fitting or other parts, having either integral class
862 kPa companion flanges. When such construction is used, the 1.6 mm raised face on the steel flange
shall be removed. When bolting such flanges together using a ring gasket extending to the inner edge of
the bolt holes, the bolting shall be of carbon steel equivalent to ASTM A-307 Grade B, without heat
treatment other that stress relief. When bolting such flanges together using full face gasket, the bolting
maybe heat treated carbon steel or alloy steel.
E. 2069 kPa steel flanges maybe bolted to cast iron valves, fittings, or other parts having either integral
class 1724 kPa cast iron flanges or screwed class 1724 kPa cast iron companion flanges without any
changes in the raised faces on either flange. Where such construction is used, the bolting shall be of carbon
steel equivalent to ASTM A-307 Grade B, without heat treatment other than stress relief.
6.10 Fittings
A. The minimum metal thickness of all flange or screwed fittings and the strength of factory made welding
fittings shall not be less than that specified for the pressure and temperatures in the respective American
standard.
B. All fittings in nominal sizes above; 80 mm for pressure above 1724 kPa but not above 2758 kPa; 50mm
for pressure above 2758 kPa but not above 4137 kPa, and 40 mm for pressure above 4137 kPa but not
above 17238 kPa shall have flanged ends or welding ends.
6.11 Gaskets
A. Gaskets where required, shall be of a material that resist attack by the fluid carried in the pipe line, shall
be strong enough to hold the pressure, and perform the purpose intended throughout the temperature range
encountered. Gaskets shall be as thin as the finish of surface will permit to reduce possibility of blowing
out.
B. Paper, vegetable fiber, rubber or rubber inserted gaskets shall not be used for temperatures in excess
of 121 C.
C. Asbestos compositions gaskets maybe used as permitted in the American standard for steel pipe flanges
and flange fittings. This type of gaskets shall not be used on lines carrying oil or other liquids above their
spontaneous ignition temperatures.
D. The use of metal or metal asbestos gaskets is not limited as to pressure provided that the gasket material
is suitable for the service temperature. These types of gaskets are recommended for use with small male
and female or the small tongue and groove facings. They may also be used with steel flanges having large,
male-and-female, large tongue and groove, or raised face.
6.12 Hangers, Supports, Anchors
A. Piping and equipment shall be supported in a thoroughly substantial and workman like manner, rigid
enough to prevent excessive vibration and anchored sufficiently to prevent undue strains on boilers and the
equipment served. Hangers, supports, and anchors shall be made of durable materials. In tunnels and
buildings of permanent fire proof construction, piping may be supported on or hung from wood structures if
all piping used for conveying fluids at temperatures above 121 C is spaced or insulated from such wooden
members to prevent dangerous heating.
B. Hangers and supports shall permit free expansion and contraction of the piping between anchors. All
piping shall be carried in adjustable hanger properly leveled supports, and suitable springs, sway bracing,
vibration dampener, etc. shall be provided where necessary.
6.13 Pipe sleeves
A. Where steam pipe pass through wall, partitions, floors, beams, etc. , constructed of combustible material,
protecting metal sleeves or thimbles shall be provided to give a clearance of not less than 6.35 mm under
hot and cold conditions all around the pipe, or pipe and covering. When steam pipes pass through metal
partitions, etc. a clearance of at least 6.35 mm under hot and cold condition shall be left all around the pipe,
or pipe covering. In any cases, if the fluid temperature exceeds 121 C, the pipe shall be insulated inside
the sleeve with a covering of at least standard thickness.
B. Walls, floors, partitions, beams, etc., shall not be cast solidly to or built up around and in contact with a
steam, hot water, or hot oil pipe. Where such pipe must be installed in a concrete floor or other building
member., it shall be protected for the entire buried length with a suitable protecting pipes sleeve of steel,
cast iron wrought iron or tile; exception maybe taken to the proceeding rules where pipes pass through
walls; floors, partitions, etc., that must be kept water light.
6.14 Drains, Drips, and Steam Traps
A. Suitable drains or drips shall be provided whatever necessary to drain the condensate from all sections
of the piping and equipment whenever it may collect. Suitable drains shall also be provide to empty water
lines, water storage tanks, equipment containing water, etc., when such piping and equipment is out of
service. At least one valve shall be place in each drip or drain line.
B. Drip lines from the steam headers, mains, separators, and other equipment shall be properly drained by
traps installed in accessible locations and below the level of the apparatus drained. Drip pumps, drip maybe
used in lieu of traps, if they are safely installed, protected and operated under a regular supervision. All
drain lines shall have drip valves for free blow to the atmosphere.
C. Drip lines from the steam headers, mains, separators, and other equipment operating at different
pressure shall not be connected to discharge through the same trap. Where several traps discharge into
one header which is or maybe under pressure, a stop valve and a check valve shall be placed in the
discharge line from each trap.
D. Trap discharge piping shall have the same thickness as the inlet piping unless it is vented to atmosphere
or operated under low pressure and has no stop valves. The trap discharge piping shall have at least the
pressure to which it may be subjected against freezing when necessary. Drainage from the straps, if open
to atmosphere, shall be safeguarded to prevent accidents from hot discharge.
6.15 Hydrostatic tests
A. Before Erection. All valves, fittings, etc. shall be capable of withstanding a hydrostatic shell test made
before erection equal to twice the primary steam service pressure, except that steel fittings and valves shall
be capable of withstanding the test pressure as given in the American standard for steel pipe flanges fittings
for the specific material, pressure standard and facing involved. Pipe shall be capable of meeting the
hydrostatic test requirements contained in the respective specifications in table 11.6.2, under which it is
purchased.
If a hydrostatic mill test pressure for pipe is not stated in any of the specifications enumerated in table
11.6.2, the pipe shall be capable of meeting a minimum internal hydrostatic test pressure determined from
the formula;
𝑃=
2𝑆𝑡
𝐷
Where:
P= test pressure in kPa
t = nominal pipe wall thickness in mm
D= pipe outside diameter in mm
S= allowable stress in material in kPa and which shall be taken as not less than 50 percent of the specified
yield point of the material except that hydrostatic test shall not exceed 17238 kPa for sizes 80mm and
below, or 19306 kPa for sizes over 80 percent of the specified yield point.
B. After erection. All piping systems shall be capable of withstanding a hydrostatic test pressure of one and
one-half times the design pressure, except that the test pressure shall in no case exceed the adjusted
pressure temperature rating for 38 C as given in the American standard for steel pipe flanges and flange
fittings for the material and pressure standard involved. For systems joined wholly with welded joints the
adjusted pressure rating shall be that for ring joint facing, for system joined wholly or partly ith flanged joints
the adjusted pressure rating shall be that for the type of facing used.
6.16 Expansion and flexibility
A. Piping systems are subject to a diversity of loadings creating stresses of different types and patterns, of
which only the following more significant ones need generally be considered in piping stress analysis:
1. Pressure, internal and external
2. Weight of pipes, fittings and valves, containing fluid and insulation, and other external loadings such as
wind.
3. Thermal expansion of the line.
B. Materials. The thermal expansion range shall be determined from the table 11.6.16.2 as the difference
between the unit expansion shown for the maximum normal operating metal temperature and that for the
minimum normal operating metal temperature. For materials not included in this table, reference shall be
made to authority source data, such as publication of the National Bureau of Standards. The cold and hot
moduli of elasticity, Ec and Eh, and the moduli of torsional rigidity, Gc and Gh, respectively, maybe taken
as the values shown for the minimum and maximum normal operating metal temperatures in table
11.6.16.2a for ferrous and table 11.6.16.2b for non –ferrous materials.
C. For flexibility calculations, Poisson’s ratio may be taken as 0.3 at all temperatures for all ferrous materials.
D. The S values, Sc and Sh at the minimum and maximum operating metal temperatures, respectively, to
be used for determining the allowable expansion stress range SA shall be taken for the type of piping
system involved from the applicable tables in the respective sections of the code. In the case of welding
pipe, the longitudinal-joint efficiency maybe disregarded in calculating expansion stresses.
6.17 General
A. Piping systems shall be designed to have sufficient flexible to prevent thermal expansion from causing:
1. Failure from over-stress of the piping material or anchors
2. Leakage at joints
3. Detrimental distortion of connected equipment resulting from excessive thrusts and moments.
B. Flexibility shall be provided by changes of direction in the piping through the use of bends, loops, and
off-sets; or provision shall be made to absorb thermal strains by expansion joints of the slip joints or bellows
type. If desirable flexibility maybe provided by increasing or corrugating portions or all of sufficient strength
and rigidity shall be installed to provide for end of forces due to fluid pressure and other causes.
C. Basic assumptions and requirements
1. Formal calculations or model test shall be required when reasonable doubt exist as the adequate
flexibility of a system. Each problem shall be analyzed by a method appropriate to the conditions.
No hard and fast rule can be given as to when as analysis should be made. However, in the
absence of better information the need for a formal stress analysis for a two-anchor system of uniform pipe
𝐷𝑌
size is indicated when the (𝐿−𝑈)2 ≤ 0.03 following approximate criterion is not satisfied:
Where:
D= nominal pipe size, 1 mm
Y= resultant of movements to be absorbed by pipe line, mm
U= anchor distance, meter
L= developed length of line axis, meter.
1. In calculating the flexibility of a piping system between anchor points, the system shall be treated
as a whole. The significance of the whole parts of the line and of all restraints such as solid hangers
or guides, including intermediate restraints introduced for the purpose of reducing moments and
for forces on equipment or small branch lines shall be recognized.
2. Calculations shall take into account stress-intensification factors found to exist in components other
than plain straight pipe. Credit may be taken for the extra flexibility of such components. In the
absence of more directly applicable data, the flexibility factors shown in figure 11.6.17.3 may be
used.
3. Dimensional properties of pipe and fittings as used in flexibility calculations, shall be based on
nominal dimensions. The pressure stresses for services subject to severe corrosion shall be based
on the reduced thickness of the pipe.
4. The total expansion range from the minimum to the maximum normal-operating temperature shall
be used in all calculations, whether piping is cold sprung or not. Not only the expansion of the line
itself, but also linear and angular movements of the equipment to which it is attached, shall be
considered.
5. Calculations for expansions stress 𝑆𝐸 shall be based on the modulus of elasticity 𝐸𝑐 at room
temperature.
6.18 Stresses and reactions
A. Using the foregoing assumptions, the stresses, and reactions due to expansion shall be
investigated at all significant points.
The expansion stresses shall be combined in accordance with the 𝑆𝐸 = √𝑆𝑏2 + 4𝑆𝑡2
Following formula
Where:
Sb = iMb/z= resultant bending stress Kpa
St = Mt/2z = torsional stress
Mb = resultant bending moment, newton metre
Z = Section modulus of pipe (m3)
I = stress intensification factor
B. the maximum computed expansion stress, SE based on 100 percent of the expansion and EC for the
cold condition shall not exceed the allowance stress range, S A
Where :
SA = f ( 1.25 Sc + 0.25 Sh) in the above formula
SC = allowable stress (S value) in the hot condition
Sh = allowable stress (S value) in the hot condition
SC and Sh are to be taken from table in the application sections of the code
f = stress- range reduction factor for cyclic conditions. In the absence of more applicable data.
The values of f shall be taken from the following table :
Attach Fig. 11.6.1.7.3 © and Fig. For graph for k and i.
Total No. of Full Temp.
Cycles Over Expected Life
Stress Reduction
Factor f
7 000 and less
14 000 and less
22 000 and less
45 000 and less
100 000 and less
250 000 and less
1.0
0.9
0.8
0.7
0.6
0.5
By expected life is meant total number of years during which system is expected to be in active operation.
The sum of the longitudinal stresses due to pressure, weight and other sustained external loadings shall
not exceed Sh.
Where the sum of these stress is less than Sh the difference between Sh and this sum may be added to the
term 0.25 Sh in the above formula. The longitudinal pressure stress Sep be determined by dividing the force
due to internal pressure:
𝐹=
𝑝𝜋𝑑 2
4
By cross-sectional area of the pipe wall
𝐴=
𝜋 2
(𝐷 − 𝑑 2 )
4
Or
𝑆𝑒𝑝 =
In which
Sep = longitudinal pressure stress, Kpa
P = internal pressure , Kpa
𝐹
𝑝𝑑
= 2
𝐴 𝐷 − 𝑑2
D = nominal outside diameter of the pipe minus two times the normal wall thickness in
mm
D = nominal outside diameter of pipe mm
(a) The reactions (force and moments) Rh and RC in the hot and cold conditions,
𝑅𝑛 = (1 −
2
𝐸ℎ
𝐶) 𝑅𝐶
3
𝐸𝐶
𝑅𝑛 = (1 −
𝑆ℎ 𝐸𝐶
.
)𝑅
𝑆𝑒 𝐸ℎ
𝑅𝑛 = 𝐶𝑅 , or
Respectively, shall be obtained as follows from the reactions R derived from the flexibility
calculations based on the modulus of elasticity at room temperature Ec.
Whichever is greater and with the further condition that:
𝑆ℎ
𝑆𝐸
𝐸
. 𝐸𝑐
ℎ
is less than 1
Where:
C = cold spring factor varying from zero for no cold spring to one for 100 percent cold spring
SE = maximum computed expansion stress
EC = modulus or elasticity in the cold condition
Eh = modulus of elasticity in the hot condition
R = range of reactions corresponding to the full expansion range based on Ec
Rc and Rh represent the maximum reactions estimated to occur in the cold and hot conditions,
respectively
B. the design and spacing of the support shall be checked to assure that the sum of the longitudinal
stress due to weight, pressure, and other sustained external loading does not exceed S h .
Section 7.0 Industrial Gas and Air Piping Systems
7.1. This includes air and gas in mines, power plants, industrial and gas manufacturing
plants.
A. Piping with metal temperature above 232 ®C or below -2.9 ®C.
B. Air piping systems operating at pressures 207 kPa or less.
C. Piping lines with firebrick or other refractory material use for conveying hot gasses.
7.2. Wall Thickness of Pipe
The minimum thickness of pipe wall required shall be determined by the following formula
for the designated pressure and for the temperature not exceeding 232 ®C.
𝑡𝑚
𝑃𝐷
=𝐶
2𝑆 + 0.8𝑃
Where:
P= maximum allowable, operating pressure in kPa. The value obtained maybe rounded to the net
higher unit of 10. The maximum allowable operating pressure computed with S values permitted
under this paragraph, shall not exceed two-thirds of the mil test pressure for a service temperature
of 38 ®C or less five-ninths of the mil test pressure for a service temperature of 232 ®C.
S= maximum allowable hoop stress in kPa, see table 11.7.2
For steel or wrought-iron pipe, the value of S shall be 0.6 K for a service temperature of 38 ®C or
less or 0.52 K for a service temperature of 232 ®C where K is the stipulated minimum effective
yield strength calculated in the manner described in section 11.7.3.
Tm = minimum pipe wall thickness in mm
C= corrosion in mm obtained from the ff:
Type of pipe inches(mm)
Threaded steel, wrought-iron or
1.7 mm whichever is larger
Grooved steel or wrought-iron
Plain end steel or wrought-iron
Value in C in
Depth of thread or
Depth of groove
1.7 mm
D= outside diameter of pipe in mm
7.3. Effective Yield Strength (K)
The effective yield strength K of steel or wrought-iron pipe maybe determined by taking the
product of Y, the stipulated minimum yield strength , and E, efficiency of the longitudinal joint. The
value of E shall be taken from the following:
Specification
Number
ASTM A-53
Pipe type
Steamless
Electric resistance welded
Furnace lap welded
Furnace butt welded
F (Factor)
1.00
1.00
0.80
0.60
ASTM A- 106
ASTM A-134
ASTM A-135
ASTM A-139
ASTM A-155
API 5L
Seamless
Electric fusion welded
Electric resistance welded
Electric fusion welded
Electric fusion welded
Seamless
Electric resistance welded
Electric flash welded
Furnace flash welded
Steamless
Electric resistance welded
Electric flash welded
Submerge Arc Welded
1.00
0.80
1.00
0.80
1.00
1.00
1.00
1.00
0.80
1.00
1.00
1.00
1.00
Alternatively, the effective yield strength maybe determined by internal hydrostatic pressure test on
finished lengths of pipe or on cylindrical samples cut from the results of such tests in accordance
with the following formula:
𝐾=
𝑃𝑦 𝐷
2𝑡
Where:
K= effective yield strength in kPa
Py= pressure at the yield stress or the pipe in kPa
This maybe taken as the pressure required to cause a volumetric offset of 0.2 percent of as the
pressure required to cause a permanent increase in the circumference of 0.1 percent at any point,
but other suitable methods of determining that the stress in the steel has reached the yield strength
maybe used, provide such methods conform in all respects to recognized engineering practices,
T= stipulated nominal pipe wall thickness in mm
D= stipulated outside diameter of pipe in mm.
Section 8.0 Refrigerator Piping Systems
8.1. Refrigeration piping shall be understood to comprise all refrigerant and brine piping, whenever
used and whether erected on this.
8.2. Minimum design pressures for refrigerant piping
A. Piping systems for refrigerants shall be designed for not less than the pressures given
in table 11.8.2.1
B. For refrigerant not listed in table 11.8.2.1 the design pressure for the high-pressure side
shall not less than the saturated vapor pressure for the low-pressure side shall not be less than the
saturated vapor pressure of the refrigerant at 32 ®C. For the refrigerant not listed in the table 1.8.2.1
and having a critical temperature below 54 ®C, the design pressure for the high pressure side shall
be not less than 1.5 times the critical pressure and the design pressure for the low-pressure side
shall be not less than the critical pressure. In no case shall be design pressure be less than 207
kPa.
C. Piping system for the brine shall be designed for the maximum pressure which can be
impose in the system in the nominal operation, but not less than 689.5 kPa including for cast-iron
pipe, the water hammer allowance as shown in table 11.8.2.3
D. For working temperatures below 18 ®C, an allowance for brittleness of castings,
forgings, bolting, and pipe shall be made as follows:
CAST IRON, WROUGHT IRON, and CARBON STEEL ferrous materials shall have the design
pressure including allowance for water hammer increased 2 percent for each degree below 18 ®C
and shall not be used below -73 ®C.
COPPER, BRASS, BRRONZE. No adjustment
8.3. Thickness of Pipe
The minimum thickness of pipe wall required shall be determined by the following formula:
𝑡𝑚 =
𝑃𝐷
=𝐶
2𝑆 + 0.8𝑃
Where:
Tm = minimum pipe wall thickness in mm
P= maximum internal service pressure in kPa (plus allowance for temperatures as provide in
section 8.4 and hammer water allowance for cast-iron pipe as provide in section 8.4). the value of
P shall not be taken at less than 689.5 kPa for any condition of service or material.
D= outside diameter of pipe in mm
S= allowable stress in material, mechanical pressure, kilopascal Table 11.8.3
C= allowance for threading, mechanical strength, and/or corrosion in mm, obtained from the
following list:
Type of pipe
Cast-iron pipe centrifugally
Cast or cast horizontally in
Green sand molds
Cast-iron pipe, pit-cast
Threaded steal, wrought-iron or non-ferrous
pipe
3/8 inch and smaller
½ in. and larger
Groove steel, wrought-iron or not ferrous pipe
Plain-end, steel or wrought-iron pipe
25 mm size and smaller
Sizes larger than 25 mm
Plain-end non-ferrous pipe or tube
8.4 Piping of pressure relieving devices
value of C in mm
3.556 mm
4.572 mm
1.27 mm
Depth of thread
Depth of groove, mm
1.27 mm
1.651 mm
zero
The most important design factor about pressure relieving devices is the underlying
principle of intrinsic safety. They must “fail safe” or not at all. Therefore, the solution to problems in
pressure relief piping must be based on sound design practices. Because failure is intolerable,
simplicity and directness of design should be encouraged as a mass to reliability.
There are at least four good reasons why the installation of pressure safely valves and
discs should be engineered with care.
A. The inlet and outlet piping can reduce the capacity of the device below a safe valve.
B. The operation of the device maybe adversely affected to the point where the opening
or closing pressure is altered. In the case of safely valves, premature leaking or
simmering may occur at pressures less than the set pressure or chattering may occur
after the valve opens.
C. The reaction thrust at the same time the device starts to discharge can cause
mechanical failure of the piping.
D. Good design saves maintenance pesos.
8.5. Safety valve inlet piping
In order to operate satisfactory, a safety valve must be mounted vertically. It should be
directly on the vessel nozzle or on a short connection fitting that provides direct and unobstructed flow
between the vessel and the valve. Safety valves protecting piping systems should of course be mounted in
a similar manner. The device may never be installed on a fitting having a small inside diameter than the
safety valve inlet connection.
Pipe diameter sizes
100mm to 250 mm incl.
300mm to 350mm incl.
400mm to 4450mm incl.
500mm
600mm
750mm
900mm
1050mm to 1500mm
Water hammer allowance, kPa
827 kPa
758 kPa
689.5 kPa
621 kPa
586 kPa
552 kPa
517 kPa
483 kPa
8.6. Pressure drop
The pressure drop between the vessel and safety valve inlet should not be so large that
the valve is “starved” or chattering will result. The following limitations are suggested:
A. The pressure drop due to friction should not exceed 1 percent of the accumulated relieving
pressure.
B. The pressure drop during the velocity head loss should not exceed 2 percent of the
accumulated relieving pressure.
Some safety valve manufacturers suggested a maximum total pressure drop of 2 percent of
set pressure. In the absence of test data, it is recommended that this more conservative limit
be used.
These recommendation are based on a blow down of 4 percent. Within limits, if the blow down
setting is increased, the pressure drop maybe increase proportionately. Remember however,
that pressure lost in the inlet piping must be taken into consideration when sizing the safety
valve. Pressure lost in the discharge piping should be minimized by running the line as directly
as possible. Use long-radius bends and avoid close-up fittings. In no case may the crosssectioned area of the discharge pipe be less than that of the valve outlet.
8.7. Piping supports
Safety valves, although they may not be included under the heading of “delicate
instruments”, nonetheless instruments. They are required to measure within three percent and to
perform a specific control function. Excessively-strain on the valve body adversely affects its ability
to measure and control.
Supports for discharge should be designed to keep the load on the valve to a minimum. In
high temperature service high loads will cause permanent distortion of the valve because of creep
in the metal. Even at low temperature, valve distortion will cause the valve to leak at pressures
lower than the set pressure and result in faulty operation. The discharge piping should supported
free of the valve and carefully aligned so that the forces acting on the valve will be at the minimum
when the equipment is under normal operating conditions. Expansion joints or long radius bends
of proper design and cold spring should be provided to prevent excessive strain. The major stresses
to which the discharge pipe is subjected are usually due to thermal expansion and discharge
reaction forces. The sudden release of compressible fluid into a multi-directional discharge pipe
produces an impact load and bourdon effect at each charge of direction. The piping must be
adequately anchored to prevent sway or vibration while the valve is discharging.
NOTES:
A. The maximum weight per span is based on bigger steel pipe size weight full of water fittings
and insulated.
1. The copper tubing and fittings (for instrument airlines) shall be supported not more than 5
feet on centers or as shown on the drawings.
2. Vertical risers shall be supported from the building construction by means of approved pipe
clamps or U-bolts at every floor. Provide slide guides for pipes subject to thermal
expansion. Supports shall be of adequate size structural shapes or sections where pipe
clamps are too short to connect to the building.
B. Pipe anchors and restraints
1. Where piping is subject to thermal expansion and where expansion loops, expansion joints,
and offsets are indicated, provide suitable designed pipe anchors to limit pipe thermal
expansion and over stressing of pipe and adjacent connecting structures.
a. Rigid pipe anchors shall either be welded type construction or clamp-bolted type
whichever is suitable to the requirement.
b. Directional type pipe anchors where pipe movement is allowed in any one plate shall
be designed to prevent excessive stresses to the pipe and interference with adjacent
pipes or structures.
2. Piping restrains shall be provided to prevent unnecessary pipe movements due to
vibrations and seismic forces and damage to pipe joints such as cast iron pipe, soldered
copper pipes and other as required.
8.8 Reaction Forces
The total stress imposed on a safety valve or its piping is caused by the sum of these
forces:
A. Internal pressure
B. Dead weight of piping
C. Thermal expansion or contraction of either the discharge line or the equipment upon
which the valve is mounted and
D. The bending moment cause by the reaction thrust of the discharge
All of the stresses except the latter are common to practically every problem in piping stress
analysis.
The magnitude of the reaction force resulting from the instantaneous release of a
compressive fluid may be calculated from the two simple formulas below.
For a safety valve:
F1 = (K + 0.2) AP1
For safety disc:
F1 = 0.63(K + 0.2) AP1
Where:
F1 = reaction force, Kg
A = area of valve orifice or disc, sq. mm
P1 = inlet pressure at time of opening, kPa
K = ration of specific heats, Cp/Cv
Note: Psi x 6.895 = kPa
If it is possible for air to be relieved from the system under special conditions, use a
minimum valve of K=1.4 for design.
Calculation of the reaction force for liquid service demonstrates that this force is negligible.
However, since it is usually possible to trap air or gas in any pressure system, it is
recommended that K-1.4 be used in the above formulas as a basis design for liquid
services.
Here are values of K which can be safely used for common fluids.
Fluids
Air and diatomic gases
Steam
NH3 , CO2 , CH4 and
SO2 vapors
Helium, Argon
K
1.4
1.3
1.3
Rc
0.53
0.55
0.55
1.67
0.49
8.9 Compressor Piping
Pipes in a compressor circuit should connect directly point to point; bends instead of elbows
give less friction loss and less vibration; angular branch connections eliminates hard tees and gives a
smoother flow; double offsets for directional charge should be avoided; closely integrated inter-coolers with
the machine minimizes piping; pulsation dampeners should be located on the cylinders without any
interconnecting pip; knockout drum should be adjacent to a machine; several after-coolers or exchangers
in the circuit should be stacked as much as possible for a direct gas flow; and equipment in the circuit
should be in process flow sequence.
Because of the over present vibration problems at reciprocating compressors, pipe
supports have very important role in piping design. Supports independent of any other foundation or
structure is almost mandatory. Pipe systems “nailed down” close to grade is a much preferred arrangement.
If badly design compressor piping has to be connected after start-up of the plant, it can become very
expensive.
Reference:
Philippine Mechanical Code 2003 Edition