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8 EFFECTS OF MOVEMENT AT SUPPORTS, ANCHORS AND TERMINALS

8 EFFECTS OF MOVEMENT AT SUPPORTS, ANCHORS AND TERMINALS

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53

3.9.2

AS 4041 — 1998

Design pressure for reheat piping

3.9.2.1 Time-independent In reheat systems where the design stresses of the piping are
time-independent, the design pressure shall be the highest pressure at which any safety
valve on the reheat system is set to lift. When no safety valves are mounted at the
reheater inlet, the design pressure of the reheater inlet piping shall be the highest pressure
at which any reheater outlet safety valve is set to lift, increased to take account of the
pressure drop through the reheater corresponding to the most severe conditions of
operation.
3.9.2.2 Time-dependent In reheat systems where the design stresses of the piping are
time-dependent, the design pressure shall be the lowest pressure to which any safety valve
on the reheat system is set to lift. When no safety valves are mounted at the reheater inlet;
the design pressure of the reheater inlet piping shall be the lowest pressure at which any
reheater outlet safety valve is set to lift, increased to take account of the pressure drop
through the reheater corresponding to the most severe conditions of operation.

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3.9.3 Design pressure for piping for reduced pressure systems For reduced pressure
systems, it is permissible for the pressure to be controlled at a value below that in the
originating piping system by reducing valve or by the pressure drop across a fixed
restriction such as an orifice or the blading of the turbine.
Where a protective device consisting of a safety valve or valves or a suitable appliance
for automatically cutting off the supply of steam at a predetermined pressure is fitted, the
design pressure for piping systems, whose design stresses are time-independent, shall be
that to which the pressure under the most arduous condition is limited by the proper
operation of such a device. Where similar provisions are made on piping systems whose
design stresses are time-dependent, the design pressure shall be the highest controlled
operating pressure, provided that the average pressure in any one year does not exceed
that pressure and that the fluctuations in controlled pressure at no time exceed the design
value by more than 20%.
Where no protective device is fitted, the design pressure shall be the greatest pressure
therein attainable under the most arduous operating condition, i.e. with the originating
piping system operating at its design pressure, with the upstream valves (including any
reducing valves or restrictions) fully open, and with the downstream valves (other than
non-return valves) fully closed.
The relieving capacity of safety valves (as determined in accordance with fitted
downstream pressure reducing valves shall be such that the operating pressure limitation
shall not be exceeded by more than 10% if the reducing valve fails in the open position
with the downstream valves (other than non-return valves) fully closed.
3.9.4 Design temperature for steam piping The design temperature for main and
reheat steam piping for a land boiler shall be taken as the design temperature at the
following points:
(a)

For non-superheated main steam piping . . . . . . . . . . . . . at the boiler stop valve.

(b)

For superheated main steam piping . . . . . . . . . . . . . . . . at the superheater outlet.

(c)

For reheater outlet steam piping (hot reheat) . . . . . . . . . at the boiler reheater
outlet.

(d)

For reheater inlet steam piping (cold reheat) . . . . . . . . . at the turbine high
pressure cylinder exhaust outlet, or turbine steam by-pass system outlet, whichever
is the greater.

(e)

For by-pass systems, the piping for a length of 5 diameters after the high pressure
by-pass valve should be designed for both —
(i)

the cold reheat pressure and temperature; and

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AS 4041 — 1998

54

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(ii)

the condition of cold reheat pressure and a temperature 50°C less than the
main steam temperature. Recognizing the intermittent operation, a fraction of
the boiler design life is appropriate and 30 000 hours is recommended.
The design temperature for other than main steam piping shall be the highest rated
temperature at the higher temperature end of the piping.
The design temperature may be exceeded during the design life of the piping where at
design pressure, the annual average operating temperature does not exceed the design
temperature; and —
(i)
for ferritic piping having a design temperature equal to or less than 380°C, variation
above the design temperature is not greater than 10 percent of the design
temperature; or
(ii) for ferritic piping having a design temperature greater than 380°C —
(A)
normal variations above the design temperature is not greater than 8°C of the
design temperature; and
(B)
abnormal variation above the design temperature is not greater than the
following in any one year:
(1) 20°C for a maximum of 400 h.
(2) 30°C for a maximum of 100 h.
(3) 40°C for a maximum of 60 h.
When a piping system is operated above these limits, the design life shall be
reduced.
For piping material not provided for above, see Clause 3.10.3.
Where the above temperature limitations are expected to be exceeded, the design
temperature shall be increased appropriately.
3.9.5 Design pressure and temperature for boiler feed water piping The piping
shall be designed for both —
(a) the shut-off pressure of the boiler feed pump when pumping water at 15°C and a
design temperature of 15°C; and
(b) the most arduous combinations of temperature and pressure that can occur in
operation for each section. If a protective device is fitted, the design pressure shall
be the set pressure of the device.
Specific allowance shall be made for water hammer if it results in pressure surges of
20 percent over the design pressure.
3.9.6 Design pressure for blowdown and drain systems
3.9.6.1 Upstream design pressure The design pressure upstream and including any shut
off valve, control valve, or trap shall be that of the upstream component to which they are
connected, but not less than 700 kPa if the system is handling a flashing liquid.
Where a control or restriction orifice is fitted, then this shall be considered as a control or
shut off valve.
3.9.6.2 Downstream design pressure The design pressure downstream from the last
shut off valve, control valve, trap or restrictor treated as a control in accordance with
Clause 3.9.7.1 shall also comply with Clause 3.9.7.1, except that where —
(a) the downstream pipe has a cross-sectional area of not less than 2.5 times the
combined simultaneous areas that can discharge into it; and
(b) further that this downstream pipe discharges freely into an adequately vented
receiver;
then the design pressure may be taken as one-half of the upstream pressure specified in
Clause 3.9.7.1 but shall not be less than 700 kPa if the system is handling a flashing
liquid.
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55

AS 4041 — 1998

3.9.6.3 Blowdown and drain vessels design pressure The design pressure of blowdown
vessel or a drain vessel shall be the maximum pressure that can be imposed upon it in
operation but not less than the lower value of 700 kPa or 25% of the maximum
permissible working pressure of the boiler. See Clause 3.25.2 for specific design
requirements.
3.9.7

Design temperature for blowdown and drain systems

3.9.7.1 Upstream design temperature The design temperature for systems described
under Clause 3.9.6.1 shall be that of the upstream component.
NOTE: Where the design stress is time-dependent, the design lifetime will be the same as that
of the upstream component except where a control or restriction orifice is fitted between the last
valve and the drain discharge point when for that section of pipe between the last valve and the
orifice a reduced design lifetime may be used if the drain is used intermittently.

3.9.7.2 Downstream design temperature The design temperature for systems described
under Clause 3.9.6.2 shall be the greater of —
(a)

the design temperature T (in °C) determined from:
T =

Ts – 41
1.15

. . . 3.9.8.2

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where
Ts is the design temperature (in °C) of the component from which the drain
or blowdown system originates; and
(b)

the saturation temperature at the design pressure of the system derived from
Clause 3.9.6.1.

NOTE: The reduced time design life for intermittent use is also applicable to the systems
covered by this subclause.

3.9.7.3 Blowdown and drain vessel design temperature The design temperature T (in
°C) of a blowdown vessel, or drain vessel, or atmospheric vent shall be determined from:
T =

Ts – 41
1.15

. . . 3.9.8.3

where
Ts is the design temperature (in °C) of the component from which the drain or
blowdown system originates.
The design temperature shall neither be higher than the highest design temperature of any
pipe discharging into the vessel nor lower than saturation temperature at the vessel design
pressure.
3.9.8

Design conditions for safety valve discharge piping

3.9.8.1 Design pressure The design pressure of the discharge piping shall be the
maximum pressure which can be imposed upon it, but in no case less than 350 kPa. See
Appendix J for calculation method. ANSI/ASME B31.1 provides an alternative method.
3.9.8.2 Capacity of safety valve The capacity of the safety valve for the purpose of
calculation shall be 1.11 times the certified discharge capacity as defined in BS 6759.1.
NOTE: The discharge piping system should be such as not to create a built up back pressure,
measured at the safety valve outlet connection, of more than 12% of the set pressure of the
safety valve, subject to a maximum of 1700 kPa. If the discharge piping system gives rise to a
higher built up back pressure, the design should be referred to the safety valve manufacturer for
agreement that the safety valve performance will not be adversely affected.

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© Standards Australia

AS 4041 — 1998

56

3.9.8.3 Design temperature
piping shall be:
T – 41
T = s
1.15
where

The design temperature T (in °C) of safety valve discharge
. . . 3.9.9.3

Ts is the temperature (in °C) of steam at the safety valve body inlet.
NOTE: For the purpose of calculating the thermal expansion of the discharge pipe, a
temperature 25°C higher than this design temperature should be assumed.

3.9.9 Design temperature for structural attachments
structural attachments shall be as follows:
(a)

Welded to pipe: T = Tf − 10°C.

(b)

Clamped to pipe: T = Tf − 20°C.

(c)

Insulated pipe, outside insulation: T = 80°C

The design temperature for

where
T

= design temperature

Tf = fluid design temperature.

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3.10

DESIGN CRITERIA

3.10.1

Pressure-temperature design criteria

3.10.1.1 Components having specified ratings The pressure-temperature rating of a
pressurized component complying with a nominated Standard shall not be exceeded.
3.10.1.2 Components not having specified ratings A pressurized component complying
with a nominated Standard that does not specify a pressure-temperature rating but does
specify the nominal thickness and the material, may be rated as seamless pipe of the same
nominal thickness as determined by Clause 3.12 for material of the same type having the
same design strength.
NOTE: The design pressure of pipe with a design strength complying with Clause 3.12 may be
limited by other clauses in this Standard.

3.10.2 Normal operating conditions Piping is considered safe for normal operation if
the coincident pressure and temperature on a component do not exceed the design pressure
and design temperature or the pressure-temperature rating of that component.
3.10.3 Variations in normal operating conditions Occasional variations in pressure
and temperature during the design life of ferrous piping are acceptable within the
following limits:
(a)

Where the fluid is steam . . . . . . . . . . . . . . . . . shall not exceed those specified in
Clause 3.9.4.

(b)

Where the fluid is boiler feed water . . . . . . . . . shall not exceed those specified in
Clause 3.9.5.

Where the fluid is other than steam or boiler feed water, a piping system shall be
considered safe during those variations when all the following conditions are fulfilled:
(i)

The piping does not contain pressurized components made from cast iron or other
non-ductile material.

(ii)

For piping not in the creep range, the hoop stress is not more than the hot yield
strength at the highest temperature occurring during the variation.

(iii) The number of significant variations, or cycles of pressure during the design life, is
not more than 7000. In this requirement a pressure variation of greater than ±20%
of the design is significant.
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57

AS 4041 — 1998

(iv)

The highest pressure occurring during the variation is less than the hydrostatic test
pressure.

(v)

Occasional variations above the design pressure and temperature comply with the
following:
(A)

The period of the variation is less than 10 h at any one time and the sum of
the periods is less than 100 h in a year. The pressure rating of a component
or the yield strength at the highest temperature during any of the variations
may be increased by not more than 33 percent.

(B)

The period of the variation is less than 50 h at any one time and the sum of
the periods is less than 500 h in a year. The pressure rating of a component
or the yield strength at the highest temperature during any of the variations
may be increased by not more than 20 percent.

(vi)

An evaluation of the combined effects of the sustained and cyclic variations on the
design life of all components is made and the results of the evaluation are agreed
between the parties concerned.

3.11

DESIGN STRENGTH

3.11.1 Design strength for pressure-retaining components The value of the design
strength for a pressure-retaining component in tension shall be appropriate for the
material, design temperature and design life. Design strength values for piping to
Classes 1, 2A and 3 are given in Appendix D. Tables of design strength in Appendix D
are independent of weld joint factor (Clause 3.12.2).
Because of the many popular pipe specifications nominally covering the same pipe but
perhaps with slightly differing specified mechanical properties, Table D3 deems the listed
pipe to take the values of design strength of BS 3601, Grade 320 in Table D2. Similarly
Table D4 deems the listed pipe to take the values of API 5L B in Table D2. Design
strength for Class 2P are not listed but are 0.72 of the specified room temperature yield
stress (see Appendix I). Values at intermediate temperatures may be obtained by linear
interpolation.
The design strength value determined in accordance with Appendix I may be used without
verification of the ReT values provided that the heat treatment of the completed pipe
complies with the material standard and is as given in AS 4458.
Allowance shall be made for any degradation of the properties of the material which could
reduce design strength of the piping due to the methods used during fabrication, e.g. hot
bending.
NOTE: Clause 2.11 specifies design strength requirements for a material selected for low
temperature application.

The design strength for unlisted materials shall be in accordance with Appendix I unless
otherwise agreed between the parties concerned.
3.11.2 Compressive stress The value of the stress in compression shall be appropriate
for the material and design temperature, and shall not exceed the design strength in
tension.
3.11.3 Shear stress The value of any primary shear stress shall be appropriate for the
material and design temperature. It may be noted that AS 1210 quotes 60% of the tensile
design stress for vessels and ANSI B31.1 quote 80% for piping.
3.11.4 Bearing stress The value of the stress in bearing shall be appropriate for the
material and design temperature, and shall not exceed 160 percent of the design strength
in tension.

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AS 4041 — 1998

58

3.11.5 Sustained longitudinal stress The sustained longitudinal stress (fL), being the
sum of the longitudinal stresses due to pressure, weight, and other sustained loads, shall
be not greater than 100 percent of the design strength listed in Appendix D at the
temperature under consideration.
3.11.6 Longitudinal stress due to sustained and occasional loads The longitudinal
stress due to the sum of the sustained loads (fL) as defined in Clause 3.11.5 and the
occasional loads (fo) (due to wind, earthquake and the like) shall be less than 1.33 times
the allowable design strength from Appendix D.
It is recommended that design strength values be limited to 75% of the Appendix D
values or two thirds of the yield strength at design temperature, whichever is the least, at
flanged joints or where slight deformation can cause leakage.
3.11.7 Design stress range The design stress range (fa), being the maximum
displacement (expansion or contraction) stress range permitted for the displacement stress
range calculated in accordance with Clause 3.27, shall be determined from one of the
following equations as appropriate:
fa

=

F(1.25fc + 0.25fh)

. . . 3.11.7(1)

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or, where fh > f L,
fa

=

F[1.25(fc + fh) − fL]

. . . 3.11.7(2)

fa

=

design stress range, in megapascals

where

A1


F = stress-range reduction factor for the total number of displacement cycles

over the design lifetime. See Table 3.11 or calculate using equation:

F = 6(N)−0.2 but ≤1.0



N = equivalent number of full displacement cycles during the expected

service life of the piping system

fc

= design strength at the minimum metal temperature expected during

operation or shutdown, in megapascals (see Note)

fh = design strength at maximum metal temperature expected during operation


or shutdown, in megapascals (see Note)

fL = sustained longitudinal stress, in megapascals.


 In the determination of fa, the value of the weld joint factor (e) shall be taken as unity.

Rm
R
 In no case shall the value exceed the minimum of
and 2 eT at minimum metal
3
3
 temperature (see Appendix D).
3.11.8 Creep-fatigue interaction
Standards may be used:

For

creep-fatigue

interactions

the

following

TRD 300, Design
TRD 301, Design
TRD 301 Design, Annex 1
TRD 508 Annex 1
Code Case N 47 of ANSI/ASME BPV-III.
NOTE: TRD documents may be obtained from TUV Germany.

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59

AS 4041 — 1998

TABLE

3.11

STRESS RANGE REDUCTION FACTOR
Total number of full temperature
cycles during the design life
(N)
≤7 000
≤14 000
≤22 000

1.0
0.9
0.8

≤45 000
≤100 000

0.7
0.6
0.5

>7 000
>14 000
>22 000
>45 000
>100 000

Stress range reduction
factor (F)
(Notes 1, 2 and 3)

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NOTES:
1

F applies to uncorroded piping. Corrosion may severely reduce
cycle life, therefore corrosion-resistant materials, environment
improvement, or lower stress are appropriate where a large
number of high stress cycles is expected.

2

The fatigue life of material operating within the creep range will
be reduced.

3

Where the range of temperature varies, the equivalent full
temperature cycles, N, may be determined from the following
equation:
5

5

5

N = NE + r1 N1 + r2 N2 + rn Nn

. . . 3.11.7(3)

where
NE

=

number of cycles of full temperature change
∆TE for which displacement stress-range (fe)
has been calculated.

fE

=

(fb2 + Ft2)½

fb

=

resultant bending stress, in megapascals

ft

=

torsional stress, in megapascals

N1, N2 ... Nn

=

number of cycles of
change ∆T1, ∆T2, etc.

r1, r2 ... rn

=

ratios of lesser temperature cycles to that for
which fc has been calculated, i.e.
∆T1
∆TE

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,

∆T2
∆TE

, ...,

lesser

temperature

∆Tn
∆TE

© Standards Australia

AS 4041 — 1998

3.12

60

DESIGN FACTORS

3.12.1 General
Clause (3.12).

The design factors shall not exceed the values specified in this

3.12.2 Weld joint factor A weld joint factor (e) shall be applied to pipe, to recognize
the quality of the welding process, mill quality control, and non-destructive examination
of the longitudinal or spiral weld.
NOTE: The weld joint factor is not intended to apply to circumferential welds.

The value of weld joint factor (e) to be used
Equation 3.14.3(2) for various classes shall be as follows:

in

Equation 3.14.3 (1)
e

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A1

Piping class

(a) For seamless pipe with hydrostatic test . . . . . . . . . . . . . . . 1.0

Any

(b) For welded pipe with NDE equivalent to API 5L examination
and with hydrostatic test . . . . . . . . . . . . . . . . . . . . . . . . . 1.0

Any

(c) For welded pipe with no obligatory NDE . . . . . . . . . . . . 0.85

2A, 2P, 3

 (d) For CW (BW) welded pipe irrespective of NDE with

hydrostatic test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.6
(e) For welded pipe with NDE and no hydrostatic test . . . . .
(f)

0.85

For brazed pipe to AS 1751 . . . . . . . . . . . . . . . . . . . . . . . 1.0

and

2, 3
2A, 2P, 3
Any

For common pipe specifications these rules have been used to create Table 3.12.2.
Pipe made by non-continuous (workshop) methods shall take the weld joint efficiency
factor appropriate by treating the pipe as a pressure vessel and using AS 1210.
3.12.3 Class design factor A class design factor (M) shall be assigned to piping to
recognize the overall quality control of the piping construction process.
The value (M) used in Equation 3.14.3(1) and 3.14.3(2) and Equation 3.14.5 shall be as
shown in Table 3.12.3.
3.12.4 Casting quality factor A casting quality factor (N) shall be assigned to a
casting to recognize the type of examination carried out on that casting.
The value (N) used in Equation 3.14.5 shall be as shown in Table 3.12.4. For welded
castings, the product of e and N shall be used.

TABLE

3.12.2

WELD JOINT FACTOR EXAMPLES

© Standards Australia

Specification

Manufacturing
method

Weld joint factor
(e)

API 5L
ASTM A 53
ASTM A 106

ERW
ERW
Seamless

1.00
1.00
1.00

ASTM A 312
ASTM A 312
ASTM A 333

Seamless
Welded
Welded

1.00
0.85
0.85

ASTM A 334
ASTM A 587
AS 1074
AS 1074

Welded
Welded
CW
ERW

0.85
1.00
0.60
0.85

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61

TABLE

AS 4041 — 1998

3.12.3

CLASS DESIGN FACTOR

A1

Piping class
1
2
3



Class design factor (M)
1.0
1.0
0.7

TABLE

3.12.4

CASTING QUALITY FACTOR
Type of examination

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Radiographic
Ultrasonic
Others specified in AS 1210
All other

Casting quality factor
(N)
1.0
1.0
1.0
0.8

3.13 ALLOWANCES
3.13.1 General The pressure design wall thickness (tf) for a pipe or a
pressure-containing component manufactured from pipe shall be increased by an amount
equal to the allowance (G) to compensate for a reduction of thickness due to corrosion,
erosion, threading, or grooving, or to add mechanical strength and any other necessary
parameters. Where a pipe is to be bent, an allowance to compensate for thinning may be
required. For castings, an allowance may be required to compensate for shrinkage,
core-shift and distortion.
Allowances for separate items are not always additive, e.g. allowances for corrosion and
threading.
3.13.2 Manufacturing tolerances Where a pipe or fitting is manufactured to a
Standard that specifies an under-thickness tolerance on the wall thickness, the allowance
shall include an amount equal to the tolerance. This allowance is not included in G, but is
applied in 3.14.2.
3.13.3 Corrosion or erosion Where corrosion or erosion or both are expected the
allowance (G) shall include an amount equal to the loss in wall thickness expected during
the design life.
3.13.4 Threading, grooving, or machining Where a component is to be threaded,
grooved, or machined, the allowance (G) shall include an amount equal to that which will
be removed and, where a tolerance on the depth of cut is not specified, the allowance
shall be increased by 0.5 mm.
3.13.5 Mechanical strength If the pressure design wall thickness is not sufficient to
enable the pipe to withstand expected loads other than those resulting from hoop stress,
the allowance (G) shall include an amount that would provide the required wall thickness,
e.g. to compensate for bending between supports or loads or damage during handling or
construction (see Clause 3.11.6).
Where it is impracticable to increase the wall thickness, or where an increased wall
thickness would cause excessive load stresses, other means shall be taken to protect the
piping. These means include the use of additional supports, the provision of protective
barriers, and the relocation of the piping.
Consideration should be given to the mechanical strength of small bore piping
connections, such as that for instrument, sampling and control lines, particularly at the
point of connection to the main pipe.
Lagging, coating, or lining shall not be considered to add strength to the pipe.
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AS 4041 — 1998

3.14

62

WALL THICKNESS OF STRAIGHT PIPE

3.14.1 Required wall thickness The required wall thickness (tm) of straight pipe or a
pressure-containing component made from pipe shall be determined from the following
equation:
tm = tf + G

. . . 3.14.1

where
tm = required wall thickness, in millimetres
tf = pressure design wall thickness, in millimetres
G = summation of appropriate allowances (see Clause 3.13), in millimetres.
3.14.2

Nominal wall thickness

The nominal wall thickness (tn) shall be —

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tn = tm + pipe manufacturing under tolerance but in no case shall be less than that
given in Item (a) or (b) as follows:
(a)

For Class 1 . . . equal to or greater than the required wall thickness (tm) and should
be not less than the thinnest wall thickness appropriate to the diameter nominated in
the appropriate pipe standard or 1 mm.

(b)

For Class 2 and Class 3 . . . equal to or greater than the required wall thickness (tm)
and not greater than that shown in Table 3.14.2 for respective class.

Where the pressure design wall thickness or the nominal wall thickness is greater than
that specified in Table 3.14.2, the piping shall be fabricated to the requirements of Class 1
or Class 2, as appropriate.

TABLE

3.14.2

MAXIMUM WALL THICKNESS FOR CLASS 2 AND CLASS 3 PIPING
Wall thickness, mm
Material
Steel group
A1, A2
A3
B
A1



A1



Type
Carbon and carbon-manganese steel
High yield strength C-Mn steel
Low alloy steel (alloy < ¾)

Class 2
piping
tn* and t f†
32
16
20

Class 3 piping
t n*
20
12
12

t f†
12
12
10

16
0

0
0

0
0

16

0

0

0
0
0

0
0
0

0
0
0

E

Cr-Mo steel (¾ ≤ total alloy < 3)
Vanadium and medium Cr-Mo steel
(3 ≤ alloy < 10%)
3½ nickel steel

F, G
H
J

9 nickel and QT steel
Martensitic chromium steel
Ferritic high chromium steel

K
L
M

Austenitic Cr-Ni steel
High chromium steel
Ferritic austenitic steels

32
0
32

20
0
10

12
0
5



Non-ferrous alloys

10

6

6

C
D

*

tn = nominal wall thickness at any weld



tf = pressure design wall thickness

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63

AS 4041 — 1998

3.14.3 Pressure design wall thickness for pipe, under internal pressure The
pressure design wall thickness (tf) for cylindrical pipe, or pressurized components, under
internal pressure, shall be determined as follows:
(a)

Where the pressure design wall thickness is less than D/6, the pressure design wall
thickness, under internal pressure, shall be determined from the following equations:
(i)

Where outside diameter is used as the basis of calculation:
pD
tf =
2feM + p

(ii)

. . . 3.14.3(1)

Where inside diameter is used as the basis for calculation:
tf =

pd
2feM − p

=

outside diameter, in millimetres

. . . 3.14.3(2)

where

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D

M =

class design factor (see Clause 3.12.3 and Note below)

d

=

inside diameter, in millimetres

e

=

weld joint factor (see Clause 3.12.2 and Note below)

=

N for castings (see Clause 3.12.4)

f

=

design strength (see Clause 3.11), in megapascals

p

=

design pressure, in megapascals

tf

=

pressure design wall thickness, in millimetres

The product of e and M need not be taken as less than 0.6.
NOTE: e relates primarily to hoop stress across a longitudinal weld and percentage NDE. N
relates primarily to hoop stress in casting and percentage NDE. M relates primarily to
longitudinal stress and percentage of NDE. The use of 0.6 minimum avoids doubly
penalizing longitudinal joints.

(b)

Where the pressure design wall thickness is equal to or greater than D/6 or d/4, or
where p/fe or p/fM is greater than 0.385, consideration shall be given to the design
and choice of material. If such thick pipe must be used, the use of a thick wall
equation is recommended and the value of the pressure design wall thickness shall
be agreed. The possibility of failure due to fatigue and thermal stress shall be
investigated and the findings of the investigation shall be agreed.

3.14.4 Wall thickness of pipe under external pressure The pressure design wall
thickness (tf) and any stiffening requirements for straight cylindrical pipe under external
pressure shall be determined in accordance with AS 1210, except that where D/t < 10 the


pD 
calculated hoop stress 
 , shall be the lesser of —
 2t f 
(a) 1.5 × (the lesser of the design strength given in Appendix D at design metal
R
temperature and m ); and
3
(b) 0.9 × specified minimum yield strength at design metal temperature.
3.14.5 Pressure design wall thickness of cast pipe The pressure design wall thickness
(tf) of ductile pipe, other than ductile iron, shall be determined from Equation 3.14.5 but
shall be not less than 10 mm.

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