Pipe Thickness Calculation as per ASME B31.3 | Pipe
Thickness Calculator (With PDF)
whatispiping.com/pipe-thickness-calculation-per-asme-b31-3/
Rehan Ahmad Khan
May 8, 2020
Pipe wall thickness calculation is one of the important basic activities for every piping
engineer. Process plants deal with the fluids that flow inside the pipe at high pressure and
temperature. So, the pipe deals with high circumferential pressure which can cause the
bursting of the pipe if the pipe schedule or thickness is not enough. Hence, The
designers need to find out the required piping thickness as per section “304.1.2 of
ASME B31.3” to resist the internal line pressure. The operation must be leak-free.
Pipe Thickness Calculation followin...
Pipe Thickness Calculation following ASME B31.3
In this article, I have simplified the pipe thickness calculation procedure. A sample
pipe wall thickness calculation problem is discussed mentioning the calculation steps.
Process Piping Code ASME B31.3 is used as the basis for the Pipe thickness
calculation.
Why is Pipe Thickness Calculation Important?
The minimum required thickness of a pipe must be calculated to ensure
The selected pipe will be able to withstand the pressure at the design temperature
without failure.
To avoid being over-conservative and thus optimize cost.
If a supplied pipe is not from a standard pipe class defined in a project, then the
pipe thickness calculation will ensure that the pipe can withstand the internal
pressure without rupturing or leaking. Failing to specify the correct thickness can
result in catastrophic failures, posing safety hazards and potential environmental
damage.
Some Important Points regarding Pipe thickness Calculation
Before starting the piping thickness calculation, the engineer should be aware of the
following points:
Process plants are designed for 20 years or 7000 cycles. (Considering 1 cycle per
day; the Total number of cycles in 20 years=20*350=7000 cycles)
Pressure and temperature can vary from line to line and from time to time.
Fluid could be corrosive and toxic in the system.
Corrosion allowance for pipe material is decided based on service fluid. Typical
values are 3 mm for Carbon Steel and zero mm for stainless steel.
Mill tolerance for the seamless pipe is 12.50% and 0.3 for the welded pipe.
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How do I Calculate Pipe Thickness?
Let’s consider the following details for the pipe thickness calculation of a seamless
Carbon Steel pipe.
MOC (Material of Construction) of the pipe – ASTM A106 Gr. B
NPS (Nominal Pipe Size) – 4”
Manufacturing type of the pipe (SMLS, EFW, ERW) – Seamless (SMLS)
Design Pressure (PSI) – 1200 PSIG
Design Temperature – 500° F
Mechanical, corrosion, and erosion allowances – 3 mm
Mill Tolerance – 12.50% of the thickness
Pipe Wall Thickness Calculation Formula | Equation for Pipe
Thickness Calculation
As per clause 304.1.2 (a) of ASME B31.3, the internal pressure design thickness for
straight pipes with t<D/6 can be calculated using the following formula (Equation
(3a):
Fig. 1: Internal Pressure Design Thickness Equation per ASME B 31.3
Here,
P: Internal Design Gage Pressure=1200 PSIG as per problem definition
D: Outside Diameter of the pipe
The equation for the pipe wall thickness is based on the outside diameter of the
pipe, rather than the inside diameter. This is because the outside diameter of the
pipe is constant, it is independent of the wall thickness. Hence, the pipe wall
thickness can directly be calculated easily using the pipe’s outer diameter.
ASME B31.3 provides another formula (Equation 3b) for calculating pipe thickness based
on the inside pipe diameter as mentioned in Fig. 2 below. However, this equation is
seldom used but is provided here for academic purposes.
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Fig. 2: Pipe Thickness Calculation formula using pipe inside diameter
In the pipe thickness calculation methodology explained below, we will use the pipe
thickness calculation formula mentioned in Fig. 1 containing the pipe’s outer diameter.
The outside diameter has to be taken from the below standardsASME B36.10M: for ferritic steel (seamless & welded wrought steel pipes).
ASME B36.19M: for austenitic steel (stainless steel pipes)
Fig. 3: Outside Pipe Diameter from ASME B 36.10M
So from Fig. 3, D= 114.3 mm
S: Allowable Stress value of the Pipe Material (A 106-B) at Design
Temperature (500° F)
Refer to Table A-1 (or Table A-1M) of the ASME B31.3 (Fig. 4) for getting the value of
the allowable stress. Travel in the horizontal (x) direction for allowable stress value and
vertical (y) direction for pipe material, and the match point to get the value (refer to Fig.
4). If required, use interpolation to calculate the middle value.
Note: the value of the allowable stress in Table A-1 is given in KSI, So we need to
convert the value in PSI.
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Fig. 4: Allowable Stress Value from Table A-1 of ASME B31.3
As per Fig. 4, the allowable stress for ASTM A106 Gr. B is 19,000 psi at 500°F.
E: Quality factor
Quality Factors are used in Pressure Design and applied at Longitudinal and Spiral
Weld Joints and for Castings. The maximum value of quality factors is 1.0.
The value of E, Longitudinal Weld Joint Quality Factor, or Casting Quality Factor can be
found in Table A-1A or Table A-1B of the ASME B31.3. The weld joint factor (E) is 1 for
our problem case (Refer to Fig. 5).
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Fig. 5: Quality Factor for Longitudinal Weld
W: Weld Joint Strength Reduction Factor
As per section 302.3.5(e) of ASME B31.3, The weld joint strength reduction factor, W,
is the ratio of the nominal stress to cause the failure of a weld joint to that of the
corresponding base material for an elevated temperature condition of the same
duration. It only applies at weld locations in longitudinal or spiral (helical seam)
welded piping components.
Weld Joint Strength Reduction Factors are used because at elevated temperatures
the weld joint creep rupture strength can be lower than the base metal.
The value of W can be found in Table 302.3.5 of ASME B 31.3 (Refer to Fig. 6) and for
our problem the value of W=1
Fig. 6: Weld Joint Strength Reduction Factor
Y: Values of Coefficient from Table 304.1.1,
The factor “Y” depends on temperature. At elevated temperatures, factor Y
increases leading to a decrease in the calculated required pipe wall thickness.
Refer to Table 304.1.1 of ASME B31.3 for finding the value of Y, It is Valid for t <
D/6 and materials shown below The value of Y may be interpolated for intermediate
temperatures. For material A106 Gr. B, Y is given 0.4 (refer to Fig. 7)
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Fig. 7: Values of Coefficient Y
Pipe Thickness Calculation Steps
Step 1. Put the above values in the equation shown in Fig. 1
t=(1200*114.3)/{2(19000*1*1+1200*0.4)}=3.52 mm; Hence calculated thickness (t)=
3.52 mm
Step 2. Add the corrosion to the calculated thickness.
tc = t + c = 3.52 + 3
tc = 6.52 mm
Step 3. Add the mill tolerance to the thickness after adding the corrosion value.
tm = tc + 12.50 % of the pipe thickness
tm =tc/0.875 =6.52/0.875 = 7.45 mm (This is required thickness)
Step 4. Select the next Ordering thickness available in ASME B36.10M considering
the required thickness.
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Fig. 8: Dimensions and weights of Steel Pipes
So from Fig. 8, The Ordering thickness is 8.56 mm or Schedule 80.
Note:
1. Ordering thickness for seamless pipe will always be the next greater value available
from Schedule to schedule.
2. Whereas for welded pipe any next greater value will be the ordering thickness.
3. Extra thickness can be calculated by ordering thickness minus the required thickness =
(8.56 – 7.45) = 1.11 mm.
Use of the Extra thickness available in the pipes
For calculating the life of a pipe after 20 years.
For calculating the maximum pressure holding capacity of the pipe.
For checking extra thickness is sufficient to take care of thinning, if the same pipe is
used for manufacturing the bend.
The extra thickness also minimizes deflection and reduces the number of pipe
supports.
To compare with flange pressure holding capacity, to declare pipe is stronger than
the flange.
Parameters Affecting Pipe Thickness
By now you must have understood all the parameters that affect the pipe thickness. The
parameters are mentioned below for easy understanding
Design Pressure: With an increase in internal design pressure the thickness of a
pipe increases.
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Design Temperature: With an increase in the design temperature, the allowable
stress value reduces which, in turn, increases the pipe thickness.
Pipe Outer Diameter: With an increase in piping OD the pipe thickness
corresponding to the same pressure increases.
Assumptions for Pipe Thickness Calculation
For the above-mentioned pipe thickness calculation steps following ASME B31.3, the
following assumptions are made
The pipe is a thin cylinder and the value of thickness t is less than D/6.
The value of P/(SE)<0.385
The pipe is subjected to internal pressure only, For external pressure thickness
calculation additional parameters need to be considered as mentioned here.
Pipe Thickness Calculator
A pipe thickness calculator is a tool that calculates the pipe thickness when all required
inputs are supplied. Pipe wall thickness calculators can be developed in the form of an
Application, Visual Basic program, or Excel sheet program. All equations are programmed
inside the utility to help piping professionals calculate design pipe thickness with ease.
Inputs Required for the Pipe Thickness Calculator
To use any pipe thickness calculator (attached below), you have to be ready with the
following inputs:
The Pipe material of construction for knowing the Allowable Stress, in a consistent
unit
Pipe Outside Diameter, in consistent unit.
Pipe internal design pressure
Design temperature, to select the allowable stress.
Quality Factor, E from Table A-1A/A-1B of the code based on the pipe construction
type: Seamless, EFW, ERW, etc.
Co-efficient Y from Table 304.1.1
Corrosion allowance for material and operating conditions.
Mechanical allowance.
Mill tolerance.
A pipe thickness calculator using an Excel sheet is attached herewith for your reference.
The pipe thickness calculation formula is also mentioned inside the calculator.
Pipe-Wall-Thickness-CalculatorDownload
Video Tutorial on Pipe Thickness Calculation
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Refer to the following video tutorial to further clarify your doubts about Pipe thickness
calculation using B31.3
Still in doubt!! Simply click here and attend this course to clarify all your doubts
from industry experts.
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