Wall Thickness Calculation: ASME B31.4

This is for pipeline used to transport liquid between production fields or facilities, tank farms, above or belowground storage facilities, natural gas processing plants, terminals, and other delivery and receiving points as well as pipelines transporting liquids within pump stations, tank farms, and terminal associated with pipeline systems. The code specifies the criteria the nominal wall thickness of straight section of steel pipe shall be equal to or greater than t_n   as per below equation:

Where:

• A  =  sum of the allowances for threading, grooving,

corrosion and erosion as required paragraph 403.2.2 through 403.2.4 and increase in wall thickness if used as protective measure in   paragraph 403.1.

• t = pressure design wall thickness calculated in

accordance with the following equations:

Customary Unit:

SI Unit:

Where:

• D = Outside Diameter of pipe, in. (mm)
• P_i = Internal Design Gage Pressure, psi (bar)
• S = Applicable Allowable Stress Value, psi (MPa),

 As determined by the below equation:

S = F x E x S_y

• F = Design Factor, maximum 0.72.
• E = Weld Joint Factor as per Table 403.2.1-1
• Sy= Specified Minimum Yield Strength of pipe, psi (MPa)

 So, the formula to calculate the wall thickness would be:

Customary Unit

SI Unit

Some of input required for the above formula is as below:

• Corrosion: A wall thickness allowance for corrosion is not required if pipe and components are protected against corrosion in accordance with the requirements and procedures prescribed in Chapter VIII of ASME B31.4

• Threaded and Grooving: An Allowance for thread or groove depth in inches (millimeters) shall be included in A of the above equation when threaded or grooved pipe is allowed by ASME B31.4.

• Weld Joint Factor: as per below table sample.

For complete table please refer below:

Table 6.1.  Longitudinal Weld Joint Factors E for Seamless

Example Calculations

8 inches Potable Water Pipeline with Design Pressure of 600 psig at Design Temperature of 100^oF, ASTM A53 Grade B with SMYS of 35,000 psi, No Corrosion Allowance needed

Find the Wall Thickness!

Answer:

• P = 600 psig
• OD = 8.625 inches
• F, Design Factor = 0.72
• E, Weld Joint Factor = 1.0
• Sy, SMYS = 35,000 psi

Formula:

Based on the commercially available, the selected wall thickness is 0.109 in. However, the final selection is subject to client approval, which they may have their own standards and requirements. Below is the table to show the result of the wall thickness calculation for design factor of 0.5, 0.6, and 0.72.