Early In 1951 the Executive Committee of the ASA B31 Sectional Committee, Code for Pressure Piping, authorized the formation of a Task Force to try to resolve the differences in points of view on the criteria to be used in calculating the wall thickness required for high-pressure steam piping. After considerable study and discussion, this Task Force recommended to the Executive Committee the formula given in the following paragraph. Inasmuch as this formula has now been adopted by the Power Boiler Section of the ASME Boiler Code, and has been approved by the Power Piping Committee of the ASA B31 Code for Pressure Piping, it was believed that the detailed work of this Task Force and, in particular, the development of this particular formula, should be published; that is the purpose of this paper.

Wall-Thickness Formula [30]

The formula developed by the ASA B31 Task Force is as follows:
t = minimum thickness; p = internal pressure; D = outside diameter; S = Code allowable S-value

In this formula, y is a temperature-dependent parameter with the following values:

y, ferritic steels:

Temp F 900 and below = 0.4

Temp F 950 = 0.5

Temp F 1000 = 0.7

Temp F 1050 = 0.7

Temp F 1100 = 0.7

Temp F 1150 and above = 0.7

y, austenitic steels:

Temp F 900 and below = 0.4

Temp F 950 = 0.4

Temp F 1000 = 0.4

Temp F 1050 = 0.4

Temp F 1100 = 0.5

Temp F 1150 and above = 0.7

For values of y of 0.4, the foregoing formula reduces to the former ASME and ASA B31 Code formulas for calculating the thickness of high-pressure steam piping.

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