How does AutoPIPE calculate ASME B31.12 expansion calculation?
As mentioned in B31.12 section IP-2.2.10(d), equations 1a and 1b. When AutoPIPE's Sustain Margin (Y/N/E) is set to N, equation 1a is used. If the Sustain Margin is Y, equation 1b is used. If the Sustain Margin is E, the program determines based on the rules outlined in IP-2.2.10(d) which equation is used.
Furthermore, the range stress allowable is tied to the sustained load margins following the setting for Sustain Margin (Y/N/E). Setting this option to N will prevent the expansion allowable from changing albeit by removing sustain margin from the allowable calculations. Higher primary stresses maybe due to the moment increase of GR in analysis set combinations, which is an analysis consideration, not code-specific.
ASME B31.12 questions