Question:

What temperature is used to determine the value of Sh in a code-compliant calculation for the sustained category when the model has multiple defined analysis sets?

Example: Model piping code is ASME B31.1 2024, 2 temperature cases, and 4 analysis sets

- - T1 = -20 deg F
  - T2 = +800 deg F
  - Ambient = 70 deg F
  - Analysis set configuration:

The sustain allowable calculation or this specific piping code is single material property, Sh. Will the allowable be based on the hot allowable from T1, T2, or both T1-T2 for all analysis sets imaged above?

Answer:

To understand this answer, first refer to the AutoPIPE help documentation, which states:

- - - "If more than one temperature load case exists in a code compliance combination (e.g., "T1 to T2") there may be more than one S_H value. Results are output for the case which produces the smallest margin (i.e., smallest value of "allowable stress" - S_E) at each point."

Another words for each location, the most conservative (lowest) allowable stress is used for code compliance at each point, based on the temperatures present in the analysis sets. The documentation does not specify a single temperature is globally used but rather calculations are performed using material properties at the relevant temperature, and the most limiting (i.e. conservative condition / lowest allowable) governs the result at each point in the system.

For your scenario, the sustained allowable stress calculation are based on which temperature case:

- - Analysis Set #1: Sh based on T2 temperature
  - Analysis Set #2: T1 is the only temperature case, Sh based on T1 temperature
  - Analysis Set #3: T2 is the only temperature case, Sh based on T2 temperature
  - Analysis Set #4: T1 and T2 are added to this set, AutoPIPE will compare all relevant values present in Set 4 based, reporting the result for the case with the most conservative condition / lowest allowable at each point.

Question: Why is Sh based on T2 in analysis set #1?

Answer: When a combination contains (LONG) and (HOOP), and if the analysis set does not contain a temperature case, AutoPIPE will compare all temperature cases in the model, reporting the result for the case with the most conservative condition / lowest allowable at each point; which is T2 in this example.

Note:

1. 1. The answer assumes the material properties Hot Allowable for T1 ≥ T2.
  2. If the model contained (n) number of Temperature cases, the value of Sh for analysis #1, would be based on evaluation of all Thermal cases in the model. Again, reporting the result for the Temperature case with the most conservative condition / lowest allowable at each point. Meaning, the results may not be based on a single Temperature case for every node point. The evaluation would be dependent on material properties applied to each node point.

Q. What temperature is used to calculate the allowable for multiple analysis sets in AutoPIPE?

See Also