Limitations of Appendix P:

A conservative formulation of the allowable expansion stress range for many codes in CAESAR II is calculated from:

SA = f (1.25 Sc + .25 Sh)…………………………………Without Liberal

When the user requests that the "Liberal Allowable" be used, the difference between Sh and Sl, provided Sh > Sl, will be added to the term inside the parenthesis, i.e.

SA = f [1.25 Sc + .25 Sh + (Sh - Sl)]……………………………With Liberal

Longitudinal Stresses SL: The sum of the longitudinal stresses, SL, in any component in a piping system, due to sustained loads such as pressure and weight, shall not exceed the product ShW;

f: stress range factor

Sc: basic allowable stress at minimum metal temperature expected during the displacement cycle under analysis

Sh: basic allowable stress at maximum metal temperature expected during the displacement cycle under analysis

The liberal expression will only be employed when there is at least one sustained stress case in the load set. If there is more than one sustained stress case in a single problem, then the largest of Sl, considering all of the sustained cases, for any single element end will be chosen to subtract from Sh. Because the sustained stress varies from one pipe to another, the allowable expansion stress will also vary.

Appendix P

Allowable Operating Stress Limit: The greater of the maximum operating stress and maximum operating stress range in a piping system shall not exceed the allowable operating stress limit, SoA

The operating stress is the calculated stress at any operating condition, including pressure, weight and other sustained loads, and displacement. Occasional loads are not required to be included.

The operating stress range is the range of stress between any two operating conditions, including the ranges between operating conditions and a sustained case with the piping at ambient temperature.

SoA = 1.25 f (Sc + Sh)…………………………………………Appendix P

Conclusion: Based on above explanation Appendix P is not applicable for Expansion stresses.

If we select the Appendix P (in configuration setup) while doing stresses analysis we have to take care below points:

1. Allowable stresses are applicable for only operating (OPE) cases.

2. For Expansion (EXP) Cases these allowables are not applicable.

3. For complying Expansion (EXP) Cases better we have to check the piping system without selecting Appendix P (in configuration setup)


If any Augmentations welcome.


Thanks & Regards

Sathya Prakash Reddy

Engineer-Piping