Understanding Piping Code Stress Evaluation Paradoxes And ASME B31.3 Appendix P

[sachinchavan777]

A piping system is designed based on the piping code created for each individual industry.
There are several different piping codes in U.S and the World to cater to the different
natures of the industries. To ensure the structural integrity of the piping, each code will
start out with allowable materials and their basic allowable stresses and then will figure
out what stresses need to be calculated and how to calculate them. Finally, a set of
allowable stresses, comprising the basic allowable stresses, is set to validate the structural
integrity of the piping system. At each code, the allowable stresses are consistent only
with the stresses calculated using the method of the individual code. Therefore, it is
obvious that the allowable of one code should not be used for the stress calculated with
another code. In fact, all the codes have warned that each code must be applied in its
entirety.
The different stresses calculated by each code together with different allowable values
permitted by each code have created considerable paradox in the piping community.
Engineers are often confused about what to do when alternative methods to the code may
be required to deal with special cases. This paradox has recently crept into ASME B31.3
Appendix-P. This paper will present the stress criteria background and explain why the
Appendix P is formulated based on confusing logic that may very well lead to unsafe
design of the piping system.