Hey Y'all,
It is interesting to note that if you were to look at para. 1-705.2 (Satisfaction of Primary Plus Secondary Stress Intensitiy Range) of the olde B31.7 (1969) document you would find the same approach.
The range of stresses is defined as the difference in stresses resulting from the consideration of two sets of loading conditions (i.e., P+W+T)and......
"the unloaded set (Po=0, Mi=0, delta T =0, Ta=Tb+70 deg.F) shall be considered a loading condition"
Now, if only B31.3 would include the "Forward" of B31.7-1969, which is titled "Design Philosophy" as a non-mandatory appendix. Those four pages are worth their weight in gold to new piping analysts who are looking at Appendex "P" for the first time. Maybe COADE would reproduce those pages on a web site for all of us to read over??????? Hmmmmm...just a thought.
Regards, John.
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John Breen