Hi all,

Michael its right, the second loads set is the correct one. This is valid for ASME B31.1 / ASME B31.3 Codes.

The B.31.1/31.3 provisions which require this approach are old enough (definitely they were in role twenty years ago...) and I am really surprised that such elementary issue still raises doubts among stress engineers.

Regarding B31.3 - see Para. 302.3.6:

<<...THE SUM OF THE STRESSES due to sustained loads, such as pressure and
weight, SL, AND OF THE STRESSES produced by occasional loads, such as wind and earthquake, may be as much as 1.33 times the basic allowable stress provided in Table A-1 or Table A-1M at the metal temperature for
the occasional condition being considered...>>

So, it is NOT written "the sum of the stresses due to sustained and occasional loads". This means that the absolute values' summation of the longitudinal stresses devloped bu SUS and exclusive OCC loads needs to be checked against Code allowable limit. There is NO ALGEBRAIC summation to be performed.


In B31.1 the formulation is slightly different, but with the same meaning - see Para. 102.3.3:
<< The SUM OF THE LONGITUDINAL STRESSES produced by internal pressure, live and dead loads, AND THOSE produced by such occasional loads as the temporary supporting of extra weight may exceed the allowable stress values given in the Allowable Stress Tables by the amounts and durations of time
given in para. 104.8.2.>>

In B31.1, the absolute summation is clearly documented by formulas (15) and (16), which stipulates the summation of the BENDING STRESS terms corresponding to SUS and exclusive Occasional loads.

I repeat, these are elementary issues for Piping Stress Engineers involved in onshore or offshore topside PIPING systems.

For offshore Pipeline systems (B31.4/B31.8), as I remember briefly (I am not frequently involved in such projects...), the approach is different. Maybe another Forum member with current/extensive Offshore Pipeline analysis experience may complete these considerations.

Regards,