Can anyone give some insight/opinion on this topic? We have a disagreement/difference of understanding in our office on whether the approach adopted is correct or not. In effect, we have a calculation that uses the operating loads and the total allowable stress 1.25(Sc+Sh) but during some reading into the background of the approach it is being called into question (which is then calling into question the industry wide approach adopted on Kellogg trunnion calcs).

Kellogg subject 3810 states 'all attachments to the pipe shell such as trunnions, clips, lugs etc.. shall be so designed so that the pipe shell bending and pressure stresses as outlined in the following paragraphs do not exceed the total allowable'

Further in the paper there is a note/statement which reads

'thermal loads may either be plus or minus, but shall be added to other loads numerically, disregarding sign, to give maximum absolute value'.

Normally we utilise the worst bounding load of all operating and sustained cases and assess against these, however in light of the note above its being argued that we should be using the absolute of the sustained loads plus the absolute maximum thermal loading + abs minimum thermal loading giving a total bounding load, this seems overly conservative and may mean a whole host of trunnion calcs undertaken in industry are incorrect.

Things are further compounded by the wording in the kellogg - design of piping systems book under local components (pg85) it states

'the combined local stress due to thermal reactions and internal pressure is held to the same total allowable stress range as for the piping itself [1.25(Sc+Sh)]. As noted previously, the thermal reactions must be based on the full expansion and the cold modulus of elasticity. The individual hot and cold reactions cannot be used for this purpose.'

So there are two trains of thought, utilising the maximum operating loads or going down the route as stated above.

Anyone any thoughts on this or pointers, I'll be honest I only have odd page of the kellogg book so need to get the pages prior to the paragraph above to determine the wording application?

I recommend to you to read the explanation of this approach in a book named (Piping stress engineering) chapter 6 and you will find an example in it