Burst Testing of a Larger Vessel - UG-101(d)

[steris]

Reading UG-101(d)(1)(c) the code explicitly states that for a burst test to cover "duplicate parts", the duplicate vessel must have the same nominal dimensions (width, height, diameter) as the burst vessel. This section says that duplicate vessels may not have longer lengths but allows for shorter lengths. However it does not allow for a shorter width, height or diameter. UG-101(d)(2) states that for geometrically similar parts a series of burst tests must be performed to cover the whole range of sizes.

My question is this: If you burst test the worst case scenario ie: the largest size with the largest spans, what is the concern regarding smaller sizes? Intuitively, I would think that as long as material thicknesses are not decreased, and as long as joints and welds have the same design/dimensions, then a smaller vessel could only be stronger the its larger counterpart. Clearly UG-101(d)(2) was put in place specifically to address these issues, however, I don't understand what the concern with smaller vessels actually is. Can anyone explain the reasoning behind UG-101(d)(2)?

Thanks!

-Steris

 

[Duwe6]

Conservatism.

Just present your arguments/reasoning to your AI. He should agree that 'smaller is stronger'. Sect VIII Div-1 is avoiding 'blanket endorsements' of uncalculated vessels. They want an AI specifically involved with the 'strange stuff'.

 

[steris]

Hi Duwe - Thanks for the reply. I guess, to me, the code reads such that it explicitly prevents "grandfathering" in smaller vessels. I just wasn't sure if either I was reading this right or if that was in fact the intent of the code.

 

[steris]

Does anyone else have any thoughts on this? I couldn't find any code cases or interpretations on this topic. I can definitely have a conversation with the AI about it but I was hoping that there may be a more concrete document that sheds some light on this. Any help would be appreciated!