Good day!
Is there a requirement for the minimum thickness for external attachment pad such as for external pipe support/platform clips, lifting lugs, saddle wear plate, etc..

These pads can be thinner than Vessel thickness or
can eliminate the pad by direct welding the attachment-plate/steel shapes/etc. with dissimilar material to Vessel?

Thanks,

ASME BPVC Sec VIII-1 doesn't cover it, but it requires you to take it under consideration. Some justification will presumably be required by your AI. Sometimes enough justification is "the pad is damn thick", sometimes some strength caculations or analysis may be needed, particularily when you're in a cyclic service range, or some creep may be anticipated. Anyway, it's up to the AI whether he buys your story, so call him and just ask what he will expect.
Regards

_________________
Konrad Anikiel

Remember that the pad itself is also a structural element: it is exposed to the same loads that the attachment clip must sustain.

There is a big difference in strength between, for example, a nozzle with a reinforcing pad and a clip that is welded to a reinforcing pad that is in turn welded to the shell. In the case of the nozzle the pad is attached to the shell at the nozzle OD (perhaps via the nozzle) and at the OD of the pad. Whereas in case of a clip welded only to the pad the pad is less rigid and must transfer the load across its entire width, not just 1/2 width (as for nozzle).

This issue can be extremely important when considering clips with very large loads, such as lifting lugs, turning trunnions, etc. In some cases it may be necessary to attach the clip or lug directly to the shell, then fit the reinforcing pad around it.

The issue also arises when you calculate stresses in the shell due to the clip loads. Stresses are often calculated using WRC-107 bulletin and assuming that the shell thickness is the combined thickness of the shell and reinforcing pad. This can be justified only if the two plates act integrally for the bending moments. A wide, relatively thin reinforcing pad may flex under bending and will no longer act as a unit with the shell.

I agree with tom that WRC 107 analysis is considering combined shell and pad thickness and a separate pad, welded only at edges will not act as an integral unit and specially in case of large loads we need to take care of it.

WRC 3xx (do not remember exact number) probably address pad as an intergral (inserts) or a separate units.

As such code is concerned, it does not address whether a thin or thick pad as compare to shell thickness is to be provided.

I would however not recommend to use a thicker pad since it will create undue stress in shell due to different strength/ expansion etc specially in case of high temperature/ pressure.

Regards

JUST TO ADD ,

IN ASME SEC. III NC -3237 MAXIMUM LIMIT OF THICKNESS IS GIVEN AS 1.5 TIMES THK OF SHELL.