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Fatigue calcs for non-integral equipments

Fatigue calcs for non-integral equipments

(OP)
Dear All

Recently I was working on fatigue calculations for a vessel as per ASME BPVC Sec.VIII-2. I wanted to exempt the vessel from detailed fatigue calculations as per fatigue screening methods but exemption of the vessel was not possible with any of the methods.
Then the owner has asked to change the nozzles from pad reinforced to self reinforced. Even with this method the vessel cannot be exempted. However, the owner wants the vessel with integrally reinforced nozzles.
If an equipment cannot be exempted from detailed fatigue calculations, is it against the code to make the vessel with nozzles that are reinforced with pads?
In other words if I want to do detailed fatigue calculations is it a must that the vessel shall be integrally fabricated or is it just some recommended practice?

Warm Regards

RE: Fatigue calcs for non-integral equipments

Provided that you perform the calculations correctly including the effects of the non-integral attachments, there is no such requirement, Remember that for thermal transient effects, you are not permitted to take credit for heat transfer across non-integral attachments (e.g. between a vessel and the repad, except at the the welds).

RE: Fatigue calcs for non-integral equipments

There is nothing from what I've seen that says you must use integral construction for vessels subject to fatigue analysis.

That said, integral construction normally has a much higher likelihood of passing the fatigue calculations without additional modifications. Also, although I've never had to do it, my understanding is that performing fatigue calculations on a nozzle with repads is not trivial. You are introducing large areas of 'no penetration' analysis to your FEA results, which will be painfully slow to analyse.

Cheers,

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