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Part UHX Tube-sheet Stress During Hydrotest

Part UHX Tube-sheet Stress During Hydrotest

Part UHX Tube-sheet Stress During Hydrotest

(OP)
We are currently fabricating replacement u-tube bundles.

The bundles are Figure UHX-12.1 Configuration D with extended flange, the gaskets either side of the tubesheet are the same configuration and as such no bolt load gets transferred into the tubesheet during normal operation.

The intent is that the new bundles will be hydrotested in the workshop using a test blind directly bolted to the tubesheet. Calculations have been provided to determine the tubesheet bending stress in accordance with UHX-12.5.8 (accounting for both nominated assembly bolt load and hydrotest pressure). This stress is limited to 2*S.

My question is should this stress be limited to 90% of Sy (yield) for hydrotest or should it be limited to 2 * 90% of Sy?

I'm a little confused considering the 2*S limit, primary bending in a flat plate is fairly straight forward as it is limited to S however the bending in the tubesheet is treated differently.

Appreciate any feedback.

RE: Part UHX Tube-sheet Stress During Hydrotest

From a code prospective, there is no limit on stresses during the test condition.

If your client has limits, ask them.

RE: Part UHX Tube-sheet Stress During Hydrotest

(OP)
Apologies, my initial query was somewhat rushed being late on a Friday.

My query is whether we run a risk of yielding the tubesheet if the stress limit is set to 2 * 90% of Sy?

My understanding is that this is a primary bending stress and therefore I would typically limit this stress to 90% of yield, however, the allowable stress in the ASME formulas limits stress to 2*S so maybe my understanding is incorrect here and infact the stress isn't primary in nature?

I know ASME doesn't set limits on stress in hydrotest however other recognised codes around the world do (90-95% of yield).

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