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Flange Overstressed during Hydrotest
2

Flange Overstressed during Hydrotest

Flange Overstressed during Hydrotest

(OP)
Hi,
I'm dealing with a flange connection that exposed to piping system hydrostatic test pressure preformed exceeding the allowable by ASME B16.5 (2.6).
Flanges: Class 150 WN.RF. Material: SA-105N. Gasket: Spiral-wound metal, with nonmetallic filler (group Ib). Bolts & Nuts: SA-193 B7 / SA-194 2H.
Pipes: NPS 4" Sch. 40 Material: SA-106 Gr. B
My questions are:
Shall these flanges be replaced?
Is there a way to determine whether the flanges were overstressed?
Are there any code requirements / restrictions?

RE: Flange Overstressed during Hydrotest

Did they leak?

RE: Flange Overstressed during Hydrotest

(OP)
No, they didn't.

RE: Flange Overstressed during Hydrotest

Don't overly concern yourself about it.

RE: Flange Overstressed during Hydrotest

Weldstan - very sound advice. I agree.

RE: Flange Overstressed during Hydrotest

Replace the bolts/studs [possible over-stress], put a memo in the equipment file and use it in good health. You have the best-hydro'd flanges in your plant.

RE: Flange Overstressed during Hydrotest

Flange ratings are quite conservative. You could recalculate the flange at the hydro pressure used. Another reassuring fact is that the yield strength you are calculating the hydro case with is appr. 95% of a value that most likely is lower than the actual yield strength of the material used. If you have material certificates you could confirm for yourself if this is true.

RE: Flange Overstressed during Hydrotest

It's far easier to damage flanges by (massively) overtightening the studs than by internal overpressure. Flanges fail generally by leakage, which unless your hydrotest is really poorly designed, serves in practice to "clamp" the maximum pressure they experience to a certain value.

RE: Flange Overstressed during Hydrotest

In regards to moltenmetal's and Duwe6's responses, I tend to agree more with moltenmetal and think that Duwe6's response is excessive and unlikely to help.

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