Flange Overstressed during Hydrotest 2

[Shmulik]

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?

 

[weldstan]

Did they leak?

 

[Shmulik]

No, they didn't.

 

[weldstan]

Don't overly concern yourself about it.

 

[TGS4]

Weldstan - very sound advice. I agree.

 

[Duwe6]

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.

 

[OSIRIS7]

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.

 

[moltenmetal]

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.

 

[TGS4]

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.