Maximum Hydrotest Pressure for flange rating exceeded

[SandmanR]

Hello,

Can someone advise what the factor of safety for a flange may be, for example, in one situation a flange rating of 300# *max hydro-test pressure of 1125 psig) was hydro-tested to 2160 psig. The pressure held and nothing failed. Is that okay?
Please advise.

 

[racookpe1978]

What otehr flanges, sizes, and ratings were tested to that high a value?

Did the entire PV - I assume it would have been rated at about 750 psig for a 300# flange to be used! - get hydro tested to 2160?

 

[SandmanR]

It was primarily the 300# flanges (I said 1125 psig since that was the maximum allowable non-shock pressure); sizes ranging from 3", 6" and 8" line.
the piping is fine since it has a much higher burst pressure.

 

[Afox88]

I would say if everything passes, that is great, but you can still only rate the flange to the maximum design pressure at the design temperature.

 

[racookpe1978]

??

No, if the flanges were hydro'ed to twice the specified test pressure, and the flanges were attached to the PV, then the entire PV and all of its pipes and valves and flanges and expansion joints were over-stressed.

But why are the pipes so over-rated that you feel they were not also over-stressed?

Exceeding a hydrostatic test pressure by 50 psig is bad. Exceeding it by 150 or 200 psig is worse.

But by over 1000 psig?

( comparing a "maximum allowed non-shock pressure" for a 300# flange of 1125 with a system-wide single time hydrostatic test pressure (1.5 x maximum allowed operating pressure) you are compounding the problem resolution.)

 

[SandmanR]

Thanks. Yes, I understand. It was erroneously Hydro-tested at a much higher pressure, the pipe and flange held pressure well. I just was wondering if the Flange would be affected in any way.

 

[LittleInch]

Its difficult to say with any certainty. At that level of overpressure there is a risk something yielded and hence is work hardened. The fact it didn't leak would imply the bolts were over tightened out were "made up" during the test to stop them leaking.

At those sizes you've probably got away with it, but the issue is then risk and liability in case of future leak or failure. Its up to you how much a replacement set of piping is going to cost versus a law suit because even if it has nothing to do with it, the finger of blame will point to the over pressure during the test.

I don't think you'll get anyone to sign this off or take responsibility. You'll probably spend more time and money trying to make this FU smell of roses than it takes to rebuild it and test it properly. That's the way of the world these days.



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