CL 150 Flange Overstressed during Hydrotest

[phil23]

We have over stressed a cl 150 Flange during hydrotest. The flange is part of a piping spool. Is there a way to prove the integrity of the flange or should it be replaced?

Thank-you

P

 

[jte]

How have you determined that the flange was overstressed? Usually that would be kind of hard to do without overstressing the adjoining spool.

jt

 

[phil23]

Thanks jte

One end of the spool is a cl 600 ansi flange & at the other end a cl 150 ansi flange. The flange rating of the cl 600 flange was used for hydrotest.

P

 

[gr2vessels]

phil23,
If you can prove that the 150# flange was not permanently damaged during the hydrotest, will you use it for Class 600# pipe rating, with the wrong flange hanging on the end of the pipe spool?
If not, what's the point of identifying the degree of damage on a useless flange, when you'll have to replace it regardless of damage or not.
However, if you intend to salvage the flange for second hand application, think twice. It might prove dangerous.

 

[JohnGP]

This was a mistake, right? The spool should have a Class 150 rating, with a spec break at one end? I'm with gr2vessels, replace the existing Class 150 flange, and retest for that rating (assumimg you need a spool with Class 600 and Class 150 flanges).

 

[SNORGY]

I did exactly that same thing once. Missed a specification break error on a hydrotest P&ID, and a 150# flange pair ended up hydrostatically tested to 1.5 x 900# rating, even though where they were installed was in fact a 150# system. The calculations that forced replacement of the flange set were based on yield considerations, not non-shock loading pressure considerations.

oops.

Regards,

SNORGY.

 

[unclesyd]

You haven't given any dimensions or properties of your particular flange. Can you come back with the details?

Normally if the flange measures out dimensionally, the flange face isn't cupped/rolled the flange was not affected by the over pressure.

 

[phil23]

Thank you all for responding.

It is common for us to mix flange classes in a spool. We can have a higher class depending on the equipment the flange mates with. If we have a spool with mixed flanges then the lowest flange rating detemines the hydrotest.In this situation the spool should been hydrotested at 1.5 x 150#. The mistake was to hydrotest at 1.5 x 600#. I apoligize for not making myself clear.

 

[unclesyd]

Questions,

Did the Class 150 gasket hold for the test?

What type gasket was used?

 

[rumandcola]

Out of curiosity, why would 600# flanges be used on a spool that only required 150# flanges?

 

[JohnGP]

mbc2009, if there is a spec break at a control valve, say, then the connecting spool would need to cater for the higher rating flange on the valve and the lower rating system downstream.

 

[phil23]

unclesyd

The gasket was a 150# flexitallic. The gasket did not leak.

 

[unclesyd]

Congratulate the piping crew, not for the over pressure , but for the flange makeup. Normally one wouldn't expect a spiral wound gasket to hold made up with Class 150 flanges at this pressure, double the maximum allowed hydrotest pressure, unless everything was perfect.

Just for curiosity was there a blind on this flange?
What is the flange size?

To answer a couple of questions posted above.

We have a lot of very similar spools where we have a different Class flange on each end. We have this on PRV systems on steam loops (Class 600 and 300), polymer bypass and vent systems (Class 2500 and 1500) and process vent systems (Class 300 and 150).