Exceeding MAWP: Pressure Vessel rating 4

[Jitsukablue]

Hi All,
Can someone point me to the standard that covers rules around how much the MAWP can be exceeded by before a pressure vessel has to be re-rated, or even de-rated? Is it just a pressure (I.E. anything over 1.3x MAWP), or is there other nuances like duration of over-pressure event etc.

 

[FormerAIS]

The rating of the vessel is just that, the Maximum Allowable Working Pressure. If there is visible deformation of the vessel due to the over-pressurization, the vessel could be scrapped, depending on your insurance provider and/or your jurisdiction.

You could feasibly perform a redesign of the vessel to increase the MAWP of the vessel, but you would probably have to perform a hydrostatic test to satisfy an AI of the new higher MAWP.

Quality is not an act, it is a habit - Aristotle

 

[TGS4]

A little more context for your question seems in order. Is this related to an actual event or is it a hypothetical?

 

[Jitsukablue]

It's a common question I've seen in relation to over-pressure protection. It's both hypothetical and based on actual events, i.e. if a relief valve fails to lift within the code allowance, what are the ramifications of an over pressure event that exceeds the code allowable of 110% of MAWP (or 121% for fire case... but let's ignore that one for now), on the vessel... I'm not particularly interested on what happens to the RV.
When testing a RV that failed to lift, API RP allows you to go as high as 150% (for what benefit is arguable), which I presume is based on the original hydro. test. I'm really chasing API RP or code rules on exceeding over pressure allowances... as in we all know it's not allowed, but what is the reality of exceeding over pressure? Lots of engineering work to re-certify the vessel? Scrap it? De-rate it?

 

[TGS4]

I absolutely would not junk the vessel.

The ASME Code really doesn't have anything to say. It is a code of Construction, but not of operation.

My experience has been to treat this type of incident as a damaging event that necessitates a fitness-for-service evaluation. All potential failure modes must be evaluated, which might require additional inspection.

In general, if there is no permanent plastic deformation, there isn't much that needs to be done to return it to service.

Of course, it goes without saying that performing a root cause failure analysis to ensure that it doesn't happen again, is a necessity.

 

[LittleInch]

You might find some sections in ASME FFS-1 which apply, e.g. operating in the creep zone or section 14 for fatigue life.

Depends how much time you want to spend inspecting and testing it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[r6155]

For calculation method of MAWP see API-510, API-579 and ASME PCC-2.; ASME VIII shall not be used.

Regards

 

[Jitsukablue]

Thanks for the feedback all.