rerating testing requirements 1

[flaco1967]

Hi everyone

i need to rerate an old vessel for propane service at -22°F. I´ve checked fitness for purpose API579 Sec 3 and computed a MDMT of -55°F for ASME VIII UCG66.1.

Do I need to Xray the vessel again? or just hydrotest?
thank you in advance for your advice

Andres

 

[metengr]

flaco1967;
You mentioned re-rating, are you referring to a reduction in the minimum design metal temperature and/or maximum allowable working pressure?

Re-rating of pressure containing objects at least in the US is done to the National Board Inspection Code, API is an alternative approach. Re-rating can be considered an alteration if the minimum design metal temperature is lowered or the maximum allowable working pressure is increased. In either case, if the re-rating is considered an alteration, an Inspector must review your calculations and a pressure test is normally required in accordance with the original code of construction. An alternative approach could be nondestructive testing to verify the integrity of the altered item. The alteration will require stamping a new nameplate.

 

[vesselguy]

flaco1967,
I interpret from your post that you're just doing calculations to re-rate an existing vessel for a new service and NOT doing any welding to repair or modify the vessel. Is that correct. If so, then there is no need to re-hydrotest or X-ray. The code does not required it unless it is new construction or welding has been performed on the pressure membrane. You would however require to register the vessel with the local boilers branch for new service and submit calculations to support the registration. You should contact your local boilers branch to get exact requirements. Also, you should perform a grid (or 100% depending on how severe your new service is) UT inspection to obtain remaining thicknesses for use in your rating calculations.

Just ma 2 cents worth.

 

[eliebl]

Even somthing like a change of sevice should be closely looked at. I know of a vessel which experienced autorefrigeration at the new service conditions but at steady state there were no changes required.

EJL

 

[flaco1967]

Thank you all for the input

to clarify issues. I´m trying to use and old gas separator as a liquid propane vessel in Argentina (here API std´s and RP´s are considered requirements). The original operating temp. is 50°F intended operating temp is -22°F. Actual calculation indicates that MDMT is -55°F.

Thickness measurements and visual inspection shows no indication of in service degradation.

The remaining question is if new Xray is needed besides new hydrotest for new service conditions?

 

[robsalv]

I see this thread has gone cold.

If the vessel is being rerated to a higher pressure and/or higher temperature, then a new hydrotest is required. (I include temperature, because our plant standards factor in a temperature ratio into the hydrotest formula - it needs to be thought about at least).




This brings up an interesting question. If the rerate is to a higher design pressure and the change of service is one which water is a poison, then a pneumatic test may be the only pressure test option available.

BUT!

If the pnuematic pressure test (usually 1.1 times ...)is equal or LOWER than the original hydrotest (usually 1.5 times ...) AND all components are at nominal thicknesses (no inservice degradation), then I see NO reason/value for the pressure test. If the NDE wasn't already extensive, I would conduct extensive NDE. Be prepared to dig out and repair previously unknown defects that don't comply.


Speaking of NDE, the Australian pressure vessel code has several construction classes. The higher the class, the lower the conservatism and the more NDE required. The classes often relate to service requirement, e.g. toxic service. SOOO, if the new service requires a higher class, therefore a higher degree of NDE, then to rerate to the new service, the NDE will need to be increased... as I said above, be prepared to do some repairs.



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[metengr]

If so, then there is no need to re-hydrotest or X-ray. The code does not required it unless it is new construction or welding has been performed on the pressure membrane.

This is an incorrect statement in relation to alterations of pressure retaining items either with or without physical work being performed.