ASME Section VIII and re-rating a vessel's MAWP 5

[PSP113]

I was looking through Section VIII on how to re-rate a vessel's MAWP. At first crack, it seems all I can do is use the design calculations and hope the manufacturer underrated the vessel. Does anyone have any experience with this?

 

[SnTMan]

PSP113 re-rates can be difficult, and without complete information, impossible. You have to account for each feature of the design such as opening reinforcements, nozzle flanges, bolted joints, etc, and not just the shells and heads. Calculate the MAWP of each, the lowest is the vessel MAWP.

It will be unusual to gain more than a few PSI as there is normally just not that much fat in it.

Re-rates are normally done under the NBIC, rather than ASME I believe.

Regards,

Mike

 

[metengr]

PSP113
Re-rates of pressure retaining items are not covered in ASME B&PV Code because this is a construction code not an in-service repair or alteration code. One could also look at API. However, these are not ANSI standards, like ASME B&PV Code or the NBIC.

 

[AIOR]

Because this is a post-fabrication issue, ASME Code may be used only as a construction standard to support an in-service repair/alteration code accepted by a local jurisdiction, like NBIC in USA. Per NBIC, re-rating is a part of alteration and can be done by a R-Stamp holder in compliance with NBIC 2007 Edition, paragraph 3.4.1.

Thanks,
AIUS
Oregon

 

[spayette]

API-510 contains requirements for the rerating of pressure vessels. At a facility where I work the owner has adopted this as the governing document for rerating of pressure equipment previously built to both ASME and API-ASME Codes.

As pointed out by SnTMan rerating involves all pressure containing and pressure/temperature impacted components of the vessel, as well as all applicable loadings. The analysis may also need to consider piping loads, wind, seismic conditions, liquid level, skirts, saddles, internals, external attachments, vacuum, steamout, etc.--the list can be very extensive. Original calculations are not needed but a knowledge of the materials of manufacture, and such parameters as joint efficiency, original hydrotest pressure, fillet weld sizes, impact testing temperature, and component thicknesses, are required. For vessels built to API-ASME, it is also desirable to know whether or not the vessel received PWHT.

Having personally been involved with literally hundreds of rerates, I would recommend that only those who are very experienced in pressure vessel analysis should tackle such a project. Ideally, these tasks should be left to those who also have prior experience performing rerates.

 

[chicopee]

As AIOR indicated, the NBIC covers rerating of fired and u fired pressure vessels