Working pressure upgrade

[sbush]

Can the working pressure of an ASME code pressure vessel with U-stamp be upgraded (re-rated) from 75 psi to 100 psi? Perhaps by incorporating radiography? Has anyone ever encountered a request like this?

These vessels are currently operating at a water treatment plant in New Jersey and were installed in 1992.

S. Bush

http://www.water-eg.com

 

[Christine74]

You cannot re-rate simply by conducting more extensive radiography, even if you were to completely remove all of the existing welds, re-weld everything, and then x-ray everything. However, you might be able to re-rate by using the higher allowable stresses that went into effect in 1999, depending on your jurisdiction.

Also note that just because the nameplate says "MAWP 75 psi" doesn't necessarily mean that that's really the MAWP. More likely, that was just the design pressure, and the actual MAWP might be a bit higher. You'll have to run calculations to determine the actual MAWP.

 

[metengr]

This really depends on two factors; 1). If the vessels are used for water service, in other words no air cushions, they may be exempt from Jurisdiction regulation, and you are legally free to do what you want despite having a U-Stamped vessel OR 2). the vessels are regulated by your local Jurisdiction and, in such case, the requirements of the NBIC must be followed to re-rate this vessel. For 1)., I would still suggest you follow guidance from the NBIC to assure safety if you intend to re-rate the vessel. Your insurer of the vessels may also require you to follow the NBIC requirements for re-rating.

A re-rate of this type is considered an alteration and would be performed under the National Board Inspection Code, Part RC-3000 (2001 Edition, 2003 Addendum). The requirements for re-rating the vessel are very specific and are in the NBIC (review Part RC-3022, paragraphs a-d).

 

[robsalv]

S Bush. I'm not in the U.S., but all rerates work with the same fundamental principle... you cannot upgrade working pressure without a new set of calcs showing that the vessel is adequate for the new service conditions.

Any PV designer with an appropriate drawing could get this part sorted.

The rest depends on your regulatory environment.

Cheers