Hi guys. Dumb question from a Code neophyte. I am involved with a Section VIII Div. 1 vessel with nameplate stamped at MAWP of 250 psig at 100° F. The Owner wants to operate this vessel at 0.5 psig and 250° F. This of course is outside of the temperature stamped nameplate value. I believe he needs to get a recertification to operate at this temperature because it is outside the stamped nameplate. What say ye?

Thanks! Pete

Yes, the vessel needs re-certification to 250F. More of paper work than anything, except for a new nameplate affixed to the vessel (assume only temperature change, no process changes).
Cheers,
gr2vessels

Yes, stare at API 510 or NBIC.

What is the new design pressure and temperature you want to set above 0.5 psig/250 F ? You shall have some margin to maximize the use of the vessel in case your owner want to change again in the future. You can set MAWP equal to the new design pressure in your case and stamp it. For sure you will need to run a new calculations for all pressures parts including static head, making sure re-pad is not governing, and wind/seismic load, if any, will not be a problem. Then follow NBIC or API. You can weld the new stamp next to the existing stamp without welding a bracket to the pressure part.

If the existing MAWP can not be reused due to new higher design temp that lowers down the allowable stress, take a look on the pressure relief valve, which most likely shall be replaced for the new pressure, And also check all connecting piping. They may also have relief valve in them. Re-rating needs a system or process engineer to look at the overall picture (P&ID) and impact before it can be initiated. New design conditions shall be set by them.

Take a look U-1 of Section VIII, Div.1 - based on the new design conditions you've given this vessel may now be outside of the scope of Section VIII. Rather than a re-rate it may be a better (more economical) choice to simply remove the name plate and no longer maintain the vessel as a "Code" stamped unit - this, of course would need to be authorized by the owner, inspector and local jurisditional authority.

Agree with Numberfive -- run the vessel at less than 15 psig, and chisle off the Code Date Plate and deface the "U" stamp. ASME Sect Viii does not apply to vessels operated at 15 psig or lower, nor does NBIC or API-510. The applicable code at less than 15# and more than atmospheric is API-620 [15# max].

Guys thanks for the awesome replies. I had not even thought about the U-1 end-run around re-certification. So I reviewed U-1 and that approach is definitely a possibility. I have heard of this being done in the past: the nameplate is cut off and destroyed under the witness of an AI. The AI then files a report that the vessel has been de-certified. The hitch here of course is ensuring that the now not-a-vessel is never operated at pressures greater than 15 psig, so controls would have to be put into place to ensure that. Thanks guys!

But remember, through this whole process of "code compliance and re-labeling", the physical threats actually present:

You're wanting to go outside the stamp (the nameplate) but you're lowering pressure from 250 psig to near-zero. Temperature of the vessel is going up (above boiling point of water) but well below the significant loss of metal strength you get from heat. (Compare a process at 250 Deg F at near-zero pressure with one at say 800 or 900 degrees at 400 or 500 psig.)

Thus, you're going in a safe direction with the change, but still need to satisfy the legal/insurance requirements.

Tests? How are you going to verify no leaks if you don't pressurize the system? Are you sure you want to write the new label for "only" that 1/2 psig and not something higher, like 10 or 20?

Another issue with treating it as a non-code vessel is what overpressure scenarios do you have and are you still protected? If the vessel is designed with a PSV intended to protect it with a design pressure of 250 psig, it's not going to have sufficient capacity at your new 'design' pressure.

Consider my opinion posted on June 19. You still want to make this a coded vessel for future process change so your owner won't regret later. If your owner want to change once, he may want to change again. Maximize the use of this vessel, and watch out the PSV and other connecting piping system.

KernOily, spend a little money if necessary, get it rated for the additional (new) design condition, have something of value in the future. Once de-certified, it might be hard going back.

Regards,

Mike