Damaged Surface of New U-Stamp Pressure Vessel

Can you give full details as to material, design thickness, decreased thickness in the damaged area, etc.?

Whoever damaged the vessel should probably be responsible for repairing/replacing it, but such avenues may be difficult to pursue.

If a recalculated (lower) MAWP is adequate for the intended service, that might be the best way to go. It might be wise to grind the scratched area so as to remove sharp edges and stress risers, but I don't know if your local Code or insuring agency would permit this.

The direction of the scratch (longitudinal vs circumferential) may also play a part.

These are just some ideas; you should get more before deciding and proceeding. In any event, be sure to file a damage report with transportation company, unless the damage has occurred locally.

Dear Tornado,

Thank you very much for your reply.

As for the details, shell is made up of SA 516 Gr.60. Shell governed vessel MAWP, used thickness is 20 mm and required minimum thickness as per calculation is 17.88 mm. The new thickness on damaged part is 18.5 mm. Vessel is designed as per ASME Sect. VIII Div. 1.

As for the MAWP, vessel is stamped with MAWP base on 20 mm thickness. Now that the new minimum thickness of shell at damaged part is 18.5 mm, should vessel be again stamped with a lower MAWP?

Vessel will be put in service in Saudi Arabia. If vessel needs to be re-rated with new MAWP, what code shall be applicable for the re-rating?

Again thank you very much.

If I read the paragraph correctly that the required thickness is 17.88mm, even your damaged thickness of 18.5mm should still suffice. (The 20mm plate would simply be the next standard size higher.) I would still want to smooth out the scratched area to avoid sharp edges/notches/stress risers.

No matter how you slice-and-dice this, it is an irregularity. Seek second and third opinions, and document everything.

What are the vessel dimensions and design MAWP? What is the setting of the relief device? What pressure range will the vessel actually encounter in normal service? What does it contain?

[As coincidence would have it, there is an ammonia receiver in my plant that some vandal gouged about 0.020 inches with an angle grinder(!) It is a very shallow groove, and the edges are not abrupt. Probably not a problem, but still under consideration.]

One question to clarify: how did you determine the minimum thickness? If you accounted for corrosion allowance, you are probably okay but if you didn't you may be borderline compliance with code at the current vessel rating. When the scratch is removed, check the thickness again, because you may require re-rating to a lesser MAWP.

I believe you have another more serious concern, though. If the fabricator didn't use the specified thickness of shell material, where else might he have deviated from spec and good manufacturing practice? Are other pieces under spec thickness? Are the welds according to best practices? If it were me, I'd demand the fabricator do another thorough inspection and show that design and purchased specs were met.