Repair in Fabrication Shop 1

[PAN]

We found incorrect elevation of nozzle during final dimension check. The fabricator proposed to repair by patching (double v-groove butt weld) at the shell. They confirm the quality by RT 100%.

Is this conformed to ASME Sec. VIII Div. 1? Please comment.

 

[jonesey]

Why don't you just just alter the mating piping to suit the new nozzle standout ? It's a lot cheaper thatn changing the vessel.

 

[VeryPicky]

PAN

If you can not alter the piping think about blanking the existing, incorrect nozzle off and adding a nozzle in correct location.
This is by far the most acceptable solution when the vessel integrity is concerned.
I assume that both nozzles meet the requirements for reinforcement and the material is available. You need to have a look at the price of alterations. The other thing to consider is the process the stagnant volume after this blanking off might be not acceptable in your application.
Please let me know what was your final solution.

Putting Human Factor Back in Engineering

 

[metengr]

Yes. Installation of a flush patch that is full penetration welded to the shell wall is acceptable under Section VIII Div 1, and has been done before provided all Code design, material, welding and NDT requirements are followed. Was a final hydro performed on the vessel before the nozzle elevation deficiency?

The fabricator must get concurrence from the AI for this repair to the vessel wall because this is a new vessel. Make sure you have discussed this with their AI for all necessary QC hold points and NDT.

 

[PAN]

Thank you for all comments.

jonesey & VeryPicky,
The nozzle is for adsorbent unloading (size 6"). The elevation before repair is 10 cm above the required elevation. Therefore, We cannot blank or accept without repair. After repair, the reinforced pad will cover the entire of repair area.

metengr,
We will perform hydrostatic test after pass NDT. Thanks again for your comment.

 

[codeeng]

Since you would be cutting into the repaired area with the correct nozzle location perhaps you should consider installing an insert plate in the shell rather than using a repad. This makes more sense and its a better job.

 

[VeryPicky]

I hope the nozzle orientation will be different after repair to that form before. If you keep the orientation it seems the welds of the repair patch and the new nozzle will intersect and at an awful angle. My advise is try to avoid that. Stress pattern in such an intersection is unpredictable. Covering the whole repair with a repad might not be such a good idea since you might want to monitor the patch in service with visual and NDE. I concur with Codeeng that bigger insert plate (if you need extra reinforcement - thicker with an ASME transition) seems a better idea. Check nozzle loading to ensure this scenario is feasible.

Putting Human Factor Back in Engineering

 

[PAN]

VeryPicky,
Thanks for your comment. There are 2 unloading nozzle at the opposite site. The incorrect elevation was found only 1 nozzle. Therefore, I keep the orientation. You are right...The repair area and nozzle intersect. The fabricator fit up the upper moon cressent section with the removed lower moon cressent section.

Due to no deviation from ASME Sec. VIII Div. 1, I cannot refuse the proposed repair procedure from this fabricator. Any further comments will be appreciated.

 

[VeryPicky]

Dear PAN.

You can reject any repair, within reason. I understand that you ordered a new vessel and getting a repaired one.
To me this is a reason enough for the client to be involved in the repair. You have to ask yourself if the repair is acceptable from technical point of view for your application.
I am just saying that I don't have enough data for welds intersecting at the tangent like in the patch described by you and the nozzle loading. I would expect that the fabricator did proper stress analysis in that particular corner.

If you happy there is nothing more to say.

Putting Human Factor Back in Engineering