repair options for coded pressure vessel 1

[nutriarat]

What repair techniques are acceptable to repair corroded areas in the shell and head of a pressure vessel? Are weld metal buildup and/or flush patches basically the only two options?

 

[metengr]

You have two options, follow the repair requirements in the National Board Inspection Code, or follow the requirements in one of the API Codes.

Since I am most familiar with the NBIC, I can tell you that thinning can be repaired by either weld overlay or a flush patch plate. Regarding weld overlay, this can only be performed on the side of the vessel that has the wastage. So, if the wastage is on the ID surface, you can weld repair from the ID side of the vessel. If this is not possible, you need to use a flush patch plate.

Have you used API 579 to evaluate if you can leave the thinned area?

 

[nutriarat]

Thanks metengr,

It turns out that I was able to lower the tmin. Can you tell me where in the NBIC weld overlay requirements for wasted areas are discussed. Section RD-2030 mentions buildup of wasted areas, but I do not see where the repair has to be performed on the side of the vessel with the wastage.

 

[metengr]

The weld build-up must be performed on the side of the vessel that the Inspector can see because if you read thru the entire paragraph in RD-2030, the Inspector may require an appropriate method of NDT. How would the Inspector be able to see the wasted area on the ID surface of the vessel (UT is not a visual inspection method)?

By the way, we are considering the use of an external weld build-up to restore the integrity of the pressure retaining component that has suffered from ID wastage (based on UT) to be included in the NBIC. At this point, it is not permitted.

 

[GenB]

metengr
It sounds very nice:
"we are considering". Is the forum considering!!!
Oh I figured out, you seat in the NB commitee.

My opinion is that external weld build up can be dangerous unless NDT test (RT) can assure the weld.
genb

 

[MattJK]

Follow the Jurisdictional requirements and the National Board Inspection Code. Part RC of the National Board Inspection Code is for Repairs and Alterations of Pressure-Retaining Items. But don't forget to review the Jurisdictional requirements.

 

[metengr]

GenB;
Yes, I am very involved with the NBIC committees. Also, the ASME Post Construction Committee has endorsed external weld build-up of pressure retaining items in their Standards. These will be published, shortly by ASME.

I share your same concerns. However, given sufficient constraints and NDT requirements, this repair will eventually be endorsed by the NBIC.

 

[CodeRef]

If I may.... since this post is less than 6 months old....
How about this scenario..... I have a heat exchanger shell with wastage that needs repair to restore minimum wall to within Code construction requirements. There isn't access to the interior wasted area to complete the visual inspection or to perform radiography. Additionally, a window patch/flush patch is out of the question since the Inspector cannot verify a Code Required "Type 1" weld joint unless UT in lieu of RT is performed. This leaves the only "good" alternative of performing weld build up for strength consideration on the outside only with surface examination each pass (PT or MT) any suggestions?

There are three kinds of people in this world. Those who can count and those who can't.

 

[metengr]

CodeJackal:
Given your scenario, I believe you have an excellent argument to perform this repair. I would also add UT as a final NDT to assure adequate thickness and coverage of the external weld build-up. Also, you need to specify the geometry (circular or oval)of the build-up, and the ends of the weld build-up taper angle (45 deg).

However, it is not up to any of us in this forum, it is up to your Jurisdiction/regulatory body where the heat exchanger is installed and/or if you have the equipment insured, the insurance agency. I would present the repair option and make sure you have all the technical rationale covered for the reasons to do the external weld build-up and your NDT requirements. If you are self-insured, go for it.

 

[CodeRef]

metengr,
Thanks for the reply, I agree, I just wanted to validate my own thoughts on the extent of repair. The NBIC has not addressed this scenario, (exterior only buildup) or perhaps the reason for not specifically addressing it is because this type of repair requires a concensus opinion for those required to be involved.


There are three kinds of people in this world. Those who can count and those who can't.

 

[Formyla]

Provide a full penatration weld with a flush patch. Radius the corners or the flush. PT root and final. Shearwave welds then hydrotest. Should satisfy API.

 

[Cymry]

Does anyone have experience repairing unfired cast iron vessels, in particular exit holes 1" diameter on cast iron heads? Corrosion extends slightly greater than 2" diameter.

Numerous fixes are possible but none seem to conform to my interpretation of the ASME code...

 

[deanc]

Cymry

There are acceptable repairs,but need more info. Do you have an "R" Stamp?