Flush patch repair 3

[nasser358]

A company in California holding an R1 certificates will repair an epoxy lined pressure vessel with a 2-inch diameter hole on the shell. Aside from the hole, there are corrosion damage (pittings)around the bottom of the distributor. Question:

1. The hole would be repaired by flush patch and inspected by means DPT on root and final passes in lieu of hydrotest. Is it OK to DPT the patch as long as the AI is informed?

2. The pittings around the bottom of the tank might have gone to some extent that the wall thickness has reduced considerably low. What is the remaining plate wall thickness that should be considered for replacement?

Design pressure: 75 psi
Design Temperature: 150 Deg F
Corrosion Allowance: None

Thanks in advance

 

[vesselfab]

AI should be informed before any repair or alteration required a "R" stamp. No RT or UT?

remaining wall thickness is dependent on what the calculations call for as minimum thickness.

 

[metengr]

1. The hole would be repaired by flush patch and inspected by means DPT on root and final passes in lieu of hydrotest. Is it OK to DPT the patch as long as the AI is informed?

Informed? You mean having the AI review and approve your repair method per the NBIC. Regarding volumetric examination, this depends on the original NDT of the vessel and service conditions. If the welds were spot radiographed - I would see no reason to use RT or UT for a flush patch repair and use surface NDT methods. If the vessel was radiographed 100%, you would most likely need to have the flush patch welds subject to the same level of NDT (my professional opinion only). Your AI will make the final call.

For determining remaining wall thickness to retain pressure I would require API 579 to rely on my justifcation for not having to restore wall thickness. Not an easy task but can be done.

 

[brandonb73]

In response to #1: Make sure no RT is listed on the data report. NDE methods for repairs must be per the original code of construction. If there is no RT, then DPT is acceptable with the AI's agreement. Also check for any PWHT requirements.

In California, any alternatives to NDE or PWHT require not only permission from your AI, but also permission from State of California.

In response to #2: Ditto on vesselfab's comment, with an additional comment that this will also require DPT per the original code of construction (assuming it's ASME Sec. VIII Div. I)

 

[vesselfab]

I guess I am old fashioned.

If I was welding in a window (flush patch) in the side of a vessel, and not doing a hydrotest, I don't really care what the original data report says, I am going to 100% RT the weld.

sorry

just the way we do things.

 

[nasser358]

Thanks for the help guys.

 

[GenB]

AI has to approve the repair and inspect results.
NDE in CA will be per AI approval and will depend of the
original construction.-
The vessel use is important for the AI to make a decision on the method of testing.
good luck