Repair of corrosion hole on nozzle

[ddhardy]

I have a storage tank with a corrosion hole on the neck of a manway nozzle located at the base of the tank.

653 tends not to give much guidance on repair methods so I'm wondering what might be the best course of action might be. The corrosion hole is small (1" x 1") and the surrounding area has good metal remaining.

I'm thinking of cutting out an area of the nozzle and placing a patch in. Is this right, and if not, what other courses of action might be appropriate?

Thanks,

Devin

 

[fegenbush]

The most cost effective solution may be to cut the nozzle neck before the pentration and replace the neck and flange. This would be much easier than a button weld patch.

 

[jte]

fegengush has a good point, but a small diameter butt patch could be feasible as well, and with less welding. A few considerations for a welded repair can be found in Part 2 of ASME PCC-2 Repair of Pressure Equipment and Piping, though be aware that there is no Article which specifically tells you how to fix it. If you choose to put a butt patch in, it'll provide some general guidance, along with other possible repair techniques such as a fillet welded lap patch which could (and I have) be placed on the inside.

 

[valleytank]

How thick is the manway neck? Is it one continuous rolled plate with a butt-welded long seam? Or is it an older 12c style with the two press-formed halves with one big circ-seam joining them?

 

[Samm17]

I would agree with Fegenbush, best to replace the manway. While API 653 does not directly address holes in the necks of manways it does state that the minimum size of a shell patch plate shall be 12" (9.2.2.1). It will also be difficult to meet weld spacing requirements (Fig 9.1). These don't specifically address necks but they are good starting points to consider when evaluating your repair.

 

[IFRs]

The neck is not on the pressure boundary of the tank and clearly has no relationship to the global failure of the tank. What's wrong with using a backup strip, welding the hole shut, get complete penetration and fusion, MT the final both sides, grind it flush and call it a day? Not much worse than buttering a shell gouge and grinding it flush. "Where grinding to a smoothly contoured surface will result in unacceptable shell plate metal thickness, the shell plate may be repaired by deposition of weld metal, followed by examination and testing in accordance with 12.1.8." This is a bit more extreme, but the downside risk is a leak, not catastrophic failure of the tank. I'd even go for a lap patch, if this is unpalatable.

 

[r6155]

Prepare a hole and install a solid round bar, full penetration weld.
Regards
r6155