Plug hole in vessel wall

[KevinNZ]

Hi all

We have an ASME VIII Vessel with a DN25 NPT tapped hole. We now need to fill the hole and make the OD surface flush. What would be a suitable detail to fill the hole?

Wall thickness 23mm.

We are thinking of the placing a thread plug, then cutting this back to the surface and a seal weld.

Thanks

 

[JStephen]

The detail I see most commonly is to put a small plate on the inside and fill the hole with weld metal- used on spinholes on heads.
Refer to the welding requirements to see if your detail is adequate.

 

[MJCronin]

Your proposed solution is inadequate and dangerous

Do it the right way !!!! There is no place for "whatdoyathink" repairs to vessels !!

The ASME pressure vessel and other codes have specific rules about nozzle reinforcement and full-penetration welding.

Take your small hole, make it larger and install a larger, code approved nozzle design ...

MJCronin
Sr. Process Engineer

 

[JStephen]

See UW-34 also.

 

[chicopee]

For pressure vessels, full weld penetration is strongly advised as shown by MJCronin's drawing.

 

[r6155]

See API 510 8.1.6.2.2 Insert Plates.

Regards

 

[KevinNZ]

Thanks all

I do not disagree with the fully welded plug. The original vessel designer has proposed the seal welded plug.

What is the different between the original design with a screwed in pipe nozzle and a screwed in plug and seal weld?
If there is a long term with concern with corrosion then the a seal weld could also be added to the inside.

 

[mk3223]

IMO, you may want to prove the specific repair with FEA, i.e. repairing with a plug and seal weld, since it's not a typical reinforced nozzle connection per ASME. For a typical BPV nozzle, I agree that a nozzle with reinforcement and full penetration weld are acceptable without argument.

 

[KevinNZ]

MK3223

There is no problem with the reinforcement. The original design is a threaded hole with a pipe screwed in.

 

[JStephen]

When I read this earlier, I missed your point that this will be a threaded plug, not just a little metal slug welded into place.
That said, if the threaded plug was adequate in the first place, I don't think your repair is any less adequate, from a strength standpoint.
Per the code, it's sort of a neither-fish-nor-fowl type arrangement that doesn't fit the standard details normally used on small fittings, so it's difficult to judge acceptability. There's a clause towards the front of the code somewhere address items or details not addressed in the code equations. Assuming that arrangement doesn't actually violate some other rule, you'd use it to show acceptability.

 

[SnTMan]

Threads provide the strength, welds provide the seal. No reason it wouldn't work. But.

I would not want it on one of my vessels. Nasty detail.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[DekDee]

Never been able to understand the acceptability of seal welding of threaded plugs from an engineering perspective.
Codes require a minimum gap before socket welding pipe to alleviate any induced stresses that may be caused by weld shrinkage.
Welding a threaded plug is basically the same as a socket weld - how does the weld expand/contract if it is locked in by the threads ?
Cheers,
Shane

 

[chicopee]

Seal welding is normally performed on expanded and then beaded tube ends. This practice is often performed on fire tube boilers where beaded tube ends protrude thru the fireside of tube sheets. Seal welding is not a strength weld.

 

[r6155]

Why not install the plug without seal weld?. You can use this as inspection opening.

Regards