Backwelding plug on U-stamped vessel

[timsch]

This is an ASME U installation where we have had our ASME rated welders weld barstock inserts into a reactor. The customer doesn’t want to use these any more and wants to weld a threaded plug into the barstock. Please refer to the attached file.

Does backwelding this plug put us out of compliance with Section VIII, Div.1?

Thanks & Regards,
Tim

 

[SnTMan]

New construction or not? Plugs are seal welded to couplings and so forth all the time. If the vessel has been in service it will most likely will be done under NBIC.

Regards,

Mike

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

 

[timsch]

It is a modification to existing equipment.

 

[SnTMan]

In that case you do not need to comply w/ Sec VIII, Div 1 as it is for new construction only.

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

 

[timsch]

Reviewing the 2015 NBIC part 3, there are many references back to the original code of construction.

I don't know how applicable section 3.3.4.4 is to my situation, but it seems to be a close approximation of what we want to do. I mention this only because it stresses that the "requirements of the original code of construction are satisfied."

 

[SnTMan]

Well, as I said, plugs are seal welded to couplings and so forth all the time.

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

 

[metengr]

Does backwelding this plug put us out of compliance with Section VIII, Div.1?

No. The NBIC refers back to the original code of construction for rules related to materials, welding, etc. If the original code of construction does not address the issue, you can use the applicable section of the NBIC closest to the work being performed.

 

[every_name_is_taken]

Would this even fall under the geometric scope of VIII or NBIC? I'm fairly certain I've seen plugs seal welded into code vessels without the R stamp holder issuing any R1. And certainly couplings are listed on the U1, but there's no mention of the plug or connecting piping. And similarly if you received a vessel with a nozzle that was going to be directly welded to piping, that weld would be under the scope of the piping code, right?

 

[metengr]

Yes. Seal welding has always been addressed as a repair by the NBIC for use of pressure retaining components.

 

[timsch]

Thank you all for your input. I will look into the NBIC for reference to seal welding.

 

[jte]

With regard to whether a threaded plug is in scope of VIII-1, see U-1(e)(3).

...the scope of this Division shall include...
(3) pressure retaining covers for vessel openings,
such as manhole or handhole covers, and bolted covers
with their attaching bolting and nuts;

My perspective is that a threaded plug is functionally the same as the specific items listed in (3) and therefore I'd interpret this as being in spec. I'd have to ask my heat exchanger focused colleagues as to whether or not the plugs on a plug sheet of an air cooled heat exchanger are typically considered in- or out- of scope. Seems to me they should be in scope.

 

[GenB]

Jte. Ouside the vessel plugs can be part of it if listed in the data sheet the same as covers, these are all mechanical attached arts. When seam welded in the field can be part of the piping work if desired and with people documentation by the piping contractor. By itself is under the NBIC. Now this one is in the inside of the vessel and must be by the NBIC and addressed as a repair or alteration.

General Blr. CA,USA

 

[Nutsforbolts]

Backwelding is generally preformed in the piping world but there are a few precautions you should take to prevent any issues. I recommend preheat and ensuring the threaded components are assembled clean, without dope or tape. Make sure the welder consumes all the threads if you are attaching pipe or other tubular fittings. Also you might want to consider removing the threads and converting it to a socket welded connection to allow the joint to shrink with the weld, might depend on what you are welding. I attached an article Bill Bruce wrote back in 1983. That's my two cents.

Nutsforbolts

"Give me pipelines, or give me death!"

 

[moltenmetal]

Code experts can beat me up, as usual, with chapter and verse if I'm wrong.

But here goes...

The scope of the pressure vessel ends at the coupling, in the same way that if you build a pressure vessel which has a pipe nozzle intended to butt-weld into a piping system, without an attachment flange, the vessel scope ends at the end of that pipe nozzle. You can weld to that pipe nozzle without having to follow the requirements of the pressure vessel code in relation to hydrotesting etc.

However...

...that doesn't mean you can just weld and walk away!

The ongoing O&M codes DO set rules in relation to this kind of work. Minimum requirements will include compliance with ASME IX for welding, welder and procedure qualifications etc., as well as the NDE/testing requirements of the associated in-service code, or piping code in the case we're talking about my example of a weld to a pipe nozzle.

As has been mentioned, seal welding of existing threaded connections to prevent future leakage is something that is done all the time. It is also a questionable practice for new construction in my opinion, with the socket weld being preferable, but there are conditions under which it can be done without significant concern of future problems. The big issue is getting the threaded joint clean enough so that sound welding can be done- removing thread sealant completely from a threaded joint post assembly can be very difficult to accomplish, and it's an easy corner to cut when nobody is looking since the final joint can't be RT'd in any meaningful way. This is one place where careful supervision is required.

Hope that is accurate, and if it is accurate, I hope that helps!

 

[timsch]

Thanks again for the responses. Given the location of the plug, we will follow the recommendations to remove the threads and any other contamination in the area before weld-sealing this connection.