Circumferential welded joint (type 3) for a thick wall vessel 1

[eHerrera]

Hello everyone.

Currently, I'm evaluating to do a weld repair which involves to realize a circumferential weld within the main shell of a ASME VIII-1 pressure vessel with this features: Thickness = 2,5 in; Inside Diameter (ID)= 56 in.

ASME VIII-1, UW-12 gives me three types of joints [Type N°(1), (2) or (3)] for a welded joint category "B". It's not possible to do a joint type (1) or (2), because I'm not have internal access to vessel to realize a double-welding type (1) or to install a backing strip required to joint type (2). The only joint that I see possible according this case is a type (3) single-welded joint without backing strip, but this joint is limited to butt joints not over 5/8in thick and not over 24 in outside diameter [!]

Which is the best weld type / detail for this case?

Thanks.

 

[GenB]

You ask for one of the 3 but you know that you can't use 2 of them. In my opinion you use tp2. You can perfectly make the opening slightly oblong and insert a baking ring.
OR change the design by making a flash butwelded pad.

 

[Don56]

This could be a type 1 joint if you qualified a procedure with a TIG or GMAW STT or RMD process.

UW-12 Butt joints as attained by double‐welding [highlight #FCE94F]or by
other means that will obtain the same
quality of deposited weld metal on the inside
and outside weld surfaces to agree with the
requirements of UW-35[/highlight]

 

[eHerrera]

Thanks GenB, but it's not possible to make a opening slightly oblong, if that were possible it would be a great solution.

Thanks Don56, but where does that say? Any paragraph in ASME VIII-1 be explicit with that?
UW-35 (a) is about ensure a complete penetration and full fusion. "this could be a type 1 joint if you qualified a procedure with a TIG or GMAW STT or RMD process"

Another thing is that I don't know if the ASME Interpretation VIII-1-83-220 from february 22, 1984 validates this case.

Regards

 

[dhengr]

EHerrera:
It never ceases to amaze me how little important engineering and design info. you people seem to think you should provide, if you want a meaningful discussion and solution to your problem. These details are important for a good practical solution.

What’s wrong with the existing weld that it needs to be repaired, what is the nature of the defect? Is it cracked all the way through the thickness of the vessel, or only part way through the thickness? Is it cracked all the way around the vessel? Is it an internal defect which could be gouged out and repaired? Is it a fairly clean crack, such that you might gouge (or machine) down to within 1/8" +/- of the i.d., leaving an 1/8" land (root face) as the base for your weld repair. An experienced welder should be able to do this gauging or machining and welding without any problem. And, the remaining crack, at the land, is remelted during the first weld pass, just as one of your three details probably shows. This crack, as the land, may be no worse than a backer bar and/or an intentionally prepared land.

You will likely have to do some testing and write a repair procedure to prove that this will work, but don’t just blindly follow some code or standard for original manufacture of vessels without understanding its intent and when it applies and how to apply it. I don’t have copies of the codes you are looking at, in front of me, so I don’t know some of the code details that you might have to comply with. Isn’t there a specific code section on repairs like this?

 

[eHerrera]

dhengr:

I don't have any problem with a existing weld, I have two sections from a shell vessel that I need to weld with a circumferential seam from outside, as "simple" like that. This job is considered a welded repair by API-510 (the repair code) and will be referenced by the design code ASME VIII-1, which presents some requirements and limitations according thickness and diameter (UW-12), that is the reason of this thread. My only way is to follow these codes, that impplies "blind me" with them.

Thanks for your comment.

 

[r6155]

eHerrera
If your consult is not clear the Code shall not clear for you.

Regard
r6155

 

[weldstan]

Don56 has provided the answer to your query. If you choose not to hear, so be it. The method(s) proposed have been used countless times in vessel construction.

 

[chicopee]

If you consult the NBIC, you may have some latitude with the repair. I do not have the latest copies of the NBIC, however, my 1987 edition, chapterIII, first paragragh states "...all repairs and alterations shall conform insofar as possible to the ASME code section...". The term "insofar as possible" suggest slight deviation from the code is possible.

 

[eHerrera]

Thanks for your answers. Very useful for me each one.

Regards.