Stub In or Stub On welding design for tapping on a blind 1

[Pradeeprajen]

Hello everyone,
We are going to redesign for a tapping connection on one of the process line with 100+ BAR service pressure for purging connection. The tapping is on a 24" blind on a TEE. Tapping is a 1" Inconel line on a 24" CS+Inconel clad blind.
Question is if the tapping connection should be a Stub-on (Full penetration butt weld) or Stub-in (Inside and outside fillet weld)?
kindly give your suggestions and references regarding joint selection for the above mentioned tapping connection.

 

[LittleInch]

I would always prefer a full butt weld as the strongest joint which has less stress concentration and fatigue issues, but a simple sketch would help to make sure we're all talking about the same thing.

A 1" connection like this is very likely to have other forces, moments etc applied to it in its lifetime so you need to factor that in as well as the higher NDT you can do on a butt weld.

~The last ting you want is this 1" stub shooting out like a bullet.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Pradeeprajen]

Hi,
Thanks for the response. My immediate thought also was for a butt weld design. But just to get an insight about the difference in strength made me post this question.
Also I need something strong to present to my contractor why they need to weld it as a full penetration butt instead of fillet welds. I'm looking more for a standard reference regarding this issue i'm facing.
I made a rough sketch about the design in question. Give me your feedback about Figures A & B and which would have more strength and less susceptible to crevice corrosion. Also note that the blind is a CS+ 3mm Inconel clad material and the tapping pipe is 1" inconel 825.

 

[LittleInch]

It all depends how tight you can make the fit between tube and hole.

If you've got Inconel it's there for a reason and the issue with the stub on will be corrosion inside the hole you've just drilled through your blind flange which will be very diffilut / impossible to clad or coat.

It might be better to drill the hole as tight a tolerance as you can get and stick the pipe through the blind so that you fillet weld using inconel filler between the clad face and your inconel tube and then just fillet weld the outside to avoid any movement of the tube within the hole having an impact on the inside fillet weld.

I don't think there is a "standard reference" or code requirement for this, only company or your own specification.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[david339933]

Pedantic maybe, but this is a groove weld, not a butt weld.

 

[AGazo]

Pradeeprajen,

1. Stub on has Full penetration fillet weld (not butt)
2. I Recommend Fig B. Min 2pass for each weld joint. It's like a Slip-On welding.
3. Finally, you need to consider flexibility/rigidly of this line, if required additional support (angle 40x6 or plate)

 

[mk3223]

IMO, the Fig. A of the stub-on connection won't work for your process since the "CS" material of 24" blind is to be exposed to the process stream without the cover of Inconel material.

 

[GD2]

Stub-on or Stub-in can both be made with full penetration weld. With 100+ bar pressure, whatever option you use, design the joint for full penetratio n. The real challenge would be how you apply the clad to the weld joint? Cladding should be considered on the 1" tapped line upto the isolation valve (process fluid contact) to prevent from corrossion.

GDD
Canada

 

[DekDee]

Not sure if it would affect flow rate or even be practical but what about a 2"x 1" CS reducer, internally clad and then welded stub on to the blind ?
Or if available a 2" x 1" inconel reducer.
On completion of the full penetration weld the weld internal and 2" bore can then be clad ?


Surely if you are the designer you instruct the contractor as to what you want ?

Regards,
Shane