Flange ID Weld

[loilfan]

My colleague is trying to do a 10" blind and flange repair at the end of a header in a Sec 1 boiler. They don't have access to the outside of the flange and were wondering if they can machine the pipe/flange so that a full pen butt weld is done from the inside of the pipe. I couldn't think of a reason why not. Does anyone see an issue with that?

 

[racookpe1978]

Yes. Tell him to take a 10 inch pipe to the workshop, clamp it in place - JUST AS IT WILL BE DONE IN THE FIELD, put a 10 inch flange on the end and try to prep it, fit it, and weld it from the inside.

 

[DekDee]

No problem at all.
As long as you can produce a full penetration weld (if that is what is required) then you are good to go. How you produced the FP weld does not matter.
However, racookpe1978 has made a valid point - if you can't achieve a sound joint via mock-up in the workshop you have no hope in the field / boiler.
Cheers,
DD

 

[loilfan]

Thanks for the responses!

 

[davefitz]

There exists ID bore orbital welders that can provide a full pen weld from the ID. Incidentally , the max stress during startup of the boiler will be at the ID of this weld if the flange is not supplied as a "weld neck" flange; the temperature difference between the flange face and the pipe ID is significant during statup, and if the ID has a root pass defect ( as would occur if welded from the OD) then a crack can be formed from thermal stress at that defect. So, welding from the ID has the advantage of avoiding the root pass defect at the ID.

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