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Heating duplex weld joint by TIG arc welding

Karik87

Karik87

Mechanical
Aug 24, 2021
19
Hi experts,
The welder has just completed a weld on a Duplex stainless steel pipe (A790 UNS S31803). After welding, He noticed a significant misalignment between the tee and the pipe — clearly, the joint has distorted more than expected.

To correct this, he applied TIG arc heat onto the cap layer of the weld in an attempt to realign the components. No filler was added — he simply used the arc to locally reheat and relieve stress in the distorted area.

My question is:
🔧 Is this practice acceptable for duplex stainless steel welds?
⚠️ Are there any risks to mechanical properties or corrosion resistance from using TIG arc for distortion correction like this?
❌ Is this prohibited or discouraged in any applicable welding or metallurgical guidelines?

I understand that duplex materials are sensitive to heat input and thermal cycles, so I’m concerned this may affect the phase balance or introduce unwanted microstructural changes like intermetallics.
I’d really appreciate insights from others who have dealt with similar issues. Have you used this method before? Did you perform any tests (e.g., hardness, corrosion, microstructure) afterward?
Thanks in advance!
 
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Some photo?
More info: dimensions, amount of misalignment............?

Where was the welding supervisor? .......

Is he a qualified welder?.Did the welder perform the repair without consulting anyone?
 
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The duplex weld procedures that I have written would not allow this.
If the joint was cold when he did this and he didn't apply enough heat to get the inside of the pipe up to 600F then it might be nothing.
Or he could have just created a location that is loaded with intermetallics and as such has very poor ductility and terrible corrosion resistance.
 
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EdStainless said:
The duplex weld procedures that I have written would not allow this.
If the joint was cold when he did this and he didn't apply enough heat to get the inside of the pipe up to 600F then it might be nothing.
Or he could have just created a location that is loaded with intermetallics and as such has very poor ductility and terrible corrosion resistance.
Click to expand...
Thanks EdStainless. Can you plase advise me how to repair this joint.
 
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Karik87 said:
It will be cut out. But can you please advise me how to repair this weld joint?
Click to expand...
MRB condition. Basicly I would consider it rejected. not be repairable.
Cut it out. Obtain a new part if possible with excess for fitting and trimming.
Use the excess trim length from the new
Part to fit up properly.
And reassemble a new segment.
If the cost is not prohibited.
 
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You have to cut back beyond the HAZ on each side in order to repair this.
If space allows keep the two new welds well apart from each other to prevent overlapping HAZs.
And be more careful with the fit up.
 
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EdStainless said:
You have to cut back beyond the HAZ on each side in order to repair this.
If space allows keep the two new welds well apart from each other to prevent overlapping HAZs.
And be more careful with the fit up.
Click to expand...
Yes should have included that as well.
Basically parent material with no HAZ

To Op
And it's important for a nice square cut.

If imay add , a failure analysis can add value.
As it can add as a correction of more training.
For the WPS to add preheat. As it reduces stress
Due to higher thermal condition as not to cause
Shock which induces stress.
In heat treat after during elevated temperature
As means to reduce stress thus distortion is to Mar temper also know as Mar quench in quench solution heated to general 400 degrees F
As to allow the grain structure formation at a slower. My best definition as non professional metalurgist. But a specialist.
The other issue is thick and thin section.
The thin sections will cool much much faster
Than thick section thus inducing stress.
Thus causing distortion. I am sure the welder meant well, by inducing heat thus stress relieving the welded assembly. Which part of the reason
Of post weld heat treat. Which I like to call a stress relief. Remove stress and other requirements
 
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Karik87,
As Ed Stainless has noted there are too many unknowns with the state of the weld metallurgically.
First - raise an NCR to capture the unauthorised repair work.
Second - if you do not already have then you should initiate Repair Request forms so any repair is approved and documented.
Third - cut out and start again.

For future issues of distortion you should consider qualifying a PQR with an additional Tig Wash.
If you can prove mechanical, metallurgical and most importantly corrosion resistant properties are maintained you may well be able to convince your Client to approve the repair.
 
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I'm with Ed on this. The procedures I wrote would never permit this. And apparently the welder's attempted correction was not effective. An NCR should be written with proposed repair specified including addressing technique/fixturing to produce the desired result.
 
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You have to be careful preheating duplex because you need to keep the interpass temp very low.
If you want to know, after you cut this out take some impact samples and test them at -40.
Look up A923.
 
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EdStainless said:
You have to be careful preheating duplex because you need to keep the interpass temp very low.
If you want to know, after you cut this out take some impact samples and test them at -40.
Look up A923.
Click to expand...
How does a guy in the field do that with a rose bud torch in field?
 
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We try to be perfect in design but that's what red pens are for . We depend on the shop to catch our mistakes but not add to it.
They have saved my bacon so many times.
I had good group of guys in my last employment.
We all make mistakes. We worked as a team.
An experienced fitter and welder is immensely important. Or any shop person. I can count on them to meet my requirements, I don't have worry about quality issues.
 
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IR guns are notoriously unreliable, especially on the higher temperatures and on reflective surfaces like stainless steels. Here, I'd suggest contact probes.

mfgenggear said:
If imay add , a failure analysis can add value.
As it can add as a correction of more training.
Click to expand...
Great idea, use a real life case like this instead of some generic tool box meeting template for training.
 
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Considering that I usually use a max 200F interpass temp the only preheat allowed is to dry the surface.
They have to stay under 200F.
Contact temp measurement is preferred.
 
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I presume that there are cases where it will be exceeded, so there is some margin in it.
In 2205 I could live with and actual upper limit of 250F, maybe even 275F.
It really depends on what the heat input in the weld is.
In a superduplex though I would stick with 200F.
I'll clarify that every duplex application that I work with is pushing the limits on corrosion resistance.
 
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