How does heating a weld joint for bending purposes affect the steel quality?

[QCJT]

The design code is B 31.3. Production uses heat extensively to align the joints and we are talking about 304H steel small size piping (pig tails). It's GTAW welding, so they simply use the rod tip to heat the existing weld and sometimes the joint comes into position without additional force applied, just due to thermal shrinkage but sometimes they also apply some force. Is this a point of concern?

 

[metengr]

What is the limitation on heat applied? Do you have a procedure, if not, you should develop one.

 

[QCJT]

Metengr, it's simply not measured. I guess it would be the same as that of the interpass (177-200 Deg.C) but it's only a guess. Why do you think this might be a concern if there isn't a documented procedure? What are the advisable limitations on this kind of procedure? Below transformation limits?
Thanks for the input

 

[metengr]

Because having a procedure demonstrates control of the process. In your situation, you mention no temperature limits. Improper application of heat or re-welding to induce local residual stresses can be harmful to the weld joint. Do you perform any NDT after using heat to enhance alignment?

 

[QCJT]

I absolutely agree on the point of having more control of the process but it is hard to convince the production guys on this issue unless you present them with real dangers of this activity, because these guys have been doing it all the time and they haven't had any problem (until now). In most cases there is no NDT after heat application... what kind of potential defect might occur?

 

[metengr]

You may have had product performance problems in the past because they did not show up until after the part was placed into service. I can't tell you how many times I heard the phrase “we have never seen this before". Either way, your organization needs to have some established practice to avoid this type of repeat performance. If a subsurface weld defect were to propagate to the surface after the application of heat or during the application of heat in an uncontrolled manner, wouldn't you want to know this, this is why surface NDT after heat alignment is cheap insurance.

 

[QCJT]

Metengr, thanks a lot. I will take your advise