P91 Distortion

[Rich2001]

How to straighten P91 tubing that is distorted due to welding. Tube is 50.8mm od, 8mm thick, 20 to 25 mm distortion.

Vita sine litteris mors est.

 

[metengr]

Rich2001
You have less than a 50/50 shot at trying to attempt to remove distortion from welding in this Grade of tube material. You can use local force + local heat with a limitation on heat (using a neutral flame torch) at 1300 deg F max to avoid altering the bulk properties of this creep strength enhanced ferritic steel. You need to know the exact location of the bend and start from there with local heat and apply force using a cantilever effect. This approach may chnage depending on the type of distortion (which you did not mention).

The problem is that these CSEF steels retain strength at elevated temperatures so even the application of heat is going to require a significant amount of force. If you are successful at reducing distortion from welding, make sure you perform some type of nondestructive surface examination of the entire region where the force and heat was applied to ensure you have no cracks. A portable hardness test should also be performed of this same region.

The only other option is the above does not work is to reheat treat the tubing per SA 213 for Grade 91.

 

[hrsgguru]

I second the hardness testing. T91 is touchy about hardness in both ways - apply heat and force to straighten the tube you will see some work hardening. But if you get it too hot or over heat-treat it, you can also end up with it being too soft. A reasonable range for your finished product is going to be 190 to 275 Brinell hardness. Outside of that and you could invite trouble.

 

[stanweld]

We have used resistance heating coils and induction heating to better control temperature along with applied force to correct distortion of tubes and small bore pipe. We do not permit the use of oxy-fuel gas heating; there is too great a chance for overheating. All such corrective eforts must be directed to Metallurgical Engineering and approval obtained (together with a written procedure) prior to making the corrective action. Hardness testing and MT of the "warm" worked area is also performed. On large bore piping, we have simply prohibited such corrective actions.