Preheat VS Post weld heat treatment 1

[hcjulien]

We are creating a 3/4'' thick butt weld on a P4 (1.25Cr-0.5 Mo) low alloy steel material.

According to the weld procedure we are keeping a preheat temperature of 350F.

The welder during the welding process has dropped by mistake a big glass of water on the surface of the weld and the temperature went down very fast. We have increased the butt weld/HAZ/base material temperature at 350F as soon as possible...

I have a lot of concerned about the final quality (grain sizes) of the weld/HAZ/base material. Does the Post Weld Heat Treatment to be done at 1350F (holding time = 2 hours) will resolve all my concerns?

Thanks in advance,

hcjulien

 

[metengr]

Does the Post Weld Heat Treatment to be done at 1350F (holding time = 2 hours) will resolve all my concerns?

Yes. Despite the momentary drop in preheat, you were able to restore it. The thermal gradient was probably not significant enough to cause any problems.

 

[TomEun]

I agree with metengr. You may consider the main purposes of Preheat below.

- Reduce the level of thermal stress due to slow cooling
- Compensate for high heat loss
- Minimize the rate of welding hardening
- Reduce porosity
- Reduce hydrogen cracking

The most importance in your case is to keep the minimum preheat temperature just before the welding. The quenching effect may not be expected by dropping of a big glass of water during preheating below 350F. I believe the PWHT will give you sound properties unless there are any other issues.

Thomas Eun

 

[hcjulien]

Thank you! Your answers are very appreciated!

But let's continue our discussion with let's say the same story with a 1/4'' thick plate (heat loss higher than 3/4'')?

 

[Guest102023]

I have seen welders smoking under their masks but never drinking from a glass

 

[Wrenchbender]

I would be more cautious that the others. My main concern would be cracking, which surely no amount of reheating would cure.

You indicated that the presumably hot weld bead was quenched during the actual welding process. Then it was not yet in equilibrium with the surrounding plate. How hot was it? If the temperature was >>350F, conceivably the 'big glass of water' may have contracted the surface enough to cause tensile cracking. At least NDT the part afterward, especially if it’s for an important application.

If your plate is 1/4-inch rather than 3/4-inch, or more agitated water is used, or the material temperature is raised above critical, the problem potential increases simply because the quench rate increases. (Perhaps these geometries can be modeled by knowing bulk mechanical properties and heat transfer coefs as functions of T and phases present. Or see if the welder would like to try another experiment ?.)