Stress Relief of A572 Gr 50 Steel Beam Structure Member

[ODOPTU]

I have a question regarding a current project of fabricating a BOP Trolley Beam that was welded. The Material is A573 GR 50. Problem is, these beams have had a lot of weld repairs, and also has been heat straighten on multiple occasions. the heat used for the straighten was no more than 600 degrees, Also there were cement weights placed on the beams until such time the heat was at room temperature. My question is would there be a need to perform a Stress Relief on these Trolley Beams due to the amount of times it has been heat straighten? The welding process used to weld the Trolley beams was a FCAW process, and it itself it a hot process... There was also numerous Weld repairs performed using the same FCAW Weld Procedure. We have not performed a harness on these beams as of yet, we are just trying to get the fabricator to pursue the Stress Relief.

Therefore my question again is; is there a need to perform the stress relief, if so, what code or standard would direct me to do this.

We will also have the fabricator perform a PQR with adding the stress relief process if needed... but first I need to understand if the Stress Relief is valid to perform.

Thank you

ODOPTU

 

[metengr]

You have a situation where heat straightening was intentionally done to introduce residual stresses for the benefit of straightness. Performing a stress relief will undo these residual stresses and cause distortion, which means either additional straightening, weld repair and machining to straighten. So, no, I would not perform a stress relief.

Have you done surface NDT on the trolley beams to at least ensure no cracks from previous weld repairs and straightening? If not, I would at least do the surface NDT in areas where previous weld repairs were performed.

 

[ODOPTU]

Yes we did perform a NDT both Ultrasonic examination and Magnetic particle.. Beams have been cleared and found acceptable. Would you agree at a minimum that we should perform a Hardness evaluation on these Beams?

 

[ODOPTU]

In what Code will address my concern with the Stress Relief issue that I am currently discussing....

 

[metengr]

AWS D1.1 would be applicable for stress relief requirements. The hardness evaluation will not be that practical. Unless you have exceeded temperatures in excess of 1300 deg F, exclusive of weld repaired areas, it will be of limited use for the locations where you only heated to 600 deg F.

Again, why are you so concerned with stress relief? If you heat the beam to 1150 deg F, which is typical PWHT temperature for carbon steel or carbon low alloy, it will distort and you will be back to heat straightening.

 

[ODOPTU]

I have to agree with you, and all the information that you provided, I would think that I would just leave it alone, and possible ask our fabricator to perform some additional testing to ensure that these Trolley Beams are fit for purpose. It is our Customer that is bent on having a Stress Relief performed... It isn't me, I am just trying to follow up with reasons why we don't have a requirement to perform the Stress Relief.

And you gave me all the information I need... Thank you Sir...

ODOPTU

 

[gtaw]

Thermal stress relief might be warranted if the welded structure is to be machined and tight tolerances have to be maintained. However, there is little to be gained in this case. The residual stress is on the same order of magnitude as the yield strength of the base metal. Heat straightening introduces a residual stress that counters the residual stress that causes the distortion to originally take place.

Best regards - Al