Stress Relieving A572 Gr. 65

[mhopgood]

Good afternoon all,

A consultant on the project I am working on has requested that we stress relieve our weldment at 1050[deg. F] for an unspecified length of time, and no ramp up or cooling rates - looking for us or the stress relief contractor to provide this information. I am looking to find out if anyone has any experience with stress relieving A572 Gr. 65 and knows of any negative side effects - I have found numerous mentions that PWHT of A572 Gr. 65 is not recommended as it may adversely affect material properties in the HAZ.

I have found plenty of research on Gr. 50, but am having trouble finding corroborating material on Gr. 65.

The weldment is basically a ring-shaped box beam to be installed onto a cylindrical vessel. The weldment is made up of the following:

1. One (1) 3 1/2" PL. x 18" wide ring of A516 Gr. 70 inner flange - 3 separate pieces to be welded together
2. Two (2) vertical 3" PL. A572 Gr. 65 web plates welded 2" from flange edges - 3 separate pieces to be welded together
3. One (1) 3 1/2" PL. x 18" wide ring A514 Q&T outer flange

The fabrication will proceed with the inner A516 Gr. 70 ring being fully fabricated
Next, all but one of the A572 web plate welds will be completed on each web plate
Each ring will be fit onto the A516 Gr.70 flange and welded out.

The consultant has requested stress relieving after items 1 and 2 have been welded together - peening to be performed after welding the A514 flange.

 

[metengr]

The only way to understand the effects of welding on base metal heat affected zone and weld metal properties is to qualify a welding procedure using the above materials. I am surprised you did not even mention having a qualified welding procedure or your consultant requesting one.

With that said, qualify a WPS for the stated material combination with and without PWHT and decide on what you need. This way your approach is defendable and you can't argue with the mechanical test results for the project.

 

[weldstan]

The maximum thickness of Grade 65 is 1 1/4". How can you have 3" thick plate?

 

[mhopgood]

Good morning all,

@metengr

There is an original procedure qualified using a 70[ksi] filler metal with PWHT for the Gr.50 material - on the first fabricated assembly there was a timeline and availability issue for the A572 Gr. 65 material and so we used a thicker A572 Gr.50 as was clarified and approved by the original consultant. I was hoping to find out if anyone had any particular experience with the Gr. 65 as this is what the new consultant is requesting; however, someone on the client side has mentioned to us that you can't PWHT this material and that we should look into it further. I can't find any information stating that you can't, only that consideration needs to be taken into the specifics relating to mechanical properties being affected in the HAZ of the weld metal. However, you are definitely right and from a due diligence standpoint we should qualify a new WPS and go from there.

@weldstan

This is going to be a custom mill run with 100% UT scan for lamination.

Thanks for the input guys!

 

[weldstan]

Without adding Aluminum for fine grain melting and tying up nitrogen, the addition of V and Nb(Cb) will reduce impact toughness in the HAZ after PWHT due to secondary carbide and carbonitride precipitation. The lower PWHT recommended may mitigate some of the toughness loss. Design/service conditions will determine whether the reduction of toughness is detrimental.

If the service is cyclic, PWHT will reduce the high residual welding stress; thereby increasing fatigue life of the weldment.

 

[metengr]

Again, you should be qualifying a welding procedure using the high strength, Grade 65 steel and determining if PWHT will effect your base metal HAZ properties. It is relatively simple and the results will be defendable. I would not count on using opinions to decide what effects PWHT will have on mechanical properties unless you have actual data. One of the steel plate manufactures cautions about PWHT on notch toughness behavior but this is cautionary does not say it can't be done.

 

[weldstan]

mhopgood,
It wouldn't matter if it's a special mill run or not. The max T is still 1 1/4" for Grade 65 under A-572. You could of course order the material as A-572 50 with a minimum 65 Ksi yield strength and design as you are currently doing. Full penetration welds in 3" thick plate have high residual welding stress, which may well become a cracking issue during/after welding. Second metengr re qualification of a WPS on the production material.