Lack of Preheat

[joro]

Hello,

Here is my dilemma. A recent inspection revealed that the required preheat was not followed per AWS code. The joint: A36 base plate (2 inches thick), A992 Column (W10 x 77). Required preheat was 150 F.
Visual inspection showed no sign of cracking. The ambient conditions are not known. Weld in a shop in Alaska (June). I don’t know if the material was stored outside prior to welding, therefore the actual temperature of the steel is not known. Assuming the temperature was greater than 25 F. The joint could see a large shear force (will be the support column in a high seismic zone).

Looking for advice on how to assure the joint is okay, short of re-welding the joint. Also, what type of failures might occur once the structure is loaded and in use.

Any assistance would be greatly appreciated.

Thanks
joro

 

[rustbuster1]

Since the preheat you say is "required" is so low and the materials are uncomplicated alloys, there is not any practical concern, as long you have verified the weld quality is acceptable.
A 150F preheat mostly dispels moisture and too-rapid cooling of the first pass. So, the joint properties are not likely to be compromised if the preheat was omitted. Checking hardness is another way to confirm this.
A992 supposedly contains:
Cu, max 0.60; Ni, max 0.48; Cr, max 0.35 and Mo, max 0.15. I guess this is intended to make it more of a weathering steel. Nevertheless, it is alloyed high enough to be a P-4 (ASME Code) material - because it has less than 0.5% Cr - so preheat really is only recommended, not required.

If you have to demonstrate the point, do a weld coupon about 1/2 in thick with and without preheating and see if bend or tensile test results are affected.

 

[GRoberts]

The main reason to preheat in mild steel is to avoid hydrogen cracking. I would UT the joint a minimum of 48 hours after welding, and if there are no cracks, the weld is as good as one made without preheat. The preheat is just a measure to ensure there are no-cracks without the need for inspection. If you get into other steels, preheat takes on other purposes also.

 

[joro]

Thanks,

Additional thoughts, I know that the weld process deviated from the code, therefore I am liable if this joint fails (if I accept the deviation). Per the code, the course of action would be to qualify the weld duplicating the conditions actually used (a new WPS with the lower/no preheat) and if the mechanically tested specimens exhibited the ductility, strength, and soundness required by the code the weld could be qualified. Ideally, this would have been carried out prior to fabrication.

I also believe that this weld was only a single pass (1/2" fillet) and I agree that cracking would of been the expected discontinuity because preheat levels were not maintained (our friend, Hydrogen). Therefore, if the joint was visual & UT inspected and there is no sign of "cold" cracking the joint should be okay. My only concern is that this doesn't qualify the weld. Back to the legal perspective. Trying to close the loop and know I have a "sound" joint as well.

Joro

PS: Am I out of line by requesting the weld be qualified?

 

[GRoberts]

I do not think it would be out of line to request additional qualification. However, if they only used it for a fillet weld, they could do a fillet weld qualification, which is much less involved than a groove weld qualification.

 

[welding1]

The AWS method of calculating pre heat tends to be conservative. The European system tends to give lower temperatures but is much more difficult to apply. I have some info on preheat, including a calculator, which I can
E-mail to any one interested.

The problem is hydrogen cracking which is not always easy to find by normal NDT methods.

Regards
John
post@gowelding.com

http://www.gowelding.com