Definition of thickness for preheating purposes

Question

Definition of thickness for preheating purposes

holdpt (Structural)

(OP)

23 Nov 15 17:02

I would appreciate any help in determining what the thickness definition of AWS D1.1 is regarding preheating. If I may further explain: A customer is stating that they want 1 1/2" thicknesses preheated to 150 F which was not included in previous pricing for fabrication. The push-back from our adder to go beyond what D1.1 states is: The customer wants all of the plates measured with a mic and if anything (which will be all) are over 1.500, 150 preheat is expected. I have seen "nominal" thickness used all over D1.1 but not applied to preheat thicknesses. So, 1.51" measured plate would need 150 degree F preheating?

racookpe1978 (Nuclear) · Answer 1 · 2015-11-23 21:21:47

1. Use a tape measure. Forget the micrometer .... unless you are a lawyer.

Measure the thickness of the appropriate part of the whole metal that will be welded, NOT the thickest section anywhere at any direction across the whole part. Preheat is to protect the steel within and across the WELD from failure, NOT the "contract writer's estimate" nor the "lawyer's thickness per contract" ...

A 1.560 piece will need the same preheat - but will retain that heat for a few seconds longer - than a 1.440 piece if the two are both going to be welded using the same process.

holdpt (Structural) · Answer 2 · 2015-11-23 22:08:30

racookpe1978,
Thanks for your reply. I would not refute anything you stated and I think we both understand the intent of preheating related to thickness and that the industry standard is nominal thickness in D1.1 preheat tables. Again, though, with your analogy of 1.560" thickness requiring a preheat of what D1.1 calls for with 1.5": Where is it in writing that says or allows such?
Yes, this is extremely silly but such is common with quite a few customers.

racookpe1978 (Nuclear) · Answer 3 · 2015-11-23 23:12:41

I work B31.1 and 31.3 piping and steam power, so I will not pretend to quote the structural guides, nor do I have my copies of the standards on my desktop here on site. But. For forged steel vessels and valves of differing thickness (much thicker regions than near the welded joint itself), the thicker of the two welded pieces always controls preheat, maintenance heat, and PWHT. The thickness is judged (measured) at (around) the welding prep area, not the ultimate thickness of the PV someplace else not being heated up.

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Definition of thickness for preheating purposes