Preheat requirements.

Date 04-05-2012 18:57

I intreprep the thickness as the thickness of the thicker part is used when figuring out the pre-heat for different thickness materials.
But if welding 2" plate to 2" plate then you would determine the preheat using the chart with the grade of material, process used to weld it and the 2" plate thickness; not 4".
Hope this helps

By 803056

Date 04-05-2012 19:17

The Engineer (read this as God) is the authority in all matters relating to AWS D1.1.

Since you already said the WPS is not prequalified, tables 3.1 and 3.2 are not necessarily applicable.

If the plates involved are a flange and a cover plate, the total thickness is 4 inches. It is not the same as a butt joint where the plates are edge to edge. Since the material thicknesses combined increases the mass involved, hence the cooling rate, the Engineer is taking a conservative position to ensure the cooling rate is sufficiently slow to reduce the potential for cracking.

Best regards - Al

By ctacker (****)

Date 04-05-2012 19:54

Isn't that the reason you run a procedure, which I did. using the highest preheat requirement (of only one) of the two plates. Procedure accepted, but I'm being asked to revise my WPS to use the combined thickness. it's just a matter of revising my WPS which is no problem.
I think that would be the easiest at this point. were only talking about a 100º difference on 2 @ 1" plates, which don't take that long to heat.

By 803056

Date 04-05-2012 20:40

There is always more to the story than what we see in the post. The joint configuration can come into play and a host of other considerations may have to be factored in.

The code delineates the minimum requirements. The Engineer has to consider other factors and impose any additional requirements he feels is prudent to ensure the product delivered meets all the requirements, both the code minimum requirements and those that ensure the product meets the customer's expectations.

There is more to life than simply meeting the minimum code requirements.

Best regards - Al

By ctacker (****)

Date 04-06-2012 12:56

Al, you were right, there was more to the story.
I just didn't have all the info from project manager.(as usual)

he handed it to me after I made the post, and right there in big green letters was the sentence, "use combined plate thickness for preheat requirements".

Regards,
Carl

By 803056

Date 04-06-2012 15:05

Paul Harvey returns to the program.

Al :cool:

By ctacker (****)

Date 04-06-2012 16:57

Paul harvey, I miss him. but i feel more like Ray Charles going into a job blind.

By Tyrone

Date 04-11-2012 11:22

He ctacker,
My response is a little late for this thread, but I thought it would clarify things in the future....

There are two main methods to calculating preheat. One uses combined thickness, the other uses the thickest member.

1) HAZ control method uses combined thickness. It is used because the heat flows impact the critical cooling rate. A simple T-joint will have 3 thicknesses, or 3 directions the heat will flow and cool down.

2) Hydrogen control method uses the thickest member for calculations. It tries to limit the amount of hydrogen pickup, and maximize the time for it to dissipate after welding.

So, to answer your question...
It depends on which method used be the Engineer.

Tyrone

By ctacker (****)

Date 04-11-2012 20:54

Thats Interesting, I had never heard of that before. so your saying a T-joint you would combine 3 thicknesses? combining 1 thickness twice?
I will definately be looking into this further when the chance arises.
It makes sense, but at the same time, if your using the highest preheat of the 2 different steels, I still don't see the need for combining.
I suppose thats why you Weld Engineers make the big bucks. :)

I appreciate your response.

Carl

By Tyrone

Date 04-12-2012 11:11

Hey Carl,
Glad I can help out.

You are correct. T-joint would combine 1 thickness twice.

You can't use thickest material for the HAZ control method because you have to pick which cooling curve to use (each curve is based on thickness of material). The simple t-joint cooling curve for 3 thicknesses looks far different than the single thickest cooling curve. Therefore, the preheat calculated could be way off.

The Hydrogen Control method is a much simpler method, in my opinion, where you can just use the thickest material.

When you have time, look in D1.1 - 2010, Annex I Guideline on Alternative Methods for Determining Preheat
Table 1.2 Minimum Preheat .....
Note "a" - tells you to use the thickest material.

Tyrone