AWS D1.1 minimum preheat consideration

By Somkiat Date 11-11-2019 05:18

I have review MTC for material grade A572-50, The actual result for mechanical & chemical test state on MTC are comply with grade 50 (preheat category B) and also comply with grade 65 (preheat category C).

Grade 50 - YS=345 MPa, TS-450 MPa. EL=18% (min)
Grade 65 - YS=450 MPa, TS-550 MPa. EL=15% (min)

Actual value - YS=500 MPa, TS-617 MPa. EL=31%

My question is what's the minimum preheat consideration?

By SWN1158 (***)

Date 11-11-2019 11:38

The minimum preheat for these two prequalified base metals are located in Table 3.3 of AWS D1.1, Categories B and C, and the minimum preheat is based on the welding process, which you make no mention of.

By welderbrent (*****)

Date 11-27-2019 16:39

Good Day Scott,

I would somewhat challenge that statement. Preheat is not really based upon welding process. It is based upon thickness and material class which is determined by the material grade.

As Al stated, that is not really based upon any tests beyond those performed to assure compliance with the applicable standard, A572-50.

The only time process comes into play is if the job specs will allow anything other than Low-Hy processes and the material falls into Category A steels.

He Is In Control, Have a Great Day, Happy Thanksgiving One and All, Brent

By SWN1158 (***)

Date 12-02-2019 11:43 Edited 12-02-2019 18:57

Brent,

Respectfully, I'm fully aware that it's based on the thickness thickness and material grade, but the welding processes are included in Table 3.3 for a reason. If for no other reason, the “process” with SMAW electrodes “other than low hydrogen” and the “process” with SMAW “low hydrogen” electrodes require different minimum preheat temperatures. Technically speaking, its the same process, but the preheat and interpass temperatures are a little different within the four categories; in particular, when the material thickness exceeds 2 1/2". The original post mentioned A572 Grades 50 (Category B) and 65 (Category C) which both require a low hydrogen electrode, but the original post failed to mention the material thickness, which is part of the equation. The other part of the equation is the process, which was also not mentioned. While not a consideration for this particular application, its still, at some point in time, a consideration, simply because it is not a given that the SMAW “process” requires the same amount of preheat for a given thickness. In my humble opinion, I simply thought it was worthy of mention for future reference. Maybe my original response warranted more of an explanation.

By 803056

Date 11-11-2019 14:14

The inquiry mentions D1.1 is the applicable code. The code mandates the minimum preheat based on the material specification. It is not unusual for the material to be "stronger" than specified by the material specification. The contractor can impose more restrictive preheat requirements based on actual chemistry, thickness, degree of restrain, and hydrogen control, provided the minimum preheat is not less than what is required by the code without agreement of the Engineer representing the Owner/customer.

Al