Expected hardness after welding/pwht carbon steel 1

[rmillercwi]

We are building several carbon steel tube panels (upper/lower header joined with boiler tubes) and the client is asking for final hardness testing. Nothing special about the project. ASME Sect I. Header pipe SA 106C, sa 51670 end plates and SA 192 finned tubes. PWHT per pw.39 for P1 materials

I have never had this come up before. Having some trouble finding what the final harndness number should be max/min. Thinking 200 BHN max is appropriate? E70T1 flux core/100% co2 on nozzles and er70s-2 GTAW on tube to header welds.

 

[weldstan]

Low end hardness about 140 BHN, high end less than 200 BHN.

 

[kingnero]

If you're looking for a source, try the welding procedure qualification standards.

 

[Jovi Zhu]

I've been working on Section I pressure parts and experienced the similiar customer requirement.

It will be good to communicate with the client that the purpose of the hardness test for welds is to verify the proper heat treatment is done. Section I never requires this and I remember B31.3-2012 and earlier edition had such requirement for P No.3 ~ 6 and P 15E only. B31.3-2014 revised in its entirety and have no hardness requirement any more.

The hardness testing practice after PWHT is still performed by manufacturers probably for P No. 15E only as PWHT is always required for these mateiral regardless of thickness, welding parameters, etc.. Hardness criteria is established with the corelation to the min. and max. PWHT temperature to develop the desired microstructure.

For other grades, PWHT can even be exempted as per PW-39 which means under certain condition the joints are acceptable to have a as-supplied raw material(normalized or N+T), as-welded HAZ(partly normalized) and as-welded weld metal(like an un-tempered cast structure cooled from liquid phase) and normally able to pass procedure qualification tests and be sucessfully put in service.

From a quality assurance purpose, its not about how "hard" a weld metal is(except for hard-facing overlay welds for wear resistance), it's more about the assurance of PWHT.

There is a chance that a client can be convinced of such "konw-how" in order to cancel the required hardness testing for P No.1.

 

[SJones]

If the client wants the test, they should also specify the acceptance criteria. If the test is not for acceptance/rejection, they should simply state that the results will be informative only.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.