Welding and PWHT of T-22, T-91 AND P-22, P-91 3

[ukmet]

Respected researchers and experts,

I am working for coal fired power plant where all the subjected materials are being used. Following are my questions please guide me:

1. T-22 and P-22 are similar in regard to welding metallurgy and pwht requirement?

2. T-91 and P-22 are similar in regard to welding metallurgy and pwht requirement?

3. I had read some articles online which suggest that irrespective of thickness PWHT is very critical for T-91 and P-91. Some of the thickness for these materials are less than even 10mm some are as high as 50mm. So as per ASME Sec-1 below 25mm PWHT not required. What to do in this case? (Same for T-22 and P-22)

4. It also suggest that after welding and before PWHT minimum 95C temperature should be maintained. If you cannot maintain you should go for hydrogen bake. But nothing such is defined in ASME Sec-1

5. If they welding is so critical for these alloy steels which if not controlled can result in cracking , why the code do not allow 100% RT? It say no RT below 4inch diameter.

Please guide me and if there is some other point also to control or look after do suggest.

Thank you

 

[weldstan]

Under ASME I PWHT is always required for P91/T91. PWHT is required for P22 pipe welds greater than 4" diameter or > than 1/2" thick. Since T22 tubes are expected to be less than 4" in diameter, PWHT is not required. There are further relaxations to PWHT requirements under the NBIC regarding repair welding of these materials.

 

[metengr]

1. T-22 and P-22 are similar in regard to welding metallurgy and pwht requirement?

Yes, except pipe (P) may require PWHT based on thickness that exceed PWHT exemptions per Section I.

2. T-91 and P-22 are similar in regard to welding metallurgy and pwht requirement?

These materials are not similar, they are considered dissimilar materials for welding.

3. I had read some articles online which suggest that irrespective of thickness PWHT is very critical for T-91 and P-91. Some of the thickness for these materials are less than even 10mm some are as high as 50mm. So as per ASME Sec-1 below 25mm PWHT not required. What to do in this case? (Same for T-22 and P-22)

P91 or T91 are considered creep strength enhanced ferritic steel and require preheat and PWHT unless exemptions are performed under very specific applications, like in-service applications under the NBIC.

4. It also suggest that after welding and before PWHT minimum 95C temperature should be maintained. If you cannot maintain you should go for hydrogen bake. But nothing such is defined in ASME Sec-1

Correct, this is a process/fabrication detail and is not a code requirement.

5. If they welding is so critical for these alloy steels which if not controlled can result in cracking , why the code do not allow 100% RT? It say no RT below 4inch diameter.

This is typically for workmanship concerns rather than boiler safety.