PWHT Dissimilar Metals/9cr-2.25cr
PWHT Dissimilar Metals/9cr-2.25cr
(OP)
In process of writing a spec for welding 9cr-2.25cr. Section 1 HRSG Superheater. MAWP about 2500psi, steam temp about 900f. Field install.
The header itself is going to be 9cr. (header pipe, endplates, nozzle, etc). There will be 2" od 2.25cr stubs welded to the 9cr header to transition into 2.25cr in the field. Field supply is header with stubs. Boiler tubes installed in the field one tube at a time.
The question is regarding PWHT. I have typically chosen the PWHT temp for matching 9cr materials to be 1375 to 1425. I have typically spec'd 9cr-2.25cr PWHT @ 1300-1350.
The rub here is this is this is a 9cr header with 2.25 stubs that will be fabricated as a whole and stressed as a whole. The majority of the materials are 9cr.
Not sure to go with the 1375 to 1425 stress temp or the 1300 to 1350. I have read the relevant code and see the requirement for P15E dissimilar metals is min 1300. In this case to do you favor the 9cr stress temps or the 2.25cr?
Perhaps the answer is obvious. Stress the entire header at the 1375 to 1425 and be done with it.
The header itself is going to be 9cr. (header pipe, endplates, nozzle, etc). There will be 2" od 2.25cr stubs welded to the 9cr header to transition into 2.25cr in the field. Field supply is header with stubs. Boiler tubes installed in the field one tube at a time.
The question is regarding PWHT. I have typically chosen the PWHT temp for matching 9cr materials to be 1375 to 1425. I have typically spec'd 9cr-2.25cr PWHT @ 1300-1350.
The rub here is this is this is a 9cr header with 2.25 stubs that will be fabricated as a whole and stressed as a whole. The majority of the materials are 9cr.
Not sure to go with the 1375 to 1425 stress temp or the 1300 to 1350. I have read the relevant code and see the requirement for P15E dissimilar metals is min 1300. In this case to do you favor the 9cr stress temps or the 2.25cr?
Perhaps the answer is obvious. Stress the entire header at the 1375 to 1425 and be done with it.





RE: PWHT Dissimilar Metals/9cr-2.25cr
RE: PWHT Dissimilar Metals/9cr-2.25cr
If the material is a P-No 15E Gr 1, Grade 91, this type of weld joint should have been designed as a dissimilar metal weld joint and safe ended using Grade T23 tube material or Grade T5 material, so the field welding would be T23 or T5 to T22 tube material. If you are stuck with welding Grade 91 to T22, you should use E9013/ER90S B3 filler metal and PWHT at 1380-1425 deg F. The lower critical transformation temperature for T22 material is 1480 deg F, so you have some margin.
RE: PWHT Dissimilar Metals/9cr-2.25cr
If there is no major P91 butt weld included in the instant header assy and the stub weld filler will match the 2.25 Cr 1 Mo tubes then the lower PWHT temperature above 1300 F as per table PW-39-5 notes (2) and (3), and not use the NEM correlation if the P91 header ass'y was previously PWHT'd.
"Whom the gods would destroy, they first make mad "
RE: PWHT Dissimilar Metals/9cr-2.25cr
Regarding base materials, I am not understanding the question. Header pipe/nozzle SA 335 P-91, tube stubs are SA-213 T-22,SA 387-91 end plates....
RE: PWHT Dissimilar Metals/9cr-2.25cr
RE: PWHT Dissimilar Metals/9cr-2.25cr
My apologies for dragging this out. I see that you said "if" which make me think there is a choice here .Would you not recommend B9 filler for the tube to header welds? If so, what would you recommend for soak temp?
From a fabrication standpoint, keeping the filler rod, pre-heat etc. the same does have some benefit and is what I predict the vendor is going to come up with. Maybe not. Just trying to be informed of possibilities.
I do understand the recommendation above of using T-23 tube stubs. It would simplify things but have had some bad experiences with it in the past.
RE: PWHT Dissimilar Metals/9cr-2.25cr
RE: PWHT Dissimilar Metals/9cr-2.25cr
The decisions mentioned above is where I am at with this now. The client is looking to us for guidance. We have a well known oem doing the work but history has shown that oem suggestions alone is no sure thing in all cases. I like to do my own homework before accepting any unorthadox weld procedure.
If advice I receive here jibes with others/the oem suggests.....I can typically feel good about it. If not.....I keep digging.
RE: PWHT Dissimilar Metals/9cr-2.25cr