PWHT After a Repair to a Boiler Superheater Header
PWHT After a Repair to a Boiler Superheater Header
(OP)
We have a new ASME Section I boiler under construction and have found an issue with the Secondary Superheater Outlet Header. One of the top support lugs was installed in the wrong location. The superheater header is a P5B material, 1.5" thick, 18" ID and was PWHT'd at header fabrication. We'd like to weld a new support lug/pad to the top of the header shell, at the correct location. The attachment fillet welds are much greater than 1/2" throat so PWHT would be required. The Contractor is proposing to use a 'donut' heating pad around the lug/pad.
Is this acceptable? How can this conform to the ASME Section I, Paragraph UG-40 where local PWHT must be done with a circumferential band all around the shell? How could they possibly do a circumferential band around the header shell when the bottom half of the header is all tube stub attachments?
Wouldn't it be better to use a high preheat and a temper-bead welding technique?
Is this acceptable? How can this conform to the ASME Section I, Paragraph UG-40 where local PWHT must be done with a circumferential band all around the shell? How could they possibly do a circumferential band around the header shell when the bottom half of the header is all tube stub attachments?
Wouldn't it be better to use a high preheat and a temper-bead welding technique?





RE: PWHT After a Repair to a Boiler Superheater Header
RE: PWHT After a Repair to a Boiler Superheater Header
Where are the P1 and P3 limitations for temperbead welding? The only place I can find these limitations is in ASME Section VIII, Div. 1, UCS-56. There are no P number limitations indicated in ASME Section I or ASME B31.3, that I could find.
RE: PWHT After a Repair to a Boiler Superheater Header
Second, please re-read PW-40 REPAIR OF DEFECTS, most important below
PW-40.3 Defects in P-No. 1, all groups (if not otherwise
exempted by Table PW-39-1), and P‐No. 3 Group
Nos. 1 and 2 materials, and in the welds joining these materials,
may be weld repaired after the final PWHT but
prior to the final hydrostatic test. The welded repairs shall
meet the requirements below.
The requirement for temper bead is listed in PW-40.3.4
RE: PWHT After a Repair to a Boiler Superheater Header
For the required width of the circumferential band, I remember completing alterations to pressure vessels in the past where we added nozzles to the shells of PWHT'd vessels. A circumferential band was used to PWHT the nozzle attachments. The width of the band included the nozzle and several inches beyond the edges of the nozzle attachment welds, depending on the shell thickness. If there was another nozzle in the shell, on a slightly different plane, the width of the band would be increased to include the other nozzle(s) and beyond. At times the band would be quite wide and temporary supports would be required.
My concern with the superheater header is, when we do the circumferential band around the shell, including all affected tube stub attachments at the bottom of the header, the band ends up being very close, but not including adjacent tube stub attachments. Is this going to cause issues with these tube stub attachments just outside the required band width? Should the width of the band be greatly increased so we can control the gradients better? Does anyone have experience performing local PWHT on boiler headers (waterwall, superheater, reheater, etc.)?
RE: PWHT After a Repair to a Boiler Superheater Header
No problem. First, temper bead repairs outlined in PW-40 applies only to P-No 1 and P-No 3 base materials because this is the introduction to PW-40. All of the rest of the paragraphs in PW-40 deal with specific repair requirements using welding again only applicable to P-No 1 and P-No 3 base materials.
I can assure you temper bead repairs under Section I cannot be applied to P-No 4 or P-No. 5 A or B or C base materials, period. I had to struggle to re-write the temper bead for PW-40 for P-No 1 and P-No 3 base materials as a TPM for Section I.
Since temper bead repairs are not permitted for materials above P-No 3, you have little choice other than using the circumferential band method. And yes, you can increase the band width to accommodate what you need.