[MW:23255] Re: Welding P91 without PWHT

The assertion that NBIC has no provision for weld repair of Grade 91 steel without PWHT is not correct. Welding Method 6 currently allows for you to weld tube to tube connections internal to the Boiler or HRSG setting without PWHT for P15E materials using approved Ni-base alloys. This will appear in print in the 2015 edition, in the mean time many EPRI members are using this method as once the language is approved, you are allowed to use it provided the local jurisdiction allows. If you do a simple search for Welding Method 6, you should be able to find the approved language in the NBIC since the NBIC makes the edits publically available for comment prior to print. 

Also note that there is a second complication in that for repair, NBIC Part 3 does not necessarily apply to ASME B31.1 Construction. Many people adopt NBIC Part 3 for repair of B31.1 piping and valves but it is not mandated practice (I have reached out to George Galanes to confirm and will post his response after this response). Thus, for valves which are often constructed and welding into piping systems that fall under B31.1 you may have additional relaxation of traditional rules. For issues with drain lines and thick to thin transitions to valves, it has been common practice (as just one example) to weld a Ni-base raft that on the valve body and weld the thin connection directly to the Ni-base raft being careful not to extend the weld around the thin component beyond the circumference of the raft. This has been done for stub to header welds as well, and with good success in CrMoV and low alloy steels. For Grade 91 steel, this would be a viable option - the extent of "permanency" for this type of repair may be a function of your willingness to perform inspection and the operating behavior of the component (primarily base-load or flexible operation). The second option, which may be regarded as a more permanent type repair is welding the thin component directly to the Grade 91 valve using 9Cr-1Mo filler metal (ER80S-B8 and E8015-B8) without PWHT. We currently have one member who has operating a full-penetration dump valve to Grade 91 main steam line (1.5 inches thick) using 9Cr-1Mo filler metal and No PWHT for 5,000 hours. It was recently inspected and had no damage indicating that this "repair" is of acceptable integrity and of no concern at this time. Thus, the use of 9Cr-1Mo filler metal for repair of Grade 91 steel should also warrant serious merit. We always emphasize that repair is not a one-size-fits-all solution, and that many times the integrity of the repair is dependent on many factors that must warrant consideration (and as detailed in EPRI Report 3002003822). As part of EPRI's mission statement, we feel it is vital to reach out to the greater public and all of industry to make critical documents publicly available and we continue to do this. 

On Saturday, May 9, 2015 at 12:23:28 AM UTC-4, José Luís Ferreira wrote:

Is there an alternative to weld P91 to P91 (Cr-Mo-V) without performing PWHT? I need to weld (repair) small valves (socket welds) in field.

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