Can I suppress Preheat welding T22?

[fborela]

Hello
I must build 2 coils for a superheater for a Boiler. The coils will be manufactured with tube Ø51 x 5.6 mm quality 10CrMo9-10 (=SA213-T22) welded to fin of plate ?5 mm. quality SA387-Gr22. Every fin will be welded both sides with process GMAW with solid wire Ø1.2 mm. ER90S-B3. The fillet welds will have 5 mm. of thoat.
The problem is that is very cost and difficult to Preheat before welding because of that the machine moves automatically welding two welds fin-tube simultaneously with 2 torches GMAW. We´ll make PWHT at 700 ºC of all the superheater in furnace. Is it possible to suppress the Preheat making the PWHT?
In fact by ASME I code, if you preheat to 150 ºC you can suppress PWHT for this size of throat of weld. But is it possible suppress preheat making PWHT. Can I find this answer in ASME code.

Thank you in advance:
Fernando.

 

[Mr168]

See PW-38. Your limiting factor from a code perspective is going to be the temperature at which your welding procedure was qualified. The preheat requirements invoked in the PWHT exemption rules do not apply to welds that are subject to PWHT.

 

[metengr]

Preheat requirements in Section I construction are recommended, not mandatory. If you qualify your welding procedure specification with preheat, you are permitted to drop the preheat by a limited amount, based on the essential variable requirements in ASME B&PV Code, Section IX.

See below, excerpt from Section I, 2010 Edition

PW-38 PREHEATING
PW-38.1 The need for and the temperature of preheat
are dependent upon a number of factors such as chemical
analysis, degree of restraint of the parts being joined, elevated
temperature mechanical properties, and material
thicknesses. Some practices used for preheating are
described in A-100 as a general guide for the materials
listed by P-Numbers of Section IX. It is cautioned that the
preheating suggested in A-100 does not necessarily ensure
satisfactory completion of the welded joint and that the
requirements for individual materials within the P-Number
listing may have preheating more or less restrictive than
this general guide. The welding procedure specification
for the material being welded shall specify the minimum
preheating requirements described in the welding procedure
qualification requirements of Section IX.

 

[fborela]

Mr168, metengr, Thank you very much for your answers.
My PQR is with Preheat 150 ºC and without PWHT. Probably i´ll make a new PQR without Preheat and with PWHT 700º 30 minutes. This way I´ll be in according with ASME I code? And what about the sound engineering for this welds? Is it posible to avoid absolutely hydrogen crack in welds before PWHT without Preheat?

 

[metengr]

Yes, use low hydrogen filler metal. Also, with the GTAW or GMAW process, there is less chance for hydrogen to be generated and absorbed (not adsorbed) in the weld region.

 

[Duwe6]

Hydrogen cracking can also come from hydrocarbon contamination of the filler wire or weld surfaces. Keep those areas clean, since you have no preheat to burn off the oil.

 

[MJCronin]

Nando...

Are you part of a certified boiler repair shop ?

In an effort to ensure we understand which code governs, in just what country are you located ?