Hi Prem,
Cupro Nickel would require root protection for single sided FP welds by GTAW. Otherwise the root will get oxidized (typically bluish/ black in appearance). For services like water this may be O.K but in broader sense oxidized root may spell trouble in service in corrosive media.Thus advice is to incorporate the root purging. Some recommendations for welding of this alloy are as follows:-
- TIG (GTAW) welding will give the best quality weld metal and a well shaped root bead. DC-ve (DCSP) current should be used. Pulsed current will give good control and a neat appearance for positional welding.
- A large a ceramic shroud equipped with a gas lens is recommended to give the most effective gas shield and the arc length should be kept short; 3.5-4.5mm.
- Argon or argon with small amounts of hydrogen, (1- 5%) are the appropriate shield gases with the Ar/H mixtures providing higher heat input.
- Above about 6mm thickness, TIG welding should preferably be replaced by the higher deposition rate MIG process, although mechanized/automated systems such as orbital TIG are very cost effective.
- A root purge of argon is recommended when welding a TIG root run and the next couple of fill passes
You may find more details in the attached link below.
Thanks.
Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist & Consultant
Ontario,Canada.
Email-pgoswami@sympatico.ca,
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of prem nautiyal
Sent: Saturday, December 24, 2011 1:10 PM
To: materials-welding@googlegroups.com
Subject: [MW:13296] Back purge for CuproNickel welding
| Hi friends I am establishing a welding procedure for welding of 90-10 Cu-Ni 6mm thick tubes, UNS C70600 as per ASME SecIX. All joints are single sided joints and i will be welding them with TIG: ER CuNi filler wire. My only query was that do i need to back purge the weld joints ? Regards Prem S Nautiyal |
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