Crack in flange side when weld Flange CuNi to Tee CuNi

[Thuhuongengineer]

Hi Friends,
Our project had serious problem. All weld joint between Pipe-CuNi to Flange-CuNi had defect crack in Flange side (Pipe side no problem). I would like give you some information to you give me advice:

Base: CuNi
Thickness: 7 mm
Welding Process: GTAW
Welding Consumable: ER CuNi, Lincoln LNT CuNi30
Backing Gas: 100% Agron
Preheat: Ambient (30 degree)
Max Interpass: 85 Degree
Heat input: 1-1.5 (Kj/mm)
PWHT: No
Parameter: 87-90 A, 10-13 V

 

[Thuhuongengineer]

sorry gents, I have misstake Tee replace Pipe

Pipe Tee-CuNi to Flange-CuNi

 

[stanweld]

Is this a corner groove weld or a butt weld? Is the flange cast or forged? Is the crack in the HAZ or at the fusion line?

 

[Tmoose]

what style of flange?

http://www.lordtk.com/Flange/Flange-Flat-Flange-Tread-Flange-Slip-on-Flange.gif

 

[Thuhuongengineer]

Hi Gents,
This is weld neck flange. Attach picture for you refer

 

[weldstan]

With the very low heat input, LOF may be the actual flaw; however, if you have confirmed cracking, contaminants left on the Flange due to the heavy machining operation could be the problem or contaminants in the flange material itself could be the problem. A metallurgical examination of the defect and flange base material is recommended.

 

[jwhit]

LOF is a very strong possibility. Welding technique with CuNi is tricky, the filler metal sometimes appears to be pushed away from the joint. As I understand, the filler carries whatever heat is in the puddle away and actually quenches it resulting in LOF. Your welder wants to make sure he has a fully fluid puddle before dipping the rod into it, heat then needs to stay on long enough to melt the filler before pulling the rod. Something else that seems to help is to weld towards your ground whenever possible.