RE: [MW:11138] Porosity issue in CuNi welding

Hi
 
Copper-nickel alloys like this one are generally susceptible to porosity because of the high solubility for hydrogen at elevated temperatures. Could you specify  as to where in the weld the porosity occurs? Are there more pores in the root pass or are they evenly distributed over the whole weld?
 
The first suggestion would be to avoid the formation of moisture on the workpiece at all cost. Therefore a mild heating before welding is advisable, even though CuNi-alloys generally do not require preheating. Heating up to 80°C - 100°C should be enough to evaporate all remaining moisture (condensate) on the workpiece surface.
 
Also, a helium-containing welding gas might be beneficial, as it helps keeping the weld pool liquid for a longer period of time thus enabling better degassing (VARIGON He30 or even VARIGON He50 may help - source : Linde / BOC)
 
It should be ensured that welding is carried out with sufficient weld metal, to use the deoxidising effect of the little titanium addition that the ERCuNi has.
 
More information is available here: http://www.copper.org/publications/pub_list/soldering.html --> http://www.copper.org/publications/pub_list/pdf/a1050.pdf
 
I hope this helps.
 
Best regards,
Diganta Sarma

 

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Date: Sun, 22 May 2011 10:40:40 +0400
Subject: [MW:11114] Porosity issue in CuNi welding
From: romiomdabre@gmail.com
To: materials-welding@googlegroups.com

Dear All

 

We have noticed porosity issue in CuNi piping.

 

Material - ASTM B466 UNS C70600

Pipe Size 1/2" to 6"

Pipe Wall hk - 2.77 to 4.0mm

Welding Process - GTAW

Filler Wire - ERCuNi

Welding Position - 6G

Purging / Shilding - 99.995 % Ar.

Flow rate Shileding 15 - 25 Cfh

Flow rate Purging - We have welded  coupons with different flow rate like 15 -25 , 20 - 30 then 30-40

Interpass 100°C Max.

 

Please note that we have taken all general care like, cleaning, SSwire brush, Grinding wheels etc.

 

Request your valuable suggestion  & if there is any documentes / articles on CuNi welding pls provide.  

 

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