Welding Dupex 2205 GTAW

Date 09-06-2005 06:24

I Have done two WPQ about 2205 with GTAW,and the wire is from Avesta,the steel plate thickness are 6mm and 14mm,with the requirement of ferric chloride corrosion according to ASTM A923 Method C.The standard require the weight loss no more than 10mdd under 22c.The former(6mm) passed and the later(14mm) failed.Why?Any response will be appreciated?Thanks.

By - Date 09-06-2005 12:27

If the 6mm thickness passed and the 14mm did not, it is apparent you deviated from something. Weight loss can come from a couple of things. First of all, both the base metal and the consumables must be absolutely clean. Each pass must be cleaned after welding to remove the chromium depleted oxide layer to insure no weight loss is possible due to the oxide layer. I don't know what your purge gas is, but a nitrogen content of more that 3% can lead to breakdown of your tungsten and leave undetectable tungsten inclusions. ASTM A923 should be an easily achievable test if all is clean and the purge gas is acceptable. Without knowing everything you did, it is near impossible to figure why you passed one and failed the other.

By jiweiming (**)

Date 09-08-2005 04:17

Thanks Chuck.
For the root pass,two welders weld from each side at the same time with GTAW.Thus,we can avoid back gouge and purge gas.Moreover,it is high efficient.In fact,after corrosin test,one of the test coupon's weight loss rate is about 50 mdd.I wonder whether there are too much SIGMA phase.

By - Date 09-08-2005 12:42

In 2205 Duplex, any sigma is too much sigma. I have seen fabricators try the very thing (2 welders exactly opposite each other) and it caused a vortex in the area being welded. Just be careful that you don't have your shielding gas turned up too high. It is pretty unlikely that sigma will form on the coupon using this technique. Of course, if the coupon is small enough (width, length, and thickness) to allow a very slow cooling rate, it is possible for sigma to form.

Chuck