Welding duplex SMAW+SAW

Date 09-05-2005 11:04

I have qualified WPQR for duplex material A240 S31803 double Vee joint by weld process SMAW +SAW and back chip and weld SAW use electrode from SANDVIK 22.9.3LR +22.8.3.L , all mechanical test are accepted. Except for pitting corrosion test as per ASTM G48 Methode A that weight loss is fail 6.4 g/m2 ( spec not more than 4 g/m2 )but on speciment surface no pitting , why weight loss ? I has test 3 time already, do we need gas backing ( nitrogen 99.99 % ) during weld SMAW? How to control weight loss?

Thanks many for help

By - Date 09-05-2005 12:59

4g/m2 is a rather easy pitting test to control. It is a standard requirement for Duplex stainless steels in a lot of specifications. In the case of SAW and SMAW, I can most assuredly believe the weight loss is attributed to the fluxing from the electrodes or the flux shielding from the SAW. You must clean each pass very carefully when using these processes. Most of the time, very lightly grinding is recommended. If you consider using 99.99% nitrogen as a purge, you will very likely have a low, or even unacceptably low ferrite count. Nitrogen lowers the ferrite count significantly because nitrogen is a strong austenite former.

Chuck

By jiweiming (**)

Date 09-06-2005 05:35

What's ur method for back gouge?If u use carbon arc,probabaly the weld metal may have too much carbon content,which can lead corrode easily.

By - Date 09-06-2005 12:17

Carbon arc gouging is not recommended for the reasons you stated. If you are going to back gouge, plasma gouging is probably the best and safest method. Using a flux shielding type of welding process, it is not unreasonable to consider lightly grinding each pass.