Oxidation at Root on Alloy 2507

[pipewelder1999]

I am observing welding on a Duplex Alloy 2507 Heat Exchanger and observed isolated oxidation (sugaring) on the internal surface of whe root pass. This entire weld is going to be ground flush however should the areas with severe oxidation should have the weld metal background to remove some of the weld metal along with the oxidation?

The Process is GTAW, .65 +/- KJ/mm heat input with 100%nitrogen backing gas, 97/3 Argon/Nitrogen shielding gas. The material is approx 8mm thick.

The majority of the root shows light gray oxidation however some areas actually sugared. Any suggestions or references. I have read through most of the product literature I have found referenced on this forum but nothing that addresses any corrective action.

Also is there any post weld test that can be performed on this allow to predict/compare succeptability to pitting?

Thanks

Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[bmoorthy]

If you are going to flush grind and also going to Pickle/passivate as well (Inside flush grind thereby removing the oxideformation), then so long as you meet the ferrite % requirement (Min 30%) and the penetration and fusion are Ok, you have nothing to worry.

Any way check your back purging. (It is good idea to have Argon + N2 purging)

Good Luck

 

[unclesyd]

Here are couple of sites concerning the welding of 2507. We had the same problem on autogenous welds on 1" 14 gauge tubes. The first one is Dr. Saidov’s work and the second two are for the work done by Sandvik, Swagelock and EWI. I have more information will try to round it up. This may give you an idea of how to approach the problem.

http://www.geocities.com/saidov_r/appendix4.htm

http://www.ewi.org/labservices/pegtaw/orbital.pdf

Sorry about the long link.

http://www.businesswire.com/cgi-bin/cnn-storydisplay.cgi?story=/

http://www/bizwire/webbox/bw.043001...elok/swagelok_storyfooter.htm&bgcolor=#FFFFFF

 

[metengr]

For welding duplex alloys like 2507, it is recommended to use welding grade (100%) Argon gas for shielding and back purge.

Despite the visual appearance of the weld root, I believe you should be ok because the "sugaring" is simply surface oxidation and if you are going to blend grind the weld root this should remove the surface oxidation.

If you are concerned about pitting resistance, you could do a weld coupon simulating your original welding conditions above and perfom a ferric chloride pitting test in accordance with ASTM G48, Method A.