PQR Corrosion Test fail per ASTM A923 Method C

[ZHA]

Hello All,
Hope all are healthy and safe!

I had a question related to the corrosion test and ferrite test.
Construction Code – ASME B31.3.
We did a Duplex PQR and it needed to be:
1) Corrosion tested per ASTM A923 Method C. (Temperature - 25 C. Time - 24 hours)
2) Ferrite point count method per ASTM E-562.
(We are also doing Tensile, Bend and Impacts)
Material – SA 790 (S31803/S32205). 4” S/80S Pipe. ER2209 filler wire (MTR Attached). PQR done in 5G. Interpass – 200 F. The coupon cleared RT.

The corrosion test failed in the root and in the cap. I have attached the images. After the corrosion failed, I asked the lab to do the ferrite only on the cap and the ferrite % on the cap were 73.8 +/- 3.7. The ferrite % needs to be between 30% - 65%. (We didn’t do any ferrite test on the root and the mid-weld since the corrosion had failed and we only wanted to have the ferrites on the cap for information).
The heat input for the cap was 23 Kj/inch and for the root pass it was 48.49 Kj/inch.
What changes can I do with the welding to get the corrosion test cleared. For the ferrite % to be lower, I feel the cap needs to be welded with a higher heat input.
Waiting on y 'all's opinion.

 

[weldstan]

We normally used about 40 KJ/in in the cap pass when we passed the test.

 

[EdStainless]

But be careful, as I am sure that you know higher temperature favors more ferrite (There is an optimal range of temp) and slower cooling is more likely to result in the formation of secondary phases.
Don't over do it.
Are you using Nitrogen in weld gas?

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P.E. Metallurgy

 

[ZHA]

100% Argon for shielding and backing.

 

[weldstan]

We have also used 2% Nitrogen to the shielding gas and purge gas.

 

[minibenny]

We have also used 2% nitrogen in the shielding gas after struggling to get acceptable results when using only argon. It appeared to make a significant difference in ferrite and corrosion test results.

 

[ZHA]

minibenny - Did you use 98Argon-2Nitrogen for purging also?

 

[EdStainless]

We used slightly higher levels, about 4% for both weld and purge.

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P.E. Metallurgy

 

[ZHA]

EdStainless - Thanks for the info but I have seen certain customer specifications where they are not allowing more than 2% Nitrogen. Have you guys seen such restrictions?
Just an update we have welded a coupon with 98 Argon - 2 Nitrogen and I am waiting on the results now.

 

[EdStainless]

We never ran into that with work that we were doing, but yes I know that it out there.
Heat input on these alloys is tricky, there really is a sweet spot.

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P.E. Metallurgy

 

[ZHA]

The ferrite test and the corrosion test came out to be good. Thanks all for their input. We used 98 Argon 2 Nitrogen as the shielding and purging gas.

 

[EdStainless]

Thanks for the report.
Glad that it worked out for you.

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P.E. Metallurgy