Hi Forum, One of my colleuge is 1

[RauMech]

Hi Forum,

One of my colleuge is having some Supler Duplex 2507 SS pipe welding to be done for our project. Some of requirments that is proposing is not been agreeing by all parties -
1.Qualify welders on Super Duplex material itself.
2.Oxygen content in backing gas shall be 2500ppm max
3.Backing gas shall contain minimum 5% nitrogen
The weld process intend to use is GTAW for now, but also intend to use MCAW/FCAW as well.
So if anybody can have input in this really appreciated.

Thanks for your help in advance,
Rahul

 

[metengr]

RauMech;
Please see my comments below;

1.Qualify welders on Super Duplex material itself.

Agree, and should be required.

2.Oxygen content in backing gas shall be 2500ppm max

Disagree. This should be less than 0.005% or 50ppm. The welding grade Argon backing or shielding gas should be 99.995% pure.
3.

Backing gas shall contain minimum 5% nitrogen

Suggest using Formier gas, the nitrogen content should be 90% by volume and 10% hydrogen or if using Argon, keep the nitrogen content less than 1.8%.

[quote[The weld process intend to use is GTAW for now, but also intend to use MCAW/FCAW as well.[/quote]

Heat input is critical for optimum corrosion resistance. Depending on wall thickness, I would stay with GTAW.

 

[weldtek]

RauMech,
Clarifying, while the Argon gas you use for shielding and backing must be 99.997% pure as required in Sec II Part C ( 5.32), the the backing gas purge must be effective in reducing oxygen to an acceptable level. We've found 0.25% max to be a good threshold value. It can be easily verified by using a multi gas monitor.

 

[RauMech]

Thank you both metengr & weldtek,
But attaining 50ppm seems very difficult to acheive, comment?

 

[weldtek]

RauMech,
The gas you purchase for shielding will meet or exceed that requirement. Your method of purging including, containment methods, flow, vent location and size, etc, must be effective in reducing oxygen to acceptable levels. I don't want to put words in his mouth, but I didn't take Metengr's comments to mean you must get oxygen below 0.005%. As I mentioned, we've successfully welded duplex for many years using 0.25% max as the threshold for oxygen content.

 

[EdStainless]

How much nitrogen in the torch gas?
I have seen it taking 10% N in the torch gas and backing gas.
Nitrogen in the backing gas alone is not sufficient to maintain the N level in the weld.


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