Shielding gases for P22 FCAW welding 3

[bagnamento]

I'm reviewing some documents reporting 100% pure CO2 as shielding gas for FCAW welding of P22 pipes.
Is this shielding gas suitable for P22 welding?
If not (as I think), is it not suitable at all or just not recommended?
Which gas mixtures are recommended?

As far as I know, gas mixtures (Ar-CO2) with 2,5% CO2 max should be used for Cr-Mo steel with Cr content above 2%.

 

[metengr]

The Argon-C02 secondary shielding gas is better suited for welding P22 material, which is a low alloy steel. Your stated range of a minimum 2.5% C02 is less than what I have seen used, typical gas blends are 5% C02 in Argon for all poistion welding on carbon and low alloy steel. I have seen 100% C02 limited to flat position FCAW welding, and mostly for carbon steel.

 

[weldtek]

I'm most familiar with FCAW wires which use either a nominal 75% ARGON / 25% CO2 or straight CO2 shielding gas. You might look at the class of wire, if there's an M in the classification number the wire was qualified by the manufacturer with the Ar/ CO2 mix. If not then it was either qualified with straight CO2, or it's self shielded. See Sec II Part C. We've used 100 % CO2 in qualifying all of our FCAW procedures on P4 & P5A & P5B materials. Don't let me confuse he issue with P4 /P5, here I'm referring to the P numbers as noted in ASME Sec IX. The material you referrred to, P22 is actually a P5A. (Im assuming SA 335 P22)

 

[MetalsInc]

metengr is right. 2.5% CO2 is very low. I wouldn't go below 5% and would be much happier at 25%. That is "the standard" and you're more likely to find procedures that us that mixture. Inspectors will also be happier using 25% (only because it is "normal").

 

[GRoberts]

2.5% CO2 is sometimes used for GMAW, but for FCAW, both 100% CO2 and 75%Ar/25%C02 are very common, and either one can produce high quality welds in all positions. As mentioned before though, if the wire is designe for CO2 shielding gas, it will be E91T1-B3, or if it is designed for mixed gas, it will be E91T1-B3M. (or similar depending on which filler mteal you are using) Many of the welders like the mixed gas better though, as it produces less fumes and spatter.