MIG weld for impact test @ -50 F

[kentor]

Does someone has experience of using MIG weld ( ER70S-6 wire ) to make a coupon to pass impact test @ - 50F? I know that MIG is NOT usually used for low temperature pressure vessel. Did someone ever try it? Using what kind of shielding gas? Thanks.

 

[metengr]

ER70S-6 solid wire will not achieve what you need at -50 deg F. You will need low alloy with Nickel.

 

[kentor]

Yes, normally ER70S-6 solid wire is for at -20 deg F, it is in ASME CODE. But our supplier can supply C of C and C of welding testing, which shows ER70S-6 can used @ -50 F and pass impact test @ -50 F. I believe that was done under Spray Arc mode. For me, I need Short Circuit for root pass and Spray Arc for fill and cap, I am not sure it is still work.

 

[metengr]

I doubt you will be able to qualify by impact testing at -50 deg F to any of the ASME B&PV Code book sections. You may have a C of C for impact values at -50 deg F which are probably below what is required by ASME B&PV Code.

 

[Inspectoriam]

I must ask what are you building? Or better, why is the use of GMAW and ER70S-6 required? SMAW and SAW processes both offer -50 electrodes verified by the manufacture. You could weld up a coupon and have it tested at -50 but that is one test, Lincoln and the others do not rate their prodcuts being based on one test result. If it a vessel then SAW would be the better choice for speed, but millions of vessel have been built using SMAW.

To answer your question, yes I think some batches would make the test at -50, but consistanly, no they wont or the manufacture would have listed it as such.

Just my opinion.

 

[Guest102023]

I concur as usual with metengr. SMAW and SAW can achieve -50F in carbon steel, but not GMAW. Nickel is the secret sauce you need.

Do not attempt to use a filler metal at a MDMT less than the test temperature listed in the SFA specification, to which consumables must be certified.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[kentor]

We have SMAW and SAW, but SAW cannot be used for 6G, SMAW is much slower than GMAW. As I said ER70S-6 we used has the C of C and C of welding testing which is for -50F. If the coupon we will make for PQR passes the -50F impact test, it complies with ASME sect IX.

 

[gtaw]

You have options you can consider; SMAW, GTAW, GMAW-S, FCAW, SAW, etc. There are serious concerns about fusion type defects when using GMAW-S. A better choice might be FCAW or perhaps GMAW-P. Personally, I have issues with GMAW-P because too many welders use the low ranges for their parameters and they too encounter fusion type defects. The "cure" is to develop a WPS with the welding parameters "boxed" in to ensure adequate heat input to obtain proper fusion consistently.

Consider welding several fillet weld samples that are easily evaluated to ensure proper fusion to the base metal and between weld beads is ensured. Use those values to qualify the groove test assembly. Limit the welding parameters listed by the WPS to those that produce properly fused and acceptable welds.

Best regards - Al

 

[kentor]

Yes, you are right. I have the experience that using GMAW-S for root pass and GMAW-P for fill and cap failed bending test. I try to find what are the root causes, heat input or shielding gas?

 

[weldstan]

We have routinely impact test qualified welding procedures using ER70S-6 at -50 F with the GMAW process. Because customers now prefer to add restrictions when using filler metals not defined as meeting impact toughness at -50F in the AWS/SFA specifications, we now use ER80S-Ni1.

 

[kentor]

Hi weldstan,

Could you please tell me more info regarding to your welding procedures using ER70S-6 at -50 F with the GMAW process, such as shielding gas for GMAW-S and GMAW-P, heat input etc... Thank you.


Best regards - Ken

 

[weldstan]

75% Ar 25% CO2 for short arc root, 90% Argon min / 10% CO2 max for Spray. Have not impact test qualified with pulsed transfer. Have also qualified full out to 3/8" with short arc with 75Ar - 25CO2. Thin bead multi-pass critical for maintaining fine grain and tempering of previous passes.

 

[kentor]

Thanks weldstan,

Also, Could you please tell me same info using ER80S-Ni1. Thank you.


Best regards - Ken

 

[weldstan]

Same gas mixtures. Higher heat input can be used (qualification done with about 36 KJ/in).

 

[kentor]

Thanks weldstan,

But for short arc root, heat input should be much lower than 36 KJ/in, is it right?