sub arc chemical analysis

Date 12-11-2008 15:39

New York State has a requirement for chemical analysis of the deposited weld metal on PQRs performed using weathering steel. Many pqrs are submitted that do not meet the required chemical analysis. One of the parameters is that carbon be at 0.12 max. Now AWS lists the allowable carbon for SAW filler materail EM12K in the range of .05 to .15. It would appear to me that if the filler material used was in the upper range of the allowable carbon there is no way to meet the New York spec. I am not even sure why NY has this requirement. It seems to me if a fabricator used a wire flux combination that is listed in the AWS spec then the chemical composition is what it is and should be acceptable. Is there something that I am missing?

Respectfully
Dave

By js55

Date 12-11-2008 18:04

I think you'll find that the great majority of EM12K's are below the .12%. though you have to run deposit tests to prove it. You will also generally lose even more C in the reaction with most fluxes.
I'm sure the thinking is a crack sensitive carbon equivalence thing.

By dmilesdot (**)

Date 12-11-2008 18:32

The Pqr that i have has carbon at .15. The mtr that came with the pqr shows the base metal carbon at .17 (its astm a709 gr 50w) Im still at a loss as to why the NY Steel Constrution Manual holds carbon to .12 max. I wouldnt think that was a high enough percentage to cause cracking problems.

Dave

By js55

Date 12-11-2008 20:04 Edited 12-11-2008 20:08

Actually I had a brain fart.
You clued me in on the BM chem.
Your problem isn't so much filler chem, its dilution.
You may lose carbon from the flux but you will gain carbon from the BM through dilution.
If you are doing standard AWS spec type deposit chems you run layers enough to minimize the dilution effect. But in PQR's you won't have this buffer. And so I would have to agree that meeting the NY spec would be very difficult indeed. It seems to me you would have to start with an extremely low C filler, or make sure your chems were taken a layer or two at least away from the BM to make it.
However, I'm still a little suspect of the PQR chems. Do you have lab reports?
And what is the carbon content range of 709?
If you have that, and an actual MTR, and an actual MTR from your filler metal and an estimate of your dilution you could determine where you are. You could even use a PMI to determine dilution and then calculate the C content. In other words, the amount your Mn changes will tell you the amount the dilution is effecting your C.

By ravi theCobra (**)

Date 12-12-2008 20:02

My memory from the days of doing A 588 weathering steel was that there were many electrodes you could use that had the 8018 - G designation for weathering steel. Because of all of the "salesmanship" I think it became mandatory to do a deposited weld chemistry so that you hd something to use as a baseline composition.

I know one problem we had was that the welds didn't exactly match the base metal -

By ravi theCobra (**)

Date 12-12-2008 20:06

May I add that that matching I was refering to was color (weathered ) match , never had a problem with physicals -

By dmilesdot (**)

Date 12-15-2008 13:38

The MTR lists Carbon at .16, the ASTM spec. allows .19 max. The fabricator didnt supply me with the filler material specs. The Mn for the base metal is reported as 1.17 and the weld metal chemistry reports 1.14, not being a metalurgist I dont know if this change is significant to show carbon migration from the base metal.

Dave

By HgTX

Date 12-30-2008 20:01 Edited 12-30-2008 20:06

The 0.12 limit matches the limit given in AWS A5.23 Table 2 for those same electrodes. It applies to B1, Ni1, Ni2, Ni5, and W, and all those have a limit of 0.12% carbon in the weld metal in A5.23. The range given in A5.23 Table 1 for EM12K is for the electrode composition, not the weld metal composition.

That said, the chemistry test in A5.23 is based on a very different specimen from that in D1.5, so it may not be a valid question nor a reasonable requirement to have D1.5 test plate chemistry match A5.23 test chemistry. If the D1.5 specimen is more subject to base metal dilution (theoretically if you take your specimen from the same area the AWMT comes from it might not be), then you can't expect the same results. Plus, you could pick a particularly low-C batch for your PQR and then use any electrode that satisfied A5.23 in production, so I'm not sure what that gains them either. NYS always thinks they know best, though. (Yeah, Joe, you heard me.)

Hg