Wednesday, April 30, 2014

Those damn CVN requirement...

Do you mind my asking a quick question drawing from your expertise of AWS D1.1?
Table 4.6 of AWS D1.1-2010 is a list of supplementary essential variable changes that would require WPS requalification due to CVN (Charpy V-Notch) testing requirements.  Under base metal (item 2) it indicates:

“minimum thickness qualified is T or 5/8” whichever is less except if T is less than 1/4” then the minimum thickness qualified is 1/8”

I take this to mean that to qualify a PJP groove weld of a 3/16” plate a weld procedure would have to be qualified using 3/16” thick material  (“minimum T or 5/8” whichever is less”).  Do you agree?

I had been going off of the table 4.2 where a 1” plate would qualify for a range from 1/8” to unlimited thickness.  But that table is not intended for Charpy requirements.  So I may have been wrong with using table 4.2 when Charpy requirements exist. I can see the need to qualify the thinner materials when CVN is required due to the heat input changes due to the thickness changes.  But just want a second opinion.


Oh those damn CVN requirement...
I currently have 2 clients that I'm working with on this issue. Your assessment of the CVN Supplement is correct.
What we advised for our client to do was to machine the test plates to a nominal of 0.230" (because I also wanted to insure I was under 6mm to eliminate any code questions). We completed PQR's on 0.230", 0.3125" and 1.0" material, that covered our range.

Other things that bite ya for CVN requirements is...
"Multi vs Single Pass": Most PQR's that are typically run are multi pass.  These multi-pass PQR's would not qualify single pass welding.
"Max. Interpass Temp": If interpass tempuratures were to be measured under 125F the Maximum qualified interpass tempuature qualified would be under 225f. This would limit Preheat Catigory A and C Steels to 1-1/2" max. and Catigory B Steels to 2-1/2" max.

Good to hear from ya Wes.

Tuesday, April 29, 2014

GMAW Globular Transfer

I work at a machine shop where I am employed as a qualified welder to AWS-D.1.1. I was wondering why it is that you can certify 75% argon and 25% CO2 when you are not allowed to use a short circuit transfer on materials over 3/16". I read your article every month and in order to obtain a spray transfer you need at least 83% Argon but yet I passed on a 1 inch test piece.

Thanks K. B.

Your question insinuates that if your shielding gas mixture is not Argon rich enough to obtain a Spray Transfer mode the only alternative is Short Circuit Transfer, that's just not the case.
When using a 75% Argon and 25% Co2 mix you would not be able to achieve a Spray Transfer, but achieving a Globular Transfer would be no problem. It is quite common to complete the test you discribed (Unlimited Thickness to D1.1) in the GMAW Globular Transfer mode for all positions (3G/4G) successfully.  This is a fairly typical test commonly given in todays construction industry.  I think you will find Globular Transfer a prefered transfer mode in industries that utilize a 75/25 mix.
As for Short Circuit, when I mentioned in an earlier article, the possibility of incomplete fusion being a concern on materials greater than 3/16th inch, I prefaced that by including, "... in certain positions and progressions...".  Completing an open root limited thickness Welder Qualification in the Vertical progression (Root Down/Fill & Cover Up) is a very common transfer mode used during testing.  In fact, a test of that nature, Root Pass with Short Circuit, Fill and Cover Pass in Globular, would successfully qualify a Welder in 2 processes (GMAW-S & GMAW) in a single test.
That would be a good Welder Qualification to have in your wallet.