by Jason Becker
There seems to be a huge disconnect amongst the younger generation of welders when it comes to (CJP) prequalified weld tests, structural applications, and Flux Core Welding. I never realized how many "welders" didn't understand the aforementioned topics until we released this video.
We received a ton of comments in this video and some videos past about flux core. Several people didn't know that there are actually two types of flux core wire. Those requiring shielding gas and those that are self shielded. Additionally, they were un aware of the polarity differences between the two. There was also some confusion about the test plates for Complete Joint Penetration using a backing strip. Over the course of this article, Id like to take some time and discuss the misconceptions relating these topics.
Let's start off with the flux core process; as we discussed earlier, we have two types of flux cored wire; self shielded and gas shielded. There are really two major differences between the two electrodes. The self shielded electrodes typically run on DC- (Straight polarity), and the weld pool is shielded by the flux inside the wire and does not require external shielding gas. Shielding gas should not be added if the wire does not require it. On the other hand, the gas shielded wire will need to operate on DC+ (Reverse Polarity) and must have an external shielding gas to be used correctly. These electrodes are completely different from one another and cannot be use interchangeably by adding or retracting shielding gas or switching polarity. The user should consult the Electrode Classification of the intended wire and cross reference the manufacturers recommendations as to the correct polarity and type of gas to be used.
We also had a good portion of questions regarding the backing strap that was used in the video. This joint designation is a typical 2G weld plate according to the specifications of AWS D1.1:2015. The bottom plate was a 90° square edge while the top plate was beveled at 45° with a 1/4" root opening between. This is a very common joint fit up and weld out in the field for structural applications. Case in point, when 2 vertical columns are spliced together, the engineer usually requires a full-pen (Complete Joint Penetration) weld for the weldment. If the weld passes, the backing strip can remain in place with no removal of plate needing to take place. Even during some testing procedures, the backing strip can stay in place during inspection. The one time the backing plate should be removed is for bend testing in which the backing is completely removed and the coupon is ground smooth to be prepared for a the bend test.
I hope that clears up some of the misunderstandings surrounding prequalified (CJP) weld tests, structural applications, and Flux Core Welding. I know it can be a little confusing, but the more you utilize these products and methods, the more it will make since. I hope you enjoy the video and the blog article. Until next time make Every Weld Better Than Your Last.