There is a misconception among many that GTAW (TIG) is somehow the “best process” for welding. Using that “mentality” is similar to saying a ratchet and socket is the best way to tighten a nut. Yet I guarantee that many of the people with that mentality have some channel locks, combination wrenches, locking pliers, slip joint pliers and other tools suitable for the task, just maybe not the best! This is not about “knocking” one process over another. It’s more about the need to realize the fact that advantages and disadvantages exist with every welding process and our awareness of this fact as welding professionals can be valuable.
The GTAW Process
One thing that is never seldom addressed besides the lower deposition rate and production factor as compared to some other processes is the fact that the process just doesn’t use electricity as well as other processes. That coupled with variations in technique can result in fusion-related issues.
Here is a chart from the AWS Welding Handbook Volume 1, 9th Edition that shows data from some research. There is “MUCH MORE” about heat transfer in welding in the AWS Welding Handbook. This is only one small bit of information and is supported by other research but in real life, the proof is in the puddle! Here is another article full of math and science information.
That coupled with the ability to easily add filler metal in a way that removes the energy from the underlying base/weld metal makes for a potential “disaster” when it comes to fusion. One of the troubling things about this possibility is that the type of discontinuity formed does not lend itself to being detected by radiography. The bends you see in this picture were visually inspected after polishing and prior to bending. No visible discontinuity existed.
My observations over the years.
Understand that I am not the authority on all things welding and my observations were not under controlled conditions with documented settings and statistics. However, the issue is something that became obvious to me when I 1st saw someone walking the cup. This happened while someone was showing me how to “cap” a pipe after walking the cup. I noticed the front edge of the puddle was beginning to build up preventing the arc from melting the base metal underneath.
B31.3 Piping at a paper mill.
I 1st observed this while working as a QC inspector for a large Southeastern construction company. They were installing piping at a paper mill in Northeast Alabama. They had purchased a large number of pre-fabricated spools from a Tennesee Piping Fabricator. All of t his was B31.3 piping and a minimal amount of RT was performed.
During installation, it was noted that an elbow was rotated the wrong way. I witnessed the item being cut to allow for us to document the item to keep the weld maps accurate. It was a piece of 6″ or 8″ schedule 10 stainless. It had a cap on it that you could have measured with calipers and not discovered a ripple or bead width that varied more than .015″.
After it was cut, a distinct line was observed almost all the way around the circumference when looking at the face of the pipe. VERY tight, but it was there! The underside of the line was the underside of the filler metal and the top was the surface of the root bead. I informed the QA manager of this issue and tried to write an NCR but was stopped. (Job Politics-I left not long after that).
Maybe in most conditions, this type of discontinuity goes un-noticed by RT and as far as normal fluid service goes, it never causes an issue. But you can be sure of this, there are some slick Tig welds out there with non-fusion.
Welder Testing on Super coupons
A few years ago, I was tasked with supervising the testing of about 40 welders for a company performing work in our area. This was all ASME Sec. IX testing which has very liberal visual acceptance criteria however it wasn’t needed. These folks were SLICK as far as Tig went. Of the 40 welders tested, about 8 failed guided bend tests. All of the bends exhibited discontinuities oriented as shown in the picture above. Some were shorter though.
This guy “double wired” his at about 170 amps (within the broad range on the WPS). (His wife came to the shop later t(y)elling me how he was “one of the best welders in Texas and never failed an X-ray”). Well, he failed a bend test! Doesn’t mean he was a bad welder, it was a different test and he used some techniques that had worked on other occasions.
On an informational note, the visual inspections of all GTAW welds passed before bends. About 15 of the 40 GTAW/SMAW welders were “looked out” before getting to the bending stage. Of the GTAW/SMAW bends…NONE FAILED!
KNOW your process
In a world full #ratemyweld, #weldporn, #tigtuesday pictures on various types of social media, its easy to get wrapped up in the “artistic quality” of a nicely colored weld bead but understand this, I have seen some slick ones that were not very good and I have seen a few ugly ones pass RT and bends.
Incorrect settings and techniques can easily be masked by “pretty” welds with some processes. An incorrect travel speed (Too Slow) could lead to lack of fusion as shown in this picture. This was an item I inspected at a fabricator near the MS gulf coast.
Process knowledge and understanding has some value!
Cranking up the voltage on a process without compensating in other ways can make a nice visible profile on the outside but because of the increasing arc length, fusion may reduce.
Though the manual dexterity required for welding surpasses the requirements for so many other jobs, the understanding of the process and techniques used can be much more valuable in certain situations.
The pipe welders on the tests referred to above were taking tests for a position that paid $38.00 an hour! Do you think they wished they had read this before…or even listened to me when I reviewed some of the “issues” that had been observed with some of the previous welders.
So a pretty costly bit of knowledge contained in one sentence could have been pretty valuable.
If you don’t see the arc melting at the front edge of the puddle, it may not be! As professional welders, our skills are incredible. Those skills coupled with process knowledge and a deep understanding of what we do can be a great asset for a potential employer.
If you would like to see a video about this same topic made by the best welding educator in the world, take a look at https://youtu.be/CqL8k8GVDtM