This is little anecdotal and windy but explains our efforts to embrace the GMAW/FCAW world. We never gave up on using the process as we tested each and every variation that came down the pike as it would have been a money saver in some cases for us. This post is just to emphasize my concern over GMAW/FCAW wasn’t something picked up or passed on, it was the result of actual experimentation and testing, NDT, Physical, and Metallurgical of which I was a major participant.
I agree that FCAW can produce an acceptable/passable weld under the proper conditions with a skilled motivated welder. I also agree that LOF is prevalent and in most cases not detected nor is it detrimental unless close to the surface or surface breaking in a non-cyclic service. A sound root and cap can carry some poor filler passes. But on a consistent basis I can achieve better results, though a little more costly, with OA (OFW), or CAW-T. I want say SMAW (BMAW) bare wire, pine block backing as its been a while.
Being close to the AWS we started to investigate GMAW at its’ introduction to the fabrication industry due to what was touted to be inherent advantages over other welding methods. I might add at this time we were welding HP Tubing C/S 2" x 1/2" wall with OA. On different recommendations we purchased equipment to try spray transfer, then globular. All efforts to consistently produce a satisfactory weld were to naught. Later we tried pulsed and short circuit again no consistent welds, we fought the gas and wire battles like everyone else. We had the capabilities of mixing and analyzing any gas mixture required and did. When FCAW came on the scene we had some C/S jacketed housings fabricated by one of the largest fabricators in the US. These are in service at 600°F cooled and cycled to 1000°F on a 21 day schedule. All have required refurbishing due failing welds. During this time the company owned a large fabrication shop where we monitored the weld quality. After much experimentation and testing they also relegated GMAW to skids and supports. The same holds true for FCAW.
Our results with FCAW-S were the same, no consistency even with extra NDT testing. Our best results, percentage wise, was with FCAW-G. It still was nowhere near the quality of welds were getting from our welders and the onsite maintenance contractor’s welders. Normal ANSI 31.3 inspection requirements wouldn’t catch enough of the problems for our service.
Our weld quality was a reflection of ours’ and the contractors’ welders. We maintained onsite a repair rate of < 0.5% and a reject rate of < 0.1%. We could put our welding program up against any in the industry. In the 42 years I was associated with the site we never had a catastrophic weld failure, though we caught a few in progress. We only encounter welding problems, as noted in previous posts, when the company started low bidding some contracts on some very large projects.
Our group had the ultimate responsibility for QC on all welding on site and supervisory control on all off site welding, this ended in mid 80's. Initially we performed all onsite NDT work in-house under the supervision of Metallurgists/Welding Engineers. We had three large areas where 100% RT was required. We also required 100% NDT inspection on all vessels (some 3000 stamped, not including boilers) on site. On most of the initial GMAW testing the NDT cost were not that much of a consideration as it was within our responsibilities so we could do the extra testing at minimal cost to a project.
When we started the FCAW testing our welding inspection QC had came under control of a Level III (5 disciplines) with a BS degree in NDT. He also carried all the Navy aviation certifications and all the API certifications as they pertain to the Chemical industry. All UT and RT work was under the supervision of another Level III (4 disciplines) with teaching credentials for other organizations.
Again I have to state this post concerns C/S only and as stated you don’t want to hear about the S/S problems we encountered.