Many specs in the past have restricted GMAW to .250 thickness and less assuming that the metal transfer would be short circuiting mode.Welding heavier section thicknesses in this mode may increase the possibility of fusion problems. This concept has carried on despite advances in electrodes, gases and equipment. A progressive firm with a firm handle on welding process and application control usuually can prevail in an appeal to the EOR but I emphasize the program must have adequate focus on process control.
Ther are no prohibitively negative points for using GMAW. In fact if yousee UW 27 it clearly permits use of GMAW. However in some of the purchase spec you would find there are prohibitions for using FCAW in certain joint types. This is a ghost from the past.
But there could be some hair splitting before using FCAW in a pressure vessel. The argument posed by one of the purchase inspector is that as per UW, FCAW is not clearly/Explictly permitted, since in Sec IX GMAW and FCAW are treated differently. Although there could be some scope of dispute our local AI said that (This job involved AI and Purchase Inspector and we wanted to use FCAW)FCAW is permitted for welding joints in pressure vessel. However in order not to confront the Purchase inspector, we used Shielding gas while welding FCAW!
The ability exist with this process to have a very low heat input depending upon the operators settings. The process is fine however the short circuiting transfer mode has led to lack of fusion in thicker welds.
ASME does not restrict this process for fabrication however there are restrictions on the qualification ranges. For most proccesses the thickness range is 2 times the original material tghickness. For GMAW short circuit, this is reduced to 1.1 times "T".
For performance qualification the use of RT is allowed for inspection, however GMAW Short Circuit requires guided bend tests. Lack of fusion parallel to the film plane does not show up by RT.
I've made bad welds with most manual/semi auto processes. Usually it was my fault and not the process. Sometimes it was me, sometimes I chose the wrong process.
