There are four modes of metal transfer possible when welding with GMAW.
Short circuiting transfer is characterized as low heat input and prone to fusion type discontinuities. Hence the well earned bad reputation because so many welders/fabricators have attempted to use it for "heavy", i.e., thick, base metals. This process is typified as using low voltage, low current, i.e., low wire feed speeds, low heat input, but capable of welding carbon steels and high strength low alloy steels in all positions.
Globular transfer is a higher heat input process that requires higher voltage (compared to short circuiting transfer), higher wire feed speeds, higher amperage, and high percentages of carbon dioxide shielding gas. The transfer mode is largely restricted to flat and horizontal fillets and flat grooves.
Spray transfer is a high heat input process that requires similar welding parameters as globular except that the shielding gas must contain a high percentage of argon (above 80% is recommended). The balance can be up to 15% carbon dioxide or up to about 3% oxygen (some people use higher percentages of oxygen, but I tend to go with 2% oxygen) when welding carbon and high strength low alloy steels. Like globular transfer, spray transfer is limited to flat and horizontal fillet welds and flat grooves.
Pulsed spray transfer uses the welding parameters of spray transfer for peak values with back ground parameters similar to short circuiting transfer to provide good penetration and fusion, but with the ability to weld in all position. The hook is that the welder must be capable of pulsing.
One reason I can see that would cause an owner to balk at using GMAW on any project is the tendency of many welders to use short circuiting welding parameters even when spray mode or globular mode transfer is specified. It is more comfortable for the welder to weld at lower heat input. A simple ban eliminates the need to "bird dog" the welders to make sure they are not using the short circuiting transfer mode. Life is good.
The other problem could be the need to have adequate gas shielding. The opening of a door or hatch can easily blow the shielding gas away from the weld pool and result in gross porosity.
Like all welding processes, there are limitations that need to be observed to optimize the results. Failure to recognize the limitations and to control the parameters can result in unacceptable weld quality.
Best regards - Al
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