The welding machines used for the wire-fed processes are different than the standard, constant current (CC) unit that is so commonly seen on the back of pipeliner rigs. The power source would have to provide the CC output for SMAW of the root, but would also need to provide a constant voltage (CV) output, as well as withstand the field environment on the pipeline. The wire feeders that had been seen in fab shops were large affairs designed to be placed on the top of a large, stationary welding machine. A component of this sort would not work on the pipeline. One of the advantages of the familiar SMAW approach for the pipeline is the limited cables and hoses needed. A welder only needs the electrode holder and a ground cable. The wire feeders seen in shops had multiple cables and hoses attached. These would likely be a problem on a pipe string. All of these issues were also affected by the actual process being used. Obviously, the SAW process was not viable. Solid wire GMAW provided the best deposition, but due to the requirement for all-position welding, it could only be used in the lower current range known as short circuiting transfer. There was much anecdotal evidence in the pipe industry about short circuiting being “too cold” and having a possibility of incomplete fusion between passes or at the weld toes. The pulsed gas metal arc process (GMAWP) was capable of all-position welding, but it required more complicated equipment and controls. A few initial trials with GMAW were attempted, but the results were not as desired. The self-shielded flux cored wire process (FCAW-S) was appealing since there is no need for a shielding gas, with the associated cylinders and hoses, but it was felt a high degree of manual dexterity was needed with it. The gas shielded flux cored process, FCAW-G, seemed to present the best overall solution. This process was already used in some structural field applications, it provided good deposition rates, it was not as challenging to run compared to self-shielded flux cored, it didn’t present the historical issues associated with short circuiting transfer, and it could be used with basic wire feed equipment. In communicating with some equipment suppliers, it was learned that the FCAW-G process had considerable success on larger diameter pipeline projects in Europe and even here in the States. It appeared that the gas shielded flux cored (FCAW-G) process presented the best potential for success. Selecting Equipment It was necessary now to find the best welding equipment to use for FCAW-G. With help from Norco Welding Supplies in Boise, Idaho, a welding power source and wire feeder package was suggested. The Miller XMT 350 VS, which is small, lightweight, and often used for structural welding in the field, was chosen. It is an inverterbased machine and capable of multiprocess operation. A portable, suitcase style wire feeder was found. The suitcase feeder has been used for many years in shipbuilding and structural welding. The X-TREME 12VS wire feeder was selected. This wire feeder is equipped with Arc Reach™, which allows the operator to make adjustments to the welding parameters, wire feed speed, and voltage, without the need for an additional control cable from the power source to the feeder. All control signals travel over the welding lead. With this capability, the welder has the ability to make adjustments to the voltage as needed. In this case however, with the gasshielded flux cored process selected, NOVEMBER 2016 / WELDING JOURNAL 47 Fig. 4 — The Pipecat mounted with equipment needed for the operation.
Welding Journal | November 2016
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