the voltage was the same for each weld pass and required no changes The Movable Enclosure The next concern was that the tent enclosure, the welding power source, and the wire feeder needed to be easily moved from weld joint to joint. Further, there needed to be some way to supply electrical power to the welding power source. This was accomplished by assembling a support tractor that was called a “Pipecat,” which started as a basic Caterpillar® tractor. On this tractor was mounted a generator for three-phase electrical power and an air compressor (Fig. 4), along with enclosures and boxes for the welding power source and all of the other various tools needed at the welding location. A tubular steel frame was fabricated so that the cutting and shielding gas cylinders were safely secured during both welding of and travel between joints. To the front of the Pipecat was mounted a hydraulic crane along with a knuckle boom. The welding enclosure was supported by the hydraulic crane, leaving the knuckle boom available for positioning of the pipe or any other lifting chore. A remote control pendant was used to control the boom from the ground. Reels were installed for convenient storage of both air and cutting torch hoses. A plasma cutting power source was also mounted to the Pipecat. The welding enclosure is a tubeframed tent built with open spaces in the ends specifically for fitting over a pipe — Fig. 5. The ends of the tent could be wrapped below and around the pipe to block the wind. The wire feeder was hung inside and stayed in place as the tent moved from joint to joint. The voltage sensing wire feeder required a sensing lead be connected to the pipe. Obviously the welding ground also had to be connected. This was accomplished by the use of a large on/off magnet bolted to both the ground cable and the voltage sensing lead. This was hung inside the tent so that it dropped back down onto the top of the pipe as the tent was lowered into place. An “umbilical cord” bundle was made up of all of the hoses and cables that needed to pass between the Pipecat and the tent. This bundle included the welding positive lead to the feeder, the welding ground, and the shielding gas hose for the feeder, a 120-VAC cord, and a large air hose. While it is typical that electrical grinders are used on pipelines, it was determined that air-powered grinders were faster and tougher on the job. Mechanization to Increase Productivity It has been documented that some companies are performing the welding of large-diameter, long-distance pipelines with mechanized equipment. These machines run around the outside and/or inside of the pipe and use wire-fed processes. To perform this same type of operation, CWC considered a tractor from Bug-O Systems. The Universal Bug-O-Matic was selected for the pipe application. This product includes a linear weaver that provides controlled dwells at both ends of the oscillation to help in the wetting of the weld onto the pipe bevel. It also has a hand-held control pendant with a steering device so the operator can keep the weld where it should be. The tractor travels on an extruded aluminum rail that has a gear rack mounted to the face. A pinion on the output shaft of the drive motor engages the gear rack and provides control of travel. The aluminum rail is rolled to fit around the outside of the pipe and is also equipped with a hinge and latch mechanism along with spring-loaded foot assemblies to allow it to be installed around the pipe. One concern was that it would take a long time to install the ring and the tractor around the pipe, but a hinge and latch on the ring rail allows it to be mounted around the pipe in less than a minute and the tractor can be installed on the ring in a similar amount of time. The welding gun is connected to the weaver arm of the tractor with a clamp. The company purchased a complete system and proceeded to develop welding procedures. This presented some considerable frustration as there was no readily available data that could be easily accessed. However, the company, with help from the distributor and equipment manufacturer, was able to create welding procedures that satisfied the requirements. Trying the System Once everything was assembled, and quite a few trial runs made, CWC took on a short run pipeline project with its field-portable, wire-fed, mechanized pipe welding system. The bene- 48 WELDING JOURNAL / NOVEMBER 2016 Fig. 5 — Fitting the tent over the pipe.
Welding Journal | November 2016
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