High-Speed Tandem GMAW for Pipeline Welding

Abstract

Tandem gas metal arc welding (GMAW) differs from conventional GMAW as two welding wires are passed through the same welding torch. A single torch with two contact tips is used to feed both wires into a single weld pool. Although the potential of the multi-wire GMAW process was first explored as early as the 1950’s, it has not become commercially viable until relatively recently due to performance limitations associated with the power source technology, that resulted in process instabilities. However, with the advent of modern microprocessor-controlled inverter power sources and an improved understanding of metal transfer characteristics, tandem GMAW is now being successfully applied in many industries. Over the last four years, Cranfield University’s Welding Engineering Research Centre and TransCanada Pipelines have developed tandem GMAW for pipeline welding. Cranfield have developed a tandem GMAW torch specifically for use with narrow gap weld preparations utilized in pipeline welding. The process has been proven capable of high deposition rates and welding speeds two to three times those of conventional mechanized pipeline welding. Based upon this earlier work, the Cranfield Automated Pipewelding System (CAPS) is now being developed. This uses two tandem torches on a single carriage (dual tandem welding). The high speed of tandem GMAW is retained and two passes are deposited simultaneously which further reduces welding times. This results in a significant reduction in the number of welding stations required to achieve a given number of weld’s per day and leads to major savings in labor and equipment costs. In comparing welding systems for a recent project estimate, CAPS resulted in a 26% saving in alignment, welding, NDT and coating costs when compared with conventional mechanized welding systems. A major benefit of CAPS is that it has evolved from existing technology. It is not a ‘one-shot’ process. The completed weld has a very similar profile to conventional mechanized pipeline welds so conventional radiography and automated ultrasonic testing can be used for weld inspection. The weld metal microstructure and metallurgical properties are also similar to conventional mechanized pipeline welds. CAPS is therefore suitable for use on all linepipe materials including X80 and X100 steels. This paper reviews the development of the process and equipment together with information on productivity and metallurgical properties.

Joint welding of mild steel using a GMAW hot-wire process

“…For all processes, however, it can be seen that both arcs form a common melt pool. [10] The tandem process uses two electrodes that are electrically insulated from each other and operated with individual power sources. This process thus has a high degree of exibility, as the two arcs can be operated independently of each other.…”

“…[11] Following Larkin et al (2011) [12], the tandem process can achieve high welding speeds, deposition rates and versatility with little thermal effect on the base material. Blackman et al (2002) [10], in a paper on tandem welding of pipelines at high speeds, state that the deposition rate can be increased to up to 24 kg h -1 . This means that large plate thicknesses can also be welded in a single layer.…”

hybrid Laser-GMA girth welding technologies for transmission pipelines

“…If permitted by length of the pipeline and profile of the ground, a number of these orbital units are used at the same time with every single station having been designed for one-or two-pass welding and then being displaced to the next pipe joint to produce the same weld there. Such production aggregates often rely on several welding heads per unit thus representing a high state-of-the art [1], both in relation to equipment and welding. This, however, is connected with a high expenditure on personnel and plant engineering ( Figure 1).…”

The Selection of Parameters for Automatic Welding of the Nuclear Reactors Pipelines

“…The need to eliminate these shortcomings, the increased requirements for the reliability and quality of welded joints of pipelines, improving working conditions of one of the most harmful manufacturing professions determine the need to automated argon arc orbital welding (welding of fixed pipe joints). The use of protective argon environment allows to obtain a higher quality weld, allowing to prevent chemical changes in the metal connections [1][2][3].…”