An economic assessment of mechanized welding of high-strength linepipe for the Australian pipeline industry

FORAGIVEN pipeline, the choice of material and welding process can have a significantimpacton the total capital expenditure. The use of higher-strength linepipe requires less steel, and the reduced tonnage can resultin a significant cost reduction even after paying a premium £/tonnerate. For large-diameter pipellnes mechanized welding provides a much higher productivity than manual welding and requires less labour and equipment, and so significant cost savings can be achieved. However, this is not the case for smaller pipe sizes and this, together with potential technology problems, means that mechanized welding can be significantly more expensivethan manual welding. The Australian pipeline industry typically uses high-pressure, small-diameter, thin-wall pipelines for gas transmission, and the use of mechanized welding has been very limited. This has held back the implementation of high-strength steels, as selecting higher-strength linepipe has an impact on the choice of welding process, with mechanized welding being preferred for higher-strength steels. In some circumstances, the choice of higher-strength steel and the consequential need to use mechanized welding may be considered detrimental in the perception that gains in material savings may be more than offset by the higher costs of welding. This paper reviews the economicbenefits to be obtained from higher-strength steels, and assesses the selection and implementation of mechanized welding processes to provide guidance to the Australian pipeline industry in selecting the lowest-cost solution.