Ensuring the required mechanical-technological properties of welds is a critical issue in the application of multi-wire submerged arc welding (SAW) processes in the manufacture of large-diameter pipes made of high-strength fine-grained steels of grade X70 and higher according to API 5L. Excessive heat input of up to 10 kJ/mm is one of the main causes of the formation of microstructural areas in the heat-affected zone (HAZ) with deteriorated mechanical properties, such as impact toughness and tensile strength. In this work, a variant of a five-wire SAW process is proposed that reduces the weld volume and the heat input, while retaining the high process stability and production speed of multi-wire SAW. By adapting the welding wire configuration of a five-wire SAW process and the energetic parameters of the arcs, the high penetration depth of approx. 24 mm and a 10 % reduction in the weld cross-section could be achieved compared to the usual process configuration. This effect was transformed into a higher welding speed, which led to a reduction in the heat input. A concept for process monitoring is proposed in order to maintain constant manufacturing quality in large-diameter pipe production. In addition to the analysis of electrical process signals such as welding current and welding voltage, acoustic process monitoring using vibro-acoustic sensors provides reliable information on the stability of the welding process. The evaluation of characteristic process features is presented and discussed in this article.
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