Essential welding aspects for high strength linepipe

The exploration and exploitation of remote natural gas fields results in pipeline designers facing challenging conditions, and materials have to be tailored to the needs of these conditions. Challenges include - thick wall, high strength, deep sea locations, corrosion resistance against sour gas, low temperature toughness for arctic use, and crack arrest toughness. As well as the technical challenges noted above, operating gas pipelines are expected to perform safely over long time periods and be built as economically as possibly to minimize costs to consumers. Consequently the applied technologies from steel making to pipe production are continuously being improved in order to increase the pipe quality level and also the productivity by reducing non-quality critical costs. In this paper special attention is paid to the control of the welding process for the longitudinal seam as this is of essential importance for the intrinsic pipeline safety. Various quality requirements are defined by customer specifications for the weld seam with respect to mechanical properties, shape and allowable size of imperfections. Sometimes these requirements work in opposing directions and measures chosen to fulfill one requirement can prevent achieving another target. The key factors to guarantee high weld seam quality are tight control of welding parameters and optimized selection of welding consumables. In the first part of this paper, it will be shown how the weld seam quality can be improved by use of modern welding technology and process control. Furthermore, it will be discussed how unbalanced requirements for the weld bead profile can lead to the unnecessary use of high heat inputs. In the second part, the role of the welding consumables will be discussed. The different types of welding fluxes and the most common welding wire types are presented and compared with regard to their properties. (AU) Copyright © 2013 Companhia Brasileira de Metalurgia e Mineração (CBMM) All Rights Reserved