Development of Sour Service Offshore High Strength and Heavy Wall Line Pipe by Double Submerged Arc Welded (DSAW) Process

摘要

The presence of severe corrosive environment along with higher external pressure in the Black sea has led to develop high strength heavy wall offshore sour service linepipe. The paper will cover the successful development of high strength API 5L X70 Sour Service, Fracture arrest properties, Dimensions, High Utilization (SFDU) (33 inch OD x 39.5 mm WT) linepipe manufactured by the J-C-O-E technology. Pipe rolling and welding parameters were controlled to minimize the circumferential residual stress and weld and Heat Affected Zone (HAZ) hardness in order to enhance the Hydrogen Induced Cracking (HIC) / Sulphide Stress Corrosion (SSC) resistance. The proper selection of wire and flux has resulted in average Charpy V-Notch (CVN) energy >100 J at -30°C in the weld centerline. The study of weld microstructure showed the co-relation of weld ductility (measured in all-weld specimens) with grain boundary ferrite. The hardness of the weld centerline was <225 HV 10 kgf even with overmatching of weld tensile strength. Plate selection with respect to alloy design and microstructure was critical to obtaining good HIC and SSC resistance for heavy wall linepipe. The levels of S<0.0010% and P<0.008% along with low value of Nb+V+Ti <0.055%, Parameter crack measurement (Pcm)<0.15% and Carbon Equivalent (CE)<0.38% were obtained in the plates.