Development of High-alloy Seamless OCTG and Its Manufacturing Technologies

In order to meet the worldwide growth in energy demand commensurate with the recent economic growth of emerging countries, developments of manufacturing technology for large-diameter (OD >178 mm) high-alloy seamless OCTG which enable high productivity of natural gas and OCTG material which safely withstand the ultra-deep gas developments have been required. In order to manufacture large-diameter high-alloy OCTG, Mannesmann mandrel mill rolling method which consists of piercing and mandrel mil processes is necessary. However, high-alloy pipes produced by the Mannesmann mandrel mill rolling method didn’t have enough high quality as commercial products due to its imperfections on internal surfaces in piercing process and some rolling troubles in mandrel mill process so far. A new 3D finite element model for rotary piercing has been developed to optimize rolling conditions for high-alloy materials. An analytical model considering material property of high-alloy materials in continuous hot rolling conditions has been newly introduced for optimization of mandrel mill rolling conditions. Thus mass-production technology for large-diameter, high-alloy OCTG was established. In addition, an ultra high strength Ni alloy OCTG meant for ultra-deep gas well development applications has been developed by adding rare earth micro alloying resulted in enhancing the SCC (Stress Corrosion Cracking) resistance, as well as improving the hot workability