The Development of Hot Rolled Coil of API5l-X65 Specifications with Improved Bauschinger Effect Resistance for Oil and Gas Linepipe Applications

by Handrito I. Bharata, Ahmad Desrianto, Zaenal A. Muslim

Publisher - PT Krakatau Steel, Indonesia

Category - General Novel

Steel for a thick-wall pipeline, especially for oil and gas pipeline application, requires not only high toughness, high strength and good weldability, but also good Bäuschinger effect resistance during pipe manufacturing. The requirement of mechanical properties of the steel can be fulfilled by chemical composition adjustment and appropriate controlled rolling. This work is concerned with the development of High Strength Low Alloy (HSLA) steel strips in term of low carbon high manganese for thick-wall pipeline applications. The addition of solid solution strengthening elements up to 0.3% Ni, 0.3% Cu, 0.2% Cr, and grain refinements strengthening elements up to 0.06% Nb, 0.08% V into steel containing 0.07% C and 1.2% Mn, combined with controlled rolling process resulted in an excellent impact properties up to 285 Joule at 0 OC, high yield strength of 470 ~ 570 MPa, tensile strength of 560 ~ 700 MPa, and fine ferrite grain size of 5 µm. A special effort has been addressed to investigate the effect of some micro-alloys such as niobium, vanadium and nickel on steel microstructures and mechanical properties in term of improving the Bäuschinger effect resistance. The investigation clearly shows that there is no decreasing of yield strength from hot rolled coil to pipe.

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