Co-relation of Microstructural Features with Tensile and Toughness Characteristics of X70 Grade Steel

API 5L X70 line pipe steel grade has been very popular for the pipe manufacturing in sour/non-sour and offshore/onshore applications. This steel is available in various delivery conditions such as controlled rolling and TMCP with or without accelerated cooling. The selection of plate or coil depends on the type of pipe manufacturing and its final application. Co-relation of steel microstructure with tensile and toughness properties, before and after pipe manufacturing is required for the selection of suitable steel for a given application. For a given application and pipe manufacturing process, steel cleanliness, and allowance for Bauschinger effect, strain hardening, SCC and HIC resistance plays a prominent role. Present work is about microstructure and its co-relation with properties for X70 steel plates and coils supplied by 12 steel mills. Evaluation of alloy design with respect to microstructural features and its effect on tensile and toughness properties change from plate/coil to pipe is discussed.