Jai Dev Chandel, Nand Lal Singh
The metallurgical science has been used to develop new weldable high strength steel plates having strength and toughness of API-5L, X-120M for manufacturing line pipes for transportation of petroleum products. A pan cake type microstructure design has been used to ensure the strength level of X-120M and ductile fracture behavior at temperature down to -20 ºC. Ultra refined, lean micro-alloyed chemistry design and plate rolling through TMCP (thermomechanical control processing) in combination with AC (accelerated cooling) steel has been produced of lower transformation microstructure in the steel plates. The steel chemistry and TMCP and AC plate rolling designed in such a way that the plate should be of lower bainite and lower martensite to achieve the strength level of X-120M line pipe. The provision was made in the chemistry so to have minimum effect of welding heat input on the base metal or so called heat affected zone (HAZ) in the submerged arc welding of long seam weld of line pipe.
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