PIPELINE STEELS

摘要

Large diameter pipes for the transportation of crude oil and natural gas have been the frontrunner in the development of high strength low alloy (HSLA) steel. For the last three decades the processing route for pipe steel is via the thermomechanical rolling process, for which niobium microalloying is eminently suited. The steel grade X 70 was dominant in this period and it still maintains its position. Several new demands arose in recent years: 1.The aim for higher transportation capacity promotes the application of steel with higher strength than X 70, such as X 80 to X 100. Even steel grade X 120 has been developed and is considered for new lines. 2.The exploitation of deeper wells brings up sour gas-containing media. Their transportation requires pipelines to be resistant to hydrogen induced cracking. 3.Offshore pipelines need relatively high wall thickness in combination with good toughness, a demand which often cannot be fulfilled by conventional thermomechanically rolled (TM) steel. For all these new demands clean steel is required, with a low amount of non-metallic inclusions but also low amounts of undesirable elements such as phosphorus, and with a low amount of second phase such as pearlite, which is correlated with the demand in low carbon content.