The production of Q&T line pipe steels for heavy wall pipe requires several properties to be fully matched.Among them is the yield strength for strain based criteria pipelines for subsea application.Yield strength must match the required minimum under elevated temperature conditions [60 & 160 ℃] and at the same time do not exceed the surface hardness that will make the welding inadequate.Maximum of 220 vickers hardness has been set for some of the subsea projects.Production in a busy Q&T line requires simple tools to predict the time and temperatures to achieve the desired properties.The classical strength and logarithm of time,after Bhadeshia [1],has been used with excellent results in these line pipe steels of different wall thickness.
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