L51562 A Study of the Yield-Tensile Ratio and Its Effect on Line Pipe Behavior

Considerable research has been conducted to define the significance of the yield-to-tensile (Y/T) ratio for line-pipe steels. In the late 1960s and early 1970s, a study was completed in which a series of burst tests was conducted on 41 pipes ranging from 8 to 42 inches in diameter and representing API Specification 5L Grades A through X65. In this study, only 2 of the 41 materials studied had a yield-to-tensile ratio greater than 0.9, and these were artificially created. With the advent of the X70 and X80 steels, higher yield-to-tensile ratios have developed as the yield strength increased. A re-examination of this question in terms of the higher strength materials is presented herein. The objective of this research is to determine if the high yield-to-tensile ratio of X70 and X80 line-pipe steels in any way restricts such operating practices as hydrostatic testing, operating stress level, and flaw behavior.