Effect of strain aging on properties of X90 line pipe

Abstract

Tensile and impact toughness tests under different aging conditions were conducted to study the effect of strain aging on service properties of X90 line pipe. Results indicate that the yield strength and yield ratio of X90 pipeline steels increase significantly after strain aging, while the impact toughness and tensile strength show little correlation with strain aging. Moreover, the impact toughness decreases after 200 °C, 5 min aging, however, it rises with the increase of aging temperature and aging time. The tensile strength changes slightly after strain aging, however, the yield strength and yield ratio increase significantly after strain aging, and the rising range of which decrease with the increase of aging temperature and aging time. Comprehensive analysis shows that the aging treatment contributes to different service properties of X90 pipeline steels, mainly due to the difference of microstructure and chemical composition. The results of aging sensitive coefficients analysis show that microstructure yields more significant effect on service properties of X90 pipeline steels than that of chemical composition, and X90 pipeline steel with dual-phase microstructure contains higher aging sensitivity coefficient.