| X100 line-pipe steel is a milestone in the evolution of pipeline materials. It shows a great potential in the high efficiency of gas conveyance over a long distance under a high operating pressure over 15MPa. However, a main concern for the selection of X100 steels used for a long-term pipeline service condition in Northern Regions is the undetectable strain-aging (SA) induced deterioration in as-received mechanical properties, e.g., fracture toughness. Owing to the likelihood of the SA phenomenon along the longitudinal direction (LSA) of in-service pipeline, the features of X100 steel may over time be impaired by this adverse impact. The property degradation jeopardizes the safety and reliability of pipeline service. According to the diffusion theory, this thesis presents the SA behavior of X100 steel and describes a kinetic method to predict the LSA-induced property variations of this steel during long-term pipeline service by Arrhenius Kinetics and accelerated aging tests in the laboratory. This is beneficial to pipeline design, operation and maintenance. The cores of this prediction are the solutions of both activation energy (Q) and equivalent aging time (EAT). The experimental results show that the magnitude of Q for the designated X100 steel is 22.78kcal/mole at the pre-strain of 2%. This low value, close to 20kcal/mole of mild steel, represents the susceptibility of this material to SA. The predictive method is feasible and effective, but complicated and time-consuming. |
