Effect of microstructure refinement on hydrogen-induced damage behavior of low alloy high strength steel for flexible riser

The effect of different microstructures on hydrogen-induced damage behavior of low alloy high strength steel for flexible riser was studied by hydrogen permeation test and electrochemical hydrogen charging test. The mechanism of hydrogen-induced damage behavior in tested steel was elucidated in terms of microstructure characterization, calculation of hydrogen permeation parameters and sensitivity analysis of hydrogen-induced cracking of tested steel. The results indicated that the microstructure of the tested steel was tempered martensite with precipitated phase, and the microstructure was finer and contained more proportions high angle grain boundaries after multi-stage heat treatment. After multi-stage heat treatment, the irreversible hydrogen traps and total number of hydrogen traps in the microstructure increased significantly, resulting in a significant decrease in hydrogen effective diffusion coefficient (D-eff). Compared with quenched and tempered heat treatment, the crack sensitivity of hydrogen-induced cracking in microstructure obtained by multi-stage heat treatment decreased greatly, and the crack mainly presented transgranular propagation and more tortuous.