The Effect of Water Flow Rate Upon the Environmentally Assisted Cracking Response of a Low-Alloy Steel: Experimental Results Plus Modeling

Abstract

The presence of a critical concentration of sulfides at the tip of a crack is thought to be a prerequisite for environmentally assisted cracking (EAC) in low-alloy steels. Sulfides can be “supplied” to the crack tip by a growing crack intersecting and dissolving embedded MnS inclusions present in the steel as an impurity. Sulfides can be removed from the crack tip by diffusion, ion migration, fatigue pumping, or convection induced within the crack by external water flow. EAC can result when the supply of sulfides exceeds the loss by mass transport. This paper presents results of experiments conducted on relatively large semi-elliptical surface cracks subjected to mean free stream velocities of 0.56, 1.71, and 5.00 m/s. The two higher velocities resulted in mitigation of EAC, while the lowest did not. A computational fluid dynamics computer code, FIDAP®, was employed to model the interaction between the flow within the crack cavity and the free stream flow. The model demonstrated that the two highest free stream velocities produced a significant interaction between the two regimes, but that the lowest free stream velocity produced minimal interaction. Thus, there was good qualitative agreement between the experimental and analytical results.