THE EFFECT OF WATER-FLOW RATE UPON THE ENVIRONMENTALLY ASSISTED CRACKING RESPONSE OF A LOW-ALLOY STEEL - EXPERIMENTAL RESULTS PLUS MODELING

The presence of a critical concentration of sulfides at the tip of a c rack is thought to be a prerequisite for environmentally assisted crac king (EAC) in low-alloy steels. Sulfides can be ''supplied'' to the cr ack tip by a growing crack intersecting and dissolving embedded MnS in clusions present in the steel as an impurity. Sulfides can be removed from the crack tip by diffusion, ion migration, fatigue pumping, or co nvection induced within the crack by external water flow. EAC cart res ult when the supply of sulfides exceeds the loss by mass transport. Th is paper presents results of experiments conducted on relatively large semi-elliptical surface cracks subjected to mean free stream velociti es 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 dyn amics computer code, FIDAP(R), was employed to model the interaction b etween the flow within the crack cavity and the free stream flow. The model demonstrated that the two highest free stream velocities produce d a significant interaction between the two regimes, but that the lowe st free stream velocity produced minimal interaction. Thus, there was good qualitative agreement between the experimental and analytical res ults.