Effect of Rising and Falling K Profiles on SCC Growth Rates in High Temperature Water

Effects of rising and falling stress intensity factor (K) profiles on the SCC growth rates of stainless steel and nickel alloys has been studied in high temperature water. Sophisticated test control software was used that changes loading (P) based on crack length (a) to achieve a specific K trajectory by controlling dK/da, not simply dP/dt. The majority of SCC problems develop adjacent to welds, which have a complex residual stress profile vs. wall thickness. This, coupled with the dependence of K on crack length, causes K to change as the crack grows, not per se with time (t). The effect of “K-dot” on crack tip strain rate and the associated crack growth rate is discussed, along with the repercussions to understanding and dispositioning SCC response.