Initiation of stress corrosion cracks in Alloy 690 in high temperature water is a rare occurrence and depends on the method by which the sample is loaded. Only in dynamic straining experiments is crack initiation consistently observed. Stress relaxation in constant deflection tests, and lack of a means of rupturing the oxide film in constant load tests are the principle reasons for the difficulty of initiating cracks in these tests. These observations, combined with those from the much more susceptible Alloy 600 form the basis for a mechanism stress corrosion crack (SCC) initiation of Alloy 690. SCC initiation is proposed to occur in three stages: an oxidation stage in which a protective film of Cr₂O₃ is formed on the surface over grain boundaries, an incubation stage in which successive cycles of oxide film rupture and repair depletes the grain boundary of chromium, and a nucleation stage in which the chromium depleted grain boundary is no longer able to support growth of a protective chromium oxide layer, resulting in formation and rupture of oxides down the grain boundary. The mechanism is supported by the available literature on oxidation and crack initiation of Alloy 690 in hydrogenated primary water conditions.

在高温水中在690合金中引发应力腐蚀裂纹的情况很少见，并且取决于加载样品的方法。只有在动态应变实验中才能始终观察到裂纹萌生。在恒定挠曲试验中应力松弛，以及在恒定载荷试验中缺乏使氧化膜破裂的方法，是这些试验中难以引发裂纹的主要原因。这些观察结果与易感性较高的Alloy 600的观察结果相结合，形成了690合金的机械应力腐蚀裂纹（SCC）引发的基础。SCC引发建议分三个阶段进行：氧化阶段，其中Cr的保护膜₂ ö ₃在晶界上方的表面上形成一个，一个连续的氧化膜破裂和修复循环耗尽铬的晶界的温育阶段，以及一个贫铬的晶界不再能够支持保护层生长的成核阶段。氧化铬层，导致沿晶界的氧化物形成和破裂。该机理得到了有关在氢化初级水条件下690合金的氧化和裂纹萌生的现有文献的支持。