The Effect of Turbine Steam Impurities on Caustic Stress Corrosion Cracking of NiCrMoV Steels

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Abstract
The stress corrosion cracking (SCC) of NiCrMoV steel in 40% caustic at 100 C was studied using the slow strain rate technique. Controlled potential tests exhibited significant SCC only when the potential was held above a critical value of − 800 mVH. Tests at uncontrolled potential in uncontaminated 40% caustic showed marginal SCC, as the free corrosion potential was below the critical value. However, the addition to the caustic solution of a number of impurities identified in low pressure steam turbine deposits shifted the free corrosion potential to above the critical value. Tests at uncontrolled potential in these impurity-containing solutions showed significant SCC. This enhancement of caustic SCC by certain impurities was also seen in constant load testing.

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