IGA rates in neutralized solutions of caustic and organic environments

The objectives of this work were to: establish laboratory test environments consistent with those believed to exist in operating steam generators; produce laboratory IGA specimens consistent with specimens removed from operating plants; and conduct limited remedial action tests designed to arrest intergranular attack (IGA). Various laboratory tests performed by Westinghouse are summarized. Tests involving caustic solutions, organics, silicates and their tube sheet crevice simulator are summarized. The capsule tests with caustic showed that no environment was more aggressive than 40% NaOH + 10% KOH + 12% Cr2O3 at 6500 for producing IGA of mill annealed alloy 600. Sulfate, carbonate and silica additions to that environment appeared to reduce the rate of IGA. The tests with mixtures of caustic and silica are described. The tests showed that within the range studied no Na/Si ratio was found to support a super heat of 80 F0. This implies that with additions of silica, crevices with a caustic environment could be dried out. C-ring (TLT) and pressure balanced capsule tests were performed in autoclaves with organic environments. These tests and test results are discussed. The organics tested included sodium acetate, phenoxide, and formate with and without additions of Cr2O3. No IGA or IGSCC was detected in exposure to sodium acetate. Both IGA and IGSCC were observed in exposures to sodium phenoxide and formate. Cr2O3 additions appeared to retard IGSCC and enhance IGA. The test results are summarized