The Benefit of Hydrogen Addition to the Boiling Water Reactor Environment on Stress Corrosion Crack Initiation and Growth in Type 304 Stainless Steel

Intergranular Stress Corrosion Cracking (IGSCC) in Type 304 stainless steel in high temperature high purity water requires the simultaneous presence of sensitized material, high tensile stress and oxygen. Laboratory and in-reactor stress corrosion tests have shown the benefits of adding hydrogen to the boiling water reactor feed-water to reduce the dissolved oxygen concentration and thereby reduce the chemical driving force for IGSCC. The purpose of this program was to verify the benefit of hydrogen additions on the stress corrosion crack behavior. The program investigated the fatigue and constant load crack growth behavior using fracture mechanics specimens in hydrogen water chemistry (HWC). Isothermal heat treatments were used to sensitize Type 304 stainless steel. Additionally, full size pipe tests containing actual welds were used to evaluate crack initiation, as well as propagation of cracks, to verify the results of the fracture mechanics tests. These pipe tests were performed under a trapezoidal loading cycle. The results of the small specimen tests show that HWC inhibits IGSCC in Type 304 stainless steel. The effects of cyclic loading at slow frequencies which promote IGSCC were also evaluated. Computer aided methods were used in the collection and interpretation of the high temperature crack growth data. The full-size component tests substantiated the benefit of HWC in both crack initiation and growth. All results presented were compared to baseline test data to put the results into perspective.