SCC INITIATION AND GROWTH RATE STUDIES ON TITANIUM GRADE 7 AND BASE METAL, WELDED AND AGED ALLOY 22 IN CONCENTRATED GROUNDWATER

摘要

The stress corrosion crack initiation and growth rate response was evaluated on as-received, as-welded, cold worked and aged Alloy 22 (UNS N06022) and titanium Grades 7 (UNS R52400), 28 (UNS R55323) and 29 (UNS R56404) at 105 - 165 ℃ in various aerated, concentrated groundwater environments. Time-to-failure experiments on actively-loaded tensile specimens at 105℃ evaluated the effects of applied stress, welding, surface finish, shot peening, cold work, crevicing, and aging treatments in Alloy 22 (UNS N06022), and found these materials to be highly resistant to SCC (none observed). Long-term U-bend data at 165℃ corroborated these findings. Titanium Grade 7 and stainless steels were also included in the 105℃ test matrix. Long term crack growth rate data showed stable crack growth in titanium Grade 7. Recent creep tests in air confirm literature data that these alloys are quite susceptible to creep failure, even below the yield stress, and it is unclear whether cracking in SCC tests is only accelerated by the creep response, or whether creep is responsible for cracking. Alloy 22 exhibited stable growth rates under "gentle" cyclic loading, but was prone to crack arrest at fully static loading. No effect of Pb additions was observed.