Accelerated corrosion tests were conducted by the Naval Surface Weapons Center on CAPTOR mine strongback bands. Strongback bands are part of the CAPTOR suspension system, which interfaces the mine to the delivery system of minelaying aircraft and surface ships. The laboratory tests were performed to recreate the stress corrosion cracking failures observed in CAPTOR stockpile storage. The tests were designed to produce the same failures during weeks of laboratory testing which occurred after several years of stockpile storage. This magnitude of accelerated testing required the use of aggressive corrosion test environments.
Eight strongback bands, representing (known) problem bands (H925 heat treated 17-4PH stainless steel), the present-use bands (H1015 heat treated 17-4PH stainless steel), and the proposed replacement bands (Inconel 718), underwent side-by-side testing. Both (known) problem bands failed by stress corrosion cracking: the first during 28-day temperature and humidity testing, and the second during the subsequent 1000-hour salt spray test. None of the three present-use or three proposed replacement bands failed through the temperature and humidity test, salt spray test, and twelve months of outdoor exposure. These failures indicate that the test environments are sufficiently aggressive to recreate fleet-observed stress corrosion cracking failures, but in a much shorter time.