Answer
Galvanic corrosion occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte (like salt water). Stainless steel (302/316) is more noble than carbon steel. In this 'galvanic couple,' the carbon steel housing acts as the anode and corrodes preferentially, while the stainless ring acts as the cathode. The corrosion typically happens inside the groove, where the housing material is eaten away. This 'undercuts' the ring, eventually leading to a loss of the groove wall and the ring being ejected under load. In marine environments, this is prevented by using matching materials, applying protective coatings, or using sacrificial anodes. The 'Area Rule' also applies: a small anode (housing) and a large cathode (ring) is the worst-case scenario.
