【2026 Valve Corrosion】Valves are highly susceptible to pitting in environments containing chloride ions
Thread Content
Coastal chemical plants and seawater cooling systems often encounter pitting problems with stainless steel valves, where pinhole-like holes appear on the inner surface of the valves and gradually expand and penetrate.
How chloride ions penetrate stainless steel: The “stain resistance” of stainless steel comes from a dense layer of chromium oxide passivation film on its surface. Chloride ions have a strong penetrating ability; they can locally destroy this passivation layer, exposing the fresh metal substrate, thereby forming pitting nuclei that gradually spread deeper. 304 stainless steel (CF8) is particularly susceptible to damage in conditions with high chloride ion concentrations.
In seawater or conditions with high chloride ion concentrations, 304 valves are highly likely to suffer severe pitting corrosion in a short period of time; even 316L is not sufficient – dual-phase stainless steel is required as a minimum alternative.
Stress corrosion cracking is even more terrifying: pitting is visible, while stress corrosion cracking is an “invisible killer”. When all four conditions are present – sensitive materials (304/316), chloride ions, high temperatures above 60°C, and tensile stress – the valve body can suddenly crack without any warning. Areas with high residual stress, such as the welding heat-affected zone and threaded connections, are most prone to problems.
Control strategies: 304 valves should not be used in seawater or high-chloride saline systems; 316L is only a minimum acceptable option, and 2205 duplex stainless steel is the preferred choice. Pipe design and welding processes should eliminate residual stresses, with post-welding solution heat treatment. Conduct regular non-destructive testing to detect potential surface cracks in a timely manner.