Estimate of Hydrogen Density at Starting Point for Crevice Corrosion and Cracking of Cold Rolled Type 304 Stainless Steel

A cold rolled type304 stainless steel pipe with shot peening was prepared. A crevice was created between the outside of the pipe and an O-ring. Cracking from a corrosion pit was observed previously on a sample inserted with a press-fitting part in a chloride environment, and it was presumed to be Hydrogen Embrittlement-Stress Corrosion Cracking (HE-SCC). Using the samples with no press-fitting parts, cyclic corrosion tests were conducted in this work. To estimate the hydrogen density at the initiation point of crevice corrosion and cracking, the hydrogen amount diffused from the corrosion pit was measured using Thermal Desorption Spectroscopy (TDS), and the number of pits was measured. The average hydrogen quantity in a pit was derived, and diffused hydrogen density was calculated using a simulation model which is based on diffusion in a half sphere shape (simulating diffusion of hydrogen at the pit surface). The calculation results show that at 0.3 ppm of hydrogen density, Hydrogen Embrittlement can occur.