Abstract: An incorrect hole on a cold-high pressure segregator was plugged up by welding.The cold-high pressure segregator runs in the environment of high pressure and high H₂S.Accordingly, the accident of sulfide stress corrosion cracking (SSCC) should be taken into account.The SSCC sensitivity and cracking time of 16Mn(HIC) steel used to make the cold-high pressure segregator and common 16Mn steel in solutions with various H₂S contents and pH values, simulated solution and operating solution were investigated by constant strain bend and slow strain rate test (SSRT).Hydrogen diffusion coefficients of 16Mn(HIC) steel, 16Mn steel and their welded seams were also tested by the electrolyte hydrogen charged method.Safety evaluation of the cold-high pressure segregator was given with above results.