Corrosion potential copper-chloride-water

Fig. 3 shows that the corrosion potentials of steel in dry and chloride-free BMIBF4 in the presence of MBT shift to more positive values, and that both anodic and cathodic currents are depressed by MBT. This indicates that MBT is a mixed corrosion inhibitor (that acts in both a cathodic and an anodic manner). Qualitatively similar shifts in corrosion potential and depression of corrosion currents on the both sides of corrosion potential are reported in Fig. 4-8 for steel, zinc and copper in the presence and absence of water and chlorides. 

H2S can cause corrosion of stainless steels such as 316 and 410 stainless in the form of sulfide stress cracking. (Other factors, such as pH, chloride concentration, and temperature also affect the potential for steel cracking.) Copper alloys corrode rapidly in H2S service. An industry value that has been developed is NACE MR-01, 2003, from the National Association of Corrosion Engineers. In the gas phase, a stream is sour if the H2S partial pressure exceeds 0.05 psia. If a single phase hquid is in equilibrium with a gas phase, where the gas phase H2S partial pressure exceeds 0.05 psia, then that hquid is also considered to be sour. If the liquid is not in equihbrium with the gas phase, then the liquid is considered sour, if this bubble point gas phase H2S partial pressure exceeds 0.05 psia. The presence of water is not required for a gas and/or hquid to be considered to be sour, nor is there a minimum pressure to avoid designating a gas or hquid as sour. 

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