A corrosive environment said to be sour if H2S(hydrogen sulphide) is present in that environment. If there is none,the environment is not sour.
In other to determine the corrosivity of the flüid in a vessel a knowledge the % composition of the vessel's content is required.The following substances are corrosive:CO2,SO2,Chlorides,H2S; acid forming salts and gases in general. The Oxygen content of the vessel aslo determines corrosivity. The temperature of the environment also plays important role. others such as the level of agitation, if liquid has effect,etc