Here is a general guide for wet H2S service (SSC).
NACE MR0103 is for refinery processes which have wet H2S in the hydrocarbon. However the sulfide stress corrosion (SSC) can be occurred in other services including H2S and condensed water in the solution if the wet H2S corrosion reaction is proceeding in accordance with the following formula.
<Fe + 2(H2S) + H2O> is going to be <FeS + 2H+ + 2S- + H2 (gas) + H2O>
2H+ in the products will be the seed of SSC.
NACE TM0177 requires SSC test by the H2S saturated aqueous BRINE solution (acidified and buffered for promotion of reaction speed). Hydrocarbon is not used for the SSC test.
Water will be the most critical factor for SSC because 2H+ cannot be produced without soluble water. For instance, most fuel oils/gas have some H2S contents, but not included the condensed water, Therefore normally fuel oils/gas are not considered as wet H2S service. Like this, the chemical solution including H2S may or may not be considered as wet H2S service. It depends on the existence of condensed water in the solution and a certain amount of H2S contents (> 50 ppm in water).
Unfortunately there are no NACE standards for wet H2S corrosion for Chemical processes. However, if the reaction per the above formula is expected in chemical process, the hardness control may also have to meet the NACE MR0103 requirements to avoid SSC (strong recommendation).
