A method was developed to screen refining equipment, including trayed towers, for wet H2S environments. After applying process modeling to simulate environments to which equipment is exposed, the results can be used to predict whether an aqueous phase is likely to occur and the total disolved sulfides in that aqueous phase. Subsequently, susceptibility to wet H2S cracking can be assessed. Examples are given to demonstrate the calculation method. It was found that for trayed towers, the operating temperature is a key parameter in determining if an ordinarily assumed dry tower is prone to aqueous condensation. Tower trays at lower temperatures are more likely to be exposed to a free water phase. Because it is inevitable to have some levels of H2S in refinery
streams, as long as the operating conditions allow an aqueous phase to exist, the resultant wet H2S concentration should not be overlooked. Thus, most of the “wet” towers with a separate aqueous phase contain areas susceptible to wet H2S cracking. The disolved sulflde levels on different trays can be predicted by this method. For other types of equipment, water content, as well as temperature, is used to determine if wet H2S damage is likely.
KEY WORDS: sulfide stress cracking, hydrogen induced cracking, hydrogen sultlde, predictive calculations, sour environments, modeling