The corrosivity of four mercaptans and selected crude oil fractions were measured in lab tests. Conclusion: Mercaptan corrosion can contribute significantly to the total sulfur related corrosion in the temperature range 235–300°C, which agrees with observations of elevated temperature corrosion in refinery distillation equipment.
There are three known types of high temperature sulfidation present in the refining industry. Two of them have industry recognized methodologies for damage prediction, and they both manifest as general thinning morphologies. They are known as H2-free sulfidation and H2/H2S corrosion. The third type, although recognized as H2-free, low-sulfur corrosion, does not have an accepted chemical theory or a prediction tool, and it manifests as a localized thinning morphology. This third type of sulfidation is much less common and occurs in units and process conditions where little-to-no H2S would be expected to be present. This paper discusses the operating conditions in two known damage cases presented here and provides a viable chemical theory that could lead to the observed damage profile. In addition, an approach to mitigation of this attack is discussed.