Questions of when, where and why hydroprocessing units within oil refineries can see naphthenic acid corrosion are often raised, and to date, there has been little, if any published data to answer these questions. This has resulted in a variety of different metallurgies being chosen, some of which compromise on other desired properties and/or cause costly requalification of fabricators’ procedures. This paper helps answer some questions by surveying numerous units processing high naphthenic acid-containing feeds, e.g. feeds with high total acid number (TAN). The survey lists the unit temperatures, TAN’s, flow schemes, materials and corrosion history. A beneficial effect of hydrogen was shown, as no corrosion has occurred on 300 series SS materials downstream of the hydrogen injection point. Theories for why the hydrogen is beneficial are presented and attempts to prove/disprove various theories by reviewing the chemical reaction dynamics of the corrosion reactions were made. However, the necessary constants were not readily available, and hence, no theory was conclusive enough to explain the benefit. Regardless, the experiential data seems strong enough to use as a basis for setting inspection strategies and selecting new materials.
Key Words: Naphthenic acid, hydroprocessing units, materials selection, hydrogen