API 571 Certification (Corrosion & Materials) Practice Test 2025 - Free Practice Questions and Study Guide

In applications involving naphthenic acid, an environment often encountered in refining processes and certain petrochemical operations, stainless steel grades exhibit varying resistance to corrosion. 316 stainless steel is particularly effective in combating naphthenic acid corrosion due to its composition, which includes a significant amount of molybdenum. This addition enhances the steel’s resistance to pitting and crevice corrosion, particularly in acidic environments.

The overall alloying elements present in 316 stainless steel, such as chromium, nickel, and molybdenum, create a strong and stable passive oxide layer that provides better protection against corrosive agents. While other types of stainless steel may be useful in various applications, they do not offer the same level of resistance as 316 in naphthenic acid scenarios.

Grades like 410 stainless steel and even 304L stainless steel are not optimized for this type of corrosion and may fail or suffer significant degradation under such conditions. The 300 series stainless steels, while including options like 304L and 316, their overall performance against naphthenic acid is generally less effective than that of 316 specifically. Therefore, 316 stainless steel is often the preferred material choice in environments where naphthenic acid corrosion is a