A Comparative Analysis of Nitric Acid and Citric Acid Passivation of Stainless Steel Cargo Tanks on Chemical Tankers

Abstract

Stainless steel cargo tanks on chemical tankers are often passivated to maintain and/or restore the integrity of the chromium oxide (Cr2O3) passive layer on the surface of stainless steel bulkheads. Traditionally, nitric acid was used as the standard passivating agent due to its unmatching efficiency in restoring the passive layer. However, due to increasing environmental and safety concerns, the chemical tanker industry has recently begun shifting to an alternative method citric acid passivation. This study presents a comparative analysis of nitric and citric acid passivation, focusing on their effectiveness in restoring the passive layer of stainless steel cargo tanks on chemical tankers. The research explores the efficiency of each acid in passivating stainless steel cargo tanks by reviewing previous research and studies conducted by reputable organizations, as well as by interviewing several seafarers who have extensive experience in conducting both nitric acid and citric acid passivation on chemical tankers. The results of the research indicate that, although citric acid passivation is safer, more environmentally friendly, and has proven to be at least equally effective as nitric acid passivation in shore-based industries, nitric acid passivation is found to be more effective in passivating stainless steel cargo tanks on chemical tankers. Hence, it is recommended that the chemical tanker industry keep both passivation methods in use in parallel and evaluate each case individually to determine which acid will be more suitable for passivation in each situation.