51316-7392-Corrosivity Study of Sulphur Compounds and Naphthenic Acids under Refinery Conditions

Available for download

Product Number: 51316-7392-SG

ISBN: 7392 2016 CP

Author: Qin Xin

Publication Date: 2016

Member Price: $0.00

Non Member Price: $20.00

Price: $20.00

Qty:

The potential corrosivity of crude oils is a major concern for refineries. Plant experience has shown that current methods using correlations based on crude sulfur content and total acid number (TAN) do not predict corrosion rates reliably. In particular a better understanding of the relative importance of corrosion mechanisms is needed to better predict crude corrosivity when both sulfidic and naphthenic acid mechanisms are present. Previous work focused on the influence of organic acid structure on corrosivity. In this paper the relative corrosivity of different types of sulfur species is explored. Four model sulfur compounds were chosen based on relative thermal stability of sulfur bonds which increased in the order of 1-octanethiol < dioctyl sulfide < diphenyl sulfide < dibenzothiophene (DBT). Corrosion rates for these compounds in white oil were measured using carbon steel (1018 CS) coupons in a test unit that simulates a vacuum distillation tower. Test conditions were varied including the temperature and whether or not naphthenic acids were present. Under the pure sulfidic corrosion conditions results showed that corrosion rates increased as temperature increased where corrosion rates in liquid phase were normally higher than those in vapor phase. Relative corrosion rates correlated well with the thermal stability of the sulfur bonds in the chosen compounds at each temperature. When the testing media contained the same contents of sulfur and elevated TAN values there were significant differences in corrosion rates and surface morphologies of the coupons for the different sulfur species. The results were consistent with a corrosion mechanism that depended on the release of hydrogen sulfide (H2S) by thermolysis of the sulfur compounds. There was clearly a competition present between the H2S and acids for the metal surfaces. In general there will be a threshold amount of H2S relative to the amount of acids present above which the excess H2S will be able to form a protective film on the metal surfaces. For these tests vapor phase results were obtained both below and above this threshold. In liquid phase H2S was able to form a film and protect the metal surface from naphthenic acid corrosion during all test conditions. For comparison to the 1018 CS coupons three types of stainless steel materials (410 304 and 316) were tested. Results showed that 304 SS and 316 SS were sufficient to resist the most corrosive (low-shear) conditions chosen.Key Words: Refinery Corrosion Sulfur Compounds Naphthenic Acid