Analysis of Oxide Scales Formed in the Naphthenic Acid Corrosion of Carbon Steel

Abstract

Naphthenic acid corrosion of steel is a major challenge in oil refineries. Iron sulfide scales, formed by corrosion due to sulfur compounds found in the crude oil, have shown unpredictable behavior when it comes to their protectiveness. Recent results show that simultaneous formation of an iron oxide scale formed by corrosion due to naphthenic acids may explain part of the variability and contribute to corrosion resistance of the scale formed on 5Cr steel. In depth analysis identified magnetite in the sections of the scale just adjacent to the metal surface. Currently reported research focuses on investigating conditions that lead to the formation of the iron oxide layer on carbon steel. A comparison of different oxide layers formed on carbon steel from a pure model acid (palmitic acid) and a commercial naphthenic acid mixture derived from petroleum shows different behavior when it comes to corrosion protection. The two acids also show different behavior in the presence of sulfur containing compounds (a model compound and native sulfur compounds found in a heavy lube basestock). These results suggest that the molecular structure of the acid is an important factor in the formation and the protectiveness of an iron oxide scale.

The Coupling Effect of O2 and H2S on the Corrosion of G20 Steel in a Simulating Environment of Flue Gas Injection in the Xinjiang Oil Field

“…Specimens for weight loss measurement were brushed to mechanically remove loose corrosion products, rinsed with acetone, exposed to the Clarke solution (ASTM G103) to dissolve the remaining corrosion products [17,18], dried again in N 2 gas flow, and finally weighed.…”

Synergistic Effect of the Total Acid Number, S, Cl, and H2O on the Corrosion of AISI 1020 in Acidic Environments

“…Generally, carbon steel and organic acids form oil-soluble corrosion products ( eq 7 ), but due to the presence of active sulfur, the formed FeS protective film hinders the corrosion of steels by naphthenic acid to some extent ( eq 8 ). 17 , 23 , 30 , 31 …”

High-Temperature Corrosion by Carboxylic Acids and Sulfidation under Refinery Conditions—Mechanism, Model, and Simulation

“…In our prior research into the mechanism, a multilayer corrosion product scale was found to have an inner oxygen-containing layer underneath an outer sulfide layer after the concurrent sulfidation and NAC. , The inner layer (inner scale) was found to be a mixture of nanoparticulate magnetite and pyrrhotite while the outer layer (outer scale) was composed of pyrrhotite only. It was determined that the presence of magnetite in the inner scale significantly enhanced the layer protectiveness. − The formation of magnetite in the inner scale was rationalized to be the result of thermal decomposition of iron naphthenates (iron carboxylates) formed by acid attack on the metal followed by the disproportionation of wüstite (FeO) trapped underneath the outer scale (reactions and ). − …”

“…In our prior research into the mechanism, a multilayer corrosion product scale was found to have an inner oxygen-containing layer underneath an outer sulfide layer after the concurrent sulfidation and NAC. 16,17 The inner layer (inner scale) was found to be a mixture of nanoparticulate magnetite and pyrrhotite while the outer layer (outer scale) was composed of pyrrhotite only. It was determined that the presence of magnetite in the inner scale significantly enhanced the layer protectiveness.…”

“…In our prior study, scales formed on specimens by sulfidation and NAC are challenged by an acid only flow at TAN 3.5. 16,17 When the experiment was performed in a flow through mini-autoclave (FTMA), oxygen in the inner scale was observed to enhance the scale protectiveness when challenged by acids alone. 47,48 The composition, location, and thickness of the scales in this study were taken as evidence that solid state diffusion of iron was the controlling mechanism, i.e.…”