Behavior of Thermal Spray Aluminum Coating in Wet H2S Environments

Kane, Russell D. (InterCorr International Inc) | Joia, Carlos (Petrobras Cidade Universitaria) | Bererra, P. (FBTS)


Sulfide stress cracking (SSC) and hydrogen induced cracking environments. Metallic thermal protect carbon steel from the (HIC) can cause severe damage in spray coatings based on aluminum corrosive media, when wet H2S program, a series of electrochemical tests were conducted. These tests involved exposure of coated samples to various environments containing .HJ3, ammonia~ chloride and cyanide to study the behavior of the aluminum coating associated with a stainless steel interlayer both applied by thermal spray. Results showed that the aluminum layer was corroded rapidly in solutions with pH higher than 11. In alkaline solutions with pH lower than 9 a protective aluminum layer and the corrosion rate was very low.

The high corrosion resistance of aluminum makes metallic thermal spray coatings based on aluminum alloys a natural choice to protect steel equipment from exposure to many corrosive environments, However, the performance of these coatings in wet HzS environments found in the petroleum industry has not been examined to a great extent in the published literature. It is already known that, in water at 25 C, aluminum has a good corrosion resistance in the pH interval of 4.0 to 8.5(1) because it is protected by a passive, aluminum oxide layer. Outside of this pH range, the. corrosion rate of aluminum depends on the nature of the individual ions in the solution. The corrosion rate is extremely high in hydrofluoric acid, sodium carbonate and sodium hydroxide, but very low in acetic acid and sodium disilicate. Konstantinova etalz~2)measured the corrosion rate of aluminum tubes in seawater at 90 C in the pH range of 6 to 9 as a function of time. Results showed that corrosion decreased considerably at lower pH values in this range, whereas, in other media aluminum had a tendency to form pits. This pitting tendency increased in the presence of CaCO~, CU2+and Cl- and decreased at temperatures higher than 60 C. The addition of Cl- to water, ethanol and water-ethanol solutions at ?(3)Results showed an increase in the corrosion different temperatures were studied by Persiantseva etah rate with chloride addition along with a sharp increase in hydrogen evolution. A ten fold increase in hydrogen evolution tier Cl- addition to a 0.5 M H2SOdsolution was similarly detected by Zartsyn et t#ii(4).