Desenvolvimento de ligas especiais resistentes à corrosão para revestimento de dutos, reservatórios e equipamentos ligados ao petróleo e derivados.

Abstract

Corrosion is responsible for major part of accidents with petroleum occurring currently, specially in the cases of corrosion of oil pipes, gas pipes, tubes used for transporting chemical products and petroleum derivatives, metallic cases for petroleum wells, ships and boats, industrial equipments, tanks for storage of oil, petroleum derivatives and chemical products and many other important installations, causing incalculable damage to the environment. Therefore, it is necessary to develop advanced materials, which seek to combat or decrease the effect of corrosion. The proposed study aims at optimization of operational parameters for electrodeposition of Ni-W-B and Co-W-B alloys, and characterization regarding their resistance against corrosion. The electrochemical bath used for electrodeposition of Ni-W-B alloy was composed of the following reagents: nickel sulfate, sodium tungstate, boron phosphate, sodium citrate and 1-Na-dodecylsulfate. The electrochemical bath used for electrodeposition Co-W-B alloys was composed of cobalt sulfate, sodium tungstate, boron phosphate, sodium citrate and 1-Na-dodecylsulfate. The study was performed at 9.0 pH, which was adjusted by ammonium hydroxide or sulfuric acid. The films of Ni-W-B and Co-W-B alloys were initially electrodeposited on a copper substrate, and then on the on the surface of a pipe sample carbon steel API 5L, with surface area of 8.0 cm2 and 11.8 cm2 , respectively. The anode used was made of cylindrical Pt-gauze. Within the range studied, it can be affirmed that: for Ni-W-B alloy the optimized values of current density 20 mA/cm2, temperature 70 °C and mechanical agitation 15 rpm, giving a deposition efficiency of 50%; and for Co-W-B alloy the optimized values of current density 20 mA/cm2, temperature 70 °C and mechanical agitation 15 rpm, giving a deposition efficiency of 35%. The electrodepositions realized on the pipe samples presented similar behavior to those deposited on the copper substrates for both alloys studied. The Ni-W-B alloy present better characteristics the Co-W-B alloy, principally in relation to the resistance against corrosion. A further study is necessary for elimination of microcracks present on the deposition of Ni-W-B and Co-W-B alloys.