Abstract
The stability of an electrodeposited nanocrystalline Ni-based alloy coating in a H2S/CO2 environment was investigated by electrochemical measurements, weight loss method, and surface characterization. The results showed that both the cathodic and anodic processes of the Ni-based alloy coating were simultaneously suppressed, displaying a dramatic decrease of the corrosion current density. The corrosion of the Ni-based alloy coating was controlled by H2S corrosion and showed general corrosion morphology under the test temperatures. The corrosion products, mainly consisting of Ni3S2, NiS, or Ni3S4, had excellent stability in acid solution. The corrosion rate decreased with the rise of temperature, while the adhesive force of the corrosion scale increased. With the rise of temperature, the deposited morphology and composition of corrosion products changed, the NiS content in the corrosion scale increased, and the stability and adhesive strength of the corrosion scale improved. The corrosion scale of the Ni-based alloy coating was stable, compact, had strong adhesion, and caused low weight loss, so the corrosion rates calculated by the weight loss method cannot reveal the actual oxidation rate of the coating. As the corrosion time was prolonged, the Ni-based coating was thinned while the corrosion scale thickened. The corrosion scale was closely combined with the coating, but cannot fully prevent the corrosive reactants from reaching the substrate.
Highlights
IntroductionOil well tubes account for about 40% of the total steel consumption in the oil and gas industry
According to the statistics, oil well tubes account for about 40% of the total steel consumption in the oil and gas industry
The Ni-based alloy coating mainly consisted of Ni crystals and small amounts of NiW2P3 and
Summary
Oil well tubes account for about 40% of the total steel consumption in the oil and gas industry. More than half of oil well tubing failures are caused by corrosion-related problems [1]. About 1/3 of oil and gas fields in the world contain H2 S. The newly developed oil and gas fields in Sichuan and Xinjiang in China have very high contents of H2 S and CO2 , and in certain regions, such contents even exceed 10%. The H2 S/CO2 corrosion of oil tubes has become an increasingly prominent problem [2,3,4,5,6]. The most common anti-corrosion measure is to adopt anti-corrosive metals for oil and gas tubes. Stainless steel tubing is generally preferred for deep gas wells in an environment without H2 S.
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