This paper compares the cathodic reactions occurring on steel in aqueous solution containing dissolved H 2 S or CO 2. In aqueous solutions containing these weak acids, the rate of the cathodic reaction is enhanced in comparison with strong acid solutions at the same pH. In the case of dissolved CO 2 , this phenomenon is fully explained by a buffer effect, contributing to the transport of proton at the steel surface. In the case of H 2 S containing solutions, this chemical mechanism is no more sufficient to explain the cathodic polarization curves. An additional electrochemical reaction is clearly observed, with strong links with H 2 S concentration.
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Abstract:Ultra-deep water (up to 3000 m) is one of the next frontiers for oil offshore exploitation. It requires the use of conduits having to resist in the long run (durability about 25 years) the mechanical and environmental requests. One of the key points is the thermal insulation of the structure to avoid the formation of hydrates and paraffin plugs inside of the steel pipe. Over the past 10 years, many studies were performed to better understand the behaviour of the syntactic foams used as thermal insulation of pipes for deepwater production, but few tests were run on industrial prototypes to reach the actual thermal properties of the systems. This paper presents the numerical and experimental characterizations of an industrial multilayered insulated pipeline tested in service conditions. Two thermomechanical finite element modellings of the coated pipeline have been developed to predict its behaviour during service condition tests. The first model considers pure conduction through the inner air inside of the structure and the second model considers convection phenomenon between the inner air and the metallic surfaces inside of the structure. In parallel, industrial pipe tests on an immersed instrumented pipeline, internally heated to temperatures up to 95 °C and subjected externally to hydrostatic pressure up to 300 bar are presented. Experimental data obtained during industrial pipe tests and related model predictions are compared and discussed. Thermal properties of the syntactic foam are determined with steady and transient states analysis. In complement, a study of the model results sensitivity to the input Poisson coefficient is presented.
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