Inflatable Tubes Materials Design And Development

This paper introduced the expandable tubular technology and its applications in the oil and gas industry. And it also analyzed the working principle and key points of this technology. Based on the theory of advanced steels, combined with the various performance requirements of the expandable tubular materials which were determined by the practical engineering, we designed and developed three types of expandable tubular materials successfully by making use of the stacking fault energy and thermodynamic theories, i.e. twinning induced plasticity steel, transformation induced plasticity steel and dual phase steel. Three types of sample tubes were refined, processed and prepared in the laboratory and the corresponding heat treatments were been done. We researched these steels’ microstructure by the modern analytical test methods such as OM, SEM and XRD. We also tested the mechanical properties. We did the expansion tests to three types of sample tubes with different expansion rates.Using the stacking fault energy thermodynamic model of the alloy system, this paper calculated the stacking fault energy of the TWIP steel theoretically. TWIP steel will twinning during the deformation process. Its strength and ductility properties will get a greatly improvement.According to the law of mixture, this paper calculated the strength of the dual phase steel theoretically. Its tensile strength can reach900MPa grade. After heat treatment, the fiber mixed dual phase texture of ferrite and martensite could be obtained.This paper calculated the martensite transformation start-temperature and the bainite transformation start-temperature of TRIP steel theoretically. The heat treatment process of TRIP steel was intercritically annealed at740℃and isothermally treated at400℃. After heat treatment, the complex phase texture of ferrite, bainite and retained austenite could be obtained. The retained austenite will produce the martensite transformation during the deformation process, and transform to the ε-martensite. The strength and ductility properties will be increased by the TRIP effect.The mechanical tests showed that three types of steels had good strength and ductility properties, and the properties could meet the performance requirements of the expandable tubular materials.The expansion tests showed that the strain transfer mode during the deformation was the key factor which had an influence on the expansion successful or not. The strain transfer mode was determined by the trend of the strain hardening exponent which was changed with the deformation intensification.Through the theoretical analysis and testing, the expandable tubular materials’design rules were put forward from four aspects, i.e. the chemical composition, microstructure, strengthening of the material and mechanical properties.