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Discussion on the performance of expansive pipe casing
- Oct 30, 2018 -

The performance requirements of the expansion pipe casing mainly include the difficulty of expansion and the performance of the expansion. for two aspects, the latter should be the primary consideration. In order to meet the requirements of engineering application, we must first ensure that the mechanical properties after expansion reach the corresponding level of the API 5CT standard steel casing, but also to meet the requirements of pressure and corrosion resistance. Therefore, the expansion of the pipe column needs to have high resistance to extrusion, high toughness, high strength, corrosion resistance and wear resistance and other capabilities. In addition, in order to take into account the expansion process requirements, so that the pipe string is easy to expand and avoid the expansion process of concentrated deformation and damage and wall thickness reduction, the pipe should have a high wall thickness uniformity, uniform mechanical properties, non-yield platform characteristics of the stress-strain curve, good strength ductility matching, high deformation enhancement index (n value), High plastic strain ratio (r value), low yield point and aging index, etc.

Because of the wide application of expansion pipe casing, its specific performance requirements are also different, so it is difficult to form a unified product specification. In general, the soft phase in the expansion casing material tissue can be ferrite or austenite, the hard phase can be martensite, bainite or carbide particles, etc., and even the transition phase residual Yu O body can be. According to different operation requirements, special expansion casing composition design and tissue target control are required. For example, if the expansion casing is applied to the service environment with low pressure requirements, the tissue characteristics of a large number of ferrite or austenite can be designed to ensure excellent plastic deformation ability, and if the expansion requires a high resistance to internal and external pressure, its microstructure can be composed of polygonal ferrite plus a large number of small hard phase particles scattered on the ferrite matrix, In order to weaken the adverse effect of the significant decrease of the anti-extrusion strength caused by the combination of wall thickness thinning and bausinger effect caused by the expansion process, it can also take into account the good expansion performance. In addition, phase change induced plastic steel (TRIP), twin induced plastic steel (TWIP) and q& The development of advanced steel materials such as P (quenching-carbon distribution) steel is mature and widely used, which provides a lot of useful enlightenment for the development of high-end expansion casing for equal well diameter drilling.