High Sour Gas Field Corrosion Resistant Nickel-based Alloy G-3 Tubing

The key technology for the development production of nickel base G-3 alloy oil pipe used in severe sour gas field was studied in this paper.As the G-3 alloy has bad hot plasticity,the convention methods such as hot-rolling or hot punching can't be used in the G-3 oil pipe production.The way used in our development production was composition optimizationâ†'laboratory testsâ†'corrosion resistant evaluationâ†'centrifugal casting and forging stockâ†'hot-extrudingâ†'cold-rolling etc.The research production in this paper further gave addition to the G-3 alloy basis data and made good preparation for the G-3 alloy pipe production in China.The present status of nickel base corrosion resistant alloy development was generalized aider document retrieval and studying,then the work as following was done,(1) On the base of optimum design of G-3 alloy chemical composition used in the experiment, the relation between deformation rate,temperature and the thermalplastic of corrosion resistant alloy G-3 were studied by thermal simulation test and sensitizing test.Then the microstructure developing in the deformation alloys and the corresponding mechanics were analyzed.The precipitated phase developing in the alloy and corresponding mechanics were analyzed by Scanning Electron Microscope(SEM)and Transmission Electron Microscope(TEM)after X-Ray Diffraction(XRD)and Thermo-Calc software analysis, which could direct the industrial production.(2)The relation between cold-working rate and strength of hollow forging was explored by cold-working experiment and mechanical property test,which gave reference to the cold-forming of oil pipe.(3)The performace evaluation was done to oil pipe.The following conclusions were obtained from the study above:(1)The G-3 alloy had large resistance to deformation and narrow hot deformation temperature.The hot plasticity would become worse with the increasing of the strain rate, while the maximal resistance to deformation would be higher.The dynamic recrystallization would take place in G-3 alloy at appropriate deformation condition.And the grain size would become smaller with the growth of Zener-Holloman parameter(Z).(2)The alloy element Cr,Mo and W could improve the G-3 corrosion resistance,however,they could also acceleration the embrittlement phase to precipitate.There were large quantity precipitated phase in and around the alloy grain boundary when the temperature was low. They were mainlyσand M₂₃C₆ phase,which would effect the hot plasticity and corrosion resistance severely.The precipitated phase would dissolve gradually with the temperature become higher.And the M₂₃C₆ phase dissolved more quickly.They dissolved absolutely when the temperature become 1150℃,in which there were conversion from M₂₃C₆ toσphase.The main factor that effected the alloy hot plasticity at high temperature was the growing up of grains.The grain size at 1220℃was about 5 times of that at 1050℃.(3)The cold-working experiment and tensile test at room-temperature were done to explore the cold-forming characteristic of G-3 alloy.The austenite grain size was uniform if the alloy was solution treatment at 1140℃for 40min at which oil pipe with high strength-high plasticity-refine grain size could be produced.The cold-working rate should be 27～30%for 110ksi oil pipe,while it became 35～38%for 125ksi oil pipe.(4)The performance especially corrosion resistance ofφ88.9×6.45mm oil pipe was evaluated by the API SPEC 5CT-2005 standard and it showed that the result was conformity with the standard,that is the pilot-production of G-3 alloy by using the method of centrifugal casting and forging stockâ†'extrudingâ†'cold-rolling was successful.