Analysis Of Fatigue Properties Of CT80 Coiled Tubing Stell

Coiled tubing(CT) is used extensively in well wokrover, welldrilling, well eompletion, well logging and well stimulation in oll-gas field. It plyas a more and more important part in exploration and produetion.It will improve the effieieney of exploration and exploitation, studying, developing and using coiled tubing technology.Therefore, the development of domestic CT materials and manufacturing technology are great significance. Coiled tubing have relatively poor working conditions and complex force state.In the forms of failure, fatigue fracture failure is the larger proportion. For the fatigue failure is a typical low-fatigue. The Microstructure of coiled tubing, fatigue properties, cyclic stress-strain behavior are in-depth study in the paper. It covers the following contents.Analysis the effects of annealing temperature on the strength, plastic, microstructure, hardness and hardening index of coiled tubing.Results show that with the annealing temperature increased, the strength, hardness decrease, grain size, hardening index increases, improved ductility of the coiled tubing steel; The performance of coiled tubing pipe weld is a weak area.Used coiled tubing low cycle fatigue test device,test the fatigue life of coiled tubing and evaluate coiled tubing heat treatment process. Results show that coiled tubing have a higher fatigue life of the temperature range in 760℃to 780℃.To study of coiled tubing steel cyclic stress-strain behavior was found that:The same sample at different constant strain rate, the performance of cycle characteristics is different.At lower annealing temperature obtain high strength and high yield ratio showed cyclic softening feature easily.That is detrimental to the using life of coiled tubing. With the annealing temperature increased,cyclic softening rate decreases at high strain rate, cycles become stable gradually under the lower strain rate and the cyclic stability of the strain rate is significantly higher;Cyclic strain hardening idex increases with rising temperature of heat-treatment.