Study On Hydrogen Permeation Behavior Of High Strength Casing Pipe Steel Under Coupling Stress And Corrosion

In recent years,with the growing demand for oil and gas resources,petroleum and natural gas exploitation situation is becoming increasingly complex.In the process of oil production,the casing pipe facing a complex situation with high temperature,high pressure and high H2S/CO2,caused the Environment sensitive fracture in the course of service.Hydrogen damage is an important type of the Environment sensitive fracture,the pipe material damage in synergistic effect of hydrogen and tensile stress.Hydrogen damage leads to the decrease of oil pipe strength,which could threat the safety production of oil and gas wells and cause disastrous consequences of people’s lives and property.Therefore,the study of pipe steel hydrogen permeation behavior and the embrittlement mechanism is very necessary.As the pipe serving underground,hydrogen,stress and corrosive environment always exist at the same time,however,the study of the synergistic effect of hydrogen,stress and corrosive environment is still very limited.The specific research achievements are as follows:(1)Three kinds of pipe steel,C110,Q125 and 140,were selected for test materials.Through the regular performance of three kinds of material physicals and chemical properties and mechanical properties test,get the corresponding chemical composition,microstructure and inclusion analysis,the nature of the hardness and the stretch mechanics performance;provide the basis for subsequent experimental analysis.(2)Using Devanathan-Stachurski hydrogen permeation technique,hydrogen permeation experiment of high strength steel was conducted in acid corrosion environment containing H2S to investigate the hydrogen permeation behavior influence law and mechanism of material and environment.The results show that with the increase of charging current and temperature,the hydrogen diffusion coefficient increased as well as the susceptibility of hydrogen embrittlement;With decrease of the strength,pH value,the hydrogen diffusion coefficient increased,the hydrogen concentration increased and the hydrogen embrittlement susceptibility increased.(3)A new type of fixture and sample was designed to improve the hydrogen permeation experiment method.The slow strain rate tensile test and the Devnathan-Stachurski double electrolytic cell technique were connected to detect the combining influence of stress and corrosion environment,so that the influence law of hydrogen permeation behavior and embrittlement mechanism can be investigated.The experimental results show that with the increase of stress level,the hydrogen diffusion coefficient increases,the hydrogen permeation enhanced,and the yield strength decreased.Stress level has a strong decision function on hydrogen permeation properties of pipe steel,and the higher strength of pipes,the hydrogen permeability is more sensitive to stress change.This research provides a new method and idea for environmental cracking applicability evaluation of the casing pipe,and direction and basis for strength design,heat treatment process,grain structure and the content of alloy elements,as well as an important reference for on-site casing pipe selection.