A Stress Corrosion Behavior Of Near α Titanium Alloy In The Land Oil And Gas Field Pipe

With the continuous deterioration of the working environment in ultra deep wells in oil and gas fields,ordinary steel casing can no longer meet the demand for material properties in harsh drilling environments.Titanium alloy has good corrosion resistance,high specific strength,and low modulus.Using titanium alloy as a material to make casing has become the development trend of oil well tubing at home and abroad.In drilling operations in onshore oil and gas fields,the casing made of titanium alloy is not only load-bearing,but also needs to withstand the corrosion of hydrochloric acid.Under the combined action of stress and corrosion,the alloy is prone to stress corrosion cracking.Therefore,this article aims to conduct immersion experiments,electrochemical experiments,slow strain rate tensile experiments,constant stress loading experiments,and other experiments for a land oil and gas field ultra-deep well casingαThe stress corrosion behavior of titanium alloy ZSA-6 in 20%hydrochloric acid solution was studied in order to provide a reference for its application in ultra deep wells in oil and gas fields.The main results obtained from the thesis work are as follows:In the immersion experiment,with the prolongation of immersion time,the corrosion rate of the alloy first increased and then decreased,and the corrosion rate reached its maximum after48 hours of immersion;In electrochemical experiments,the corrosion resistance of the alloy increases with the prolongation of pre immersion time,and the self corrosion potential of the alloy is the highest,0.085V,after 10 days of immersion;The self corrosion current density is minimum,2.70×10^-8A（cm²）;Maximum polarization resistance,1.29×106Ω（cm²）,relatively optimal corrosion resistance.The results of slow strain rate tensile tests show that all alloys exhibit a high stress corrosion sensitivity index,indicating a tendency for stress corrosion cracking in all alloys;As the strain rate increases from 1×10^-6s^-1rises to 5×10^-5s^-1,the stress corrosion sensitivity index of the alloy decreases,and the stress corrosion tendency of the alloy decreases.The experimental results of constant stress loading show that when the loading constant stress amplitude is 870MPa and 827MPa,the strain loading time curve presents three distinct stages:transient deformation stage,steady deformation stage,and accelerated deformation stage,and the alloy breaks during the test time;When the loading constant stress amplitude is 783MPa,740MPa,and 696MPa,the strain loading time curve presents a transient deformation stage and a steady-state deformation stage,and the alloy does not fracture during the test time;When the stress amplitude is less than 870MPa,the slope difference in the steady-state deformation stage is small.With the increase of the loading constant stress amplitude,the plastic loss of the alloy first increases and then decreases.When the loading constant stress amplitude is 827MPa,the elongation after fracture decreases by 45.5%,and the reduction of area decreases by 19.1%;When the loading constant stress amplitude is 783MPa,the elongation after fracture and the reduction of area are both the lowest and decrease by 68.9%and 23.6%,respectively;When the loading constant stress amplitude is 696MPa,the elongation after fracture decreases by 37.0%and the reduction of area decreases by 1.8%.The characteristics of stress corrosion fracture include shallow dimples,tear ridges,secondary cracks on the side of the fracture,and micropores.The mechanism of stress corrosion of alloys in 20%hydrochloric acid is a hybrid mechanism of hydrogen adsorption promoting dislocation emission and motion theory（AIDE）and hydrogen promoting local plastic deformation theory（HELP）.