The Research Of Aluminum Alloy Drill Pipe Material Corrosion Mechanism And Its Surface Protection

Aluminum alloy drill pipe has been used as a preferred material system for drilling pipe in geological drilling due to its own advantages.But the weakness of poor wear resistance and resistance to salt corrosion often lead to the failure of aluminum alloy drill pipe.Especially corrosion wear failure in the surrounding environment of drilling fluid,restricting the development of drilling engineering.In this paper,the corrosion failure of aluminum alloy drill pipe in field drilling application is analyzed.Ultrasonic cold forging technology(UCFT),micro-arc oxidation(MAO)and UCFT+MAO surface strengthen technology are applied to the typical 2618 aluminum alloy pipe materials,followed by corrosion in pH = 10 saturated salt drilling fluid at room temperature(720 h)and 150 ?(72 h)respectively.Combined with CSM friction-wear tester to study the corrosion wear performances of surface modification aluminum alloy in the drilling fluid environment.The microstructures,corrosion morphology,wear scars morphology,phase composition and corrosion products of the samples were characterized by optical microscopy,white 3D surface profilometer,X-ray diffraction,scanning electron microscopy and transmission electron microscopy.Thus revealing the corrosion mechanism and surface protection technology of aluminum alloy drill pipe.The results are as follows:(1)The corrosion failure of field application aluminum alloy drill pipe is mainly pitting,spalling,micro-cracks and corrosion products attached.The corrosion products are mainly Al2O3 and Al(OH)3.Corrosion resistance of upsetting drill pipe is the best.Drill pipe and steel connection occurred galvanic corrosion.(2)The results of electrochemical experiments show that Ecorr of the surface modified sample is close to that of the UN sample,but Icorr,?Wi and Pi decrease by an order of magnitude.The corrosion resistance is improved,and corrosion resistance of UCFT+MAO sample is the greatest.In the medium-high frequency,the UCFT+MAO sample undergoes the electrochemical reaction of the composite coating with the electrolyte,and the aluminum alloy substrate is dissolved at the low(3)frequency.The electrochemical process of other samples mainly occurred in the metal dissolution.(4)UCFT,MAO and UCFT+MAO surface modification treatments have improved the corrosion wear performance of aluminum alloy drill pipe materials in pH=10 saturated salt drilling fluid,especially salt corrosion resistance.But compared with room temperature,the salt corrosion resistance significantly reduced at 150 ?.The corrosion pattern of aluminum alloy is mainly pitting,accompanied by microcracks and NaCl attachment.The corrosion products are mainly Al2O3.Compared to UN samples,the wear rate was significantly reduced.The wear rate of UCFT+MAO sample was reduced by 94 % at room temperature drilling fluid for 720 h.Under the two environments,the surface modification aluminum alloy and SiO2 ball on the grinding,the wear mechanism is abrasive wear.Based on the comprehensive analysis,the corrosion-wear resistance of UCFT+MAO sample is the most excellent in the pH=10 saturated salt drilling fluid.