Study On The Effect Of Basic Working Conditions On Corrosion Of Hard Chromium Plating On Screw Drill

With the further development of China's oil and gas development industry and the gradual maturity of underground oil and gas drilling technology,screw drill is often widely used in directional wells and horizontal wells in the drilling process.However,according to field applications in oil and gas fields,brine drilling fluids are often used in the drilling process,resulting in severe corrosion of hard chrome plating on the surface of the auger.Serious corrosion will shorten the service life of the screw drill,a direct result of increased economic costs,may also cause increased risk of accidents,and even the possibility of injury.At present,there are many researches on chloride ion corrosion at home and abroad,but there are few systematic studies on the corrosion behavior of screw drilling tools in brine drilling fluid,and the manufacturing enterprises also lack sufficient reference.Therefore,it is of great academic value and engineering significance to study the corrosion law of hard chrome plating of screw drilling tools under practical working conditions.In this paper,by collecting the current screw drill in the underground work conditions,the parameters of the basic working conditions are worked out,that is temperature,pressure and chloride ion concentration,and the range of parameters.Using the high temperature and high pressure reactor to simulate the basic working conditions of the screw drill in the underground,corrosion and detection of hard chromium plating on the surface of screw drill,and the corrosion test and electrochemical parameters of chromium plating layer at room temperature and atmospheric pressure are taken as a reference.The effects of temperature,pressure and chloride concentration on the corrosion of hard chrome plating were studied by orthogonal experiment.The electrochemical parameters and corrosion characteristics of hard chrome plating were studied by open circuit potential,dynamic potential scanning and weight loss corrosion.The micromorphology and surface composition of the plating were observed and analyzed by scanning electron microscopy and energy dispersive spectroscopy.It was found that the factors that affected the corrosion rate of hard chrome plating were the chloride ion concentration,followed by temperature and pressure again.The corrosion rate of the plating decreases with the increase of chloride concentration,increases with the increase of temperature and increases with the increase of pressure.From the field data can be inferred hard chromium plating corrosion is the most serious situation in the temperature of 180 ?,the pressure of 15 MPa and chloride ion concentration of 30g/L near the conditions.It can be observed from the morphology before and after corrosion that the Chloride ion will cause Pit initiation in sensitive area preferentially.Pitting continuously formed on the deposit surface under the catalysis of simulating occluded corrosion cell,and the corrosion holes would extend to macroscopically corrosion pit.In particular,deep-hole,peeling and penetration of the deposit surface can be found in a small part of the deposit surface,in severe cases,forming the galvanic corrosion between cathodic coating and substrate.