| Mud pumps are weak links in oilfield drilling.The parts of mud pump are easy to wear and lose efficacy due to poor working environment.Piston is the most vulnerable component to failure.China is a major producer of crude oil,and improving the service life of mud pump piston is of great significance to the energy saving and consumption reduction of oil industry.To extend the service life of mud pump piston reciprocating in the cylinder liner,the wear resistance of piston is needed to increase.Over the past seventy years,surface engineering methods for changing surface morphology have been proven to be effective in reducing friction and wear.After millions of years of evolution,some organisms have developed surface textures with excellent friction characteristics,and theirs surface textures can be used in the design and manufacture of wear resistant equipment.Basing on the function of earthworm body surface and combining with a large number of research results on wear resistance and drag reduction,the bionic piston of mud pump with dimples and stripes on the surface was designed in this paper.The performance of bionic piston was studied theoretically and experimentally.Dimple piston and stripe piston with different structure parameters were designed.The contact pressure on piston surface was related to the piston seal performance,and the friction stress was related to the piston wear resistance.Therefore,finite element software was used to analyze the contact pressure and friction stress on the bionic piston surface.The results showed that the maximum contact pressure and maximum friction stress on the bionic piston surface were larger than that of the standard piston.The maximum contact pressure and maximum friction stress of the dimple piston were most affected by the dimple diameter,followed by dimple angle and dimple depth.The dimple diameter 4.5mm,dimple angle 15° and dimple depth 4mm,the maximum contact pressure of the dimple piston was 31.1200 MPa,which was 138.21% higher than that of the standard piston.The dimple diameter 1.5mm,dimple angle 20° and dimple depth 2mm,the minimum value of the dimple piston maximum friction stress was 3.0408 MPa,which was 61.87% higher than that of the standard piston.The maximum contact pressure and maximum friction stress on the stripe piston surface were more affected by stripe number than by stripe depth and stripe inclination angle.When the stripe inclination angle 60°,stripe depth 3mm and stripe number 3,the maximum contact pressure of the stripe piston was 69.8620 MPa,which was 439.02% higher than that of the standard piston.The stripe inclination angle 45°,stripe depth 2mm and stripe number 1,the minimum value of the stripe piston maximum friction stress was 1.9792 MPa,which was 8.69% higher than that of the standard piston.According to the simulation results of finite element analysis,it was concluded that the local stress concentration at the edge of dimple or stripe increased the contact pressure and friction stress on two bionic pistons surface.With the assistance of Daqing Drilling Company No.4,the actual drilling tests of seven dimple pistons for F-1300 mud pump were completed.The results showed that the service life of dimple pistons was higher than that of standard pistons,and it was more than 20% longer.The bionic piston with a diameter of 4mm,an angle of 15° and a depth of 3mm had the longest service life,which increased 37.21%.There were obvious wear scratches on the surface of standard piston,and the wear scratches were relatively deep.However,the surface wear of the dimple piston was relatively uniform,the piston had relatively small wear scratches,and there were no obvious deep scratches throughout the entire piston surface.At the same time,the inner wall of the standard piston cylinder liner had many deep furrows and the inner wall of the dimple piston cylinder liner was relatively smooth.It could be seen from the damage on the surface of the standard piston cylinder liner that the furrows on the inner wall of the cylinder liner were not caused by the defects in the cylinder liner itself.When the inner wall of the cylinder liner and piston surface worn,the gap between the two would increase.The mud particles under the action of pressure entered the contact surface between piston and cylinder liner through the gap,and secondary damage to the cylinder liner was caused.The friction heat of standard piston and dimple piston cylinder liner was analyzed by finite element transient structure.When the friction heat was analyzed,the piston was set to suction and discharge mud with two strokes in the cylinder liner,that was,the piston reciprocated twice.The analysis showed that the temperature field on the piston surface increased gradually from the piston lip to the piston root at different times.This was mainly due to the heat accumulated on the piston surface during the entire stroke of the piston.When the piston reciprocated within the cylinder liner for 4 strokes(2s),the surface temperature of both the standard piston and the dimple piston increased significantly.At different times,the surface temperature of the dimple piston was higher than that of the standard piston.The surface temperature of the cylinder liner did not change much at different times,but the temperature was slightly higher at the piston stop.With the increase of the piston reciprocating motion times,the surface temperature of cylinder liner changed little in mud discharge stroke,but increased in mud suction stroke.The actual operating conditions of mud pump piston were in mixed lubrication conditions.The wear resistance of piston surface was directly related to the lubrication effect of piston cylinder liner.Fluid Flow(CFX)module in Workbench was applied to simulate the pressure and flow lines of lubricating oil on the surface of different dimple pistons.The wear resistance mechanism of bionic dimple piston was analyzed.The hydrodynamic effect produced by the bionic dimple structure increased the pressure of lubricating oil,and then the load of lubricating oil between piston and cylinder liner was increased.Thus the increased lubrication reduced friction and wear on the piston surface.At the same time,the dimples changed the distribution of lubrication field on piston surface.The velocity of lubricating oil in the dimple area was decreased,the residence time was increased,and the lubrication state between piston and cylinder liner was improved.The dimples stored the lubricating oil.The vortex velocity of the upper lubricating oil was more severe than that of the bottom,which can provide the secondary oil supply for the inevitable dry friction between the piston and cylinder liner of mud pump.This improved the lubrication and wear resistance of piston.The dimple on the piston surface of mud pump could also store abrasive particles or mud particles,which reduced the particles on the secondary damage of the piston and cylinder liner surface. |
PDF Full Text Request