Failure Analysis And Surfacing Research Of The Pump Valve Surface Of The Drilling Pump

With rapid development of petroleum drilling,demand of drilling pumps by domestic oil and gas fields must be higher,and working environment of drilling pumps will become harsher.During starting up and shutting down,drilling pump contacts the muddy sands and the corrosive slurry and bears the hydraulic load caused by high-pressure pump.The pump valve surface is eroded.The fatigue is generated under the cyclic stress action.Valve body and valve seat are components of drilling slurry pump which are most likely in failure.Therefore,valve body and valve seat are often replaced on site,which wastes a lot of time.Aimed at above problems,this paper shows the main reasons of valve surface failure through macroscopic and microscopic failure analysis of surface of valve of drilling pump.TIG technology is adopted for Stellite6 cobalt based alloy built-up welding on pump surface.Hardness test,impact toughness contrast test and wear contrast test with or without surfacing layer are implemented.Those tests indicate that the cobalt based alloy on the valve surface can improve the performance of pump valve;valve body movement is approximately calculated by Mathcad software,and the result is regarded as the initial condition to write the UDF language to develop flow field simulation analysis of valve surface and to analyze and research the shear stress and erosion characteristics of valve surface;finally,fatigue life of valve surfaces with different materials is preliminarily analyzed and researched.During researching,the following main achievements are obtained:(1)The surface of body and seat of scrapped valves of slurry pumps are treated with macroscopic and microscopic failure analysis by scanning mirror and metallurgical microscope.The valve seat materials and the heat-treated structures are analyzed.The main failure reasons of valve surface are abrasive wear,erosion wear,fatigue wear,etc.(2)TIG build-up welding technology is adopted to build up the cobalt base alloy on 20CrMnTi steel surface,resulting in increase of element concentration gradient and enhancement of diffusion effect.In build-up welding,there is the inter-diffusion among elements of surfacing layer and base metal in fusion line and the metallurgical bonding is good.After build-up welding,the tests prove that the mechanical property of valve surface is improved at certain degree.HRC and HV of valve surface with surfacing layer are 45 and 412 respectively.The impact toughness is 20%higher and the mass wear rate is only about 32%of that without build-up welding.(3)In the flow field of pump valve suction stroke,shearing force of body and seat of suction valves shows the trend of firstly increase and then decrease.The maximum shearing force on valve body wall is in the conical surface of valve body.The maximum shearing force on valve seat wall is in boundary of conical surface and vertical surface of valve seat.Due to the structure features of valve body and valve seat,there is transition between conical surface and vertical surface and so,the stress of valve surface in valve clearance is higher than that of other positions,which is the main reason of massive fall off of lower part of valve body and valve seat.(4)Because the drilling fluid erosion on valve surface is severe,the erosion characteristics of valve surface is analyzed to obtain the result that the erosion damage distribution trends of valve surface with or without surfacing layer are basically the same and the distribution trends of erosion rate and of shearing force on valve surface are basically the same.It is found from valve surface with and without surfacing layer that the cobalt base alloy on working surface of pump valve can effectively reduce the erosion and abrasion to valve surface.In the paper,the main reasons of valve surface failure are found at certain degree based on research,analysis,test and simulation.Besides,the feasibility of improving valve surface performance by TIG Stellite6 cobalt base alloy on surface of pump valve is indicated,which has certain reference value for subsequent reinforcement of surface of valve of drilling pump.