Study On Wear And Failure Analysis Of Drilling Pump Valve System

Drilling pump is important for circulating the drilling fluid of the bottom hole. In the process of drilling, bearing large and unstable loads lead to bad working environment. Because of that, there are some vulnerable parts in the hydraulic end, including pistons, cylinder liners, pump valve systems (valve body, valve seat, rubber ring platens, rubber rings, etc.). These vulnerable parts have a great effect on the working efficiency of the pump and restrict the product efficiency heavily. In view of the problems above, this paper first do a failure analysis on the pump valve system, and establish the main failure mechanism of it. And then, solve the kinematics differential equation of the valve body by MATLAB software. Using the kinematics parameters as the initial condition, then carries out simulation of the flow fields and analysis of impact process between valve seat and valve body. After that, this paper does some researches on the failure life for pump valve system with different valve seat types under pulse cyclic stress. According to the simulation analysis results, at last puts forward two improvement schemes based on the original valve system, to improve the impact wear resistance and erosion wear resistance. Preliminary study is conducted for the improvement schemes. During the study, this paper has achieved the following results:(1) According to the analysis of common failure ways in valve system, and comparison with the wear mechanism, the main failure mechanismes for valve system include erosion wear, impact wear and abrasive wear, etc;(2) After solving the kinematics differential equation, and getting the displacement curves of valve body, we can find that the curve is approximately parabolic type or spindle type. Besides, the valve cone angle, opening lag angle and stroke have a great effect on the motion of valve body.(3) In the flow field of pumping valve system, because of Venturi principle, the flow speed of valve gap is bigger than other positions. At the same time, the flow field has strong vortex on some points, such as the position on the hydraulic cylinder close to the valve body, valve body upper surface, and hydraulic cylinder end cover. These vortexes are caused by uneven flow distribution, and will increase the flow speed. This will make the particles have a great erosion effect on the pump valve system and hydraulic cylinders. Factors affected the distribution of flow field in the pumping valve system include valve body cone angles, strokes, etc. The size, shape, velocity, impact angle of the paticles have a great effect on the erosion between the paticles and the tagets.(4) Because of the great impact force between the valve body and valve seat, there will be stress concentration points on the impact system. After repeated fatigue impact forces, the stress concentration points will fail because of impact fatigue wear. At the same time, the outlet thickness of the rubber ring, cone angle of valve body, outer cone angle of valve seat, valve seat type have an important effect on the impact characteristic of the pumping valve systems.(5) Two structure improvement schemes are raised up, including using the spherical contact surface to replace the cone one and adding a buffer cylinder structure under the valve seat. Wherein, the first improvement scheme can reduce the erosion wear with reducing the flow speed. The second improvement scheme can reduce the impact wear according to slow down the compact speed between the valve seat and valve body.This paper establishes a set of method to analysis the wear and failure of pump valve system on the view of main failure type. This method has a certain reference value for the subsequent structure design and parameters optimization of drilling pump valve system.