| The oil-well pump is not only the most important lifting equipment in sucker-rod oil pumping system, but also one of weakness of the system. The oil-well pump is always subjected to cyclic loading, liquid corrosion and sand wear in the process of use; the invalidation of oil-well pump is becoming more and more serious. Among others, fatigue fracture and wear leakage are the main pattern of failure. In this paper, according to the current serious status of pump failure, reliability analysis of fatigue life for oil-well pump is carried out, which provides theoretical guidance for fair use and reasonable maintenance of oil-well pump, decreases oil cost and improves the exploration efficiency, and the research is of great practical significance. The chief research contents are presented as follows:Fault Tree Model of oil-well pump is established based on different failure patterns; by applying the methods of fault tree analysis, this paper analyzes fault tree of oil-well pump by quantitative analysis and qualitative analysis. The analysis shows that traveling valve cover rupture, standing valve seat wear, standing valve cover rupture and pump piston-pump barrel wear have a significant impact on pump failure.By using the basic theories of multiphase flow and gas polytropic process, the liquid pressure in the pump barrel is investigated; calculation models of environment load for pump structural components are built respectively; considering the influences of fluid resistance, condensability of liquid and gas, and also takeing into account the Westphal’s phenomenon of pump valve motion, dynamic characteristics of the pump valve-ball’s movement and the condition of continuous flow for the liquid in the pump barrel, mathematical models of the valve motion at different times are established.The stress analysis models of pump structural components are established; the maximum impact stress of the pump valve is studied by ANSYS/LS_DYNA and a regression model of impact stress is built; considering various factors that influences oil pump’s fatigue life, combining the material S-N curve and linear cumulative damage theory of fatigue, calculation models of pump parts’ life are established; taking into account the load measurement error, the uncertainty of the mechanical properties, the quality of machine parts and so on, reliability predication models of the fatigue life for pump structural components and the impact fatigue life for pump valve assemblies are set up. Reliability predication model of wear life for the pump piston-pump barrel is established, considering the randomness of material hardness, wear particle density, wear particle diameter and so on, the numerical solution of the model is obtained with the Monte Carlo method.Oil-well pump life reliability simulation software is written by VB6.0computer language; this paper studies the motion law of oil-well pump valves, analyzes the influence of stroke and rate of pump, dynamic liquid level, etc on the speed of valve ball and pump parts’life reliability; analyzes the impact of material hardness, wear particle density and diameter, etc on the wear life reliability of the pump piston-pump barrel friction pairs, puts forward several measures of increasing the fatigue reliability. |
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