Failure Analysis Of Valve Pump Valve Box

Frac-pump, as the key frac-equipment to increase reserves as well as production, is required to work steadily and reliably in the oil and gas industry. However, the pumps’service life is genenally low because the frac-pump fluid cylinder often cracked failure, which has seriously affected the fracturing operation efficiency and becomes a bottleneck to enhance the overall performance of frac-equipments.In order to figure out the failure causes of cracking, crack propagation mechanism, a series of research, from failure analysis experiments to fatigue life prediction for the dormant cylinder on the basis of materialogy, fracture mechanics, metallography, FEM as well as strengthen treatment process, is conducted. The closer examination of fatigue damage mechanism and fatigue life prediction methods of the fluid cylinder has been carried out. Main work has been done as following:(1) Through widely consulting the inland and foreign information, this paper have in-depth researched about the capability and using instance of the frac-pump, and fully comprehended, analyzed as well as mastered the develope trends and level of it. After the investigation of failure mode, failure criteria as well as the analysis of failure data obtained from field survey, the paper hold the standpoint that the fatigue cracking is the main and the most dangerous failure mode;(2) Such as metallographic examination, hardness test and chemical composition analysis, series of physical and chemical testing of the fluid cylinder materials, were carried out. The result of chemical composition analysis indicates that the material of the fluid cylinder contains more alloy elements, resistant to corrosion and wear-resistant, can improve the material properties of fluid cylinder. The result of metallographic examination shows that the heat treatment process of the fluid cylinder is reasonable for the matrix structure are tempering sorbite and ferrite, finding no congenital defects such as material inclusions, tissue segregation and stomatal. The result of hardness test concludes that the working medium can corrode the fluid cylinder materials and can reduce the material properties;(3) Fracture analysis of the failure fluid cylinder fatigue crack illustrates that its cracking is caused by fatigue. The macro-morphology analysis explains that the crack growth is non-continuity and most of the crack morphology is linear. The microstructure observing concludes that the fatigue-stripes on the fracture surface is in brittle way to extension;(4) Established the fatigue life prediction mechanical model for fluid it, and three different kinds of fatigue life prediction methods have been proposed on the basis of total life analysis, strain-life methodology as well as crack growth simulation. The simulation result showes that fatigue crack starts at the bore intersection as well as the top of conical surface of discharge and suction valve seat bores, where large stress concentration closing to fatigue limit. Fatigue damage cause from high alternating stress;(5) The measures and effects of improving the fatigue life of fluid cylinder are discussed and contrasted with each other in details, such as autofrettage technology, surface strengthening technology, surfacing machining accuracy, material selection etc. The research result points out that autofrettage and shot blasting technology can improve the fatigue life effectively, and high strength materials with fine toughness should be selected for fluid cylinder’s blank;(6) Tensile mechanical properties tests, conventional fatigue tests, corrosion fatigue tests of the fluid cylinder material have been carried out, then mastered the basic mechanical properties of the material and the effect of corrosion on the fatigue life. The experimental test datas shows that corrosion can reduce the fatigue life about 50% in the 613Mpa stress level.Generally speaking, through this paper’s research, found the failure mode, the failure mechanism and failure causes for fluid cylinder, established different fatigue life prediction methods and measures to improve the fatigue life, provided some new ideas and research approachs for fluid cylinder’s research and development. Therefore, this paper has practical value to same extent.