Fatigue Analysis And Optimization Of High Power Fracturing Pump Crankshaft

As the main equipment for hydraulic fracturing operation, fracturing pump is usually applied in the middle and late mining of conventional oil and gas field, unconventional oil and gas reservoir, such as shale gas, coalbed methane, tight oil etc. The performance of its structure is directly related to the degree of the original oil and gas production. Crankshaft is one of the key motive mechanisms of the fracturing pump, its parameters and dynamic characteristic have an important influence on static strength, stiffness, fatigue of the crankshaft’s structure, and then security operating of fracturing pump will be effected. Fatigue damage of the crankshaft becomes a main failure mode due to the complex alternating stress of the crankshaft. With the development of fracturing pump in the direction of high power, fatigue damage problem become more prominent.Up to now, most studies about crankshaft are confined to fatigue analysis under static condition and ignore the mutual influence of elastic deformation, motion state and load. Therefore, fatigue analysis of the crankshaft under dynamic is particularly essential. Taking the crankshaft of the high-power fracturing pump as study object, it solved the problem of fatigue life analysis and improved structural performance of the crankshaft via focusing on the design of positive bias crankshaft structure, analytic computation, dynamics analysis of flexible body system, dynamic response analysis, fatigue life analysis, structure optimization. Thus it provided a set of effective analytical methods for the structure design and fatigue calculation of the fracturing pump crankshaft. The concrete research contents are as follows:(1) In order to carry out motion and load analysis on the crosshead and relative components, the crankshaft adopted the design of five cranks and six supports structures, the power end adopted the design of positive offset slider crank mechanism, according to performance characteristic of high-power fracturing pump and design requirement of light-weight. Then it studied the influence of the bias ratio and crank radius ratio on the suction and drainage and load performance of the fracture pump. Correlation dimensions of it were optimized via MATLAB. Connecting rod force of the crankshafts was calculated by using optimized dimensions. Reaction loads of cranks were calculated with the theory of statically indeterminate structure.(2)The 3D models of crank and relative components were established in Creo. Flexible bodies were established by modal analysis and modal compression. Bearing mechanical model was built by adopting the theory of Hertz contact. Then, it completed the motion characteristic and dynamic loads properties in the motor process of elasticity deformation through flexible multibody system dynamics model of the crankshaft, which was established in MSC.ADAMS. Compared the results of these with results that obtained by analytical method, each part’s vibration obtained by crankshaft model of flexible multibody system dynamics analysis made the crankshaft’s motion condition become more realistic and it could reflect actual motion better.(3)It also completed the task such as establishing assembly model of the crankshaft and the outside spline bushing, finishing setting of the dynamics loads and boundary of every position, founding dynamic response analytical model of the crankshaft, fulfilling calculation of each corner’s von-Mises, positive-stress, shear-stress and deformation under ten main working conditions. Then it confirmed the weakness positions of the structure, and checked the crankshaft from stiffness, static strength and fatigue strength.(4) Flexible multibody system dynamics model of the crankshaft was carried out under all working gears and dynamic loads of one single cycle were extracted. Fatigue load spectrums of cranks and crank throws were compiled according to the least common multiple of integers combined with working performance of fracturing pump gears. Material fatigue characteristics was fitted on the basis of P-S-N. Correspond fatigue load spectrums of cranks and crank throws to the load response data in unit by applying FE-SAFE. Then, Fatigue life was calculated after establishing crankshaft model of fatigue life.(5) Related impact factors of dangerous artifacts were obtained from position of the maximum stress and low fatigue life. The crankshaft structure was optimized by means the method of genetic algorithm and co-simulation of Creo and AWE. After optimization, crankshaft maximum stress decreased by 14.5% and fatigue life increased by 22.5%.