Failure Analysis And Improvement Of Throttle Throttle Valve Spool

With the development of West-East National Gas Transmission Project, as the vanguard of this great energy engineering and supply project, a large domestic gas field is taking the major responsibility in the national economy and security. In the process of gas field exploitation, a special device-the throttle valve (commonly known as the "choke") is used on the oilfield to balance between the pressure of the gas in bottom hole and the pressure allowed for the gas conveyed in the pipe before transiting to treatment plants. However, the throttle valve main accessories carbide erosion wears due to the huge difference between the high pressure of the underground gas and the allowed pressure in the transit pipe has not only resulted more and more frequent efficiency loss, but also has placed serious impact on the gas field production safety requirements. Moreover, the operational and maintenance cost has greatly increased from the frequent replacement of the throttle valve carbide. Thus, the gas analysis research to the throttle valve erosion failure of cemented carbide has become particularly important to ensure the stability of the gas field production and to reduce the operational and maintenance cost. This paper studies hard alloy erosion morphology characteristics and erosion mechanism, based on which, improved technology is proposed to improve erosion resistance of the carbide and inhibit oxidation.Failure analysis theory and method is applied in this paper, on the basis of analyzing the working condition of the field environment, the erosion wear samples for failure analysis, using the scanning electron microscope (SEM) to observe and analyze the cemented carbide surface erosion morphology; using EDS spectrometer, combined with the failure surface elemental composition parts of the scanning electron microscope; and using X-ray diffraction to analyze the surface phase. Through the above three methods of analysis to explore the throttle carbide surface failure forms and characteristics of erosion types and reasons, the failure mechanism is concluded.According to the erosion failure analysis, it can be concluded that the natural gas in the process of cemented carbide in the throttle material erosion wears result from three ways: fatigue crack, scour, and oxidation reaction. For gas erosion failure mechanism of cemented carbide, surface coating is used to speed up the cemented carbide surface erosion resistance and inhibiting oxidation phenomenon. According to the physical and mechanical properties of different kinds of coating materials and matrix matching analysis of the research, TiN coating material is selected for field working condition. TiN coating on the PVD, PCVD and CVD technology deposition on organization structure and the physical and mechanical properties test, using X-ray diffraction phase analysis of coating surface and crystal preferred orientation, using a scanning electron microscope observation of surface morphology and surface composition spectrometer analysis, Use the digital micro hardness tester was carried out on the coating hardness measurement. According to the load-indentation depth values calculated coating elastic modulus, via the MFT-4000type multifunctional material surface performance tester on coating surface scratch is used to measure film-base bonding strength.Through erosion wear test of coating, it revealed that two kinds of different coating on matrix erosion wear characteristics of sedimentary process. It also revealed the coating adhesion strength, hardness and elastic modulus of the effect of comprehensive hedge the corrosion and wear properties, and the influence of the matrix hardness hedge erosion wear.