The Erosion Analysis And Improved Design Of High Pressure Fluid Control Components

In recent years, with fewer and fewer resources of oil reserves, the difficulty of exploitation is increasing. During the fracturing process, it often encounters some quality problems, such as the movable elbow crack or burst caused by erosion damage. The main reason is that the strength and impact toughness of the product is not enough. Therefore, this paper is aimed at the problems in using presently of the high pressure fluid components, conducts the erosion analysis and improved design of the representative movable elbow.This paper summarizes several more convincing erosion theories at present, and analyzes their advantages and disadvantages and the scope of application. Combining with the actual working conditions of fracturing manifold, establish the erosion mechanism of the movable elbow eroded by the liquid-solid two-phase flow. Sum up the main influence factors of the elbow erosion rate, can be divided into four areas:(1) Particle properties:include particle density, shape factor, size, fragmentation,etc.; (2) The factors of target:include material composition, mechanical properties and organizational structure, etc.; (3)The factors of fluid:include velocity, particle mass flow, viscosity,etc; (4) Environmental factors:include the temperature, pressure and the properties of the medium,etc. Besides, introduce the influence of the various factors on the erosion in detail.This paper is based on the characteristics of the eroded high pressure movable elbow, establishes a CFD mathematical model of the liquid-solid two-phase flow, including basic control equations, turbulence model, discrete phase model and erosion calculation model. The basic control equations include three conservation equation, that is mass, momentum and energy conservation equations; The turbulence model which is frequently used in FLUENT software mainly includes two categories:k-ε model and k-ε model. According to the characteristics and the scope of application of the turbulence model, the erosion analysis of the high pressure movable elbow this paper studies is the liquid-solid two-phase flow, belongs to the turbulent flow field, so it mainly uses the standard k-ε model and conducts the related processing.In this paper, the erosion analysis of the movable elbow belongs to the turbulent flow containing a small amount of particles, so it uses the discrete phase model. Discrete phase model can track particle directly and can analyze the force between the particles, as well as the interaction between continuous phase and discrete phase. The erosion model of this paper is the one offered by FLUENT software. The theory is that the erosion rate is related to the materials, mass flow rate of particles, impact angle and impact velocity.This paper analyses the erosion effect of fracturing fluid on the elbow, and the influence of various factors on the erosion rule of the movable elbow by means of numerical simulation. It analyzes respectively from the angle of the elbow, flow velocity, mass flow rate of particles, impact angle, particle diameter, particle density, R/D ratio, fluid viscosity and particle shape factor and so on. Obtain the following conclusions:the inner wall of the outer arc of the elbow is the most serious erosion area; With the angle of the elbow increasing gradually, the maximum erosion rate decreases gradually and the erosion area develops for the direction of export; Under a certain flow rate, the maximum erosion rate is near 65°～75°, it is consistent with the conclusions of existing literature; With the flow velocity increasing, the maximum erosion rate of the elbow increases exponentially, according with the relationship: ε= K·vn.With the particle size and particle density increasing, the maximum erosion rate of the elbow increases gradually. With the R/D ratio and the liquid viscosity increasing, it is reduced; The particle shape factor also has effect on the erosion rate, the smaller it is, that is the more sharpen the particle is, the greater the erosion rate.Based on the results of erosion analysis and the failure modes of the elbow appearing in the use, the structure of wall thickness of the elbow and raceway position are improved.(1)The improvement of wall thickness:the wall thickness design methods of the elbow of GB 50253-2003 oil pipeline standard and AME B31.1-2004 pressure pipe standard are compared, according to the hoop stress distribution shows that the design formula of ASME B31.1-2004 is more reasonable. Finally, the wall thickness of the elbow changes from the Equal cross section to the unequal cross section. Under the condition of meeting the force of the inner wall, increase the outer wall thickness appropriately, thereby increasing the service life of the elbow;The improvement of raceway position:based on the regular equal-diameter straight raceway structure, design three structures, namely improved two steps unequal diameter raceway structure, improved two steps equal raceway structure, improved three steps unequal diameter raceway structure. And conduct the stress analysis for these four different structures through the ANSYS software. The analysis results show that:the stress situation of improved three steps unequal diameter raceway structure is best, it improves the stress state of connecting parts, the maximum stress is reduced by 33% compared with the conventional structure, thereby increasing the strength of the movable elbow.Through CFD numerical simulation, this paper analyzes the erosion wear mechanisms of the movable elbow under different fracturing conditions, the research results for enriching erosion mechanisms, understanding the law of material erosion, improving manifold safe operating conditions, improving equipment security and reliability, and guiding fracturing process have great theoretical and engineering significance.In addition, according to the erosion analysis of high-pressure fluid control components, and then improve the structure of movable elbow, improve the force situation, increase the strength of the movable elbow substantially, so as to extend its service life.