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Key words: steel pipe hydraulic pressure tester; hydraulic system; AMESim; modeling and simulation Introduction Steel tubes for various purposes, such as low and medium pressure boiler tubes, high pressure boiler tubes, ship tubes, chemical tubes, oil well tubes and nuclear engineering The use of pipes, etc. are generally under the harsh working conditions of certain temperatures and pressures. Therefore, in order to avoid the dangers of using steel pipes as far as possible, pressure tests must be carried out for the full-scale range of the manufactured steel pipes. The steel pipe pressure testing machine is Steel pipe for pressure testing of mechanical equipment. The process flow of the steel pipe hydrostatic testing machine is: First, the steel pipe is transported to the pressure testing station by a walking beam transport device. The clamp clamps the steel pipe and locates the pressure testing center. The water filling head and exhaust head successively withstand the steel pipe and are The pre-sealed pressure causes the sealing ring to clamp the steel pipe, the filling valve and the exhaust valve open, the emulsion enters the test steel pipe, and the gas in the pipe is exhausted by the exhaust valve. After the gas in the steel pipe is completely discharged, the filling valve and the row are exhausted. The gas valve is closed, the supercharger starts to pressurize the emulsion in the steel pipe, and after the set pressure is reached, the pressure is maintained. After the pressure is maintained for a set time, the pressure relief begins, and the pressure release process and the pressurization process are reversed. [1 ,2]. It can be seen from the process flow that the entire pressure test process is mainly performed by the hydraulic system to complete the pressure increase. It has very important significance for the stability and safety of the entire steel tube pressure test process, so the hydraulic system is modeled and simulated and analyzed. Can deepen the understanding of the entire system process, but also laid a solid theoretical analysis basis for further fault diagnosis, forecasting and other hydraulic pressure testing machine.
Because the hydraulic pressure tester of the steel pipe is equipped with a plurality of hydraulic components, the pressure and flow rate of the hydraulic oil in the high pressure system change very violently, and as the research progresses, the model is expected to have good expandability, so the traditional matlab modeling method is difficult to establish. Accurate dynamic mathematical model. AMESim (English full name: Advanced Modeling Environment for Simulation of engineering systems, the advanced modeling and simulation environment for engineering systems) is a hydraulic/mechanical system modeling, simulation and dynamics based on power bond diagram introduced by Imagine in France in 1995. Analysis software, a large number of documents show that: AMESim can effectively perform modeling and simulation research on various complex engineering machinery hydraulic systems [3-6]. In this paper, AMESim is used to simulate and analyze the main hydraulic system of the steel pipe hydrostatic testing machine of No. 3 line in a steel mill. The satisfactory results are obtained, and the understanding and understanding of its working mechanism are deepened, and the dynamic process of the system is realized. Exploring provides preconditions and data support for further fault diagnosis and forecast research of hydrostatic testing machines.
1 Hydraulic Test System of Steel Pipe Hydraulic Pressure Tester The principle of the hydraulic pressure tester is complex. The main structure of the tester is summarized in Fig. 1, in which various hydraulic components are made by Rexroth. 
The test pressure medium for the steel pipe hydrostatic testing machine is the emulsion. The theoretical basis for the test is to fill the test tube with the emulsion and then rely on the external force to compress the emulsion to increase the pressure [7] so as to achieve the purpose of pressure test. At present, the steel pipe hydraulic pressure tester generally adopts the method of adding oil (emulsion), and the pressure is increased by the high pressure booster. In the steel pipe pressure test, the pressure keeping curve is required to be stable and the efficiency is high. Therefore, the hydraulic system is required to be capable of rapid pressure increase and smooth pressure relief. In order to achieve the above requirements, the hydraulic system adopts the constant pressure source oil supply method. The constant pressure source is composed of a constant pressure variable displacement pump A4VSO constant pressure variable axial piston pump, an accumulator and an overflow valve.
The main hydraulic control system consists of three parts: booster-pressure-pressure relief control system, pressure balance regulation system, and pipe joint clamp pressure regulation system [8]. The former two use electro-hydraulic servo pressure closed-loop control. Using electro-hydraulic proportional open-loop control, these three parts of performance have a very important role in the operation of the entire system. For the pressurization side, the hydraulic oil is output to the electro-hydraulic servo valve by the hydraulic pump, and the flow of the hydraulic oil flowing into and out of the hydraulic cylinder is adjusted by controlling the valve opening of the electro-hydraulic servo valve, thereby adjusting the pressure of the emulsion in the steel pipe; On the balance side, the hydraulic pressure of the hydraulic cylinder rod follows the pressure of the pressurized side emulsion proportionally, so that the steel pipe will not move too much. At present, the clamp system of a steel mill adopts a fixed set pressure, and the entire system adopts pressure. control. The working principle diagram of the entire hydrostatic testing machine is shown in Figure 2. 
There are 4 working modes in AMESim: Sketch Mode, Submodel Mode, Parameter Mode and Run Mode [13]. Users can build system solutions in these 4 modes. Modify component submodels, set model parameters, and run simulations. The setting of the model parameters is particularly important. It has a very large impact on the system's results. The average user sets the parameters based on actual requirements or the actual system.
2.2 The establishment of the simulation model The hydraulic system is an important part of the hydraulic pressure tester of the steel pipe. Only with the help of the hydraulic energy, the pressure test of the steel pipe can be realized. Hydraulic pressure testing machine main hydraulic system is mainly composed of oil source system, booster system, balance system and clamp system. Since the oil supply of the hydrostatic testing machine is provided by a constant pressure variable displacement pump, the simplified model oil source system can be replaced by a constant pressure variable displacement pump and relief valve, and auxiliary components such as coolers and filters on the main oil line are also used. Can be omitted, according to the working principle shown in Figure 2 can be established as shown in Figure 3 simulation graphics. 
In AMESim, the same component icons can represent different component models, and some components do not exist in the existing model library. Therefore, when the model is built, different sub-models should be selected according to requirements or HCD sub-models that meet the requirements should be established. Because AMESim does not meet the needs of pressurized cylinders, steel tubes, shuttle valves, etc., it is necessary to establish component sub-models that meet the requirements based on the element mechanism and actual requirements. As shown in Fig. 3, the left side 1 represents the sub-model of the booster cylinder, which consists of a piston cylinder and a plunger cylinder. The mass in the cylinder represents the mass of the cylinder and the friction generated when the piston moves; 7 represents the steel tube. , can simulate the tiny turbulence of the steel pipe; 8 use the friction force to simulate the clamp force; 3, 4, 5, 6 represent the shuttle valve, because the existing shuttle valve in the software can't express the influence of the leak on the system, so in the system The use of AMESim can facilitate the establishment of the function of the super element. A shuttle valve sub-model is set up according to the model structure of the shuttle valve as shown in FIG. 4 , and the super element is represented by the shuttle valve element in the existing model library. The shuttle valve has two input ports and one output port, which is equivalent to a selector valve, and the output port is always connected with the input pressure port. However, since the valve core moves back and forth under pressure, there will always be wear. Therefore, when the submodel is established, the analog leakage module is added, as shown in Fig. 4 on both sides of the green mass. Suppose the input pressure in Fig. 4 is greater than 3 input pressure. When the shuttle valve is leaked, 1 fluid flows into the 3 ports through the leakage module. Although the 2 output port still communicates with the 1 input port, the pressure and flow rate are not exactly the same. In 1; vice versa. This simulates the working condition of the shuttle valve when the valve core is damaged, and can modify the size of the leak according to different needs, and simulates the working state when the damage degree of the shuttle valve valve core is different. 
The initial piston displacement, bore diameter, piston diameter, piston rod diameter and stroke length of the booster and balance cylinders are calculated and set according to relevant parameters in the field. The model of the electro-hydraulic servo valve adopts a three-position and four-fluid liquid proportional valve. The dynamic characteristic of the spool movement is a second-order oscillation. According to the test procedure of the hydrostatic testing machine, the desired pressure is set to pressurize-maintain pressure-discharge pressure, so that the working position of the electro-hydraulic servo valve is left position, center position, right position, and the servo valve of the pressure increase stage is working in the left position. The hydraulic oil pushes the piston of the booster cylinder up. Because of the area difference, the pressure of the emulsion in the piston cylinder is increased. When the system pressure is increased to the test pressure, the servo valve works in the middle position, and the system maintains pressure for a period of time. Time; When the dwell time is over, the system begins to depressurize, and the servo valve works in the right position. Under the action of gravity, the booster cylinder moves downwards to lower the system pressure and relieve pressure. The parameters used in the electro-hydraulic servo valve in this system are set according to Rexroth 4WSE3EE servo valve. The specific parameters are set in reference [15]. The setting of the steel pipe determines the setting of the test pressure. In this simulation system, the length, diameter and corresponding expected pressure curve of the steel pipe can be easily modified according to the test data in the field.
4 Simulation results In the operation mode, the simulation time can be selected according to the historical data of the field test. In this example, the diameter of the steel pipe is 73.02mm, the length is 9m, and the corresponding test pressure is 720bar. The actual hydraulic pressure tester works under the above conditions. The required time is about 16s, so here the simulation start time is set to 0s and the end time is 16s. Fig. 5 is a comparison of the simulated output test water pressure and the actual collected data. The dotted line indicates the emulsion pressure curve in the model output steel pipe, and the solid line is the actual pressure curve. It can be seen from the figure that the model output and the actual output are not much different. 
In the above model, not only the pressure curve but also the steel pipe displacement curve and the shuttle valve output pressure curve can be output. Among them, the steel pipe displacement curve corresponds to the balance cylinder displacement variable in the actual system. As shown in Fig. 6, it is a variable showing the state of the balance system of the hydrostatic testing machine. It has a certain range, forward 20 mm and negative 8 mm. The four shuttle valve output pressure curves correspond to the pressures of the four seal rings in the actual system, and the leakage coefficient in the shuttle valve submodel can be set to simulate the different degrees of leakage of the shuttle valve spool, facilitating the user to study the shuttle valve leakage. The impact of the system test process. FIG. 7 shows the output pressure curve of the shuttle valve 3 , under normal conditions, their output pressure is the same. 
The establishment of this model lays a theoretical foundation for the study of the dynamic performance of the system and the performance analysis and optimization of hydrostatic test equipment in the future, various control algorithm testing, fault diagnosis and prediction.
Modeling and Simulation of Main Hydraulic System of Steel Pipe Hydraulic Tester
Abstract : Taking the hydraulic system of hydraulic pressure tester of steel tube as the research object, the work flow of the hydraulic pressure tester and the working principle of the main hydraulic system are expounded. AMESim is selected as the software environment, and the main sub-model of the system based on AMESim is established and set up. The complete hydraulic pressure testing machine main hydraulic system model of the No. 3 line of a steel plant was set up with the main parameters in the model to realize the dynamic performance simulation of the hydraulic system. The simulation results show that the application of AMESim software can effectively simulate the main hydraulic system of the steel pipe hydraulic tester and obtain good results, which lays a solid foundation for further in-depth study. 5 Conclusions This paper adopts advanced hydraulic software AMESim to conduct modeling and simulation analysis of a steel pipe hydrostatic testing machine. The simulation results show that this model can effectively study the dynamic characteristics of the hydraulic system of steel pipe hydrostatic testing machine, and the error of simulation results is within the allowable range. The model can easily extract the data of each variable, providing data support for the study of the intrinsic characteristics of the system. Also, in this model, other hydraulic components can be easily added to further improve the model. In addition, AMESim provides interfaces with various other software, such as Matlab, Adams, etc., which can be easily combined with other software, which also provides the prerequisite for further research and analysis.
(Fig. 1 Composition of Steel Pipe Hydraulic Pressure Tester)
(Fig. 2 Schematic diagram of working principle of hydrostatic testing machine)
2 Establishment of simulation software and simulation model 2.1 Introduction of simulation software AMESim is a high-level modeling and simulation platform for engineering systems. The software contains many modules that are suitable for simulating dynamic characteristics [9]. They are fluid, liquid, gas, mechanical, control, Electromagnetic engineering systems provide a more comprehensive simulation environment [10,11]. AMESim is a modeling platform based on an intuitive graphical interface. It uses the easy-to-recognize standard ISO icon symbols and simple and intuitive multi-port block diagrams [12] to represent the various components in the system, thus freeing the user from tedious mathematical modeling. Focus on the design of the physical system itself. AMESim's existing application libraries include mechanical libraries, signal control libraries, hydraulic libraries (including pipeline models), hydraulic component design libraries (HCD), etc. Users can use existing models or create new submodels (superelements). It is convenient to establish complex systems and specific requirements of the system [11], and it is possible to modify the model and parameters to achieve simulation under various conditions, draw curves and analyze simulation results, and also output simulation results as files for other software. Or algorithm for further data analysis. (Fig. 3 Hydraulic Pressure Tester Main Hydraulic System Simulation Model, 1-Boost Cylinder, 2-Pressure Sensor, 3, 4, 5, 6- Hydraulic Pressure Tester's 4 Shuttle Valves, 7-Pipe, 8-Clamp ,9-balanced side hydraulic cylinder)
Because the clamp is set to a fixed force, the control of the entire hydraulic system is mainly composed of two parts, namely the left side of the booster system and the right side of the balance system, the principle of the booster system and the balance system are the same, are through the pressure The source inputs the desired test pressure so that the emulsion in the booster cylinder reaches the desired pressure and a hydrostatic test is achieved. Among them, the pressure sensor 2 outputs the emulsion pressure in the steel pipe, and then is the deviation signal of the closed-loop PID control after being compared with the expected pressure signals of the pressure increase side and the balance side. (Figure 4 shuttle valve submodel, 1, 3 input ports, 2 output ports)
3 parameter setting
After completing the system simulation platform setup (scheme mode) in AMESim, the sub-model (sub-model mode) and the setting of the model parameters (parameter mode) [14] are selected according to the requirements. In the whole simulation, not only the model is set up. The mathematical model of the structure plays a decisive role in the result, and the parameters of the submodel and the submodel have a very important effect on the result. In the simulation of this system, the model parameters debugging process takes a lot of time, such as pressurized cylinder and balance cylinder, electro-hydraulic servo valve on both sides, steel pipe and so on. (Figure 5 pressure output)