| The pressure vessel and pipelines applied in petroleum, chemical engineering, electric power always work under high temperature for long period so that the unrecovered deformation is unavoidable. To guarantee the security of devices, deformation monitoring is the most direct and reliable method. In this thesis, a sensing device that can monitor high temperature deformation for long term is designed and its performance is studied. The research content and achievements are given in detail as follows:According to the characteristics of high temperature deformation and installation requirements, two types of sensing device for long term monitoring of high temperature deformation are designed:shoulders type and local deformation monitoring type. The precision of the sensing devices are tested and verified by the room temperature experiment, in which the value from sensing device are compared with reference sensors.The deformation of pipe is extremely small. To improve the resolution of the sensing device, the idea of the amplification of the deformation is proposed. Take the structure of sensing device and characteristics of deformation, the introduction of micro-displacement amplifier is a potential way. Among the existing three kinds of amplifiers, the bridge-type amplifier possesses the advantages of compact size, linear output and high amplification ratio. Accordingly, a bridge-type amplifier is designed for the resolution improvement of sensing device. The structure applied the circular flexure hinge as the elastic element for its large compliance and high precision. The design formula of amplification ratio of the structure is analyzed by both geometrical relationship and elastic analysis, and the calculation accuracy depends on the computational accuracy of flexure hinges’stiffness.The accuracies of various circular flexure hinge equations(PW(full), PW(Simp), WZ, Lobontiu, Tseytlin and Smith) are analyzed using3-D FEA(Finite Element Analysis) within2<b/t<12,0.1<t/R<0.6. The results show that the analysis results are not only related to t/R but also b/t, so the performance of flexure hinge can’t be modeled by2-D element or a3-D one that has a certain thickness. The results attained by PW(full)、WZ and Lobontiu design formulas are same. According to the error analysis results, the rotational stiffness and x-direction translational stiffness of the flexure hinges in amplifier are calculated by Smith and PW(simp) design formulas respectively. The calculated stiffness is substituted into the amplification ratio design formula of amplifier. The calculated ratio is compared with FEA results which are taken as the benchmark. The maximum error is less than2%. The results illustrates that the selected design formulas of flexure hinges are right and the deducted amplification ratio design formula is accurate.To extend the application range of the designed displacement amplifier, the large deformation of the structure is analyzed. The amplifier is first simplified by PRBM(Pseudo Rigid Body Model), and then analyzed using MPE(Minimum Potential Energy). The rotational stiffness of the flexure hinge is not a constant when the deflection angle exceeds a certain value. The ANSYS is utilized to analyze the relationship between the deflection angle and rotational stiffness of flexure hinge. The MPE are applied to analyze six designed amplifiers with different value of l and b, in which the geometrical dimensions of flexure hinge are same. The results by MPE are compared with that of ANSYS. Results by two methods agree well with each other. Take the ANSYS as the benchmark, the maximum error of MPE method is less than6%, which proves the results by MPE method. The following experiment verifies the aforementioned results. At last, two sensing devices are installed on a calibrator and compared. One incorporates the designed amplifier, while the other doesn’t. The results show that designed amplifier can improve the resolution of the sensing device by the times of the value of the amplification ratio.To verify the precision and long term reliability of designed sensing device under high temperature, the sensing devices are installed on the high temperature pipelines in a thermal power plant. The measured results are compared with results by FEA and a commercial available high temperature strain gages. The agreement with FEA results and the strain gage proves the precision of sensing devices under high temperature and the following6000-hours long-term test shows the long-term reliability of sensing devices. The residual lives are attained through Monkman-Grant relationship according to the strain rates measured by devices. |
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