Optical Fiber Grating Strain Gauge Technology Research On Monitoring Strain Of High Temperature Pressure Pipes

High temperature pressure pipes were widely used in the chemical, oil companies and power plants, but the pipe burst incidents occurred from time to time, which had caused some damages on people’s lives and property. Extensive research data indicate that if the real-time surface strain of high temperature pressure pipes is monitored, the pipe incidents will not be occurred. Thus, based on the study of its stress distribution, it can make warnings to the pipe explosion with a strain monitoring device and remind enterprise of changing pipes in time. It also has very important meaning to ensure the safe operation of pipes.In this paper, based on model of high temperature pipes stress and strain, it makes the stress distribution and strain condition analysis of high temperature pipes typical parts of running by the finite element method. The analysis shows that the stress and strain of the straight pipe section is concentrated on its outer surface; the stress and strain of the bend pipe section is concentrated on its inner arc District; the stress and strain of the tee pipe section is concentrated on its joint external surface.Based on the analysis above, two two-dimensional FBG(Fiber Bragg Grating)strain gauge structures which consists of three FBGs, a one-dimensional H type FBG strain gauge structure and a diamond strain FBG sensor are designed and fabricated because of their sensing properties and heat resistance characteristics. The strain gauges can be used for the real-time surface strain monitoring of high temperature pressure pipes, providing real-time data for the life evaluation model. The problem of strain and temperature cross-sensitivity, the transverse effect of the fiber Bragg grating, strain gage structures design, selecting the appropriate materials, the study of strain transfer, and bonding technologies are the main research work. Finally, the experimental system is designed and built for the determination of four kinds of fiber grating strain structures, and the measurement results and analysis are given.The test results show that:the strain gauge has a feature of high temperature resistance, temperature compensation and two-dimensional strain measurement. And, the sensing ranges of temperature is0～300℃. Also, in the strain aspects, the strain gauge "H" type of hysteresis error, repeatability error, nonlinear error and comprehensive error are0.71%,0.78%,0.01%and1.36%; In the temperature aspects,"H" type temperature strain gauge of the hysteresis error, repeatability error, nonlinear error and comprehensive error are0.32%,0.96%,0.36%and1.83%; Compressive strain sensitive coefficient, tensile strain sensitivity coefficient and temperature sensitive coefficient are1.051pm/με,0.5401pm/με and0.02521nm/℃; Strain resolution and temperature resolution are9με and0.4℃. In the strain aspects, the strain gauge "T" type of hysteresis error, repeatability error, nonlinear error and comprehensive error are0.31%,0.59%,0.87%and0.68%; In the temperature aspects,"H" type temperature strain gauge of the hysteresis error, repeatability error, nonlinear error and comprehensive error are0.22%,0.21%,0.24%and0.37%; Compressive strain sensitive coefficient, tensile strain sensitivity coefficient and temperature sensitive coefficient are1.051pm/με,1.04pm/με and0.0213nm/℃; Strain resolution and temperature resolution are9με and0.5℃. In the strain aspects, the one-dimensional H type FBG strain gauge of hysteresis error, repeatability error, nonlinear error and comprehensive error are1.7%,1.3%,0.05%and2.14%; In the temperature aspects, the hysteresis error, its repeatability error, nonlinear error and comprehensive error are0.72%,1.5%,2.0%and2.6%; Compressive strain sensitive coefficient, tensile strain sensitivity coefficient and temperature sensitive coefficient are0.9000pm/με,0.8796pm/με and0.0223nm/℃; Strain resolution and temperature resolution are11με and0.45℃. In the temperature aspects, the diamond strain FBG sensor of hysteresis error, repeatability error, nonlinear error and comprehensive error are0.94%,0.52%,0.23%and1.10%; its temperature sensitive coefficient is0.0128nm/℃.