INTERFACE PRESSURE FOR CONTACTING SURFACES

Abstract

Gasketed flange joints in pipelines experience leaks which can be costly or even dangerous. The ability to measure and monitor the pressure distribution between the mating flanges would contribute towards a better understanding of leakages and hence improve sealing. The objective of this project is to develop a sensing system capable of measuring and monitoring the pressure distribution between contacting bodies such as mating flanges. Several types of sensing methods were looked into and these included two piezoresistive and three optical fiber sensors. The first piezoresistive sensor, called the Tekscan force sensor, is based on a semi-conductive ink whose resistance changes with applied pressure. The second piezoresistive sensor is based on the semiconductor Aluminium Gallium Arsenide or AIGaAs for short. The optical fiber sensors included a microbend sensor, a Mach-Zehnder interferometric sensor and a polarimetric fiber sensor. Single-mode and polarization-maintaining optical fibers which were embedded with and without their plastic coatings were used in the construction of the various configurations of the interferometric and polarimetric sensors. The sensors were subjected to several pressure and temperature tests to determine their suitability for the intended application. Sensor characteristics such as linearity, repeatability and hysterisis during unloading were studied. In addition, the responses of the embedded optical fibers in the interferometric and polarimetric sensor configurations were calculated using theoretical models relating strain or stress in the fibers to the phase change of light (Toh et al, 1996). The embedded fiber in the Mach-Zehnder configuration showed good linearity and repeatability and little hysterisis during unloading (Cheng et al, 1996a, 1996b ). The Tekscan and fiber polarimetric sensor also showed good linearity with increasing load but experienced large hysterisis during unloading. The sensors' output also changed with time when a constant load was applied. The response of the fiber polarimetric sensor to load was found to vary with the orientation of the plane-polarized light launched into it (Asundi et al, 1996). Its sensitivity also depended on the type of material in which the fiber is embedded. The above sensor configurations should be developed further and their problems overcome so that they could be used to measure contact pressure distribution more accurately and effectively.