Passive Wireless Method for Measuring the Preloads of Threaded Pipe Joints

Threaded pipe joints are widely used in engineering applications. However, vibration and shock loads during operation can cause preload reduction, potentially leading to issues such as leakage and fatigue failure. Hence, real-time preload monitoring is essential for threaded pipe joints. Generally, to measure preloads, strain gauges can be bonded to the outer surface of the nut, as it is sensitive to slight deformations caused by preload changes in threaded pipe joints. However, traditional strain-gauge-based preload measurement methods require either an embedded battery or an external wired power supply, along with cables for signal transmission, making them unsuitable for confined or inaccessible locations during practical applications. To address these shortcomings, the present study proposes a novel passive wireless method for measuring the preloads of threaded pipe joints. This method includes a power supply, a sensor, and reading modules. It also includes a direct-current filtering technique to mitigate the impact of electromagnetic interference on strain-gauge measurement accuracy. In addition, a temperature compensation model based on multiple linear regression is applied to reduce the sensitivity of preload measurements to temperature. A functional measurement device was subsequently built based on this method. Experimental results validated the greater accuracy and reliability of this method compared to those of other methods, demonstrating its strong potential for engineering applications.