Condition monitoring of hydraulic cylinder seals using acoustic emissions

In recent years, there has been a growing concern for fluid spill from hydraulic cylinders in the offshore oil and gas industry. To diagnose the leakage from hydraulic cylinders, there have been attempts made in literature using fluid and pressure-based condition monitoring techniques. However, there have been limited attempts to monitor leakage from hydraulic cylinders using acoustic emissions. Therefore, in this paper, an attempt has been made to understand the fluid leakage in the hydraulic cylinder based on acoustic emissions. An experimental study was performed using a test rig (with a water-glycol as hydraulic fluid) which closely replicates the operation of a hydraulic cylinder. As piston rod seal failure is the foremost cause for leakage, experiments were performed using unworn, semi-worn, and worn piston rod seals. For each seal condition, experiments were performed for five strokes at pressure conditions of 10, 20, 30, and 40 bar. In this study, the continuous acoustic emission signal was observed for each hydraulic cylinder stroke. Acoustic emission data was analysed using different techniques such as time domain, frequency domain, and time-frequency technique. By using acoustic emission features such as root mean square (RMS), peak, skewness, median frequency, and mean frequency, it was possible to identify and separate non-leakage and leakage conditions in the test rig. By using AE bandpower and power spectral density features, it is also possible to identify the leakage due to semi-worn seal and worn seal in the test rig. This study lays a strong basis to develop a real-time monitoring technique based on acoustic emissions to monitor the health of piston rod seals used in the hydraulic cylinder in the offshore industry