Diagnostics of seal and rod degradation in hydraulic cylinders using acoustic emissions

Abstract

External leakage from hydraulic cylinders is of a major concern for the offshore oil and gas industry. This occurs mainly as a result of physical damage to the piston rod or due to degradation of the piston rod seals. Numerous studies have been conducted to diagnose leakage from hydraulic cylinders due to seal failure using fluid, pressure, accelerometer or acoustic emission-based condition monitoring techniques. However, very few attempts have been made to diagnose multiple faults in hydraulic cylinders at the same time. Therefore, in this study, acoustic emission-based condition monitoring technique is used to detect and separate acoustic emission features due to different faults that are observed in hydraulic cylinders. An experimental study was performed on a test rig using water glycol as hydraulic fluid. Experiments were performed with different combinations of seals (unworn, semi worn and worn seals), and piston rods (unworn and worn). Acoustic emission features such as root mean square, peak, mean, kurtosis, skewness, mean frequency, median frequency and bandpower were used to identify seal and rod conditions. By using acoustic emission median frequency and mean frequency features it was possible to detect and separate leakage, and seal and rod degradation in the test rig over a large range of hydraulic working pressures. This study indicates that acoustic emission monitoring can be a strong basis for future research to identify and segregate other types of faults that are observed in hydraulic cylinders.