Acoustic Emission-Based Condition Monitoring and Remaining Useful Life Prediction of Hydraulic Cylinder Rod Seals

Jørgen F Pedersen,Leo W Caspers,Thomas J J Meyer,Vignesh V Shanbhag,Rune Schlanbusch

doi:10.3390/s21186012

Abstract

The foremost reason for unscheduled maintenance of hydraulic cylinders in industry is caused by wear of the hydraulic seals. Therefore, condition monitoring and subsequent estimation of remaining useful life (RUL) methods are highly sought after by the maintenance professionals. This study aimed at investigating the use of acoustic emission (AE) sensors to identify the early stages of external leakage initiation in hydraulic cylinders through run to failure studies (RTF) in a test rig. In this study, the impact of sensor location and rod speeds on the AE signal were investigated using both time- and frequency-based features. Furthermore, a frequency domain analysis was conducted to investigate the power spectral density (PSD) of the AE signal. An accelerated leakage initiation process was performed by creating longitudinal scratches on the piston rod. In addition, the effect on the AE signal from pausing the test rig for a prolonged duration during the RTF tests was investigated. From the extracted features of the AE signal, the root mean square (RMS) feature was observed to be a potent condition indicator (CI) to understand the leakage initiation. In this study, the AE signal showed a large drop in the RMS value caused by the pause in the RTF test operations. However, the RMS value at leakage initiation is seen to be a promising CI because it appears to be linearly scalable to operational conditions such as pressure and speed, with good accuracy, for predicting the leakage threshold.

Highlights

Hydraulic cylinders are linear actuators that exert a linear actuating force with precise positioning and are used in a multitude of industry applications, such as bulk loading and handling systems, oil drilling equipment, compensating systems, and wireline tensioning systems
A trend clearly seen in the root mean square (RMS) feature for all run to failure studies (RTF) tests was the initial drop in RMS levels, most notably seen in the RMS feature for all RTF tests was the initial drop in RMS levels, most notably seen in the results from test 1
This study investigated the relationship between acoustic emission (AE) features and the initiation of external fluid leakage due to seal wear in a hydraulic test rig

Summary

Introduction

Hydraulic cylinders are linear actuators that exert a linear actuating force with precise positioning and are used in a multitude of industry applications, such as bulk loading and handling systems, oil drilling equipment, compensating systems, and wireline tensioning systems. To contain the pressurized fluid inside the cylinder, a piston rod sealing system is used. Fluid leakage occurs in hydraulic cylinders because, over time, the piston rod seals lose their required sealing effect due to material degradation and mechanical wear processes. Seal wear occurs due to contaminants such as abrasive particles that are present in the fluid, excessive loads or pressures, or nonconcentric rod and cylinder bores [1]. Because the seals are concealed within the system, the inspection of the seals cannot be made without at least partial disassembly of the cylinder [2,3]. For a more practical solution to monitor the health of seals at regular time intervals, a condition monitoring (CM) strategy is needed

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