Root cause analysis of hydraulic oil leakage in high-pressure stressing machines

Hydraulic oil leakage in high-pressure systems reduces equipment reliability and may also indicate degradation of technical and procedural controls during operation. This study investigates the root causes of recurring hydraulic oil leakage in high-pressure stressing machines using a 6 M-based root cause analysis (RCA) framework covering man, machine, method, material, measurement, and environment. The analysis was supported by field observations, maintenance records, and technical interviews. The results show that leakage recurrence is associated with interacting factors, including seal condition and material suitability, rod and housing surface deterioration, inconsistent installation and maintenance practices, hydraulic fluid contamination, pressure instability, and limited condition monitoring. These findings indicate that leakage should not be treated solely as an isolated component failure, but as a systemic problem involving cross-domain interactions. Based on the RCA results, the study proposes practical control improvements through reinforcement of the seal–surface interface, standardization of work procedures, better contamination control, and improved monitoring for early leak detection. This field case study demonstrates the value of RCA in supporting maintenance decisions and reducing recurrence risk in high-pressure hydraulic operations.