Highly-loaded low-speed roller bearings are frequently used in equipment offshore e.g. slew bearings in crane, sheave bearings and FPSO turret bearings. Reducing maintenance costs, increasing productivity, ensuring safety of people and structural integrity and longevity assurance of equipment can be achieved by the condition monitoring of highly-loaded low-speed roller bearings.

Currently, very limited research is performed in the field of condition monitoring with acoustic emission (AE) monitoring for highly-loaded low-speed (<10 rpm) bearings with naturally developed damage. Acoustic emission monitoring has shown promising results in early stage and real time identification of defects according to literature. Furthermore, contamination of wear particles in lubricant shows an increase in AE activity according to literature.

In this research, the applicability of AE monitoring for damage assessment of highly-loaded low-speed roller bearings is investigated in a full scale duration test. Furthermore, the influence of contaminated lubricant with steel particles is investigated in the contamination test to study the feasibility of real-time detection of contaminated lubricant during operations and as a supporting technique for wear debris analysis in lubricant.

From the results, an increase in AE activity expressed in hit-rates is observed for a wide frequency band of 40 - 580 kHz during the duration test where the basic rating lifetime (L10) is consumed from 40% to 50%. Wear development in the bearing is observed during visual inspection and has been quantified with lubrication analysis.
A safety limit and a limit if the bearing is at risk for the AE activity has been defined with the results of the baseline and duration test. This research suggests that AE monitoring can be applied on highly-loaded low-speed bearings to assess the damage for representative operational conditions.

From the results of the lubricant contamination test, an increased AE activity with respect to higher lubricant contamination levels were observed. Furthermore, with a proper choice of the SNR-level, there is no masking effect of acoustic emission signals due to contaminated lubricant. The results of the contamination tests, indicates the possibility of detecting contaminated lubricant with AE monitoring.