Crown-mounted compensator bearing damage monitored for months offshore

Bearing damage on the fast-line side of a crown block sheave at an offshore drilling rig was monitored for months before replacement. Condition monitoring solutions for marine and offshore, using patented high-definition technology and Ex-approved equipment, provided adequate prewarning for planned maintenance.

Application and monitoring setup

In offshore drilling environments, the drilling system is installed in the derrick, with the crown-mounted compensator located at the top. The sheaves operate at rotational speeds of approximately 5 to 180 rpm, while a wire from the drawwork runs between the upper sheaves and those in the travelling block, governing the vertical movement of the top drive.

Monitoring was performed using DuoTech accelerometers on each side of the crown-mounted compensator, connected to an Intellinova Parallel EN Ex online system, intended for use in potentially explosive atmospheres. Rotational speed was derived from the drawwork RPM and calculated using the sheave diameter together with the wire speed between the drawwork and the sheaves.

Results and benefits

Following system installation, early indications of outer race bearing damage were identified in the FFT, with a clear correlation to BPFO. All enabled technologies exhibited the same FFT characteristics, and the Colored Spectrum Overview visualised the progression of the damage.

Analysis using the Decision Support System revealed a gradual increase in the health score trend for BPFO with HD ENV4. Because the bearing condition could be tracked for several months before replacement, planned maintenance was possible, and the risk of unexpected downtime was reduced. After replacement, the outer race bearing damage was visually confirmed.