Marine Crane Slewing Bearing Inspections

We are specialists in crane slewing bearings, carrying out detailed slewing bearing assessments during general crane check-ups and overload tests and as a standalone slewing bearing inspection service. We also provide new slewing bearings at competitive prices and oversee crane slewing bearing change-outs on a turn-key basis.

Slewing bearing assessments in the marine sector

Classification organisations require a crane’s slewing bearings to be assessed for wear every year. During these inspections, the bearing clearance is measured, grease is taken for a ferrography analysis and, in the case of Class ABS, that slewing bearing bolts are NDT tested. Without accurate slewing bearing inspections, the classification may not be completed, and more wear may have occurred than the tests revealed.

This process is commonly but inaccurately called a rocking test. The rocking test methodology is irrelevant in the marine sector as ship cranes do not have a counterweight so cannot rock. This means the measurements acquired show only the slewing bolts’ elongation, reflecting the difference in the forward tilting moment of the boom high versus boom low position. These results can be highly misleading and do not indicate the bearing’s condition and pass on these artificially low values as the actual bearing axial clearance.

The depression test method is also adopted across the merchant shipping industry. This can be problematic because there are no base values and/or no machined reference surfaces to take the measurements. 

About Alatas class-approved slewing bearing tests 

Applying over 30 years of crane engineering experience, we developed our own class approved slewing bearing assessment procedure. Based on the rotation method, our slewing bearing inspection ensures accurate measurements and safety assurance. Our experienced engineers perform the tests for precise and repeatable readings crane owners can rely on.

Our engineers carry out the following measurements and assessments within a general inspection and overload test scope.

  • Axial clearance measurement via rotation method
  • Taking grease samples for ferrography analysis
  • Visual examination of the slewing bearing, grease lines and state of greasing
  • Assessment of slewing gear rim and pinion condition
  • Bearing noise assessment
  • Ping test of slewing ring bolts
  • Taking back-lash clearance readings of slewing pinion
  • Assessment of the crane’s past utilisation, age and operation hours
  • Crane motion checks, max slewing speeds, ramping up and down adjustments, brake timings

Based on the engineer’s findings, a bearing condition report will be submitted by our office. Take a look at a sample report below.

Marine crane slewing bearing inspections


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