Transcript
Stern Bearing DamageStern Bearing Damage
Mr. Geir Magne Bakken (M.Sc.)DNV Rotating Machinery Marindagen Gøteborg; 2007-03-22
DNV Rotating Machinery/GMB Slide 220 March 2007
Stern Tube Bearing Damage – The story!Stern Tube Bearing Damage – The story!
An oil tanker was rebuild
Earlier conversed from fixed pitch to controllable pitch
A tunnel thruster to be installed in the aft ship
After conversion The ship in service Stern bearing damage
DNV Rotating Machinery/GMB Slide 320 March 2007
The Ship’s PropulsionThe Ship’s PropulsionConventional direct propulsion; 19620 kW @ 91 rpmOriginally design with fixed pitch propellerShaft supported by two stern tube bearings & intermediate bearing
DNV Rotating Machinery/GMB Slide 420 March 2007
Troubleshooting CaseTroubleshooting Case
DNV was contacted by owner to assist the owner in the site investigation and to follow-up the repairing process
The vessel was build in 2001
The vessel had recently been rebuilt
Tunnel thruster installed in the aft ship
Bearing damage occurred after conversion
DNV was requested to identify the cause of the damage and recommend actions to be taken in order to rectify the problem
DNV Rotating Machinery/GMB Slide 520 March 2007
The Thruster Tunnel InstallationThe Thruster Tunnel Installation
DNV Rotating Machinery/GMB Slide 620 March 2007
Tunnel thruster installed in the aft hull structureExtensive welding work in the aft shipResidual stresses from the welding work deform the aft part of the hull
The conversion – Thruster installationThe conversion – Thruster installation
DNV Rotating Machinery/GMB Slide 720 March 2007
The Detection of the DamageThe Detection of the Damage
The Damage was detected due to leakage of oil from the aft sterntube of the vessel
DNV Rotating Machinery/GMB Slide 820 March 2007
On Site Investigation On Site Investigation
Flakes of white metal in way of the shaft sealing
DNV Rotating Machinery/GMB Slide 920 March 2007
Visual Inspection of the DamageVisual Inspection of the Damage
DNV Rotating Machinery/GMB Slide 1020 March 2007
Spalling of the Bearing MetalSpalling of the Bearing Metal
DNV Rotating Machinery/GMB Slide 1120 March 2007
Circumferential Crack in Bearing Metal Circumferential Crack in Bearing Metal
DNV Rotating Machinery/GMB Slide 1220 March 2007
Visual Inspection of the DamageVisual Inspection of the Damage
DNV Rotating Machinery/GMB Slide 1320 March 2007
Cause of the DamageCause of the DamageThe original alignment of the shaft
Stern bearing pressure; Actual 8.3 bar (criterion 8 bar)
Relative slope: Actual 0.33 mm/m (criterion 0.3 mm/m)
DNV Rotating Machinery/GMB Slide 1420 March 2007
Measurement of the Present AlignmentMeasurement of the Present Alignment
Laser
FlywheelStern Tube Int.Bearing
The measurements were carried out and the alignment was recalculated based on these laser measurements
DNV Rotating Machinery/GMB Slide 1520 March 2007
Cause of the DamageCause of the Damage
Calculated alignment
according to measurements
Initial calculated alignment
according to specification
DNV Rotating Machinery/GMB Slide 1620 March 2007
Shaft Deflection in Stern TubeShaft Deflection in Stern Tube
Static; zero pitch
Running (in operation)
Edge contact
Running MCR
DNV Rotating Machinery/GMB Slide 1720 March 2007
Max oil pressure in Stern BearingMax oil pressure in Stern BearingAlignment after conversion Stern bearing pressure:
Peak pressure
> 100 bar (at edge)(Projected pressure slightly above the 8.7
bar)
Stern bearing pressure:
Peak pressure
~ 40 bar (at edge)(Projected pressure slightly above the
8.3 bar)
Original alignment
DNV Rotating Machinery/GMB Slide 1820 March 2007
Cause of the DamageCause of the Damage
Misalignment caused by:
The original installation “Designed at the limit”
Conversion of the vessel
- Tunnel thruster installation without pull out the propeller shaft
- The alignment not checked after extensive welding work
DNV Rotating Machinery/GMB Slide 1920 March 2007
Suggested AlignmentSuggested AlignmentRestriction was not to change the main engine position
Stern bearing pressure:- Modified slope bore - Improved load distribution
Peak pressure < 30 bar
DNV Rotating Machinery/GMB Slide 2020 March 2007
Benefits to the CustomerBenefits to the CustomerSuggested repairs that solved the problem
Forward sterntube bearing lifted upwards
Aft sterntube bearing lifted upwards
Aft sterntube double-slope bored
Suggested repairs that minimized the time and cost for carrying out the repairs
Improved understanding of shaft alignment
Revised procedure for conversion of vessel
DNV Rotating Machinery/GMB Slide 2120 March 2007
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