Identifying potential issues before they escalate into fully developed problems offers obvious benefits in all industries, from manufacturing to sea-based commercial shipping. Preventive measures, like planned diagnostic programs and condition monitoring, help maintenance engineers identify areas of concern before they result in unplanned downtime, costly maintenance, hazardous conditions and loss of revenue. As technology has advanced, the ability to apply specialty devices and use data to understand the granular details of an operation’s systems and equipment has become invaluable. Systems can be scrutinized for areas of concern not visible to an operator and fixes can be applied to avoid catastrophic failures. In all, these measures can reduce maintenance expense, maximize productivity and profits, and assure safe working conditions.
This blog presents a case study detailing how Gram Car Carriers employed an effective online condition monitoring system based on Parker Acoustic Emission (AE) technology to identify the cause of premature bearing failure and prevent future problems.
Gram Car Carriers is a specialized supplier of vessels to the world’s major sea-based vehicle transportation companies. Their unique fleet, includes four Pure Car Carrier Roll-On/Roll-Off vessels. Each of these vessels has a Gross Tonnage of over 20,000 tons and the ability to carry 2000 vehicles. These vessels are each powered by a pair of 6-cylinder medium speed diesel engines. The propulsion shaft is driven through a RENK gearbox, which also drives the main ship’s alternator via a PTO shaft. The vessels were built in 2009 and 2010.
Three of the vessels suffered alternator-specific bearing failures in the first year of operation. While the vessels have a pair of auxiliary generators, these are not able to supply the power required to operate the bow thruster. This lack of power resulted in the cost of hiring additional tugs to maneuver the vessels in port. This was a serious consequence of the bearing failures. The total costs of the additional tugs ran to six figures. The bearings were replaced and ran without incident until another failure in 2015.
At this point, Gram Car Carriers decided to install on-line condition monitoring on the alternator bearings and the gearbox PTO shaft output bearings. The Parker Sigma Bearing Monitor was fitted on the four vessels. This product is based on Parker's Acoustic Emission (AE) technology, and was chosen over more traditional vibration monitoring as it provides a cost-effective solution and is simple to use. It involves the detection of high-frequency structure-borne sound generated by friction and impacts generated by operating machinery, as its condition deteriorates. It was immediately apparent that there was a problem with the alternator bearings on one of the vessels; the “City of Oslo”: The bearings were found to be seriously damaged.The system was used to allow the operator to manage the replacement of the bearings so that there was no impact on the ship’s schedule.
The Sigma Bearing Monitor continued to indicate that there was a problem with the alternator, despite the fact that new bearings had been fitted. This indicated that the mechanism, which had caused the problem, was still present and, left un-checked, would begin to damage the new bearings. The diagnostic output showed that there was a single impact with every revolution of the shaft — a characteristic of misalignment / out of balance.
A specialist maintenance company was contracted to carry out the remedial work and confirmed that the system was out of balance and misaligned. After adjustments were made, the readings from the Sigma Bearing Monitor indicated that the bearings were running smoothly. The bearings have continued to run without issue for the last 12 months.
The Sigma Bearing Monitor allowed the operators to:
Identify that there was a serious problem with the alternator bearings.
Track any further degradation and manage the timing of the bearing replacement.
Detect that the installation of new bearings had not solved the problem.
Diagnose that the underlying problem was due to misalignment and out of balance.
Confirm that realignment and balancing had cured the problem.
Confirm the smooth running of these bearings over the next 12 months.
The Sigma Bearing Monitor is a unique, highly sensitive hand-held instrument, providing maintenance engineers with an easy-to-operate, simple to use, and quick method of analyzing bearing condition and lubrication state. The monitor can be used to detect when the bearings are beginning to run in a distressed state, long before any serious damage occurs. A slow increase in the “Distress” reading over several months usually indicates that the bearing should be re-greased. Re-greasing the bearing produced an immediate drop in “Distress” readings to normal levels. A temporary increase in “Distress” usually indicates that the vessel’s operating conditions are putting the alternator bearings under stress.
Chief engineers at Gram Car Carriers are using the systems to identify undesirable operating conditions and avoid them where possible. To date they have identified:
- Tight maneuvering in shallow water.
- Running at particular propeller pitch settings.
- Running at particular engine loads.
- Running on one engine only.
They have also established that heavy sea conditions are not responsible for damage to the alternator bearings.
This application illustrates how the Sigma Bearing Monitor can be used to detect damaged bearings and manage the remedial work required. The system is now being used to detect situations that will lead to bearing damage and potential mechanical failure. Early detection will minimise the time that the bearings spend in a distressed state, prolonging their life.
Acoustic emission technology can be applied to a wide range of bearings and gears across all industries. Parker Hannifin offers a range of products including both portable instruments and permanently installed systems. The commercial motivation to employ condition monitoring depends on the application. Key drivers include:
- Health and safety - catastrophic failure can be a danger to employees and the public.
- Secondary damage - bearing failure can lead to expensive secondary damage.
- Machine downtime - the financial consequences of this can be significant. It can take many forms; from a ship unable to sail to an inoperable production line.
- Reduction in spare parts inventory.
This blog was contributed by Neil Randall, technical specialist, Parker Hydraulic Filtration Division EMEA.