Advanced maintenance technologies enable shipbuilders, ship operators and marine maintenance departments to improve rotating equipment reliability, modernize maintenance practices and reduce the time vessels spend in docking and port facilities.
These technologies are well-suited for the unique demands of marine environments, where spare parts and expert assistance are often miles away and failures are extremely costly. The challenges also include harsh conditions, tight quarters, hard-to-access machinery and oversized components, such as propellers and long-drive shafts.
Figure 1: Handheld condition-monitoring instruments, such as devices for detecting erosion in electric motors, can help spot problems early and improve the reliability of rotating machinery aboard ships. (Photo courtesy of SKF USA Inc.)
Installing Massive Components
The huge size of many marine components has spurred wider use of advanced installation methods, particularly oil injection. This technology efficiently mounts and dismounts large marine components, including propellers, couplings, gears and rudder assemblies.
Oil injection uses pressurized oil to drive large components onto shafts. The components are pressed onto shaft seatings via a hydraulic ring or nut. The newest oil injection systems typically feature built-in pressure gauges, oil reservoirs and high-pressure piping, producing maximum pressures in the range of 400 MPa.
Oil injection is more efficient for mounting large components than the main alternative, heat mounting. For example, a 50-ton propeller can be mounted in less than an hour using oil injection. The same propeller can be dismounted in less than 15 minutes. There are no special requirements for shaft machining or keyways.
New generation marine components, such as couplings, are often designed to accommodate oil injection mounting. One highly popular coupling, for example, comes equipped with a thin inner sleeve having a tapered outer diameter. The inner sleeve is positioned on the shaft. An outer sleeve with a matching tapered inner surface then fits over the inner sleeve. After oil is injected between the two sleeves, hydraulic pressure drives the outer sleeve up the inner sleeve's taper, forming a secure interference fit. The fit enables the couplings to transmit torque and axial load over the entire shaft circumference.
New coupling varieties that accommodate oil injection were recently introduced for marine shaft line applications. Here, they can potentially replace large flange couplings and eliminate the need for costly reinforcement sleeves.
Mounting Smaller Components
Shipbuilders and operators around the world often employ induction heating technology to mount small and medium size bearings and other components. Induction heating expands the inner rings of components, forming a tight fit when the components cool.
Many newer heaters are lightweight and portable, making them ideal for the limited storage space and tight quarters aboard ships. For example, an induction heater weighing only 10 pounds, one of the smallest available, heats bearings with bores up to 100 mm and weighing up to 11 pounds. Another, slightly larger device, can heat a 61.6-pound (28 kilogram) bearing in only 20 minutes.
The long coupled shafts employed in marine propulsion systems can be prone to misalignment, which increases wear on seals and often results in premature bearing or coupling failure. Shaft misalignment also causes increased friction and vibration, reducing efficiency and wasting energy.
Manual alignment methods using straightedges are still widely used, but they are steadily losing ground to advanced alignment technologies with highly accurate laser sighting. These instruments require no special training and can be easily mastered by marine maintenance technicians in shipyards and aboard vessels.
One advanced laser-equipped system, for example, consists of a hand-held control unit linked to dual measuring units, which are each capable of projecting laser lines and detecting those produced by the other unit. During alignment procedures, maintenance technicians can view realtime values on the control unit's screen, allowing them to gradually adjust the coupled shafts until they are properly aligned.
Belt alignment systems can be utilized to align pulley-driven applications aboard ships, including galley machinery, laundry equipment, pumps and fans. They can detect horizontal, vertical and parallel misalignment between pulleys that are up to 20 feet apart. The most advanced systems accurately align the grooves of pulleys rather than their faces, allowing alignment of pulleys with unequal widths or dissimilar faces.
Figure 2: For alignments involving long, coupled shafts, laser-equipped alignment systems offer much higher accuracy than alignment methods using straightedges. (Photo courtesy of SKF USA Inc.)
Condition-based monitoring programs utilizing advanced monitoring instruments are also becoming more popular in marine applications. The programs can detect rotating equipment problems at an early stage and generally begin with detailed mapping of a ship's critical machinery.
An application's monitoring status is determined by evaluating its operational impact and maintenance complexity. The critical applications covered usually include engine room fans and blowers, cargo pumps, turbochargers, and main and auxiliary engine lubrication systems.
Recently, a ship operator developed a monitoring program for thruster applications aboard a drilling ship. The program equips maintenance workers with handheld detectors to record vibration levels at key machine points, including on the thrusters' bearings and gears. After data is collected, it is transmitted off-site and reviewed by vibration analysts, who produce reports on the thrusters' operating condition. The reports enable the ship operator to fine-tune maintenance practices aboard ship and improve thruster reliability.
Monitoring programs aboard ships often include lubricant analysis, which can detect changing lubricant properties, such as grease hardening or softening and thermal degradation.
One suitcase-sized grease analysis kit, for example, contains the tools necessary to conduct grease consistency, oil bleeding and contamination tests. The tests are performed using only 0.5 grams of grease. They allow maintenance technicians to instantly assess the suitability of greases for a given application and optimize relube intervals. The tests can also help determine the shelf life of greases stored aboard ship.
In summary, any maintenance departments can realize substantial benefits from the latest generation of maintenance technologies, which range from heavy-duty mounting devices to hand-held monitoring instruments. The technologies are well designed for the rigors of industrial applications. They can be deployed to speed maintenance activities, help prevent potential failures and improve the reliability and performance of rotating machinery.
Paul Michalicka is the North American area sales manager for maintenance products, SKF USA Inc. In this capacity, Michalicka assists users of rotating equipment with maintenance expertise and consulting services, with an emphasis on tools and instruments that contribute to machine service life and reliability. www.skf.com