In the maritime industry – where financial pressures continue to be the driving factor behind almost all operational decisions – measures such as effective condition monitoring and reliability-centered maintenance can help deliver tangible results in maximizing earnings potential.
The recent drop in global fuel prices has provided some relief to ship owners and operators. However while fuel costs still represent the majority of the operational cost of a vessel, there are other important factors to be considered where real savings can be made. The cost of the fuel, for example, is covered by the charterer. However, the ship owner/operator is responsible for the cost of cylinder lube oil, a critical aspect of reliable, consistent operational output and the lifeblood of many valuable assets.
Slow-speed, two-stroke marine engines require steady lubrication at the interface between the cylinder liner and piston rings. This is a total-loss application, with the oil fed continuously into the top of the combustion chamber through injectors situated around the piston ring pack.
Among other additives, the cylinder lube oil is formulated with alkaline detergents (cited as base number or BN) to neutralize acidic combustion byproducts. While some of the oil burns, the waste is scraped down into a drain line and held in a storage tank for subsequent disposal. Representing up to 60 percent of the technical budget of a vessel, it is vital to ensure that the condition of this cylinder lube oil is monitored and the operational lifespan is optimized.
As marine engine designs evolve to drive improvements in efficiency, consideration must be given to the effect this has on the operation of the vessel. In most new engines the piston stroke is longer to improve fuel efficiency. This results in a cooler operating temperature and causes condensation to form on the surfaces of the cylinder. With older designs, the sulfur in the engine was in gaseous form (SOx), but now the gas combines with the liquid condensate and forms sulfuric acid. The iron compounds formed by this acidic corrosion process are flushed into the cylinder oil, leading to excessive wear of the cylinder liner.
With the average cost of a replacement liner at over $150,000, as well as the cost of the downtime required for installation, this is a repair bill that shipowners can ill afford.
One way of combating the higher levels of corrosive acid on the cylinder liner is to increase the feed rate of alkaline lubricant to prevent damage. This solution however has only short-term benefits, as the increased cost of lubricant oil will then hit the bottom line.
Even a 0.1 gram per kWh increase in lubricant oil consumption can represent a significant cost increase to the ship owner. With often up to four times the normal level of required lubricant being used to combat corrosion, this cost becomes unmanageable. However, there is a balance to be struck to ensure that corrosion does not cause costly damage and unscheduled downtime, while keeping the feed rates and oil expenditures to a minimum.
Traditionally, the level of lubricating oil required has been determined by inspections while in port and laboratory testing of scrapedown oil. Most of the major oil suppliers provide drain oil analysis programs, designed to monitor the engine to identify sensitivities within certain parameters in order to improve maintenance management.
The service provided by Flame Marine Ltd., for example, is used by an extensive number of ships worldwide. In order to manage the cost of overlubrication, which the company estimates to be over $100,000 per ship per year, the service reduces the feed rate and monitors the performance characteristics of the engine and the chemical composition of the cylinder drain oil to provide a comprehensive picture of the operating conditions within the cylinder. This allows the operator to identify wear in the piston or liner, incomplete combustion, piston misalignment, and issues relating to fuel systems.
While this approach helps the operator to manage the cost of lubricant oil and effectively schedule maintenance, it does present drawbacks. For example, while the data gathered is comprehensive and detailed to allow operators to make informed decisions, there is an inherent delay in highlighting any issues – meaning that potentially costly damage has already been done and opportunities to realize savings have been missed.
In addition, the reliability of the data depends on testing a representative sample. In an industry where budgets are stretched, which includes funds allocated for training, the necessity of having a trained and experienced engineer onboard who understands how and where to draw a sample can be problematic. It is far simpler to have a solution in place that does not rely on these skills being readily available.
Electronically controlled lubricating systems represent the next step in moving towards a more robust solution. Systems such as the Alpha Lubricator, from Man Diesel & Turbo, and the Wartsila Pulse Lubricating System inject cylinder oil at the exact position and time where the effect is optimal. These systems have achieved significant savings. For example, the guide feed rate for Wartsila RTA and RT-flex engines equipped with the Pulse system as original equipment is now 0.7 to 0.8 g/kWh of cylinder lubricant, a significant improvement from the previous level of 1 to 1.2 g/kWh.
Employing electronically controlled lubrication does reduce cylinder oil consumption and produces cost savings. However, as an open-loop system it does not provide feedback on the impact of a reduction in lube oil feed rate. Without this essential feedback, the operator does not have the necessary data to obtain a picture of the operating conditions within the cylinder. Therefore, by adjusting feed rates based on OEM recommendations alone, serious engine damage can be caused and wear increased as a result of under-lubrication. In order to safely strike the balance in lubrication feed rates and maximized savings potential, operators can employ a range of online and offline monitoring tools.
Constant, real-time monitoring is the ultimate tool for safely optimizing cylinder lube oil feed rate. Tools are available now, such as Parker Kittwakes LinerScan system, which can be used to minimize liner wear, improve maintenance scheduling, decrease sampling and testing costs, optimize lubricant feed rate, and detect the result of the ingress of catalyst fines. LinerScan, for example, uses magnetometry to quantify the iron found in used cylinder oil, and its sensors can report changes caused by abrasive wear and even routine inspection, highlighting periods of increased physical or thermal stress.
By monitoring wear levels in real time, engineers are alerted to escalating cylinder liner damage and are able to react quickly to changes, enabling preventive maintenance during the ships passage to the next port and ensuring against expensive downtime.
LinerScan is particularly useful for reducing the risk of unacceptable levels of wear in unfamiliar environments, such as areas of high humidity where water enters the combustion chamber with air from the turbocharger; this disturbs the oil film, leading to scuffing and wear which damages the liner. When used in conjunction with onboard tests to identify iron compounds in the used oil, operators have quick and easy access to the information they need in order to identify where adjustments need to be made to alter the operating conditions within the system – effectively minimizing corrosive wear and reducing costs.
Another tool, the Parker Kittiwake Cold Corrosion Test Kit, provides an onboard measurement of nonferrous iron compounds present in a sample almost instantly, and without the delay and cost incurred when sending samples away for laboratory analysis. When used alongside ferro-magnetic analyzers, operators can identify levels of both ferrous and nonferrous compounds in their used oil. They then can isolate and address the unique processes which lead to these corrosive elements being formed.
By employing a combination of online and offline tools that encompass a comprehensive range of processes within the system, operators can best arm themselves with the data they need to manage maintenance, prevent damage and save costs.
The value that effective condition monitoring can deliver should not be overlooked. By employing a suite of tools and reliability-centered maintenance strategies, operators can make informed decisions, protect assets and maximize their earnings potential.
Steve Dye, Ph.D., has been business development and marketing manager at Parker Kittiwake in Littlehampton, U.K., since 2011. He is heavily involved in R&D and new market channels, and responsible for the condition based monitoring firms Procal and Holroyd business, which specializes in emissions monitoring and acoustic emissions technologies. For information visit www.kittiwake.com, or e-mail Dye at steve.dye@parker.com. Phone: +44 1903 731 470