Understanding remote fluid analysis on ships
For electronic systems such as ECDIS and VDRs, the equipment needs nothing more than a power supply to operate and maintenance is limited to removing dust build up on cooling fans, cleaning screens or the occasional replacement of an internal battery. Mechanical equipment is much more demanding and all machines regardless of type need lubrication between moving parts to prevent heat build-up and wear.
On most equipment such as pumps, compressors, winches and the like, lubricant levels need only regular checks and the occasional change. However, engine lubricants are a much more challenging area and need constant attention, regular adjustment and special attention of lubricant choice dependant on the fuel being used. There are also two areas of the engine that may or may not have different lubricating requirements – Cylinder and Crankcase or circulating oil.
In any engine operating on residual fuels containing sulphur, cylinder lubricants have three main purposes; to provide a barrier to metal to metal contact between piston rings and the cylinder liner, neutralising any sulphuric acid to control corrosion and to clean the cylinder liner and piston rings preventing damage from combustion and neutralisation residues.
In four-stroke trunk piston engines the same oil is used for cylinder lubrication and cooling. Some of the cylinder oil by-passes the piston rings and ends up in the combustion space, where it is “consumed”. However, the piston in a four-stroke trunk piston engine has an oil scraper ring that scrapes most of the oil supplied to the cylinder liner back to the engine’s oil pan, from where it is drained, cleaned and recycled.
In general four-stroke engines are less complicated as regards lubrication than two strokes. The two-stroke crosshead engine is different from the four-stroke in that it has no connection between the piston underside space and the oil pan. The cylinder lubricant is not recycled and will be consumed in the combustion process making precise dosing imperative and allowing for different oil types to be used in the two zones of the engine.
The composition of cylinder lubricants must be matched to the fuel being used otherwise problems will occur. This report is not the place to cover the science or practicalities and the choice of lubricant is for the owner to determine taking into account OEM recommendations especially in regard to low-sulphur fuels needed in ECAs.
Clearly it is unwise to ignore OEM recommendations but the benefits of using a single lubricant are attractive and relieve crew of having to cope with the problems of changing lubes as well as fuel oils during approaches to ECAs. Owners should therefore communicate with their engine and lube suppliers to determine the best and safest operational strategy.
Most operators choose to use lubricants from a single maker whenever possible but even the best laid plans can go awry and it is sometimes necessary to use products from a different supplier. Except for a few specific lubricants, most manufacturers have equivalent products that can safely be used alongside competing products. Ensuring the compatibility of products before mixing is relatively simple as most makers produce charts listing compatible rival offerings. Even so, the consensus is that results from engines where multiple oils have been used may be less accurate for trending purposes as there will be no consistency in the protection the lubricants have given.
The right dosage
Ensuring accurate cylinder lubricating oil dosage is vitally important in a two-stroke crosshead engine. The challenge is to make the oil properly and efficiently fulfil its tasks before it is “lost”, partly to the combustion space where it is burned, and partly to the piston underside space as sludge. In the early to mid-2000s, computer controlled lubricating systems that could dose according to engine load, speed and sulphur content were introduced by leading engine makers.
Among these were the MAN Diesel & Turbo Alpha and Wärtsilä Pulse Lubricating systems. These were introduced before slow-steaming became a popular strategy among container operators after the economic crash of 2008 but their benefits were extolled by the engine makers as helping to overcome the problems caused by operating engines outside of design parameters and many systems have been retrofitted since. Automated dosage systems are now standard equipment on most new engines.
It is not only controlling SOx emissions that has created problems in the tribology aspect of modern engines. Addressing the twin effects of controlling NOx and meeting the EEDI requirements has led to a new phenomenon – cold corrosion. This happens when sulphuric acid forms on the liner walls in an engine cylinder and corrodes the liner surface. This abnormal corrosion then creates excessive wear of the liner material. The NOx and EEDI rules only apply to newer engines but older engines can also suffer from the problem if they are modified, as many have been, to allow for slow steaming when engine loads below the original design parameters become routine rather than exceptions.
Another mistake is over lubricating in order to reduce acidity within the cylinder liner. To meet the ideal acidity level it is not unknown for lubricant use to quadruple which is expensive and creates other problems. It is therefore advisable to monitor feed rate and seek advice. Electronic lubrication systems can reduce cylinder oil consumption, but as an open loop system it does not provide feedback on the impact of such reduction and, sensibly, a safety buffer is often applied.
Without a reliable feedback system to accurately monitor the effect on the engine, changing feed rates based solely on OEM’s recommendations could increase associated wear caused by under-lubrication and seriously harm the engine. Other testing options available include Parker Kittiwake’s LinerSCAN, which helps optimise feed rate. Using magnetometry, LinerSCAN‘s sensors fit to each cylinder of the engine and report changes caused by abrasive wear, highlighting periods of increased physical or thermal stress. By monitoring change trends and wear particles in real time, engineers are alerted to escalating cylinder liner damage.
Dosing of two-stroke cylinder lubes is important but lubricating oils can also be used as a means of ascertaining the health of any machine and proper analysis can give early warning of possible failures long before an incident occurs, allowing preventative measures to be taken. Several companies and classification societies offer analysis services and it has long been possible for crew to make basic tests themselves using proprietary test kits.
Quite clearly, sending samples away for analysis is a time consuming business and while it makes sense for the long term health of equipment, it does little for remote monitoring. Back in 2006, ExxonMobil introduced a web-based version of its Signum analysis service. It gave owners access to a database that allowed trend analysis for individual ships or engines, for all ships with similar engines in the fleet, and across the whole fleet. Allowing he results from different ships to be compared allowed benchmarking and if used properly made it possible to identify poor performers and compare the effects of different maintenance regimes.
Spotting a problem
Besides their primary role of reducing friction and keeping the engine running smoothly, lubricants other than cylinder lubes can be used as indicators of developing problems in engines. Different components of an engine are made from different metals and as they wear minute particles find their way into the oil. The scrape down oil from the cylinders shows up wear in rings and liners as well as giving clues to the combustion process, while circulating oil can carry traces of bearing wear from the crankshaft and connecting rods.
Analysis of scrape down oil can sometimes show evidence of over-lubrication and suggest adjustments can be made to the feed rate to reduce consumption of lubricant as well as preventing fouling of turbocharges, valves etc. As well as showing evidence of engine wear, analysing lube oils also gives information on the quality of the oil itself.
Lubricants breakdown gradually and their effectiveness reduces as it does so. Topping up is necessary at times but if continued for very long periods can actually result in increased consumption because all of the work of the oil is being done by just a small amount of fresh oil while the remainder may be practically useless.
In 2006, Maersk Fluid Technology demonstrated for the first time a new device which although not in common use a decade later, could be a step change in lube analysis. The SEA-Mate X-ray analysis system uses X-ray fluorescence to identify chemical elements and although it is programmed to recognise only a limited number, it is possible for other elements to be added to its library. This permits it to be customised to cover most or all of the elements likely to be found in the components of every piece of machinery on the ship. If an element shows up in a sample of lube oil then it should be relatively easy to determine the component in which it was found; by considering the level present, the rate of wear can then be deduced. The system matches samples to the point on the engine where they were taken from and records all data for trending purposes.
Almost every major lubricant producer runs a testing and analysis service and there are also several independent service providers such as Kittiwake and Intertek. Engine makers are also becoming more involved with MAN Diesel & Turbo’s Fluid Monitoring service being a prime example.
Recording and monitoring the lube analysis data along with the more traditional temperatures and pressures permits for a better picture of what is happening inside the machine and so makes for a more accurate prediction as to the need for overhaul. Every analysis should be able to determine and identify the various metals and alloys found in the samples but engine makers argue that since they alone know the composition of all internal components, they are best placed to say what is wearing and to what extent.