Beating cold corrosion, the downside of fuel-efficient engines
Dr Steve Dye, business development and marketing manager, Parker Kittiwake explains why frequent condition monitoring is the most effective measure in combatting the recent cold corrosion phenomenon.
Amid escalating fuel costs and increasingly stringent environmental regulations, shipowners are favouring new generation engines, such as Mark 8.1 or newer, which offer improved fuel consumption. These newer engine designs achieve improved fuel oil consumption by using longer piston strokes, allowing the cylinder walls to cool more than the older engine designs. This then allows water to condense on the surfaces of the cylinder liners, which reacts with the sulphur dioxide in the combustion gasses, leading to the formation of sulphuric acid and resulting in corrosion on the liner surface. The resulting iron compounds formed by this process are flushed into the cylinder oil, leading to excessive wear of the cylinder liner, the average replacement costs of which are $150,000.
In recent service letters MAN Diesel & Turbo highlighted the importance of accurate and efficient monitoring of the conditions within the cylinder chamber in order to minimise cold corrosion. Having conducted extensive research into the issue, Parker Kittiwake has concluded that identifying the level of damaging corrosive elements within the cylinder chamber and understanding the processes that cause them is the most effective way of preventing wear. Frequent testing provides shipowners with a comprehensive overview of conditions within the cylinder chamber, allowing operators to avoid costly repair bills by addressing harmful levels of corrosive elements before they cause damage.
Measuring the concentration of iron compounds in used cylinder oil will give an indication of the level of corrosion within the cylinder. In order to prevent cold corrosion from causing preventable damage, shipowners must identify the underlying causes and eradicate or at least limit the effects of corrosive wear, thereby ensuring optimal operational efficiency and minimising costs.
The iron figure indicated by most commonly available condition monitoring tests gives the combined level of both metallic and non-metallic compounds in the cylinder oil. However each of these elements have differing properties. For example, the iron particles worn from the cylinder liner by cat fines are magnetic and can be detected by tests such as the Parker Kittiwake LinerSCAN online sensor. However, non-metallic compounds such as iron sulphate are caused by reactions in the cylinder liner during the combustion process, and these cannot be detected magnetically. Ship operators ideally need to monitor the levels of both metallic and non-metallic elements separately in order to understand where corrosive wear originates from and therefore take action to prevent it. This can be achieved through regular and efficient condition monitoring.
Currently there are few tests available on the market, and the majority of tests require samples to be sent to a laboratory for analysis with results often taking a number of weeks to return. Those kits that are available and are capable of providing results on-board generally take several hours to complete and give only a total figure for all iron, metallic and non-metallic, in the scrape down oil. With accurate and detailed data key to preventing corrosion, ship owners need quick and easy access to the relevant information.
New condition monitoring technologies are essential in identifying the exact causes of cold corrosion so that they can be prevented. The recently launched Parker Kittiwake cold corrosion test kit is designed to give comprehensive analysis of corrosive wear in cylinder lubricants. The test alters the colour of an oil sample which indicates the concentration of non-ferrous iron compounds. This provides a measurement of the corrosive wear present within the sample almost instantly, negating the need to send samples to a laboratory for analysis and potentially preventing damage before it occurs. When used in conjunction with ferro-magnetic analysers such as LinerSCAN, or the Shell Analex Alert, the shipowner will have an actual measurement of both metallic and corroded iron in the scrape down oil, rather than just the total combined iron figure offered by other test kits or laboratory analysis. Having access to comprehensive data on-board means that operators can understand the exact operating conditions within the cylinders and easily identify where adjustments can be made to minimise corrosive wear and reduce cost.
With engine manufacturers (OEMs) now advocating the use of higher BN lubricants in newer engine designs in order to minimise the issue of corrosion, it becomes increasingly important to monitor the condition of the cylinder oil. The scrape down oil is continually exposed to acidic combustion products that need to be neutralised before they corrode engine parts. Frequently testing the residual base number (BN) of used cylinder lubricant will prevent damage to engine parts by ensuring that alkaline reserve levels required to neutralise the acid are sufficient, preventing unnecessary corrosive damage to costly engine components such as cylinder liners. The updated Digi TBN Test Kit detects residual BN levels in used cylinder oil, giving an on-board reading in minutes. MAN Diesel & Turbo has specifically recommended the use of the Parker Kittiwake test kit in its latest service letters. The test allows operators to monitor efficiency of lubricants over a period of time, maximising the potential life of the product, as well as saving both the cost and time incurred with repairs resulting from corrosive damage.
In a challenging economic climate, the shipping industry needs to be increasingly focused on maximising efficiency and cutting costs. Coupled with more stringent environmental regulations, shipowners and operators are under increasing pressure to adopt new engine designs and technologies that achieve greater fuel efficiency. As a result, awareness of the necessary operational changes to mitigate the risks associated with newer engine designs is paramount.
With fast and easy access to the necessary data, ship owners and operators are better armed against cold corrosion. Accurate condition monitoring provides a means of mitigating the risk before it occurs, preventing damage to engine components and achieving optimum operational efficiency.
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