Combat Cold Corrosion via Condition Monitoring

Parker Kittiwake explains why frequent condition monitoring is the most effective measure in combating the recent cold corrosion phenomenon

The recent trend in favoring newer generation engines which offer improved fuel consumption by using a longer stroke reflects the marine industry’s focus on energy efficiency. While this design does aid operators in reducing fuel consumption, it has also created the new issue of cold corrosion. The longer stroke allows the cylinder walls to cool more than with older engine designs, allowing water condensation to form on the surface which then reacts with the sulphur dioxide in the combustion gases to form sulphuric acid, a corrosive element which damages the liner surface. The iron compounds formed by this process are then flushed into the cylinder oil, leading to excessive wear of the cylinder liner with the cost of a replacement at an average cost of up to $150,000.
To benefit from the more fuel-efficient engines without creating a related issue that could potentially cause damage to costly engine parts, operators need to carry out effective and accurate condition monitoring. In recent service letters, MAN Diesel & Turbo has reiterated the importance of monitoring of the conditions within the cylinder chamber in order to minimize the effects of cold corrosion. Having conducted extensive research into the issue, Parker Kittiwake have concluded that identifying the level of damaging corrosive elements within the cylinder chamber and understanding the processes which lead to these levels building up is the most effective way of preventing wear. Frequent testing provides ship owners 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.
To obtain an indication of the level of corrosion within the cylinder operators can measure the concentration of iron compounds in used cylinder oil. Once the underlying causes have been identified and understood they can be eradicated or limited, preventing cold corrosion from causing damage. Most commonly available monitoring tests indicate the total iron figure in the cylinder oil, including both metallic and non-metallic compounds. These elements have differing properties and are caused by distinct processes. Iron particles worn from the cylinder liner by cat fines are metallic and can be detected by onboard ferro-analyzer tests. 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. In order to identify the causes of corrosion ship owners need to monitor the levels of both metallic and non-metallic elements separately so that preventative measures can be taken.
With accurate information key to preventing corrosion, shipowners need information. While there are onboard testing solutions available, these often take several hours to complete and do not provide separate data for the level of metallic and non-metallic iron compounds in the sample.
The recently launched Parker Kittiwake Cold Corrosion Test Kit is designed to give the most comprehensive analysis of corrosive elements in cylinder lubricants, providing a measurement of non-ferrous iron compounds present in a sample almost instantly, negating the need to send samples to a laboratory for analysis and avoiding the time and cost this incurs. By having quick and simple access to this information onboard, operators can identify where adjustments need to be made to alter the operating conditions within the cylinder in order to minimize corrosive wear and reduce cost. The test kit, when used in conjunction with ferro-magnetic analyzers, will indicate the levels of both metallic and non-metallic iron compounds so that operators can isolate and address the different processes which result in these corrosive elements being formed. As the issue of cold corrosion increasingly gains recognition, OEMs are looking to identify ways to minimize the effects and prevent damage. As a result many OEMs are now advocating the use of higher Base Number (BN) lubricants in engines with a longer stroke, MAN Diesel & Turbo now recommend lubricants with a BN of 100 or higher, and so it becomes more important to monitor the cylinder oil to understand the effects of this change on the conditions within the cylinder chamber. Scrape down oil is continually exposed to acidic combustion products that need to be neutralised before they corrode engine parts. By frequently testing the residual BN of used cylinder lubricant, operators can ensure that alkaline reserve levels within the oil are sufficient to neutralize these acidic products, preventing unnecessary corrosive damage. Parker has recently updated the Digi TBN Test Kit which measures the residual BN levels in used cylinder oil, providing an onboard figure in minutes. This allows operators to monitor the efficiency of cylinder lubricants over a long period of time, maximizing the potential life of the product as well as saving both the time and cost incurred with repairs resulting from corrosive damage.
Innovative engine technologies offer attractive benefits to ship owners by simultaneously addressing two of the greatest challenges facing today’s shipping industry; fuel reduction and emissions control. With immediate access to the necessary data through onboard condition monitoring tests, they are better armed against cold corrosion and can reap the benefits of eco-efficiency, minus the unwelcome consequences.

(As published in the July 2014 edition of Maritime Reporter & Engineering News - http://magazines.marinelink.com/Magazines/MaritimeReporter)