Industry Insight: Cold Corrosion - What is it, and What's the Best Way to Deal With it?

In recent service letters, MAN Diesel & Turbo has highlighted the increasingly prominent issue of cold corrosion and recommends that the best way to prevent the corrosive wear caused by this issue is through regular and accurate condition monitoring.

As the shipping industry faces the challenges of escalating fuel costs and increasingly stringent environmental regulations, ship owners are favouring new generation engines, such as Mark 8.1 or newer, which offer improved fuel consumption. By utilising longer piston strokes these newer engine designs achieve improved fuel oil consumption.

However this process allows the cylinder walls to cool more than the older engine designs, allowing water to condense on the surfaces of the cylinder liners and react 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 up to $150,000.

Costly Repair Bills

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. Operators can avoid costly repair bills with frequent testing which provides a comprehensive overview of conditions within the cylinder chamber, enabling them to address harmful levels of corrosive elements before they are able to cause damage.

By measuring the concentration of iron compounds in used cylinder oil the level of corrosion within the cylinder can be identified. In order to prevent cold corrosion from causing preventable damage, ship owners must understand the underlying causes and limit - or if possible eradicate - the effects of corrosive wear, ensuring optimal operational efficiency and minimising costs.

Most commonly available condition monitoring tests indicate the total iron level, giving 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.

Cold Corrosion Test Kit

Condition monitoring is 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 the latest innovation in the range of solutions designed to give the most comprehensive analysis of corrosive wear in cylinder lubricants.

The recently launched Parker Kittiwake Cold Corrosion Test Kit is the latest innovation in the analysis of corrosive wear in cylinder lubricants.

The test alters the colour of an oil sample which indicating 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 ship owner will have an accurate measure 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. Operators can understand the exact operating conditions within the cylinders and identify where wear can be minimised with this quick and easy access to comprehensive data on-board.

It becomes ever more important to monitor the condition of cylinder oil as increasing numbers of engine manufacturers (OEMs) now advocate the use of higher BN lubricants in newer engine designs in order to minimise the issue of corrosion.

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 newly updated Digi TBN Test Kit detects residual BN levels in used cylinder oil, giving an on-board reading in minutes. Useful in helping owners meet OEM testing guidance, 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 the efficiency of lubricants over a long 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.

Maximise Efficiency, Minimise Costs

By utilising the detailed information made available to operators through condition monitoring and applying or adapting operational practices to mitigate against the effects of cold corrosion, ship owners can maximise efficiency and minimise costs.

As environmental regulation becomes increasingly stringent, ship owners and operators are under pressure to utilise the newer engine designs and technologies that are capable of delivering more efficient fuel oil consumption. It is therefore vital to understand the potential issues that can arise and how to prevent these from causing costly corrosive damage.

Accurate condition monitoring is the most effective means of managing these risks and achieving optimum operational efficiency.