Type MC/MC-C and ME/ME-C/ME-B
MAN Diesel & Turbo released Service Letter to provide a number of possible actions in order to prevent the following problems on type MC/MC-C and ME/ME-C/ME-B MAN B&W engines: corroded or cracked engine parts (cylinder cover, cylinder liner and cooling jackets) and cooling water leakage.
Cooling Water System
MAN recommends certain intervals for the cooling water inlet pressure and the outlet pressure. Keeping the inlet pressure within the mentioned range is the most important, but in general pressure fluctuation should be avoided in order to prevent local boiling damaging the O-rings.
Fresh cooling water treatment
Like fuel oil and lubricating oil, the engine cooling water is a medium, which must be carefully selected, treated, maintained and monitored. Otherwise, there is a risk of damage to the surfaces of the cooling system, which are in contact with the water.
Risks
In case the cooling water treatment is inappropriate, the following might occur:
Corrosion is a chemical process, which removes material from the attacked surface. Over time, corrosion of O-ring sealing surfaces will lead to leakage problems.
Corrosion fatigue can develop into cracks because of simultaneous corrosion and dynamic stresses. The figure below shows the effect of corrosion on components dimensioned for an infinite life time. Cycles to failure is infinite at one stress level (for the component with uncorroded surface) and becomes finite with significantly reduced amplitude stresses (fro the component with corroded surface). The mechanish can also related to hydrogen embrittlement.
Scale formation, which reduces the heat transfer, mostly due to lime deposits.
Precautions
The above risks can be minimized by the following fresh water treatment
Cleanliness. The cooling water system should be kept clean and free from rust and deposits. If cleaning is necessary, measures like descaling and acid circulation are explained in-depth in the manual.
Filling up with freshwater. It is important to use deionized or distilled freshwater for example produced in the freshwater generator.
Adding a corrosion inhibitor. Various types of inhibitors are available, but generally only nitrite-borate based inhibitors are recommended.
For more details, please read MAN Diesel & Turbo Service Letter by clicking here
