Breakdown of machinery due to engine overspeed
From time to time Gard Marine receives reports regarding breakdown of machinery due to overspeed of either the main engine or auxiliary engines. Overspeed is any speed beyond the operating range specified by the engine manufacturer. Very often overspeed leads to serious damage, not only to the engine itself, but also to generators and gears.
There are several reasons for overspeed, but the most common is malfunction of the governor or fuel oil pumps.
As engine overspeed can result in damage to the crankshaft (deformation to push rods), broken valve seats, defective camshafts, breakdown of turbocharger and breakdown of generator and gear, the consequences can prove to be costly.
Rectification of overspeed damage may lead to the complete dismantling and control of all vital engine parts, which is both time-consuming and expensive.
To prevent breakdown, engines are equipped with electrical and mechanical protection. Almost all engines are designed with overspeed protection, normally electrical and mechanical. It is actually a class requirement that main and auxiliary engines be fitted with governors to control their speed so that it does not exceed that for which the engine is classed by more than a set margin. In some instances, a second overspeed protection device, independent of the governor, must be fitted.
The overspeed protection for machinery must be tested in accordance with the engine instruction book or the vessel’s maintenance system. On auxiliary engines this can be checked regularly without major effort, but main engines normally have to be stopped during sea voyages, which may be impractical and uneconomical. This may sometimes result in the decision to postpone the scheduled tests and/or maintenance.
Breakdowns due to overspeed are generally costly for all involved. Maintenance schedule on vital parts such as speed governors, fuel pumps and electrical and mechanical overspeed protection must be adhered to.