Immediately after leaving port ( sailing at approximately 100rpm,) a crack was discovered on the collar attached to the cylinder cover of the main engine #4 cylinder exhaust valve (C valve.) The crack extended approximately 70mm from the top edge toward the center of the collar and approximately 50mm in a downward direction. As the crack on the top surface extended to the base of the valve casing’s center cylinder, the situation was reported to the bridge and request was made for speed reduction of the main engine and for the engine to be stopped at the next possible location. 40 minutes later, the main engine was stopped and anchor was dropped.
Based on the condition of the cracks, for the time being, only the #4 cylinder B valve and C valve which had the worst cracks were replaced and voyage was recommenced towards the next port of call (Nagoya.) Decisions for repairing the cracks were based on manufacturer recommendation. Slight cracks were ground off, metaloc adhesive was applied toward those cracks which could be repaired (9 units,) and those which were extremely damaged (4 units) were unloaded and scrapped.
Although it is unknown when the cracks on the edges of the exhaust valve casings formed, it is assumed that they did not form recently. As such, although a determination of cause is difficult, the over- tightening of the clamping bolts on the exhaust valve casing is conceivable as one cause.
posted 03 Dec '18, 07:04