Cases

Techno Fysica BV is a Dutch-based engineering company, highly specialised in solving all kinds of problems related to the dynamic loading of machinery and installations. For this, several measuring and analysis techniques are used. In a series of articles, we will give examples of what can go wrong in the engineering and operating of vessels, and what errors lie at the root of the damages observed.

An auxiliary generator broke a connecting rod after only hundreds of hours of operation, which caused a hole in the crankcase, resulting in a total loss of the engine.

Metallurgical investigation revealed that the thread in the connecting rod, meant to connect the two halves of the big end bearing, had been cut with a very blunt tool. Because the bolts are tensioned by means of a torque wrench, this results in the right torque but in much too low pre-tension force. Consequently, the dynamic stresses on the bolt are much too high, which resulted in fracture of the connecting bolts.

The connecting rod led its own life and penetrated the crankcase.

       Hole in a crankcase of a medium seize marine diesel engine, caused by a fractured connecting rod

This is a typical example of a failing quality control. Although such failures can never be completely eliminated, a thorough investigation into the root case of the failure can prevent re-occurring. In this case. Checking the stock in the workshop of the client revealed more low quality piston rod. Furthermore, some weeks later, an identical  failure occurred, again related to poor quality pre-stressed bolts. The piston rod involved in this failure could be traced to the same shipment.

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