Crankshaft Failures in Medium Speed Engines 2

[saintste]

Has anyone ever come across crank web failure in medium speed engines? I've just had a 900RPM, 2.1MW generator engine break a web clean through, crankshaft is fully forged.

 

[Booth]

You will realise that there are many possible reasons for the failure of your crankshaft. Poor lubrication=bearing wear=crank deflection=failure. Booth

 

[pko]

I had this happen to me on a 720 rpm 0.6MW DC generator in 1988. Crankshaft had ~50,000 operating hours. Inspection concluded it failed in high cycle fatigue. Some lateral misalignment existed (0.035" for a 160" crankshaft length) in the foundation which undoubtedly contributed. My opinion at the time was that it was simply a case of high cycle fatigue, initiated at a tool mark (failure began at the edge of the machined radius between the conrod journal and the web). Limited records checks showed that this was the third such failure out of a total of 8 engine installations. All 3 failed between 40,000 and 60,000 hours.

 

[op9]

As pko has demonstrated fatigue is the prime culprit, but whether it is a misalignment problem; initiated by a defect "tool mark"; local overheating ...lubrication?; unbalanced or high cyl peak pressures; manufacturing fault (eg insufficient radii); has to be determined. The crack should be examined carefully to determine the source location of the crack (from where it propogated). What was the engine and model....a logical step is to inform the engine manufacturer in case there is a recurrent problem. They will naturally ask all the above and other questions. Also I assume EVERYTHING on the engine was checked when the new c/shaft went in? Rod Nissen.
Combustion & Engineering Diagnostics
canded@iprimus.com.au

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