Hydroelectric Power Plant - Thrust Bearing
Incorrect Oil Make-up / Bearing Delamination
The wear metal chart shows an increase in the tin (Sn) level that returned to normal levels after the oil change, however the lead level continued to rise. The additive levels, specifically phosphorus (P) and sulphur (S), had changed significantly indicating a top-up with different oil had most likely occurred.
Figure - Additive levels of phosphorus and sulphur (top graph) had changed dramatically. Tin levels increase dramatically (lower graph) at the same time.
Based on the oil analysis findings the Plant Mechanical Engineer made the decision to take the 2.5 MW hydroelectric generating unit out of service in order to inspect the bearings on the turbine main horizontal shaft. The main shaft is roughly 10” in diameter with the collars being an inch or 2 greater. The inspection showed that an area of delamination (babbitt had flaked away from the bearing backing) on the #2 thrust bearing.
Figure - The main bearing (left) exhibits delamination of the Babbitt overlay (inset picture on right).
It was decided that the bearing would be put back into operation and repaired at the next shut-down since that outage was to be longer and would provide the necessary time to repair the bearing. The oil was changed and the unit was put back in service. Unfortunately, as the bearing began to fail, the vibration in the power turbine unit became so excessive that it shook the plant and caused a number of machines to move on their mountings. The end result was a forced shut-down of the plant for three months to re-mount all the equipment (and to repair the thrust bearing on this power unit).
Diesel Engine - Cylinder Assembly
Dirt Ingression causing Cylinder Assembly Wear
With reciprocating machinery, such as a diesel engine, the wear particles generated tend to be small (<10 microns). As a result, ICP analysis can easily pinpoint the specific wear modes and conditions of the machine.
Figure - ICP analysis is excellent at pinpointing wearing components and ingressed contaminants.
This oil sample is from a Detroit 6V71 diesel engine. The iron (cylinders), chromium (rings), aluminum (piston), and tin (piston flashing) levels are abnormal to severe. The silicon (dirt) level is also severe. The diagnosis is that high dirt levels are creating severe cylinder assembly wear.
Figure - Dirt particles that fit between the clearances in components interrupt the lubricant film and cause wear to the machinery. Dirt particles can actually lodge into soft metals and proceed to carve out metal from opposing component surfaces.
If the dirt ingression was not severe a simple oil, oil filter and air filter change following an oil flush may correct the situation. If there was significant coarse dirt ingression then it may be necessary to do a bottom-end overhaul to replace the engine main bearings.