Coupling Failure / Shaft Misalignment

Driver and driven machine are coupled shaft-to-shaft. Misalignment (thermal growth, soft foot, worn coupling) or a degrading coupling raises vibration and cyclic loads that shorten bearing and seal life — and a badly degraded coupling can fail outright, releasing or unbalancing the train.

Misalignment is one of the most common chronic root causes in all of rotating machinery — it silently loads exactly the components (bearings, seals) whose failures dominate downtime. Catching it early is cheap; ignoring it compounds.

1. Misalignment develops — thermal growth on warm-up, soft foot, settling baseplate, or coupling wear.
2. Vibration rises with a characteristic misalignment signature (often at 2× running speed).
3. Cyclic loads accelerate bearing and seal wear on both machines.
4. Left uncorrected, secondary damage accumulates or the coupling fails outright.
5. Operator identifies the signature and schedules a controlled shutdown for alignment/coupling repair.

Widely cited industry estimates put shaft misalignment behind roughly 30–50% of rotating-machinery failures, with some sources claiming up to 50–70% of machine vibration problems (secondary/vendor training figures; ranges vary widely by source and definition…

Premature bearing and seal failure, elevated vibration, and possible outright coupling failure releasing/unbalancing the train (API 670 machinery-protection practice —…