Shaft Alignment

We used to assume that once rotating machinery equipment is installed and aligned, it will remain in the same position forever. But this is not always the case.

The alignment should be checked periodically. This valuable information will help us to find problems like pipe stress, unstable foundations, weak frames and loose bolts, among other different causes. All the efforts to align our equipment and keep it within tolerance will be worthless if our machinery can’t keep its position. Therefore, the repeatability of the alignment check is our best opportunity to see how the rotating machinery equipment behaves.

HOW OFTEN SHOULD YOU CHECK?

There are guidelines for how often the shaft alignment should be checked. According to Mr. John Piotrowski and his Shaft Alignment Handbook, for newly installed rotating machinery the shaft alignment should be checked after 500 to 2000 hours of intermittent operation, or 1–3 months of continuous operation. If there was no apparent shift in the alignment, then next check should be made between 4500 and 9000 hours of intermittent operation or 6 months to 1 year of continuous operation. If no apparent shift occurred at any time, then checks should be made every 2–3 years. This interval can of course be influenced by factors such as equipment criticality etc.

If a moderate shift in alignment occurred at any time, then the rotating machinery equipment should be aligned to within acceptable tolerances. If a radical shift occurred, then additional investigation should begin to determine what is causing the shift – a root cause analysis. For example, any indication of excessive wear and tear will also be an indicator of a “non-healthy” machinery installation.

THE IMPORTANCE OF DOCUMENTATION

To have properly documented shaft alignment checks is essential in order to avoid repeating the same installation errors, or to discover and follow up on recurring problems. As you of course understand, there is no exact answer to the headline question. But the documentation will give you a very good understanding of what happens on the way, and help to keep your machinery stay aligned as long as possible.

By Roman Megela – Senior Reliability Engineer

This article was written by our partner Easy-Laser® AB and can also be viewed on their Blog here. Enjoy!