Hot alignment checks are often unsuccessful because of delays in installing measuring devices on the equipment which has just been shut down.
Even when good planning and organization allowed you to take readings within minutes of shutdown, these readings only address the so called “Thermal Growth”. Often the effects of thermal growth on alignment had been calculated fairly accurately and the “hot alignment” check confirmed them, but still, excessive vibration persists and continues to be traceable to misalignment.
The problem is that machinery moves during operation for reasons unrelated to thermal effects.
Dynamic rather than thermally induced movements may cause machinery to operate misaligned. Since these dynamic effects disappear before the machinery stops rotating, hot alignment checks cannot measure them.
The non-thermal moves, both vertical and horizontal, are often as large or larger than the thermal moves but much more difficult to calculate. In our experience the dynamic moves are usually ignored.
These movements can be caused by foundation problems, by pipe strains and stresses, loose anchor bolts or changes in the load, etc. Whatever the cause or causes, almost the only way to determine the movements is continuous computerized monitoring of the alignment.
When coordinated with records from the control room it often becomes clear why and how the machinery changed position. Proper “cold” alignment targeting thus becomes feasible and significant operational improvements are usually achieved.
Aside from the well known consequences of less wear on bearings, seals, couplings, etc. it is sometimes possible to increase the load for the equipment and last but not least, power consumption will reduce and result in savings which are a multiple of the cost of the monitoring equipment.
Several monitoring systems have been on the market for many years using dial indicators or proximity probes, etc. and now, fully automatic laser systems like the PERMALIGN and the new Rotalign Ultra LIVE TREND are available with suitably large measuring range.