Shaft Alignment
So, how can you detect misalignment?
The best way to determine proper alignment is by measuring the equipment’s shaft alignment prior to initial startup or just after equipment repairs. Measurement tools vary from simple tools such as a straightedge ruler to more advanced options like dial indicators and laser guides. Generally speaking, laser-guided tools are the most accurate and easy-to-use tools. In addition, potential equipment thermal growth, equipment foundation, and proper shimming (to avoid soft foot induced equipment deflection) should be considered. This requires trained rotating equipment technicians equipped with the proper alignment tools.
When in operation, qualified technicians using vibration analysis as well as thermography can effectively evaluate if equipment is out of alignment. Typically high vibration at a frequency of two times the shaft running speed in the radial direction indicates potential parallel shaft misalignment. High vibration at the same frequency of the shaft running speed in the axial direction indicates potential angular misalignment. In some cases, both types of vibration readings occur, indicating a combination of angular and parallel misalignment.
Another effective vibration technique to confirm misalignment employs one times shaft running speed vibration phase readings. The phase reading is the angular measurement in degrees that the peak one times vibration occurs versus a reference point. If the shaft is aligned, the phase angle should be similar from driver to the driven equipment bearings. If the angular readings are off by 90 to 180 degrees this can indicate misalignment.
In addition to vibration, thermography can also indicate if there is shaft misalignment. If the temperature of the bearings next to the coupling and the coupling itself are at an elevated temperature, it can help confirm shaft misalignment. Together vibration and thermography can be a powerful combination to detect misalignment.
How do you correct misalignment?
When conducting an inspection, the first step is to shut down the machinery and use lock-out/ tag out safety protocols. Conduct a preliminary check of all key components, such as bearings and couplings.
Once you’ve made sure all the components are in order, perform the measurement using the tools you have available. Identify if the shaft positions are within the acceptable alignment tolerance. If not, you’ll need to identify how to re-position the equipment to ensure proper alignment. Make any necessary adjustments and then re-measure the shafts to see if you have corrected the issue.
Once you have ensured proper alignment, start your equipment using your standard start-up and safety protocols. Remember, measuring alignment should not be considered a one-off event. It’s critical to conduct regular alignment checks to help identify any alignment issues before they become a problem.
To help conduct proper assessment checks, we recommend you consult with your equipment supplier or rotating equipment specialists.
