A Guide to Soft Foot and How it Can Damage Machinery
Soft foot is a condition that can cause significant damage to machinery. It occurs when one or more of a machine's feet do not make appropriate contact with the frame, baseplate, or foundation. Soft foot can be found in any piece of equipment, but it is most commonly found on motors. There are different types of soft foot, including rocking, angled/bent, squishy, and induced.
Rocking soft foot occurs when the foot is short, high, or even with the surface. Angled or bent soft foot is when the foot is bent, bowed, or angled on the baseplate or foundation. Squishy soft foot is when there are too many shims, dirt, or oil, which makes the motor bounce (acting similar to a spring). Induced soft foot occurs when external forces, such as pipe strain, cause the equipment to move and be forced out of position. A few visual examples are shown below.
It is essential to check for soft foot to prevent costly breakdowns and production downtime. Soft foot can be checked utilizing a laser alignment tool, which is much faster and less tedious than the manual method (dial indicators). Lack of training and/or experience can lead to missed soft foot, and it is vital to train personnel to identify and correct soft foot issues.
Industry standards for rotating equipment recommend no more than 5 shims with a maximum height of ⅓ of an inch except in exceptional circumstances. This prevents damage to the equipment from excessive shimming.
Soft foot can cause significant damage to machinery, and it is crucial to address it during installation or after any maintenance event. When soft foot is present, it can cause misalignment between driven equipment and motor and be very destructive to the coupling, bearings, mechanical seals, shaft(s) and/or any other component.
In vibration analysis, soft foot typically shows up with a high 1X with a lower 2X and a higher than usual 2X line frequency. These vibrations can be easily measured with an accelerometer utilizing a wireless sensor or vibration analyzer.
In conclusion, soft foot is a condition that can cause severe damage to machinery. Adding a standard procedure to check for soft foot after any machinery maintenance event is optimal so it can be identified and eliminated. By identifying and correcting soft foot, maintenance professionals can prevent costly repairs and downtime, ultimately leading to optimal reliability of plant machinery. Check out this video to learn more!