Soft foot is a condition in which one or more machine feet do not sit flat on the baseplate, leading to distortion in the machine frame. Addressing this issue is crucial as it can result in
misalignment, increased vibration, and premature component failure.
What is the Impact of Soft Foot?
The consequences of soft foot include accelerated
wear of bearings, couplings, and seals, reduced machine life, increased unscheduled downtime, and potential safety hazards. According to ANSI/ASA S2.75-2017/Part 1, addressing soft foot is essential to ensure the proper alignment and
operation of rotating equipment.
Where to Inspect for Soft Foot?
Key inspection points include machine feet, baseplate, coupling, shaft alignment, and foundations. Tools such as dial indicators, feeler gauges, and
laser alignment tools are used for measurement.
Why is it Important to Address Soft Foot?
Addressing soft foot prevents costly repairs, enhances safety, and ensures reliability. Misalignment caused by soft foot can lead to significant issues such as seal failures, bearing failures, and excessive vibration, ultimately impacting the efficiency and lifespan of the equipment.
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Diagnosing Soft Foot: The process involves visual inspections, measuring foot height using feeler gauges, and assessing alignment with dial indicators or laser alignment tools. ANSI/ASA S2.75-2017/Part 1 provides guidelines for identifying and analyzing soft foot conditions.
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Correcting Soft Foot: Soft foot can be corrected using methods such as shimming, machining, and re-securing bolts. Shims should be placed to ensure full contact under machine feet, and surfaces may need reconditioning in severe corrosion or fretting cases.
Importance of Foundations, Baseplates, and Construction Centerline
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Foundations: Should be stable, level, and flat to support machinery and absorb vibrations.
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Baseplates: Must be machined to be flat and coplanar, with correct shimming to ensure proper contact.
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Construction Centerline: Ensures the machine's geometric center aligns with the base, preventing misalignment.
Actionable Plan for Addressing Soft Foot
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Initial Inspection: Conduct visual and measurement inspections.
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Detailed Assessment: Use precision tools to measure gaps under each foot and determine internal distortion is to acceptable tolerance.
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Correction: Apply shims, re-machine surfaces, and re-secure bolts as necessary.
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Documentation: Record all measurements, corrections, and final alignment values.
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Preventive Measures: Schedule regular inspections, train maintenance teams, and use monitoring tools to detect early signs of soft foot.
Conclusion
To ensure reliability and safety,
diagnosing and correcting soft foot in rotating equipment is essential. Implementing a regular maintenance program can prevent soft foot and ensure the proper alignment of machinery.