ISO 21940-13:2012

Overview

ISO 21940-13:2012 - Mechanical vibration - Rotor balancing - Part 13 provides criteria and safeguards for the in-situ balancing of medium and large rotors installed in their own bearings on site. The standard describes when in-situ balancing is appropriate, the instrumentation and measurement practices required, safety implications, and the reporting and record-keeping needed to support safe, auditable balancing work. It can also be used as the basis for contracts to perform in-situ balancing. (Note: the standard does not prescribe methods to calculate correction masses from vibration data.)

Key topics and technical requirements

• Feasibility and criteria: Conduct a feasibility study before in-situ balancing to confirm accessible correction planes can influence the observed vibration. In-situ balancing is appropriate only when the cause of high vibration is understood and balancing is judged safe and practical.
• Vibration components: In-situ balancing targets the once-per-revolution (1×) component; this method is useful only when the 1× component is a significant part of overall vibration.
• Instrumentation and measurement:
  • Requirements for vibration measurement equipment and sensing (reference to ISO 2954 and ISO 10817-1 for instrument guidance).
  • Attention to measurement errors, phase reference signals, and repeatability of vibration vectors during operations.
• Operational conditions: Balancing should be performed under defined normal operating conditions; transient-speed performance may be traded off to achieve acceptable steady-state running vibration.
• Safeguards and safety:
  • Personnel safety when working near rotating shafts.
  • Special operating envelopes while correction masses are installed.
  • Integrity and secure attachment of correction masses.
  • Machine-specific precautions (Annex A).
• Reporting and records: Detailed reporting structure (equipment, results, text information) including example report templates (Annexes B and C).

Practical applications and users

ISO 21940-13 is intended for:

• Maintenance and reliability engineers performing on-site balancing
• Rotating machinery technicians and balancing service providers
• OEMs and plant engineers specifying contractual balancing work
• Condition monitoring and vibration analysts documenting corrective actions Typical applications include in-situ balancing of fans, compressors, turbines, generators and other medium/large rotating equipment where dismantling or removal to a balancing machine is impractical or uneconomic.

Related standards

ISO 21940-13 is part of the ISO 21940 series and references other standards for vocabulary and measurement practice, including:

• ISO 21940-2 (vocabulary), ISO 21940-11/12 (rigid/flexible rotor procedures)
• ISO 2954, ISO 7919, ISO 10816, ISO 10817-1, ISO 11342

Keywords: ISO 21940-13, in-situ balancing, rotor balancing, mechanical vibration, medium and large rotors, vibration measurement, correction masses, balancing report, safeguards.