Overview - What ISO 29821:2018 covers
ISO 29821:2018, "Condition monitoring and diagnostics of machines - Ultrasound - General guidelines, procedures and validation," provides international guidance for using airborne (AB) and structure-borne (SB) ultrasound in machine condition monitoring and diagnostics. The standard specifies methods and requirements for ultrasonic examination, safety recommendations, sources of error, data interpretation, assessment criteria and reporting. It applies to ultrasonic inspections above 20 kHz and includes practical material such as example leak surveys, typical test reports and a sensitivity validation procedure.
Key technical topics and requirements
- Principles of AB & SB ultrasound: how high‑frequency sound (>20 kHz) propagates through air and structures and how this affects source localization and signal attenuation.
- Ultrasound equipment and sensors: guidance on sensor types (airborne microphones, contact modules/structure-borne sensors), instrument characteristics and frequency response considerations.
- Data collection methods: comparative ultrasound scanning and the baseline (quantitative) method for establishing reference levels.
- Assessment criteria: guidelines for establishing severity‑assessment criteria for anomalies detected by ultrasound, including error sources, accuracy and repeatability.
- Interpretation and diagnostics: principles for interpreting ultrasonic waveforms and spectral data; guidance on fault generation mechanisms such as surface friction, fluid flow, ionization and impacts.
- Validation and sensitivity: procedures to validate sensor/instrument sensitivity (example: ultrasonic tone generator method included as an informative annex).
- Training, monitoring interval and reporting: recommendations for operator competence, suitable inspection intervals and standardized reporting formats (example reports provided in annexes).
- Safety and limitations: safety recommendations for inspections and discussion of potential false readings (e.g., sonic reflection, background noise).
Practical applications and intended users
ISO 29821:2018 is designed for practitioners using ultrasound as part of condition monitoring and machinery diagnostics. Typical uses and users include:
- Reliability engineers and maintenance managers implementing ultrasound programs for leak detection, bearing and lubrication monitoring, and electrical discharge detection.
- Condition monitoring technicians and NDT specialists performing airborne and structure-borne ultrasonic surveys and establishing baseline datasets.
- Plant and asset managers seeking rapid, non‑invasive methods to localize leaks, detect lubrication issues, or identify early-stage faults.
Ultrasound is particularly valuable for fast leak localization, detecting slow-speed bearing faults and assessing lubrication condition, and as a complementary method correlated with vibration, thermography and acoustic emission.
Related standards
Normative references cited include ISO 13372 (vocabulary), ISO 13379-1 (data interpretation guidelines), ISO 13381-1 (prognostics) and ISO 17359 (general condition monitoring guidelines), which support consistent terminology and diagnostic practices across condition‑monitoring activities.
Keywords: ISO 29821:2018, ultrasound condition monitoring, airborne ultrasound, structure-borne ultrasound, ultrasonic inspection, machine diagnostics, severity assessment, sensitivity validation.