ISO 24497-1:2020

Overview

ISO 24497-1:2020 – "Non-destructive testing - Metal magnetic memory - Part 1: Vocabulary and general requirements" defines the terminology and general application requirements for the metal magnetic memory (MMM) technique in non-destructive testing (NDT). This second-edition international standard establishes mandatory terms and general procedures for passive measurement and interpretation of the magnetic stray field (SF) of ferromagnetic objects to detect material and structural heterogeneities formed by fabrication and service history.

Key topics and requirements

• Vocabulary and definitions: Mandatory terms for consistent use in NDT documentation (e.g., metal magnetic memory, stray field, stray field indication (SFI), stray field gradient, median stray field gradient, magnetic index, lift-off).
• General principles: Use of residual magnetization and stray field distribution to reveal magneto-mechanical heterogeneity and likely defect locations.
• Objectives of MMM testing:
  • Detect heterogeneity in magneto-mechanical state and microstructure boundaries
  • Locate magnetic stray field aberrations for targeted inspection
  • Early diagnostics of fatigue damage and structural life estimation
  • Quick sorting of new vs. used components by magnetic heterogeneity
  • Improve efficiency by guiding other NDT methods (ultrasonic, X‑ray)
  • Quality control of welded joints (see Part 2 for details)
• Equipment requirements:
  • Sensitive magnetic sensors (fluxgate, magnetometer/gradiometer configurations)
  • Digital data acquisition, display, storage and external computer interface
  • Position-encoded sensor movement (scanner or equivalent)
  • At least two measurement channels (measurement + compensation for external fields)
  • Sensor characteristics and setup must be documented in the test report
• Inspection constraints: Effects of lift-off (sensor-to-surface distance), external electromagnetic fields, temperature changes (thermoremanent magnetization), intentional demagnetization, and surface insulation must be considered.
• Procedure & reporting: Requirements for preparation, scanning, data processing (e.g., stray field gradient, magnetic index), test reporting, and safety/personnel qualification.

Applications

• Asset inspection of vessels, pipelines, boilers, turbines, heat exchangers, rails and structural components
• Early fatigue damage detection and remaining-life estimation
• Pre-screening to prioritize targeted ultrasonic, radiographic or other NDT
• Quality control of welded joints, spot/contact welds (detailed in ISO 24497-2)
• Sorting and acceptance of manufactured or in-service ferromagnetic parts

Who should use this standard

• NDT engineers and inspectors using or specifying MMM testing
• Manufacturers of MMM instrumentation and NDT service providers
• Welding quality assurance and maintenance teams
• Certification bodies and standards developers requiring consistent terminology

Related standards

• ISO 24497-2 - Testing of welded joints (application details)
• ISO 9712 - Qualification and certification of NDT personnel
• ISO/TS 18173 - General NDT terms and definitions

Keywords: ISO 24497-1:2020, metal magnetic memory, MMM, magnetic stray field, stray field indication, non-destructive testing, NDT, welded joints, fatigue diagnostics, stray field gradient, lift-off.