Overview: ISO 24497-2:2020 - Metal Magnetic Memory (MMM) for Welded Joints
ISO 24497-2:2020 defines requirements for applying the metal magnetic memory (MMM) technique as a non-destructive testing (NDT) method for quality assurance of welded joints. The part covers inspection principles, manual and scanning procedures, data processing and reporting for welded joints in ferromagnetic products (pipelines, vessels, equipment and metal constructions). It references ISO 24497‑1 for vocabulary, equipment and preparation and requires follow-up conventional NDT where stray field indications (SFIs) are detected.
Key topics and technical requirements
- Scope & materials: Applies to welds in ferromagnetic and metastable austenitic steels and cast irons (evaluation on ferromagnetic phases only).
- Basic principle: MMM measures distribution of magnetic stray fields (SF) caused by residual magnetization from welding; SF patterns indicate probable defect zones.
- Temperature range: Measurement range from −20 °C to +60 °C (limited by sensor/operator).
- Inspection modes:
- Manual scanning: Perimeter and perpendicular scans of weld, HAZ (typically 30–50 mm width), recording SF extrema and H = 0 crossings.
- Scanning systems: Multi‑channel sensor heads (e.g., flux‑gate transducers, gradiometer configurations) with position encoder for continuous mapping.
- Measurement parameters:
- Magnetic field gradients K = ΔH/Δx (along a line) and K = ΔH/Δy (between lines).
- Magnetic parameter m = K / K_med to quantify non‑uniformity; areas where m exceeds a threshold m_lim are identified as SFIs.
- Sampling distances must be set according to weld geometry and should not exceed wall thickness or sensor size.
- Post‑processing & reporting:
- Marking of segments with SFIs, calculation of K and m values, and preparation of test reports (Annex A) and logbooks.
- Mandatory follow-up with conventional NDT (e.g., UT, radiography) per ISO 17635 for confirmation.
Practical applications and users
ISO 24497-2 is intended for organizations that need early detection and localization of probable weld defects and for optimizing welding procedures:
- NDT engineers and technicians performing magnetic testing and weld inspection.
- Welding quality assurance (QA) teams in fabrication shops, pipeline and pressure‑vessel construction.
- Asset owners / operators conducting in‑service inspections and repair assessments.
- Third‑party inspection bodies and certification organizations verifying weld integrity.
Benefits include rapid surface/near‑surface screening over long weld runs, targeted follow-up inspections, and improved efficiency in maintenance and safety programs.
Related standards
- ISO 24497-1:2020 - Metal magnetic memory - Vocabulary and general requirements
- ISO 17635 - Non‑destructive testing of welds - General rules for metallic materials
Keywords: ISO 24497-2:2020, metal magnetic memory, MMM, NDT, welded joint inspection, magnetic stray field, flux-gate sensor, HAZ, weld inspection, stray field indication (SFI).