BS ISO 24497-1 pdf free download
BS ISO 24497-1-2020 pdf free download.Non-destructive testing — Metal magnetic memory Part 1: Vocabulary and general requirements.
4 General requirements
4.1 The MMM technique is based on measurement and analysis of the SF distribution of ferromagnetic objects. The magnetization can reflect the microstructural and technological past and load history of ferromagnetic metallic components, including welded joints. SFs generated by the residual magnetization formed in magnetic fields during the process of the fabrication and the service life time of the IO shall be used during testing.
4.2 The ММM technique enables the detection of SFIs and gives recommendations for additional non- destructive testing of vessels, pipelines, equipment (e.g. steam generators, turbines, heat exchangers, rails), and construction welded joints. ISO 24497‑2 shall be applied for testing of welded joints.
NOTE SFIs of IOs are conditioned by the fabrication technology (fusion, forging, rolling, turning, press forming, thermal treatment, etc.).
4.3 Under certain conditions the MMM technique can be used on non‑magnetic IOs, particularly if a ferromagnetic phase is present (e.g. metastable austenitic steels, mill scale, coatings).
NOTE Metastable austenitic steels can be inspected if their microstructure is sensitive to γ ‑ α phase transformation [18] . The evaluation of SFs is restricted to the ferromagnetic phase.
4.4 The temperature range during MMM testing shall be within the normal and safe working range for the operator (NDT inspector).
5 Requirements for the inspected object
5.1 Equipment and structures (IOs) should be inspected by MMM in in‑service state (under load) as well as in the maintenance state (after removal of operating loads). If possible, the initial magnetic service state of the IO should be determined.
5.2 Surface dressing and preparation are not required. It is recommended to remove insulation to reduce sensor to surface lift‑off to gain reliability and avoid SFI from the insulation. In particular cases, non magnetic insulation can be allowed during inspection. Any permissible insulation layer shall be verified experimentally. The results shall be attached to the test report.
5.3 Limiting factors for the application of MMM testing are the following:
— de‑magnetization and intentional magnetization of the IO;
— foreign external (electro-)magnetic fields near to the inspected object, near the inspected region of interest;
— temperature changes can influence the test results (e.g. at Curie temperature);
— Sensor to IO surface distance (lift‑off) and its changes during the measurement.
5.4 Strong temperature changes in the IO cause changes of the thermoremanent magnetization and should be taken into account during processing of the inspection results.
5.5 Sources of SFI along the IO are the following:
— shape and geometry of the IO (geometry changes and the edges of the IO) are sources of SF and have to be considered, because surface geometry are sources of strong local stray and demagnetizing fields [24][25][46][60] ;
— high mechanical stress gradients;
— boundaries of heterogeneous plastic deformation;
— changes in the microstructure;
— external magnetic fields, e.g. (welding) electric current flow at the inspected object, strong and heterogeneous magnetic fields close to the tested area;
— foreign ferromagnetic material on the inspected object and near the region of interest;
— local “artificial” magnetization, induced due to former magnetic fields;
— second phase particles with different magnetic properties;
— temperature changes.
All the above sources can influence the evaluation of an SFI and should be taken into account for SFI assessment.
6 Requirements for the test equipment
6.1 The operation principle shall be based on sensitive magnetic sensors detecting the SF of the near-surface area of the IO. Magnetic-sensitive probes (e.g. fluxgate transducers) in magnetometer or gradiometer configuration can be used.BS ISO 24497-1 pdf download.
