ISO 24497-3:2007

INTERNATIONAL ISO
STANDARD 24497-3
First edition
2007-11-01
Non-destructive testing — Metal magnetic
memory —
Part 3:
Inspection of welded joints
Essais non destructifs — Mémoire magnétique des métaux —
Partie 3: Examen des assemblages soudés

Reference number
©
ISO 2007
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©  ISO 2007
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ii © ISO 2007 – All rights reserved

Contents Page
Foreword. iv
1 Scope . 1
2 Basic principles . 1
3 Inspection conditions. 2
4 Inspection devices. 2
5 Inspection planning. 3
6 Inspection procedure . 4
7 Processing of results . 5
Annex A (normative) Inspection report. 7
Annex B (informative) Example of stress concentration zones defined by a device with digital
indication of the magnetic field intensity. 9
Annex C (informative) An example of stress concentration zones defined by the device having
recorder and scanner . 11

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
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International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
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International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 24497-3 was prepared by the International Institute of Welding, Commission V, Quality control and quality
assurance of welded products, recognized as an international standardizing body in the field of welding in
accordance with Council Resolution 42/1999.
Requests for official interpretations of any aspect of this part of ISO 24497 should be directed to the ISO
Central Secretariat, who will forward them to the IIW Secretariat for an official response.
ISO 24497 consists of the following parts, under the general title Non-destructive testing — Metal magnetic
memory:
⎯ Part 1: Vocabulary
⎯ Part 2: General requirements
⎯ Part 3: Inspection of welded joints

iv © ISO 2007 – All rights reserved

INTERNATIONAL STANDARD ISO 24497-3:2007(E)

Non-destructive testing — Metal magnetic memory —
Part 3:
Inspection of welded joints
1 Scope
This part of ISO 24497 specifies the general requirements for the application of the metal magnetic memory
inspection method (MMM inspection) as a non-destructive testing method for quality assurance of welded
joints of pressurized components.
This part of ISO 24497 may be applied to welded joints in any type of products, pipelines, vessels, equipment,
and metal constructions, as agreed with the purchaser.
The terms and definitions for the process are contained in ISO 24497-1, and the general requirements of the
process are in ISO 24497-2.
2 Basic principles
2.1 МММ inspection is based on measurement and analysis of the distribution of self-magnetic-leakage
fields (SMLF) in the material of welded joints reflecting their technological history. Natural magnetization,
induced during the welding process in the Earth’s magnetic field, is used for the inspection.
2.2 МММ inspection permits the detection of mechanical stress concentration zones (SCZ) and gives
recommendations for additional non-destructive inspections in critical zones of vessels, pipelines, equipment,
and construction welded joints.
2.3 МММ inspection is complementary in its capability to other well-known non-destructive testing methods
(ultrasonic inspection, magnetic particle inspection, liquid penetrant inspection, and hardness testing).
2.4 МММ inspection allows the testing of welded joints of any size and configuration (butt, tee, fillet, lap,
edge, intermittent, etc.) regardless of weld material thickness on all types of ferromagnetic and austenitic
steels and alloys, as well as on cast irons.
2.5 МММ inspection may be carried out on the original weld after construction, during operation, or after
repair.
2.6 The following conditions can be found during MMM inspection:
⎯ residual stress concentration zones caused by welding, and their distribution along the welded joint;
⎯ zones of probable location of all types of micro- and macro-defects (pores, slag inclusions, discontinuities,
cracks, ruptures).
Defect classification by magnetic parameters is carried out following special testing techniques for a specific
welded joint.
2.7 MMM inspection can be used for inspection of the following:
⎯ the degree of quality degradation of welds by defects, and presence of developing defects;
⎯ the quality of welded joints at time of certification, choice, and optimization of welding technology.
2.8 The MMM inspection temperature range is from −20 °C to +60 °С, limited only by the conditions of the
operators’ and inspection tool’s normal operation.
2.9 Following MMM inspection, conventional non-destructive testing methods are applied in detected zones
of maximal stress concentration and probable location of micro- and macro-defects.
3 Inspection conditions
3.1 Structures and components as inspection objects (IO) may be inspected using MMM both while
operating under load and after releasing the working load.
3.2 No special surface preparation is required. It is recommended to remove insulation. In individual cases
non-magnetic insulation is allowed during inspection. The maximum permissible insulation layer thickness
shall be determined experimentally.
3.3 The permissible range of material thickness is defined by the descriptions of the techniques for specific
inspection applications.
3.4 The limiting factors for MMM application are the following:
⎯ the presence of artificial material magnetization;
⎯ the presence of a foreign ferromagnetic product near the IO;
⎯ the presence of an external magnetic field or an electric welding current flow closer than 1 m to the IO.
3.5 Acoustic noise or mechanical vibrations close to and at the IO do not influence the inspection results.
4 Inspection devices
4.1 For inspection of equipment using the MMM, specialized magnetometric devices are used. The
standard procedure for the definition of stress concentration zones (SCZ) is described in the manual of the
devices.
4.2 The principle of the operation of the specified devices is based on the registration of induced electrical
voltage impulses in the flux-gate sensor coil, when this sensor is placed in the self-magnetic-leakage field
(SMLF) in the near-surface area of the IO. Flux-gate sensors or other types, such as field meters or
gradiometers, may be used as SMLF intensity measuring sensors.
4.3 The devices shall have a display for the graphic documentation of the used inspection parameters, a
recording device with a microprocessor, a memory unit, and scanning devices realized by specialized sensors.
The device shall be able to transfer the information to the computer, in order to produce inspection reports.
The software for the processing of computerized inspection results should be provided with the device.
2 © ISO 2007 – All rights reserved

4.4 The specialized sensors shall be provided with the device. The individual sensor type to use is defined
by the MMM technique and the requirements of the IO. The sensor should have not less than two channels:
the measuring channel and a channel for the registration of the Earth’s external magnetic field.
With the sensors, an electronic module for the amplification of the measured field and a sensor for measuring
the inspected scan path length shall be supplied.
4.5 The admissible error of magnetic field intensity measurements is defined in the description of the
individual techniques depending on the IO.
4.6 The devices shall have the following metrological characteristics:
⎯ The relative error of the measured magnetic field for each measurement channel should not exceed ±5 %.
⎯ The relative error of the measured scan path length should not exceed ±5 %.
⎯ The measurement range of the devices should be not less ±1 000 A/m.
⎯ The minimal scanning step (distance between two adjacent scanning points of the inspection) is 1 mm.
...