Introduction

Magnetic Testing (MT) is a non-destructive testing (NDT) method used to detect surface defects using a magnetic field. ISO 17638 is the international standard for magnetic testing, outlining the requirements and guidelines for this technique.

Fundamental Principles of Magnetic Testing
Magnetic testing operates through the application of a magnetic field. The basic principles are:

1.The tested material is placed within a magnetic field.
2.The magnetic field is applied perpendicular to the material's surface.
3.If there is a defect within or on the surface of the material, the magnetic flux lines will follow these defects and emerge from the material's surface.
4.The presence of defects is detected based on the changes in the magnetic flux lines.

Scope of the Standard
ISO 17638 covers the application, qualification, and personnel certification for magnetic testing. The standard encompasses the following topics:

1. General Requirements: General requirements regarding the fundamental principles and application of magnetic testing.
2. Inspection Procedures: Determination, implementation, and documentation of inspection procedures.
3. Material Properties: Properties and classification of materials to be inspected.
4. Equipment and Material Selection: Selection and calibration of equipment and materials to be used for magnetic testing.
5. Qualifications of Inspection Operators: Qualifications, training, and certification of operators who will perform magnetic testing.

Application of Magnetic Testing
The application of magnetic testing involves the following steps:

1.Surface Preparation: The surface to be inspected must be cleaned of contamination and prepared appropriately. Oil, dirt, paint, rust, or other contaminants on the surface can affect the magnetic flux and lead to incorrect results. Surface preparation is performed through methods such as cleaning, grinding, or surface treatment.

2.Magnetization: The tested material is magnetized to create an appropriate magnetic field. The magnetic field can vary depending on the material's properties and inspection requirements. The magnetic properties of the material should be considered during the magnetization process. Magnetization can be achieved through various methods, such as temporary or permanent magnets, electromagnetic coils, or magnetic flux permeable materials.

3.Defect Detection: A suitable method is used to identify defects on the magnetized material. These usually include magnetic particle inspection or magnetic flux leakage methods. Magnetic particle inspection relies on the principle of applying magnetic particles to the magnetized surface and detecting defects through these particles. Magnetic flux leakage involves visualizing the magnetic flux lines on the magnetized surface and detecting defects through changes in these flux lines.

Magnetic testing (MT) is a commonly used method for inspecting welded joints. Some defects that can be detected during this test include:
- Surface Defects: Magnetic testing is generally used for detecting surface defects. These may include cracks, holes, depressions, surface pits, and blemishes. These defects can result from errors during the welding process or problems in material preparation.
- Lack of Penetration: Magnetic testing can also detect situations where the penetration within the weld is insufficient. This can occur when the weld material does not melt and join properly, or when the weld filler material does not penetrate deeply enough.
- Lack of Fusion: Magnetic testing can identify instances where the weld material or filler material does not join adequately, resulting in a lack of fusion. This can happen when insufficient heat is applied during the welding process or when the weld material does not flow correctly.
- Weld Cracks: Magnetic testing can detect cracks that occur in the weld zone. These cracks can result from stresses or material defects during welding.
- Cold Laps: Situations where various defects occur as the weld material cools can also be detected through magnetic testing. These defects can arise when the cooling rate during the welding process is uncontrolled or when the material is not preheated properly.
The detection of these defects is crucial for ensuring the quality and safety of welded joints. Magnetic testing can provide reliable results when performed in accordance with specific standards and procedures.

4.Defect Evaluation: The size, shape, and significance of the detected defects are evaluated. This evaluation is based on inspection specifications, industry standards, or customer requirements. The size of the defects should be within acceptable limits depending on the type of defect, material properties, and operating conditions.

5.Reporting: A detailed report of the detected defects is prepared and communicated to relevant stakeholders if necessary. The report should include the location, size, type, and class of the detected defects. Additionally, details of the inspection process, equipment used, information about the inspection operator, and interpretation of the inspection results should also be included in the report.

The magnetic testing application process should be carried out by trained and certified personnel. The use of correct equipment and adherence to standard procedures ensure reliable and repeatable results.

Conclusion
Magnetic Testing (MT) is a widely used non-destructive testing method for detecting surface defects. The ISO 17638 standard standardizes the application and evaluation of magnetic testing, which is essential for obtaining reliable results.