Análise de métodos de testes não destrutivos: Teste de partículas magnéticas (MT) – fornecendo soluções de tubulação

Analysis of Non-Destructive Testing Methods: Magnetic Particle (MT) Testing – Providing Piping Solutions

Magnetic Particle Testing Principles

Magnetic particle testing is a non-destructive testing method that uses magnetic powder as an indicator medium to detect defects. According to the type of magnetic particle medium used during magnetization, testing methods are divided into wet and dry methods. According to the application time of magnetic powder on the workpiece, testing methods are divided into continuous methods and residual magnet methods.

The part made of ferromagnetic material is magnetized. Due to the existing discontinuities, the magnetic induction lines on the surface and near the surface of the part are locally distorted, resulting in stray magnetic fields. Magnetic particles adsorbed on the surface of the part form optically visible magnetic marks under adequate lighting and thus indicate the position, size, shape and severity of discontinuities.

20231022121616 27943 - Análise de métodos de ensaios não destrutivos: ensaios de partículas magnéticas (MT)

1 – magnetic field leak; 2 – cracks; 3 – pores close to the surface;

4- scratches; 5- Internal pores; 6- Magnetic field line; 7- Workpiece

Applications for magnetic particle testing

Materials and defect properties relevant to magnetic particle testing:
Magnetic particle testing is only suitable for detecting surface and near-surface defects in ferromagnetic materials and is not applicable to non-ferromagnetic materials such as austenitic stainless steel/aluminum alloys/titanium alloys/plastics.
Relevant material areas for magnetic particle testing:
a) Magnetic particle inspection is applicable to almost all product forming processes, including castings, forgings, welds, tubes and plates.
b) The types of materials suitable for magnetic particle testing are:

  • Cast iron;
  • Various carbon and alloy steels;
  • Ferritic stainless steel;
  • Martensitic stainless steel;
  • Ferromagnetic materials such as nickel and nickel alloys.

Magnetic Particle Testing Process Flow

The process flow of magnetic particle testing essentially includes pretreatment, magnetization, application of magnetic powder, observation and evaluation of magnetic marking display, recording and post-processing.

Surface preparation and equipment for magnetic particle testing

a) Surface requirements for inspection:

  • The surface to be tested must not have rust, oxide layer, welding spatter, iron filings, burrs or various protective layers that affect the magnetic particle test.
  • The surface appearance must be checked and qualified. If the surface irregularity affects the inspection, it must be polished.
  • The coating thickness cannot exceed 0.05 mm;
  • If necessary, a contrast agent may be administered.

b) Items to be checked:

  • magnetic particles; Contrast medium (if applicable);
  • lighting equipment; illuminometers; Black light illuminator (if applicable); black light (if applicable);
  • magnetic particle flaw detector; Test block for lifting force/sensitivity test piece.

Advantages and Limitations of Magnetic Particle Testing

Advantages of Magnetic Particle Testing Limitations of Magnetic Particle Testing
Short employee training times, fast entry High personnel costs (especially with the magnetic fork method)
Easy device operation N/A
Surface and near-surface defects with high sensitivity to cracking It can only detect ferromagnetic materials; Demagnetization must be taken into account
Intuitive display; Fast detection speed; Good repeatability Two magnetization directions are required in each case, and magnetic field coverage must be taken into consideration for large parts.
Light pollution N/A

Content Requirements for Magnetic Particle Test Records and Reports

  • registration and report number;
  • The standards and levels of inspection and acceptance execution;
  • Detection object information: name, drawing number, part number, material, heat treatment status, detection location, detection proportion, surface condition, detection time, etc.;
  • Testing equipment and devices (brand, model, number);
  • The type of magnetic particle, the concentration of the magnetic suspension and the method of applying the magnetic particle;
  • Magnetization method, current type and magnetization specifications;
  • environmental conditions;
  • Checking detection sensitivity, standard test blocks, etc.;
  • Schematic representation of inspection;
  • Test data evaluation results;
  • testing personnel;
  • Exam time and location.

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