Eddy Currents Testing (ET) Level I & II

Eddy Current Testing (ET) Level I & II Course

The Eddy Current Testing (ET) Level I & II Course is designed to provide comprehensive training in eddy current testing, a widely used non-destructive testing (NDT) method for detecting surface and sub-surface flaws in conductive materials. This technique uses electromagnetic induction to detect defects such as cracks, corrosion, and material thickness variations. Eddy Current Testing is frequently applied in industries like aerospace, power generation, automotive, and manufacturing.

Course Objectives:

Level I:

• Understand the basic principles of eddy current testing.
• Learn to set up and calibrate eddy current equipment for inspections.
• Recognize and interpret basic signals related to surface and sub-surface discontinuities.
• Acquire practical experience in conducting basic eddy current inspections under supervision.

Level II:

• Gain advanced knowledge in eddy current techniques and signal interpretation.
• Independently perform complex ET inspections, including multi-frequency and phase analysis.
• Learn how to evaluate indications, prepare detailed reports, and supervise Level I personnel.
• Become proficient in using advanced ET equipment and interpreting results according to industry standards.

Key Components of the Course:

1- Introduction to Eddy Current Testing (ET)

• Basic principles of ET: Eddy currents are induced when alternating current flows through a coil near the surface of a conductive material. These currents generate a secondary magnetic field that can be analyzed for defects.
• Electromagnetic induction: The relationship between coils, magnetic fields, and conductive materials forms the foundation of eddy current testing.
• Advantages of ET:
  • Suitable for inspecting surface and sub-surface defects without needing contact with the material.
  • Can be performed on painted, coated, or thin materials.
  • Detects cracks, corrosion, and thinning in conductive metals.

2- Eddy Current Testing Equipment

• Probes and coils: Different types of probes are used depending on the application:
  • Surface probes: Used for detecting surface cracks or corrosion.
  • Encircling coils: Used for inspecting tubes or rods.
  • Pencil probes: Used for precision applications in small areas.
• Instrumentation:
  • ET instruments: Generate alternating current, measure eddy currents, and display the resulting data as signals.
  • Phase analysis: Helps distinguish between defect types based on the phase angle of the signal.
  • Multi-frequency equipment: Allows for inspection of materials with varying characteristics and different depths.

3- Material Properties and Their Effect on ET

• Understanding how conductivity, permeability, and geometry affect eddy current signals.
• Conductivity: Materials with higher electrical conductivity produce stronger eddy current signals.
• Permeability: Ferromagnetic materials require special techniques due to their high magnetic permeability, which can distort the eddy current signals.
• Geometry: The shape, thickness, and curvature of a component can affect the distribution of eddy currents and the accuracy of the inspection.

4- Types of Discontinuities Detected by ET

• ET can detect a variety of defects, including:
  • Surface cracks: Fatigue cracks, weld cracks, or stress corrosion cracks.
  • Sub-surface defects: Corrosion, voids, and inclusions up to a certain depth.
  • Thickness variations: Changes in material thickness, such as from wear or corrosion.
  • Conductivity variations: ET can detect material changes like heat treatment variations, alloy differences, or microstructural changes.

5- Eddy Current Testing Techniques (Level I)

• Basic testing techniques:
  • Surface scan: Inspecting surfaces for cracks, pits, or other discontinuities.
  • Lift-off technique: Measuring coating thickness or detecting the presence of non-conductive layers.
  • Edge effect compensation: Techniques to minimize signal interference from part edges.
• Step-by-step process for performing an ET inspection:

1- Surface preparation: Ensure the surface is clean and free from debris, although coatings do not always need removal.

2- Probe selection and setup: Choose the appropriate probe based on material and inspection requirements.

3- Calibration: Calibrate the equipment using known reference standards to ensure accuracy.

4- Conducting the inspection: Move the probe over the inspection area while monitoring the ET signals on the instrument display.

5- Signal interpretation: Identify any indications of defects based on the signal’s amplitude and phase shift.

6- Advanced ET Techniques and Signal Interpretation (Level II)

• Signal analysis:
  • Phase and amplitude interpretation: Understanding how different types of defects affect signal characteristics.
  • Frequency selection: Lower frequencies are used for deeper inspections, while higher frequencies are used for surface inspections.
  • Multi-frequency ET: Using multiple frequencies to inspect layered materials or components with varying properties.
• Advanced inspection techniques:
  • Array probes: Provide more comprehensive coverage and faster inspections.
  • Pulsed Eddy Current (PEC): A variation used for corrosion detection in thicker or layered materials.
  • Remote field testing (RFT): Used for inspecting the inside of tubes or pipes.

7- Interpretation and Evaluation of Indications

• How to classify and evaluate ET indications:
  • Relevant indications: Defects like cracks, corrosion, or thinning that affect the integrity of the component.
  • Non-relevant indications: Signals from geometry changes, edges, or surface features that do not represent defects.
• Defect characterization:
  • Understanding the depth, size, and orientation of defects based on signal analysis.
  • Distinguishing between surface-breaking cracks and sub-surface discontinuities.

8- ET Standards and Codes

• Overview of key standards and codes governing eddy current testing:
  • ASME Section V: Nondestructive testing standards for ET.
  • ASTM E309: Standard practice for eddy current examination of steel tubular products.
  • ASTM E1004: Standard practice for determining electrical conductivity using eddy current.
  • API 510: Visual inspection and NDT techniques for pressure vessels.
• Acceptance criteria: Understanding the criteria for acceptable and rejectable defects based on industry and component-specific standards.

9- Reporting and Documentation (Level II)

• Preparing detailed ET inspection reports:
  • Describing the methodology used, including equipment settings, probe types, and calibration details.
  • Documenting indications: Defining the location, size, and severity of detected defects.
  • Making recommendations: Further testing, repairs, or acceptance of the component based on the inspection results.

10- Practical Applications and Hands-on Training

• Hands-on practice in performing eddy current inspections on a variety of materials and components.
• Using advanced ET equipment such as multi-frequency instruments and array probes.
• Practical exercises in signal interpretation, defect characterization, and reporting.
• Practical exams: Demonstrating proficiency in using ET equipment, conducting inspections, and interpreting results.

Target Audience:

• NDT Technicians: Specializing in eddy current testing for quality control and material integrity checks.
• Aerospace Inspectors: Responsible for inspecting aircraft components like engines, wings, and landing gear for cracks and corrosion.
• Power Generation and Automotive Inspectors: Inspecting turbines, pipes, and other metallic components for surface or sub-surface flaws.
• Quality Control Engineers: Evaluating materials and components for defects using ET in manufacturing processes.

Certification:

• Level I Certification: Qualified to perform basic ET inspections under supervision after completing training and exams.
• Level II Certification: Qualified to independently perform ET inspections, supervise Level I personnel, and prepare inspection reports after completing advanced training and practical exams.