Mastering Electromagnetic NDT Techniques with EMWorks Solutions

Non-Destructive Testing (NDT) Inspection 

NDT refers to an array of inspection methods that allow inspectors to evaluate and collect data about a material, system, or component without permanently altering it. NDT is divided into various methods of non-destructive testing, each based on a particular physical phenomenon such as the Electromagnetic NDT: EM NDT. 

Electromagnetic inspection is a non-destructive testing method that includes magnetic fields and electric currents. It allows measuring a response caused by a defect on a metallic test object. Below are the most common electromagnetic-based NDT methods: 

• Eddy Current Testing (ECT), 
• Alternating Current Field Measurement (ACFM), 
• Eddy Current Pulsed Thermography (ECPT), 
• Magnetic Flux Leakage for Tube Crack Inspection (MFL). 

EMWorks Solution for EM NDT Applications 

Design Challenges  

CAD design and simulation process solves design challenges posed by NDT devices. It saves time and money, reduces the manufacturing cycle, and provides innovative and efficient solutions. 

The main design challenges posed by EM NDT devices are:  

• Computation of static and time-varying magnetic fields, 
• Calculate eddy currents in conductive components, 
• Optimization of inductor shapes and magnet arrangements to improve crack detection, 
• Calculate the inductance, resistance, and impedance of the sensor coil, 
• Predict the voltage and current of the coil sensor, 
• Test several configurations and design scenarios, 
• Compute temperature caused by eddy currents and other electromagnetic losses. 

Electromagnetic NDT Inspection Tools 

EMWorks Solution 

EMWorks offers a powerful and comprehensive solution to efficiently design and analyze NDT applications based on electromagnetics. This package includes the following: 

• 2D and 3D electromagnetic analysis, 
• Static and time-varying magnetic and electric field calculations, 
• Eddy currents, skin, and proximity effects, 
• Circuit parameters calculation,  
• Sensor voltage and current prediction, 
• Integrated circuit simulator, 
• Embedded Multiphysics options, 
• CAD integration for better and easier geometry handling and manipulation, 
• Single platform for 2D and 3D simulations, 
• Parametric analysis, multiconfiguration simulations. 

ECT Method 

Eddy current testing (also known as eddy current inspection) is a method used in non-destructive testing, employing electromagnetic induction to detect surface defects and slightly sub-surface flaws in materials. The main areas where ECT is used include crack and corrosion detection, non-conductive coating thickness measurement, material identification, and heat treatment conditions. This method is efficient for non-magnetic material inspection used in both surface and sub-surface defects; able to identify and quantify cracks under plates; measure the thickness of non-conductive paint and coating; investigate changes in material and microstructure properties.

The main steps of ECT inspection involve: 

• Eddy current coil generates a primary magnetic field, 
• The primary magnetic field induces eddy currents in the material, 
• Eddy currents generate a secondary magnetic field in the opposite direction, 
• Coil impedance changes, as a result, 
• Hence, the impedance change is measured, analyzed, and correlated to defect dimensions.

ECT Working Principle [1] 

Case Study1: TEAM Problem 15 [2] 

ECT Team Problem 15 Model 

Current Density Animation with Crack Presence 

Current Density Animation without the Crack Presence 

Impedance Variation with Crack Presence 

Resistance Variation with Crack Presence 

Inductance Variation with Crack Presence 

ACFM Method 

ACFM is an electromagnetic inspection technique that introduces an alternating current in the surface of a component to detect surface defects. The presence of a crack disturbs the electromagnetic field; the variation in the magnetic field is captured and analyzed by a sensor placed above the specimen; the operator is instantly alerted to the presence of defects. This technique is suitable for both magnetic and non-magnetic material inspection.  

The working principle of the ACFM method includes the following steps:  

• The ACFM sensor, which is composed of one or more coils, creates eddy currents on the tested specimen, 
  
• These eddy currents are disturbed in the presence of a crack, which also causes a disturbance in the magnetic field above the surface, 
  
• This variation in the magnetic field is captured and analyzed by a sensor that measures the location and size of the crack.
  

ACFM Principle 

Case Study 2: ACFM Device [3] 

ACFM Probe Model [3] 

Current Distribution Across Specimens with Coil Movement 

Magnetic Flux Density Across Specimen with Coil Movement 

By Variation with Probe Movement along the Crack  

Bz Variation with Probe Movement along the Crack

ECPT Method 

Infrared thermography (IRT) is one of the NDT methods that has been widely used recently in various fields such as automobile, spaceflight, and petrochemical industry. Eddy current thermography, as its name suggests, is an IRT technique based on the eddy current as the source of heat. In this method, the test specimen is exposed to an alternating magnetic flux generated by a coil; the magnetic flux induces eddy currents which, in turn, heats the inspected region according to Joule heating law. An IR camera captures the thermal response of the tested object.  Electromagnetic-thermal non-destructive inspection has been proposed as an alternative to classical ECT techniques, by combining electromagnetic excitation, induction heating, and inspection by transient infrared thermography technology. 

ECPT Inspection Probe 

Advantages of ECPT 

• High reliability and accuracy, 
• Wide scope, 
• High detection speed, 
• Contactless inspection. 

Case Study 3: Crack Inspection by ECPT [4] 

ECPT Inspection Model [4] 

Current Density Plot of the ECPT Design 

EMWorks solution includes several embedded multi-physics options like steady and transient thermal calculations. The electromagnetic study can be coupled to a thermal solver to get temperature results along with all magnetic results. This is performed within the same and single study. Fringe plots of the temperature caused by joule heating are shown in the figures below. The crack area was modeled as a separate part to better investigate the temperature. There is a high temperature around the crack which is captured and detected by the infrared camera in real life.  

Temperature Distribution across the ECPT Design 

Magnetic Flux Leakage for Tube Crack Inspection- MFL  

MFL is a magnetic NDT method used to detect corrosion, pitting, and wall loss in steel structures. It uses permanent magnets or electromagnets to magnetize the tank floor, then the resulting magnetic field changes are recorded and analyzed. The corrosion, pitting, wall loss, or defects cause leakage of the magnetic field which is captured by a sensor. This helps determine the location and severity of the defect of the tank floor for both near and far surfaces. 

MFL Inspection Principle [5] 

MFL Advantages 

• High-speed inspection, 
• Very good sensitivity to pitting and circumferential grooves, 
• Identification of the ID pitting from the trailing coil. 

Case Study 4: Pipe Inspection using MFL Sensor  

MFL for Tube Inspection 

Magnetic Flux Density Animation across Tube Sections with and without Cracks 

Streamline Plot of Leaking Flux across Tube Section with MFL Probe 

Magnetic Flux Variation with and without Cracks 

Conclusion 

In conclusion, electromagnetic NDT techniques offer a powerful, non-invasive way to inspect materials for defects. EMWorks software stands at the forefront of this technology, providing robust solutions for Eddy Current Testing, ACFM, ECPT, and MFL inspections. By leveraging EMWorks, professionals can achieve higher accuracy, efficiency, and reliability in their NDT applications, ensuring the integrity and safety of materials in various industries.

References