Technology and Data

The MagControl Technique

Eddy current testing is an established technology for testing metallic components for surface fracture defects. The technology is used for component testing in the aerospace and automotive industries, but can also be used to detect defects in the volume of non-ferritic metal structures. A special variant of the eddy current testing is the eddy current testing developed and used by us with direct current premagnetization “MagControl technology”, which makes it possible to determine volume defects on both sides of the material, even with thicker ferritic steel components and material coatings. The MagControl technology uses a combination of a direct and alternating current magnetic field. In the event of damage or corrosion in the tested material, the field lines of the eddy current field change, which means that corresponding defects can be detected.

In the principle mentioned, DC magnetization field lines are generated by a magnet in the material to be tested. At the same time, a coil loaded with a certain frequency is positioned in the centre of the magnet, which generates a primary magnetic field according to Lenz’s law. This in turn generates an eddy current field in the material to be tested. Without changes in the two electromagnetic fields, no change is measured in the balanced impedance display of the coil – i.e. no signal is displayed.

In the event of surface damage or material changes, the induced eddy current field in particular changes directly, which is displayed in the eddy current impedance level of the coil sensor as a signal with a preselected signal phase and signal amplitude strength (left diagram).

In the case of damage or material changes at the bottom of the material, the DC magnetic field is first changed, which has a changing effect on the induced eddy current field. This change in the eddy current field causes the impedance of the coil to change, which can be measured as a signal.

The different changes in the induced fields due to damage or material changes on the top and bottom or in the material itself can be analyzed directly by signal phase changes. The signal amplitudes are affected by the size of the volume of damage or material changes. Signal phase differences and changed signal amplitudes are used in the software to generate high-resolution color C-scans, which means that damage sizes and extents can be displayed very well in images.

A major advantage of the MagControl technology is the ability to test through coated or plated steel objects such as pipes or plates with specific sensors without having to remove them.

The advantages of the MagControl technology used by InnetiQs include

The technology makes it possible to differentiate between external and internal defects in the material to be tested
It is possible to test through coatings or protections as well as directly on the material to be tested
The type of damage can be detected (e.g. the test data can be used to distinguish between microbiological corrosion, corrosion caused by CO2, and between corrosion and cracks or a combination of these)
MagControl can also be used with non-ferromagnetic materials
The technology enables fast and efficient scanning up to one meter per second as well as C-scan mapping of large areas
Compared to the older MEC technology, MagControl contains a higher number of modern sensors, which results in twice the resolution compared to the previous technology

Advantages of MagControl compared to ultrasonic technology

As an electromagnetic method, the cleaning requirements prior to performing an inspection using MagControl technology are significantly less than when performing a measurement using ultrasonic technologies. As long as the scanner is able to pass through the pipe, it can measure through non-metallic contaminants.
As a pure electromagnetic technology, MagControl can measure through non-metallic coatings of several millimeters. A measurement through a 15 mm thick coating was successfully carried out in a test setup.
MagControl can also measure through a metallic, non-ferritic coating. Only the acquisition parameters have to be adjusted accordingly. Detection through 3mm stainless steel or monel has been done in many cases. It is irrelevant whether or not this metallic component is bonded to the ferritic steel component.
The magnetization in MagControl results in a signal volume that extends much further than the defect itself. This means that even small defects can be found. The detection of pinholes is possible.

The MagControl technology described above, sometimes combined with ultrasonic sensors, is used for our scanning systems. The possible applications, characteristics and advantages of these technologies are compared in the following table:

The following table shows the application recommendations depending on the system configuration:
The MagControl Data Collection Process and Software
InnetiQs in house developed desktop software MatriQs communicates with the inspection system electronics eddyVision which is the latest multi-channel, multi-mode and multi-frequency eddy current based technology. The acquisition software at multi-channel mode allows handling a variety of analysis modes at the same time which allows displaying near surface and far side condition at the same time. The high-resolution data of the scanned area is transferable for the material C-Scan mapping with the required material position information. The high detection capability of the technique combined with the high-resolution data recording supports the individual finding sizing in its 3 dimensions. The software allows to transfer the high-resolution data directly to matrix data in typical data format as integrity assessing systems can easily import. Below is the schematic of InnetiQs data collection to data provision.

The MatriQs Software has a multiple capability set up, which allows to deliver the MagControl data acquisition and data handling with multiple-mode, multi-channel and frequency towards selected analysis windows on the Eddy Current based impedance signal handling, parallel time charts per channel in transfer to calibration selected colour codes.

Far side defect display and near side defect display:

As InnetiQs has implemented in particular for splash zone and subsea inspection systems parallel technologies as Ultrasonics, the MatriQs software allows a parallel operation with MagControl and Ultrasonics. Below is displayed the MatriQs Ultrasonics Software display, in use for thickness mapping in parallel operations to MagControl.