If you work in an industry that relies on nondestructive testing (NDT) to meet required standards and regulations, selecting the right inspection method is an important part of ensuring reliable results. With several technologies available, each offering different strengths and limitations, it’s important to understand the advantages of and disadvantages of each to make an informed decision on which to choose for your desired purpose.

Eddy current testing (ECT) is a widely used NDT method across industries such as aerospace, automotive, and manufacturing. Like any inspection technique, it offers distinct advantages as well as limitations depending on the application. In this article, we will explore the advantages and disadvantages of eddy current testing to help you evaluate whether it is the right solution for your needs.

Advantages of Eddy Current Testing

Using technology that detects defects in materials is vital in industries where health and safety are involved. In this section, we will discuss the advantages of eddy current testing:

• Enables inspection through paint coatings: Enables inspections to be performed through paint coatings without requiring surface preparation or coating removal, helping reduce inspection time and minimizing downtime.
• Sensitivity to surface defects: The smallest defects can weaken materials such as conductive alloys, compromising certain safety standards. Eddy current testing equipment can accurately detect defects of 0.5 mm (0.02 in.) in length under favorable conditions.
• Detects through different layers: Eddy current equipment can identify defects in multilayered materials without significant interference from planar interfaces. Detection capability depends on the material type, layer configuration, and inspection conditions.
• Quick and simple: Eddy current is a quick, simple, and reliable inspection technique, which is ideal if you’re conducting regular testing and speed is important.
• Measures material conductivity: Eddy current testing can be used to measure a material’s ability to transmit heat or electricity. This can be a critical factor in the selection of material for a given application.
• Measures of nonconductive coating: Eddy current testing is a practical method for measuring nonconductive coatings because of its versatility—it can test anodic coatings in addition to most nonconductive coatings.
• Fast hole inspection using high-speed rotating scanner and surface probes: Effective eddy current hole inspection requires a rotating scanner, rotary probe, and an instrument that records and displays the resulting data. Eddy current equipment is popular choice to conduct NDT bolt hole inspections because of its speed and efficiency.
• Portability: Eddy current testing equipment is small and light, making it easy to carry around on the job.
• E quipment can be automated: Relatively uniform parts can be inspected quickly and accurately using automated or semiautomated equipment.
• Contactless inspection: Eddy current testing equipment doesn’t need to be in contact with the part under inspection to take an accurate measurement.

Limitations of Eddy Current Testing

We have discussed the advantages of eddy current testing, but it’s also important to look at the disadvantages to understand if it’s what your industry requires. Here are the disadvantages of eddy current testing:

• Susceptible to magnetic permeability changes: Small changes in permeability can make testing of welds and other ferromagnetic materials difficult.
• Only effective on conductive materials: Eddy current can only be used to measure materials that support the flow of electrical current.
• Defect orientation affects detectability: Eddy current flow is generally parallel to the surface of the material. For a defect to be reliably detected, it must interrupt or disturb the eddy current flow. As a result, defects oriented perpendicular to the eddy current flow are typically easier to detect.
• Will not detect defects parallel to the surface: The flow of eddy currents is parallel to the surface. This means eddy current test equipment cannot detect defects that do not cross or interfere with the current.
• Signal interpretation required: There are a number of factors that can affect eddy current testing. This requires careful interpretation of signals to distinguish between relevant and nonrelevant indications.
• Not suitable for large areas: Eddy current testing on large areas requires the aid of a scanning device. Complex geometry also makes it more difficult to differentiate between defect signals and geometry effect signals.

Advantages of Eddy Current Array Testing

Eddy current array (ECA) is a form of nondestructive eddy current testing that involves electronically driving eddy current coils aligned next to each other in a testing probe. Each coil produces a signal, and the strength of the signal depends on the phase and amplitude of the test material. This signal can be measured, and the data is recorded to carry out tests.

Eddy current array has several advantages over other eddy current testing methods:

• Faster inspection time: Using a multicoil probe, the user can scan the material in a single pass. This means the scan takes just a few minutes and is quicker than conventional ECT and certain other NDT methods, such as magnetic particle inspection (MPI) and liquid penetrant inspection (LPI).
• Covers a larger area in one pass: Using multiple coils enables the user to complete the inspection in a single pass. Single-coil probes require the technician to scan the material multiple times.
• Simplifies inspection: Using eddy current array reduces the complexity of mechanical and robotic scanning systems required to move the probe.
• Inspects complex shapes: Eddy current array probes can be customized to the profile of the part being inspected. This reduces inspection limitations caused by complex test materials.
• Real-time cartography: Eddy current array technology provides real-time cartography of the inspected region, facilitating data interpretation.
• Increased accuracy: Using eddy current array probes improves the reliability and probability of detection (POD).

Eddy current array testing is used in a range of different industries. It can be used to measure the thickness of ocnductive alloys and to detect corrosion. One of the unique benefits of eddy current array is that multicoil probes can be used on diverse materials, such as vessels, columns, storage tanks and spheres, piping systems, and structural applications.

This article should help you decide if eddy current testing is the right method for your industry. If you’re interested in eddy current testing equipment, see Evident’s range of eddy current flaw detectors and probes.

Types of Eddy Current Probes