Eddy current testing (ECT) is fundamentally the same as it was when first introduced in 1879 by David Hughes, yet it remains among the best inspection techniques for use in many cases today. While the technology itself is unchanged, its applications have become much more sophisticated, particularly over the past twenty years. NDT professionals across manufacturing, oil and gas, aerospace, power, and various other industries are able to perform NDT technicians plus detect and size flaws with greater speed and accuracy than ever before.
How and when ECT is used has changed remarkably, and the digital age has brought transformational change for inspection technology. Recent advancements in eddy current tools have simplified not only the inspection process, but also the training and collaboration processes involved across industries, increasing the scope of applications and usefulness of the technology. As inspection technologies become more advanced, the need to recruit, train, qualify, and retain skilled nondestructive testing (NDT) personnel becomes increasingly important, especially in an industry where the workforce is rapidly aging.
The Move from Analog to Digital
One of the key benefits of ECT for inspection technicians is its transportability, which can be traced back to the early 1990s. This was a turning point for the technology because it allowed technicians to bring the technology they needed into the field. The transition from large, analog technology to more compact, digital systems allowed inspectors to adapt the testing process for more NDE applications. For its previous 100-year history, performing ECT required the equipment under review to be brought to a laboratory; now, inspectors could bring the ECT equipment to the object in the field.
Of course, transportability is a relative term, and in its first outside the lab incarnations, ECT equipment was transportable on par with a refrigerator or a safe. The difference was significant enough, however, that ECT could now be performed on equipment in the workplace. In the early field inspections, ECT was used to check steam generators at nuclear power plants, to ensure that high-pressure radioactive steam from inside the reactor was not escaping to the environment.
As the technology improved, the number of industries and applications using ECT grew. Given the increasing number of facilities and systems that required constant NDT, performing and staffing regular inspections became a major challenge especially for teams that were top heavy with advanced NDT technicians. In the 1990s, the company Zetec introduced a new method where an on-site team transmitted inspection data to a centralized analysis team using a satellite or online connection. This advanced process relieved the need for the experts to remain on site for analysis and final decisions. Zetec improved the productivity of NDT Level III technicians by enabling a given crew to support testing at multiple sites simultaneously. The Internet made data transfer even simpler and, not long after, software emerged to improve the quality and analysis of data, laying the foundation for how ECT is used today.
Making Smarter Machines
Eddy current testing equipment has tremendous sensitivity. The technology can detect defects that are well defined and discern defects even through significant noise in the data signal. This also means that very minor patterns in a sample could give a response very similar to a defect signal. Noise, or signal interference, can be caused by naturally occurring factors such as temperature, changes in conductivity, and magnetic permeability.
The creation of noise-filtering technology opens the use of ECT to a broader, constantly growing range of applications. Researchers discovered that various types of signal noise occurred in recognizable or predictable patterns. Anticipating and eliminating these effects using software-based processing on the source data essentially erases noise signals and leaves the rest of the picture, allowing ECT to reliably provide clear diagnostic images.
The effect of noise-filtering algorithms on ECT has been profound. Research at Michigan State University validated the accuracy of noise filtering algorithms and led the Electric Power Research Institute, a worldwide consortium of utility companies, to recommend to member utilities that use of defect recognition software be the primary means for signal identification. Experts are used in supporting and verification roles, to corroborate and validate the indications called out by the software.
Advancements in technology have vastly improved the NDT process. For instance, the nuclear plant steam generator inspection that originally required six NDT technicians working up to 28 days can now be completed in under a week with half the NDT technicians and with far greater confidence in the data.
With technological advancements also come training advancements. Because ECT devices provide clear interpretations of scan results, less experienced NDT technicians are capable of making critical decisions that previously required the approval of NDT Level II and III certified technicians. Moreover, as ECT equipment becomes smaller and less costly, its use expands far beyond the nuclear reactor, airplane manufacturing floor, and petrochemical processing operations that have long been its focus. One can now find high end auto mechanics using ECT equipment to detect whether parts are suitable for use or require replacement.
New Frontiers for Eddy Current Testing
There are several current and emerging trends that promise to further revolutionize ECT for the next phase of inspection. One notable trend is the recent emergence of powerful, networked portable devices.
Previous generations of inspection technology often required the NDT technician to carry cumbersome equipment, diagrams, maps, and numerous other paper documents for information on the testing process and the standard requirements for the test. Given the complex and often harsh industrial environments NDT technicians work in, this process was far from ideal and introduced several variables that could affect the accuracy of test results.
Recently, GE launched the Mentor EM. With this portable device, the testing process is automated on-screen, including all relevant information on test metrics, procedures, and standards. There are no physical dials or other external variables on the device to affect test results; the probe used to perform the inspection is the only external feature.
Where previous ECT devices have been standalone units that perform a reading Mentor EM incorporates a comprehensive information system. Not only can NDT technicians capture its readings onto a network database, but future versions of the system will be capable of finding and opening information on the network. The NDT technician can be relieved of carrying paper documents, which instead are directly viewed on the instrument’s tablet. Printed documents expire; online documentation can be managed to provide only current information.
The new system also can create standardized NDT workflows. It can automate the NDT process, which again is a seemingly small advancement that could have tremendous implications. Large organizations with numerous NDT technicians at multiple facilities might find that their ECT is performed differently, with slightly different results achieved by everyone. By developing a standard practice, the company can be confident that all its weld inspections, for example, are being performed in the same way, with results that can be duplicated by any one of its NDT technicians.
Using connectivity technology, NDT technicians can bring others into the NDT process as needed, without having to wait for them to physically arrive on site, saving time and money. In addition, a higher-level engineer located anywhere in the world can work with the NDT technician, directing all of his or her actions to achieve unambiguous results. The equipment also offers the foundation for a broad rethinking of the process of ECT inspection within a company, perhaps realizing untold means of efficiency or advancement of skill and corporate knowledge.
Conclusion
Eddy current inspection has become one of today’s most useful and essential modalities for NDT. It has achieved this status by evolving in reaction to technological advances over the past decades.
A number of new advances have been introduced to ECT, including networked communications, collaborative features, and an application programming interface, that promise to expand the horizons of this test modality dramatically, making it feasible for a far wider range of applications and bringing new NDT technicians and operators up to speed more quickly and efficiently.