Best Practices for Eddy Current Testing of Heat Exchanger Tubes

Eddy current testing (ECT)  is one of the best methods of measuring wall thickness and circumferential cracks when testing heat exchanger tubes. But it takes quality instrumentation to capture defects accurately. Heat exchanger tubes are subject to heavy stress due to high-fluid pressure, including expansions and contractions of the tubes themselves. ECT is one of the most ideal inspection methods, as this form of NDT comes with an exceptional signal quality that detects precarious stress points in heat exchanger tubes.  

In terms of eddy current testing of heat exchanger tubes, one of the most important best practices to follow is to procure high-quality instrumentation, automated analysis software and multipurpose probes from an experienced NDT company that invests in innovative technologies. The probes should foster wider coverage per coil density, while the best instruments have the performance capabilities to procure quality data with a single pass. The automated analysis software should provide tube change trends over time and eliminate variability seen in a manual inspection analysis process. The best heat exchanger methods include a multiplex/simultaneous injection instrument or a tubing/surface array instrument, including probing that combines bobbin and array features. 

ECT Instrument Choices

Users have two primary choices when it comes to instrumentation, but both can lead to faster inspection times and better data. A testing instrument combining multiplex and simultaneous injection (SI) technologies is solely reserved for the inspection of heat exchanger tubes, while a tubing/surface instrument supports heat exchanger testing in addition to other applications. Both instruments can support bobbin probing and array probing. 

A heat exchanger testing instrument that comes with a multiplex functionality can test the most tubing types, including magnetic alloys. Using this type of ECT instrument, users can detect abnormalities such as cracking, pitting, and cuts. The instrument also provides remote field testing (RFT), allowing users to get the best data in any testing radius. RFT is ideal for ferromagnetic tubes, such as carbon steel, and ferritic stainless steel. With such an instrument, NDT analysts take advantage of the following:

• Multiplex frequencies that enhance detection probability for surface and subsurface flaws; and
• SI technology that boosts quick testing, fosters RFT, and supports up to eight coil pairs or four frequencies.

Furthermore, multiplex readiness allows analysts to conduct more thorough inspections in less time. The processing power of the automated analysis software streamlines data effectively while providing in-depth analysis and enhanced resolution. Meanwhile, the instrument itself allows users to detect varying levels of defects, ranging from surface-level cracking to entrenched flaws that may have been missed by analysts using other NDT methods. 

A remote data acquisition unit with tubing and surface array configurations, on the other hand, can perform the same duties as the heat exchanger-specific instrument, but also has the ability to detect surface and subsurface indications using surface array.

Best Practices for Choosing Heat Exchanger Testing Equipment

Regardless of the type of instrument used, the best equipment should always include the following notable features:

• Superior detection quality
• Lightweight portability
• Automated analysis software
• Fast testing speed

It takes the right NDT company to create state-of-the-art instruments that yield high-quality signaling. Inferior equipment fails to yield strong signal quality, leading to missed flaws and possible operational failures. High detection quality will help users find additional flaws faster, including underlying defects. Additionally, its processing acumen will instantly recognize and configure probes once they connect to the instrument, reducing setup time while increasing ease of use.

Perhaps the most important aspect of all is the software. The best ECT analysis software is automated, able to provide fast analysis results and reporting as data is acquired and capable of distinguishing between circumferential and axial indicators. This is a unique find in the industry and is one of the best ways to assess the defect orientation. However, these special indicators are only available with the right type of solution. 

ECT Probe Choices

Probes that combine bobbin and array features further outline the profile of a flawed section in greater detail. Durable probes made from reputable NDT companies are long-lasting, saving users on replacement costs. Most importantly, an optimized probe can shorten inspection times, increasing overall efficiency as well as safety by allowing inspectors to minimize time spent in potentially hazardous environments.

Example: An NDT analyst must test a section of tubing in a nuclear plant. However, the analyst must test in an area that has some of the highest radiation levels, and their protective suit will provide limited safeguards from the radiation. However, the plant contacted an NDT company last week and obtained new equipment and customized inspection strategies. The new, higher quality instruments and probes help acquire more data more quickly than was possible in the past, allowing the analyst to complete the inspection and vacate the high-risk area in a timely manner.

NDT inspectors can use special probes for nuclear tube testing, or a bobbin/array combination that fosters a more comprehensive tubing analysis. The bobbin coils provide users with trusted data, while the array coils assist in detecting circumferential flaws and other defects. 

Effective ECT of Heat Exchanger Tubes

Eddy current testing of heat exchanger tubes means detecting more circumferential and axial cracks, including wall thinness. For the best heat exchanger testing, users can choose between a multiplex/simultaneous injection instrument or a tubing/array instrument, with probes featuring either bobbin or array compatibility or—ideally—both.

Equipping analysts with the best instruments and software will save companies on maintenance expenses, as will repairing or replacing tubes before the heat exchanger material degrades further. A heat exchanger tube that suffers cracking can cause operational failures in power generators and steam generators, including chemical plants and oil refineries. Utilizing high-quality instrumentation and probing is the best way to detect anomalies and flaws during the early stages and prevent critical failures down the line.

Zetec is an experienced NDT company that offers custom inspection plans involving eddy current instruments and probes. For more information on our eddy current testing solutions, contact Zetec today.