Low Frequency Electromagnetic Technique (LFET)

Low Frequency Electromagnetic Technique (LFET) was developed to inspect flat bottom stor- age tank floors. Over time, scanners have been contoured to inspect convex or concave ferrous and nonferrous metal tubing/piping surfaces. Various scanners are available for most applications.


  • Boiler Waterwalls
  • Reheaters/Superheaters n Storage Tanks
  • Pipelines
  • Service Water Piping
  • Fire Protection Piping n Coal Mill Piping
  • General Piping
  • Pressure Vessels
  • Heat Exchanger Shells


The TesTex TS-2000 LFET Tube Scanning System uses the Low Frequency Electromagnetic Technique (LFET) to quickly scan tubing in boiler waterwalls, reheaters and superheaters in utility boilers and large industrial boilers.

Inspection are performed from the tube OD (outer diameter), but flaws can be detected on both the OD and ID surfaces.

In addition, both magnetic and non-magnetic metals can be scanned (as can economizer tubing).

The TS-2000 scanners have concave surfaces to match the OD of the tubing. Depending upon the tube’s diameter, either eight (8) or sixteen (16) sensors are used, and they are equally spaced within the concave surface of the unit. The sensors do not touch the surface of the tube.

Usually a 120-degree span of the circumference is scanned as TS-2000 moves along the tube’s length.

The TS-2000’s sensors are very small–a few millimeters in diameter–greater detection capabilities for smaller flaws such as pitting as well as the display of high resolution, real time, 3-D, color graphics of the scan results. Results can be saves for further analysis or permanent archiving.

The TS-2000 System detects flaws, including corrosion cells and hydrogen damage, caustic and phosphate gouging, oxygen pitting, departure from nucleate boiler, ID pitting, corrosion, and erosion.

Cracking is also detectable and its detection can be optimized by modifying the pick-up coil configuration.

Additional features of the TS-2000 are:

  • Special Scanners made that only have ½” stand-off therefore being able to scan reheater tubing
  • No surface preparation needed for gas or oil burning boilers
  • Quality high-pressure water blasting usually sufficient for coal burning boilers
  • 2,000 – 3,000 linear feet of tubing can be scanned in a 10-12 hour shift with one inspection team
  • Scanning can be conducted from skyclimbers or hard scaffolding
  • Low signal-to-noise ratio
  • Scanner sizes from half-inch (½″) OD tubing up to maximum tubing OD

Report Excerpts

Advantages over Competing Technologies

Other methods of boiler tube inspection include:

  • Ultrasound (or UT), which scans for thickness, A-Scan, B-Scan, C-Scan, time of flight diffraction, and phased array;
  • RT or X-Ray
  • ElectroMagnetic Acoustic Transducer or (EMAT)

For ultrasound and ElectroMagnetic Acoustic Transducer methods, boiler tubing needs to be sandblasted, or spot-prepared for individual discreet UT thickness readings. In addition, neither the ultrasound nor ElectroMagnetic Acoustic Transducer method provide rapid scanning coverage; UT merely involves spot checks while EMAT only scans a strip of tubing less that one-quarter-inch (¼″) wide.

RT/X-Ray methods have obvious deficiencies, including getting coverage and limitations to testing while other outage activities are occurring.

Unlike competing products, for both natural gas and oil burning boilers, the TesTex TS-2000 LFET requires no surface preparation, and in coal burning boilers, a quality, high-pressure water blast usually suffices for the TS-2000 to be effective.

The TS-2000’s efficacy is due to the fact that the TesTex LFET is a non-contact method; the scanner surface containing the sensors does not touch the tubing. Because the TS-2000 operates as a very low frequency (usually 10Hz or lower), any non-magnetic deposits do not affect the passage of the electromagnetic field. In fact, iron oxide does not affect the signal path because it is a very “puffy” material compared to the base metal of the tube.

Falcon 2000 LFET Scanner

The TesTex Falcon Mark II LFET Above Ground Storage Tank Floor Scanning System uses the Low Frequency Electromagnetic Technique (LFET) to quickly and accurately inspect ferrous, above-ground storage tank floors.

The Falcon Mark II has many packages available based on your inspection needs. Falcons can be mounted on our Viper Crawler system for wall or shell inspection and remotely-operated scanners for tank roof inspection. In addition, the Falcon complements other products like our Hawkeye system, which inspects welds, to provide comprehensive tank inspection solutions.

The Falcon 2000 LFET system uses scanners that have 16 or 64 pickup sensors equally spaced to scan flat surfaces covering four inch (102mm) or thirteen inch (330mm) swaths per pass.

Falcon Jr.

A 16- channel/16-sensor LFET scanner called the Falcon Jr., which is shown above, is used for hard to reach areas such as sumps/pumps and under heating coils and internal piping as well as the annular ring.

All scanners work from one electronics platform–a small, modular, PC-based design–and can be used interchangeably. They can be outfitted with an optional encoder and operate from 110/220v or battery packs.



Advantage of LFET Over Competing Technologies

Other methods used for inspecting above-ground storage tanks are Magnetic Flux Leakage (MFL) and Ultrasonic Testing. Magnetic Flux Leakage uses permanent magnets, which adds unnecessary weight, and it requires a cleaner, sandblasted floor surface, which is expensive and time-consuming. In addition, Magnetic Flux Leakage cannot determine whether a flaw is on the top surface or bottom surface of the tank floor and cannot test through coatings.

Like MFL, ultrasonic testing requires a cleaner floor surface and is very time consuming due to the lack of surface area which can be scanned at any one time.

Our Low Frequency Electromagnetic Technique (LFET) products does not use permanent magnets, so are lightweight  (under 30 lbs) and are is easy to handle and transport. LFET-based tests require minimal floor preparation; it tests through coatings and determines top surface flaws from bottom surface flaws. Moreover, the Falcon LFET scanners will continue to show flaw responses even after the unit has stopped moving.

Our Reporting software generates a tube sheet map for you examine the results of LFET tube inspections and a tank floor map for LFET tank inspections respectively.

The Line CAT Plus takes the field knowledge we have gained from using the Line CAT and leverages it to create a robust tool for the detection of flaws in pipes and pipelines. Based off of our LFET technology, the Line CAT Plus is able to scan through coatings and paints to detect both internal and external defects. The Line CAT Plus has several new features that greatly enhance its ability and ease of use.

Scanner Pods

The new scanner pods are equipped with either four or eight distinct pickup channels, depending on the size of pipe you are scanning. This allows for a higher resolution scan and more accuracy when determining the exact location of the flaws and their volume. Each scanner pod is equipped with an LED indicator that illuminates when the scanner is over a flaw so you can determine visually where the flaw begins even without looking at the display screen.


The software has been refined to allow you to see the largest flaw response from each individual scanner pod, so you can see a zoomed out view of the pipe as it has been scanned. You are also able to zoom into the pods and see the individual channels just from one pod or all the pods in a general area.

Computer and Hardware

Instead of relying on a laptop receiving and processing information from the electronics box, we have combined the electronics box with a fully functional MS Windows computer. The Line CAT Plus is able to handle a total of 288 individual channels allowing it to handle more scanner pods and give higher resolution imaging. More area can be scanned in a single pass, speeding up the overall inspection. Linear and angular encoders allow for accurate flaw location. The computer stores scanned data, and can be accessed via VPN with an iPad, Tablet or laptop wirelessly to show real time acquisition results, or it can be connected to a monitor via VGA output. Data can be extracted using a USB drive or network port

The TesTex PS-2000 Multichannel NDT inspection system quickly and accurately inspects ferrous and non-ferrous metal tubing from the pipe’s OD.

The PS-2000 is based on the Low Frequency Electromagnetic Technique (LFET) and normally has eight channels for detection of microbiological induced corrosion (MIC) Attack, flow accelerated corrosion (FAC), cracking, erosion, corrosion, and pitting wall losses.

Report Excerpt:


The PS-2000 LFET scanner has the following features:

  • Light weight scanner attachments
  • Large frequency range 5Hz to 30KHz
  • Real-Time Display
  • Operates manually or with motorized crawler
  • Scanner cable lengths up to 100’ (30 m)
  • Scans through paints and coatings

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