Standardizing Guided Wave Testing Methods and the Role of Sonyks™

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Guided wave testing (GWT) was developed in the 1990s for detecting corrosion in pipelines, with the first products released in the early 2000s. Following well-defined procedures and international standards such as ISO 9690, GWT has proven to be a reliable inspection technique for identifying corrosion defects, balancing sensitivity (5% cross-sectional area loss) and range [up to 30 meters (100 feet) on typical above-ground pipe]. Recent advancements in guided wave technology necessitate a better standardization of the method and clarification of terminology to differentiate it from other ultrasonic wave methods. This application note aims to define GWT using test frequency as the primary differentiator.

The Challenge

Standardize and clarify the language around guided wave testing to differentiate it from other methods using ultrasonic waves.

Guided wave testing on pipelines employs low-frequency ultrasound (approximately 20-200kHz) to detect corrosion by propagating sound axially along the pipe. Changes in the pipe's cross-section cause sound reflections back to the tool, allowing for the detection of defects without probes needing to be directly over the inspection area. Despite its value in productivity and unique inspection capability, the broad term "Guided Wave Testing" has become too vague for specific pipeline inspections. There is a need to separate GWT into distinct categories to prevent confusion.

Figure 1: Comparing GWT to conventional NDT methods showing that the metal loss can be found without the tool being located directly over the metal loss.

The Solution

Categorize guided wave testing into three subcategories based on frequency: Long-Range Ultrasonic Testing (LRUT), Medium-Range Ultrasonic Testing (MRUT), and Short-Range Ultrasonic Testing (SRUT).

To address this, GWT in pipelines can be divided into three subcategories based on frequency: Long-Range Ultrasonic Testing (LRUT), Medium-Range Ultrasonic Testing (MRUT), and Short-Range Ultrasonic Testing (SRUT). Each subcategory is defined as follows:

Subcategory Frequency Range Expected Test Range Sensitivity
Long Range Ultrasonic Testing <100kHz (usually 20-80kHz) 10s of metres 5% Cross-sectional area
Medium Range Ultrasonic Testing 100-200kHz (usually 110-150kHz) Up to 12m 1% Cross-sectional area
Short Range Ultrasonic Testing >200kHz (usually scanning-based technologies) 1-2m Dependent on application

The Sonyks™ instrument by Eddyfi Technologies stands out in the marketplace for its ability to use both piezoelectric and magnetostrictive transduction methods. The segmented magnetostrictive tool used by Sonyks allows for secondary focusing, providing additional information about anomalies. This method is particularly suitable for MRUT due to its lightweight, low-profile tools and tunable frequency by changing coils, eliminating the ringing often seen with shear-based piezo transducers. Eddyfi Technologies has introduced LRUT and MRUT versions of these collars, targeting smaller diameter inspections [38-200 millimeters (1.5-8 inches)].

Check out the Eddyfi Academy for our Introduction to Guided Wave Ultrasonic Testing and related courses to stay Beyond Current.

Application Note by Paul Jackson


  • Improved clarity and understanding of guided wave testing methods
  • Better matching of inspection techniques to specific applications
  • Enhanced effectiveness of Sonyks™ instrument

Categorizing GWT enhances clarity and allows end-users to choose the appropriate inspection technique. The attributes of the Magneto tool options for LRUT include conventional pipeline inspection, a lower frequency (64kHz), long range over sensitivity, 5% sensitivity, and standard GWT procedures compliant with ISO and ASTM standards. Applications of LRUT include inspection of road crossings using guided waves, inspection of fire water ring main lines, and field use of Sonyks. MRUT is ideal for in-plant pipework or piping inspection, characterized by high frequency (128kHz), sensitivity and resolution, <1% sensitivity, and up to 10m inspection lengths with application-specific procedures. MRUT applications include U-bolt clamp inspection on small diameter pipes, sprinkler system inspections, finding small defects in pipelines, and stainless-steel inspection.

Discuss the applicability of our guided wave testing solutions for your precise application with our NDT experts today!