Guided Wave Ultrasonic Testing (GWUT)

Guided Wave Ultrasonic Testing (GWUT) also referred to as Long Range Ultrasonic Testing (LRUT) is an inspection system used for screening and detecting changes in cross-section of pipes and plates. It is typically used for non-piggable pipelines, road and river crossings, risers, power plant tubing, jetty lines, pipe support wear, corrosion under insulation, buried piping, and wall penetrations. GWUT can achieve much greater inspection ranges than conventional ultrasonic testing methods because they utilize the structure itself as a waveguide by exploiting resonances between the boundaries of the surfaces of a plate or the OD and ID of a pipe. In ideal conditions, the GWUT system can reliably detect flaws over 100 meters away from the inspection location. Typically in-service piping inspections have an effective inspection length ranging from 5 to 80 meters.

Waves are generated by a ring of piezoelectric transducers coupled to the surface, guided waves are produced that propagate down the pipe. Any cross-sectional change will create reflections which propagate back to the ring where they are received and the received signals are plotted as a function of distance from the ring.

    The benefits of GWUT include:

  • 100% coverage throughout the thickness of the structure
  • Pipelines are able to stay operational while inspections are being performed
  • Inspections can be completed over long distances from a single probe position
  • The ability to inspect hidden and inaccessible regions of structures as well as structures underwater, coatings, insulation, and concrete
  • Beam focusing capability provides an improved probability of detection and inspection confidence, reduced false alarm rate
  • Improved defect resolution and scan coverage
  • Cost-effectiveness because of inspection simplicity, speed, and avoidance of removal/reinstatement of insulation or coatings, except at the location of the transducer tool

Flaws that are routinely detected with this technology are areas of erosion, corrosion, pitting, material loss or thinning, and circumferential cracking.

    Limitations of the GWUT technique include:

  • Attenuation of the signal due to coatings, pipe contents, corroded test material, ground compaction, piping components and welds
  • Small isolated pits or “pin holes” are usually not detectable using the technology
  • GWUT cannot provide actual remaining wall thickness values, accurately size discontinuities or differentiate between ID and OD

Conventional Ultrasonics, Automated Ultrasonics and or Computed/Digital Radiography are typically used to verify and provide quantitative data on areas of concern identified by Guided Wave Inspections.