Guided Wave Testing – GWT

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Guided wave ultrasonic testing (GWT) detects corrosion damage and other defects over long 5 m – 50 m (33 feet – 165 feet) distances in piping. A special tool (transducer ring) is clamped around the pipe and transmits guided waves in both directions along the pipe. Reflected signals from defects and pipe features such as welds are received by the transducer ring and then analysed.


  • Inspecting sleeved road crossings
  • Detecting riser soil to air interface losses
  • Detecting corrosion under insulation
  • Accessing difficult locations, such as pipe in pipe racks, losses in-situ
  • Inspecting insulated lines
  • Inspecting buried lines


  • Efficient method of screening pipe for corrosion and/or erosion wall loss
  • Inspects difficult to access components without extensive excavation or insulation removal
  • Portable, battery powered equipment
  • Sophisticated software routines help identify and classify pipe signals
  • Rigorous operator training and certification with individual electronic keys which activate the system and track its use by each operator
  • Embedded reporting software allows the operator to analyze the results and produce a report on the spot
  • Surface preparation is usually limited to scraping off loose paint and scale


  • GWT is a screening inspection and does not provide remaining wall thickness in areas of corrosion; a complementary inspection like UT or RT is needed to map out and size flaws found
  • Under good conditions, GWT inspects over 100 m (330 feet) in uncoated, straight, gas-filled pipe; most pipes will have an effective range of between 5 m – 50 m (16 feet – 165 feet)
  • Coatings: bitumen wrap and similar heavy coatings cause high attenuation
  • Pipe condition: corroded lines scatter UT signals and reduce range
  • Features such as welds: each weld typically reflects 20% of the signal; without other limiting factors, inspecting past six welds is the maximum range
  • Bends and ‘T’ junctions: these features distort the signal, and testing cannot generally be done beyond a bend
  • Pipe contents: high viscosity liquids or waxy deposits attenuate the signal
  • Special soil conditions can cause additional attenuation and are usually associated with wrapped pipe
  • Access to the pipe surface and removal of about 1 m (3.3 feet) of insulation at each test point
  • At least 75 mm (3 inch) of clearance between pipes to fit the transducer ring