Countries

LIMITATIONS​

• 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