Long range ultrasonic testing (LRUT), also known as long range UT, allows you to test large areas of material from a single test point.
Pioneered at TWI alongside the Imperial College London in the 1990s for the in-service assessment of metal loss in pipelines and piping, research led to TWI’s creation of the first commercially-available guided wave ultrasonic testing system. Since then, we have continued to develop the process with upgraded testing systems. Frequently used by the oil and gas industry, modern LRUT equipment is effective across a range of pipe sizes and conditions, creating longitudinal, torsional and flexural guided waves.
Applications and Advantages
Long range ultrasonic testing is widely used to inspect pipelines , where it can deliver 100% coverage of the pipe wall from a single location, even on sleeved or buried pipes, including areas such as at clamps. It lowers the costs associated with gaining access to hard-to-reach pipelines or removing and replacing insulation or coatings, and can be used on unpiggable pipelines.
Outside of oil and gas, LRUT has also found applications in other industries, such as aerospace and rail, where it can provide the cost effective, rapid screening of large structures. Unlike conventional ultrasonic testing, LRUT does not require the use of couplants and is able to detect weld root corrosion faster than with conventional methods.
How LRUT Works
LRUT uses transducers, a low frequency flaw detector, a device to control the system and, for attenuated LRUT, a pulser receiver unit. The transducers are uniformly spaced across or around the structure to be tested so that the low frequency guided waves that are emitted propagate symmetrically along the surface. The waves propagate axially along lengths of pipe or along a structure until their energy dissipates or is attenuated.
When the waves detect corrosion, erosion or other discontinuities in wall thickness, the waves are reflected back to the transducer, which measures the time taken for the signal to return to locate the defect.
The interpretation distance of LRUT can be reduced by factors that may negatively affect the sensitivity, including:
- Size of Defect: If a large amount of the area is lost to a defect like corrosion, it can affect the interpretable range due to excessive noise
- Axial Extent of Defect: LRUT is less sensitive to axial defects, although longer defects create a stronger signal than short ones
- Pipe and Asset Features: Features such as butt welds, bends, branches, and attachments will be recognised as discontinuities by the guided waves, so will affect the signals
- Material Thickness: Excessively thick materials and large diameter pipes can reduce the effectiveness of the guided waves
- Coatings: Some coatings will affect the ultrasound’s rate of attenuation, reducing the effective test range
- Signal-to-Noise Ratio: There needs to be a minimum ultrasound signal-to-noise ratio in order to maintain the required sensitivity to defects
LRUT at TWI
Our experts can assist in the use of long range ultrasonic testing for a range of applications. Our decades of experience in non-destructive testing and the oil and gas industry allowed us to pioneer the use of guided wave ultrasonic testing for pipelines and produce the first commercially-available testing system.
As one of the first organisations to fully understand LRUT, TWI has the necessary knowledge and expertise to assist with its use, while our expertise in a range of materials and industry sectors allows us to locate the best solution for your requirements, including how to mitigate against drawbacks to get the best results from LRUT.
Contact us to find out more by emailing contactus@twi.co.uk.