Long Range Ultrasonic Testing (LRUT) is an efficient technique used to test large volumes of material from a single test point.
LRUT for the in-service surveying of metal loss in pipelines and piping was developed in the 1990’s through a UK Technology collaboration of Imperial College and the Research Institute TWI which culminated in the release of the first Guided Wave testing product Teletest® in 1998. This technology was further improved over the next 20 years until the brand was sold to Eddyfi Technologies in September 2017.
The impetus for the development of LRUT is that ultrasonic thickness checks for corrosion, erosion, etc. are very localized, in that they only measure the thickness of the area under the UT transducer.
Localized, single-point inspection
The operation of the LRUT technique is shown schematically in the figure and Teletest® uses low frequency guided ultrasound travelling along the pipe providing 100% coverage of the pipe wall without moving the transducer tool.
Depending on pipe conditions, up to 350 metres of pipework can be inspected from a single test point. LRUT reduces the costs of gaining access and avoiding extensive removal of insulation (where present). The whole pipe wall is tested, achieving a 100% examination (including areas such as at clamps, and sleeved or buried pipes).
Long Range UT inspection
The development and improvement of LRUT has been rapid over the first 20 years since the first product has been commercially available. The equipment can now generate and fully utilise any of the three main Guided Wave types (longitudinal, torsional and flexural). There has also been significant developments in utilising phased-array technology making it possible to focus the ultrasound and analyse the circumferential responses of potential defects. In addition, the boundaries for inspection has increased such that the inflatable collars, modules and transducers are capable of inspecting pipe sizes up to 78” and increased temperature capability of 240°C.
Ask an ExpertThe earliest work showed that the smallest area of metal loss which LRUT can detect is approximately 3% of the pipe wall cross-section. The reporting level which is normally used is a signal amplitude equivalent to 9% area, to ensure that false call rates are kept to an acceptable level. These thresholds were verified through 'blind trials' without knowledge of any defects and the results were independently evaluated. In all of the independent trials conducted over the last 20 years Teletest operators have found all defects over 4.5% cross-sectional area loss over a variety of pipe sizes and pipe conditions.
Long-range ultrasonic testing using guided waves is one of the few test methods which is able to examine 100% volume of pipe wall from one tool location so has found widespread applications in non-piggable pipeline where efficient inspection coverage is required or the pipeline in question has hard to reach areas. Successful inspections have been carried out in the following applications:
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