Northern NDT increases long range ultrasonic inspection capability
Keywords: Ultrasonics, Inspection, Pipes
Northern NDT Services Ltd, with offices in Stockton-on-Tees and Ellesmere Port, UK, has now added a. second Teletest long range ultrasonic inspection system to the portfolio of specialist inspection techniques which it offers to the processing, oil and gas, power generation and general engineering sectors. The second system has been purchased because of the continuing success of the technique and will allow Northern NDT to respond more quickly to clients requests for its application.
Long range ultrasonic inspection is a technique which has been developed for the rapid detection of corrosion and other metal loss defects in pipes. It is particularly applicable to in-service pipework, as it requires minimum site preparation, in terms of scaffold erection and insulation removal and there is no need for radiation protection.
The technique relies on the propagation of low frequency sound waves, which are guided between the internal and external faces of a pipe wall, in much the same way that Lamb waves travel in plates. The sound waves, which are generated by piezoelectric transducers, lie in the kHz range rather than the MHz range associated with conventional ultrasonic probes. They have the property that they can travel many metres from a single test point, with minimal attenuation.
The inspection equipment consists of a bracelet array of nominally identical,equally spaced transducers, a low frequency flaw detector and a personal computer. In operation, the transducer array is wrapped around the pipe and a specially designed pneumatic collar is activated to ensure good contact between the transducers and the pipe surface. There is no need for a couplant and the pipe surface reportedly requires only minimum preparation, typically the removal of any loose scale or rust, so that set-up time is said to amount to no more than 20 minutes. The flaw detector energises the transducers and the ultrasound is propagated along the pipe within the pipe wall. Any discontinuities in the wall thickness, as evidence of corrosion, are reflected back to the transducers,as are weldment, bends, pipe supports and flange indications. The resulting data is passed to the personal computer, which is also used to drive the flaw detector, and can be evaluated on-site, transmitted electronically for remote analysis or downloaded for subsequent evaluation.
The new long range ultrasonic testing technique has already found application in the inspection of pipework, particularly in oil and gas and petrochemical installations. It is reported to have been used to detect corrosion in pipework at a typical line inspection rate of 1km per day and has been successfully employed to detect corrosion under insulation, corrosion in buried pipelines and corrosion at normally inaccessible locations, such as road crossings, under pipe supports, under bridges etc. Offshore, it is thought to offer a cost effective solution to riser inspection. It is stated to be suitable for pipe diameters between 2 inches and 60 inches, at temperatures up to 125C. Long range ultrasonic inspection is sensitive to both internal and external metal loss equivalent to 9 per cent of wall cross section and is equally applicable to stainless steel lines and spirally welded pipe.
Northern NDT Services offers a range of conventional and specialist inspection techniques, from manual ndt carried out by experienced and qualified personnel to specialist services, including P- and T-Scan inspection, automated ultrasonic inspection using Time of Flight Diffraction, boiler/ heat exchanger tube inspection, crack detection, monitoring and sizing, various miniature ccd camera systems and thermal scanning, as well as long range ultrasonic inspection.
Details available From: Northern NDT Services Ltd. Tel: +44 (0)151 373 4800;Fax: +44 (0) 151 373 4801; E-mail: martin.hockley@northrn-ndt.couk
