Ultrasonic Pipeline Inspection

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The Principle and Purpose of Ultrasonic Pipeline Inspection

Sound waves at frequencies beyond the range of human hearing have long been adapted for a wide range of applications. Of these, the most familiar to the general public are probably the sonar systems used to detect underwater objects and the non-invasive technology employed by doctors to inspect the internal organs of their patients. However, the same basic principle that can produce video images of a foetus in the womb can also be adapted to perform an ultrasonic pipeline inspection, with the use of a device known in the trade as an intelligent pig.

Intelligent in-line inspections (ILI) are a type of non-destructive testing that can be used to detect flaws in a pipework system that might compromise its safety or performance. Though very different in its design, an intelligent pig operates in much the same manner as the sonar buoys used to map the terrain of the seabed and to detect wrecks. In order to perform an ultrasonic pipeline inspection, it is inserted into a pipe and propelled along its length. It transmits high-frequency sound waves and measures the time taken for them to be reflected by the inner wall of a pipe back to the on-board receivers.

While there are one or two other techniques with which to check the interior of a pipe for signs of wear and tear, the use of ultrasound technology offers one significant advantage. With the aid of sophisticated computer algorithms, the data collected can be processed to provide inspectors with the quantitative measurements needed to evaluate the significance of any internal irregularities.revealed by the ultrasonic pipeline inspection and to determine what, if any, remedial action may be needed.

When oriented at right angles to the interior wall, the transducers are positioned to measure variations in its thickness due to metal loss. Modern equipment is able to detect variations with an accuracy of +/- 0,4 to 0,5 mm, whether on the inner or outer surfaces and even when presenting as gaps inside the metal of the pipe wall. Although some systems actually have a maximum resolution as low as 0,06 mm, it is common practice to set the threshold for an ultrasonic pipeline inspection at 1 mm.

The same technology can be used to locate and size cracks in the wall of a pipe. In this type of operation, the transducers must be oriented not at right-angles to the wall, but in a manner that will ensure the incident sound waves will be reflected at 45° or less. In this configuration, the device can locate and determine the size of a crack and whether it is on the internal or external surface of the pipe.

The in-line, ultrasonic pipeline-inspection tool is of sufficiently flexible design to negotiate most bends without getting stuck. However, to ensure that a line can be successfully navigated by the device, a preliminary gauge-pigging exercise using a different type of pig will sometimes prove necessary.

Pigging in general and performing an ultrasonic pipeline inspection are highly technical procedures that demand specialised equipment and knowledge of the industry as well as skill and experience. These are four very good reasons why so many local companies put their trust in Oleum Process & Pipeline Services.

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