tailieunhanh - PIPELINE PIGGING TECHNOLOGY- P2

PIPELINE PIGGING TECHNOLOGY- P2: Why pig a pipeline? This paper introduces a number of reasons for doing so, together with a discussion of the advantages and alternatives. In general terms, however, pigging is not an operation to be undertaken lightly. There are often technical problems to be resolved and the operation requires careful control and co-ordination. | Pipeline Pigging Technology SPECIALIST APPLICATIONS The field of pigging is expanding towards ever more sophisticated devices and specialist applications. In particular the requirement to survey pipelines to detect not only dents and buckles but also corrosion pitting and cracks has lead to the development of intelligent pigs. Pigging systems have also evolved to satisfy other demands such as the ability to paint the internal bore or to install a retrievable subsea safety valve similar to a down-hole safety valve or to plug the pipeline so that maintenance can be carried out without a shut down and so on. The following paragraphs look at these applications which are also summarized in . Magnetic-flux leakage intelligent pigs A brief mention was made above of the regular use of calliper pig surveys to detect pipeline geometry defects and compare with a baseline run during commissioning. More sophisticated techniques allow the determination of wall thickness over the entire pipe surface as well as picking up dents buckles and pipe ovality. One such technique is magnetic-flux leakage detection. The principle of magnetic-flux leakage detection is used to determine the volume of metal loss and hence the size of defect. The pigs will function in both gas and liquid lines. Since the shape of the magnetic output trace has to be interpreted the characterization is often improved by running a series of surveys over a number of years to establish trends. The alternative to using an intelligent pig to survey the wall thickness of the line is to take ultrasonic measurements at key points along the pipeline such as bends crossings tees etc. Such measurements could easily miss a problem and lead to a false sense of security they are no match for the comprehensive information obtained via intelligent pigs but are obviously much cheaper. Ultrasonic intelligent pigs Using the internal fluid as a couplant ultrasonic pigs measure the wall thickness of the entire pipeline surface.

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