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Displaying records 572 through 572 of 2180
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Title: Development of the Pearson survey technique for epoxy coated pipelines
Category: Pipeline Industries Guild technical library
Downloadable: Yes 
Catalog No.: PIG0025
Date of Publication: April 5, 1982
Price: $25.00 US
Authors: I R Burrows
Abstract: The Pearson survey is used to detect holes in coatings on buried pipelines. It is carried out by impressing a 900 Hz ac signal on the pipe. At a coating defect this signal leaks off the pipe at a much greater rate and causes an increased ac voltage in the soil. This increased ac voltage in the soil is detected by two linewalkers connected together, walking 5 m apart, wearing cleated boots, making continuous electrical contact with the soil. Any ac potential change between the linewalkers is detected by a receiver as an increase in amplitude of the 900 Hz audio signal. This technique has worked satisfactorily on coal tar enamel coated lines. However it was found that a known coating defect could not be located on an epoxy coated line.

Investigation of the electrical properties of coal tar enamel and epoxy coatings showed that at 900 Hz five times the amount of signal leaked through epoxy coating. Thus the problem of Pearson surveying epoxy was due to there being an insufficient ac potential difference in the soil between a coating defect and sound coating.

The electrical properties of epoxy were found to be equivalent at 200 Hz to those of coal tar enamel at 900 Hz. The Pearson survey equipment was therefore redesigned to operate in the region of either 200 Hz or 900 Hz. The redesigned survey, operating at 175 Hz, has successfully detected coating defects on epoxy coated lines. It should also be more sensitive to coating defects on coal tar enamel coated lines.

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