8 www.megger.comPractical Example of Test Method2A petroleum company had a 10-in. pipeline 6300 ft long running through rugged terrain. After a corrosion leak, they wanted to check out earth resistivity along the line. Low-resistance spots would most likely require attention. They used a Megger earth tester to make a survey along the line.First, average depth of the pipeline was found from a profile map. It was 4 ft, so four electrodes were tied together 4 ft apart with strong cotton cord. They decided to check soil resistivity every 20 ft along the line. Fig. 2 shows a portion of the results; pit depth corrosion and Megger earth tester readings are plotted for points along the pipeline. Note that for low resistance readings, more corrosion was found.Fig. 2: Earth resistivity survey of pipeline shows where corrosion is most likely to occur (source: Ref. 18)2 Reference 18 (page 77)
