Large linear magnet that is placed in the return mud flow (usually in the mud ditch). This device is approximately a 2 feet section of a 4X4 lumber. This magnet collects steel filings from the mud return flow. It is usually cleaned once every 24 hours and the steel filings collected from the magnet are weighed. The weight of these cuttings is a qualitative indication of the casing wear, which take place during the 24 hours. Sudden increase in the filings collected is a good indication of a problem with casing wear. Although there is no known way to determine a quantitative relation between collection rate and total casing wear, increases in collection rate changes have proven to be a warning worth heeding.
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