Scale formation in two unlined steel, and two HDPE-lined steel, slurry pipelines has been examined. The scale forming mechanism is not the same in all four pipelines. It is easy to control scale deposits in unlined steel pipelines where wire brush pigs can be used without damaging the pipe wall. The bond between the scale and the HDPE surface appears to be much weaker than for steel pipe, and removal does not require anywhere near as much force. Pigging of HDPE-lined pipe should be carried out more cautiously in order to prevent damage to the liner. The integrity of the liner must be established prior to pigging the pipeline. The HDPE liners integrity can be established by inspecting thredolets that are used at each flange joint. The scale material volume being removed from the HDPE-lined pipe is potentially larger, as it is more easily removed from the wall, and the transport of that large volume could present operating difficulties for the owner. Provision for removal of large quantities of scale from the pipe after scale has been dislodged needs to be considered as part of the programme in order to avoid those operating problems. In the case of the Century line, the scale was soft, and easily transported using foam pigs; in the case of the copper concentrate line, the hard scale dislodged in sheets from the HDPE surface would present a much larger challenge. It will require more frequent pigging in order to keep the thickness of the scale to a minimum. The health of the HDPE liner is integral to the performance of the pipeline, and routine inspection every few years of the thredolets is vital to confirm that the liner remains in contact with the pipe wall, and that there are no breaks in the HDPE surface along the entire length of the pipeline. Liner damage must be repaired before any pig runs can be made, and this can delay removal of scale by pigging. One potential solution for liner failure is to bond the liner to the pipe wall following its installation. This technique has not been proven yet, and it would incur additional construction costs. Use of magnetic scale removal techniques in the case of pipelines subjected to scale deposits due to calcium ions should be investigated.
Control of scale deposit problems in slurry pipelines
2007
11 Seiten, 4 Bilder, 1 Tabelle, 4 Quellen
Conference paper
English
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