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Pipelines should be tested before commissioning to check the strength of watermain and the absence of leak. Before carrying out hydrostatic pressure test, swabbing is conducted to clear out rubbish and dirt left inside the pipeline during construction. Swabbing is required for pipes less than 600mm diameter because for larger size of pipes, they can be inspected internally to ensure cleanliness.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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