A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
it will be subjected to.
After adding water to the pipeline, 24 hours are usually specified before
actual measurement. This stabilization time is required because both the
escape of air trapped at pipe joints and water absorption take time to
complete.
It is recommended that backfilling to pipes shall be partly-completed before
the conducting of water test to cater for possible floating of pipelines in the
event of accidental filling of pipe trench with water. Moreover, it is
recommended to place adequate sidefill to restrain the pipeline to prevent
movement of pipeline during water test. Otherwise, excessive movement of
pipeline from water pressure may result in failure at joints.
24. Why is air test considered for checking leakage in pipes though
there is no direct relation between air loss and water leakage?
There is no correlation between air loss and water leakage owing to the
physical difference between air and water and the difference in behaviour
of air and water under pressure conditions. Someone may doubt the
philosophy in using air leakage to test for water leakage in pipes.
For cracks and openings of capillary tube size, surface tension may hinder
the flow of water while air would still pass through the minute cracks.
Based on past experience, for pipes passing air test is deemed to have
satisfied water test (infiltration or exfiltration). For pipes which fail air test, it
should also be subjected to water test before considering any replacement
or rehabilitation.
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