The main function of PVC lining is to protect concrete surface against hydrogen sulfide attack. Moreover, it also guards against attack by a wide range of acids and alkalis. Hydrogen sulfide generated in sewerage by bacterial action under anaerobic (absence of oxygen) conditions is converted to sulphuric acid by aerobic bacteria growing on wet sewer walls. This acid reacts with the lime in the concrete, causing breakdown of the concrete pipes. The addition of lining could also improve the flow capacity.
Only the concrete above the line of minimum flow shall be attacked by hydrogen sulfide and therefore PVC lining is needed above this flow line. For medium to large pipe sizes, partial lining of 300 degree with 60 degree pipe invert exposed proves to be effective against attack. Small diameter pipe may warrant complete linings of pipes.
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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