"Whole of life" cost benefit
Maintenance Costs
Maintenance costs of gravity sewerage systems generally relate to clearance of blockages and restriction of infiltration which can result from root intrusion at joints, faulty pipe and joints and loose manhole branch joints.
Hepworth SuperSleve calsined clay pipe and joints offer superior features to past and current Australian manufactured clay pipes - these are explained in detail under “Pipeline System Features”.
The Hepworth SuperSleve Coupling is manufactured from polypropylene which retains its properties better than uPVC at high temperatures with a quoted maximum of 100oC compared with 60oC for uPVC. The copolymer polypropylene materials used have a balance of creep properties and excellent impact properties even at low temperatures.
Hepworth Polypropylene Couplers were first introduced in 1965 and there are no known failures in the many millions of metres of sleeved pipes that have been laid over the period. The SuperSleve Coupler’s performance is enhanced by the inherent strength of the coupler as it is reinforced by internal and external ribbing which is not possible on conventional uPVC pipe. This ribbing together with the support from the rigid clay pipe prevents ovality in the coupling. It is recognised that ovality is the predominant factor to failure of uPVC pipes and especially at joints where differential deformation can occur because of the difference in thickness of the spigot and socket.
Hence the SuperSleve Coupler can be confidently expected to have a projected life at least equal to the projected life of the clay pipe.
Hepworth’s SuperSleve calsined clay pipes also offer advantages over uPVC pipes in the reduction of maintenance costs. In particular long term clearance of roots and blockages utilising the latest technology of powered rodding tools and high pressure jetting is likely to be compromised as the uPVC ages and the pipe becomes brittle.
Unfortunately there is no known published historical financial data on maintenance available to apply to the various pipe materials in a whole of life cost analysis. Hepworth SuperSleve clay pipe and even uPVC pipe have not been used for a sufficient period in Australia for comparative financial data to be collected. However, based on Auckland City Council’s data and assessments in their decision to utilise clay pipe exclusively, for every $1.00 spent on maintenance they expected to be able to reduce this to $0.40 by using clay pipes in their sewerage systems.