Long Life of PVC Pipes Confirmed
The Millewa Water Supply Scheme was constructed during the early 1970s to provide reticulated water to 126 farm holdings and two urban areas in North-Western Victoria.
Approximately 600Km of PVC pipelines were installed, operating under a variety of pressures and external load conditions. The PVC pipes were manufactured by several pipeline manufacturers, namely Vinidex and included rubber ring joint and solvent cement joint pipes.
The actual service conditions involve mainly gravity flow under pressure, with some surge situations, along with operating temperatures up to 300C. Terrain conditions include both sand and solid limestone, the latter requiring 80mm of sand bedding beneath the pipe, regardless of pipe class. Pipes were also installed under roads and railway lines with no adjustment of pressure class to allow for dynamic loads.
In 1996 it was decided to exhume a selection of these pipes in order to determine whether they had shown any signs of deterioration and to assess their condition relative to contemporary production.
Tests conducted included fracture toughness, tensile strength, impact and flattening resistance.
Conclusions
After almost 30 years of service, the PVC pipes, incorporating all classes, with both rubber ring joints and solvent cement joints, continue to perform well under a variety of operational conditions. Fracture toughness levels exceeded the levels reported for pipe made in the UK at about the same time, as well as the enhanced levels specified in AS/NZS 1477 - 1999.
Tensile properties are still consistent with those listed in published literature demonstrating there has been no deterioration in the strength of the PVC during the life of the pipes.
Variability of impact and flattening results is attributed to surface damage arising from the exhumation of the pipes, as well as the effects weathering prior to installation. The performance of the pipeline has not been adversely affected by surface damage occurring prior to installation.
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