Materials and their Characteristics
Plastic Pipes Conference Association # 1982 York
van den Hevel
The field performance of PVC pressure pipes is generally acceptable. Yet a substantial international research effort is being devoted to spontaneous brittle failures.
A model describing the nature of such failures will be presented. In this model a pipe is considered to be a matrix with defects. To obtain satisfactory pipe durability, the matrix strength must be sufficient to withstand "common defects under service conditions. It is hypothesised that the relevant matrix toughness is dominated by gelation.
The way in which this hypothesis was checked experimentally will be presented.
The field performance of PVC pressure pipe 1s generally acceptable and the failure rate low (ref. 1.). Sporadic brittle failures do occur but are not sufficient to justify the substantial international research effort being devoted to PVC pressure pipe reliability. This effort has probably been stimulated by the lack of predictability of spontaneous brittle failures.
A vast amount of literature is devoted to the nature of brittle failures.
Although significant progress has been made in that area, the answers to many questions still have to be found. It is not the intention of this paper to review the present state of the art. Instead, a model has been formulated which, if confirmed, could further reduce the incidence of brittle failures in PVC pressure pipes. It assumes that the relevant pipe property to control brittle failure is matrix toughness. Because this property is difficult to measure directly, it is hypothesised that gelation is the main characteristic which controls matrix toughness.
The hypothesis was checked in the following way. Three pressure test techniques were selected in accordance with the model. These tests, in combination, are assumed to simulate the effects of typical field conditions on pipe durability. The pressure tests were applied to commercially available pipes in a wide range of pipe sizes (diameters and wall thicknesses) obtained from different sources. The results of the pressure tests were then related to those of a new gelation test.
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