Development for polymers in pipemaking

Pioneering work on plastics pipe made from thermoplastic polymers began in 1928 following the production on the technical scale of the first few tonnes of polyvinyl chloride, and later in 1935 with the commencement of the production of low density polyethylene.

The first service evaluations on the product and its properties were made in chemical works and also in water supply systems From the mid-fifties onwards to the present day plastics pipe has shown steady growth wherever it has been used.

Systematic investigation into the relationship between molecular weight and the specific mechanical properties of pipe and pipe fittings was begun at that time. Based on experiments with high temperature steels and steel alloys, it was recognized that for the determining of the behaviour of plastic pipe under internal pressure, fatigue tests were required (I), (2).

It is now 20 years since measurements of that nature were commenced, in a number of testing stations These were mainly trials with PVC, LDPE and HDPE. One of the characteristic properties of thermoplastic materials is the irreversible deformation of a component under load stress (e.g. a pipe under internal pressure).

The resulting deformation is a function not only of the general stress conditions but is also temperature and time dependent, so that according to the extent of these environmental variables, failure of the test piece may occur, An equally important part in the characteristic behaviour mentioned is exercised by mean molecular weight, molecular weight distribution, and depending on the type of polymer, density.