The durability of PVC pipes is related, as it is for all other thermoplastics materials, to the chemical degradation of the polymer used in the pipes. However unlike other thermoplastic pipes PVC pipes do not oxidise.
Stabilisers are used in PVC pipes to prevent degradation of the polymer during the extrusion process and storage of the pipes before they are buried in the ground. However, when the pipes are buried in the ground, no chemical degradation is expected to take place. For this reason the durability of the PVC material in buried pipes is expected to be very good (maybe even be more than 1000 years.
In standardised pipes for potable water the expected lifetime of PVC pipes under pressure is extrapolated based on hoop stress testing of pipes for up to 20000 hours. This allows an estimation of the durability by extrapolation to a life expectancy under pressure of 50 to 100 years.
PVC-U piping systems belong to the category of so called "flexible designed pipes". This flexibility provides a great advantage compared to pipes made of traditional materials such as concrete or clay.
For flexible designed pipes: the soil supports all the stresses on the pipe (including soil weight) and the pipes deform slightly but do not break. For pipes made of traditional materials, the soil concentrates the stresses directly on to the crown of the pipe; these pipes do not deform but a failure mode results in a break in the pipe.
For most of the "good quality soils" (e.g. granular types of soil) the soil supports all the stresses and, as this type of soil can be easily compacted, the deformation of the PVC pipes is only 1 or 2% which does not affect the functional properties nor the tightness of the systems at all. In weak soils ("plastic soils") the PVC piping systems deform slightly more (in the range of 5 to 10%) but they still perform perfectly well.
For all piping materials very difficult soil conditions will need a thorough examination or calculation by qualified civil engineers and certain European or national standards ask for static calculation for the piping systems.
HDPE pipes with a history of 60 years of technological developments that have positively influenced and until today has become one of today's most preferred tube.