Viscoelastic Weaknesses of Plastic Pipes

What Engineering Data Reveals

Plastic pipes (primarily PVC and PE) have become widely used in potable water and drain-waste-vent systems. They are marketed for their durability, ease of installation, and lower cost, yet engineering studies and forensic reviews show plastic pipe materials have mechanical behaviors very different from metals. These behaviors introduce long-term performance concerns that designers and contractors must account for when designing systems and specifying materials.

Research on the longitudinal mechanics of thermoplastic pipes demonstrates that pressure cycles, bending, soil movement, temperature changes, and installation stresses interact in ways that can produce failure modes unique to plastics. Recent reviews of real-world failures of plastic pipe systems reinforce these findings and highlight the importance of understanding how plastics age under sustained stress.

Plastic pipes are viscoelastic, meaning their shape and mechanical properties change over time. Under load, they gradually deform. Under sustained strain, internal stresses relax but deformation remains. This time-dependent behavior – creep, stress redistribution, slow crack growth, and