Results of long-term hydrostatic strength study of piping systems made from polyethylene with increased temperature resistance PE-RT type II of Hostalen 4731B without reinforcement are presented and discussed in this paper. The different approximations of durability curves and various equivalent stress measures are considered and compared. An analytical expression for the maximum allowable internal pressure as function of service life of pipes, temperature, geometrical parameters of pipe cross-section and material properties is given. Pipes without reinforcement with nominal outer diameters from 32 mm to 225 mm were analyzed to assess long-term hydrostatic strength using equivalent stress, provided that there is no change in mechanism of damage accumulation. This allowed us to use linear extrapolation into area of long service life. The results indicate possible use of pipes SDR7.4 in heating networks for 50 years with heat transfer fluid parameters of 95 °C and internal pressure of 1 MPa.