Hydrostatic Design Stress, Density & Vicat Softening Point
Hydrostatic Design Stress
From AS1640:1989, this is defined as the maximum hoop stress in the pipe wall due to internal hydrostatic pressure that can be applied continuously with great certainty that failure of the pipe will not occur in a long period of time, as it is obtained by the application of a safety factor to the extrapolated 50 year long-term hydrostatic stress value.
The hydrostatic design stress for our Polyethylene pipe is 5.5MPa (800 P.S.I.) at 20˚C. A high hydrostatic design stress (such as that in PB-1) means the pipe is able to take great internal pressure.
The mass per unit volume for Polyethylene is 0.955 kg/L at 25˚C.
Vicat Softening Point
Polymers tend to soften rather than melt and the point at which the polymer specimen is able to be penetrated to a depth of 1mm by a flat-ended needle is known as the Vicat softening point.
The Vicat softening point for Polyethylene is 116˚C.