HDPE (PE100) has a MRS of 10 MPa. The hydrostatic Design stress for the material is determined by applying a safety factor of 1.25. The design life for the water industry requires a minimum life of 50 years, therefore the design stress for PE 100 is ( 8 MPa ). Polyethylene pipe pressure ratings are generally referred to in bar; 1 bar is approximately equivalent to 10.2 meter head.