What is the typical design life of PE pipe ?
PE pipe systems are usually designed by our customers based on empirical and actual test data on the basis of a 50 year service life.
Under normal operating conditions the actual life is expected to be considerably greater.
Plastic pipes are made from visco-elastic material which means the tensile or hoop stress capacity varies with time. Long term strength is determined by the results of long-term pressure testing and performing regression analysis on the test data. This gives the design stress of the material for the service life, and hence maximum operating pressure. This method takes into account the creep of the material over its design life.
To obtain the regression curve, laboratory tests are normally carried out on pipe samples subjected to a range of internal pressures, and hence pipe stresses, at 20°C, 60°C and 80°C. The test regime is designed to obtain burst test results at intervals from one hour to more than 10,000 hours (approximately 14 months). Regression analysis is carried out on the test results to predict the long term strength at 50 years and 20°C.
PE100 material has a 50 year Minimum Required Strength (MRS) of 10 MPa. In practice however the actual strength is greater than the design strength and hence the expected resulting service lifetimes are greatly in excess of the nominal 50-year requirement when the pipe is operating within its design envelope.
- ISO 1167-1:2006, Thermoplastics pipes, fittings and assemblies for the conveyance of fluids - Determination of the resistance to internal pressure - Part 1: General method
- ISO 1167-2:2006, Thermoplastics pipes, fittings and assemblies for the conveyance of fluids - Determination of the resistance to internal pressure - Part 2: Preparation of pipe test pieces
- ISO 9080:2003 Plastic piping and ducting systems – Determination of the long-term hydrostatic strength of thermoplastic materials in pipe form by extrapolation
- ISO 13761:1996 Plastics pipes and fittings - Pressure reduction factors for polyethylene pipeline systems for use at temperatures above 20° C
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The service lifetime is influenced by five factors: The pipe operating conditions (temperature and pressure) The pipe material used External pipe loading (traffic loading, high water table, etc.) The surrounding environment, including the chemical loading from, for example, contaminated soil. Installation conditions and methods As an example, for design purposes the MRS is specified at a nominal temperature of 20°C. Many buried pipelines, particularly in Europe, operate at temperatures...Read more