Long-term hydrostatic strength

Sh Mean long-term hydrostatic strength (LTHS) kPa psi... 

ISO/DIS 9080, Thermoplastics pipes for the transport of fluids - Methods of extrapolation of hydrostatic stress rupture data to determine the long-term hydrostatic strength of thermoplastics pipe materials, 1992. 

EN 12107 Injection moulded thermoplastics fittings, valves and ancillary equipment -determination of the long-term hydrostatic strength of thermoplastics materials for injection moulding of piping components. 

Long-term hydrostatic strength (LTHS) the hoopes stress that, when applied continuously, will cause failure of the pipe at 100,000 h. 

Test Methods for Determining Long-Term Hydrostatic Strength... 

Once the best-fit straight hue is calculated to 10,000 hours, it is extrapolated to 100,000 hours (about 11 years). The hoop stress level that coincides with the point at which the line intersects the 100,000-hour time line represents the calculated long-term hydrostatic strength of that particular material. 

FIGURE 13.3 Stress rupture data plotted as best-fit straight line and extrapolated to determine long-term hydrostatic strength. (Derived from A.G.A Plastic pipe Manual for Gas Service)... 

Because Amdevco/Century no longer exists. Safety Board investigators could locate no records to indicate the qualification steps Amdevco may have performed before Century marketed its pipe to Iowa Public Service Company. A plastic pipe manufacturer would normally have obtained documentation from its resin supplier indicating that the resin material had a sufficient long-term hydrostatic strength. Code B31.8 required and ASTM D2513 recommended that polyethylene pipe manufacturers perform certain quality control tests on production samples, including twice-per- year sustained pressure tests. 

Although adherence to ASTM appendixes is not mandatory, the PPI procedure was the only industry-accepted mechanism to determine long-term hydrostatic strength and hydrostatic design stress. 

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