What Does Hydrostatic Design Basis (HDB) Mean?
Hydrostatic design basis (HDB) can be defined as the estimated long-term strength of a plastic pipe material in the hoop or circumferential direction of the pipe when subjected to certain end-use conditions. Plastic materials such as polyvinyl chloride (PVC), glass reinforced plastic (GRP) and high density polyethylene (HDPE) are subjected to an HDB test to determine its long-term material properties. GRP, HDPE and PVC are used extensively in the trenchless industry for the purpose of repairing or replacing damaged sewer and water pipes without digging the surface.
Trenchlesspedia Explains Hydrostatic Design Basis (HDB)
Pipes are subjected to internal pressure at varying levels that duplicate the conditions that the pipe will experience while in service, and the time to failure is measured. The data obtained for pipe failure is extrapolated to a 50-year time period to obtain a design value. The time period is a reference point from which the product design can be determined after long-term safety factors have been applied. The time to failure is noted when the water starts passing through the pipe wall by weeping, cracking, bursting or splitting.
The American Society for Testing and Materials (ASTM) test method D 2837 "Standard test method for obtaining hydrostatic design basis for thermoplastic pipe materials" is used for the purpose of determining HDB. To determine HDB, factors such as long-term hydrostatic strength at 100,000 hours, long-term hydrostatic strength at 50 years, stress that gives five percent expansion at 100,000 hours etc. are considered for evaluation.