Hydrostatic design basis – HDB

The design of GRP pressure pipes are based on establishing the time dependent pressure performance of the material. Pipes are subjected to varying levels of internal pressure and the time to failure is measured. This data is then extrapolated to a rating point from which the pipe design can be established.

The failure data is extrapolated to 50 years to establish a design value. The 50-year value–often termed the hydrostatic design basis–is not the expected life of the product, but rather serves as a point from which, after the application of appropriate long-term safety factors, the product design can be determined. The expected life of the product is considerably longer.

The tests are conducted with a sealing and restraint system that duplicates the in-service condition. Time to failure is determined as passage of water through the pipe wall. It is important to note that for FLOWTITE pipes this is typically evidenced by “weeping”, which appears as a drop of water on the outside of the pipe specimen, rather than a burst failure mode which is prevalent for other materials and manufacturing methods. FLOWTITE pipes have thus a considerable reserve strength compared to other products.

Testing of HDB is not a one-time procedure. The performance of the product must continue to be evaluated and monitored to verify that the performance is consistant. This is done by periodically conducting confirmation tests to assess the product performance. Simply, confirmation testing compares the results of a reduced series of HDB tests to the orginal HDB line to demonstrate that the products continue to be of the same family and data group.

FLOWTITE Technology has been conducting confirmation testing since the publication of the base HDB report. A series of confirmation tests on a range of products have been carried out over the years. The data shows that the original HDB line is consistently confirmed over the years.

Reports on pressure regression and confirmation testing can found be here.