The underground piping market in North America has seen tremendous growth over the last 30 years in the use of thermoplastic materials. Benefits such as corrosion resistance, improved hydraulics, and reduced installation costs have been paying large dividends for owners of watermain, sanitary and storm sewer systems.
The most widely used and accepted of this group of nonmetallic polymers is Polyvinyl Chloride, also known as 'PVC' or 'vinyl'. Vinyl has a successful track-record in the application of underground pipe dating back to the rebuilding of post-WWI Germany. It has long been considered to be one of the most durable polymers for both underground and above-ground piping systems.
Another thermoplastic used in the underground pipe market is High-Density Polyethylene (HDPE). This material has been used for well pipe, gas piping and drainage tubing before recent entry into the watermain and sewage forcemain markets.
HDPE and PVC are remarkably similar in their nature of responses to such stress loadings as internal pressure and soil loads. Although responses are similar, they are not identical. In fact the magnitudes of their respective strengths are dramatically different.
This report is intended to investigate some of the similarities and differences between the design of PVC and HDPE in terms of the application of underground pressure piping.
PRESSURE RATING
The long-term pressure rating of a thermoplastic pipe is defined as the maximum internal pressure at which the pipe can operate continuously. The ratings of both PVC and HDPE are found using the ISO Equation for thermoplastics: . . .
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