Innovation in the Operating Temperatures of Plastic Pipes Requires Updated Testing Methods

Plastic piping covers a wide range of applications. Many of the standardized tests to determine material properties are created with those applications in mind. As innovation in the industry continues, the boundaries of those tests are pushed and new approaches to testing may need to be developed. One area of innovation is application temperatures: increasing the maximum operating temperature and decreasing the minimum operating temperature. So the temperature range that a test (say, pressure testing) can be conducted under must also expand and the internal and external test fluids must be considered carefully.

In long-term pressure testing, the test environment is defined by the internal and external fluid, which is most commonly water. The use of water as the internal fluid is due primarily to its availability but also its incompressibility. At the pressures under which long-term testing is conducted the water volume does not change significantly. Any release of pressure often results in very little volume change. In contrast, if air were used as the internal fluid, it could be significantly compressed and a release in pressure could result in a rapid increase in volume (also known as an explosion). So, while it’s readily available, using air internally results in a much more hazardous test.

For testing above 203° F, the external environment shifts to air with testing occurring in an oven. This represents increased risk as any failure will release the pressurized water into the oven. Thus, when examining failures in an oven, appropriate safety precautions should be undertaken. Also, if the failure mode releases a significant volume of water that may convert to steam, the pressure within the oven may also rise. NSF has years of experience in testing at these conditions and mitigating any safety concerns.

For testing below 32° F, the external environment must also shift to air, and the internal environment must shift from water to a fluid with a lower freezing point. Interestingly, ISO 9080, Plastic piping and ducting systems – Determination of the long-term hydrostatic strength of thermoplastics materials in pipe form by extrapolation states that “the data obtained may be used for predicting the strength down to 20° C below the lowest test temperature.” Since the lowest temperature typically tested is 20° C, this implies that the lowest strength prediction is for 0° C, yet for some applications understanding the strength of the material at lower temperatures becomes important. Using the appropriate set-up, this low temperature strength can be determined.

Innovative product designs and applications can result in tests needing to adapt and change to meet more exotic requirements. These requirements may include increasing the testable temperature range or changing the test fluids. Our expertise in these areas can help you obtain the information needed.