PVC is rated based on its pressure and temperature performance, which is represented by its pressure rating at a specific temperature and a derating factor for higher temperatures.
Here's a breakdown:
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Pressure Rating at Standard Temperature: PVC pipes are typically given a pressure rating (e.g., 230 psi) at a standard temperature (often 73°F or 23°C). This rating indicates the maximum internal pressure the pipe can withstand at that temperature before failing.
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Temperature Derating: As the temperature increases, the strength of PVC decreases. To account for this, a derating factor is applied to the pressure rating. This factor reduces the allowable pressure based on the operating temperature.
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Example: At 130°F (54.4°C), PVC has a derating factor of approximately 0.31. This means the pressure rating at this temperature is calculated as:
Pressure Rating at 130°F = Original Pressure Rating x Derating Factor
Pressure Rating at 130°F = 230 psi x 0.31 = 71.3 psiThis calculation demonstrates that the maximum allowable pressure for PVC significantly decreases as the temperature rises.
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CPVC Consideration: CPVC (Chlorinated Polyvinyl Chloride) has a higher temperature resistance than standard PVC. Therefore, it has a higher derating factor at the same temperature. For example, at 130°F (54.4°C), CPVC has a derating factor of 0.57, making it pressure rated up to 131.1 psi (230 psi x 0.57 = 131.1 psi).
In summary, PVC is rated by its pressure rating at a standard temperature, and its performance at higher temperatures is determined by applying a temperature derating factor to this initial rating. The derating factor is crucial for ensuring safe and reliable operation at elevated temperatures.
