ISO 13479 provides a standardized method for determining the resistance of polyolefin pipes to slow crack growth. The test involves applying constant internal hydrostatic pressure to a pipe segment with precisely machined longitudinal notches on its outer surface. Conducted at elevated temperatures, typically around 80 °C, the test measures the time it takes for a crack to propagate and cause failure.
ISO 13479:2022 specifies a method for testing the resistance of polyolefin pipes to slow crack growth. This is assessed by measuring the time to failure of a pipe sample subjected to a hydrostatic pressure test. The pipe used in the test has precisely machined longitudinal notches on its external surface, which simulate crack initiation points. The test is conducted at elevated temperature and constant internal pressure to accelerate the failure process. The result provides an indication of the material’s durability and crack resistance under long-term stress conditions. This method is applicable to polyolefin pipes with a wall thickness greater than 5 mm./p>
The test procedure described in ISO 13479:2022 involves evaluating the resistance of polyolefin pipes to slow crack growth by subjecting notched pipe samples to hydrostatic pressure under controlled conditions.
First, a section of the pipe is prepared by machining three equally spaced longitudinal notches on the outer surface along the pipe’s length. The notches are created using a defined geometry to ensure consistency across samples. The depth and sharpness of the notches are critical, as they serve as initiation points for slow crack growth during the test.
The notched pipe sample is then mounted in a pressure test apparatus capable of maintaining constant internal hydrostatic pressure and temperature over extended periods. The test is typically performed at an elevated temperature, often 80 °C, to accelerate crack propagation. The internal pressure applied is selected based on the pipe’s design and material characteristics, ensuring that it promotes slow crack growth without causing immediate failure.
Once the test begins, the sample is monitored continuously. The time from the start of the test until the pipe fails (defined by the development of a through-wall crack or sudden drop in pressure) is recorded. This duration is referred to as the time to failure and represents the pipe’s resistance to slow crack growth under the given conditions. The results are used to compare the SCG performance of different pipe materials or manufacturing processes and to assess long-term durability for applications involving sustained internal pressure.
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