ISO 9967 ISO 9967 is an international standard that outlines a method for determining the creep ratio of thermoplastics pipes, particularly those used in non-pressure applications such as sewer and drainage systems. The standard focuses on evaluating the pipe’s ability to resist deformation under a long-term constant load. It involves applying a sustained external force to a test sample and measuring how much the diameter of the pipe changes over a set period, typically 30 minutes and 10,000 hours. The creep ratio is then calculated by comparing the short-term deformation to the long-term deformation. This test is crucial for assessing the long-term structural stability and performance of buried plastic pipes, helping manufacturers and engineers ensure that materials meet the necessary durability and quality standards..
The ISO 9967 test procedure begins by preparing a ring-shaped specimen from a thermoplastic pipe. The ring is typically cut to a length equal to the pipe’s outer diameter and must be free of visible defects. Before testing, the sample is conditioned, usually at 23°C for at least 24 hours. During the test, the specimen is placed vertically between two flat, parallel plates in a compression testing machine. A constant external force is applied to the ring to compress it until a deformation equal to 3% of its mean diameter is reached. This loading should occur gradually, typically within one minute. The test apparatus must maintain this compressive load over an extended period, most commonly 10,000 hours, under controlled environmental conditions. The deformation of the ring is measured at defined intervals during the test using a precise displacement measurement device. Initial and long-term measurements are used to calculate the creep ratio. This ratio quantifies how much the ring deforms over time under constant load, which indicates the material's long-term behavior and suitability for buried, non-pressure pipe applications. Accurate time tracking and temperature control are critical throughout the process to ensure valid results. The test concludes by comparing the deformation at 30 minutes and at the final time point to calculate the creep ratio according to the formula provided in the ISO 9967 standard
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