Determination of resistance to rapid crack propagation (RCP)
ISO 13477, S4-test
ISO 13477 specifies a test method also known as the Small-scale steady-state test (S4 test) for determination of arrest or propagation of a crack initiated in a thermoplastic pipe at a specified temperature and internal pressure. The aim is to assess the performance of thermoplastics pipes that are intended for the supply of gases or liquids. In the latter case air may also be present in the pipe.
A section of a thermoplastic test pipe of a specific length, maintained at a specified test temperature, containing a fluid at a specified test pressure, is subjected to an impact, near one end, in order to initiate a fast running longitudinal crack. The crack initiation process itself is designed to disturb the test pipe as little as possible.
The test temperature and test pressure are defined in the appropriate standards. The fluid is either identical to the one used in the intended application or an equivalent substitute. Rapid decompression ahead of the propagating crack is retarded by internal baffles and by an external cage which restricts flaring of the test pipe at the edges of the fracture. Hence this technique achieves steady-state rapid crack propagation (RCP) in a short pipe specimen at a lower pressure than in a full-scale test. The tested pipe is examined to determine whether arrest or propagation of the crack has occurred. From a series of tests at different pressures and at constant temperature, the critical pressure or the critical hoop stress for RCP can be determined. Similarly the critical temperature for RCP can be determined by testing at different temperatures at constant pressure or hoop stress.