Determination of ring flexibility on thermoplastic pipes according to EN ISO 13968

The mechanical properties of thermoplastic pipes are of great importance for their possible applications in various branches of industry. For example, the pipes are exposed to high pressure loads when laying drinking water and waste water pipes or irrigation and drainage systems. EN ISO 13968 specifies the test methods for determining the ring flexibility of pipes to ensure that the materials can withstand the bending stress requirements.

In accordance with EN ISO 13968, the ring flexibility is determined by determining the bending radius at which the pipe exhibits a defined deformation. The test is carried out on pipe sections with a specified diameter and a defined wall thickness. The pipe section is placed in a compression testing machine between two compression plates, which allows the pipe to bend evenly.

The standard defines various parameters that are measured during the test, including the maximum bending radius, the maximum load and the permanent deformation after the test. These parameters allow a comprehensive characterisation of ring flexibility and serve as a basis for assessing the suitability of the material for the intended application.

Apex pressure testing machines from Hegewald & Peschke are used to test thermoplastic pipes in accordance with EN ISO 13968. One advantage of these machines is that they can be built with different test chamber dimensions in order to test different pipe diameters. The testing machines are equipped with large pressure plates and special compression gauges for determining the deformation of pipe segments.

The test system is also used to determine the ring stiffness in accordance with EN ISO 9969. The ring stiffness describes the resistance of a pipe to deformation by a vertically acting force. The pipe is compressed at a constant deformation speed in accordance with DIN EN 9969. The applied force is measured using a transverse force-stable ring force transducer. The deformation is determined using special extensometers on the inner wall of the pipe and corresponds to the change in the inner diameter.

The test procedures specified in the relevant standards can be set up and carried out in a user-friendly way using the LabMaster materials testing software. LabMaster offers great flexibility when integrating external devices such as the compression tester as well as when importing and exporting data for customised software such as QDAS or SAP.