Ring stiffness, ring flexibility and tensile properties are, together with dimensional stability, important quality characteristics for pipes. Depending on type and application, other tests, such as short-term creep behavior or assessment of welded joints in tensile or flexure tests are also used.

The nature and scope of the tests, together with the standards to be applied, are usually stipulated in specification standards or agreed between supplier and customer.

Testing plastic pipes – two new machine types
The lengths of pipe used for testing ring stiffness vary according to whether the test is to international standard ISO 9969 or the German DIN 16961 Part 2. The ISO standard permits testing on a 300 mm length of pipe for internal diameters up to 1500 mm, which means that testing machines with relatively small compression platens can be used for this test. However, for testing ribbed pipes the DIN standard specifies a length of pipe equal to twice the internal diameter, up to a maximum length of 1 meter, which means that all pipes with an internal diameter of 500 mm and above must be tested using the maximum permitted length of 1 meter.

For customers exclusively using EN and ISO standards there is now a new ProLine series testing machine available from Zwick. This machine has a capacity of 50 kN and is equipped with a 400 mm x 400 mm lower compression platen for ring stiffness and ring flexibility tests and can quickly and easily be adapted for tensile tests and other standard specimens.  A range of fixtures for additional tests are also available. Measurement of ring deformation on the inside diameter is carried out via a special displacement transducer located inside the pipe; alternatively special feeler arms can be used in conjunction with the long-travel extensometer employed for tensile testing. The machine can be configured for tests on ribbed pipes as described in the DIN standard using a testing machine and associated fixtures. 1020 x 1020 mm compression platens and a maximum load of 50 kN allow reliable performance of ring stiffness tests on ribbed pipes from RR 1 - 5. A displacement transducer for tracking the internal diameter of the pipe can optionally be mounted laterally on the load frame. In addition to DIN testing this machine is also suitable for tests to international standards such as ISO 9969 (ring stiffness), ISO 9967 (creep behavior) and EN 1446 (ring flexibility).

Both testing machines are controlled by Zwick’s testXpert^® II intelligent testing software, in which the test sequences for the individual standards are already stored as ready-to-use Test Programs, providing solutions for customized requirements in every situation. Operation is remarkably straightforward via easily understood symbols, a clear menu structure and wizard technology. testXpert^® II has been developed for international use - one mouse-click is all it takes to change languages.