Ring Stiffness

Published: December 21, 2018 | Last updated: July 5, 2023

What Does Ring Stiffness Mean?

Ring stiffness of a pipe can be defined as its ability to resist radial forces acting on it and the pipes resistance to ring deflection and structural damage. This test is done as per American Society for Testing and Materials (ASTM) D2412 for thermoplastic and EN 1228 for glass reinforced plastic pipes (GRP). Buried pipes such as sewer and water pipes are subjected to soil pressure, hydrostatic pressure and live loads from traffic.

Tests to determine the ring stiffness of a pipe are carried out prior to burying them to ensure that the pipe material used can withstand expected soil conditions and loads when buried. It's advisable to carry out a ring stiffness test to prevent failure and costly rehabilitation of untested pipes when subjected to real loads.


Trenchlesspedia Explains Ring Stiffness

This test requires a section of the pipe to be tested to be cut into a test length. The length of the pipe section depends on the nominal diameter (ND) of the pipe. Pipes with diameter up to 1500 mm are tested in lengths of 300 mm. The pipe section is placed between two flat platens and subjected to a force to deflect the pipe by three percent of its diameter and the slowly allowed to relax for two minutes. The force is applied again at this point and pressed again to 27 mm at a rotation of 120 degrees and allowed to relax again. The pipe is deflected again at 240 degrees rotation and the deflection is noted.

Once the test is performed at the three rotations, the average of the force and deflection are averaged to determine the ring stiffness.


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