What’s the ring stiffness mean?

The ring stiffness of a tube can be defined as its ability to resist radial forces acting on it and its resistance to ring deflection and structural damage. Buried pipelines such as sewers and water pipes are subject to soil pressure, hydrostatic pressure and traffic load.

 
Before burying, test to determine the ring stiffness of the pipe to ensure that the pipe material used can withstand the expected soil conditions and loads during burial. It is recommended to conduct a ring stiffness test to prevent failures and expensive repairs of untested pipes under actual loads.
This test requires cutting a part of the pipe to be tested into a test length. The length of the pipe section depends on the nominal diameter (ND) of the pipe. The test length of pipes up to 1500 mm in diameter is 300 mm. The pipe section is placed between two flat plates and is forced to deflect the pipe by 3% of its diameter, and slowly relax for 2 minutes. At this time, force is applied again and again with a rotation of 120 degrees to 27 mm and relax again. The pipe was again deflected with a 240 degree rotation and the deflection was recorded.

Once tested under three rotations, average the average force and deflection to determine the ring stiffness

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