→Mainly two different procedures are used to measure and evaluate the pipe stiffness:
Testing under constant load according to DIN16961-2: Thermoplastic pipes with profiled wall and smooth pipe inside
Testing under constant speed according to DIN EN ISO9969: Thermoplastic pipes-determination of Ring stiffness
→At both procedures a cut length of pipe (typically up to 1m long) is being horizontal supported and compressed vertically between two parallel flat platens.
→Alternative Test Procedures for Ring Stiffness: use of pipe segments
The ring test acc. DIN16917 is carried out with 79° segments, extracted from one pipe. The ring stiffness is defined by measuring of strength and deformation under a constant deformation rate. A pipe segment is used instead on a complete pipe. The pipe segment is deformed vertically under a constant rate. The deformation of a segment corresponds to the amount of deformation of a complete pipe (3%).
→The test body ( 79° pipe segment) is pressed together at a constant speed acc. Specification of the standard ISO9969. The measuring values of force and deformation has to be recorded continuously until a deformation corresponding to a deformation of the complete pipe of 0.03di is reached.