Overview
EN ISO 13968:2008 - Plastics piping and ducting systems - Thermoplastics pipes - Determination of ring flexibility (ISO 13968:2008) specifies a standardized laboratory method to measure the ring flexibility of circular thermoplastics pipes. The procedure records the force and diametric deflection produced by compressing a ring section until a specified deflection (commonly 30% of outside diameter unless otherwise stated) or fracture occurs. The method enables determination of the deflection and the force at which physical damage (if any) appears, providing reproducible data for product characterization and specification.
Key topics and requirements
- Test principle: Diametrical compression of a pipe ring at constant speed while measuring force and deflection to produce a force/deflection graph.
- Test pieces: Three rings prepared from the same pipe (designated a, b, c); referring standards may require longer pieces than ISO 9969.
- Apparatus: Compression testing machine and dimensional/force measurement devices as specified in ISO 9969, capable of achieving the required diametric deflection.
- Deflection: Unless the referring standard specifies otherwise, continue compression to 30% of outside diameter or until failure.
- Failure monitoring: Observe and record events such as cracking/crazing, wall delamination, permanent buckling; note that whitening alone is not considered a mechanical failure.
- Data output: Force/deflection curves for each test piece and identification of the force/deflection at which events occurred (including maximum force if applicable).
- Reporting: Test report must reference EN ISO 13968:2008 and the referring standard and include pipe identification (manufacturer, type, dimensions, production date, mass per metre, test temperature), force/deflection graphs, event points, and test date.
Practical applications
- Product development and quality control for thermoplastics pipes (PE, PP, PVC, etc.) to quantify flexibility and mechanical behaviour under diametric loads.
- Performance specification and acceptance testing for buried or installation scenarios where ring flexibility affects installation stresses and long-term integrity.
- Comparative testing for material selection, design validation, or failure analysis where ring stiffness/flexibility and damage thresholds matter.
- Use in procurement specifications and compliance testing for standards that reference EN ISO 13968:2008.
Who should use this standard
- Pipe manufacturers and R&D teams developing thermoplastics piping systems
- Independent testing laboratories and certification bodies
- Product engineers and designers specifying pipe mechanical properties
- Regulatory agencies and procurement officers requiring standardized test evidence
Related standards
- ISO 9969 - Thermoplastics pipes - Determination of ring stiffness (normative reference)
- EN 13476-1 - Structured-wall piping systems (referenced for related performance characteristics)
Keywords: EN ISO 13968:2008, ISO 13968, thermoplastics pipes, ring flexibility, diametric deflection, force/deflection graph, ring stiffness, compression testing.
