Overview
ISO 13968:2008 defines a standardized test method for measuring the ring flexibility of thermoplastics pipes with circular cross-sections. The procedure determines the force and diametric deflection at which physical damage (if any) occurs when a pipe ring is compressed. The method is intended for consistent evaluation of a pipe’s ability to resist diametric deflection without loss of structural integrity, supporting quality control, design verification, and product specification.
Key topics and requirements
- Scope: Applies to thermoplastics pipes; measures ring flexibility by diametrically compressing pipe ring sections.
- Test principle: Record force and deflection while compressing a ring at a constant speed until a specified diametric deflection is reached or fracture occurs.
- Test pieces: Prepare three test pieces from the same pipe (designated a, b, c); conditioning follows ISO 9969.
- Apparatus: Use a compression testing machine and dimensional/force measuring devices capable of the required deflection and loads.
- Deflection: Unless otherwise specified by the referring standard, the test continues to 30% of the outside diameter. The referring standard can define different deflections or longer test pieces.
- Monitoring and inspection: Generate force/deflection graphs for each piece and inspect for specific failures:
- cracking or crazing
- wall delamination
- permanent buckling
- other events specified by the referring standard
- Note: whitening is explicitly not considered a mechanical failure.
- Documentation: Test reports must reference ISO 13968:2008 and the referring standard, identify the pipe (manufacturer, type, dimensions, production date, mass per metre, test-piece lengths), state test temperature, include force/deflection graphs, record forces/deflections at observed events and maxima, and list any factors affecting results.
Applications and users
ISO 13968:2008 is used by:
- Manufacturers for product development, quality control and production verification of thermoplastics pipes.
- Independent testing laboratories performing certification, compliance and batch testing.
- Design engineers and specifiers assessing pipe performance for buried or installed piping and ducting systems.
- Regulatory bodies and procurement teams needing objective, repeatable data on ring flexibility for acceptance criteria.
Practical uses include material selection, comparison of formulations or wall constructions, and ensuring compliance with performance requirements in piping systems.
Related standards
- ISO 9969 - Thermoplastics pipes - Determination of ring stiffness (normative reference for apparatus and basic procedure).
- EN 13476-1 - Structured-wall piping systems (referenced in ISO 13968:2008 bibliography).
- Prepared by ISO/TC 138 (Plastics pipes, fittings and valves).
Keywords: ISO 13968:2008, ring flexibility, thermoplastics pipes, ring diametric deflection, force/deflection test, ISO 9969, plastics piping systems.
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