Overview
EN ISO 9080:2012 - "Plastics piping and ducting systems - Determination of the long-term hydrostatic strength of thermoplastics materials in pipe form by extrapolation" - specifies a statistical method to predict long-term hydrostatic (hoop) strength of thermoplastic materials tested in pipe form. Developed from pipe-system test data, the Standard Extrapolation Method (SEM) uses regression and extrapolation to estimate material performance at service conditions (for example, the conventional reference of 50 years at 20 °C) and produces a 97.5% lower prediction limit (LPL) for strength.
Key topics and requirements
- Scope: Applicable to all thermoplastics in pipe form at relevant temperatures, using water (or air) as the external test environment where appropriate.
- Standard Extrapolation Method (SEM): Statistical framework based on multiple linear regression of log(stress) vs. log(time) to extrapolate stress-rupture data.
- Lower Prediction Limit (LPL): The SEM yields the 97.5% LPL, used for material classification and design values.
- Design metrics:
- MRS (material categorization) and CRSθ (categorised stress for a given temperature/time) are derived from the LPL in accordance with ISO 12162.
- Models supported: 2-, 3- and 4-parameter extrapolation models; choice balances fit vs. predictive uncertainty.
- Knee detection: Procedures (including automatic methods in Annex B) to identify transitions in rupture behaviour.
- Polymer-specific guidance: Extrapolation time factors and approaches for polyolefins and vinyl chloride–based polymers (see clauses 5.2–5.4).
- Test data & reporting: Requirements for data acquisition, distribution of pressure/time ranges, software validation, sample calculations and a specified test report format.
- Normative and informative annexes: Methods of analysis, knee detection algorithms, SEM examples for different polymer types, and software recommendations.
Practical applications
- Derive long-term hydrostatic strength values for material selection and product standards.
- Classify thermoplastic pipe materials (MRS) and establish design allowable stresses (CRSθ) for pipeline design and certification.
- Support product development, quality control, and regulatory compliance by predicting stress-rupture behaviour at service times and temperatures.
- Validate or compare alternative test methods and commercial SEM software (see Annex E).
Who uses this standard
- Material manufacturers and compounders of thermoplastics
- Pipe and multilayer system producers
- Independent test laboratories and certification bodies
- Pipeline designers and engineers setting allowable pressures
- Standards committees and regulators determining classification criteria
Related standards
- ISO 12162 - classification and design values (MRS, CRSθ)
- Product-specific piping standards that use SEM outputs for design and classification
- ISO/TC 138 (technical committee responsible for plastics pipes standards)
Keywords: EN ISO 9080:2012, long-term hydrostatic strength, thermoplastics, pipe form, statistical extrapolation, Standard Extrapolation Method, lower prediction limit, MRS, CRSθ, ISO 12162, stress-rupture, multiple linear regression, knee detection.
