Overview
EN ISO 10928:2025 (ISO 10928:2024) - Plastics piping systems - Glass‑reinforced thermosetting plastics (GRP) pipes and fittings - Methods for regression analysis and their use - specifies statistical procedures for analysing time‑dependent test data for GRP pipes and fittings. The standard addresses regression analysis of log‑transformed data that display either normal or skewed distributions and describes two prescribed methods (Method A and Method B) for extrapolating short‑term test results to long‑term performance predictions (commonly extending data from ~10 000 h to a 50‑year prediction).
Key topics and technical requirements
- Scope of analysis: Applies where values, when converted to logarithms, have a normal or skewed distribution. Intended for GRP pipes and fittings but can be used for other datasets.
- Two analysis methods:
- Method A (Covariance method) - suited to skewed log‑data; adopted because many destructive test datasets are skewed. Includes procedures for variance calculation, extrapolation checks and lower confidence/prediction limits (Annex B).
- Method B (Regression with time as independent variable) - simpler method used when log‑data are approximately normally distributed, often applicable to non‑destructive creep or relaxation tests.
- Data prerequisites: Analyses typically require that log‑data:
- produce a regression line with a negative slope;
- have a sufficiently high regression correlation;
- and either be normally distributed or handled by the covariance approach for skewness.
- Extrapolation limits: Typical practice is to extrapolate from data gathered over ~10 000 hours to a maximum prediction horizon of 50 years.
- Annexes: Includes an informative Annex A on second‑order polynomial relationships (useful for certain creep/relaxation curves) and a normative Annex B for calculation of lower confidence and prediction limits for Method A.
- Document role: EN ISO 10928 addresses data analysis only - test procedures, sample sizes and collection schedules remain the responsibility of referring product standards and test methods. Clause 6 explains application to product testing and design.
Applications and who uses it
- Manufacturers and product designers - for estimating long‑term strength, creep, relaxation and durability of GRP piping systems during product development and design validation.
- Test laboratories - to apply standardised regression techniques when reporting long‑term property predictions from accelerated or time‑limited tests.
- Certification bodies and conformity assessors - for assessing declared long‑term values and conformity to performance requirements.
- R&D and quality assurance teams - for statistical analysis of destructive and non‑destructive test datasets.
Related standards and governance
- Prepared by ISO/TC 138 (Plastics pipes) and adopted by CEN/TC 155 as EN ISO 10928:2025; it supersedes earlier EN 705 editions. The standard is intended to be used alongside ISO product standards and test methods that define sampling and test procedures.
Keywords: EN ISO 10928:2025, ISO 10928:2024, GRP pipes, regression analysis, covariance method, long‑term prediction, log‑transformed data, plastics piping systems, Method A, Method B.