Overview
ISO 8149:2025 defines how to predict the long-term strength of extruded unplasticized polyamide (PA-U 180) pipes as a function of time and temperature. It provides reference lines (mathematical models and tabulated values) for expected hoop strength used in design and lifetime calculations of PA-U11 180 and PA-U12 180 pressure piping. The standard covers temperatures from 20 °C to 120 °C, notes hydrolytic ageing effects, and excludes other polyamide types (e.g., PA-U 160) until sufficient data are available.
Key topics and technical requirements
- Reference lines: Generic minimum long-term hydrostatic strength described by two mathematical branches (applicable models for interpolation and controlled extrapolation). The reference lines are based on ISO/TS 26873 methodology.
- Temperature and time range: Models applicable between 20 °C and 120 °C. Extrapolation limits are specified (e.g., 1 year testing at 80 °C with additional tests at 110 °C and 120 °C).
- Extrapolation time limits (minimum values from Table 1):
- 120 °C: 0.2 years, 110 °C: 0.5 years, 100 °C: 1 year, 90 °C: 2.5 years, 80 °C: 6 years, 70 °C: 18 years, 60 °C: 50 years, ≤50 °C: 100 years.
- Hydrolysis and ageing: Tests use water; hydrolysis of amide bonds reduces molecular weight and affects ductility and strength. The standard explains kinetics and notes differing water uptake for long-chain polyamides (PA-U11/12).
- Tabulated expected hoop strengths: Table 2 provides calculated hoop stress (MPa) vs time and temperature (values are without safety or design factors). Example: at 20 °C the 1‑year expected hoop strength ≈ 20.2 MPa.
- Conformity and testing: Demonstration per Annex A requires evaluation under ISO 9080 and internal pressure tests per ISO 1167‑1/2. Tests shall be carried out at 20 °C, 60–82 °C, and 100–120 °C; at least 97.5% of experimental results must lie on or above the reference line.
Applications and who uses it
ISO 8149:2025 is intended for:
- Pipe designers and mechanical engineers performing long‑term strength and pressure‑rating calculations for PA‑U piping systems.
- Manufacturers of PA‑U 180 extruded pipes, fittings and assemblies for quality control and product certification.
- Test laboratories and conformity assessors applying ISO 9080 and ISO 1167 methods.
- Infrastructure and industrial specifiers (gas distribution, oil-field piping, above‑ground industrial lines) evaluating plastics as alternatives to metal piping.
The standard helps reduce variability by providing unified reference lines for design and lifetime assessment of PA‑U 180 pressure pipes.
Related standards
- ISO 9080:2012 - Long‑term hydrostatic strength by extrapolation (referenced for evaluation).
- ISO 1167‑1 / ISO 1167‑2 - Resistance to internal pressure test methods.
- ISO 16486 series - PA‑U piping systems for gaseous fuels (PA‑U minimum strength context).
Open preview (PDF)Unplasticized polyamide (PA-U) pipes — Effect of time and temperature on the expected strength
