Overview
ISO 24033:2025 - Polyethylene of raised temperature resistance (PE‑RT) pipes defines how the expected long‑term strength of PE‑RT pipe materials varies with time and temperature. The standard provides mathematically defined reference lines (and tabulated/graphical values) for PE‑RT Type I and Type II over the typical service range (20 °C to 110 °C). These reference lines are intended for use in strength calculations, material qualification and design of piping systems exposed to elevated temperatures.
Key topics and requirements
- Reference lines and formulae: Expected strength is given by log‑time equations of the form log t = A + B/T + C log σ + (D/T) log σ. PE‑RT Type I uses two branches (20–95 °C) plus a separately determined 110 °C formula; Type II uses a single formula up to 110 °C.
- Temperature range: Reference lines generally apply between 20 °C and 110 °C; 110 °C data are determined from tests with water inside and air outside.
- Tabulated and graphical data: Tabled hoop stresses for various temperatures and service times (no safety factors included) and graphical plots are provided for easy lookup.
- Extrapolation limits: Minimum extrapolation time limits are specified (based on 1 year testing at 110 °C and Arrhenius extrapolation with Ea = 110 kJ/mol). Example: ≤60 °C corresponds to 100 years, while 110 °C has shorter extrapolation limits.
- Conformance testing: Annex A requires evaluation per ISO 9080 or equivalent, using internal pressure tests in accordance with ISO 1167‑1/2. At least 97.5% of test points must lie on or above the reference lines; additional checks prevent brittle “knee” failures.
- Design guidance: Annex B explains deriving maximum calculated S values and minimum wall thicknesses relative to application classes (e.g., hot water, underfloor heating), using Miner’s rule and references such as ISO 10508 and ISO 13760.
Applications and users
ISO 24033:2025 is essential for:
- Pipe and compound manufacturers qualifying PE‑RT grades for hot‑water and heating systems.
- System designers and plumbing/HVAC engineers calculating required hoop stress and wall thickness for long‑term performance.
- Test laboratories performing long‑term hydrostatic strength tests and extrapolations.
- Standards bodies and specifiers writing system standards for potable hot water, underfloor heating and high‑temperature radiator systems.
Keywords: ISO 24033:2025, PE‑RT, expected strength, reference lines, hydrostatic strength, hoop stress, extrapolation limits, ISO 9080, ISO 1167.
Related standards
Open preview (PDF)Polyethylene of raised temperature resistance (PE-RT) pipes — Effect of time and temperature on the expected strength