Overview
ISO 17456:2006 - Plastics piping systems - Multilayer pipes - Determination of long-term strength specifies two alternative methods to determine the long-term hydrostatic strength of multilayer pipes. It covers:
- Procedure I (calculation) - a method for multilayer P pipes (all polymer layers) using layer material long‑term strength and the Annex A equation, with mandatory validation tests.
- Procedure II (pressure test) - a test method applicable to both multilayer P and multilayer M pipes (polymer + metal layers), using pressure-to-failure data and statistical analysis (ISO 9080).
ISO 17456 is intended for multilayer constructions only and excludes pipes consisting of a single stress‑designed polymeric layer or pipes with a non‑stress-designed external polymer layer.
Key topics and requirements
- Two alternative methods: calculation for P‑type multilayer pipes; experimental pressure testing for both P and M types.
- Reference test standards: test pieces and pressure tests are prepared and performed in accordance with ISO 1167‑1 and ISO 1167‑2; long‑term strength analysis follows ISO 9080.
- Validation: Procedure I requires confirmation testing of each pipe design. Typical validation conditions include T = 80 °C for t = 3 000 h or T = 95 °C for t = 1 000 h (lower temperatures may be used to avoid degradation).
- Test planning and groups: For Procedure II, test at least one diameter per dimension group (≤26 mm, >26–≤63 mm, >63 mm). For multilayer M pipes use the diameter with the highest metal‑layer SDR.
- Statistical and reporting requirements: Pressure‑to‑failure datasets must conform to ISO 9080 spread and reporting rules. Confirmation testing requires a minimum number of failures (e.g., at least 18 failures spread from 10 h to 10 000 h, with other distribution constraints).
- Control points and confidence limits: Procedures define calculation of long‑term hydrostatic strength (LTHS) and lower confidence limits (LPL) for required times (e.g., 22 h, 165 h, 1 000 h) and extrapolated 5‑year p values.
Applications and who uses it
ISO 17456 is used by:
- Pipe manufacturers developing multilayer polymer and polymer/metal composite pipes to demonstrate long‑term hydrostatic performance.
- Test laboratories performing pressure‑to‑failure and long‑term strength testing following ISO 1167 and ISO 9080 methodologies.
- Design and specification engineers, product certifiers and regulators who need validated long‑term pressure ratings for multilayer piping systems used for the conveyance of fluids.
- Quality and R&D teams assessing new multilayer constructions or validating calculation models against experimental results.
Practical benefits include consistent determination of long‑term hydrostatic strength, validated calculation workflows for polymer-only multilayer pipes, and clear test/validation criteria for product certification.
Related standards
