ISO 9967:2016

Overview

ISO 9967:2016 - Thermoplastics pipes - Determination of creep ratio specifies a laboratory test method to determine the creep behaviour of circular thermoplastic pipes. The standard defines how to prepare pipe test pieces, apply a sustained compressive load between parallel plates for 1 008 h (42 days), record deflection over time and extrapolate a two‑year deflection to calculate the creep ratio (two‑year deflection divided by the 6‑min deflection). The result supports long‑term static calculations and pipe design where soil installation and settlement are considered.

Key topics and technical requirements

• Scope and principle
  • Test applies to circular‑section thermoplastics pipes; deflection under a constant compressive force is monitored and modelled vs. log(time).
• Test pieces
  • Three test pieces (A, B, C) cut from the same pipe, marked and oriented (rotated 120° for B and C).
  • Length requirements: typically (300 ± 10) mm for pipes ≤ 1 500 mm DN, or ≥ 0.2·DN for larger pipes; special rules for structured‑wall and corrugated pipes.
  • Age at test start: (21 ± 2) days.
• Conditioning and environment
  • Condition test pieces ≥ 24 h at test temperature, normally (23 ± 2) °C (or (27 ± 2) °C where standard lab temp is 27 °C).
• Loading and measurement
  • Use flat, non‑deforming plates and a compressive loading machine maintaining forces to within 1 %.
  • A pre‑load is applied (7.5 N for small pipes; for larger pipes a calculated pre‑load per the standard).
  • Full load is applied to achieve a deflection ratio of (1.5 ± 0.2) % at 6 min; deflection readings are taken at 6 min, 1 h, 4 h, 24 h, 168 h, 336 h, 504 h, 600 h, 696 h, 840 h and 1 008 h.
• Measurement accuracy
  • Length: ±1 mm; inside diameter: ±0.1 mm or 0.2 % d_i; timer: 1 s accuracy for the first 6 min, 0.1 % thereafter.
• Data analysis
  • Plot deflection (m) vs. log(time) and perform linear regression over successive point sets to determine gradient and intercept.
  • Extrapolate to a two‑year deflection and compute the creep ratio. Correlation coefficient R ≈ 0.99–1.00 indicates good linearity.

Applications and users

ISO 9967:2016 is used by:

• Pipe manufacturers for product verification and quality control.
• Materials and R&D labs evaluating long‑term deformation of thermoplastics.
• Design engineers and geotechnical consultants for long‑term static calculations (soil‑installed pipes).
• Test laboratories and certification bodies performing standardized performance tests.
• Regulators and procurement teams specifying performance criteria for buried pipelines.

Related standards

• ISO 3126 (referenced for π‑tape and dimensional checks)
• Other ISO plastics piping standards for material, dimensional and installation requirements

Keywords: ISO 9967:2016, thermoplastics pipes, creep ratio, creep testing, pipe deflection, plastics piping, long‑term performance, ring stiffness, test method.