Overview
ISO 23766:2022 specifies laboratory equipment and procedures for determining the coefficient of linear thermal expansion (CLTE) of thermal insulating products for industrial installations at sub‑ambient temperatures (−196 °C to 25 °C). The standard covers test methods, specimen preparation, conditioning, measurement accuracy and reporting. It excludes products that change dimension due to loss of hydration water or other phase changes during the test.
Key topics and technical requirements
- Scope & limits: Test range from −196 °C to 25 °C; subject to specimen temperature limits. Not applicable to materials with phase-change or dehydration‑induced dimensional changes.
- Two measurement methods:
- Method A - Optical method (optical dilatometry): uses an InGaN‑based light source and collimator lens to project a parallel planar beam (parallelism within 2″ ≈ 0.009696 mrad) across a specimen (typically 10–30 mm). A detector and digital edge‑detection processor measure length changes.
- Method B - Displacement method: uses a displacement sensor (reading to 1 µm) to record dimensional change; special loading rules apply for soft products.
- Apparatus & environment:
- Test chamber and cooling system capable of controlled cooling (liquid nitrogen commonly used) and maintaining specimen mean temperature within ±0.5 K (optical) or ±1 K (displacement) of target.
- Cooling rate limits (e.g., ≤1 °C/min between setpoints; conservative limits for last 50 °C) and temperature stabilization (typical hold ≈30 min) to ensure uniform specimen temperature.
- Temperature measurement: calibrated thermocouples/temperature sensors with ±0.5 K accuracy; minimum three sensors recommended for displacement tests to determine mean specimen temperature.
- Specimen prep & conditioning:
- Typical specimen shapes: cylinder or cuboid; remove skins/facings; sawn or cut with thin‑walled steel tube.
- Conditioning: at least 6 h at (23 ±5) °C (or (23 ±2) °C and 50 ±5 % RH if disputed); tropical option (27 ±5 °C, 65 ±5 % RH).
- Data handling: Record continuous length/temperature curves, report reversible changes; repeat cycles until only reversible change remains. Calculate CLTE from reversible readings.
Applications and users
- Practical for manufacturers, test laboratories, material scientists, quality engineers and specifiers working with cryogenic and low‑temperature insulation (e.g., LNG, cryogenic piping, industrial refrigeration).
- Use cases: product R&D, conformity testing, acceptance testing, product comparison, and design input for thermal strain and stress analyses in cryogenic systems.
Related standards
- ISO 18099 - Coefficient of thermal expansion (general method)
- ISO 9229 - Thermal insulation - Vocabulary
Keywords: ISO 23766:2022, coefficient of linear thermal expansion, thermal insulating products, sub‑ambient temperatures, optical dilatometry, displacement method, liquid nitrogen, cryogenic insulation, thermal expansion testing.
Open preview (PDF)Thermal insulating products for industrial installations — Determination of the coefficient of linear thermal expansion at sub-ambient temperatures
