ISO 7326:2016

Overview

ISO 7326:2016 - Rubber and plastics hoses: Assessment of ozone resistance under static conditions specifies standardized methods to assess the resistance of hose outer covers to atmospheric ozone. The standard defines five test methods, required apparatus, conditioning and exposure protocols, inspection intervals and reporting requirements to evaluate ozone cracking on hose covers and assemblies.

Key topics and requirements

• Five test methods (scope):
  • Method 1: For bore sizes ≤ 25 mm - test carried out on the hose itself.
  • Method 2: For bore sizes > 25 mm - test on a strip from the hose wall.
  • Method 3: For bore sizes > 25 mm - test on a strip from the hose cover.
  • Method 4: For all bore sizes - hose wound on a cylinder for testing.
  • Method 5: For expandable hoses (e.g., textile-reinforced) - test with an inserted rod.
• Apparatus: Ozone cabinet with ozone generation and control (per ISO 1431-1), appropriate holders/jigs, cylinder and round rod for methods 4 and 5.
• Test pieces & conditioning: Three test pieces per test; no test within 24 h of manufacture; condition test pieces 48 h in an ozone‑free atmosphere following ISO 23529.
• Exposure conditions: Default exposure in ozone cabinet to (50 ± 5) pphm ozone at (40 ± 2) °C for up to 72 h, with inspections at 2, 4, 24, 48 and 72 h under ×2 magnification.
• Reporting: Test report must reference ISO 7326:2016, describe the hose, state the method used, list test conditions and elongation, record any cracks (nature and time observed) and test date.
• Comparability note: Results from different methods may not be directly comparable; the product standard should specify the method to use.

Applications and who uses it

• Manufacturers of rubber and plastics hoses: validate cover compound formulations and production quality for ozone resistance.
• Quality control and test laboratories: perform routine acceptance and conformance testing.
• Product designers and materials engineers: compare candidate materials and predict service life in ozone-prone environments.
• Procurement and regulatory bodies: specify and verify compliance with ozone-resistance requirements in product standards.
• Failure analysis teams: determine whether ozone cracking contributed to hose deterioration.

Practical uses include material selection, batch acceptance testing, end‑use risk assessment (outdoor or ozone-rich environments), and supporting product standards or warranty claims.

Related standards

• ISO 1431-1: Resistance to ozone cracking - static and dynamic strain testing (referred for ozone cabinet and test details).
• ISO 23529: Preparation and conditioning of rubber test pieces.
• ISO 8330: Vocabulary for hoses and hose assemblies (terms and definitions referenced).

Keywords: ISO 7326, ozone resistance, rubber and plastics hoses, hose testing, static ozone test, ozone cracking, ISO 1431-1, ISO 23529.