ISO 7686:2005

Overview

ISO 7686:2005 specifies a test method for the determination of the opacity of plastics pipes and fittings. The standard defines how to measure the percentage of visible light (540–560 nm) that passes through pipe walls or fittings, establishes sampling and measurement procedures, and gives guidance on acceptable light transmission for opaque products used in water supply (to prevent algae growth).

Key topics and technical requirements

• Scope and purpose: Method for measuring light transmission (opacity) of plastics pipes and fittings; includes a note that sufficient opacity is necessary for pipes exposed to visible light in service to suppress algae.
• Definitions: Opacity = light energy transmitted through the wall, expressed as a percentage of the incident light energy.
• Principle: Measure scattered and unscattered light at 540–560 nm; express transmitted light as I / Im × 100 (I = transmitted intensity, Im = incident intensity).
• Apparatus:
  • Photoelectric detector with linear response down to at least 0.01 Im; detector mounted at right angles to the optical axis.
  • Integrating sphere allowed as an option (internal reflectance > 70 %, with baffles; incident beam centered on entrance port).
  • Stable adjustable lamp with spectral filter for 540–560 nm (±1 % stability).
  • Diaphragm and optics to produce a parallel-sided beam sized relative to the test piece and instrument entrance port.
  • Support to hold the test piece perpendicular to the optical axis.
• Sampling and test pieces: Test the thinnest wall product in a manufacturer’s range. Cut a sample length into four circumferential strips; flattening is allowed for small-diameter pipes provided thickness is not significantly altered.
• Procedure and calculation:
  • Verify zero reading (dark), 100 % with no sample, and opacity check with an opaque reference (