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ISO 7686 Opacity Testing for Plastics pipes and fittings

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ISO 7686 Plastics pipes and fittings — Opacity — Test method

ISO 7686 principle consists in measuring the light flux passing through a test piece cut from a pipe or fitting as a percentage of the incident light flux on the test piece. The standard lays down the maximum acceptable limit for the light which may pass through the wall of the pipe or fitting, if the product standard specifies that they shall be opaque.


What's plastic pipe opacity testing?  plastic pipe opacity test for ISO 7686, IS 12235 (Part 3)? 


Pipe Opacity Testing: These tests are performed to determine the opacity of pipes and fittings. The pipes must meet ISO 7686:2005 standards that specifies a method for the determination of the opacity of plastics pipes and fitings. lt is an ideal device for pipe manufacturers, research and inspection institutions. 

UnitedTest UT2033 Opacity testing is a process of testing how opaque and also how transparent a particular substance is. Opacity testing can also be used to test the quality of Plastics Films.


ISO 7686 Test Principle:

Measure total transmitted light energy (both scattered and unscattered) at a wavelength of 540–560 nm (green-yellow visible spectrum) passing through a test specimen.

Opacity is calculated as:

ISO 7686 Opacity Testing for Plastics pipes and fittings

The standard defines maximum allowable transmittance for pipes/fittings required to be opaque (per product specifications).


Test Method: 

Sample Preparation

- Cut a straight tube segment with a length ≥100mm, split it along the axis and flatten it, ensuring the beam fully covers the sample (to avoid edge light leakage).

- Surface treatment: Wipe the inner and outer surfaces with a lint-free cloth to remove oil, scratches, or impurities.

Test Procedure

- Use a stable light source with a wavelength of 540-560nm (fluctuation within ±1%) to irradiate the sample vertically.

- Measure the ratio of transmitted light flux to incident light flux and calculate the light transmittance (T%).

Standard Requirements

- Most countries mandate that buried or exposed pipes have a light transmittance ≤0.2% (such as PE and PP-R pipes).

- The testing instrument should have features such as 24-bit high-precision analog-to-digital conversion circuits and an automatic grating replacement system.


ISO 7686 Opacity Testing for Plastics pipes and fittings
ISO 7686 Opacity Testing


Application scenarios: 

The pipe opacity tester is mainly used to measure the opacity of plastic pipes and fittings, and is suitable for the following scenarios:

Production quality control of plastic pipes and fittings: used to test the opacity of plastic pipes and fittings to ensure product quality meets standard 1.

In the field of architecture and engineering, it is used to evaluate the transparency of plastic pipes and ensure their effectiveness in specific environments.


Opacity Test Specimen Information: 

Source: Cut from plastic pipes or fittings (representative of production material).

Shape: Flat, uniform wall section; free of scratches, bubbles, or defects.

Dimensions: Typical wall thickness matching the product; diameter ≥ light beam size (≥10 mm recommended).

Condition: Test at 23 ± 2 °C; condition specimens at this temperature for ≥4 hours before testing.

Number: Minimum 3 specimens per test batch for statistical validity.


Key word: 

opacity: light energy which has passed through the wall of the test piece, expressed as a percentage of the incident light energy on the test piece

light intensity: light energy which has passed through the test piece

maximum light intensity: maximum light energy received from the light source


Calibration of ISO 7686:

The calibration between 1 % and 0,1 % can be checked by using a neutral density filter of a density of between 2,0 and 3,0 (see 6.1). These filters are available from most national calibration laboratories.


Importance of ISO 7686 Opacity Test for Industry: 

1. Prevent the growth of microorganisms: Transparent pipes can easily cause the proliferation of algae and bacteria, contaminating fluid media (such as drinking water).

2. Delay material aging: Ultraviolet light passing through the pipes can accelerate the oxidation and degradation of plastics, shortening their service life.

3. Ensure the safety of fluid media: Prevent light from causing chemical decomposition or microbial contamination.

Related products and device

ISO 7686 Pipe Opacity Tester

The pipe opacity tester can be used to determine the impermeability determination of plastic pipes and fittings (showing results as a percentage). The instrument is controlled by an industrial touch screen and operated by a touch screen. It has the function of automatic analysis, recording, storage, display.

ISO 7686 Pipe Opacity Tester (Single sample)

Opacity Tester for Pipes based on standard ISO 7686, used to measure the opacity of plastic pipes and fittings with our Opacity Tester. Ideal for HDPE, LDPE, and PVC pipes to ensure quality and performance. Pipe Opacity Tester, also named ISO 7686 Plastic Pipes Opacity Tester, which is used to determine the opacity of plastic pipes and fittings.

FAQs about ISO 7686 Opacity Test (Plastics Pipes & Fittings)

Q1: Why is testing a pipe's opacity so important?

A: Opacity testing is crucial for preventing light-induced degradation. For pipes used above ground, sunlight penetration can cause algae/bacterial growth inside (a hygiene risk for water pipes) and photo-degradation of the plastic material itself, leading to embrittlement and reduced lifespan.


Q2: Can I use a regular spectrophotometer for this test?

A: You need a spectrophotometer or opacimeter adapted for this standard. The key requirement is a parallel light beam and a specimen holder that accommodates the natural curvature of the pipe without flattening it, as flat samples give inaccurate results.


Q3: How is ISO 7686 different from other transparency/opacity tests?

A: ISO 7686 is specifically designed for the cylindrical geometry of pipes. Common tests like ISO 13468 (for total luminous transmittance) are for flat plaques. Testing a curved pipe wall correctly requires the parallel beam method specified in ISO 7686.


Q4: What does a "fail" or low opacity result indicate for a pipe?

A: A low opacity result (high light transmission) indicates the pipe is too transparent for above-ground use where light exposure is expected. The material compound may lack sufficient pigment (like carbon black) or UV stabilizers, making it unsuitable for such applications unless installed in complete darkness.


Q5: What wavelength does ISO 7686 use?

A: The test uses visible light in the range of 540–560 nm (green‑yellow region).


Q6: What does the test measure exactly?

A: It measures total light transmittance through the pipe wall. Opacity performance is judged by how low this transmittance is.


Q7: What are the key calibration steps in ISO 7686?

A:Zero (dark) calibration (0% transmittance)

100% (full light) calibration (no sample)

Opaque reference check to verify low‑transmittance measurement

Linearity check of the detector

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