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Oxygen Induction Time


Testing Specification Design

Plastic Pipes Conference Association # 1995 Edinburgh


Pipes for the distribution of gas and water are generally installed underground, well protected from the destructive influence of UV radiation from the sun. So why bother about UV stabilization for products that will never be exposed to sunshine?

Unfortunately the real world has its limitations. Even when business is good and pipes are sold before they are produced, it takes some time before they can be installed. For practical reasons, they often have to be stored for some time at both the production and the installation site.

One solution would be to always store pipes indoors or under cover. It would be a very expensive solution, however, if even possible at installation sites.

Thus outdoor storage is necessary and sufficient protection against UV light must be incorporated in the material.

The pipe industry is currently discussing, within the framework of the IS0 and CEN how to ensure through standardisation that pipes have sufficient UV protection.

In the existing CEN proposal for gas pipes. dating from May 24, 1994. UV exposure IS set at min. 3.5 GJI, which approximately corresponds to one year outdoor in Great! Britain or in Sweden.

With modem stabilisation, there is no doubt that pipes will be virtually unaffected by the proposed radiation dose and will meet the test requirements on mechanical properties. The question really is, how to ascertain that welding properties afler outdoor storage are not influenced by oxidation of the pipe surface.

The controversial point of discussion is how to verify that a pipe still has sufficient thermal stability in the layer next to the surface after outdoor exposure. Today, most specifications include measurements on pipes after ageing, using some version of the Oxygen induction Time, or OIT method.

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