New Testing Method for Permeability of Plastic Pipes

The SKZ Plastics Centre has developed a new testing method that significantly speeds up the determination of the permeability of plastic pipes. While conventional tests take several weeks or even months, the newly developed method delivers reliable measurement results within just a few hours. This opens up significant opportunities for pipe manufacturers in terms of quality assurance, testing costs, and development times.

Plastic pipes are used for the safe transport of gases and liquids. Ideally, the transported medium reaches its destination completely and unchanged. In practice, however, even minor material permeability poses a significant challenge. So-called permeability – that is, a material’s ability to allow certain media to pass through – is therefore considered a key quality characteristic in pipe manufacturing and is tested in accordance with standards.

Standard-compliant permeation testing has been time-consuming to date. Testing the permeability of pipes according to DIN 53380-3. Due to the geometry, material thickness and the required steady-state measurement conditions, these tests often take several weeks to months. This represents a significant time and cost factor, particularly in development, approval, and complaint resolution processes.

IGF project “Rohr-Perm” enables drastic reduction in testing times

In the IGF project “Rohr-Perm” (Project No.: 01IF22636N), funded by the Federal Ministry for Economic Affairs and Energy, the SKZ in Würzburg, Germany, developed an alternative testing concept. The goal was to significantly shorten the testing time required to determine the permeation properties of plastic pipes without compromising the reliability of the results.

Test approach based on planar specimens and validated correlations

At the heart of the new method is the examination of a planar chip taken from the pipe. Its permeability is determined using established test methods for flat specimens in accordance with DIN 53380-2, which allow for significantly shorter measurement times. Using correlation factors determined and validated in the project, the permeability of the entire pipe can then be reliably calculated. The correlation factors were systematically determined by comparing measurements on pipes and chips according to different standards, as well as using a rapid helium test developed at SKZ.

High correlation demonstrated for PE, PP, and PVC pipes

The investigations on pipes made of polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC) showed a high degree of agreement between the measurement results from pipe and chip tests. Thus, the “Rohr-Perm” project makes a significant contribution to the accelerated and practical determination of the barrier properties of plastic pipes. “Especially for PP and PVC, we were able to demonstrate a significant correlation of results when using identical measurement gases. The developed method enables the pipe industry, for example, to reduce measurement time from several weeks to a few hours when testing oxygen permeability,” explains Franziska Eichhorn, Senior Engineer at SKZ.

Greater efficiency and quality assurance for the pipe industry

The industrial benefits of the new testing method lie particularly in the significant reduction of testing times and costs, as well as in the possibility of using permeation tests more widely in quality assurance in the future. “The project highlights the added value of methodological transfer. Established measurement methods from other product areas can – with appropriate validation – be successfully transferred to new applications. This often results in significant potential for efficiency gains and cost savings,” emphasizes Dr. Linda Mittelberg, Head of the Quality and Lifecycle Division at SKZ.

The “Rohr-Perm” project (grant number 01IF22636N) is funded by the Federal Ministry for Economic Affairs and Energy (BMWE) pursuant to a resolution of the German Bundestag.

(Source: SKZ – The Plastics Centre)