Detailed Program of the 22nd ISC 2024

Testing elastomeric materials in liquified gases

Summary

Polymers play an important role as sealing materials in refrigeration systems and heat pumps. Knowledge about the interaction of these materials with refrigerants is therefore of interest. Consequently, the compatibility testing of sealing materials is already a topic in standards for refrigeration systems and heat pumps such as ISO 14903 and ISO 21922.

The test method described in these standards covers aging in liquid refrigerant. The post-exposure test procedure includes a test in “wet” and “dry” condition. The wet state is defined as testing within 30 minutes of removal from the test chamber, while the dry condition means that the samples are degassed until the mass is constant.

As part of a project to investigate the in-situ swelling behaviour of elastomers, the performance of the materials in liquid refrigerants was investigated. The tests were carried out in a sight glass autoclave equipped with a high-resolution camera system. In parallel to the in-situ investigations, standard aging tests were carried out in stainless steel pressure vessels. The investigation focused on how the materials behaved during and after depressurisation in the autoclave. The data clearly indicate that "after removal from the test chamber" is not a defined state and is insufficient to ensure comparable measurements.

The time interval between depressurization and measurements, rather than the time after sample removal, is critical as the most important changes in volume and other properties occur within the first 15 minutes after the onset of depressurization.

To ensure that the compatibility tests are comparable, it is proposed to replace the wording "after removal from the test chamber" with "after the onset of depressurization". In addition, the speed of the pressure drop must be defined, as decompression phenomena can significantly change the measured values.