Polymers are used as container, tubing or sealing materials in a number of technical applications in contact with compressed gases. In all cases the gas penetrates the polymer to some extent leading to loss flows into the atmosphere which is especially important in flexible gas and oil ducts in off shore operation. The permeability of a polymer depends on its specific structure and physico-chemical properties like the glass point but also on the operational conditions like the type of gas, pressure and temperature. Different measuring techniques have been reported on in order to determine permeability of polymers, the simplest of which is based on direct measurement of the gas flux passing a polymeric sheet. Using easily available equipment this method is limited to relatively low pressures. In this work the diffusion coefficient is retrieved from sorption kinetics which is obtained by recording the polymer mass at relevant operating conditions in a gas atmosphere. The course of the polymer mass allows to deduce additional information qualitatively like the diffusion mechanism, swelling behaviour and extraction of additives. A gravimetric method was applied to determine the sorption kinetics of gases into polymers. Diffusivity as well as sorption capacity are determined directly. Data of gas permeability that are required for calculating leakage rates in polymeric flexile gas and oil ducts may be retrieved by multiplying the obtained diffusion coefficients and the gas solubility. In general carbon dioxide enters polymers to the highest extent. In industrial practice, the high solubility of CO2 e.g. may lead to explosive decompression of sealings once the operating pressure is reduced to atmospheric conditions. Diffusion coefficients are presented in the range of 75 to 130 C at 2 to 30 MPa.
Sorption kinetics of high pressure gases in polymeric tubing materials
Sorptionskinetik von Hochdruckgasen in Rohrleitungen aus Polymerwerkstoffen
2006
4 Seiten, 7 Bilder, 6 Quellen
Aufsatz (Konferenz)
Englisch
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