Techniques: There are several tests for measuring of petrol through petrol tanks. The most common ones as the SHED-test and the ECE 34-test are performed on whole petrol tanks. They require a lot of space and are time consuming. At SINTEF a small scale test method has been developed based on gas chromatography (GC).

Our apparatus: The sample is clamped in a specially designed apparatus, and GC samples can easily be taken out and analyzed during the test period. It is important that the surfaces of the membranes are as plane as possible and that the thickness of the membranes are uniform and equal for all samples. The test cell was made of stainless steel at the SINTEF workshop. The cell was placed in an oven at 40°C and kept at this temperature during the test period. With a sample mounted, the test cell was divided into a primary and a secondary compartment. The secondary side was flushed continuously with nitrogen to keep the partial pressure of petrol as low as possible on this side of the sample. Prior to a GC analysis, nitrogen flushing was stopped, and the secondary compartment was sealed over a period of time, usually 100 minutes. GC samples were taken out with a syringe inserted through the septum and analyzed on the GC. The amount of petrol diffused during a given time was determined from GC calibration.

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