consisted of cooling down from room temperature to cryogenic temperature and then

warming up to room temperature. Initially, specimens were placed at room temperature

(T=300K). And, then the specimens completely submerged in an insulated container

filled with liquid nitrogen. The specimens stayed in the container for approximately 2

minutes. When the specimen reached the boiling temperature of liquid nitrogen (T= 77K),

the liquid nitrogen boiling disappears. The specimens were taken out of the container and

placed at room temperature. The specimen was held at room temperature for

approximately 5 minutes. The cryogenic cycling procedure is repeated for desired

number of times.

 Testing Procedure

 Before starting the permeability test, a thin coat of silicon grease was applied on the

gasket and an O-ring was placed to improve sealing of contact surfaces on a specimen.

The excessive silicon grease was wiped out to avoid obstructions of permeated gas on the

transmitting surface of the specimen. All outlet valves were opened initially to avoid

sudden pressurization of test gas. The specimen was placed horizontally on the gasket of

the upstream chamber. And then, the downstream chamber was placed on the top surface

of a specimen. The specimen was mounted between the chambers. Both chambers were

aligned and mated as close as possible. The specimen was mounted between the

chambers and clamped firmly with a compressive force. Then, even distributed forces

were applied to the sealing materials of the chambers.

 The test gas was admitted to the upstream chamber by opening the gas release

valve of the gas tank. While all outlet valves remained opened, the test gas was filled in

the upstream chamber and ventilated though the outlet vent to atmosphere. Any residual

air in the upstream chamber was purged for 1 minute. The outlet valve on the upstream