Abstract: Establishing that pressure-influencing factors other than leakage of gas have stabilized before testing the integrity of a vessel in a system including the vessel, a reference vessel that can be connected to and isolated from the vessel, a common source of pressurized gas, a gauge to measure the difference between the vessel pressure and the reference vessel pressure and a computer capable of recording a series of pressure-difference measurements and mathematically manipulating them, the method including equalizing the pressures in the two vessels, then isolating them from each other for a preselected time period, then recording the pressure difference between them at the end of the time period, again equalizing the pressures and repeating that sequence until the pressure difference at the end of two consecutive time intervals is the same, thereby establishing that pressure-influencing factors other than leakage have stabilized.

Abstract: A double-walled vessel for containing fluid, the vessel having an annular space between the walls wherein a compressed gas at a pressure higher than any pressure in the inner vessel is maintained, the vessel including a monitoring device to sense the escape of gas from the annular space such as decrease in its pressure or flow of gas from a replenishing source and to sense the presence of the compressed gas in the inner vessel such as increase in pressure, sensing the composition of the compressed gas within the inner vessel or sensing an increase in flow through a vent, whereby leakage through either the inner vessel wall or the surrounding outer wall is detected and the escape of contained fluid from the inner vessel is prevented.