Meaning
Time dependent deformation measured against the original thickness of a gasket determines the long term reliability of an airtight enclosure. Seals experiencing hermetic seal creep exhibit a slow migration of material away from the primary compression zone. This movement occurs over months or years of static pressure.
Mechanical designers track the rate of thinning to predict when a container might lose its environmental seal.
Stress Mechanism
Constant pressure from the assembly fasteners drives the flow of the sealing agent. Even when the temperature remains stable, hermetic seal creep continues at a microscopic level. The material slowly redistributes itself into the available voids within the joint.
This reduces the effective clamping force that keeps the cell airtight.
Gas Permeability
Thinning of the barrier layer increases the rate at which atmospheric gases can enter the housing. As hermetic seal creep progresses, the distance that a water molecule must travel to reach the interior decreases. This ingress eventually compromises the chemical balance of the battery.
Monitoring the leak rate over time provides an estimate of the remaining service life.
Operational Limit
Failure occurs when the seal no longer prevents the exchange of gases with the external environment. Engineers set safety margins that account for the expected hermetic seal creep over a ten year period. If the material selection is incorrect, the seal will fail long before the electrochemistry is exhausted.
Testing involves measuring the seal thickness after exposure to vibration and thermal cycling. Structural failures in the sealant layer represent the primary end of life mechanism for many static storage cells.
