Correlating Gas Leakage Rates to Fluid Ingress in Sensor Seals
Correlating gas leakage rates to liquid ingress requires deriving equivalent pore radius to confirm capillary entry pressure exceeds target hydrostatic head.
Nitrile Seal Aging
Degradation Process
Chemical deterioration of butadiene-acrylonitrile copolymers occurs when they are exposed to elevated temperatures and oxidative environments over long periods. Continuous tracking of nitrile seal aging is essential for predicting the service life of industrial sealing components. This process involves the cross-linking of polymer chains, which is accelerated by thermal energy and ozone exposure.
As the cross-link density increases, the elastomer loses its flexibility and becomes increasingly brittle.
Material Consequence
Physical changes in the polymer structure reduce the ability of the seal to conform to mating surfaces. During nitrile seal aging, the compression set of the elastomer increases, which means the material does not return to its original shape after being compressed. This loss of elasticity leads to a decrease in the contact force against the sealing surface.
Eventually, the contact pressure drops below the fluid pressure, resulting in a leak.
Analytical Measurement
Laboratory evaluation of elastomer degradation involves measuring mechanical properties before and after exposure to accelerated thermal conditions. Technicians assess nitrile seal aging by monitoring hardness changes using a durometer and measuring the reduction in elongation at break. Thermogravimetric analysis can also be used to detect changes in the chemical composition of the polymer.
These measurements are used to create Arrhenius plots that predict the useful life of the seal at lower operating temperatures.
Operational Margin
Safety factors in industrial equipment design are established to ensure that seals are replaced before degradation compromises performance. The rate of nitrile seal aging is used to set maintenance schedules, with replacement intervals typically set to a fraction of the predicted service life. This margin accounts for unexpected temperature spikes or exposure to aggressive chemicals that might accelerate the degradation process.
In high-reliability applications, such as hydraulic actuators, seals are replaced during routine maintenance even if they show no visible signs of wear. This proactive replacement strategy prevents catastrophic leaks that could cause system downtime or environmental contamination, ensuring that the assembly remains within its certified operating limits throughout its service cycle.