Vacuum monitoring can be used on steel, FRP and composite tanks. A slight vacuum is drawn on the interstitial space and then monitored. The vacuum will decay if a leak exists. Some systems monitor the rate of decay and automatically re-establish vacuum when it reaches a certain level.
If the decay rate exceeds a preset threshold then the system will allow the vacuum to continue to decay until it reaches a point where an audible and/or visible alarm will be triggered alerting the operator of a problem.