Quantitative Leak Detection Compared To Non-Quantitative Detection Methods

What does the Scientific Method tell us? The quantitative detection method will not miss a leak that is within its threshold of detection. This cannot be said of the non-quantitative methods. The scientific method provides means of determining the validity of a theory. A theory is valid if there is a definitive proof that the theory is correct or if there is compelling argument for the correctness of the theory and no proof that the theory is not correct. In the absence of a definitive test for a theory, only one instance of the theory being proven wrong will invalidate that theory. In the case of the non-quantifiable leak test, there is no definitive proof that the test will detect all leaks in subject tanks. Therefore, we must look to the lack of a single case of that system missing leaks for the method to be considered scientifically valid. In the case of all know non-quantitative leak testing systems, there have been cases where the method has been found to fail to detect leaks.

The conclusion that must be drawn logically from this argument is that it is better to be absolutely sure of detecting reasonably small leaks with quantitative methods than to risk missing large leaks with non-quantifiable detection systems. Quantifiable systems do not miss leaks that are within their threshold. The nominally more sensitive non-quantifiable leak detection systems can not be proven to be 100% effective. What is worse is that in the real world there are a number of scenarios where non-quantitative detection systems are very likely to miss leaks. In order to correctly certify non-quantitative testing methods the situations where a high probability of missing leaks would have to be defined and procedures for determining those conditions derived. The most common example of a condition where the trace contaminant type of test will likely fail is the presence of a high water table in the vicinity of the tank being tested. Other scenarios involve soil conditions that allow the channeling of a leak while stagnant product in the soil presents a barrier to the movement of the trace contaminant.

How are testing systems certified? Because quantitative methods are inherently measurable, test are available to certify quantitative leak detection systems including the ability to determine which of the systems has the best leak detection threshold. No test has been devised that can prove without question that a non-quantitative leak detection method will detect all leaks within its threshold. The main problem with testing non-quantitative methods is the simulation of real world conditions. Not all conditions where leaks will occur can be duplicated in a practical test system. Most real world leaks have been present for a relatively long time. The presence of the product in the area surrounding the leak has a reasonable likelihood of masking the leak from the detection systems. Product near the leak is likely to create a channel for the leaking product where the main path of the leak is surrounded by immobile product. In that real world scenario the trace contaminant detection systems will only detect this leak if they happen to drill a detection pipe into the zone of mobile leaking product. It is impossible to predict and simulate all leak conditions for the testing of the trace contaminant type of tests. Therefore, it is impossible to certify a non-quantitative leak detection system.

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