1. Field of the Invention
The present invention is directed towards a method and apparatus for providing a safe, precise, and cost-effective storage tank leak detection system and more particularly, to a method and apparatus wherein the containment integrity of a storage tank is determined by mass measurements of the stored product.
2. Background Information
Storage tanks play a vital role in today's economy. The economy, on a global scale, depends on the proper function of these tanks as they are prevalent in several industries and virtually every geographical region in the world. In light of the vital role these storage tanks play, the integrity of the tanks is placed at a premium. That is, storage tank owners are willing to invest huge sums of money in both the maintenance and inspection of such tanks.
These tanks come in all shapes and sizes, are found both below and above ground, and are used to store a wide range of materials. Storage tank capacities range from hundreds to millions of gallons and are used to store a staggering assortment of products, including hazardous material.
As one could imagine, there are a wide range of problems associated with measuring and determining storage tank integrity, particularly in horizontally disposed cylindrically shaped tanks. These horizontal cylindrically shaped tanks are the most prevalent tank type in underground storage service. The horizontally disposed, cylindrical shape is positioned so that product surface area changes with fluid level, which will change independent of any tank leak due to fluid expansion or contraction as a result of fluid temperature changes. Such positioning and shape greatly complicates direct measurement of leaks by typical means. Typical leak detection methods require the application of an internal pressure or vacuum used in conjunction with multiple detection probes, including water level, product level, acoustic and fluid temperature. By relying on secondary indications of leaks, typical leak detection methods compromise the leak detection process, expose the tank to failure due to the applied test pressure or vacuum and open the possibility that a real leak is masked by the very application of the test. Also, such methods do not monitor loss by vaporization.
Use of a typical mass measurement based leak detection system in horizontal cylindrically shaped tanks without a direct and continuous measurement of the density of the tank's contents is fraught with the possibility for incorrect or inconclusive leak determinations. One can easily envision a scenario where the fluid product level in the tank rises due to the warming (expansion) of the tank's liquid contents even in the presence of a small leak from the tank.
However, the recognized difficulties in measuring, determining and preventing storage tank leaks does not mitigate the duties or liabilities imposed on responsible parties. Tremendous environmental and economic consequences and the threat of litigation and clean up costs associated with storage tank leaks force responsible parties to invest large sums of money in the maintenance and inspection of the tanks. Tank inspections are costly with respect to the amount of money spent, the danger presented to the inspectors and the environment, and production downtime. In fact, these inspections often remove a tank from service for more than one month. The threat of liability also forces responsible parties to spend money unnecessarily for the maintenance of these tanks. Moreover, liability does not end with litigation and clean-up costs.
Currently, responsible parties are, in some countries, being incarcerated as a direct result of storage tank leaks. These leaks have contaminated surrounding ground water, some of which serves as drinking water for local residents. As such, the facilities associated with such incidents have been shut down until compliance with emissions regulations can be established beyond reasonable doubt. Such proof, in turn, is dependent on proof of reliable and sufficiently accurate detection systems and methods for proving such compliance. Each day the shuttered facilities remain inoperative adds to an already tremendous amount of money lost.
Prior to the present invention (to be described in detail hereafter), there are simply no known direct leak measurement systems. Similarly there are no known systems for direct and quantitative measurement of potential leaks in horizontally disposed cylindrical tanks of 50,000 gallon capacity and larger. The present invention addresses this void through the combination of an extremely precise mass measurement system and an extremely precise and real-time measurement of the density of a horizontally disposed storage tank's contents.
Clearly, for the reasons set forth above, there is a dire and immediate need for the ability to determine, with far more precision than presently possible through use of presently available systems and methods, the presence and degree of leakage from such storage tanks, at least to the extent of proving compliance with applicable storage tank leakage regulations or statutes.
Storage tank leak detection systems are known in the art; however, these products are fraught with problems. The present systems are imprecise, or provide erroneous data for any or all of reasons including: the consistency of the soil acting as the tank's foundation, the temperature (thus density) stratification of the tank's fluid contents, product loss as vapor, extraneous noise sources, the effects of ground water table level, previous soil contamination, and/or tank shell dynamics.
In light of the severe consequences of failing to detect significant storage tank leaks, presently not detectable or severely compromised through use of known systems or methods, there is a compelling need for a system and method by which one can detect very small leaks even in large and very large horizontally disposed cylindrically shaped tanks, ideally in a safe and cost effective manner.
It would well serve those who are responsible for maintaining storage tank integrity to provide a safe, precise, and cost-effective direct leak detection system that 1) does not depend on the application of an internal force (pressure or vacuum) to create an indirect indication of a leak, 2) that does not require the simultaneous measurement of independent variables such as a) acoustic noise due to a leak of a gas into or out-of the tank, b) tank bottom water level due to a leak in the tank below the external groundwater level, c) fluid temperature to compensate for fluid expansion or contraction, d) fluid level and maybe used in an efficient manner thereby preserving industrial and environmental resources.