Method and apparatus for leak detection in horizontal cylindrical storage tanks

Abstract

A storage tank leak detection system for detecting and measuring very small leaks in large horizontal cylindrical storage tanks. Embodiments include two highly precise quartz crystal type pressure transducers held at a constant temperature. A bubbler to achieve access to the hydrostatic pressure at the tank bottom and just below the liquid surface. First transducer and bubbler are used to measure fluid mass while second transducer and bubbler are used to measure fluid density then used in combination with data correction and regression techniques to yield a storage tank leak detection system for use in horizontal cylindrically shaped tanks with an extremely low leak detection threshold.

We claim: 
     
         1 . An apparatus for detecting leaks in a liquid storage tank comprising:
 differential pressure sensor means having a low pressure measurement component and a high pressure measurement component;
 said high pressure measurement component being configured for measuring tank bottom pressure within a liquid in which a bubbler is immersed; 
 said low pressure measurement component being configured for receiving data indicative of atmospheric and vapor pressure substantially at the surface of said liquid; 
   barometric pressure measuring means configured for measuring atmospheric pressure substantially at the surface of said liquid;   a second differential pressure sensor means for contents density measurement having a
 low pressure measurement component and a high pressure measurement component; 
 said high pressure measurement component being configured for measuring tank bottom pressure within a liquid in which a bubbler is immersed; 
 said low pressure measurement component being configured for measuring fluid pressure just below the liquid surface; 
   barometric pressure and differential pressure calculation means configured for receiving first and second data reflecting, respectively, said tank bottom pressure and of said barometric pressure substantially at said surface of said liquid, and for adjusting said first data to substantially eliminate variations upon said measurements of said tank bottom pressure caused solely from atmospheric pressure variations to yield an atmospheric pressure adjusted tank bottom pressure;   ambient temperature measurement means for measuring ambient temperature near said storage tank;   tank dynamic and barometric pressure adjusted tank bottom pressure calculation means configured for receiving third data indicative of said atmospheric pressure adjusted tank bottom pressure, for receiving fourth data indicative of ambient temperature measurements by said ambient temperature measurement means, for receiving fifth data indicative of expansion characteristics of said storage tank, and for adjusting said third data with reference to said fourth and fifth data to substantially eliminate variations upon measurements and calculations of said barometric pressure adjusted tank bottom pressure, caused solely by dimensional changes in said storage tank resulting from atmospheric temperature variations, to yield a tank dynamic adjusted tank bottom pressure;   tank content average density calculation means for calculating average fluid density throughout the hydrostatic column; and   tank content mass calculation means for calculating mass contents of said storage tank substantially based on said tank dynamic adjusted tank bottom pressure, average fluid density, operator input data reflecting tank shape and configuration and operator input data reflecting physical characteristics of said contents of said storage tank.   
     
     
         2 . The apparatus of  claim 1  further comprising temperature management means configured for maintaining the temperature of said pressure transducers substantially at an operator-specified temperature. 
     
     
         3 . A method for detecting leaks in a storage receptacle; comprising the steps of:
 a) selecting a mass detection system comprising:   differential pressure sensor means having a low pressure measurement component and a high pressure measurement component;
 said high pressure measurement component being configured for measuring tank bottom pressure within a liquid in which a bubbler is immersed; 
 said low pressure measurement component being configured for receiving data indicative of atmospheric pressure substantially at the surface of said liquid; 
   barometric pressure measuring means configured for measuring atmospheric pressure substantially at the surface of said liquid when said protective enclosure means is immersed therein;   a second differential pressure sensor means for contents density measurement having a low pressure measurement component and a high pressure measurement component;
 said high pressure measurement component being configured for measuring tank bottom pressure within a liquid in which a bubbler is immersed; 
 said low pressure measurement component being configured for measuring fluid pressure just below the liquid surface; 
 barometric pressure and differential pressure calculation means configured for receiving first and second data reflecting, respectively, said tank bottom pressure and of said barometric pressure substantially at said surface of said liquid, and for adjusting said first data to substantially eliminate variations upon said measurements of said tank bottom pressure caused solely from atmospheric pressure variations to yield an atmospheric pressure adjusted tank bottom pressure; 
 ambient temperature measurement means for measuring ambient temperature near said storage tank; 
 tank dynamic and barometric pressure adjusted tank bottom pressure calculation means configured for receiving third data indicative of said atmospheric pressure adjusted tank bottom pressure, for receiving fourth data indicative of ambient temperature measurements by said ambient temperature measurement means, for receiving fifth data indicative of expansion characteristics of said storage tank, and for adjusting said third data with reference to said fourth and fifth data to substantially eliminate variations upon measurements and calculations of said barometric pressure adjusted tank bottom pressure, caused solely by dimensional changes in said storage tank resulting from atmospheric temperature variations, to yield a tank dynamic adjusted tank bottom pressure; 
 tank content average density calculation means for calculating average fluid density throughout the hydrostatic column; 
 tank content mass calculation means for calculating mass content data representative of the contents of said storage tank substantially based on said tank dynamic adjusted tank bottom pressure, average fluid density, operator input data reflecting tank shape and configuration and operator input data reflecting physical characteristics of said contents of said storage tank; 
 b) selecting data storage means for collecting a plurality of mass content and fluid density data as generated by said tank content mass calculation means over a plurality of points in time; 
 c) selecting computing means configured for generating a human perceptible indication of changes in said mass content data between a plurality of said points in time; 
 d) actuating said mass detection system; and 
 e) observing data indicative of changes in said mass content data attributable to leakage of said storage tank to detect of such leakage. 
   
     
     
         4 . The method of  claim 3  further comprising the steps of:
 f) securing all input and outflow orifices of said storage tank before said actuation of said mass detection system; and 
 g) substantially selectively processing said mass content data at an installation site of said system.