Automated leak detection apparatus and method

• US 5,447,055 A
• Filed: 02/09/1993
• Issued: 09/05/1995
• Est. Priority Date: 02/09/1993
• Status: Expired due to Term

• Current Assignee: Praxair Technology Incorporated (Linde Plc)
• Original Assignee: Tracer Research Corp (Linde Plc)
• Inventors: Evans, Owen D., Pfeil, William E., Thompson, Glenn M.
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): WIGGINS, JOHN DAVID
• Application Number:
  US08/015,611
• Time in Patent Office: 938 Days
• Field of Search: 73/49.2, 73/40.7, 73/23.35, 73/23.42, 73/23.41
• US Class Current: 73/49.2
• CPC Class Codes: G01M 3/226 for containers, e.g. radiators

Abstract

A system for automated soil gas sampling, analysis and reporting to determine the presence and magnitude of a fluid leak from fluid storage vessels by detecting the presence of a unique and identifiable tracer chemical in the fluid leak. The system includes an array of sampling probes disposed in earthen material supporting fluid storage vessels. Each of the sampling probes is connected to a first valve selectable between individual sampling probes in the array. The first valve is connected to a second valve which communicates a gas sample from the first valve to a sample loop and loads the gas sample into the sample loop. Switching of the second valve from the first valve to a carrier gas source introduces a pressurized carrier gas into the sample loop displacing the gas sample out of the sample loop and into a gas chromatograph for analysis. A process controller governs all switching functions of the valves, actuation of the vacuum pump and the gas chromatograph in accordance with a pre-programmed instruction set. Data output by the gas chromatograph is processed to determine the presence of a tracer in the soil gas sample and actuate a signal flag indicative of the presence of the tracer chemical in the soil gas sample.

Claims

1. A leak detection method for detecting fluid leakage on a repetitive cycling monitoring basis from at least one of a plurality of fluid storage vessels, including subsurface fluid storage tanks, aboveground fluid storage tanks and fluid pipelines disposed in or on an earthen material, comprising the steps of:

(a) doping the fluid contained with the at least one of a plurality of fluid storage vessels with a chemical tracer, the tracer having a gas chromatography signature separate and distinct from the fluid and from earthen material supporting the at least one of a plurality of fluid storage vessels and capable of molecular diffusion within the earthen material in the gas phase;

(b) disposing a plurality of sampling means for collecting soil gas samples, the plurality of sampling means forming an array in the earthen material in fluid flow proximity to the at least one of a plurality of fluid storage vessels, each of the plurality of sampling means having a gas conduit coupled thereto;

(c) selecting a first of the plurality of sampling means;

(d) evacuating a first soil gas sample from the first of the plurality of sampling means by applying a negative pressure to the first of the plurality of sampling means;

(e) loading the evacuated first soil gas sample into a sample loop by applying the negative pressure through the sample loop thereby moving the first soil gas sample from the first of the plurality of sampling means into the sample loop;

(f) connecting the sample loop to a gas chromatograph;

(g) flowing a carrier gas into and through the sample loop, thereby displacing the evacuated first soil gas sample out of the sample loop and into the gas chromatograph;

(h) analyzing the first soil gas sample in the gas chromatograph and outputting at least one data signal characterizing the soil gas sample from the gas chromatograph;

(i) processing the at least one data signal characterizing the soil gas sample from the gas chromatograph and interpolating the at least one data signal from the gas chromatograph and outputting an integrated data signal containing identification data from the gas sample from the gas chromatograph to determine the presence of tracer in the soil gas sample;

(j) activating a signal indicative of the detection of the tracer in the soil gas sample; and

(k) repeating steps d) through j) until each of the plurality of sampling means in the array have been tested.

3. The leak detection method of claim 1, wherein said step (a) further comprises the step of selecting a tracer chemical from the group consisting of fluorinated halocarbons, methanes, and ethanes.

4. The leak detection method of claim 1, wherein said tracer chemical has a boiling point in the range of about -72°

C. to about 150°

C.

5. The leak detection method of claim 1, wherein the tracer chemical has a boiling point less than the boiling point of the fluid doped with the tracer chemical.

6. The leak detection method of claim 1, wherein said step (a) further comprises doping the fluid contained within the fluid storage vessel with a tracer chemical to a concentration of about ten parts per million.

7. The leak detection method of claim 1, wherein said step (a) further comprises the step of selecting the tracer chemical from the group consisting of halogenated methanes, halogenated ethanes, sulfurhexafluoride, perfluorodecalin, and perfluoro 1,3 dimethylcyclohexane.

8. The leak detection method of claim 7, wherein the step of selecting the tracer chemical further comprises selecting a halogenated methane from the group consisting of chlorobromodifluoromethane, trichlorofluoromethane, trifluoroiodomethane, trifluorobromomethane, dibromodifluoromethane, dichlorodifluoromethane and tetrafluoromethane.

9. The leak detection method of claim 8, wherein the step of selecting the tracer chemical further comprises selecting a halogenated ethane selected from the group consisting of dichlorotetrafluoroethane, hexafluoroethane, trichlorotrifluoroethane, dibromotetrafluoroethane and tetrachlorodifluoroethane.

10. The leak detection method of claim 1, wherein said step of selecting a first of the plurality of sampling means further comprises the step of switching a first valve means for providing a fluid flow communication between the first of the plurality of sampling means and a pumping means for evacuating said first soil gas sample from the first of the plurality of sampling means.

11. The leak detection method of claim 10, wherein said step of loading the evacuated first soil gas sample into a sample loop further comprises the steps of:

(a) switching a second and a third valve means for providing a fluid flow communication between the sample loop and said pumping means;

(b) actuating the pumping means to draw a vacuum through the sample loop, the first, second and third valve means, and the probe means;

(c) operating the pumping means for a period of time to permit a soil gas sample to pass from the sampling means to the pumping means; and

(d) switching said second and third valve means to isolate the sample loop from each of said sampling means, said first valve means and said pumping means.

12. The leak detection method of claim 11, wherein said step of operating the pumping means further comprises the step of operating the pumping means for a period of time greater than or equal to the product of the rate of evacuation times the static volume of the evacuation path from the probe means to the negative pressure source.

13. The leak detection method of claim 1, wherein said step of connecting the sample loop to a gas chromatograph further comprises switching valve means to provide a fluid flow communication between the sample loop, the carrier gas and the gas chromatograph.

14. The leak detection method of claim 1, further comprising the step of outputting control signals from a process controller, thereby governing each of the steps (a) through (k).

15. The leak detection method of claim 1, wherein said step of outputting an integrated data signal further comprises the step of converting said at least one data signal by an analog-digital converter.

16. The leak detection method of claim 1, wherein said step of activating a signal indicative of the detection of the tracer in the soil gas sample further comprises the step of activating an alarm when the tracer chemical is present at a concentration level greater than a pre-determined level therefore warning of an unacceptable leak condition.

2. A system for detecting fluid leakage from at least one of a plurality of fluid storage vessels containing fluid with chemical tracer doped within, including subsurface fluid storage tanks, aboveground fluid storage tanks and fluid pipelines supported by an earthen material, comprising:

(a) a plurality of gas permeable sample probes that are tubular member disposed to form an array in the earthen material in fluid flow proximity to the at least one of a plurality of fluid storage vessels;

(b) a plurality of fluid conduit members having first and second ends thereof, the first end of each of the plurality of fluid conduit members being connected in fluid flow communication with a corresponding one of the plurality of gas permeable sample probes;

(c) first valve means connected to each of the plurality of fluid conduit members, the first valve means being selectably switchable between each of the plurality of fluid conduit members;

(d) second valve means in fluid flow communication with the first valve means;

(e) third valve means in fluid flow communication with said first valve means and second valve means and switchable therebetween to draw a vacuum through one of a sample loop bypass line and through said sample loop;

(f) a carrier gas source containing a carrier gas under positive pressure, the carrier gas source being connected in fluid flow communication with the second valve means;

(g) a sample loop connected in fluid flow communication with the second valve means;

(h) pumping means for providing a negative pressure in each of the plurality of sampling probes, the gas conduits, the first valve means and the second valve means and the sample loop, thereby evacuating soil gas samples therethrough;

(i) gas analysis means coupled to the second valve means; and

(j) control processing means for controlling switching of each of the first, second and third valve means in response to a pre-programmed instruction set governing sequencing of evacuation of each of the sampling probes, loading of the sample loop with evacuated soil gas samples and injection of the evacuated soil gas samples from the sample loop into the gas analysis means.

17. The system of detecting fluid leakage of claim 2, wherein said plurality of gas permeable tubular members are comprised of at least one of a galvanized steel, a sintered plastic and a plastic material.

18. The system of detecting fluid leakage of claim 2, further comprising a source of a calibration standard chemical for gas chromatography connected to said first valve means, said first valve means being switchable between said source of a calibration standard chemical and said plurality of sample probes.

20. The system of detecting fluid leakage of claim 2, wherein said carrier gas source contains a carrier gas under positive pressure which, upon connection to said sample loop, displaces said soil gas sample from said sample loop into said gas chromatography means under positive pressure.

21. The system of detecting fluid leakage of claim 22, further comprising at least one water trap disposed between said first valve means and said second valve means.

22. The system of detecting fluid leakage of claim 2, wherein said gas analysis means further comprises an integrator for interpolation of a data signal from said gas chromatography means prior to outputting an integrated data signal containing identification data from said gas sample.

23. The system of detecting fluid leakage of claim 21, wherein said control processing means further comprises a plurality of pre-programmed identifiers for comparison of said data signal from said gas chromatography means and means for outputting test data in the form of at least one of a textural and a graphical display.

24. The system for detecting fluid leakage of claim 22, wherein said control processing means further comprises a means for archival storage of said test data.

25. The system for detecting fluid leakage of claim 2, wherein said control processing means further comprises programming means for scheduling at least one of a series of test events and individual test events.

26. The system for detecting fluid leakage of claim 2, wherein said control processing means further comprises manual override means to disable automatic pre-set functioning of said control processing means.

27. The system for detecting fluid leakage of claim 2, further comprising an alarm which is activated if said tracer chemical is detected at a concentration greater than a predetermined level.

19. A system for detecting fluid leakage from at least one of a plurality of fluid storage vessels containing fluid with chemical tracer doped within including subsurface fluid storage tanks, aboveground fluid storage tanks and fluid pipelines supported by an earthen material, comprising:

(a) a plurality of gas permeable sample probes disposed to form an array in the earthen material in fluid flow proximity to the at least one of a plurality of fluid storage vessels;

(b) a plurality of fluid conduit members having first and second ends thereof, the first end of each of the plurality of fluid conduit members being connected in fluid flow communication with a corresponding one of the plurality of gas permeable sample probes;

(c) first valve means connected to each of the plurality of fluid conduit members, the first valve means being selectably switchable between each of the plurality of fluid conduit members;

(d) second valve means in fluid flow communication with the first valve means;

(e) third valve means in fluid flow communication with said first valve means and second valve means and switchable therebetween;

(f) a carrier gas source containing a carrier gas under positive pressure, the carrier gas source being connected in fluid flow communication with the second valve means;

(g) a sample loop connected in fluid flow communication with the second valve means;

(h) pumping means for providing a negative pressure in each of the plurality of sampling probes, the gas conduits, the first valve means and the second valve means and the sample loop, thereby evacuating soil gas samples therethrough;

(i) gas analysis means coupled to the second valve means; and

(j) control processing means for controlling switching of each of the first, second and third valve means in response to a pre-programmed instruction set governing sequencing of evacuation of each of the sampling probes, loading of the sample loop with evacuated soil gas samples and injection of the evacuated soil gas samples from the sample loop into the gas analysis means;

wherein said second valve means is at least a two way valve, switchable between a connection between said pumping means and said plurality of sample probes and a connection between said carrier gas source and said gas analysis means.