GB2250820A

GB2250820A - Method of and apparatus for detecting leaks in liquid storage tanks acoustically

Info

Publication number: GB2250820A
Application number: GB9026928A
Authority: GB
Inventors: Christopher David Hill
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-12-12
Filing date: 1990-12-12
Publication date: 1992-06-17
Also published as: GB9026928D0

Abstract

A method of detecting a hole in the wall of a storage tank (10) which contains liquid (12) is disclosed. The method comprises reducing the pressure in the tank so that air flows in through any hole. The sound of the air flowing in is detected, the frequency at which the sound is detected being in the ultrasonic range. Apparatus is also disclosed which comprises a probe (18) including one or two ultrasonic detectors (20, 22). The apparatus further includes sealing means so that the probe can be fitted in an airtight manner to a tank with the detector or detectors inside the tank. Electrical cables lead from the detectors through the hollow interior of the probe to a device, which can include a VDU, which displays the output of the detector. <IMAGE>

Description

Method of, and apparatus for, detecting leaks in liquid storage tanks.

THIS INVENTION relates to methods of, and apparatus for, detecting leaks in liquid storage tanks.

According to one aspect of the present invention there is provided a method of detecting whether there is a hole in the wall of a liquid storage tank which method comprises inserting a probe into the tank which probe includes a sound detector1 and reducing the pressure in the tank so that air flows in through any hole that exists in the tank wall, the sound generated by the flowing air being detected by said probe.

According to a further aspect of the present invention there is provided apparatus for detecting the existence of a hole in the wall of a liquid storage tank which apparatus comprises a probe including a sound detector, means for securing the probe in an airtight manner to a tank inlet with said detector within the tank, and a vacuum pump for reducing the pressure in the tank so that air flows in through any hole in the wall of the tank.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 diagrammatically illustrates tank testing apparatus; and Figure 2 illustrates part of the apparatus of Figure 1 to a larger scale.

Reference numeral 10 in Figure 1 designate a tank which contains a liquid 12. The tank is not entirely filled with the liquid and there is a space 14 above the liquid. The liquid may be water but will more typically be petrol or diesel fuel.

The apparatus according to the present invention is designated 16 and comprises a probe 18 which extends downwardly through an access opening in the top wall of the tank. The probe 18 includes two ultrasonic detectors designated 20 and 22. It will be noted that one detector is below the level of the liquid 12 in the tank and the other is in the space 14.

The probe 18 extends upwardly through a structure 24 which is in the form of a pipe 26 with an elbow 28 protruding from one side thereof. The elbow 28 is connected to a vertical pipe 30 which leads upwardly to a vacuum gauge 32, a shut-off valve 34, and a venturi 36 (see Figure 2).

The reference numeral 38 in Figure 1 designates electrical cables which are connected to the detectors 20 and 22 and which lead to a device which, as will be described in more detail hereinafter, receives the signals from the detectors 20 and 22. A switch (not shown) is provided for switching between the detectors so that it is possible to select which detector output is to be displayed and/or recorded.

Referring now to Figure 2, reference numeral 40 diagrammatically designates sealing and attachment means which enables the apparatus 16 to be secured in a fluid and airtight manner to the tank inlet. The exact form of the means 40 depends on the nature of the inlet to the tank and will not be described in detail herein.

The probe 18 has not been illustrated in Figure 2 but passes upwardly through the pipe 26 and upwardly through a gland 42 which can be tightened onto the probe so that there is an airtight connection between the probe and the structure 24.

A pump (not shown) is connected to the inlet, designated 44, of the venturi device 36 and the outlet 46 of the device 36 discharges to atmosphere.

In use of the apparatus, the cover of the access opening in the top of the tank is removed and the probe 18 lowered into the tank through the access opening. The entire apparatus moves downwardly until the means 40 encounters the rim of the access opening whereafter the apparatus 16 is suitably clamped to the access opening. It will be understood that the interior of the tank is in communication with the venturi device 36 by way of the annular gap between the probe 18 and the pipe 26, the elbow 28, the pipe 30 and the shut-off valve 34.

The pump connected to the inlet 44 is started so that a low pressure is created within the venturi device 36. The regulating valve 34 is open at this stage and gas from the space 14 is sucked out and expelled through the outlet 46. Once the pressure in the tank has been reduced to the requisite extent the valve 34 is closed and the pump switched off.

If there is a hole in the wall of the tank below the level of the liquid in the tank then the detector 20 will pick-up the sound of the air rushing in over the edge of the hole. The air entering forms into bubbles and floats up through the liquid bursting on its top surface. This also creates sound. If the hole should happen to be above the liquid level in the tank at the time of the test then the air flows in with a hissing sound which is detected by the other detector 22.

The sound of the incoming air, and the sound of the bursting bubbles, contains a large number of frequencies both in the audible and ultrasonic range.

Sound in the audible range can obviously be detected but the problem arises that traffic and other noises in the vicinity of the tank being tested tend to mask the sounds that are being sought. By using sound in the ultrasonic range, and particularly sound in the 37 kilohertz and upwards range, the extraneous masking sounds can be eliminated.

If a permanent record of the test is required then the outputs of the detectors can be recorded in digital form.

If it is sufficient that the operator merely hear the sound of air entering the tank then earphones can be used. In this form the detectors are preferably sensitive to sound in the audible range. There can, however, be means for converting the ultrasonic sound picked up by the detectors to the audible range if it is desired to use ultrasonic frequencies and simultaneously listen to the sound of the incoming air.

Claims

CLAIMS:

1. A method of detecting whether there is a hole in the wall of a liquid storage tank which method comprises inserting a probe into the tank which probe includes a sound detector, and reducing the pressure in the tank so that air flows in through any hole that exists in the tank wall, the sound generated by the flowing air being detected by said probe.

2. A method as claimed in claim 1, wherein said detector detects sound at ultrasonic frequencies.

3. A method as claimed in claim 2, wherein said detector detects sound at frequencies of 37 kilohertz and upwards.

4. A method as claimed in any preceding claim, in which the liquid remains in the tank during tank testing and the pressure in the space above the liquid in the tank is reduced.

5. A method as claimed in claim 4, and including the step of inserting a probe into the tank which has a first sound detector which is above the liquid level in the tank and a second sound detector which is immersed in the liquid in the tank.

6. A method as claimed in any preceding claim in which the low pressure zone in a venturi is connected to the tank so that air is sucked from the tank to reduce the pressure in the tank.

7. Apparatus for detecting the existence of a hole in the wall of a liquid storage tank which apparatus comprises a probe including a sound detector, means for securing the probe in an airtight manner to a tank inlet with said detector within the tank, and a vacuum pump for reducing the pressure in the tank so that air flows in through any hole in the wall of the tank.

8. Apparatus as claimed in claim 7, wherein said detector is responsive to sound at ultrasonic frequencies.

9. Apparatus according to claim 7 or 8, and including means for displaying and/or recording the signal produced by the detector.

10. Apparatus as claimed in claim 7, 8 or 9, wherein said probe includes first and second detectors, the detectors being spaced apart along the probe.

11. A detector as claimed in any one of claims 7 to 10 and including a venturi, a pipe for connecting the low pressure zone of the venturi to the tank, and a pump for forcing air through the venturi thereby to create a low pressure which sucks air from the tank.

12. A method of detecting whether there is a hole in the wall of a liquid storage tank substantially as hereinbefore described with reference to the accompanying drawings.

13. Apparatus for detecting the existence of a hole in the wall of a liquid storage tank, the apparatus being substantially as hereinbefore described with reference to the accompanying drawings.