This invention relates to a system and method for the detection, monitoring, prevention and/or reporting of leaks in liquid storage containers, and more particularly in liquid storage tanks.

Stored liquids, particularly hazardous liquids stored in large quantities, can pose a threat to the population and the environment. Liquids such as petrol and diesel fuel are stored in both above ground (AG) and underground storage tanks (UST).

A leak from either an above ground or underground storage tank can have serious long term environmental and health implications. There are also the economic concerns of product contamination and the cost of lost product.

Under the Code of Practice for The Design, Installation and Operation of Underground Petroleum Storage Systems (UPSS) (AIP CP4 - 1998), the installation of a leak monitoring system in an Underground Petroleum Storage System leads to benefits such as an improved system classification and consequent greater freedom with respect to possible sites for the system, for example near the presence of potable or non-potable groundwater. In some applications a suitable leak monitoring system can form a basis for relaxation of periodic tank testing requirements and lead to a longer useful life.

A number of mechanical methods of testing storage containers for leaks, for example methods involving bunding and secondary containment, have been employed to prevent the escape of stored liquids. Typically, such methods must generally be fitted when installing the storage container, and in many installations cannot be retro-fitted. For example, secondary containment according to the Code of Practice is restricted to double- walled Tanks; it would clearly be difficult and expensive to incorporate secondary containment to an existing single-walled container. Further, these methods generally do not prolong the life of the storage container and can be expensive, especially in large-scale applications. Bunding involves providingΛan embankment which can contain leakage from a container, but will not assist in prolonging the life of the container itself.

Another method of testing storage containers for leaks is to apply a fluid at an increased high pressure to the inside of the tank so that leaks will become obvious by the escape of the fluid. However, due to the increased pressure of the fluid, this method applies increased stresses to the container and can actually increase the probability of leaks occurring.

These problems may be overcome or at least alleviated by the present invention which provides a relatively inexpensive system and method for monitoring a storage container. The monitoring system of the present invention can also be retro-fitted to existing storage containers.

According to one aspect of the present invention, there is provided a system for monitoring a liquid storage container including: means to partition a volume within the container over substantially the depth of the container, the partitioned volume being in fluid flow communication with the remainder of the container so that the level of liquid in the partitioned portion corresponds to the amount of liquid in the container; means to monitor the depth of the liquid within the partitioned portion of the container; and means to apply a selected pressure to the partitioned volume of the container to move the depth of the liquid in the partitioned portion to a predetermined level so that the monitoring means can be calibrated.

The calibration of the depth monitoring means minimises errors in the depth reading over the lifetime of the monitoring system. The pressure within the partitioned portion may be increased, to lower the level of the liquid in the partitioned portion, or decreased, to raise- the level of the liquid in the partitioned portion, such that the predetermined level is obtained in order to calibrate the system.

Preferably, the means to partition a volume within the container over substantially the depth of the container is a tube which extends from the top of the container. Even more preferably, the tube is separate from the walls of the container.

Preferably, the means to apply pressure to the partitioned volume of the container is connected to the partitioning means at the top of the container.

Preferably, the means to monitor the depth of the liquid in the partitioned portion of the container includes a programmable data logger and control unit which monitors in particular the depth and/or rate of change of depth of the liquid in the partitioned portion of the container.

Preferably, the means to monitor the depth of the liquid in the partitioned portion of the container includes a non contact depth measuring means. Even more preferably, the non contact depth measuring means is a micro-impulse radar.

Preferably, the depth monitoring means includes an alarm means, the alarm means being activated by the detecting of an alarm state. In one embodiment, a first alarm state is when a predetermined depth or rate of change of depth is detected by the depth monitoring means. In a second embodiment, a second alarm state is when an ingress sensor for detecting the entry of water into the liquid storage container detects the entry of water into the container.

Preferably, the alarm means includes one or more visual and/or audible alarms which are mounted in local and/or remote locations with respect to the container. Even more preferably, each alarm state activates the alarm means in a distinguishable manner. In another aspect, the present invention provides a method of monitoring a liquid storage container including the steps of; partitioning a volume within the container over substantially the depth of the container, the partitioned volume being in fluid flow communication with the remainder of the container so that the level of liquid in the partitioned portion corresponds to the amount of liquid in the container; monitoring the depth of the liquid within the partitioned portion of the container; and applying a selected pressure to the partition volume of the container to move the depth of the liquid in the partitioned portion to a predetermined level so that the monitoring means can be calibrated.

Preferably the method further includes the step of activating an alarm means on the detection of an alarm state during the monitoring of the depth of the liquid within the partitioned portion of the container.

Preferably, the alarm means is activated in a distinguishable manner for each alarm state.

It will be appreciated that the applications of this invention include, protecting ships' tanks from leakage fuel oil or liquid cargo into the marine environment, and protecting underground tanks from over filling.

The system of this invention can also provide information on the status of a tank and by means of connection through modem, land line, network cable or other communications channel, provide control for valves, pumps, motors switches or any other device controlled by air, electricity, hydraulic, hydrostatic or pneumatic control. This allows control of the state of a tank system both automatically and with the intervention of a remote operator.

The system of this invention can act as the control interface for video and audio monitoring of the tank system and environment. Preferred embodiments of the present invention will now be described by example only with reference to the following drawings, in which:

Figure 1 is a general layout of the tank monitoring system according to one embodiment of the invention; Figure 2 is a schematic drawing of the partitioning means according to Figure 1 ; Figure 3 is a schematic drawing of the partitioning means according to Figure 1; and Figure 4 is a flow chart of the system in operation according to one embodiment of the invention.

Referring to Figures 1, 2 and 3, a system for monitoring a liquid storage container 10 is shown including a container 12, means to partition a volume within the container 14, means to apply a pressure to the partitioned portion of the container, not shown, and means to monitor the depth of the liquid within the container 16.

The container 12 is filled with a liquid 18 and has a means to partition a volume within the container 14. The partitioned volume is in fluid communication with the remainder of the container so that the level of liquid within the partitioned portion 20 corresponds to the level of the liquid in the container 22 under normal conditions. Accordingly, any change in depth of the liquid within the container 22 will be reflected in a change in depth of the liquid in the partitioned portion 20.

The depth of the liquid in the container is measured and monitored by the depth monitoring means 16 by measuring the level of the liquid within the partitioned portion of the container 20. It is preferred that the depth monitoring means 16 includes a non contact depth measuring device such as a micro impulse radar device. This enables the depth of the liquid to be obtained quickly and accurately. Alternatively, a depth measuring device such as a pressure transducer, a magnetostrictive sensor including a positioning float and sensor wire, or a combination or these sensors can be used. The means to selectively apply a pressure to the partitioned volume of the container can be a compressor that supplies air at a pressure above atmospheric, or that of the container, to the partitioned volume. The supply of the pressurised air to the partitioned volume, forces the liquid within the partitioned volume into the container. When the height of the liquid in the partitioned volume 20 reaches a predetermined level 24, the pressure is maintained for a period of time so that the depth monitoring means 16 can be calibrated. The pressure in the partitioned volume is then returned to the pressure of the container so that the height of the liquid within the partitioned volume 20 returns to the height of the liquid within the container 22. The pressure may be applied at any time in order for the monitoring system to be calibrated, for example upon installation and every month thereafter. The calibration of the depth monitoring means minimises errors in the depth reading over the lifetime of the monitoring system.

Figures 2 and 3 show a preferred embodiment of the current invention where the means to partition a volume within the container 14 is a hollow tube 26. The hollow tube 26 is inserted into the container and extends from the top of the container 28 over a substantial depth of the container. As the tube is open at the bottom 30, the liquid within the container is free to travel in and out of the bottom of the tube at all times as the container 12 and tube are at atmospheric pressure. A micro impulse radar device 32 is attached to the upper end of the tube and a coupling 34 also enables compressed air 36 to be selectively supplied to the tube 26. When compressed air 36 is supplied to the tube 26, the coupling 34 also closes any openings to the atmosphere so that the pressure within the tube is able to be increased and thereby force the level of the liquid down to the predetermined level 24 for calibration.

Referring to Figure 1, the depth monitoring means 16 also includes a data logger 38, a local display unit 40, an alarm system 42 and a building data system 44. The data logger 38 records the changes in height over a period of time, by recording the depth and/or rate of change of the depth of the liquid within the partitioned volume of the container 20. The data logger 38 is also capable of transferring this data to an external unit, such as a central unit to notify when the container requires refilling. The data can be transferred using any appropriate means such as via modem, land line, network connection or wireless connection. The data logger 38 may be located remote from the container 12 or locally.

The display unit 40 can display the current level of the liquid in the container, for example the percentage of the total capacity, or other value as required. This is particularly useful for inspections and for a person when filling the container.

A local alarm system 42 can be activated if for example the tank is overfilled or has been ruptured and is leaking a sufficient amount of liquid to be a hazard thereby alerting people and/or emergency services of the danger. The alarm system 42 includes one or more visual and/or audible alarms, which are mounted in either local and/or remote locations with respect to the container. It is also preferable that for each type of alarm, there is a separate distinguishable alarm. In one preferred embodiment, the container 12 is provided with a water ingress sensor that produces an audible sound at a remote service location, so that a person can be sent to service the container 12 within a short period of time.

The building data system 44 is used to keep track of all the building systems, eg lighting, heating, and air-conditioning, so that for example sufficient liquid fuel in the container is available for use by these building systems. The building data system 44 can also provide data to an inventory system, such as a Statistical Inventory Analysis system or Statistical Inventory Analysis and Reconciliation system. In one embodiment the inventory system is able to identify by the amount of liquid within the container when to order more of the liquid from a supplier. The current usage of the liquid could also be used to determine the urgency of the order. Documentation showing the amount of liquid supplied to the container by the supplier when filling the container can also be verified by the measuring system.

The building data system 44 preferably is also capable of controlling the valves, pumps, and any other devices used in the monitoring of the liquid storage container. It is also preferable that the system includes access by a remote operator to override the system for example in an emergency. The building data system 44 can also be connected to video and audio monitoring of the container and local environment to assist in any decisions by the remote operator.

Referring to Figure 4, the operation of the monitoring system includes the installation and setup of the system. After installation and setup, the monitoring system undergoes a calibration using the apparatus as outlined in Figures 2 and 3 to force the liquid to a predetermined level 24. The system is then calibrated and ready to monitor for conditions such as overfill, leakage, and water ingression. During the monitoring phase of the height of the liquid, the monitoring system displays readings on a local display and may also undergo re-calibration. The re-calibration uses the same calibration as when initially installed. This allows for creep in the sensor and other errors in measuring systems to be minimised.

The readings that are passed to the display unit are also logged and if a hazard, for example overfilling if the container, is detected, a local or remote alarm will sound.