Measuring and testing – With fluid pressure – Leakage
Patent
1996-04-04
1997-09-16
Brock, Michael
Measuring and testing
With fluid pressure
Leakage
G01M 332
Patent
active
056683081
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a leakage test which is particularly suitable for the testing of underground storage tanks such as those found at petrol stations and chemical works, and even milk storage tanks.
Because leakage from underground storage tanks cannot be readily detected externally, internal .testing methods are commonly used. .Some years ago the most common method of testing the integrity of underground storage tanks was a high pressure test. This method includes the required step of removing the contents of the tank, these normally being volatile and prone to spontaneous combustion under the influence of elevated pressures, before supplying the tank with gas at high pressure. In order to detect leakage from the tank, the tank is otherwise sealed off at the input and output connections, the pressure inside the tank is elevated to around 3,500 mb above atmospheric pressure and the pressure is read both initially and after some time finally by means of a pressure gauge fluidly connected to the tank interior. The detection of a pressure loss indicates the possibility of a leaking tank.
There are significant drawbacks to this high pressure testing method. The need to first empty the tank leads to a time consuming and costly test which requires a second tank in which the normal contents can be stored during the test. Perhaps the greatest drawback is that of insensitivity. Most underground spirit-containing tanks have large ullage spaces, and only relatively small changes in gas pressure caused by normal rates of leakage during a test. Furthermore, the high pressures are monitored by mechanical pressure gauges, which are by nature insensitive to the pressure changes created by these normal rates of leakage. It is thought that substantial leakages went unnoticed by this testing method, which has resulted in the release of significant quantities of pollutant into environments surrounding the leaking tanks. Furthermore, the amount of energy stored in a tank at such an elevated pressure is excessive and can be dangerous both to the tank itself and the testing personnel.
New and stricter legislation has now been introduced in some countries to protect the environment by placing lower limits on the amount of leakage permissible from a store of liquid pollutant (defined by the authorities as any liquid other than water), and these standards have made the high pressure tests obsolete in those countries. According to current legislation in Europe and the United States of America the integrity of a pollutant storage tank will be certified only if its rate of leakage into the surrounding environment is less than of 380 ml during the course of a single hour. Consequently, any testing methods which the authorities approve must be able to reliably detect a leakage occuring at the specified rate.
Thus, and particularly in the case of the largest of tanks, only a small number of testing methods have been approved by the authorities for meeting this sensitivity requirement.
According to one known test, an electronic sensor is lowered into the liquid contents of a tank, and the liquid level is directly measured. This test is however time-consuming and is generally undertaken overnight when the tank is out of use, and the long monitoring period can lead to inaccuracies due to effects such as thermal expansion of the tank and its contents. It is also inherently-unsuitable for tanks containing liquids which react with the material of the sensor, such as acids.
In another known test, the tank is sealed and a vacuum is applied. Air entering the tank via a leak site causes a bubbling sound which can be picked up by sonic monitoring equipment. This monitoring method however cannot detect leaks in pipelines associated with the tanks which require separate testing.
All of the known tests suffer from deficiencies where the tank is surrounded by a water table. Depending on the relative levels of liquid inside and outside the tank, a leak can be exacerbated, completely masked, or water can enter the tank via the leak site. With certa
REFERENCES:
patent: 4993257 (1991-02-01), Lagergren
patent: 5216914 (1993-06-01), Horner
Niaki et al., "Underground Tank Leak Detection Methods: A State-of-the-Art Review", EPA publication: EPA/600/2-86/001, pp. 90-90. Jan. 1986.
LandOfFree
Leakage detection does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Leakage detection, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Leakage detection will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-219936