Abstract:
In a method and apparatus for detecting leaks in riser and lid assemblies, a difference in pressure between the inside of the riser and cover assembly and the outside is created and monitored to insure that no leaks exist. Preferably, a vacuum is created on the inside of the riser and cover assembly. This vacuum is then monitored for a set period of time to insure that the total change in pressure does not exceed a threshold. In a highly preferred embodiment, an apparatus automatically creates the desired vacuum and then isolates a vacuum gauge to monitor the vacuum in the riser. Method for isolating a leak are also presented in the event that a leak is detected.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to storage tanks generally and more particularly to vacuum testing risers for storage tanks. 
     2. Related Art 
     Storage tanks are used to store a wide variety of materials. Storage tanks are often located underground to conserve space. Special concern arises when such underground storage tanks are used to store environmentally hazardous materials. For example, underground storage tanks are often used to store gasoline and other petroleum products. Underground storage tanks are also used to store hazardous chemicals or other manufacturing liquid waste and sewage (such tanks are often referred to as wastewater storage tanks). Because of the nature of these materials, concern about leaks in underground storage tanks has lead many municipalities to pass laws requiring leak detection and secondary containment systems. Even in situations where there are no laws governing underground storage tanks containing environmentally hazardous materials, concern for the environment has led many to take some or all of the aforementioned precautions in connection with their tanks. 
     The aforementioned concerns have led to the introduction of water resistant and watertight riser and cover systems in the last few years for access to and protection of the manway and/or pipe/tank connections. An example of a watertight riser and cover system is disclosed in U.S. Pat. No. 5,595,456, which is commonly owned by the assignee of the present invention. The motivation for providing a watertight riser and lid system is that many times the connection between the tank and a supply line passes through the riser, and it is possible for a leak to develop in such a connection. 
     To date, there are no known regulations concerning the watertightness of a riser and lid system. Testing the watertightness of a riser and lid system is complicated by the fact that the riser and lid system must be installed on-site rather than at the factory. 
     Fibrelite has developed a complicated and expensive system that must be installed along with the original installation of their system. A serious drawback to the Fibrelite system is that it appears to require that the actual riser lid be replaced with a special test cover. Thus, the Fibrelite system does not test the actual riser lid seals. 
     What is needed is a simple and economical method and apparatus for periodically testing the watertightness of watertight riser and lid assemblies, particularly those that are already installed throughout the country. 
     SUMMARY OF THE INVENTION 
     The present invention meets the foregoing need to a great extent by providing a simple method and apparatus for detecting leaks in watertight riser and lid system. This can be used for water resistant systems by adding the water tight lid. A difference in pressure (preferably a vacuum created on the inside of the riser) between the inside of the riser and lid assembly and the outside is created and monitored to insure that no leaks exist. The inside of the riser assembly is then monitored for a set period of time to insure that the total change in pressure does not exceed a threshold. In a highly preferred embodiment, an apparatus automatically creates the desired vacuum and then isolates a vacuum gauge to monitor the vacuum in the riser. Methods for isolating a leak are also presented in the event that a leak is detected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The aforementioned advantages and features of the present invention will be more readily understood with reference to the following detailed description and the accompanying drawings in which: 
     FIG. 1 is a side view of a manual leak detecting apparatus according to one embodiment of the present invention. 
     FIG. 2 is a schematic diagram of the apparatus of FIG.  1 . 
     FIG. 3 is an automatic leak detection apparatus according to a second embodiment of the present invention. 
     FIG. 4 is a schematic diagram of the leak detection apparatus of FIG.  3 . 
     FIG. 5 is a cross sectional diagram showing installation of a watertight riser and lid assembly. 
     FIG. 6 is a flowchart of a leak isolation method according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, numerous details, such as vacuum gauge readings and time periods, are set forth in order to provide a more thorough understanding of the present invention. These details should not be understood to limit the present invention. 
     The present invention is believed to be particularly applicable to underground storage tanks. Accordingly, the preferred embodiments discussed below are underground storage tanks. However, the present invention should not be understood to be limited to underground storage tanks. 
     Referring now to the drawings, in which like reference numerals represent like parts throughout the several views, FIG. 5 illustrates the installation of an underground storage tank  510 . The tank  510  includes a manway  520 . The manway  520  forms a structural part of the tank  510 . In the case where the tank  510  is a double walled underground storage tank, the manway  520  will often be formed such that a monitoring system that monitors the integrity of the annulus between the two walls of the double walled storage tank  510  will also monitor the integrity of the double walled manway  520 . 
     Connected to a lid  521  of the manway  520  is a supply line  530 , which includes a shut off valve  535 . The supply line  530  passes through a bulkhead fitting  532  in a wall  572  of riser assembly  17 . Riser assembly  17  is attached to a riser collar  571  that is adhered to the tank by a joint  512 . The riser collar  571  is typically installed at the factory. However, the riser wall  572  must typically be installed in the field as the height of the riser wall  572  will not be known until the tank has been installed. The supply line  535  is connected to an underground supply line  534 . 
     Also passing through the riser wall  572 , is an electrical connection  540 . The electrical connection  540  maybe used for a number of purposes including the monitoring the integrity of the interior of the riser  572  or, in other embodiments, for electrically controlling the valve  535 . 
     The connection between the riser wall  572  and the riser collar  571  is typically made using an adhesive bond. Sometimes, fiberglass (also know as fiber reinforced plastic) is also used. This is especially true where the tank  510  is a fiberglass underground storage tank and/or the riser assembly  17  comprises fiberglass. It is critical to test this connection between the riser wall  572  and the riser collar  571  because the connection is often made in the field. A riser lid  573  is attached at the top of the riser wall  572 . A riser cover  574  is provided on the riser lid  573 . The riser cover may be opened and closed by personnel needing access to the interior of the riser for preforming such operations as manipulating the valve  535 . The riser cover  574  forms an airtight seal with the riser lid  573 . An exemplary riser cover  574  is disclosed in the previously mentioned U.S. Pat. No. 5,595,456. 
     In order to protect the riser and allow access to it, a street box  550  is installed over the riser as is well known in the art. The street box  550  includes a side wall  551  and a lid  552  which is typically formed of steel. The street box  550  does not form part of the riser assembly  17 . 
     As previously discussed herein, it is desirable to monitor the integrity of the riser assembly  17 . Referring now to FIG. 1, an apparatus  100  for testing the integrity of the riser assembly  17  is illustrated. The riser cover  574  includes a bulkhead fitting  12  which establishes fluid communication between the inside and the outside of the riser assembly  17 . The use of the bulkhead fitting  12  through the riser cover  574  allows the actual seals between the riser cover  574  and the lid  573  to be tested. Tubing  11  connects the bulkhead fitting  12  to a vacuum filter  14 . The filter  14  is connected to a “T”  8 . One branch of the “T” is attached to a gauge  7 . The other branch of the “T”  8  is attached to a valve  6 . When the valve  6  is in the closed position, the gauge  7  and the interior of the riser assembly  17  will be isolated so that the gauge  7  is indicative of the vacuum in the riser assembly  17 . 
     The other end of the valve  6  is connected to a vacuum port  9  of a vacuum pump  4 . A vacuum is created at vacuum port  9  by the passage of compressed air through the vacuum pump  4 . The compressed air is supplied by a compressed air source  16 . A supply line  15   a  from the compressed air source  16  terminates in a quick coupling connector  15   b . The quick coupling connector  15   b  is connected to a quick coupling nipple  1  at the input of an air pressure regulator  2 . The air pressure regulator  2  includes a gauge  3  for monitoring the input pressure from the compressed air source  16 . Preferably, the air regulator  2  maintains the pressure input to the vacuum pump  4  at approximately 10 psig. Of course, those of skill in the art will recognize that the input pressure to the vacuum pump  4  will vary depending upon the volume inside the riser assembly  17  and the desired vacuum. It should also be recognized that the input pressure to the vacuum pump  4  can be increased during the early stages of operation to more rapidly evacuate the interior of the riser assembly  17 . Attached to the outlet of the vacuum pump  4  is vent outlet  5 . 
     In highly preferred embodiments of the present invention, a venturi-type vacuum pump as described above, rather than a mechanical vacuum pump that includes moving parts, is used. This is especially important when flammable materials such as gasoline are stored in the tank. The lack of moving parts in the venturi-type vacuum pump reduces the risk of an accidental ignition of leaking gasoline, thereby significantly improving safety as compared to a mechanical vacuum pump. 
     Operation of the apparatus of  100  of FIG. 1 will now be explained with reference to the schematic  200  of FIG.  2 . The compressed air supply  16  is regulated by the regulator  2  to maintain the input pressure at the vacuum pump  4  at approximately 10 psig. The gauge  3  may be used to monitor the input pressure to the vacuum pump  4 . Compressed air passing through vacuum pump  4  and exiting via vent outlet  5  creates a vacuum at vacuum port  9  of pump  4 . Valve  6  is initially left in the open position so that the vacuum pump  4  can create a vacuum at the interior of the riser assembly  17 . When the gauge  7  indicates that a vacuum of approximately 40 inches of water (3 inches of mercury or 1.5 psig) has been achieved, the valve  6  is then moved to the closed position, which isolates the vacuum created in the riser assembly  17  from the pump  4 . The gauge  7  is observed for approximately 15 minutes. If the gauge  7  does not indicate a drop of more than 2 inches of water after giving the vacuum a sufficient amount of time to stabilize, there is no leak and the riser assembly is watertight. If the pump  4  is unable to achieve a 40 inches of water vacuum, or the vacuum gauge indicates a vacuum drop of more than 2 inches of water during the aforementioned 15 minute period, the riser  17  is not watertight. Leak detection procedures, as will be described in further detailed below, are the employed to detect the location of the leak. 
     A second, automated version of the present invention is illustrated by the diagram  300  in FIG.  3  and the schematic diagram  400  of FIG.  4 . In this embodiment, a compressed air source  16  is connected to a nipple  302  on a control box  301  through a supply tube  15   a  and a coupling  15   b . The nipple  302  is connected to a on/off valve  315 . When the valve  315  is in the off position, the control box  301  is isolated from the compressed air source  16 . 
     When the control valve  315  is in the on position, compressed air from the source  16  supplies a vacuum pump  4 . Also connected to the valve  315 , by a T  303 , is an adjustable vacuum switch (regulator)  306 . The switch  306  is controlled by the vacuum from the vacuum port  9  on the vacuum pump  4 . When the switch  306  is in the closed position, because the vacuum sensed at the vacuum port  9  is below the desired 40 inch threshold, compressed air from the supply  16  is fed through the switch  306  to a pressure actuated valve  310 . When sufficient pressure from the supply  16  is input to the valve  310 , the valve  310  is positioned such that the vacuum port  9  of the pump  4 , which is connected on the input side of the valve  310 , is connected to the gauge  14  and the riser  17 . When the switch  306  senses that the vacuum at the vacuum port  9  reaches the predetermined 40 inch threshold, the switch  306  cuts off the pressurized air supplied to the valve  310  and causes the valve  310  isolate the riser assembly  17  from the vacuum pump  4 . A vacuum closed indicator  23  is also connected to the output switch  306 . The vacuum close indicator  23  allows the status of the switch  306  to be determined. In use, once the operator recognizes that the vacuum close indicator  23  indicates that the switch  306  has opened, thereby causing valve  310  to isolate the pump  4  from the riser  17 , the operator monitor the gauge  14  for the same 15 minute period discussed above and verifies that no more than 2 inches of vacuum loss occurs. 
     Upon the detection of a leak, the flowchart  600  is followed to isolate the location of the leak. When a leak has been detected by either the automatic vacuum test or the manual vacuum test, a soap test is performed. The soap test is performed both outside the riser assembly  17  and inside the riser assembly  17  in the case of a new installation, and only on the inside of the riser assembly  17  in the case of an existing tank or where the backfilling has already occurred. Sonic search methods, smoke stream methods, may also be used as indicated in FIG.  6 . In a new installation, the inside of the riser  17  may be filled with water and the water level allowed to drop until the level of the leak is reached. In a different test, the outside of the riser assembly  17  (e.g., the surrounding soil) may be flooded and the dry interior of the riser assembly  17  be visually monitored for any water seepage. 
     Obviously, numerous other modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the pending claims, the invention may be practiced otherwise and as specifically described herein.