Because vehicle fueling facilities, like retail service stations, are becoming more environmentally conscious, a shift has occurred from the use of rigid underground piping to flexible piping. A primary reason for this shift from rigid to flexible piping is that flexible piping has fewer pipe connections than rigid systems since the flexible system can accommodate virtually any orientation or alignment of the pumps and tanks. With fewer pipe connections, the piping system is considered more environmentally safe. Movement of the underground storage tank due to the shifting underground tanks is also more easily accommodated by flexible piping.
Flexible underground piping systems have also gained popularity because these systems are more easily installed than rigid piping systems. Rigid systems require on-site measurements and cutting of each piece, along with the intensive labor involved in making two pipe connections every time the piping undergoes a change in direction. Flexible underground piping systems thus can be installed at a lower total cost than conventional rigid piping systems.
As part of the development of underground piping systems, it has been necessary to provide a means of secondary containment for both the primary piping and for the associated fittings in order to provide a margin of safety in case of leaks or damage to the system. The secondary containment pipe protects the primary supply pipe from the ambient environment and from inadvertent damage, and further, provides for a method of containing the fluid from the primary pipe in the event of a rupture or leak of the primary pipe.
Several types of double wall flexible piping systems are known. These include systems which have a small flexible pipe housed in a larger flexible containment pipe. One such system is described in U.S. Pat. No. 4,971,477 (the '477 patent), wherein access chambers are separated by a secondary containment pipe which is sized to accept a primary pipe within the secondary containment pipe. This system, however, has a number of drawbacks, including the fact that the primary and secondary pipes are installed separately and that fittings are required for each of the two types of pipes. Moreover, because each of the pipes connects with an access chamber, a rapid and simple method of monitoring the condition of the primary piping may not be possible. Although the sumps in the '477 patent are capable of being monitored visually by an attendant, but the demand of other tasks to be performed by the attendant eventually leads to fewer and fewer inspections. Most important is that leaks may occur randomly, not only just prior to a visual inspection, and especially when inspections grow less frequent over time.
As taught in the '477 patent, the flexible piping and the secondary containment piping require a sump or access chamber each time that sections of the flexible pipe are joined together. Most other systems also require a sump at each location where sections of flexible pipe are joined together.
Other systems which have met with success using coaxial pipes and a secondary containment pipe are shown in U.S. Pat. No. 5,263,794 (the '794 patent), and U.S. Pat. No. 5,297,896 (the '896 patent) the entire disclosures of which are incorporated herein by reference. The advantages of flexible pipe systems are disclosed by these patents. Nevertheless, it is necessary to make individual connections each time sections of pipes are joined together.
The '794 and the '896 patents disclose various definitions that have become standard in the industry, for example, “tanks”, “pumps”, “dispensers” and the like. Also disclosed therein are descriptions of double wall piping systems that provide secondary containment. In a system that employs secondary containment, a primary pipe carries the petroleum product or other hazardous material from the underground tank to the aboveground dispenser. The primary pipe, also known as the supply pipe, is located inside a larger, outer secondary containment pipe, known also as the containment pipe. Access sumps and other containment components are located around the tank pump, underneath the dispenser and at various junctions of piping.
Recently, an effective system has become available and has met with substantial success in the industry. This pipe system's supply pipe is a flexible double wall pipe comprising an inner pipe and an outer pipe in radial communication with the outside surface of the inner pipe. Most preferred are pipes of this configuration that have internally facing longitudinal ribs on the inner surface of the outer pipe, or externally facing longitudinal ribs on the outer surface of the inner pipe. In either such design, a plurality of circumferentially spaced ribs extend radially from one pipe member to the other pipe member such that the ribs have a surface that confronts and snugly engages the other pipe to define an interstitial space between the two pipes.
The flexible double wall pipe described immediately above is disclosed in my U.S. Pat. No. 5,527,130 entitled Environmentally Safe Underground Piping System, the entire disclosure of which is incorporated herein by reference. The co-axial pipes disclosed in the '130 patent are normally suited for use with hazardous material transfer pipe systems of the type described herein. The inner most layer is formed from a material such as nylon, PVDF, polyethylene or the like, which is highly resistant to the hazardous transfer fluid. The outer jacket of the double wall pipe which is exposed to the ambient underground environment is formed from a material such as nylon, PVDF, polyethylene or the like, which is highly resistant to the ambient underground environment and which does not degrade over time. Between the outer wall of the primary pipe and the inner wall of the containment pipe is an intermediate layer, either in the form of ribs projecting from one surface to the other, or in a standoff layer formed from a cylindrical portion having circumferentially spaced ribs that define the interstitial space between the two pipes. As noted in the '130 patent, other layers can be present in the design, such as intermediate layers formed from lower cost materials which do not directly contact either the hazardous material being transported or the ambient underground environment.
The environment for both surfaces of the pipe is an important design aspect, which needs to be considered. Product components which make up primary or secondary containment systems for hazardous liquids, and in underground applications particularly, must be designed, manufactured and individually tested to insure that they will not fail due to material deterioration.
The material employed are preferably resistant to hydrolysis, as it is expected that water and high moisture conditions will exist in underground burial applications both for contained and non-contained underground piping applications. Resistance to hydrolysis is important since some elastomers suffer an irreversible breakdown when exposed for lengthy periods to hot water, moisture vapor or tropical climates.
In addition to the tanks, pumps, pipes and dispensers used in underground piping systems, sumps are used as part of the secondary containment system. One sump surrounds the pump on the tank and another sump is generally positioned below each dispensing system. Sumps typically have a base portion, a riser and a lid and are provided with means for permitting piping to enter and exit the sump. One type of sump called a tank sump is located on top underground storage tank and under a surface access manhole. Contained within the tank sump is a dispensing pump whereby the fuel is directed upwardly from the tank to the dispensing pump and outwardly through the opposite side of the tank sump to the next part of the system. Each time the pipe sections are connected to one another, these pipe connections are typically contained within another sump that, of course, requires a pipe penetration seal to seal the pipe entry or exit through the sump.
As can readily be appreciated, every pipe must eventually end. It then becomes necessary to connect that end of the pipe to either a pump, to a fitting joining two or more other pipes or directly to a shear valve. Typically the inner, primary supply pipe is directly connected to fittings and the like, and another primary supply pipe is connected to the other end or ends of the fittings. Merely connecting the inner supply pipes, as in the past, has been no different than connecting a single pipe system. In the evolution of piping systems as discussed above, the relationship of the outer, secondary containment pipe to the system has become more complex.
Initially, non-flexible pipes functioning as a secondary containment pipe were attached to the sump or other chambers by enlarging the hole in the sump to permit entry or exit of the outer pipe from the sump, and later by various fastening and sealing methods and devices. Initially, the interstitial space between the inner and outer pipes served as a conduit for fluid leakage to flow downhill into the next sump in the piping system. Leaks could come from fuel from the inner pipe, or from the outer pipe as ambient environmental liquids, such as water, penetrate the outer pipe.
Leak detection initially consisted of opening the sump chamber and inspecting the bottom of the sump for fluid accumulation. Of course, whatever can be visually inspected can be monitored automatically. Systems were proposed for monitoring the liquid levels in the bottom of sumps. However, every sump had to have a monitoring device since each sump, by design, represented a low point where fluid could collect. The difficulty in such two pipe systems can easily be seen by viewing FIG. 2 of '477 patent where the outer pipe has a very limited, minor function of simply isolating the primary supply pipe from the ambient environment. Also shown in that Figure is the way that the interstitial space between the primary pipe and containment pipe merely opened into the larger sumps without any recognition that there may be other purposes for the interstitial space. As is shown in FIG. 3 of the '477 patent, the secondary containment pipe merely serves as a housing or conduit for sections of the primary supply pipe which may be inserted or removed as desired.
In my U.S. Pat. No. 5,398,976, I disclosed a connecting boot that substantially improves utilization of the interstitial space. The connecting boot, commonly known as a “test boot”, comprises a device which fits onto one terminal end of a supply pipe, allowing the inner primary supply pipe to extend out from the connecting boot while the outer secondary containment pipe terminates inside the connecting boot. The exit end of the test boot where the primary supply pipe exits is clamped to, or otherwise sealingly engages, the outer surface of the primary pipe. The entrance end of the test boot that fits over the exterior of the secondary containment pipe is also clamped to, or is sealingly engaged with, the outer pipe surface. In between these two sealed ends of the test boot is a chamber, which communicates with the interstitial spaces of the two pipes and also communicates with a radially extending port. An elbow fitting and tube is usually provided which can be connected to the radially extending port and elbow fitting on the adjacent pipe, to which the primary pipe has been attached in a conventional manner.
Thus, for the first time, it was possible to connect not only the interstitial spaces of two adjacent pipes but also the interstitial spaces of an entire system, which are connected to a single monitoring device. Such a monitoring device could be a system whereby the entire interstitial space of all of the piping is filled with a liquid to a level, which registers in a predetermined range of the monitoring device to indicate a securely contained system. When the level of the fluid in the interstitial space either drops below a certain amount or rises above a certain amount, indicating a change in the system, an alarm will sound.
The test boot provided a substantial advance in the hazardous fluid piping system industry, primarily by permitting interconnection of all of the system wide interstitial spaces. The test boot, however, is not as structurally solid as an access sump, for example, and thus needs to be enclosed in a sump for protection.
There are several additional considerations that need to be addressed in designing the connections between sections of pipes, particularly between sections of flexible coaxial pipes. First, it is desirable to avoid plastic adhesion or plastic thermally bonded connections, since temperature conditions, chemical exposure, vibrations over time can cause piping joints to fail. A much better seal is achieved when metal and plastic are joined together by mechanical means. However, in such cases it is necessary to protect the metal from the environment by a coating or isolation to avoid a corrosive and unsafe condition. Coatings on metal parts, however, often peel off or become damaged during handling of the metal parts. Also, if the coatings are too thick, the necessary metal to plastic contact to establish an effective seal is not achieved.
As will be apparent from reviewing the above patents, there is an interstitial space between the inner primary supply pipe and the outer secondary containment pipe. This interstitial space has been used to transfer leaked fluid into the containment sump or access chamber. Typically, in early systems, the access chambers were inspected on a regular basis to see if quantities of fluid had collected. This, of course, does not provide a rapid response to a major leak of fluid such as fuel from the primary supply pipe.
As shown in the '794 and the '876 patents, the entire system is connected such that the primary pipe functions as a closed system, transporting fuel from the supply tank to the various dispensers. However, the interstitial space between the primary supply pipe and the secondary containment pipe is a conduit allowing leaked fluid to flow to an access chamber for observation. Although it is possible to monitor the conditions of one or all of the access chambers, for example by visual inspection, no simple method of monitoring the entire system is possible.
It is desirable to provide an underground piping system which employs coaxial pipe, such as those pipes described above, which include a inner primary supply pipe and a outer secondary containment pipe, in which the interstitial space between the two pipes can be connected to the interstitial spaces in other segments of piping to form a continuous closed system of interstitial space.
It is also desirable to provide a coupling assembly for use with coaxial pipes that permits coupling of the interstitial space between the coaxial pipes with corresponding interstitial spaces in other segments of pipe.
Such a system should also provide an effective monitoring system utilizing the interconnected interstitial space of the coupling assembly, particularly with the use of a constant vacuum or pressure applied to the interstitial space or monitoring the liquid level of a liquid filled interstice.