The present invention relates to secondary containment systems and especially, although not exclusively to a piping construction and a method for providing secondary containment systems for hydrocarbon storage and delivery systems.
A secondary containment system is one which functions to collect and contain the fluids leaking out of another and primary containment system. For example, a primary containment system may store and deliver gasoline at a filling station. A secondary containment system would collect and contain the same gasoline if a primary delivery pipe should rupture or otherwise spill the gasoline. Secondary containment systems have been developed to overcome the environmental problems that have been encountered with respect to leakage of hazardous fluids from tanks and pipe lines. As indicated, this has been a particular problem with respect to underground installations in which undetected leakage of hazardous fluids into the surrounding terrain over long periods of time has produced harmful conditions and extensive pollution which are difficult and expensive to clean.
Today there is great public concern because chemicals are penetrating into underground water supplies contaminating public drinking water and making some of the food supply unusable, among other things. The entire environment is being degraded to a serious level which tends to cast doubt on the future availability of safe water. Therefore, many government agencies have enacted and continue to enact laws which require a secondary containment system designed to capture and contain the spilled gasoline or other liquid materials thus preventing it from leaking into the surrounding earth. The capture gasoline or other liquid material may then be pumped out of the secondary container for proper disposal. This eliminates the possibility of gasoline spillage to contaminate underground water supply.
Manufacturers of containment systems have responded by developing and producing a variety of secondary containment systems for conventional underground piping which are designed to contain and prevent any leakage from escaping into the environment. Many of these systems have proven to be effective containment systems but have been found to be difficult and costly to install.
One known approach to secondary containment systems, and, in particular, the secondary containment of underground conventional piping has been to line the piping trench with an impervious flexible membrane liner or semi-rigid trough. This technique can provide a measure of secondary containment of leaky product but such an approach does not allow for effective leaking detection in that it does not permit the determination of which pipe is leaking and the location of the leak in the piping line when the same occurs. It is also difficult to test such systems using air pressure testing devices. Additionally, these secondary containment systems do not provide 360.degree. containment, and therefore can fill with water and become ineffective.
Another approach toward solving the problem of underground leakage in such conventional piping systems has been to install a large semi-conventional piping system over the conventional underground piping as a means for providing the secondary containment. With such an arrangement, the outer secondary containment rigid pipe is installed simultaneously with the product piping. The outer secondary containment pipe by necessity has a larger diameter than the supply pipe to enable secondary containment pipe to slide over the smaller pipe. The secondary containment pipe fittings are of a clam shell design adapted to fit over the supply pipe fitting and connect to the secondary containment pipe. The clam shell fitting is sealed to itself and the secondary container pipe by a variety of sealing techniques. Depending on the type of secondary containment system used, these sealing techniques could include metal or plastic fasteners used with a combination of adhesives, sealants and the like. Such secondary systems are generally expensive to install because of the cost of the components which are used and the time required to assemble both the product and the secondary containment piping systems.
Another known approach to solving the aforementioned problems is to employ a semi-conventional piping system over the conventional product piping. This type of containment system differs from the first described system in that it is not an entirely rigid straight pipe but rather a combination of rigid straight pipe with a larger diameter, convoluted plastic pipe over it which produces a telescoping effect. The convoluted section of telescopic containment pipe serves as a fitting of containment of the product, 90.degree. and 45.degree. fittings as well as unions, flexible connectors, swing joints, should they be so attached. The convoluted pipe is designed to be flexible and sized to be shifted around any angles in the production piping system.
Another type of secondary containment piping system has been developed which utilizes spaced access chambers interconnected by a secondary containment pipe to provide a sealed housing for a flexible fluid supply pipe, the ends of which are disposed within the access chambers and have a connector element at each end forming a section adapted to be interconnected to other fluid conduits. The diameter and bending radius of the fluid supply pipe and the size of the access chamber are such as to permit the fluid pipe, after uncoupling, to readily be removed from the secondary containment pipe through one of the access chambers. Should a leak occur in the piping, the secondary containment system allows the piping to be removed and replaced.
It is very difficult and expensive to meet all of the many different environmental and safety standards at a reasonably acceptable cost, particularly in light of the many state and local governments writing individual laws that impose a wide variety of standards which the manufacturers of such systems must meet.
Accordingly, an object of the invention is to provide a new and improved secondary containment system which will draw all spilled fluids that may leak from a primary supply pipe to a preselected collecting point which may be monitored.
Another object of the present invention is to provide a practical secondary containment system which may be manufactured in a factory, shipped and installed at a reasonably low cost in a fully usable manner and yet one which meets all requirements of the environment within which they must be used.
It is a further object of the present invention to provide an economical, easily installed, highly durable and environmentally secure flexible piping system. It is a further object of the present invention to provide such a flexible piping system which may optionally eliminate coextrusion.