Receptacles – Stationary tank
Reexamination Certificate
1998-07-14
2001-03-27
Castellano, Stephen (Department: 3727)
Receptacles
Stationary tank
C220S567100, C220S567200
Reexamination Certificate
active
06206226
ABSTRACT:
The present invention relates to a field applied lining system for the inside surface of fluid containment vessels. The lining provides corrosion protection, leak detection and secondary containment of leaks.
Various types of corrosion protection, leak detection and secondary containment systems are known. The conventional method is double walled tanks, with the outer wall normally comprised of steel or concrete, with the inner wall providing the primary structural basis and fluid containment for the tank. The inner wall can be anything from a plastic or fibre lining, to a second steel wall welded to the first. The interstitial space defined by the inner and outer wall of the tank provides a secondary containment chamber for fluid in the event a leak should occur through the inner wall, for example as a result of corrosion, a faulty weld or resin bond, or mechanical stress.
The interstitial space is conventionally filled with sand or other granular supporting material, but in some prior art may contain a support structure for the inner wall which permits fluid flow, such as a wire mesh or aluminum foil sheeting. This allows for avenues of fluid flow in the interstitial space and simplifies the detection of leaks. One or more fluid sensing monitors are located in the interstitial space. These must normally be located near the bottom of the tank to facilitate detection.
There are several major problems with the prior art. While double wall tanks provide satisfactory secondary containment, they are expensive and time consuming to fabricate, since they require the construction of two complete tanks of different sizes, the smaller tank being assembled inside the larger one. In addition, if there is a leak into a sand bed or other granular supporting material in the interstitial space, this material must be removed, disposed of and replaced. All three of these requirements generate further expenditure of both money and time.
Another problem is that fluid leaks are often not detected until they are quite far advanced, as the sensor locations are relatively remote from where leaks generally occur. The prior art which attempts to solve this problem, in one instance, uses a wire mesh to provide avenues of fluid communication and allow for faster leak detection. The problem with this usage is that the wire mesh is subject to corrosion and may have to be replaced, and also requires a plurality of sampling ports as fluid communication is not complete through the wire mesh. Some of the prior art uses a vacuum in the interstitial space and monitors pressure changes to detect leaks. But this system is inaccurate because changes in pressure can result from temperature changes, and fluid bleeding through walls where there is no leak.
The most important problem with the prior art is that no lining system exists which can be applied to existing tanks in the field, and so deterioration during use cannot be remedied except at great expense or by replacing the entire tank.
It is desirable to have a lining system for fluid containment vessels which is relatively inexpensive and may be installed in the field, and which provides for the rapid detection of leaks. The lining system must be corrosion resistant, structurally strong enough to provide primary containment of the fluid in question, and yet flexible enough that it does not buckle when the fluid containment vessel is subject to mechanical stress. The outer wall should be able to expand, flex or even crack and not affect the inner wall.
It is also desirable to have a lining system which does not require extensive and expensive replacement of components in the case of a leak, but which is simple and inexpensive to repair in the field if a problem develops.
It is also desirable to have a leak detection system that provides rapid and uniform leak detection for the entire vessel.
The present invention relates to a field applied lining system for the inner surface of fluid containment vessels. The primary containment membrane is constructed from manufactured Fibre Reinforced Plastic panels. These panels are joined by pop rivets which are flush on the liquid side of the membrane and extend into the interstitial space on the back side of the panels. A sealing laminate is then applied over the edges of the panels where they touch each other and at the edge of the lined area where the panels need to be joined to the inner surface of the vessel. A further advantage of these panels is that if a leak occurs in a panel or between panels, a very small area of the lining needs to be repaired or replaced. The panels need not be adhered to the outer wall, except at the edges of the liner. This means that the inner surface of the outer wall does not have to be specially prepared, although the section of the surface area to which the panels will be attached may be prepared by sandblasting and priming with a high adhesion primer. Furthermore, the outer wall can flex, expand or crack and not affect the liner. More importantly, the panels will usually fit through the existing access holes in the vessel, and accordingly, no mechanical modifications to this vessel are required. As long as the edges are properly sealed, the lining system will not be affected by most of the traditional failure mechanisms in fluid containment vessels.
The support structure in the interstitial space consists of an open grid of High Density Polyethylene, which provides shock absorption against impact damage to the panels. This grid also provides for avenues of fluid communication through the interstitial space. A vacuum can be drawn on the interstitial space at any time to confirm the integrity of both the inner and outer walls of the containment vessel. The interstitial space is quite small, and this aids in the rapid detection of leaks as very little fluid is required to fill this space. This factor has the additional advantage of requiring far fewer leak detection ports. The interstitial space may be vented, which results in a pressure differential which allows any fluid in this space to travel quickly and prevents the interstitial space from having a higher pressure and thus interfering with leak detection.
The advantage to this lining system is that it can be applied to horizontal and vertical surfaces. Further, the panels are translucent, which allows for easy tracing of leaked liquid in order to rapidly find leaks. There is no contaminated material in the case of a leak.
Another advantage of this system is that both the panels and the grid can be cut out using non-sparking or cold work methods. This is especially important where the fluid being contained is flammable or through the interstitial space very easily. Many such systems are currently available in the marketplace.
REFERENCES:
patent: 1259320 (1918-03-01), Tyler
patent: 2028957 (1936-01-01), Carlstrom
patent: 2028968 (1936-01-01), Carlstrom
patent: 4640439 (1987-02-01), Palazzo
patent: 4916939 (1990-04-01), Mogel
patent: 5018324 (1991-05-01), Lankheet
patent: 5261764 (1993-11-01), Walles
patent: 5860762 (1999-01-01), Nelson
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