Stock material or miscellaneous articles – Hollow or container type article – Glass – ceramic – or sintered – fused – fired – or calcined metal...
Reexamination Certificate
1998-12-30
2001-02-06
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Hollow or container type article
Glass, ceramic, or sintered, fused, fired, or calcined metal...
C428S036910, C428S516000, C424S411000, C424S412000, C138S141000, C138S146000, C138SDIG006
Reexamination Certificate
active
06183825
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a protective material for preventing microbiologically-influenced corrosion in buried conduits. More particularly, the present invention relates to a polyethylene sleeve used to encase buried conduits wherein the sleeve has a bactericide impregnated therein to prevent microbiologically-influenced corrosion in the buried conduits.
BACKGROUND OF THE INVENTION
Buried conduits are ubiquitously used for carrying various materials, such as water, natural gas, and sewage. A major problem with buried conduits comprised of metal or concrete with metal reinforcements is corrosion. The severity and rate of corrosion is dependent on the type of material comprising the conduit and the environment in which the conduit is buried. Insuring the longevity of buried conduits is an important part of the infrastructure in the United States and the world. Significant costs are involved in design, development, manufacture, and installation of water, gas, and sewage systems. Failure of these systems from conduit corrosion represents appreciable costs.
The longevity of buried conduits depends on several design and installation features, including resistance to corrosion. There are numerous causes of corrosion, such as oxygen replenishment, presence of sulfides, pH of the surrounding soil environment, stray direct electrical current, and microbiologically-influenced corrosion. In the early 1950's, experimentation was conducted using polyethylene film to encase buried conduits in an effort to prevent corrosion. The results showed that a sleeve of polyethylene film could be easily and quickly slipped over a conduit immediately prior to installation and the sleeve was effective in preventing corrosion, even in severely corrosive soils. Because polyethylene is inexpensive compared to other corrosion abatement systems and is easily applied to conduits, it has become the preferred corrosion abatement system relative to buried conduits.
Polyethylene film is very strong and durable, and can withstand the harsh conditions of burial for an indefinite period. For example, polyethylene sleeves that were installed on buried conduits over 35 years ago, when excavated and examined, exhibited the same physical characteristics they had when first installed. Inspections of field installations years later have confirmed that polyethylene sleeves have generally performed as expected, however, there were some instances of unexplained corrosion. Recent research has shown that colonies of bacteria form on the conduit and their secretions can cause severe corrosion, leading to failure of the buried conduit. The colonies of bacteria consists of both aerobic and anaerobic bacteria, and generally comprise slime-forming, acid-producing, sulfate-producing, nitrate-reducing, iron-oxidizing, and iron-reducing bacteria.
Microbiologically-influenced corrosion (“MIC”) from anaerobic sulfate-reducing bacteria (“SRBs”) was suspected as the most likely cause of the unexplained corrosion events. The anaerobic bacteria from the genera Desulfovibrio (e.g.
Desulfovibrio desulfuricans
) have been found to be one of the major contributing causes of MIC. However, currently available methods for controlling conduit corrosion do not address microbiologically-influenced corrosion or their application is technically complex and very expensive, or they are not suitable for buried conduits.
SUMMARY OF THE PRESENT INVENTION
It is an object of the present invention to provide an anti-corrosive material which is superior to those presently used to protect buried conduits.
It is another object of the present invention to provide an anti-corrosive material which contains a bactericide to prevent bacterial induced or enhanced corrosion of buried conduits.
It is another object of the present invention to provide an anti-corrosive material which contains a bactericide to prevent bacterial induced or enhanced degradation of the anti-corrosive material.
It is another object of the present invention to provide an anti-corrosive material in the form of a sleeve that can be easily slipped over the candidate conduit without the need for specialized technology or wrapping equipment.
It is another object of the present invention to provide an anti-corrosive material comprising a conduit-contacting layer having a bactericide impregnated therein such that said bactericide can migrate within the conduit-contacting layer to contact the conduit surface and thereby prevent bacterial induced or enhanced corrosion therein.
It is another object of the present invention to provide a multi-layered, anti-corrosive material having a barrier layer adjacent the conduit-contacting layer which prevents the bactericide from penetrating the barrier layer and entering the surrounding environment.
These and other objects of the present invention are accomplished through the use of an anti-corrosive material used to protect buried conduits from microbiologically-influenced corrosion, or “MIC”. The material preferably comprises a low, medium, or high density polyethylene sleeve having a bactericide impregnated therein such that said bactericide can migrate within the polymer matrix to contact the conduit surface and thereby prevent MIC therein. The material may further comprise a barrier layer of high density polyethylene between the bactericide-containing layer and the environment. The bactericide is able to migrate through the low or medium density polyethylene but the rate of migration of the bactericide is considerably slowed through the high density polyethylene. Thus, the bactericide is substantially prevented from entering the surrounding environment, but rather, is trapped within a “protection zone” adjacent the conduit surface to provide extended protection against microbiologically-influenced corrosion.
The advantages of the present invention include: (1) no specialized technology is required to apply the polyethylene sleeve as is required with continuous wrapping of the conduit; (2) current installation practices remain unchanged; (3) microbiologically-influenced corrosion is prevented; and (4) applicable industry standards are met without caveat. Thus, the present invention is not limited to simply overcoming the deficiencies of the prior art but introduces enhanced technical advantages in corrosion protection that were not previously available for buried conduits while continuing to meet established industry standards.
These and other objects and advantages of the invention will become apparent from the following detailed description of the preferred embodiment of the invention.
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Burr & Forman LLP
Fulton Enterprises, Inc.
Jackson Robert M.
Tarazano D. Lawrence
Thibodeau Paul
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