Fire extinguishers – Processes
Reexamination Certificate
2001-09-18
2004-07-06
Ganey, Steven J. (Department: 3752)
Fire extinguishers
Processes
C169S005000, C169S016000, C138S145000, C252S387000, C252S390000, C118S306000, C118S318000, C427S230000, C427S236000
Reexamination Certificate
active
06758282
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to fire protection pipe and methods of manufacture thereof.
BACKGROUND OF THE INVENTION
This invention relates to inline coating of a metal substrate, such as a metal tube or conduit, of the type used for applications such as fire sprinkler systems for buildings. There are two types of fire sprinkler systems, wet and dry. When each type of system is first installed, the system is filled with air, then checked for leaks, then filled with water and again checked for leaks. The difference between the two systems is that for the dry system, the system is filled with water at a prescribed pressure for about 24 hours to check for leaks, and then drained, and the system is then pressurized with air, and then placed into operation. In the wet system, after the system is filled with water and it is confirmed that there are no leaks, the system is placed into operation without draining the water.
One of the major problems in both wet and dry sprinkler systems is the formation of microbiologically influenced corrosion (“MIC”) on the interior surface of metal tubing. MIC arises from a wide variety of microbiological organisms called microbes including, but not limited to, sulfate reducing bacteria (SRB), acid forming bacteria (AFB), and slime formers. MIC can result in mechanical blockages of the piping and sprinkler heads, as well as premature performation of steel tubing. MIC is a major cause of tuberculation, pitting and subsequent pipe failure in fire sprinkler systems. More specifically, MIC can cause tuberculation and corrosion, which can further lead to pinhole leaks in carbon steel, copper and galvanized pipe systems. It is not uncommon for a dry sprinkler system to have more severe MIC than a wet system, as there may be pockets of water in a dry system, as well as the presence of air, that lead to more severe MIC than with water alone.
Besides the problem of pinhole leaks that MIC creates, tubercles and nodules located on the interior of the pipe arising from MIC are a major concern as well since the pipe roughness factor (C-factor) that is applied to sprinkler piping used to determine friction loss does not anticipate severe MIC. See, e.g., “Detection, Treatment, and Prevention of Microbiologically Influenced Corrosion in Water-Based Fire Protection Systems,” by Tariq K. Bsharat, Technical Services Manager of the NFSA, June 1998, which is incorporated herein by reference. In some cases of MIC, obstructions caused by tubercles are so great that there is almost no cross-sectional area of the opening in the pipe remaining. Id.
Fire sprinkler systems provide a favorable environment for the growth and development of bacteria resulting in MIC failures, as recognized by members of the American Fire Sprinkler Association (“AFSA”), National Fire Protection Association (“NFPA”), National Fire Sprinkler Association, Inc. (“NFSA”), National Association of Corrosion Engineers (“NACE”), sprinkler manufacturers, end users, and the fire protection service/mechanical contractors working within the industry. See, e.g., “Detection, Treatment, and Prevention of Microbiologically Influenced Corrosion in Water-Based Fire Protection Systems,” by Tariq K. Bsharat, Technical Services Manager of the NFSA, June 1998.
Bacteria are either aerobic (i.e., thrive when exposed to oxygen) or anaerobic (inhibited or perish when exposed to oxygen). Aerobic microorganisms and their secretions on wetted pipe surfaces leads to the formation of biofilms, which frequently become embedded with iron, scale, oil, dirt, and other debris. This biofilm adheres to these metal surfaces and forms a gel-like mass around bacterial deposits, which promotes the formation of differential oxygen cell corrosion. As previously noted, MIC can result in mechanical blockages of the piping and sprinkler heads, as well as premature perforation of steel tubing.
Anaerobic bacteria, such as the class
Desulfovibrio desulfuricans
(sulfate reducers) and acid producers, seek out and colonize beneath the spotty biofilms (slime layers), under debris or inside porous tubercles where the environment is deficient or devoid of oxygen. These bacteria produce metal sulfides as corrosion products and, when exposed to air or hydrochloric acid, the rotten egg odor of hydrogen sulfide (H
2
S) is easily detected. Sulfate reducing bacteria (SRB) are typical examples of anaerobic MIC and can cause rapid pitting and severe metal loss, accompanied by the H
2
S odor and black colored water frequently found in fire sprinkler systems. Another type of anaerobic bacteria is acid producing bacteria (“APB”, which is sometimes referred to as acid forming bacteria (“AFB”)). APB can be found in aerated microenvironments. One type of APB is called Clostridium, which can produce organic acids and stimulate SRB growth. Clostridium is a very important MIC microbe in carbon steel systems.
Aerobic sulfur oxidizing bacteria of the type thiobacillus can create an environment of up to about 10% sulfuric acid, thereby creating rapid corrosion. A layer of aerobic bacteria can also create a prime location in the system for anaerobic bacteria to thrive, since little or no oxygen is available below such a layer.
Prior attempts to reduce or eliminate the corrosion problems due to MIC have numerous drawbacks. A major drawback in prior techniques to treat MIC is that most of them involve treatment after MIC has already occurred and/or treatment that is post manufacture and installation of the sprinkler system.
Other drawbacks of prior attempts to treat MIC are expensive and time consuming. For example, prior attempts to treat MIC include replacement of pipe, which is extremely costly and is a time consuming operation.
Another approach is to flush the system with water. However, this can result in layers upon layers of aerobic and anaerobic bacteria as well as introduce new microbes and oxygen nutrients to the system, thereby allowing new MIC colonies to form.
Yet another approach is to drain the water out of the system, and then circulate an acidic solution throughout the entire piping system to dissolves tubercles and nodules formed by the MIC. This option requires that each sprinkler be removed and connected to hoses which connect to the main drain and to a special external pump. The acidic solution is circulated from 24 to 48 hours throughout every line and sprinkler to ensure that all corrosion deposits are dissolved. The cost of this type of treatment is about 25% to 50% of replacement of the entire piping system. See, e.g., “Detection, Treatment, and Prevention of Microbiologically Influenced Corrosion in Water-Based Fire Protection Systems,” by Tariq K. Bsharat, Technical Services Manager of the NFSA, June 1998.
Another treatment for MIC is to raise the level of pH of the water in the system to a level in which microbes cannot grow. See, e.g., U.S. Pat. No. 5,803,180, which discloses a structure and method for adjusting the pH level to a value of between 9.5 and 11. However, this method is not recommended since it does not provide a solution for the removal of existing debris. See, e.g., “Detection, Treatment, and Prevention of Microbiologically Influenced Corrosion in Water-Based Fire Protection Systems,” by Tariq K. Bsharat, Technical Services Manager of the NFSA, June 1998. Remaining nodules and tubercles can affect the flow of water and thereby add to friction loss in sprinkler pipe and tube. Id.
Another approach is to try a physical treatment called “pigging,” in which a cylindrical apparatus is fitted in specific pipe sizes. The apparatus is placed on one end of the system and large pressure is applied sending the apparatus down a run of pipe, de-scaling the walls and removing the MIC tubercles. The problem with this treatment is that it only works for one pipe size at a time. For example, a 2-inch pig only works for 2-inch pipes. Therefore, this treatment is expensive and tedious, especially since the path of travel for the pig must be isolated from cross-mains and branch lines to conserve pressure. See, e.g., “Detection,
Bussiere Robert D.
Chaudhry Manzoor
Foster Elmer H.
Norvilas Stephen T.
Pliner David S.
Allied Tube & Conduit Company
Banner & Witcoff , Ltd.
Ganey Steven J.
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