Pipes and tubular conduits – Distinct layers – Coated
Reexamination Certificate
1998-01-13
2001-04-24
Hook, James (Department: 3752)
Pipes and tubular conduits
Distinct layers
Coated
C138S139000, C138S143000, C427S410000, C427S318000, C427S386000
Reexamination Certificate
active
06220305
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to forming coatings adhered to steel pipes to waterproof and protect the pipes against corrosion, and more particularly to an improved method for coating steel pipe with coal tar enamel, and to the products thereof.
As further background, steel pipe is commonly used to convey petroleum-based materials such as gas, oil and water. In service, of course, it is necessary that the steel pipe utilized be resistant to penetration by moisture which might facilitate corrosion of the steel and/or lead to contamination or loss of the material conveyed. For this reason, it is an adopted practice to coat steel pipe with a water-resistant bituminous material such as coal tar enamel. In this regard, coal tar enamel itself does not possess the properties necessary for sufficient direct bonding to steel pipe under relatively convenient processing conditions to meet the demands in industry. Therefore, a primer coat of chlorinated rubber has usually been applied to the steel pipe, followed by coating with the coal tar enamel to provide the overall waterproofed pipe.
In the steel pipe coating industry, waterproofing processes must desirably employ readily available and inexpensive materials which require as little handling as possible. In addition, processing steps should be convenient and processing time must be kept to a minimum. On the other hand, the resulting waterproof coating must survive a battery of tests in order to provide acceptable service. For example, industry has adopted several tests for the integrity of the coating including those for resistance to heat, cathodic disbondment, impact, and hot water.
In the face of these stringent economic and technical demands, there exists a need for improved methods for forming waterproof coatings on steel pipes, and improved products resultant of such methods. The instant invention addresses these needs.
SUMMARY OF THE INVENTION
It has been discovered that a highly serviceable waterproof coating can be formed on metallic pipes such as steel pipes utilizing a primer coating consisting essentially of an epoxy resin material and a top coating consisting essentially of a coal tar enamel. Such waterproof coatings and pipes having such coatings are readily and quickly manufactured while exhibiting excellent properties relative to resistance to cathodic disbandment, heat, water and the like. Accordingly, one preferred embodiment of the invention provides a method for forming a waterproofed steel surface on a steel pipe. The method includes the steps of preheating the steel surface, preferably to a temperature of at least about 55° C., and applying to the preheated steel surface a primer consisting essentially of a thermally-curable epoxy resin composition, wherein the resin begins to cure upon application to the steel surface. Prior to completion of curing of the epoxy resin, a preheated top coating composition consisting essentially of coal tar enamel at a temperature of at least about 200° C. is applied overtop the primer. Thereafter, the overall coating is caused to cure, and the materials are cooled to form the waterproofed steel surface.
Another preferred embodiment provides a waterproofed metallic pipe such as a steel pipe. The preferred pipe includes a steel pipe having a steel surface, and a waterproof coating on the steel surface. In this aspect of the invention, the waterproof coating includes a cured primer coating consisting essentially of epoxy resin bonded to the steel surface, and a top coating consisting essentially of coal tar enamel overtop and bonded to the primer coating.
Still another preferred embodiment of the invention relates to the discovery that a silane coupling agent can be used to improve the processing and adhesion characteristics of epoxy/coal tar enamel waterproofed coatings. Thus, this aspect of the invention provides a waterproofed steel pipe which includes a steel pipe having a steel surface and a waterproof coating on the steel surface. The waterproof coating includes a primer of a thermally-curable epoxy resin composition and a silane coupling agent bonded to the steel surface. A top coating consisting essentially of coal tar enamel is bonded overtop the primer coating.
The invention thus provides in its various embodiments improved products and methods relating to waterproofed steel pipe. The improved processes are very conveniently conducted, and provide quick cure times and thus high throughput in manufacturing operations. In addition, the resulting waterproof coatings exhibit excellent bonding properties and resistance to impact, cathodic disbondment, and water penetration. Additional objects, features and advantages of the invention will be apparent from the following description.
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Henegar C. Sherill
Johnson John R.
Roder William R.
Hook James
Reilly Industries Inc.
Woodard Emhardt Naughton Moriarty & McNett
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