Fluid handling – Diverse fluid containing pressure systems – Fluid separating traps or vents
Reexamination Certificate
1997-06-27
2001-10-16
Michalsky, Gerald A. (Department: 3753)
Fluid handling
Diverse fluid containing pressure systems
Fluid separating traps or vents
C137S185000, C137S192000, C251S368000
Reexamination Certificate
active
06302136
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to steam valves having a valve plug or valve seat which have coated thereon a metal nitride and/or metal carbide coating.
DESCRIPTION OF RELATED ART
Steam is commonly transported under pressure (e.g., 35 kPa to 4200 kPa (5 psi to 600 psi)) through a pipe or tunnel system as a way to move energy from one location to another. Such energy is used, for example, for heating, drying, cooking, manufacturing processes, curing, or driving a turbine. In transporting the steam, at least some condensate or liquid water is usually formed. The condensate interferes with the efficient transport and heat transfer of the steam, particularly through a pipe. Steam valves are therefore commonly used to remove condensate from steam transport systems. Generally, such valves allow condensate to be released from the steam system, while preventing, or at least minimizing, the loss of steam during condensate release.
Steam valves typically are comprised of a conduit comprising a first opening (i.e., an inlet), a second opening (i.e., an outlet) and a passageway therethrough for (steam) fluid flow between the openings, the passageway including a valve plug and a valve seat, wherein the valve plug is movable relative to the valve seat between an “open” position where steam and condensate can pass through the passageway to the outlet for discharge, and a “closed” position where steam and condensate cannot pass through the passageway. Ideally, the steam valve allows condensate to flow through the passageway and to be discharged, while not allowing steam to pass through the passageway. Steam valves are frequently referred by the type of mechanism used to move or actuate the valve plug. Examples of steam valves include thermodynamic valves (e.g., disc valves), mechanical valves (e.g,., closed float valves, inverted bucket valves, and open bucket valves), and thermostatic valves (e.g., bimetallic valves, bellows valves, and liquid expansion valves).
Poor or defective operation of a steam valve(s) can lead to a substantial waste of energy, which in turn can lead to a substantial waste of money and natural resources. For example, as discussed in “Industrial Steam Trapping Handbook,” Yarway Corp., 1984, page 3, if 10% of the valves in a 6,000 steam valve system do not close after the condensate has been released, and 9.1 kg (20 pounds) of steam is lost per (non-closed) valve per hour, then 131,000 kg (288,000 pound) of steam per day is lost. If the cost of steam is about $11.00/kg (about $5.00/lb.), then approximately $525,000 of steam is lost (and wasted) from the system per year.
The general mechanical nature of steam valves makes them prone to wear and deterioration. A significant factor contributing to the shortened service life of a valve is typically corrosion. In addition to the steam, which is hot (about 100° C. or greater), water vapor, corrosive materials (e.g., carbonic acid is formed in steam systems from the reaction of CO
2
(e.g., from air) with water) and/or other contaminants (e.g., dirt, corrosion products, and sealants from the repair of leaky joints) are also frequently present. Another factor affecting service life of a valve is mechanical stress, which is due, for example, to repeated contacting of the valve plug and valve seat during the opening and closing of the valve. In many common steam systems, valves open and close several times per second.
Wear and deterioration of valves is generally most prevalent with the valve plug and valve seat. Typical steam pressures and velocities through steam pipes range from about 35 kPa to about 4200 kPa (5 psi to 600 psi) and about 145 km/hr to about 644 km/hr (90 miles/hr-400 miles/hr), respectively. The condensate (i.e., water droplets, which may include corrosive and/or other materials) can impact surfaces of the valve at significant velocities, further enhancing corrosion. Corrosion (e.g., resulting in pitting) of valve plug and valve seat surfaces which contact each other when the valve is closed are particularly troublesome. Such corrosion leads to an inability of the valve plug to properly couple with the valve seat and seal against or prevent passage of steam through the valve.
One approach to addressing the wear problem has been to harden (i.e., metallurgical hardening) the valve seats. Although hardening may reduce valve seat wear, the hardened valve seat may be more brittle, and hence more prone to fracture from repeated contact between the valve seat and valve plug.
One approach to addressing the corrosion problem has been to carefully monitor and control the boiler feed water in order to minimize contaminants (e.g., gases such as carbon dioxide) (see, e.g., “Industrial Steam Trapping Handbook”, Yarway Corp., Blue Bell, Pa., 1984, pp.11-12.). Although carbon dioxide is not itself corrosive, when combined with free hydrogen, (corrosive) carbonic acid can be formed.
Another approach to the corrosion problem has been to make components of the valve from more corrosion resistant materials such as stainless steel (see, e.g., “Industrial Steam Trapping Handbook,” supra) or carbide (containing tungsten carbide as the major hard constituent in a binder consisting mainly of cobalt and nickel) (see, e.g., U.S. Pat. No. 4,408,626 Fujiwara).
Still another approach to the corrosion problem has been to replace corroded or damaged components (e.g., the valve plug and valve seat) of the steam valve. Parts to repair or rebuild corroded or damaged steam valves are sold together, for example, as steam valve repair kits. For example, a repair kit for an inverted bucket steam valve typically contain a valve lever assembly (including a valve lever and plug), a valve seat, a guide pin assembly, and mounting hardware.
Although attempts have been made to address the corrosion problem, other solutions may be desirable.
SUMMARY OF THE INVENTION
The present invention provides a steam valve comprising:
(a) a conduit comprising a first opening, a second opening, and a passageway therethrough for steam fluid flow between the openings, the passageway including a valve seat that includes a valve seat mating surface; and
(b) a valve plug including a major surface which includes a valve plug mating surface, at least one of the valve plug or valve seat being moveable relative to the other (preferably, the valve plug is moveable relative to the valve seat) between at least a first position and a second position;
wherein in the first position the mating surfaces cooperate to substantially prevent flow of steam fluid through the passageway from the first opening to the second opening, and wherein in the second position the mating surfaces are positioned relative to each other to allow steam fluid to flow from the first opening to the second opening through the passageway, and wherein at least one of the mating surfaces has thereon at least one of a metal nitride or a metal carbide coating (wherein such language is intended to include combinations of metal carbide and metal nitride coatings). The term “steam fluid” refers to water vapor (steam), and/or liquid water (condensate) in a steam system, and optionally includes dissolved and/or undissolved gasses (e.g., CO
2
and O
2
), reaction products (e.g., carbonic acid), and/or other contaminants that are typically found in high pressure steam systems. Preferably, both the valve plug mating surface and the valve seat mating surface have the metal nitride and/or metal carbide coating thereon.
Preferred metal nitride coatings include coatings of titanium nitride (TiN), chromium nitride (CrN), zirconium nitride (ZrN), titanium-aluminum nitride (TiAlN), aluminum-titanium nitride (AlTiN), and titanium carbide-nitride (TiCN). Preferred metal carbide coatings include coatings of tungsten carbide (WC), hafnium carbide (HfC), silicon carbide (SiC).
In another aspect, the invention provides a steam valve repair kit comprising:
(a) a (steam) valve plug including a major surface which includes a valve plug mating surface, and
(b) a (steam) valve seat including a valve seat mating surface f
Booth Timothy N.
Weaver Billy Lee
Woiak Michael R.
3M Innovative Properties Company
Allen Gregory D.
Michalsky Gerald A.
Pribnow Scott R.
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