Patent Application
20060144843
1. Field of the Invention
The subject invention relates to pressure vessels for fluid storage, and more particularly to a metallic tank having a molded plastic liner, a thermal barrier for protecting the plastic liner during assembly of the vessel, and a connector for joining the metallic tank and plastic liner together.
2. Background of the Related Art
Pressure vessels that combine the strength of an exterior metallic tank and the passivity of an interior plastic liner are well known in the art. Such tanks have achieved widespread usage in the field of domestic fluid storage, including hot water storage tanks, hot water heating tanks and accumulators for hot water heating systems.
Because of the enclosed nature of these pressure vessels, they are more easily fabricated in several sections, which are subsequently welded together. However, great care must be taken when welding the tank sections together, to avoid damaging the interior plastic lining. Any damage or discontinuity in the lining could result in the eventual contamination of the contents of the tank and corrosion of the exterior metal components.
Several attempts have been made to overcome this problem. One solution has been to apply a liner coating to the metal tank after it has been welded together, as exemplified in U.S. Pat. No. 2,758,367. However, this limits the types of coatings that may be applied to the interior of a closed vessel. The process is also time consuming and expensive, and there is no assurance that the lining will completely cover the interior of the vessel as intended.
Another method of fabricating lined, multi-piece metallic vessels involves the use of a chill ring placed in the interior of the metallic vessel adjacent the weld area. The chill ring is usually an annular metal structure, which may or may not have a coating thereon. It serves to absorb the heat generated by the welding process such that it does not destroy the tank lining. The use of chill rings is disclosed in U.S. Pat. Nos. 2,412,271 and 2,970,719.
It is also known to utilize a rubber material as an insulating band installed adjacent to a welding area, as set forth in U.S. Pat. No. 2,587,840. However, the purpose of this insulating band is not to protect the lining of the tank, but to prevent the current generated by the electric welding process from jumping to an adjacent metallic wall.
Commonly assigned U.S. Pat. No. 4,241,843 discloses unique features to enable the welding of two metal tank sections together without causing damage to an interior plastic liner. In this instance two vertically divided foam insulation halves surround the interior plastic liner to form a heat shield around the liner and prevent damage thereto during the welding process.
U.S. Pat. No. 5,046,638 discloses a pressure vessel having an interior plastic liner, wherein a sacrificial fluoropolymer layer of material is provided adjacent the weld area, between the liner and the metallic tank, to protect the liner layer from the heat of weld formation.
Another problem associated with manufacturing a pressure vessel with an external metallic tank and a non-corrosive internal plastic liner is providing a cost efficient means for connecting the two structures together to form an integral vessel. The prior art is replete with connectors for this purpose. However, many are susceptible to leakage. Leakage at the connector can cause corrosion of the metallic components of the pressure vessel and can damage system components carrying fluid to and from the pressure vessel.
Clearly, there is a need in the art for a pressure vessel having an external metallic tank and in internal plastic liner that includes a insulated barrier for protecting the plastic liner from thermal damage during vessel assembly, and a leak-proof connector for joining the metallic tank and plastic liner together to form an integral vessel.
The subject invention is directed to a unique pressure vessel, which combines the strength of a metallic tank with the interior passivity of a plastic tank. The pressure vessel comprises a lower metallic dome having a lower rim portion, an upper metallic dome having an upper rim portion, and a plastic liner disposed within the upper and lower metallic domes. A metallic band is disposed between the plastic liner and the upper and lower metallic domes proximate the respective rim portions thereof, and an insulating material is disposed between the metallic band and the plastic liner. The metallic band and insulating material protect the plastic liner from elevated temperatures that are presented when the upper and lower rim portions of the metallic domes are welded together.
Preferably, the plastic liner is molded and has a circumferential recess about its horizontal midline for accommodating the insulating material and the metallic band. The upper rim portion of the upper metallic dome preferably forms a circumferential flange that surrounds the lower rim portion of the lower metallic dome to form weld joint.
The upper metallic dome includes a central orifice and the plastic liner includes a cylindrical neck portion that extends through the central orifice in the upper metallic dome. An annular mounting flange is welded or otherwise secured to the upper metallic dome and is dimensioned and configured to surround the cylindrical neck portion of the plastic liner. The annular mounting flange has an upper planar surface, and circumferentially spaced bolt holes are formed in the upper planar surface.
An annular connector flange is also provided. The connector flange has a radially inner annular portion that defines a central bore for communicating with the central orifice in the upper metallic dome and a radially outer annular portion configured for fastening to the annular mounting flange. An annular groove is formed between the radially inner and radially outer annular portions of the connector flange for accommodating the cylindrical neck portion of the plastic liner.
The radially outer annular portion of the connector flange has a lower planar surface and circumferentially spaced apart bolt holes are formed therein which correspond to the circumferentially spaced apart bolt holes formed in the upper planar surface of the annular mounting flange. Bolts extend through these holes to securely fasten the connector flange to the mounting flange. Preferably, a planar sealing gasket is disposed between the upper planar surface of the mounting flange and the lower planar surface of the radially outer annular portion of the connector flange. In addition, a radially inner edge of the radially outer annular portion of the connector flange is preferably truncated to form a sealing surface to accommodate an O-ring seal positioned about the periphery of the cylindrical neck portion of the plastic liner. This seal prevents liquid inside the plastic liner from contacting the metallic components of the pressure vessel.
The subject invention is also directed to a pressure vessel that comprises a lower metallic dome having a lower rim portion, an upper metallic dome having a central orifice formed therein and an upper rim portion secured to the lower rim portion of the lower metallic dome. A molded plastic liner is disposed within the upper and lower metallic domes and it includes a cylindrical neck portion that is dimensioned and configured to extend through the central orifice of the upper metallic dome. A mounting flange is secured to the upper metallic dome and it surrounds the cylindrical neck portion of the plastic liner.
The pressure vessel further includes an annular connector flange having a radially inner annular portion that defines a central bore for communicating with the central orifice of the upper metallic dome, a radially outer annular portion for fastening to the annular mounting flange, and an annular groove that is formed between the radially inner and radially outer annular portions of the connector flange for receiving or otherwise accommodating the cylindrical neck portion of the plastic liner.
The subject invention is also directed to a method of fabricating a pressure vessel which includes the steps of providing a molded plastic tank liner, circumscribing the horizontal midline of the plastic tank liner with a layer of insulation, and surrounding the layer of insulation with a metallic band. The method further includes the steps of enclosing the plastic tank liner within upper and lower metallic domes, forming a joint between the upper and lower domes proximate the metallic band, and then welding the domes to one another at the joint. Preferably, the step of forming a joint between the domes involves forming a lap joint between an upper rim portion of the upper metallic dome and a lower rim portion of the lower metallic dome, which is subsequently welded.
These and other aspects of the pressure vessel of the subject invention and the unique connector flange therefor will become more readily apparent to those having ordinary skill in the art from the following detailed description of the invention taken in conjunction with the drawings.
So that those having ordinary skill in the art to which the present invention pertains will more readily understand how to make and use the lined pressure vessel of the present invention, embodiments thereof will be described in detail hereinbelow with reference to the drawings, wherein:
Referring now to the drawings wherein like reference numerals identify similar aspects and/or features of the subject invention there is illustrated in
Referring to
A metallic band 20 is disposed between the plastic liner 18 and the upper and lower metallic domes 12, 14, proximate the respective rim portions 12a, 14a thereof. Metallic band 20 is preferably formed from steel or a similar metal, and has a preferred thickness of about 0.0234″ (24-gage). However, the thickness of the band can vary from one vessel to another depending upon specific design criteria. In addition, at least one layer of insulating material 22 is disposed between the metallic band 20 and the molded plastic liner 18. The insulating material 22 is preferably a fiber material that is not thermally consumable under the heat produced by welding, which is generally about 1500° F. It is envisioned that the insulating material can be a material other than a fibrous insulating material. For example, foam based insulating materials or gel based insulating materials can be utilized.
The metallic band 20 and the insulating material 22 circumscribe the liner 18 and function as a thermal barrier to protect the liner 18 from the elevated temperatures that are presented when the upper and lower rim portions 12a, 14a of the upper and lower metallic domes 12, 14 are welded together to form an integral pressure vessel. More particularly, the metal band serves as a heat sink to disperse heat from the weld zone. In essence, the steel band 20 decreases the heat experienced by the insulating material, so that it will not reach its consumable temperature.
Referring to
To fabricate pressure vessel 10, the circumferential recess 24 located about the horizontal midline of the plastic tank liner 18 is circumscribed with a layer of insulation 22. The insulation 22 is then surrounded by metallic band 20. The plastic tank liner 18 is then enclosed within the upper and lower metallic domes 12, 14, forming a lap joint 25 therebetween proximate the metallic band 20. Thereafter, the domes 12, 14 are welded to one another at the joint 25.
Referring to
An annular mounting flange 32 formed from steel or a similar metal is welded or otherwise secured to the exterior surface of the upper metallic dome 12. Mounting flange 32 has a central bore 34 with an inner diameter that is substantially congruent with the outer diameter of the cylindrical neck portion 30 of the plastic liner 18 so as to achieve a close fit therebetween. As best seen in
The annular mounting flange 32 has a substantially planar upper sealing surface 32a. Circumferentially spaced bolt holes 40 are formed in the upper surface 32a, which extend substantially through the mounting flange 32. These bolt holes 40 are preferably threaded.
The pressure vessel 10 of the subject invention further includes an annular connector flange 42, the structure of which is best illustrated in
The outer diameter of the radially inner annular portion 44 is substantially congruent with the inner diameter of the neck portion 30 of plastic liner 18 so as to achieve a close fit therebetween, and preferably an interference fit is achieved. Connector flange 42 further includes a radially outer annular portion 48 that is shallower than the radially inner portion 44 of connector flange 42. That is the radially inner annular portion 44 has an axial thickness that is greater than the axial thickness of the radially outer annular portion 48.
Radially outer annular portion 48 is configured for ready fastening to the annular mounting flange 32. An annular groove 50 is formed between the radially inner and radially outer annular portions 44, 48 of connector flange 42. Annular groove 50 is dimensioned to intimately receive or otherwise accommodate the dimensionally controlled cylindrical neck portion 30 of the plastic liner 18, as best seen in
The radially outer annular portion 48 of connector flange 42 has a lower planar sealing surface 48a. Circumferentially spaced apart bolt holes 52 extend entirely through the radially outer annular portion 48. Bolt holes 52 correspond to the circumferentially spaced apart bolt holes 40 formed in the upper planar sealing surface 32a of annular mounting flange 32. These bolt holes 52 are preferably counter-sunk and may or may not be at least partially threaded, depending upon the type of bolts used for fastening the connector flange 42 to the mounting flange 32.
As shown in
As best seen in
The unique construction of connector flange 42 and the complementary way in which it mates with the neck portion 30 of the plastic liner 18 allows the plastic liner 18 and the external tank formed by domes 12, 14 to move independently. Accordingly, dimensional part tolerances and pressure variations experienced during service will not have an adverse effect on the integrity of the seal when bolts 45 are loaded.
It is envisioned and well within the scope of the subject disclosure that the metal band and insulating material described herein can be employed in the fabrication of three-piece pressure vessels. Such pressure vessels include a central cylindrical section bounded by upper and lower domes, so that two distinct weld zones are defined. In such an instance, a metal band and insulating material can be employed in each weld zone to protect a plastic liner enclosed within the three-piece pressure vessel.
Although the pressure vessel of the subject invention has been described with respect to a preferred embodiment, those skilled in the art will readily appreciate that changes and modifications may be made thereto without departing from the spirit and scope of the subject invention as defined by the appended claims.
