Boiler plug
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The invention relates to an apparatus for quickly and inexpensively plugging leaks in the tubing of low pressure steam boilers. The invention uses a cap containing a gasket channel of the same diameter as the edge of the tube. The underside cylindrical wall of the cap contains an aperture in common with that of the top of the cap. A threaded rod is passed through the cap and connected to an identical plug on the other end of the tube. Simultaneously tightening hex nuts on the two rods seals the tubing ends.

Ivery, James (New York, NY, US)
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Attorney, Agent or Firm:
Richard C. Litman (Alexandria, VA, US)
I claim:

1. A plug for sealing leaking boiler heat exchanger tubes comprising: a circular steel concave cap having a top and under side; an aperture through the top center of the cap, a major circumference greater than the circumference of the tube; a channel within the major circumference of the cap on the cap under side wherein the circumference of the channel is the same as the circumference of the tube; an elongated steel cylindrical wall proceeding from the under side of the cap and having a minor circumference less than the circumference of the channel, said cylinder wall having an aperture through the length of the cylinder continuous with the aperture at the top side of the cap; a gasket contained in the channel; a rod through the cap and wall apertures, said rod containing a gasket means to seal the top of the cap aperture; and means to compress and seal the plug onto the tube.

2. The plug according to claim 1 wherein said cap wall has a frustum shape.

3. The plug of claim 1 wherein the diameter of the tube is three inches.

4. The plug of claim 1 wherein the channel is a rectangular cross section channel on the under side of the cap.

5. The plug of claim 1 wherein the channel gasket has a rectangular cross section

6. The plug of claim 1 wherein the gasket is prepared from asbestos

7. The plug of claim 1 where said rod is a full threaded rod longer than the leaky tubes

8. The rod of claim 8 placed through the cap and cylinder apertures and having a plastic gasket, steel washer and hex nut on the rod above the cap

9. The rod of claim 9 placed through the cap and cylinder apertures and having a plastic gasket, steel washer and hex nut on the rod above the cap

10. A method for seating and sealing plugs to cap leaking boiler heat exchanger tubes comprising: preparing two plugs according to claim 1 containing threaded rods; inserting the two plugs on opposing ends of a tube with the tube ends in contact with the two channel gaskets; adding gasket, washer and hex nuts to the ends of the rods; tightening the hex nuts to force the tube ends into the channel gasket



1. Field of the Invention

The present invention relates to low pressure water tube steam boilers. The invention particularly relates to an apparatus for quickly and inexpensively plugging leaks in the tubing of low pressure steam boilers.

2. Description of the Related Art

Low pressure tube steam boilers operating at about 12 lb steam pressure are in demand today for applications in industrial, commercial and public buildings. They are a vintage technology and serve their operators very well for many years when they are properly maintained. However, in time or under unusual circumstances leaks develop in the flue gas-to-water steel tube heat exchanger or conduits. These leaks, if unattended, will quickly damage other parts of the tubular heat exchanger bundle and can require a major overhaul or replacement of the entire heat exchanger. In that eventuality, the boiler may be out of service for an unacceptable length of time while the exchanger is being replaced.

The answer to the boiler tube leak problem when it occurs is a prompt plugging of the faulty tube with a tubing cross-sectional plug at a position upstream of the fluid flow. That has been the answer to tube leaks for many years, but with only partial success. The plugs that have been used in past years have themselves, sooner or later, leaked. Besides, some of them are expensive and require the boiler output to be sharply turned down, sometimes for days, before the corrective installation is complete. Some plugs have been proposed that can be installed in the boiler on-the-fly, i.e., while the boiler is still hot. While limiting the boiler total down time, these plugs, sooner or later, leak as well.

U.S. Pat. No. 5,016,674 to Kiss claims a plug for leaky tubes of a heat exchanger. The plug consists essentially of a frustrum shaped tapered hollow plug with the diameter of the top of the frustrum being the widest of the plug. A plug nut is formed on the top of the plug as part of the plug as manufactured. A threaded rod is connected to the plug nut by passing through the hollow plug; the exposed end of the rod receives a gasket and a rod nut. An “O” ring is inserted inside the leaky tube around the plug. The plug diameter at the top is less than the outside diameter of the end of the tube. Accordingly, nothing protrudes past the outside surface of the end of the tube. This allows close packing of the tubes of the heat exchanger bundle. It is claimed that the “O” ring itself, once compressed by tightening the rod nut, forms a seal that prevents the water and hot gas from mixing.

U.S. Pat. No. 685,561 to Bettermann describes a flue plug for plugging the ends of a boiler flue. The plugs are tapered in shape with annular flanges dished on their under sides. A connecting rod passes through the two plugs with a means for tightening the plugs to push the ends of the plugs into the ends of the flue.

None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus, a boiler plug solving the aforementioned problems of leak sealing is desired.


The boiler plug system of the invention is intended for plugging leaks in the steel tube flue gas-to-water heat exchangers of low pressure steam boilers which, on average, reach operating steam pressures of about 12 pounds (lbs). Excursions above 12 lbs may occur briefly, up to about 16 lbs, but only briefly. Lower operating pressures as low as 8 lbs may be maintained for a period of time to complete some ordinary maintenance of the boiler or because of low energy demand. However, to those skilled in the art it is well known that fixing leaks in the heat exchangers of high pressure boilers is a substantially different matter than that of low pressure boilers.

The preferred size of heat exchanger tubes to which the boiler plug of the invention applies is 3 inch inside diameter (ID). This is a commonly accepted size for boiler heat exchanger tubing in the industry; however, larger or smaller ID tubing can be used if the design boiler capacity substantially increases or decreases. In this specification, the elements of the invention will be described as applied to three inch ID steel tubing heat exchangers with the understanding that the boiler plug of the invention can be made smaller or larger as the particular application may require. The boiler plug of the invention is readily applicable to heat exchanger tubing of 2 to 4 inch ID.

The boiler heat exchanger panel consists of a closely packed bundle of lengthy steel tubes having a diameter of about three inches. Hot flue gasses passing from the fire box exchange heat through the tube wall with circulating water. Due to the hot flue gasses corrosive nature, tubing leaks frequently occur. These leaks must be corrected relatively promptly before a leak compromises the integrity of adjoining tubes and worsens the problem. The heat exchanger flue tubing is cut and a boiler plug is inserted to end the leaking.

The boiler plug of the instant invention seals the open end of the tubing by combining two techniques: 1) placing a steel cap over one end of the tube fitted with a precise tube end-to-cap gasket and the same type cap and gasket on the other end of the tube; 2) tighten down both caps by screwing down on nuts on the ends of a threaded rod that passes through the length of the tube and through the center of both metal caps. By this technique the line of the rod from one cap to the other cap runs exactly down the center of the tube circumference of the plug of the instant invention. Consequently, the force pulling on both end gaskets is equal around the circumference of the gaskets. This eliminates any tendency for any side of a gasket to lift and produce a suitable situation for a new leak to develop.

The major parts of the boiler plug of the invention are as follows: a domed or dished steel cap having an aperture or hole at the peaking center of the dome and a maximum circumference marginally greater than the circumference of the end of the tube. A circular channel is inscribed within the dished under surface of the domed cap next to and abutting the dome cap's major circumference edge. The circumference of the channel is the same as the circumference of the edge of the tube. The channel is designed to hold a gasket which exactly mates with the terminal edge of the tube. Preferably, the gasket is made of asbestos; however, thermally stable rubber or plastic may be used.

Attached and part of the dished under surface of the dome cap is a frustum shaped, thick wall cylinder having a center opening or aperture extending from top to bottom; the top major circumference of the cylinder is attached to the under part or dished part of the cap with the cylinder opening or aperture and the cap aperture corresponding in true alignment.

A steel rod threaded at both ends or completely threaded end-to-end is passed through the first cap and cylinder openings. The rod is longer than the length of the tube which usually runs 9 to 12 feet in length. A second plug cap and assembly of the invention is placed on the opposing open end of the tube with the rod passed through the second plug cap. The rod may be a single, continuous rod or it may be sections of threaded rod joined together by one or more couplings Next, plastic gaskets are fitted onto the ends of the rod followed by steel washers and hex nuts. The hex nuts at both ends are completely tightened, forcing the gaskets within each channel down onto the ends of the tube to seal the tube from leaking.

An important element of the boiler plug of the invention is the design of the channel and gasket that combines with the end of the tube. The gasket is preferably a flat ring with a rectangular cross-section as wide as the width of the channel cross-section. The depth or height of the channel ring gasket is at least as deep as the depth of the channel in which it is to fit or preferably slightly somewhat greater than the depth of the channel. When the plug is pressed against the end of the tube the tube end contacts the gasket in place in the channel. The tube end is then pressed onto the gasket with great force when the opposing plugs on the threaded rod are simultaneously tightened, thereby sealing the tube end and assuring the end of the leakage.

Another important element of the invention is the design of the frustum shaped cylinder attached to and part of the dished bottom of the domed cap where both apertures are in line. The shaped cylinder helps assure that the rod, when passed through the cap and shaped cylinder will remain centered within the length of the tube as the rod connects with the opposite plug. Boiler tubes are long, i.e., nine to twelve feet in length. If the rod is even slightly misaligned at one end, it will be significantly out of line when it reaches an opposing end. Consequently there will be an unequal distribution of radial forces on the opposing end gasket and a leak there will eventually develop.

These and other features of the present invention will become readily apparent upon further review of the following specification and drawings.


FIG. 1 is an environmental angular view of the boil plug of the invention as installed in repair of a section of boiler tubing.

FIG. 2 is a side view cutaway of the boiler plug and rod of the invention as installed in repair of a section of boiler tubing

Similar reference characters denote corresponding features consistently throughout the attached drawings.


The present invention as displayed in FIG. 1 consists of two virtually identical boiler plugs (10) of the invention installed on the ends of a boiler tube (11). The installation is employed merely to facilitate an understanding of the invention which consists of the boiler plug (10) itself. As illustrated, the boiler plug consists of a domed cap (12) preferably having a dished or concave under side with an extended wall (14) attached to and part of the domed cap underside. The extended wall (14) describes a truncated hemisphere or frustum in shape. The major circumference of the wall part of the domed cap underside and the minor circumference (20) form the terminus of the extended wall (14). Through the crest or center of the domed caps there is an aperture or opening through the cap large enough to admit a long threaded rod (18) sufficient to pass through the aperture of a virtually identical opposing cap (12a). The rod may be a continuous single rod or assembled in sections using couplings (22).

A circular channel for seating a gasket is contained in the under side of the cap. The channel preferably has a rectangular cross-section with a circumference larger than the maximum circumference of wall (14) and equal to the circumference of the tube (11). The gasket (24) is circular in shape with a rectangular cross-section sized to fill the channel's rectangular cross-section.

To each end of rod (18) is added a gasket (26), a washer (28) and a hex nut (30) in that order. Upon the simultaneous tightening of both hex nuts the ends of the tube are pressed into the gaskets (24) to seal the tube ends while the gaskets (26) seal the apertures in the domed cap.

Referring to FIG. 2, the figure shows the domed cap (10) with the frustum shaped wall (14), the tube (11), rod (18), the aperture gasket (28), washer ((26) and hex nut (30). FIG. 2 also shows the circular gasket (24) which sits in the circular channel (32) in contact with the edge of the tube The circumference of tube and channel are the same.

While a circular steel domed cap is preferred as the terminal piece in the boiler plug of the invention, other shapes such as square and rectangular steel caps may be used. The caps may assume any shape that can contain the same round gasket channel and a frustum or similar shaped long wall. The long wall and the thick cap aperture opening function together to assure that the direction of the rod when inserted remains true to the center of the tube circumference. This avoids biasing the seating of the opposing channel gasket.

The gasket used to mate with the end of the tube in the cannel gasket holder can be made from a variety of thermally stable gasketing material including asbestos, plastic materials, soft metal and mineral compositions and the like as known in the art.

It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.