I. FIELD OF THE INVENTION

[0001] This invention pertains to damage and leakage at the threaded junction of a tube plug and a plugsheet of a heat exchanger, particularly when tube plugs are removed during maintenance of air cooled heat exchangers (ACHEs), and pertains to a method for solving this thread damage problem in remote locations in the field.

II. BACKGROUND AND PRIOR ART

[0002] Heat exchangers such as air cooled heat exchangers (ACHEs) and other heat exchangers operating continuously and often at elevated temperatures, sometimes develop leaks in heat exchange tubes or at junctions of ends of heat exchange tubes with a tubesheet or at junctions of tube plugs in plugsheets. During maintenance, cleaning, inspection, repair and/or upgrade functions, forcible removal of tube plugs often results in serious damage to threads in plugsheets and/or tubes. This damage to threaded surfaces occurs often due to galling of adjacent contacting threaded surfaces where surface material is damaged or even removed.

[0003] Prior art includes various tube plugs with internal ducts for fluid sealant as listed below; however, none indicate any awareness of the problem or present solution for damaged threads in plugsheet and/or in heat exchange tube apertures in ACHEs in remote locations with normal repair apparatus being unavailable and a severe need for a quick and feasible solution to avoid lengthy and costly shutdowns: US patent numbers 3,240,379; 3,434,743; 3,472,301; 4,114,654; 5,249,899; 6,588,999; 6,604,899; 6,896,462; 6,902,366; 8,439,220; 2004/0109738; and JP 1993-087488.

III. OBJECTS AND SUMMARY OF THE NEW INVENTION

[0004] The present invention addresses certain problems that occur in maintenance, inspection and repair of heat exchangers and particularly the problem of damaged threads of tube plugs and plugsheets when the tube plugs are forcibly removed. [0005] One object of this invention is to provide a relatively swift and feasible solution to leakage where threads of a plugsheet and/or of a tube plug are damaged, and particularly where thread damage occurs in heat exchangers in remote locations where comprehensive repair apparatus and replacement parts are not available.

[0006] One device to address the above leakage problem is to form a conventional solid tube plug into a replacement tube plug having internal passageways for delivery of a fluid sealant to damaged threads of tube plugs and mating threaded holes in plugsheets

[0007] By the present invention a replacement tube plug may have a central bore extending less than the length of the tube plug and axially spaced branch bores extending radially to outer threaded surfaces of the tube plug. The central bore and branch bores provide passageways for a fluid sealant material to be directed through the tube plug to the regions of the threads of the tube plug and of the plugsheet. A threaded screw or other closure means will close the central passageway after fluid sealant is directed through the tube plug to the threaded region.

[0008] A still further object is to provide a method for modifying a standard solid threaded tube plug into a replacement sealing tube plug by drilling in the standard plug a central passage with radial branch passages extending to the threads. A threaded cap closes the central bore, this method of modifying a standard tube plug being feasible with minimal equipment in remote locations the field.

[0009] An exemplary replacement tube plug for sealing a threaded plug-to- plugsheet junction comprises: a. a body part having length between proximal and distal ends and a threaded outer surface, b. a main internal passageway extending generally axially from said proximal end distally a distance less than the length of said body part, c. at least one branch passageway in fluid communication with said main passageway and extending radially outward to and through said outer threaded surface, thereby defining a continuous passageway open at said proximal end of said body part and open at said threaded outer surface of said body part, and d. a cap positionable to close said proximal end opening of said main passageway.

[1010] A further exemplary embodiment is a tube plug wherein said at least one branch passageway comprises a plurality of branch passageways that are axially spaced apart relative to each other lengthwise of said body part.

[1011] A still further exemplary embodiment is a tube plug wherein said at least one branch passageway comprises a plurality of passageways which extend in different outward directions circumferentially spaced from each other.

[1012] In the above-described tube plug said at least one branch passageway may comprise a plurality of branch passageways which are axially spaced apart from each other lengthwise of said body part and which extend in different outward directions circumferentially spaced from each other.

[1013] Another exemplary embodiment is a tube plug wherein said at least one branch passageway comprises:

(i) a first branch passageway, (ii) a second branch axially spaced apart from said first branch passageway, and

(iii) the third branch passageway axially spaced from both said first and second branches, where all three branch passageways are circumferentially spaced apart 120° from the each other.

[1014] A still further exemplary embodiment is a tube plug wherein said main passageway is situated centrally of said body part, and said at least one branch passageway extends radially outward at an angle about 90° from said main passageway.

[1015] The present invention further includes a method of converting a standard solid externally threaded tube plug having proximal and distal ends along its length, into a replacement tube plug adapted to deliver fluid sealant to the region of mating threads between said tube plug threaded into a tubesheet, comprising the steps: a. drilling a central bore hole axially through said proximal end in said solid tube plug in the distal direction a distance less than the length of said solid tube plug, b. drilling at least one branch duct radially inward from said outer surface threaded region to intersect said central bore hole, thereby defining a continuous passageway open at said proximal end of said body part and open at said threaded outer surface, and c. forming threads at said proximal end of said central bore hole to receive a screw to close and seal said proximal end of said bore hole.

[1016] The present invention further includes a method of directing fluid sealant to the region of mating threads between a tube plug screwed into a bore of a plugsheet by modifying a standard solid tube plug which has proximal and distal ends, comprising the steps: a. forming threads in said bore of said plugsheet corresponding to the external threads on said tube plug, b. drilling in said solid tube plug a central internal passageway extending from the proximal end and a distal direction a distance less than the length of said tube plug, c. drilling at least one branch duct from said outer thread region radially inward to and intersecting said central internal passageway, and d. forming threads in the proximal end of said central passageway adapted to receive a screw to close said passageway.

[1017] In the above method, drilling said at least one branch duct comprises drilling three branch passageways axially spaced apart lengthwise of said tube plug body part and circumferentially spaced apart each from the others.

[1018] The present invention thus includes a method of sealing the open end of an aperture in a plugsheet with a solid tube plug having a body part with proximal and distal ends, comprising: a. forming threads in said aperture, b. forming mating external threads on the outer surface of said body part of a tube plug, and c. forming in said tube plug an internal passageway extending from the plug's proximal end opening distally a distance less than the length of said body part, forming branch passageways from said internal passageway radially outward to the threads. In regard to the invention described herein the branch passageways have been described as extending radially, but they may take any path from the main passageway to the external thread region. Also, the main passageway may be other than central. [0019] These and other advantages of the invention will be further understood and appreciated by those skilled in the art by reference to the following written specification, claims and appended drawings.

IV. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is and elevation view of a prior art he exchanger installation,

[0021] Figure 2 is an enlarged fragmentary view of a prior art tube plug installed in a plugsheet of Figure 1,

[0022] Figure 3 is a perspective view showing the new tube plug,

[0023] Figure 4 is a fragmentary elevation view in section showing the new tube plug installed in a plugsheet,

[0024] Figure 5 is a sectional view taken along line 5-5 in Figure 4 showing central and radial passageways in the tube plug,

[0025] Figure 6 is a side elevation view of the new tube plug,

[0026] Figure 7 is a distal end elevation view thereof,

[0027] Figure 8 is a proximal end elevation view thereof, and

[0028] Figure 9 is a sectional view taken along line 9-9 in Figure 6 showing internal central and radial passageways.

[0029] Features of the invention will become apparent from the following description of the exemplary embodiments taken in conjunction with the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] For convenience and clarity in describing these embodiments, similar elements or components appearing in different Figures will have the same reference numbers.

[0031] Figure 1 shows schematically a prior art air cooled heat exchanger (ACHE) 1 with multiple rows of heat exchange tubes 2A, 2B, 2C, etc., having fins 3 along their length. These heat exchange tubes extend between the opposite tubesheets 4A, 4B which are supported in frame 6. The ends 10 of the heat exchange tubes are mounted in the tubesheets 4A, 4B, and are in fluid communication indicated by arrows 5 with inlet and outlet manifolds (headers) 8A, 8B respectively. Outward of tubesheets 4A, 4B are plugsheets 4C, 4D. The finned outer surfaces of the respective heat exchange tubes are exposed to ambient air which may move by natural convection or may be exposed to forced air flow indicated by arrow 14 (fans or blowers not shown).

[0032] Figure 2 is a fragmentary enlarged view of a prior art tube plug 20 whose outer surface 22 is threaded and engages mating threads 24 in the aperture 26 in plugsheet 4C. Damage to threads 24 on tube plug 20 or threads 26 in plugsheet 4C are the principal subject of the present invention, as it is these threads which become damaged when a tube plug 20 is forcibly removed for maintenance or other purposes. Threaded surfaces often become galled and may be seriously damaged when removed, such that they can longer provide a fluid tight seal when re-installed.

[0033] Figures 3-9 illustrate a new tube plug 40 of the present invention which has head or flange 41, stem or body 42 and central passageway 43. As seen in Figure 4 tube plug 40 has length L2 of passageway 43 less than the total length LI of the tube plug and diameter Dl of body 42 less than diameter D2 of tube plug head 41. Figures 4, 5 and 7-9 illustrate how branch passageways 44 intersect central passageway 43 and extend radially outward to the threaded region. Figure 4 also shows how the three passageways 44 are axially spaced apart along the length of the tube plug stem or body part 42. Figures 5 and 7-9 show how passageways 44 are displaced 120° circumferentially from each other. These branch passageways 44 as illustrated, extend at 90° from central passageway 43, but they may extend at other angles or along other paths. This array of branch passageways allows a wide distribution area of fluid sealant 56 along and around the threads to achieve a reliable seal. Many commercial sealants are available, one example being a product sold under the label "XX Heavy Sealant #5050" by Sealweld Corporation, Calgary, Alberta, CA. Tube plug threads 52 engaged plugsheet threads 54, and sealant 56 as shown is forced into areas of damaged threads; however, sealant will not flow into regions of undamaged and tight thread engagement.

[0034] Also seen in Figure 4, after the sealant 56 is injected through central passage 43, cap screw 46 is threaded into the proximal end of passageway 43 to block escape of sealant and to block inlet of debris. Cap screw 46 may serve the additional purpose when screwed end, of pushing or compressing sealant 56 to flow in central passage 43 and thence out through branch passages 44.

[0035] While the invention has been described in conjunction with several embodiments, it is to be understood that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, this invention is intended to embrace all such alternatives, modifications, and variations which fall within the spirit and scope of the appended claims.