CA2213787A1 - Method for fabricating box headers for use in air cooled heat exchangers - Google Patents
Method for fabricating box headers for use in air cooled heat exchangersInfo
- Publication number
- CA2213787A1 CA2213787A1 CA 2213787 CA2213787A CA2213787A1 CA 2213787 A1 CA2213787 A1 CA 2213787A1 CA 2213787 CA2213787 CA 2213787 CA 2213787 A CA2213787 A CA 2213787A CA 2213787 A1 CA2213787 A1 CA 2213787A1
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- plate
- backing
- backing bar
- sheet
- box header
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- Butt Welding And Welding Of Specific Article (AREA)
Abstract
A method for fabricating a box header for use in an air cooled exchanger is provided, wherein the weld joints connecting the plates or sheets to be welded together to form the box header are prepared by securing backing bars along the two longitudinal edges of the two wrapper sheets, and securing the wrapper sheets in the desired position relative to the tube sheet and plug sheet, with the backing bars protruding away from the longitudinal edges of the wrapper sheets and abutting the adjacent tube or plug sheet to hold the pieces apart at a desired spacing. The backing bars also close off or isolate the welding process from the interior of the header and allow the root pass and any subsequent passes to be made using an automated welding process that, when performing the root pass, fuses together the adjacent sheets or plates and the backing bar. Full penetration welds are assured by using a high welding current facilitated by the isolation provided by the backing bar, and higher quality, more consistent root pass welding is attained by virtue of employing an automated welding process.
Description
METHOD FOR FABRICATING BOX HEADERS
FOR USE IN AIR COOLED HEAT EXCHANGERS
BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention is directed to a method for fabricating a box header of the type used in air-cooled heat exchangers.
FOR USE IN AIR COOLED HEAT EXCHANGERS
BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention is directed to a method for fabricating a box header of the type used in air-cooled heat exchangers.
2. Description of Related Art Air-cooled heat exchangers are commonly used in connection with engine and compressor cooling, for example, on skid mounted oil field compressor packages.
Examples of such heat exchangers can be seen in U.S.
Patent Nos. 3,627,037 and 4,437,512, assigned to Harsco Corporation, the assignee of the instant application.
Air-cooled heat exchangers typically employ box headers which receive a fluid to be cooled, and distribute the fluid into a plurality of tubes in which the heat exchange is effected. Box headers are also used to collect cooled fluid, and to direct the fluid to its subsequent destination.
Box headers are generally fabricated by welding four rectangular plates at right angles to one another into a box co~figuration. One of the rectangular plates will have a plurality of bores therein, and will serve as the tube sheet for the header. The air cooled exchangers and box headers must be fabricated and welded in accordance with the American Society of Mechanical Engineera (ASME) Boiler and Pressure Vessel Code, due to the service in which the air cooled exchanged will be placed.
Past practice for performing the fabrication of box headers has been to provide a bevel on one of the plates, and to leave an open root gap at the base of the beveled plate, as can be seen in FIG. 1. The two plates 10, 12 are joined by welding, and the open root gap 14 is bridged by a method employing manual welding for at least the first pass. Manual welding must be used for the root pass in this joint configuration in order to ensure that a full penetration weld is achieved. Manual welding is, however, time and labor intensive, and more prone to overall quality problems, than is automated welding.
The combination of using an open root gap in the joint configuration, and the need to effect a full penetration weld to achieve complete fusion, lead to the undesirable result that, in welding the plates together, the interior of the header will generally collect weld splatter and may otherwise be contaminated by the materials used in the welding process. This contamination must be cleaned out of the interior of the header, further increasing fabrication and labor time.
The only known variation on the open root gap joint configuration illustrated in FIG. 1 for fabricating box headers is shown in FIG. 2. In that joint, the open root gap is eliminated, and a bevel 20 is machined on the plate 22 that is to be positioned vertically during the welding operation, with the machined portion also providing a flat or support surface 24 on which the horizontally oriented plate 26 will rest and will be supported by the vertically oriented plate 22. While this alternate joint configuration reduces or eliminates the weld splatter and contamination problems associated with the open root gap configuration, a manual root pass is still necessary in order to ensure that a full penetration weld is achieved. In addition, this joint configuration changes the stress calculations for the header, and ultimately requires the use of more material and increased welding time to produce a satisfactory box header.
Another disadvantage of these prior art fabrication methods, and especially of the open root pass configuration of FIG. 1, is that it is labor intensive, not only in requiring a manual root pass, but also in requiring a considerable amount of hands-on labor to properly position and secure the plates relative to one another prior to the welding of the root pass. The plates making up the header have to be fit up by hand and the gap between each of the plates must be very carefully maintained. In this procedure, the plates making up the header, once properly positioned, are held together by the use of tack bars, which themselves interfere with the ability to continuously weld the root pass and the subsequent passes in the joint.
The use of a backing bar or chill ring has previously been proposed for use in welding two components to each other, principally for butt welding two pipe ends to one another. The principal reason that chill rings had .
previously been proposed for use in welding pipe joints was to prevent "icicles" from forming in the interior of the pipe from the molten metal produced in the welding process, and to prevent welding burn through. The chill rings also have been credited with facilitating the introduction of filler metal, such as a consumable electrode or welding rod or wire, during the first root pass.
The use of a chill ring or backing bar in general is not recognized in the art as rendering the joint susceptible to automated welding for the root pass. One prior patent, U.S. Patent No. 4,611,830, issued to vonAhrens, discusses the possibility of using an automated welding head to weld two pipe ends together, however, the chill ring which is disclosed in that patent as making automated welding a possibility, is provided with a protruding ridge of material that becomes filler metal when the welding operating is conducted. The patent otherwise discloses that manual welding operations are necessary when a simple backing bar or chill ring is employed.
Further, despite the fact that several prior patents have discussed the use of chill rings or backing bars in pipe welding operations, the reality in industry is that such chill rings or backing bars are highly disfavored.
Indeed, many companies, particularly in the oil and gas industry, do not permit the use of chill rings or backing bars in piping runs fabricated for their operations, and have specific prohibitions against the use of backing bars written into their welding specifications.
The most obvious drawback to the use of backing bars in welding pipe joints is that the backing bars create orifices in the finished piping runs, thereby reducing the flow capacity through the pipe, and thus requiring overdesign, l.e., increased pipe dia~eter to compensate for the presence of an orifice/backing bar, and increased cost for the system. The presence of this protrusion forming an orifice also presents a site for erosion and corrosion to take place. Additionally, the use of a backing bar in welding a pipe joint can reduce the joint efficiency from 100~ to 70~, also causing required overdesign and increased cost.
Backing bars can also interfere with the ability to obtain full penetration and complete fusion at the root of the pipe joint. This is especially the case where the backing bar or chill ring is provided with a radial protrusion that partially obstructs the toe of the bevels presented at the innermost part of each pipe end.
It is therefore a principal object of the present invention to provide an improved fabrication process for use in welding box headers, that overcomes the aforenoted problems with prior box header fabrication processes.
It is a further principal object of the present invention to provide a header box fabrication process that makes it pos~ible to use automated welding equipment beginning with the root pass, and to use greatly increased welding current to ensure increased penetration and a high quality root pass.
It is an additional important object of the present invention to provide a box header fabrication process that substantially reduces manual fit up time and the need to use tacking bars to secure the tube sheet, plug sheet, and wrapper sheets in the required positions, and to allow the use of simpler fixtures or clamps to permit the assembly to be easily tack welded to secure the pieces in position to conduct an automated welding procedure.
It is a further important object of the present invention to provide a box header fabrication process that produces a cleaner header interior by substantially preventing weld splatter from entering the interior, thereby also eliminating the labor necessary to clean the weld splatter out of the box header.
- It is a another important object of the present invention to provide a box header fabrication process that reduces the overall fabrication time and the actual hands-on labor time for producing the box header.
It is yet an additional important object of the present invention to provide a box header fabrication process having all of the aforenoted advantages and, at the same time, not requiring any recalculation of weld joint strengths or efficiencies.
SU~lARY OF T~E INVENTION
The above and other objects and advantages of the present invention are achieved by a fabrication process comprising securing a backing bar to a first of two plates that are to be welded together in forming the box header, such that the backing bar projects from the first plate to which it is secured for a distance equal to the gap between the plates that is to be employed in effecting the weld joint, and then positioning the two plates to be welded in a fixture such that the backing bar contacts or abuts the second plate substantially along the entire length of the joint to be welded. The process further includes performing a first root pass at the juncture of the first and second plates and the backing bar, and performing subsequent welding passes, using automated welding equipment, such as an automated submerged arc process.
The process will generally further include the steps of securing a backing bar at the toe of each of the longitudinally extending beveled edges for each of the four longitudinal welds that are to be effected, and positioning the four plates in a fixture or fixtures such that the protruding portions of the backing bars abut the flat plates, and then tacking the flat plates and backing bars into their final orientation and position. The process then will entail subjecting each of the four longitudinal weld joints to an automatic submerged arc welding process for a root pass that fuses the backing bar to the toe of the bevel and to the adjacent flat plate, and for any subsequent backing passes that may be necessary to fill each joint.
The process may further include conducting the process at a welding current on the order of 500 amperes, which is in excess of four times the current employed for making a manual root pass in fabricating box headers at present.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of the present invention and the attendant advantages will be readily apparent to those having ordinary skill in the art and the invention will be more easily understood from the following detailed description of the preferred embodiment taken in conjunction with the accompanying drawings wherein like reference characters represent like parts throughout the several views.
FIG. 1 is a cross-sectional end view of a prior art weld joint for a box header, in which an open gap is provided between the plates to be welded.
FIG. 2 is a cross-sectional end view of an alternative prior art joint configuration used in fabricating box headers.
FIG. 3 is an exploded perspective view of the pieces or components making up a typical box header that is the subject of the fabrication process of the present invention.
.
FIG. 4 is a perspective view of a header box to which the fabrication process of the present invention is directed, prior to the header box having been welded.
FIG. 5 is a top view of a beveled plate to be used in constructing the box header, with a backing bar tack welded thereto.
FIG. 6 iS an end view of the box header to be welded in accordance with the process of the present invention, illustrating the positioning of the plates and backing bars.
FIG. 7 is an end view of one of the joints of the box header, illustrating the condition of one of the weld joints after the root pass has been effected.
FIG. 8 is an end view of one of the joints of the box header, illustrating the joint after welding is completed.
FIG. 9 is a substantially schematic end view of a fixture that may be used to retain and position the backing bar relative to the beveled plate in securing the backing bar to the plate.
DETATT~T~n DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 3 of the drawings illustrates the components of a typical box header 100 to which the fabrication process of the present invention is directed. The box header 100 has a rectangular, longitudinally extending, tube sheet 102, into which heat exchan~e tubes (not shown) are inserted and secured, and an opposing plug sheet 104, to .
be disposed substantially parallel to the tube sheet 102.
The other two long sides of the box are made of plates referred to as top and bottom wrapper sheets 106, 108, respectively. The ends of the box header are covered and sealed by end plates 110, 112.
The box header as illustrated in FIG. 3 substantlally schematically represents that the box header, once fabricated into a single unit, will have a fluid inlet and outlet 114, 116, having bolt-through flanges 118, 120, that permit the header to be connected in line to receive and discharge a fluid to be cooled, as is well known in the art. It will be readily recognized that the number of and positioning of the inlets and outlets may vary considerably from application to application, and this forms no part of the instant invention.
FIG. 4 illustrates the tube sheet 102, plug sheet 104 and top and bottom wrapper plates 106, 108, of the box header, showing the final positioning of the components prior to welding. The end plates 110, 112 are not shown in this figure, in order to more clearly show the bevels extending along both longitudinal edges of both the top and bottom wrapper sheets.
In the prior art fabrication process previously discussed, a considerable amount of labor is involved in positioning and orienting these sheets, referred to as a "fit up", such that the necessary spacings between the toes of the bevels and the sidewalls of the tube sheet and plug sheet are set and maintained to provide the desired gap and weld joint geometry. In this prior art process, once a bevel is properly positioned relative to the tube sheet (for example), the spacing and joint geometry are maintained by welding tack bars bridging from the tube sheet to the wrapper sheet. Tack bars are used in the same manner to secure and retain the necessary spacing at each of the joints between the beveled edges of the wrapper sheets and the tube and plug sheets. In addition to this manual fit up being a very labor intensive process, the tack bars further interfere with the ability to provide a continuous weld bead along the entire extent of the joint, in that the tack bars obstruct access to portions of the joint, and require the welder to work around the tack bars.
These problems and disadvantages are overcome in the fabrication process of the present invention, as will now be discussed in greater detail with respect to FIGS. 5-8.
FIG. 5 shows one of the wrapper sheets 106, having the two bevels 122, 124, extending along the longitudinal edges of the sheet. In accordance with the process of the present invention, backing bars 126 are positioned to extend past the toes 123, 125 of the bevels for a distance equal to the desired spacing distance between the wrapper sheet and the tube sheet or plug sheet. The backing bars 126 are preferably secured to the wrapper sheets by tack weld, illustrated substantially schematically by broken lines designated with reference numeral 128. Although the tacking is shown as being done on the interior face of the wrapper sheet in FIG. 5, it will readily be appreciated that the tacking may be accomplished at the face of the bevel as well, if desired.
The step of securing backing bars 126 to each of the beveled edges may be accomplished with relatively little labor. The backing bar is preferably placed in a fixture 200, shown schematically in FIG. 9, that further provides for an automatic correct positioning of the beveled plate relative to the backing bar, once the beveled plate is brought into contact with the backing bar, and the two components are then quickly tacked together, represented by tack weld bead 128.
The use of backing bars 126 in the process of this invention eliminates the need to use tack bars to retain the tube sheet, plug sheet, and wrapper sheets in position for the welding of the joints, as can be seen in FIG. 6. The backing bars 126 are brought into abutting engagement with the tube sheet and plug sheet. The backing bars thus serve as spacers to maintain the desired distance between the inner faces of the tube sheet 102 and plug sheet 104 and the beveled edges 122, 124 of the wrapper sheets. Simple right angle fixturing or clamping, shown schematically in broken lines at reference numeral 202, may therefore be employed to hold the components in proper position, and the components themselves are tacked together prior to commencing the welding of the joints. Experience has shown that the instant process, in which backing bars are secured to the wrapper plates, is more than twice as fast as the above-described prior art fabrication process in reaching this stage where the four sheets or plates are secured in position for the welding of the seams.
Referring now especially to FIGS. 7 and 8, the fabrication process continues by making a root pass in one of the joints using an automated welding process to fuse the backing bar, the material at the toe of the weld, and the abutting plate material into the root of the weld. The fusion zone for the root pass is designated by reference numeral 130. Once the root pass is completed, the automated welding equipment is then used to make any subsequent passes 132 that may be necessary to fill the weld joint, as is known generally in the art. The process is repeated for each of the four required longitudinal welds. After any final inspection of the interior of the box header is performed, the end plates and inlets and outlets are then welded to the thus formed box in a conventional manner, to complete the fabrication.
The automated process employed in welding the longitudinal seams is preferably a submerged arc process, the operation of which is well known in the art. Other types of automated welding known in the art may be used as well. Automated welding produces far more consistent and high quality welds as compared with manual welding, and the ability to use automated welding for the root pass, enabled by the use of a backing bar, will greatly improve the quality and the consistency of the quality of the box header, while reducing fabrication costs.
The use of the backing bar to prevent splatter and blowthrough further enables the welding current to be greatly increased over the current generally employed in the prior art open root gap welding. A welding current on the order of 500 amperes is preferred in the present invention, as compared with a welding current of 120 amperes commonly used with the open root gap configuration. This increased amperage ensures that the root pass will produce a full penetration weld that includes, in the fusion zone, metal from the tube sheet or plug sheet, the adjacent wrapper sheet, and the backing bar. The backing bar presents blowthrough or weld splatter from entering the interior of the box header, even using a welding current that is more than four (4) times greater that the current employed in making the manual root pass of the prior art.
The use of backing bars 126 in forming the longitudinal weld seams in a box header does not, by nature of its joint designation under the ASME Code, require the joint to otherwise be redesigned or reconfigured. Unlike welds in pressure piping, no joint efficiency need be included in the calculations for the longitudinal welds for the box header. As noted previously, the use of a backing bar in pressure piping reduces the joint efficiency from 100 percent to 70 percent, causing significant changes in the design criteria for the joint.
The material used for the backing bar is selected to be compatible with the material from which the tube sheet, plug sheet, and wrapper sheet are constructed, as the backing bars will preferably remain in the header during the service life of the header. Use of the identical material or a weld-compatible material should ensure also that the backing bars are not subject to excessive corrosion from the process fluid. Plain carbon steel is a typical material from which box headers are constructed.
Although various details have been disclosed herein, it is to be understood that these are for illustrative purposes. Various modifications and adaptations will be readily apparent to those of ordinary skill in the art.
Accordingly, the scope of the present invention should be determined be reference to the claims appended hereto.
Examples of such heat exchangers can be seen in U.S.
Patent Nos. 3,627,037 and 4,437,512, assigned to Harsco Corporation, the assignee of the instant application.
Air-cooled heat exchangers typically employ box headers which receive a fluid to be cooled, and distribute the fluid into a plurality of tubes in which the heat exchange is effected. Box headers are also used to collect cooled fluid, and to direct the fluid to its subsequent destination.
Box headers are generally fabricated by welding four rectangular plates at right angles to one another into a box co~figuration. One of the rectangular plates will have a plurality of bores therein, and will serve as the tube sheet for the header. The air cooled exchangers and box headers must be fabricated and welded in accordance with the American Society of Mechanical Engineera (ASME) Boiler and Pressure Vessel Code, due to the service in which the air cooled exchanged will be placed.
Past practice for performing the fabrication of box headers has been to provide a bevel on one of the plates, and to leave an open root gap at the base of the beveled plate, as can be seen in FIG. 1. The two plates 10, 12 are joined by welding, and the open root gap 14 is bridged by a method employing manual welding for at least the first pass. Manual welding must be used for the root pass in this joint configuration in order to ensure that a full penetration weld is achieved. Manual welding is, however, time and labor intensive, and more prone to overall quality problems, than is automated welding.
The combination of using an open root gap in the joint configuration, and the need to effect a full penetration weld to achieve complete fusion, lead to the undesirable result that, in welding the plates together, the interior of the header will generally collect weld splatter and may otherwise be contaminated by the materials used in the welding process. This contamination must be cleaned out of the interior of the header, further increasing fabrication and labor time.
The only known variation on the open root gap joint configuration illustrated in FIG. 1 for fabricating box headers is shown in FIG. 2. In that joint, the open root gap is eliminated, and a bevel 20 is machined on the plate 22 that is to be positioned vertically during the welding operation, with the machined portion also providing a flat or support surface 24 on which the horizontally oriented plate 26 will rest and will be supported by the vertically oriented plate 22. While this alternate joint configuration reduces or eliminates the weld splatter and contamination problems associated with the open root gap configuration, a manual root pass is still necessary in order to ensure that a full penetration weld is achieved. In addition, this joint configuration changes the stress calculations for the header, and ultimately requires the use of more material and increased welding time to produce a satisfactory box header.
Another disadvantage of these prior art fabrication methods, and especially of the open root pass configuration of FIG. 1, is that it is labor intensive, not only in requiring a manual root pass, but also in requiring a considerable amount of hands-on labor to properly position and secure the plates relative to one another prior to the welding of the root pass. The plates making up the header have to be fit up by hand and the gap between each of the plates must be very carefully maintained. In this procedure, the plates making up the header, once properly positioned, are held together by the use of tack bars, which themselves interfere with the ability to continuously weld the root pass and the subsequent passes in the joint.
The use of a backing bar or chill ring has previously been proposed for use in welding two components to each other, principally for butt welding two pipe ends to one another. The principal reason that chill rings had .
previously been proposed for use in welding pipe joints was to prevent "icicles" from forming in the interior of the pipe from the molten metal produced in the welding process, and to prevent welding burn through. The chill rings also have been credited with facilitating the introduction of filler metal, such as a consumable electrode or welding rod or wire, during the first root pass.
The use of a chill ring or backing bar in general is not recognized in the art as rendering the joint susceptible to automated welding for the root pass. One prior patent, U.S. Patent No. 4,611,830, issued to vonAhrens, discusses the possibility of using an automated welding head to weld two pipe ends together, however, the chill ring which is disclosed in that patent as making automated welding a possibility, is provided with a protruding ridge of material that becomes filler metal when the welding operating is conducted. The patent otherwise discloses that manual welding operations are necessary when a simple backing bar or chill ring is employed.
Further, despite the fact that several prior patents have discussed the use of chill rings or backing bars in pipe welding operations, the reality in industry is that such chill rings or backing bars are highly disfavored.
Indeed, many companies, particularly in the oil and gas industry, do not permit the use of chill rings or backing bars in piping runs fabricated for their operations, and have specific prohibitions against the use of backing bars written into their welding specifications.
The most obvious drawback to the use of backing bars in welding pipe joints is that the backing bars create orifices in the finished piping runs, thereby reducing the flow capacity through the pipe, and thus requiring overdesign, l.e., increased pipe dia~eter to compensate for the presence of an orifice/backing bar, and increased cost for the system. The presence of this protrusion forming an orifice also presents a site for erosion and corrosion to take place. Additionally, the use of a backing bar in welding a pipe joint can reduce the joint efficiency from 100~ to 70~, also causing required overdesign and increased cost.
Backing bars can also interfere with the ability to obtain full penetration and complete fusion at the root of the pipe joint. This is especially the case where the backing bar or chill ring is provided with a radial protrusion that partially obstructs the toe of the bevels presented at the innermost part of each pipe end.
It is therefore a principal object of the present invention to provide an improved fabrication process for use in welding box headers, that overcomes the aforenoted problems with prior box header fabrication processes.
It is a further principal object of the present invention to provide a header box fabrication process that makes it pos~ible to use automated welding equipment beginning with the root pass, and to use greatly increased welding current to ensure increased penetration and a high quality root pass.
It is an additional important object of the present invention to provide a box header fabrication process that substantially reduces manual fit up time and the need to use tacking bars to secure the tube sheet, plug sheet, and wrapper sheets in the required positions, and to allow the use of simpler fixtures or clamps to permit the assembly to be easily tack welded to secure the pieces in position to conduct an automated welding procedure.
It is a further important object of the present invention to provide a box header fabrication process that produces a cleaner header interior by substantially preventing weld splatter from entering the interior, thereby also eliminating the labor necessary to clean the weld splatter out of the box header.
- It is a another important object of the present invention to provide a box header fabrication process that reduces the overall fabrication time and the actual hands-on labor time for producing the box header.
It is yet an additional important object of the present invention to provide a box header fabrication process having all of the aforenoted advantages and, at the same time, not requiring any recalculation of weld joint strengths or efficiencies.
SU~lARY OF T~E INVENTION
The above and other objects and advantages of the present invention are achieved by a fabrication process comprising securing a backing bar to a first of two plates that are to be welded together in forming the box header, such that the backing bar projects from the first plate to which it is secured for a distance equal to the gap between the plates that is to be employed in effecting the weld joint, and then positioning the two plates to be welded in a fixture such that the backing bar contacts or abuts the second plate substantially along the entire length of the joint to be welded. The process further includes performing a first root pass at the juncture of the first and second plates and the backing bar, and performing subsequent welding passes, using automated welding equipment, such as an automated submerged arc process.
The process will generally further include the steps of securing a backing bar at the toe of each of the longitudinally extending beveled edges for each of the four longitudinal welds that are to be effected, and positioning the four plates in a fixture or fixtures such that the protruding portions of the backing bars abut the flat plates, and then tacking the flat plates and backing bars into their final orientation and position. The process then will entail subjecting each of the four longitudinal weld joints to an automatic submerged arc welding process for a root pass that fuses the backing bar to the toe of the bevel and to the adjacent flat plate, and for any subsequent backing passes that may be necessary to fill each joint.
The process may further include conducting the process at a welding current on the order of 500 amperes, which is in excess of four times the current employed for making a manual root pass in fabricating box headers at present.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of the present invention and the attendant advantages will be readily apparent to those having ordinary skill in the art and the invention will be more easily understood from the following detailed description of the preferred embodiment taken in conjunction with the accompanying drawings wherein like reference characters represent like parts throughout the several views.
FIG. 1 is a cross-sectional end view of a prior art weld joint for a box header, in which an open gap is provided between the plates to be welded.
FIG. 2 is a cross-sectional end view of an alternative prior art joint configuration used in fabricating box headers.
FIG. 3 is an exploded perspective view of the pieces or components making up a typical box header that is the subject of the fabrication process of the present invention.
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FIG. 4 is a perspective view of a header box to which the fabrication process of the present invention is directed, prior to the header box having been welded.
FIG. 5 is a top view of a beveled plate to be used in constructing the box header, with a backing bar tack welded thereto.
FIG. 6 iS an end view of the box header to be welded in accordance with the process of the present invention, illustrating the positioning of the plates and backing bars.
FIG. 7 is an end view of one of the joints of the box header, illustrating the condition of one of the weld joints after the root pass has been effected.
FIG. 8 is an end view of one of the joints of the box header, illustrating the joint after welding is completed.
FIG. 9 is a substantially schematic end view of a fixture that may be used to retain and position the backing bar relative to the beveled plate in securing the backing bar to the plate.
DETATT~T~n DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 3 of the drawings illustrates the components of a typical box header 100 to which the fabrication process of the present invention is directed. The box header 100 has a rectangular, longitudinally extending, tube sheet 102, into which heat exchan~e tubes (not shown) are inserted and secured, and an opposing plug sheet 104, to .
be disposed substantially parallel to the tube sheet 102.
The other two long sides of the box are made of plates referred to as top and bottom wrapper sheets 106, 108, respectively. The ends of the box header are covered and sealed by end plates 110, 112.
The box header as illustrated in FIG. 3 substantlally schematically represents that the box header, once fabricated into a single unit, will have a fluid inlet and outlet 114, 116, having bolt-through flanges 118, 120, that permit the header to be connected in line to receive and discharge a fluid to be cooled, as is well known in the art. It will be readily recognized that the number of and positioning of the inlets and outlets may vary considerably from application to application, and this forms no part of the instant invention.
FIG. 4 illustrates the tube sheet 102, plug sheet 104 and top and bottom wrapper plates 106, 108, of the box header, showing the final positioning of the components prior to welding. The end plates 110, 112 are not shown in this figure, in order to more clearly show the bevels extending along both longitudinal edges of both the top and bottom wrapper sheets.
In the prior art fabrication process previously discussed, a considerable amount of labor is involved in positioning and orienting these sheets, referred to as a "fit up", such that the necessary spacings between the toes of the bevels and the sidewalls of the tube sheet and plug sheet are set and maintained to provide the desired gap and weld joint geometry. In this prior art process, once a bevel is properly positioned relative to the tube sheet (for example), the spacing and joint geometry are maintained by welding tack bars bridging from the tube sheet to the wrapper sheet. Tack bars are used in the same manner to secure and retain the necessary spacing at each of the joints between the beveled edges of the wrapper sheets and the tube and plug sheets. In addition to this manual fit up being a very labor intensive process, the tack bars further interfere with the ability to provide a continuous weld bead along the entire extent of the joint, in that the tack bars obstruct access to portions of the joint, and require the welder to work around the tack bars.
These problems and disadvantages are overcome in the fabrication process of the present invention, as will now be discussed in greater detail with respect to FIGS. 5-8.
FIG. 5 shows one of the wrapper sheets 106, having the two bevels 122, 124, extending along the longitudinal edges of the sheet. In accordance with the process of the present invention, backing bars 126 are positioned to extend past the toes 123, 125 of the bevels for a distance equal to the desired spacing distance between the wrapper sheet and the tube sheet or plug sheet. The backing bars 126 are preferably secured to the wrapper sheets by tack weld, illustrated substantially schematically by broken lines designated with reference numeral 128. Although the tacking is shown as being done on the interior face of the wrapper sheet in FIG. 5, it will readily be appreciated that the tacking may be accomplished at the face of the bevel as well, if desired.
The step of securing backing bars 126 to each of the beveled edges may be accomplished with relatively little labor. The backing bar is preferably placed in a fixture 200, shown schematically in FIG. 9, that further provides for an automatic correct positioning of the beveled plate relative to the backing bar, once the beveled plate is brought into contact with the backing bar, and the two components are then quickly tacked together, represented by tack weld bead 128.
The use of backing bars 126 in the process of this invention eliminates the need to use tack bars to retain the tube sheet, plug sheet, and wrapper sheets in position for the welding of the joints, as can be seen in FIG. 6. The backing bars 126 are brought into abutting engagement with the tube sheet and plug sheet. The backing bars thus serve as spacers to maintain the desired distance between the inner faces of the tube sheet 102 and plug sheet 104 and the beveled edges 122, 124 of the wrapper sheets. Simple right angle fixturing or clamping, shown schematically in broken lines at reference numeral 202, may therefore be employed to hold the components in proper position, and the components themselves are tacked together prior to commencing the welding of the joints. Experience has shown that the instant process, in which backing bars are secured to the wrapper plates, is more than twice as fast as the above-described prior art fabrication process in reaching this stage where the four sheets or plates are secured in position for the welding of the seams.
Referring now especially to FIGS. 7 and 8, the fabrication process continues by making a root pass in one of the joints using an automated welding process to fuse the backing bar, the material at the toe of the weld, and the abutting plate material into the root of the weld. The fusion zone for the root pass is designated by reference numeral 130. Once the root pass is completed, the automated welding equipment is then used to make any subsequent passes 132 that may be necessary to fill the weld joint, as is known generally in the art. The process is repeated for each of the four required longitudinal welds. After any final inspection of the interior of the box header is performed, the end plates and inlets and outlets are then welded to the thus formed box in a conventional manner, to complete the fabrication.
The automated process employed in welding the longitudinal seams is preferably a submerged arc process, the operation of which is well known in the art. Other types of automated welding known in the art may be used as well. Automated welding produces far more consistent and high quality welds as compared with manual welding, and the ability to use automated welding for the root pass, enabled by the use of a backing bar, will greatly improve the quality and the consistency of the quality of the box header, while reducing fabrication costs.
The use of the backing bar to prevent splatter and blowthrough further enables the welding current to be greatly increased over the current generally employed in the prior art open root gap welding. A welding current on the order of 500 amperes is preferred in the present invention, as compared with a welding current of 120 amperes commonly used with the open root gap configuration. This increased amperage ensures that the root pass will produce a full penetration weld that includes, in the fusion zone, metal from the tube sheet or plug sheet, the adjacent wrapper sheet, and the backing bar. The backing bar presents blowthrough or weld splatter from entering the interior of the box header, even using a welding current that is more than four (4) times greater that the current employed in making the manual root pass of the prior art.
The use of backing bars 126 in forming the longitudinal weld seams in a box header does not, by nature of its joint designation under the ASME Code, require the joint to otherwise be redesigned or reconfigured. Unlike welds in pressure piping, no joint efficiency need be included in the calculations for the longitudinal welds for the box header. As noted previously, the use of a backing bar in pressure piping reduces the joint efficiency from 100 percent to 70 percent, causing significant changes in the design criteria for the joint.
The material used for the backing bar is selected to be compatible with the material from which the tube sheet, plug sheet, and wrapper sheet are constructed, as the backing bars will preferably remain in the header during the service life of the header. Use of the identical material or a weld-compatible material should ensure also that the backing bars are not subject to excessive corrosion from the process fluid. Plain carbon steel is a typical material from which box headers are constructed.
Although various details have been disclosed herein, it is to be understood that these are for illustrative purposes. Various modifications and adaptations will be readily apparent to those of ordinary skill in the art.
Accordingly, the scope of the present invention should be determined be reference to the claims appended hereto.
Claims (11)
1. A method for fabricating a box header comprising the steps of:
securing a first backing bar along a first longitudinal edge of a first plate to be welded in forming the box header, such that said first backing bar protrudes a predetermined distance outwardly from said first longitudinal edge of said first plate;
positioning said first backing bar protruding from said first plate to abut a second plate at a predetermined orientation to be welded in forming the box header, said first backing bar maintaining a desired spacing of said first plate from said second plate;
retaining said first plate, said first backing bar and said second plate in said position and predetermined orientation so as to provide a desired weld joint configuration; and fusing said first plate, said first backing bar and said second plate at a root of said weld joint configuration by subjecting said first plate, said first backing bar, and said second plate to an automated welding process that performs a root pass in said weld joint configuration.
securing a first backing bar along a first longitudinal edge of a first plate to be welded in forming the box header, such that said first backing bar protrudes a predetermined distance outwardly from said first longitudinal edge of said first plate;
positioning said first backing bar protruding from said first plate to abut a second plate at a predetermined orientation to be welded in forming the box header, said first backing bar maintaining a desired spacing of said first plate from said second plate;
retaining said first plate, said first backing bar and said second plate in said position and predetermined orientation so as to provide a desired weld joint configuration; and fusing said first plate, said first backing bar and said second plate at a root of said weld joint configuration by subjecting said first plate, said first backing bar, and said second plate to an automated welding process that performs a root pass in said weld joint configuration.
2. A method as recited in Claim 1, further comprising making a plurality of subsequent automated welding passes to complete said weld joint.
3. A method as recited in Claim 1, wherein said step of securing said backing bar to said longitudinal edge of said first plate further comprises placing said backing bar in a fixture that will retain the backing bar in a position such that, when the first plate is brought into contact with the backing bar, the backing bar and first plate will be positioned by the fixture to provide the predetermined protrusion distance, and then tack welding the backing bar to the first plate.
4. A method as recited in Claim 1, including the further step of beveling said longitudinal edge of said first plate, and securing said backing bar adjacent to a toe portion of said bevel.
5. A method as recited in Claim 1, wherein said step of retaining said first plate, said backing bar and said second plate in position includes the step of tack welding said backing bar to said second plate.
6. A method as recited in Claim 1, wherein said fusing step is accomplished using an automated submerged arc process.
7. A method as recited in Claim 6, wherein said submerged arc process is operated at a welding current on the order of 500 amperes.
8. A method as recited in Claim 1, comprising the further steps of:
securing a second backing bar along a second longitudinal edge of said first plate, such that said second backing bar protrudes a predetermined distance outwardly from said second longitudinal edge of said first plate;
securing a third backing bar along a first longitudinal edge of a third plate, such that said third backing bar protrudes a predetermined distance outwardly from said first longitudinal edge of said third plate;
securing a fourth backing bar along a second longitudinal edge of said third plate, such that said fourth backing bar protrudes a predetermined distance outwardly from said second longitudinal edge of said third plate;
positioning said second backing bar protruding from said first plate to abut a fourth plate at a predetermined orientation to be welded in forming the box header, said second backing bar maintaining a desired spacing of said first plate from said fourth plate;
retaining said first plate, said second backing bar and said fourth plate in said position and predetermined orientation so as to provide a desired weld joint configuration;
fusing said first plate, said second backing bar, and said fourth plate at a root of said weld joint configuration by subjecting said first plate, said second backing bar, and said fourth plate to an automated welding process that performs a root pass in said weld joint configuration;
positioning said third backing bar protruding from said third plate to abut said second plate at a predetermined orientation to be welded in forming the box header, said third backing bar maintaining a desired spacing of said third plate from said second plate;
retaining said third plate, said third backing bar and said second plate in said position and predetermined orientation so as to provide a desired weld joint configuration;
fusing said third plate, said third backing bar and said second plate at a root of said weld joint configuration by subjecting said third plate, said third backing bar, and said second plate to an automated welding process that performs a root pass in said weld joint configuration;
positioning said fourth backing bar protruding from said third plate to abut said fourth plate at a predetermined orientation to be welded in forming the box header, said fourth backing bar maintaining a desired spacing of said third plate from said fourth plate;
retaining said third plate, said fourth backing bar, and said fourth plate in said position and predetermined orientation so as to provide a desired weld joint configuration;
fusing said third plate, said fourth backing bar, and said fourth plate at a root of said weld joint configuration by subjecting said third plate, said fourth backing bar and said fourth plate to an automated welding process that performs a root pass in said weld joint configuration.
securing a second backing bar along a second longitudinal edge of said first plate, such that said second backing bar protrudes a predetermined distance outwardly from said second longitudinal edge of said first plate;
securing a third backing bar along a first longitudinal edge of a third plate, such that said third backing bar protrudes a predetermined distance outwardly from said first longitudinal edge of said third plate;
securing a fourth backing bar along a second longitudinal edge of said third plate, such that said fourth backing bar protrudes a predetermined distance outwardly from said second longitudinal edge of said third plate;
positioning said second backing bar protruding from said first plate to abut a fourth plate at a predetermined orientation to be welded in forming the box header, said second backing bar maintaining a desired spacing of said first plate from said fourth plate;
retaining said first plate, said second backing bar and said fourth plate in said position and predetermined orientation so as to provide a desired weld joint configuration;
fusing said first plate, said second backing bar, and said fourth plate at a root of said weld joint configuration by subjecting said first plate, said second backing bar, and said fourth plate to an automated welding process that performs a root pass in said weld joint configuration;
positioning said third backing bar protruding from said third plate to abut said second plate at a predetermined orientation to be welded in forming the box header, said third backing bar maintaining a desired spacing of said third plate from said second plate;
retaining said third plate, said third backing bar and said second plate in said position and predetermined orientation so as to provide a desired weld joint configuration;
fusing said third plate, said third backing bar and said second plate at a root of said weld joint configuration by subjecting said third plate, said third backing bar, and said second plate to an automated welding process that performs a root pass in said weld joint configuration;
positioning said fourth backing bar protruding from said third plate to abut said fourth plate at a predetermined orientation to be welded in forming the box header, said fourth backing bar maintaining a desired spacing of said third plate from said fourth plate;
retaining said third plate, said fourth backing bar, and said fourth plate in said position and predetermined orientation so as to provide a desired weld joint configuration;
fusing said third plate, said fourth backing bar, and said fourth plate at a root of said weld joint configuration by subjecting said third plate, said fourth backing bar and said fourth plate to an automated welding process that performs a root pass in said weld joint configuration.
9. A method as recited in Claim 8, wherein said first plate is a top wrapper sheet for a box header, said second plate is a tube sheet for a box header, said third plate is a bottom wrapper sheet for a box header, and said fourth plate is a plug sheet for a box header.
10. A method for fabricating a box header wherein the box header comprises a tube sheet, a plug sheet, and a first and a second wrapper sheet, that comprise four longitudinally extending walls of the box header, comprising the steps of:
(a) forming a box header subassembly by:
(i) securing a backing bar along each longitudinal edge of each of said first and second wrapper sheets at an interior surface thereof, such that said backing bars protrude a predetermined distance outwardly from said longitudinal edges, and wherein said backing bars extend along an entire longitudinal extent of each longitudinal edge of said wrapper sheets;
(ii) positioning a first one of said backing bars of said first wrapper sheet relative to said tube sheet such that said first one of said backing bars abuts an interior surface of said tube sheet;
(iii) preliminarily securing said first one of said backing bars of said first wrapper sheet to said tube sheet in a position such that an exterior surface of said wrapper sheet is substantially at the same level as a longitudinal edge of said tube sheet;
(iv) positioning a first one of said backing bars of said second wrapper sheet relative to said plug sheet such that said backing bar abuts an interior surface of said plug sheet;
(v) preliminarily securing said first one of said backing bars of said second wrapper sheet to said plug sheet in a position such that an exterior surface of said wrapper sheet is substantially at the same level as a longitudinal edge of said plug sheet;
(vi) positioning a second one of said backing bars of said first wrapper sheet relative to said plug sheet such that said second one of said backing bars abuts an interior surface of said plug sheet, and positioning a second one of said backing bars of said second wrapper sheet such that it abuts an interior surface of said tube sheet;
(vii) preliminarily securing said second one of said backing bars of said first wrapper sheet to said plug sheet in a position such that an exterior surface of said first wrapper sheet is substantially at the same level as a longitudinal edge of said plug sheet; and (viii) preliminarily securing said second one of said backing bars of said second wrapper sheet to said tube sheet in a position such that an exterior surface of said second wrapper sheet is substantially at the same level as a longitudinal edge of said tube sheet;
(b) placing said box header subassembly so formed in an automated welding apparatus; and (c) performing an automated welding root pass to fuse each of said backing bars to the sheets of the box header to which each backing bar is secured.
(a) forming a box header subassembly by:
(i) securing a backing bar along each longitudinal edge of each of said first and second wrapper sheets at an interior surface thereof, such that said backing bars protrude a predetermined distance outwardly from said longitudinal edges, and wherein said backing bars extend along an entire longitudinal extent of each longitudinal edge of said wrapper sheets;
(ii) positioning a first one of said backing bars of said first wrapper sheet relative to said tube sheet such that said first one of said backing bars abuts an interior surface of said tube sheet;
(iii) preliminarily securing said first one of said backing bars of said first wrapper sheet to said tube sheet in a position such that an exterior surface of said wrapper sheet is substantially at the same level as a longitudinal edge of said tube sheet;
(iv) positioning a first one of said backing bars of said second wrapper sheet relative to said plug sheet such that said backing bar abuts an interior surface of said plug sheet;
(v) preliminarily securing said first one of said backing bars of said second wrapper sheet to said plug sheet in a position such that an exterior surface of said wrapper sheet is substantially at the same level as a longitudinal edge of said plug sheet;
(vi) positioning a second one of said backing bars of said first wrapper sheet relative to said plug sheet such that said second one of said backing bars abuts an interior surface of said plug sheet, and positioning a second one of said backing bars of said second wrapper sheet such that it abuts an interior surface of said tube sheet;
(vii) preliminarily securing said second one of said backing bars of said first wrapper sheet to said plug sheet in a position such that an exterior surface of said first wrapper sheet is substantially at the same level as a longitudinal edge of said plug sheet; and (viii) preliminarily securing said second one of said backing bars of said second wrapper sheet to said tube sheet in a position such that an exterior surface of said second wrapper sheet is substantially at the same level as a longitudinal edge of said tube sheet;
(b) placing said box header subassembly so formed in an automated welding apparatus; and (c) performing an automated welding root pass to fuse each of said backing bars to the sheets of the box header to which each backing bar is secured.
11. A method as recited in Claim 10 further comprising performing at least one additional automated welding pass over the root pass at each weld joint on said box header subassembly.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US70217096A | 1996-08-23 | 1996-08-23 | |
| US08/702,170 | 1996-08-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2213787A1 true CA2213787A1 (en) | 1998-02-23 |
Family
ID=24820131
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2213787 Abandoned CA2213787A1 (en) | 1996-08-23 | 1997-08-22 | Method for fabricating box headers for use in air cooled heat exchangers |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2213787A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114473391A (en) * | 2022-03-04 | 2022-05-13 | 新疆金鑫利达钢管有限公司 | Rapid production method of steel pipe |
| US11346618B1 (en) * | 2018-01-22 | 2022-05-31 | Hudson Products Corporation | Boxed header for air-cooled heat exchanger |
-
1997
- 1997-08-22 CA CA 2213787 patent/CA2213787A1/en not_active Abandoned
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US11346618B1 (en) * | 2018-01-22 | 2022-05-31 | Hudson Products Corporation | Boxed header for air-cooled heat exchanger |
| CN114473391A (en) * | 2022-03-04 | 2022-05-13 | 新疆金鑫利达钢管有限公司 | Rapid production method of steel pipe |
| CN114473391B (en) * | 2022-03-04 | 2022-09-20 | 新疆金鑫利达钢管有限公司 | Rapid production method of steel pipe |
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