Abstract:
Apparatus and methods for assembling solar receiving tubes in the field are described. In one embodiment, a welder is provided having longitudinally adjustable clamps that permit the easy restraining and adjustment of tube position for welding. In another embodiment, a system for moving along the length of a solar collector and sequentially welding tubes is described.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. 119(e) to U.S. Provisional Application No. 61/238,195 filed Aug. 30, 2009, which is incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to apparatus and methods for assembling pipes, and more particularly to methods and systems for joining tubes for solar receivers. 
     2. Discussion of the Background 
     Solar thermal power plants may be used to obtain electric power from the sun. In such plants, the solar flux impinges on tubes through which a heat exchange medium flows. In some solar thermal power plants, tubes are situated in a solar collector, such as along the axis of a parabolic trough. The heated heat exchange medium from the tubes may be used in a thermodynamic cycle to generate electric power. 
       FIG. 1A  is a perspective view of a portion of a typical prior art concentrating solar power plant  100  comprising one or more solar energy collectors  110  arranged in a field. Each collector  110  includes one or more trough-shaped structures  113  having a reflective surface  119 , two or more ground supports  111 , an absorber tube  115  that extends the length of the collector, and tube supports  117  that couple the reflector to the absorber tube. It is not uncommon for each collector  110  to have a length A of approximately 380 feet (116 meters), a width B of approximately 20 feet (6 meters), and a height off the ground H greater than 10 feet (3 meters). 
     Typically, surfaces  119  have a longitudinal axis along length A and a parabolic shape in a plane perpendicular to the longitudinal axis, and absorber tube  115  is supported along the axis, such that light normally impinging on the reflector is focused (or concentrated) on the absorber tube. A mechanism (not shown) is provided to so rotate reflective surface  119  during the day to direct incident sunlight on absorber tube  115  and thus optimize the collection of solar energy on the tube. 
     Absorber tube  115  is generally hollow to permit the flow of a heat transfer medium, such as water, salt, or some other liquid or gas, along the absorber tube, thus collecting the concentrated solar energy. The exiting heat transfer medium may then, for example, be used to drive a turbine or heat engine (not shown) to generate electricity. 
     The construction of certain solar power plants  100  generally involves the following steps: 1) placing ground supports  111  in the field, 2) attaching trough-shaped structures  113  to the ground supports, and 3) joining absorber tube  115  to tube supports  117 . To facilitate construction, absorber tube  115  may be formed by joining many smaller tubes that are joined together. The smaller tubes are sometimes referred to as “solar receiver tubes” or “heat collection elements (HCE).” 
       FIG. 2  is a partial sectional side view of a prior art HCE  200 ,  FIG. 3  is an end view of the HCE, and  FIG. 4  is a sectional end view of the HCE. HCE  200  may be, for example and without limitation, a SCHOTT solar receiver tube model PTR 70 (SCHOTT Solar, Inc., Albuquerque N. Mex.). 
     Typically, HCE  200  includes an outer tube  210  having a diameter D that is capped at each end by a metal flange  215 , an inner tube  211  and that is coaxial with the outer tube, and a metal bellows  213  that connects the flange and inner tube. Tube  210  is preferably optically transparent and is made, for example of a glass. Flange  215  is attached to a bellows  213  that extends to tube  211 . Tube  211  is thermally conductive, and may be formed from a metal, and has a length L and an inner diameter d, through which a heat transfer medium may flow. Tube  210  is generally transparent to sunlight to facilitate the solar heating of a heat exchange medium that may flow through glass tube  211 , as indicated by arrows in  FIG. 2 . Tubes  210  and  211 , bellows  213  and flange  215  are sealed to form a volume  212 , which is evacuated to provide a high thermal insulation between tubes  210  and  211 . 
     In general, the length L is from 5 feet (1.5 m) to 20 feet (6 m), the diameter D is from 2 inches (50 mm) to 7 inches (0.18 m), and the diameter d is from 1 inch (25 mm) to 4 inches (0.1 m). 
     For certain HCEs  200 , tube  211  protrudes longitudinally beyond the end of each flange  215  by a distance S, which it typically from 0.375 inches (10 mm) to 4 inches (0.1 m). The portion of tube  211  that so protrudes is referred to as a collar  214 . Forming an absorber tube  115  requires joining collars  214  of adjacent absorber tubes. In certain other HCEs  200 , the free ends of flange  215  may also have a radial protrusion at the end. 
       FIG. 1B  is a perspective view illustrating details of a prior art solar energy collector  110 . Absorber tube  115  is formed from a plurality of HCEs  200 , denoted  200   a ,  200   b , and  200   c . The ends of each pair of HCEs are support by one tube support  117 . 
     One method for joining HCEs  200  is by orbital welding. One example of such a welder system is an Arc Machines model 207 power supply controller (Arc Machines, Inc., Pacoima, Calif.) with its mating 207-CW cooling package may be used with an Arc Machine 9-7500 welder. 
     Due their length, L, and glass components, solar receiver tubes tend to be fragile, and difficult to join, typically by welding, since the collars  214  protrude beyond the ends of the glass outer tube  210  by a relatively small distance from each end. Further, collars  214  are adjacent to bellows  213 , on whose integrity the vacuum of volume  212  depends. In addition, the height C may make it very difficult to place and manipulate a welder. Solar receiver tube are thus difficult to join, especially in the field, without damaging the more fragile glass outer tube  210  or the bellows  213  joining tubes  210  and  211 . There is a need in the art for methods and apparatus that permit the easy and rapid joining of such tubes to facilitate more efficient assembly of solar energy systems. 
     BRIEF SUMMARY OF THE INVENTION 
     In certain embodiments, an apparatus for welding the ends of a first and a second HCE is provided, where each HCE includes an outer collar and a concentric and inner tube. The apparatus includes: a first mechanism for accepting the first outer collar; a second mechanism for accepting the second outer collar; and a weld head. The first mechanism and second mechanism are attached to the weld head, and where at least one of the first mechanism and the second mechanism is adjustable to translate the accepted HCE in a longitudinal HCE direction. 
     In certain other embodiments, an apparatus for welding the ends of a first and a second HCE using a weld head is provided, where each HCE includes an outer collar and a concentric and inner tube. The apparatus includes: a first mechanism for accepting the first outer collar and adapted for attachment to the weld head; and a second mechanism for accepting the second outer collar and adapted for attachment to the weld head. When the first mechanism and the second mechanism are attached to the weld head, at least one of the first mechanism and the second mechanism is adjustable to translate the accepted HCE in a longitudinal HCE direction. 
     In certain embodiments, an apparatus for welding the ends of a first and a second HCE is provided. Each HCE includes an outer collar and a concentric and inner tube. The apparatus includes a weld head, a first means for clamping the first collar and longitudinally positioning the ends of an accepted first HCE; and a second means for clamping the second collar and longitudinally positioning the ends of an accepted second HCE. The first and second means permit locating the ends of the first HCE and second HCE for welding by the weld head. 
     In yet certain other embodiments, an apparatus for welding the ends of a first and a second HCE in a solar energy system at a height above the ground is provided, where each HCE includes an outer collar and a concentric and inner tube. The apparatus includes: a vehicle having a weld head, a welding power supply, and a platform to enable a user to reach the HCEs for welding. 
     In certain embodiments, a method of assembling a solar energy system is provided, where the solar energy system includes an absorber tube formed from a plurality of joined HCEs. The method includes: placing the plurality of HCEs in the solar energy system; moving a vehicle having a weld head, a welding power supply, and a platform to enable a user to reach the HCEs along the HCEs; and welding adjacent HCEs. 
     These features together with the various ancillary provisions and features which will become apparent to those skilled in the art from the following detailed description, are attained by the tube joining apparatus and method of the present invention, preferred embodiments thereof being shown with reference to the accompanying drawings, by way of example only, wherein: 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1A  is a perspective view of a portion of a typical prior art concentrating solar power plant; 
         FIG. 1B  is a perspective view illustrating details of a prior art solar energy collector; 
         FIG. 2  is a partial sectional side view of a prior art heat collection element (HCE); 
         FIG. 3  is an end view of  2 - 2  of  FIG. 2 ; 
         FIG. 4  is a sectional end view  3 - 3  of  FIG. 2 ; 
         FIG. 5  is side view of a triple-joined HCE; 
         FIG. 6A  is a side view of a field welding vehicle; 
         FIG. 6B  is a top view of the field welding vehicle of  FIG. 6A ; 
         FIG. 7A  is a view of the back of the vehicle of  FIG. 6A  during a welding operation; 
         FIG. 7B  is a cross-sectional view of HCEs near a weld location, illustrating the use of a traveling purge dam to isolate the region being welded; 
         FIG. 8A  is a perspective view of an embodiment of a joining apparatus; 
         FIG. 8B  is an exploded perspective view of an embodiment of a joining apparatus; 
         FIG. 9A  is an end view of the apparatus of  FIG. 8  illustrating the use of an adjustable FIG. in an open configuration; 
         FIG. 9B  is an end view of the apparatus of  FIG. 8  illustrating the use of an adjustable clamp in a closed configuration; 
         FIG. 10A  as an exploded view of an adjustable clamping mechanism portion; 
         FIG. 10B  as an assembled view of the adjustable clamping mechanism; 
         FIG. 11  is a top view  11 - 11  of  FIG. 9A  showing adjacent HCEs prior to welding within the lower part of a welding apparatus; 
         FIGS. 12A ,  12 B,  12 C, and  12 D, which are sequential sectional side views  12 - 12  from  FIG. 11  illustrating one embodiment of a method of joining HCEs; and 
         FIGS. 13A and 13B  are side views different HCEs illustrating variations in HCE dimensions. 
     
    
    
     Reference symbols are used in the Figures to indicate certain components, aspects or features shown therein, with reference symbols common to more than one Figure indicating like components, aspects or features shown therein. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In general, embodiments are provided that permit the field welding of tubes (HCEs) to form absorber tubes of solar energy systems. One embodiment of an apparatus for field welding tubes is illustrated in  FIGS. 6A ,  6 B, and  7 A, where  FIG. 6A  is a side view of a field welding vehicle  600 ,  FIG. 6B  is a top view of the field welding vehicle, and  FIG. 7A  is a view of the back of the vehicle during a welding operation. Field welding vehicle  600  may be used, for example and without limitation to field weld a plurality of HCEs  200  to form an absorber tube  115 . 
     Field welding vehicle  600  includes and/or may supply all of the electricity and gases needed to operate welder  620 . Vehicle  600  may be, for example and without limitation a modified vehicle such as a cargo van or box truck. Thus, for example and without limitation, field welding vehicle  600  may include, but it not limited to, one or all of the following: a roof air-conditioning  601  for environmental control; a generator  603  within the vehicle for onboard operations; automatic self-leveling outriggers  605  to stabilize vehicle in work mode; and a slide out work platform  610 . 
     Platform  610  may include one or more of the following: a safety railing  611 , a safety rigging belt; a weld head holder bracket for welder  620 ; and auxiliary lighting for night work. Platform  610  may also include support arms  613   a  and  613   b  for alignment and support of adjacent HCEs  200  relative to welder  620  during welding, and power actuation of support arm, by electric, pneumatic, hydraulic means. 
     Prior to welding, the HCEs  200  for collector  110  are placed and secured by tube supports  117  in the approximate location where they will reside as absorber tube  115 . Thus, for example and without limitation, HCEs  200  are positioned in tube supports  117 . Structure  113  is rotated to a service position to provide access to HCEs  200 , as illustrated in  FIG. 7A . 
     Alternatively, several HCEs  200  may be joined prior to being placed in collector  110 . Thus, two or more tubes may be pre-joined, as illustrated, without limitation in  FIG. 5  as a side view of a triple-joined HCE  500  in  FIG. 5 , having an end  501  and an end  503 . HCE  500  is formed by welding three HCE  200  ( 200 - 1 ,  200 - 2 , and  200 - 3 ). Specifically, welds  505  are formed at end  203  of HCE  200 - 1  and end  201  of HCE  200 - 2 , and at end  203  of HCEs  200 - 2  and end  203  of HCE  200 - 3 . In general, the procedure for welding HCE  200  and  500  into collector  110  are the same. 
     Vehicle  600 , as shown in  FIG. 7A , preferably starts at one end of collector  110 , joins collars  214  of a first set of adjacent ends  201 ,  203 ,  501 , or  503  (referred to in general as ends  201  or  203 ), then drives to the next set of ends for joining and stabilizes the vehicle with automatic self-leveling outriggers  605 . 
     As illustrated in  FIG. 7A , the height H of absorber tube  115  off the ground is generally too high above ground level to be easily worked on. Thus field welding vehicle  600  may include a movable platform  610  to permit a worker to easily access to HCEs  200 . 
     A purge gas may be provided to the interior of the HCEs  200  by flowing the gas through the aligned HCEs. Alternative, as shown in  FIG. 7B  as a cross-sectional view of HCEs  200  near a weld location, a traveling purge dam  700  may be used to isolate regions of collars  214   a  and  214   b  being welded. After one weld is completed, dam  700  is pulled through HCEs  200  to the next weld location. 
       FIGS. 6B and 7A  illustrate support arms  613   a  and  613   b  positioned off of platform  610  such that a worker may support ends  201 ,  203  to facilitate joining the HCEs. Support arms  613   a  and  612   b  may include a cradle, or alternatively clamps, to restrain HCEs  200  near where welding is to occur, with sufficient spacing to permit access to welding equipment. 
     In one embodiment, a worker places adjacent HCEs in support arms  613   a  and  613   b , and then positions welder  620  for welding. In another embodiment, welder  620  is manually placed by a worker. In another embodiment, welder  620  is supported by a “skyhook” or other devices on vehicle  600 . 
     In many instances, variations between different HCEs  200  or the placement in supports  117  requires that adjustments be made to adjacent tubes prior to welding. Thus, for example, slight longitudinal adjustments to the position of ends  201 ,  203  (or  501  and  503 ) of adjacent HCEs  200  (or  500 ) may be required for welding. Longitudinal adjustments are provided by welder  620 . 
     In certain embodiments, welder  620  is a welding device that includes means for clamping the collar and longitudinally positioning the ends of accepted HCEs for proper welding. Welder  620  may thus include longitudinally adjustable clamps to accurately position collars  214  of adjacent HCEs  200  or  500 . As one embodiment, which is not meant to limit the scope of the present invention,  FIG. 8A  is a perspective views of an embodiment of a joining apparatus  800 , and  FIG. 8B  is an exploded perspective view of the joining apparatus. Apparatus  800  includes an adjustable left clamp  810  and an adjustable right clamp  820 , which are both means for clamping the collar and longitudinally positioning the ends of accepted HCEs 
     Joining apparatus  800  may be generally similar to welder  620 , and may include a joining device, such as an orbital welder  801 , an adjustable left clamp  810  and an adjustable right clamp  820 . Thus, for example, adjustable left clamp  810  may be used to restrain one HCE  200 , adjustable right clamp  820  may be used to restrain an adjacent HCE, and one or more of the left and right clamps may be used to position the HCEs respective collars for welding in welder  801 . 
     In one embodiment, orbital welder  801  may have an electrode  802  that moves along a circular path during welding to weld collars  214  of ends  201 ,  203 . Clamps  810  and  820  are adapted to restrain a pair of adjacent HCEs  200  and provide for longitudinal alignment of the HCEs for proper welding in orbital welder  801 . 
     In another embodiment, orbital welder  801  includes a left clamp  803 , a left clasp  804 , and a left hinge  805 , and a right clamp  807 , a right clasp  808 , and a right hinge  809 . Adjustable left clamp  810  includes the left clamp  803 , clasp  804 , and hinge  805 , a bottom adjustable clamping portion  812  and a top adjustable clamping portion  815 . Bottom adjustable clamping portion  812  further includes a portion  812   a  that is attached to welder  801  and a portion  812   b  that moves longitudinally within portion  812   a  according to the action of a lead screw  813 . Portion  812   b  presents a bottom clamping surface  814  having a seating surface  811 . Top adjustable clamping portion  815  further includes a portion  815   a  that is attached to left clamp  803  and a portion  815   b  that moves longitudinally within portion  815   a  according to the action of a top lead screw  816 . Portion  815   b  presents a top clamping surface  817  having a seating surface  818 . 
     Adjustable right clamp  820 , which is similar to clamp  810 , includes the right clamp  807 , clasp  808 , and hinge  809 , a bottom adjustable clamping portion  822 , and a top adjustable clamping portion  825 . Bottom adjustable clamping portion  822  further includes a portion  822   a  that is attached to welder  801  and a portion  822   b  that moves longitudinally within portion  822   a  according to the action of a lead screw  823  (which is shown  FIG. 12A ). Portion  822   b  presents a bottom clamping surface  824  having a seating surface  821 . Top adjustable clamping portion  825  further includes a portion  825   a  that is attached to right clamp  807  and a portion  825   b  that moves longitudinally within portion  825   a  according to the action of a top lead screw  826  (shown in  FIG. 12B ). Portion  825   b  presents a top clamping surface  827  having a seating surface  828 . 
     Bottom adjustable clamping portions  812  and  822  are thus fixed to opposite sides of welder  801 , and top adjustable clamping portion  814  and  824  are affixed to clamps  803  and  807 , respectively. Clamp  810  and  820  and may be held in a partially locked or fully locked position by clasp  804  and  808 , respectively. 
     As discussed subsequently, lead screws  813 ,  816 ,  823 , and  826  may turned to longitudinally move seating surfaces  811 ,  818 ,  821 , and  828 . Thus when left clamping surfaces  814  and  817  are closed to restrain flange  215  of one HCE  200 , and right clamping surfaces  824  and  827  are closed to restrain the flange of an adjacent HCE, lead screws  813 ,  816 ,  823 , and  826  may be used to adjust the location of a welding electrode  802  relative to the ends of the HCEs 
     In certain embodiments, welder  801  and clamps  810  and  820 , when closed about HCEs  200   a  and  200   b , for an enclosure about the welding location. The enclosure may be used, for example, to provide a purge gas to the outer portion of collars  214  during welding. In one embodiment, clamps  810  and/or  820  have components that cooperate to form an enclosure when clasps  804  and  808  are secured.  FIGS. 8A and 8B  show an enclosure portion  831 , which is attached to right clamp  810 , and enclosure portion  833 , which is attached to clamp  820 . Enclosure portions  831  and  833  permit clamps  810  and  820  to move separately, and to form an enclosure when securing HCEs  200   a  and  200   b . In one embodiment, portion  833  may include a transparent material, such as a glass or plastic, to permit a user to inspect the placement and/or adjustment of electrode  802  relative to ends  201  and  203  prior to welding. 
       FIGS. 9A and 9B  is an end view of apparatus  800  illustrating the use of adjustable clamp  810 .  FIG. 9A  is an open configuration, in which HCE  200  may be inserted or removed from apparatus  800 .  FIG. 9B  is a closed configuration, in which top portion is rotated and clasped. As shown in  FIG. 9B , clamping surfaces  814  and  817  form a circular clamping surface that may be used to retain a flange  215 . Likewise, clamp  820  has a similar open configuration and a closed configuration in which clamping surfaces  824  and  827  may also be used to retain a flange  215 . Surfaces  814 ,  817 ,  824 , and  827  may be used to electrically collars  214  with respect to welder  801 . 
     Adjustable clamping portions  812 ,  815 ,  822 , and  815  are independently adjustable in a longitudinal direction (along the axis of an accepted HCE  200  or  500 ). Adjustable clamping portions  812 ,  815 ,  822 , and  815  are also identical, and are illustrated in  FIG. 10A  as an exploded view of an adjustable clamping mechanism adjustable clamping mechanism portion  1000  and in  FIG. 10B  as an assembled view of the adjustable clamping mechanism. 
     Adjustable clamping mechanism portion  1000  includes a welder mounting plate  1010  a slidable sleeve  1020 , and a lead screw  1030 . Mounting plate  1010  has a welder mounting surface  1017 , a sleeve guide  1015 , several guide pins  1011  surrounded by springs  1013 , and a treaded hole  1019 . Slideable sleeve  1020  has a semicircular portion  1023  with a clamping surface  1025  having an innermost edge  1026 , holes  1012  and  1028 , and a surface  1027 . Lead screw  1030 , which may have a knurled head, passes through hole  1028  and into treaded hole  1019 . 
     When mounting plate  1010  and sleeve  1020  are assembled, portion  1023  passes through sleeve guide  1015 , pins  1011  pass through holes  1012  and springs  1013  push against mounting plate  1010  and surface  1027 . As shown in  FIG. 10B , the longitudinal distance between innermost edge  1026  and mounting surface  1017 , Z, is adjustable by turning lead screw  1030 . 
     With reference to  FIGS. 8A ,  8 B,  9 A  9 B,  10 A and  10 B, adjustable clamping mechanism portion  1000  corresponds to adjustable clamping portions  812 ,  815 ,  822 , and  825 ; mounting plate  1010  corresponds to portions  812   a ,  815   a ,  822   a , and  825   a , sleeve  1020  corresponds to portions  812   b ,  815   b ,  822   b , and  825   b , clamping surface  1025  corresponds to clamping surfaces  814 ,  817 ,  824 ; and  827 ; innermost edge  1026 , corresponds to seating surfaces  811 ,  818 ,  821 , and  828 ; lead screw  1030  corresponds to lead screws  813 ,  816 ,  823 , and  826 . Mounting plate  1010  may be either fixedly or removably attached to welder  801 , left clamp  803  and right clamp  807  for example and without limitation, by screws, clamps, slots, pins, adhesives, welding, or any other joining method. 
       FIG. 11  is a top view  11 - 11  of  FIG. 9A  showing adjacent HCEs  200  prior to welding within the lower part of apparatus  800 . As shown in  FIG. 11 , a first HCE  200   a  is resting in and/or supported by support arm  613   a  and a second HCE  200   b  is resting in and/or supported by support arm  613   b . Flange  215   a  and  215   b  are resting against clamp surface  824  and  814 , respectively, with ends  201   a  and  203   b  aligned along the centerlines of HCEs  200   a  and  200   b , and positioned end-to-end near electrode  802  of welder  801 . 
     A method of aligning and welding HCEs  200   a  and  200   b  is illustrated in  FIGS. 12A ,  12 B,  12 C, and  12 D, which are sequential sectional side views  12 - 12  from  FIG. 11  illustrating one embodiment of a method of joining HCEs. As shown in  FIG. 12A , HCE  200   a  is positioned with flange  215   a  on clamping surface  824  and HCE  200   b  is positioned with flange  215   b  on clamping surface  814 . 
     As is also shown, each flange  215  has a lip  216  that slightly protrudes radially outwards from the flange. Although not a necessary part of HCE  200 , lip  216  may provide a convenient feature for locating the HCE. Other techniques for locating HCE  200  within apparatus  800  may be used, including visual inspection. With electrode  802  located near ends  201   a ,  203   b , lead screws  813  and  823  are adjusted such that lip  216   a  seats against seating surface  821  and lip  216   b  seats against seating surface  811 . 
       FIG. 12A  also illustrates the rotation of lead screws  813  and  823  to longitudinally translate portions  812   b  and  822   b , respectively, relative to HCEs  200   a  and  200   b . Lead screws  813  and  823  may be adjusted so that seating surfaces  811  and  821 , respectively, are brought in contact with lips  216   a  and  216   b . In addition, lead screws  813  and  823  may be adjusted to bring the tip of electrode  802  in alignment with ends  201   a  and  203   a.    
     Next, as shown in  FIG. 12B , the top right clamp  820  is closed by rotating right clamp  807  over flange  215   a . With clasp  808  loosely tightened, lead screw  825  is adjusted such that lip  216   a  seats against surface  828 . 
     As shown in  FIG. 12C , the top left clamp  810  is closed by rotating left clamp  803  over flange  215   b . With clasp  804  loosely tightened, lead screw  813  is adjusted such that lip  216   b  seats against surface  818 . 
     A final adjustment may now be made, as indicated in  FIG. 12D . Specifically, it is important that lip  216   a  seats against surfaces  821  and  828 , that lip  216   b  seats against surface  811  and  818 , and that ends  201   a  and  203   b  align with the orbital motion of electrode  802 . Lead screws  813 ,  816 ,  823 , and  826  are rotated to achieve alignment. In one embodiment, a portion of enclosure portion  833  is a window  1200 , as shown in  FIG. 12D , which allows a user to view the location of electrode  802  during this adjustment. Clasps  804  and  808  are then tightened to lock apparatus  880  onto HCEs  200  between seating surfaces  814 ,  817 ,  824 , and  827 . 
     At this point, the user initiates the welding sequence, which may include providing an external purge gas within welder  801  and initiating the movement of electrode  802  about ends  201 / 203 . When the weld in complete, the external purge gas flow is stopped, clasp  804  is released, clamp  803  is opened, and then clasp  808  is released and clamp  807  is opened, and apparatus  800  may be moved to the next weld location. In certain embodiments, portions  815   b  and  825   b  must be moved longitudinally away from each other to clear weld head  801  and permit clamps  803  and  807  to be opened. 
     The importance of being able to make fine adjustments is highlighted in  FIGS. 13A and 13B , which are side views different HCEs illustrating variations in HCE dimensions. The dimension S is the distance from an edge of flange  215 , which may be lip  216 , to end  201  or  203 .  FIG. 13A  illustrates the case where the ends of adjacent HCE  200   a  and  200   b  have the same dimensions. Thus, the distance S=S 1  is the same for each, and the distance between adjacent lips  216  is G 1 =2 S 1 , and the weld occurs at the midpoint of G 1 . Importantly, G 1  is the space which a welder must fit to reach collars  214 . 
       FIG. 13B  illustrates another case, were each distance S is different (one is S 1 , and the other S 2 ), the total distance between adjacent lips is G 2 =S 2 +S 3 , and the weld does not occurs at the midpoint, since S 2  does not equal S 3 . Since it is important that the tip of the weld electrode be in the vicinity of end  201   a / 203   b , and since flange  205  must be clamped for welding, it is important that both the spacing and the relative position of the HCEs and electrode be adjustable, as provided by apparatus  800 . 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments. 
     Similarly, it should be appreciated that in the above description of embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this invention.