System and method for laser welding an inner surface of a small diameter tubular member

System and method for laser welding an inner surface of a small diameter tubular member. The system includes a laser for generating laser light and a mirror optically coupled to the laser for reflecting the light onto the inner surface of the tubular member to laser weld the inner surface of the tubular member. A rotator assembly is connected to the mirror for rotating the mirror in order to weld around the inner surface of the tubular member. The mirror and rotator assembly are each sized to be disposed in the tubular member at a location adjacent the portion of the tubular member to be welded. The rotator assembly has a spiral groove formed in the exterior thereof for receiving a cord wrapped around the exterior of the rotator assembly. An end of the cord is connected to a motor located externally to the tubular member, so that the cord is pulled as the motor is operated. As the cord is pulled, the rotator assembly rotates for rotating the mirror. A retainer is also provided for retaining the cord in the groove as the rotator assembly rotates. Therefore, the rotator assembly and the mirror associated therewith are rotated by a motor located externally to the tubular member. Thus, the system and method of the invention are capable of welding small diameter (e.g., diameters equal to or less than 0.313 inch) tubular members because the motor is located externally to the tubular member rather than being disposed in the tubular member.

BACKGROUND 
This invention generally relates to welding apparatus and methods and more 
particularly relates to a system and method for laser welding an inner 
surface of a small diameter tubular member, which tubular member may be a 
repair sleeve disposed in a nuclear heat exchanger heat transfer tube. 
Although laser welding apparatus and methods are known, it has been 
observed that these apparatus and methods have a number of operational 
problems associated with them that make such apparatus and methods less 
than completely satisfactory for welding an inner surface of a small 
diameter tubular member. However, before these problems can be 
appreciated, some background is desirable as to the structure and 
operation of a typical nuclear heat exchanger. 
In a typical nuclear heat exchanger or steam generator, a heated and 
radioactive primary fluid flows through a plurality of U-shaped tubes, 
each of the tubes having a fluid inlet and a fluid outlet end. The inlet 
and outlet ends of the tubes are received through holes in a tubesheet 
disposed in the heat exchanger for supporting the tubes. The heat 
exchanger defines an inlet plenum chamber below the tubesheet, which inlet 
plenum chamber is in communication with the inlet ends of the tubes. The 
heat exchanger also defines an outlet plenum chamber below the tubesheet 
and isolated from the inlet plenum chamber, the outlet plenum chamber 
being in communication with the outlet ends of the tubes. During operation 
of the heat exchanger, a heated and radioactive primary fluid flows into 
the inlet plenum chamber and enters the inlet ends of the tubes to flow 
through the tubes. After flowing through the tubes, the primary fluid then 
flows through the outlet ends of the tubes and into the outlet plenum 
chamber. The primary fluid next flows out the outlet plenum chamber to 
exit the heat exchanger. A nonradioactive secondary fluid having a 
temperature less than the primary fluid simultaneously surrounds the 
exterior surfaces of the tubes above the tubesheet as the primary fluid 
flows through the tubes. Thus, as the heated primary fluid flows through 
the tubes, it gives-up its heat to the secondary fluid surrounding the 
exterior surfaces of the tubes to produce steam that is used to generate 
electricity in a manner well known in the art. 
Because the primary fluid is radioactive, the heat exchanger is designed 
such that the radioactive primary fluid flowing through the tubes does not 
commingle with and radioactively contaminate the nonradioactive secondary 
fluid surrounding the exterior surfaces of the tubes. Therefore, the tubes 
are designed to be leak-tight so that the radioactive primary fluid 
remains separated from the nonradioactive secondary fluid to avoid 
commingling the primary fluid with the secondary fluid. 
Occasionally, however, the heat exchanger tubes may degrade and thus may 
not remain leak-tight due, for example, to tube wall intergranular 
cracking caused by stress and corrosion occurring during operation of the 
heat exchanger. Therefore, the tubes are inspected to detect such stress 
corrosion cracking or degradation. If stress corrosion cracking is 
detected at a particular location in the wall of the tube, then the tube 
is "sleeved" at that location. When sleeving is performed, a tubular metal 
sleeve is inserted into the tube, so as to cover the degraded portion of 
the tube, and affixed thereto typically by expanding the sleeve into 
intimate engagement with the tube. In this manner, the sleeved tube 
remains in service although degraded. 
However, the elastic properties of the metal sleeve may cause the sleeve to 
experience partial "spring back" after expansion. This phenomenon of 
"spring back" may in turn cause a relatively small gap to exist at the 
sleeve-to-tube interface. Such a gap is undesirable because the gap 
defines a flow path between the sleeve and the tube, which flow path may 
allow the radioactive primary fluid to flow through any crack in the tube 
and thereafter undesirably commingle with the nonradioactive secondary 
fluid. Therefore, it is desirable to fuse the sleeve to the tube by 
forming, for example, two spaced-apart weldments circumscribing the inner 
surface of the sleeve in order to seal the gap and the flow path defined 
thereby. In this regard, laser welding has been used to fuse such a sleeve 
to the tube. 
Laser welding devices are known. A system and method for laser welding a 
tube is disclosed in U.S. Pat. No. 5,182,429 titled "System And Method For 
Laser Welding The Inner Surface Of A Tube" issued Jan. 26, 1993 in the 
name of William E. Pirl, et al. and assigned to the assignee of the 
present invention. This patent discloses a system and method for laser 
welding a sleeve to the inner surface of a heat exchanger tube in order to 
repair the tube. The Pirl, et al. system comprises an elongated tubular 
housing having a rotatable distal portion connected to a non-rotatable 
proximal portion, a fiber-optic cable for conducting remotely generated 
laser light into the tubular housing, a beam deflection mechanism 
supported within the distal portion of the housing and a reflector for 
radially directing and focusing laser light received from the fiber-optic 
cable toward the inner wall of the sleeve to weld the sleeve. In order to 
weld around the inner wall of the sleeve, the Pirl, et al. device provides 
an electric motor within the proximal portion of the tubular housing to 
rotate the distal portion of the housing and the reflector supported 
therein. 
However, applicant has observed that such a prior art laser welding device 
and its associated motor are unsuitable for welding a sleeve having a 
relatively small inner diameter (e.g., an inner diameter equal to or less 
than approximately 0.313 inch). This is so because the size of 
commercially available motors is necessarily larger than the relatively 
small inner diameter of the sleeve. Therefore, a problem in the art is to 
rotate the distal portion of the tubular housing and the reflector 
supported therein without locating the motor within the proximal portion 
of the housing, so that relatively small diameter sleeves can be welded. 
Therefore, what is needed are a system and method for laser welding an 
inner surface of a small diameter tubular member, which tubular member may 
be a repair sleeve disposed in a nuclear heat exchanger heat transfer 
tube. 
SUMMARY 
Disclosed herein are a system and method for laser welding an inner surface 
of a small diameter tubular member. The system includes a laser for 
generating laser light and a mirror optically coupled to the laser for 
reflecting the light onto the inner surface of the tubular member to laser 
weld the inner surface of the tubular member. A rotator assembly is 
connected to the mirror for rotating the mirror in order to weld around 
the inner surface of the tubular member. The mirror and rotator assembly 
are each sized to be disposed in the tubular member at a location adjacent 
the portion of the tubular member to be welded. The rotator assembly has a 
spiral groove formed in the exterior thereof for receiving a cord wrapped 
around the exterior of the rotator assembly. An end of the cord is 
connected to a motor located externally to the tubular member, so that the 
cord is pulled as the motor is operated. As the cord is pulled, the 
rotator assembly rotates for rotating the mirror. A retainer is also 
provided for retaining the cord in the groove as the rotator assembly 
rotates. Therefore, the rotator assembly and the mirror associated 
therewith are rotated by a motor located externally to the tubular member. 
Thus, the system and method of the invention are capable of welding small 
diameter (e.g., diameters equal to or less than approximately 0.313 inch) 
tubular members because the motor is located externally to the tubular 
member rather than being disposed in the tubular member. 
In its broad form, the invention is a system for laser welding an inner 
surface of a small diameter tubular member, comprising laser light 
generating means for generating laser light; light reflecting means 
optically coupled to the light generating means for reflecting the light 
onto the inner surface to weld the inner surface; and rotating means 
connected to the light reflecting means for rotating the light reflecting 
means, the rotating means having a groove in an exterior surface thereof 
and a pullable cord received in the groove for rotating the rotating means 
as the cord is pulled, whereby a weld is formed around the inner surface 
as the rotating means rotates the light reflecting means. 
In its broad form, the invention is also a method of laser welding an inner 
surface of a small diameter tubular member, comprising the steps of 
generating laser light by operating a laser; reflecting the light onto the 
inner surface to weld the inner surface by optically coupling a reflector 
to the laser and to the inner surface; rotating the reflector to weld 
around the inner surface by rotating a rotatable housing having the 
reflector mounted therein, the rotatable housing having a spiral groove 
formed in an exterior surface thereof and a pullable cord received in the 
groove for rotating the rotatable housing as the cord is pulled; and 
retaining the cord in the groove as the rotatable housing rotates by 
engaging a retainer with the cord. 
An object of the present invention is to provide a system and method for 
laser welding an inner surface of a small diameter tubular member, which 
tubular member may be a repair sleeve disposed in a nuclear heat exchanger 
heat transfer tube. 
A feature of the present invention is the provision of a rotatable housing 
sized to be disposed in the tubular member, the rotatable housing having 
light reflecting means mounted therein, a spiral groove formed in an 
exterior surface thereof and a pullable cord received in the groove for 
rotating the rotatable housing as the cord is pulled, so that the 
rotatable housing and the light reflecting means mounted therein 
simultaneously rotate as the rotatable housing rotates. 
Another feature of the present invention is the provision of a retainer 
engaging the cord for retaining the cord in the groove, so that the cord 
is prevented from slipping-out of the groove as the cord is pulled. 
Yet another feature of the present invention is the provision of a motor 
located remotely from the tubular member, the motor engaging an end 
portion of the cord for pulling the cord. 
An advantage of the present invention is that tubular members having 
relatively small inner diameters may now be welded because the motor 
associated with rotating light reflecting means is remotely located with 
respect to the tubular member rather than being disposed inside the small 
diameter tubular member. 
These and other objects, features and advantages of the present invention 
will become apparent to those skilled in the art upon a reading of the 
following detailed description when taken in conjunction with the drawings 
wherein there is shown and described illustrative embodiments of the 
invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, there is shown a typical nuclear heat exchanger or 
steam generator, generally referred to as 10, for generating steam. Heat 
exchanger 10 comprises a shell 20 having an upper portion 30 and a lower 
portion 40. Disposed in lower portion 40 are a plurality of 
vertically-oriented and inverted U-shaped heat transfer tubes 50 for 
circulating heated and radioactive primary fluid therethrough. Each tube 
50 extends through its respective holes 60 formed in a plurality of 
spaced-apart support plates 70 for laterally supporting tubes 50. Each 
tube 50 may have a relatively small inside surface or inside diameter 80, 
which inside diameter 80 may be equal to or less than approximately 0.313 
inch (see FIG. 3). As shown in FIG. 1, disposed in lower portion 40 and 
attached thereto is a tubesheet 90 having a plurality of apertures 100 
therethrough for receiving open end portions 110 (see FIG. 3) of tubes 50. 
As shown in FIG. 1, disposed on shell 20 are a first inlet nozzle 120 and 
a first outlet nozzle 130 in fluid communication with an inlet plenum 
chamber 140 and an outlet plenum chamber 150, respectively. A plurality of 
manway openings 160 (only one of which is shown) are formed through shell 
20 below tubesheet 100 for providing access to inlet plenum chamber 140 
and outlet plenum chamber 150. Moreover, formed through shell 20 is a 
second inlet nozzle 170 for allowing entry of a nonradioactive secondary 
fluid into upper portion 30, which secondary fluid has a temperature less 
than the temperature of the heated primary fluid. A second outlet nozzle 
180 is attached to the top of upper portion 30 for exit of the steam from 
heat exchanger 10. 
During operation of heat exchanger 10, the radioactive primary fluid, 
heated by a nuclear heat source (not shown), flows through first inlet 
nozzle 120, into inlet plenum chamber 140, and through tubes 50 to outlet 
plenum chamber 150 where the primary fluid exits heat exchanger 10 through 
first outlet nozzle 130. As the primary fluid enters inlet plenum chamber 
140, the secondary fluid simultaneously enters second inlet nozzle 170 and 
flows into upper portion 30 to eventually surround tubes 50. A portion of 
this secondary fluid vaporizes into steam due to conductive heat transfer 
from the primary fluid to the secondary fluid, the conductive heat 
transfer occurring through the walls of tubes 50. The steam exits heat 
exchanger 10 through second outlet nozzle 180 and is piped to a 
turbine-generator (not shown) to generate electricity in a manner well 
known in the art. 
However, due to tube wall intergranular cracking or degradation caused by 
stress and corrosion, some of the small diameter tubes 50 may not remain 
leak-tight. If degradation is suspected, such a tube 50, although 
degraded, may remain in service by sleeving the degraded portion (not 
shown) of the tube 50. As disclosed in detail hereinbelow, the system and 
method of the present invention is capable of suitably sleeving such a 
degraded small diameter tube by means of laser welding. 
Therefore, turning now to FIGS. 2 and 3, there is shown the subject matter 
of the present invention, which is a system, generally referred to as 190, 
for laser welding a relatively small inner diameter 200 (i.e., inner 
surface 200) of a first tubular member, such as a tubular sleeve 210, in 
order to affix or fuse sleeve 210 to the relatively small inside diameter 
80 (i.e., inside surface 80) of a second tubular member, such as the tube 
50. In this manner, sleeve 210 bridges, covers or sleeves the degraded 
portion of tube 50, so that tube 50 may remain in service although 
degraded. 
Still referring to FIGS. 2 and 3, system 190 comprises remote laser light 
generating means, such as a laser 220, for generating high intensity laser 
light sufficient to weld the inner surface 200 of sleeve 210, such that 
sleeve 210 and tube 50 are sealingly joined or fused at the interface 
thereof. System 190 further comprises light conducting means, such as an 
elongate flexible fiber-optic cable 230, optically coupled to laser 220 
for conducting the laser light therethrough. Fiber-optic cable 230 may be 
made of silica optical fiber transparent to the electromagnetic spectrum 
of emission of laser 220 for suitably conducting the laser light 
therethrough. Fiber-optic cable 230 has a first end portion 235 in optical 
communication with laser 230 and a second end portion 237 for reasons 
described presently. System 190 also comprises light reflecting means, 
such as a planer mirror 240, optically coupled to second end portion 237 
of fiber-optic cable 230 for receiving the light emitted from the second 
end portion 237. Planer mirror 240 is also optically coupled to inner 
surface 200 of sleeve 210 for reflecting the laser light energy onto inner 
surface 200. In this regard, planer mirror 240 may be polished copper, 
molybdenum, tungsten, copper coated with silver, or the like for providing 
a high reflectivity surface while simultaneously resisting oxidation due 
to the laser light. 
Referring yet again to FIGS. 2 and 3, system 190 further comprises a 
flexible conduit 250 extending from laser 220 and into outlet plenum 
chamber 150 or inlet plenum chamber 140. Conduit 250 will extend into 
either inlet plenum chamber 140 or outlet plenum chamber 150 depending on 
the portion of tube 50 to be sleeved. Extending through conduit 250 is 
fiber-optic cable 230. It will be appreciated from the description 
hereinabove that conduit 250 therefore surrounds fiber-optic cable 230 for 
protecting fiber-optic cable 230 from damage. Engaging conduit 250 may be 
a conduit driver 260 for driving conduit 250 axially along inside diameter 
80 of tube 50 and into sleeve 210. Thus, conduit driver 260 is capable of 
advancing and withdrawing conduit 250 along the longitudinal axis of 
sleeve 210 and tube 50. In addition, in gas communication with inner 
surface 200 of sleeve 210 is a pressurized shielding gas supply 270 for 
supplying a shielding gas (e.g., nitrogen) to a predetermined weld zone 
275 located on inner surface 200 of sleeve 210 and also to planer mirror 
240, the shielding gas being supplied at a mass flow rate of approximately 
10-100 liters/minute. The purpose of the shielding gas is to prevent 
oxidation of the weld zone, to prevent impurities from migrating into weld 
zone 275 and to cool planer mirror 240. Of course, it will be understood 
from the description hereinabove, that the inner diameter 200 of sleeve 
210 is necessarily smaller than the relatively small inside diameter 80 of 
tube 50 because sleeve 210 is concentrically disposed within tube 50. For 
example, if the relatively small inside diameter 80 of tube 50 is equal to 
or less than approximately 0.313 inch, then the inner diameter 200 of 
sleeve 210 also will be relatively small (i.e., less than approximately 
0.313 inch). 
Referring to FIGS. 3, 3A and 4, conduit 250 is connected to a generally 
tubular and stationary (i.e., non-rotating) housing 280 sized to be 
disposed in the relatively small inner diameter 200 of sleeve 210. 
Stationary housing 280 has a longitudinal step-bore 290 for receiving 
fiber-optic cable 230 in the smaller diameter 300 of step-bore 290. 
Step-bore 290 includes an internally threaded portion 310 for reasons 
disclosed hereinbelow. Step-bore 290 also has a larger diameter 320 for 
receiving rotating means, such as a rotator assembly, generally referred 
to as 330, connected to mirror 240 for rotating mirror 240, as described 
more fully hereinbelow. In this regard, rotator assembly 330 includes a 
generally cylindrical rotatable housing 340 having mirror 240 mounted 
therein. Rotatable housing 340 also has a centrally disposed longitudinal 
bore 350 surrounding a generally cylindrical cable housing 360. Cable 
housing 360 in turn has a longitudinal bore 370 for housing fiber-optic 
cable 230 and an externally threaded proximal end portion 380 threadably 
engaging internally threaded portion 310 of stationary housing 280 for 
threadably connecting cable housing 360 to stationary housing 280. It will 
be appreciated from the description hereinabove, that fiber-optic cable 
extends from laser 235 and through bores 290 and 370. 
Still referring to FIGS. 3, 3A and 4, rotatable housing 340 has a helical 
or spiral groove 390 therearound formed in an exterior surface 400 thereof 
for receiving a pullable first cord 420 wrapped in a first spiral 
direction around rotatable housing 340. Rotatable housing 340 rotates in a 
clockwise first direction as first cord 420 is pulled, as described more 
fully hereinbelow. Groove 390 also receives a pullable second cord 440 
wrapped in a second spiral direction around rotatable housing 340. The 
second spiral direction is oppositely-orientated with respect to the first 
spiral direction. Rotatable housing 340 rotates in a counter-clockwise 
second direction as second cord 440 is pulled, as described more fully 
hereinbelow. In the preferred embodiment of the invention, cords 420 and 
440 are made of "KEVLAR" and may each have a diameter of approximately 
0.018 inch for being matingly received in groove 390. The material 
"KEVLAR" is preferred because it is capable of withstanding a relatively 
large pulling load in tension of approximately 80 pounds force before 
breaking. Such a "KEVLAR" cord 420/440 comprises polyamide fibers and is 
available from Synthetic Thread Co. located in Bethlehem, Pa. 
Referring to FIGS. 3, 3A, 4 and 5, retaining means, such as a retainer 450, 
engages first cord 420 and second cord 440 for retaining first cord 420 
and second cord 440 in groove 390. In this regard, retainer 450 is 
interposed between stationary housing 280 and rotatable housing 340 such 
that it retains first cord 420 and second cord 440 in groove 390 as first 
cord 430 and second cord 440 are pulled. Retainer 450 has a pair of 
recesses or cord ports 455a and 455b formed therein for reasons disclosed 
hereinbelow. Moreover, retainer 450 has a plurality of 
outwardly-projecting teeth 460 matingly engaging a corresponding cord-free 
portion of groove 390 to keep ports 455a/455b aligned with groove 390 to 
provide linear or axial motion to retainer 450 as described more fully 
hereinbelow. Also, teeth 460 engage groove 390 in such a manner as to 
connect string 510 (see FIG. 7) to retainer 450 and to transducer 500 (see 
FIG. 2) as described more fully hereinbelow. 
As best seen in FIG. 3, housed in rotatable housing 340 and coaxially 
aligned with distal end portion 237 of fiber-optic cable 230 is a pair of 
colinearly aligned transparent lenses 462 for collimating and then 
converging onto mirror 240 the laser light emitted from distal end portion 
237 of fiber-optic cable 230. In addition, mounted atop rotatable housing 
340 is centering means, generally referred to as 464, for centering the 
weld head in tube 50 and sleeve 210. The centering means 464 contemplated 
herein is of the type more fully described in U.S. patent application Ser. 
No. 08/126212 titled "System And Method For Laser Welding An Inner Surface 
Of A Tubular Member" filed Sep. 13, 1993 in the name of W. E. Pirl and 
assigned to the assignee of the present invention, the disclosure of which 
is hereby incorporated by reference. In addition, an inspection probe 466, 
which may be an eddy current probe or an ultrasonic probe, is attached to 
stationary housing 280 near the proximal end thereof for locating the 
proximal end (i.e., bottom edge) of sleeve 210. Locating the proximal end 
of sleeve 210 assists in suitably positioning the weld head at a 
predetermined axial Location within sleeve 210. Probe 466 has an 
electrical lead wire (not shown) extending through a passage 466' which 
itself extends longitudinally through rotatable housing 340. Moreover, 
stationary housing 280 may have a flow channel 467 formed axially therein 
for conducting a fluid (e.g., the shielding gas) to a radially expandable 
bladder 468 surrounding the proximal end portion of stationary housing 
280. Bladder 468 is capable of radially expanding into intimate engagement 
with inside surface 80 of tube 50 to provide a gas-tight seal between the 
weld head and tube 50. It is important that such a seal be provided. This 
is important because the seal provided by inflatable bladder 468 prevents 
contamination of the shield gas by the atmosphere in order to control the 
surface finish of the weld, the quality of the weld, and the weld 
penetration. 
Returning to FIG. 2, system 190 further comprises a first "linear" motor 
470 disposed externally to tube 50. First motor 470 engages an end portion 
of first cord 420 for pulling first cord 420. A second "linear" motor 480 
is also disposed externally to tube 50 and engages an end portion of 
second cord 440 for pulling second cord 440. Rotatable housing 340 rotates 
about its longitudinal axis in the clockwise direction as first cord 420 
is pulled by first motor 470 and rotates in the counter-clockwise 
direction as second cord 440 is pulled by second motor 480. First motor 
470 and second motor 480 may be of the type available from MicroMo located 
in St. Petersburg, Fla. Moreover, system 190 may also comprise a suitable 
robotic mechanism, generally referred to as 490, connected to stationary 
housing 280 for supporting the weld head in outlet plenum 150 or 
alternatively in inlet plenum 140. In this regard, robotic mechanism 490 
may be a ROSA (Remotely Operated Service Arm) available from the 
Westinghouse Electric Corporation located in Pittsburgh, Pa. In addition, 
system 190 may further comprise a linear displacement transducer 500 
connected to an inelastic string 510 which is preferably formed of 
pre-expanded or pre-stretched PTFE "TEFLON". Transducer 500 is itself 
electrically connected to motors 470/480 in order to control the operation 
of motors 470/480 as described more fully hereinbelow. Transducer 500 may 
be of the type such as is available from Sensotec, Inc. located in 
Columbus, Ohio. 
Referring to FIGS. 2, 3, 5, 6 and 7, first cord 420 has an end thereof 
connected to first motor 470. From first motor 470, first cord 420 extends 
through conduit 250, through a passage 510, through a cord port 520, into 
a bottom portion 530 of groove 390 that is formed in retainer 450, and 
thence into the previously mentioned cord port 455a. From cord port 455a, 
first cord 420 engages the proximal end portion of groove 390 and wraps 
around the proximal end portion of rotatable housing 340. 
Referring to FIGS. 2, 3, 6 and 7, second cord 440 has an end thereof 
connected to second motor 480. From second motor 480, second cord 440 
extends through conduit 250, through passage 560, through cord port 570, 
into a bottom portion 570 of groove 390 and thence into the previously 
mentioned cord port 455b. From cord port 455b, second cord 440 engages the 
distal end portion of groove 390 and wraps around the distal end portion 
of rotatable housing 340. 
Referring to FIGS. 2, 3, 5, 6, 7 and 8, the previously mentioned inelastic 
string 510 has an end thereof secured to retainer 450, as at location 590, 
and the other end thereof connected to transducer 500 for providing input 
to transducer 500 such that transducer 500 is capable of monitoring the 
movement of retainer 450. 
Referring to FIG. 9, a plurality of spaced-apart and generally 
arcuate-shaped gas ports 600 are formed in rotatable housing 340 and 
surround lenses 462 for allowing gas to flow around lenses 462 in order to 
ameliorate oxidation of lenses 462 as lenses 462 are exposed to the laser 
light energy passing therethrough. 
Referring now to FIG. 10, a plurality of spherical bearings 610 are 
interposed between rotatable housing 340 and stationary housing 280 for 
allowing rotatable housing 340 to readily rotate within stationary housing 
280. 
OPERATION 
Heat exchanger 10 is removed from service in a manner customarily used in 
the art and sleeve 210 is expanded into engagement with degraded tube 50 
to connect sleeve 210 to tube 50 in such a manner as to cover or bridge a 
degraded portion (not shown) of tube 50. System 190 is then disposed 
sufficiently near heat exchanger 10 to perform the required laser welding. 
In this regard, stationary housing 280, which belongs to the weld head, is 
connected to robotic mechanism 490 and then maneuvered into tube 50 by 
robotic mechanism 490. Conduit driver 260 is operated to drive conduit 250 
and the weld head connected thereto axially along inside surface 80 of 
tube 50 to a position adjacent the inner surface 200 of sleeve 210 to be 
welded. In this regard, probe 466 is activated for precisely identifying 
the proximal end or bottom edge of sleeve 210 in order to axially locate 
the weld head adjacent the portion of sleeve 210 to be welded. 
Moreover, system 190 is capable of fusing sleeve 210 to tube 50 by welding 
around the circumference of inner surface 200 of sleeve 210. In this 
regard, first motor 470 is operated to pull first cord 420. As first cord 
420 is pulled, rotatable housing 340 rotates in the clockwise direction 
due to the engagement of first cord 420 in groove 390. Also, as rotatable 
housing 340 rotates, mirror 240 will rotate to a like extent because 
mirror 240 is fixedly mounted in rotatable housing 340. In addition, as 
rotatable housing 340 rotates in the clockwise direction, retainer 450 
will travel axially downwardly due to the engagement of teeth 460 with the 
cord-free portion of groove 390. As contemplated herein, this 
configuration of rotatable housing 340 and its associated first cord 420 
will allow rotatable housing 340 to make at least eight revolutions before 
retainer 450 stops its downward travel. This is important because at least 
five test revolutions may be required to verify the rotational speed of 
mirror 240 before energizing the laser to make the weld. Applicants have 
discovered that precisely obtaining the desired rotational speed of mirror 
240 improves the quality of the weld. 
After the desired rotational speed (e.g., three revolutions per minute) of 
mirror 240 is obtained, laser 220 is activated to emit laser light into 
the proximal end portion 235 of fiber-optic cable 230. As the laser light 
is conducted through fiber-optic cable 210, it will exit distal end 
portion 237 of fiber-optic cable 230 and travel through lenses 462 which 
collimate and then focus the light onto mirror 240 which in turn reflects 
the light onto inner surface 200 of sleeve 210 to weld inner surface 200. 
Moreover, as mirror 240 and rotatable housing 280 simultaneously rotate, 
the light reflected from mirror 240 will circumscribe inner surface 200 of 
sleeve 210 for circumferentially fusing sleeve 210 to inside surface 80 of 
tube 50. It will be appreciated from the description hereinabove that the 
invention is capable of forming multiple (e.g., two) spaced-apart 
circumferential weldments on inner surface 200 of sleeve 210, if desired. 
As previously described, rotatable housing 340 will rotate in the clockwise 
direction as first cord 420 is pulled and retainer 450 will downwardly 
travel due to the engagement of teeth 460 with groove 390. The downward 
travel of retainer 450 will stop when teeth 460 reach the bottom of groove 
390. At this point, it is desirable to reposition retainer 450 at the top 
of groove 390 to perform another circumferential weldment, if desired. In 
this regard, second cord 440 is pulled by second motor 480 to rotate 
rotatable housing 340 in the counter-clockwise direction in order to cause 
retainer 450 to travel to the top of groove 390. Retainer 450 will stop 
its upward travel when teeth 460 reach the top of groove 390. At this 
point, mirror 240 is in position to perform another weldment. Of course, 
inelastic string 510, which has one end thereof secured to rotatable 
housing 340 and the other end connected to transducer 500, senses the 
extent of movement of rotatable housing 340 and provides feedback to 
motors 470/480 for controllably operating motors 470/480. 
After the required number of tubes 50 are sleeved in the manner described 
hereinabove, system 190 is removed from the vicinity of heat exchanger 10 
and heat exchanger 10 is then returned to service. 
It will be appreciated from the description hereinabove, that an advantage 
of the present invention is that it is particularly well-suited for fusing 
sleeve 210 to a tube 50 having a relatively small inside diameter 80 
(e.g., an inside diameter less than or equal to approximately 0.313 inch). 
Such small diameter tubes 50 lack sufficient room therein for receiving a 
suitable motor to rotate mirror 240. According to the invention, rotating 
means is provided that is capable of rotating mirror 240 in such a manner 
that it is not necessary to locate a motor within such a small diameter 
tube 50. 
Although the invention is illustrated and described herein in its preferred 
embodiment, it is not intended that the invention as illustrated and 
described be limited to the details shown, because various modifications 
may be obtained with respect to the invention without departing from the 
spirit of the invention or the scope of equivalents thereof. For example, 
the weld head may be axially translated in tube 50 as mirror 240 
simultaneously rotates to provide a helically extending weldment on inner 
surface 200 of sleeve 210. A helically extending weldment provides 
increased assurance that sleeve 210 is sealingly fused to tube 50 because 
a larger surface area of the inner surface 200 of sleeve 210 will be 
welded. 
Therefore, what is provided is a system and method for laser welding an 
inner surface of a small diameter tubular member, which tubular member may 
be a repair sleeve disposed in a nuclear heat exchanger heat transfer 
tube.