System for plugging tubes by welding

Semi-automatic welding apparatus is suspended from a plug body vertically force fitted into the end of a tube to which the plug is welded. The plug body configuration is disclosed, along with the internal arrangement it provides for suspending the welding apparatus. A mandrel is depicted in its movable parts which enables it to be manually linked between the plug body and welding apparatus.

BACKGROUND OF THE INVENTION 
1. Scope of the Invention 
The present invention relates to the suspension of welding apparatus from 
plug bodies welded in the end of tubes extended down through horizontal 
tube sheets. More specifically, the invention relates to linking a plug 
body, force fitted up into the end of a tube, with welding apparatus by a 
manually engageable, and disengagable, mandrel permanently mounted on the 
welding apparatus and insertable into the plug body. 
2. Prior Art 
All parts and pieces of nuclear power plants are continually inspected 
during fabrication and service. Elaborate inspection techniques ferret out 
tubes of the heat exchangers of nuclear steam generators which have 
failed, or are near failure. A deliberate plan is to provide a 
pre-determined excess of tubes for the heat exchanger. Then, if inspection 
decrees it prudent to remove a tube from service, sufficient tubes remain 
to carry on. Of course, eventually, the number of tubes plugged, removed 
from service, eventually force a shut down for a massive overhaul of the 
system. But it is practical to seal off a large number of tubes in these 
heat exchangers and continue their function without crippling the overall 
system. 
The present problem assumes the inspection technique and apparatus have 
designated one or more tubes to be removed from service. Further, the 
assumption is simply that a plug body of metallic material can be jammed 
up into the end of the designated tube and its periphery welded to the 
mouth of the tube to effectively bring about their union. 
Unfortunately, for this simple plan, these heat exchangers are "hot." The 
heat exchanger is part of the cycle containing radioactive material. 
Although the heat exchanger is drained of its fluids in anticipation of 
the tube blocking operation, a radiation level remains which must be 
accounted for in employing personnel for the plugging operation. The tube 
plugger is required to jump into the heat exchanger, locate the offending 
tube, and hammer a plug body into its open end, weld the body into place 
within a prescribed program of man-rem hours. Therefore, the less time a 
welder spends in the heat exchanger, the better. 
Although hammering a tube body up into the end of a designated tube and 
welding it in place with a hand-held welding gun is not complex by 
objective standards, its demand for manual dexterity under the stress of 
the radiation threat has created problems. Plug bodies have been 
misaligned in hammering them into their force fit position and the guiding 
mandrels of welding guns have been bent and broken in forming the welds 
between tube and plug. The technology is demanding another step forward in 
the art to raise the quality of the plugging operation. 
SUMMARY OF THE INVENTION 
The present invention provides a bullet-shaped plug, which is externally 
sized to be forced upwardly into a tube, the internal wall of the plug 
having a circular race formed horizontally within the walls to receive 
spherical locking elements moved into the race from an elongated mandrel 
positioned up inside the bore of the plug with welding apparatus suspended 
from the mandrel. The welding gun attached to the mandrel is thus fixed to 
the lower end of the mandrel and the gun and mandrel rotate while locked 
to the groove within the plugs to bring the electrode of the gun into 
uniform contact with the edges of the plug, the tube into which the plug 
is thrust, and the tube sheet surface adjacent the tube edges. 
Other objects, advantages and features of the invention will become 
apparent to one skilled in the art upon consideration of the written 
specification, appended claims and accompanying drawings.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT 
General Arrangement and Operation 
Actually, FIG. 1 provides a fairly complete disclosure of the broader 
concepts of the invention. Only a fragment of the tube sheet 1 is shown as 
having the plurality of tubes 2 thrust downwardly through the tube sheet 
in make up of a heat exchanger which is a part of the steam generator of a 
nuclear reactor. The assumption is that one of the tubes 2 has been 
inspected and found to be defective. The heat exchanger has been built 
with an excess of heat exchange tubes, so that upon failure, a significant 
number of the excess tubes may be plugged, as they become defective, 
without taking the heat exchanger out of service. At least the heat 
exchanger is not taken out of service between major shutdowns for more 
extensive repair and servicing. 
The tube 2, designated as defective by inspection, is taken out of service 
by welding a plug 3 into the open end of the tube, which extends through 
the tube sheet 1. In principal, this method of removing tubes from service 
is quite simple. In practice, the welding operation is carried out in an 
extremely awkward location. 
First, the inside of the heat exchanger is radioactive to some extent. 
Therefore, the time available to personnel to make repairs is limited by 
the number of man-rem hours which is safe. Obviously, it behooves the 
welder to get in and out of this area as quickly as possible. This haste 
makes waste in the form of broken equipment and poorly executed welds. The 
present invention provides a system wherein a plug can be accurately force 
fit into a tube and welding apparatus can be suspended from inside the 
plug and directed into automatically welding between the lower edge of the 
plug, the tube in which the plug is force fit, and the tube sheet through 
which the tube is thrust. Thus, manual operation is reduced to the level 
where quality does not depend upon unskilled labor. 
More specifically, welding gun 4 is linked to the inside wall of plug 3 
with a mandrel 5. Thus, we have the apparatus to carry out the welding 
operation on the plug, tube and sheet clinging like a bat to the underside 
of the tube sheet. From this position, the welding apparatus can execute 
its union of the plug to the tube sheet uniformly as the apparatus is 
rotated from its perch inside plug 3. 
The overall operation is quite simple. A workman with little skill can 
hurry into the area below the tube sheet and accurately drive the novel 
form of plug 3 into position. Force fit into position, the plug can 
support hundreds of pounds of weight. The workman can then thrust mandrel 
5 up into the plug, trip linking mechanism of the mandrel, to couple the 
mandrel and plug in a manner which will provide rotational movement of the 
mandrel. Essentially, the worker needs only then to punch a button to 
start the welding apparatus and depart the dangerous area, while the weld 
is completed. Returning, the workman can unlatch the mandrel with a push 
of a button, hammer another plug into place and repeat the welding 
operation. The result is a reduction in man-rem hours over previous 
accumulations involving hand-held welding equipment. The second result is 
uniform, dependable welds between the plugs, tubes and sheets. 
SUSPENSION OF WELDING GUN 4 
Heretofore, the disclosure has described the welding gun as clinging to the 
internal wall of the tube plug 3. The gun 4 can be inspected in its FIG. 1 
position. The gun is placed in this position manually by a grasp on handle 
6. The gun is placed in the position shown, mandrel 5 extending up into 
plug 3. Push rod 7 is moved upward as viewed in FIG. 1, to keep the side 
wall of the tube plug and the mandrel is disengaged. Push rod 7 is, in 
effect, linked to be manually actuated by latch mechanism 8. The operator 
actuates latch 8 to move push rod 7 upward, inserting a mandrel into the 
tube plug, and then allowing a spring to force rod 7 downward, so the 
locking elements between the mandrel and tube plug will engage. The 
operaton to carry out this function of the apparatus is readily discerned 
from inspection of FIG. 1. 
The sequence is for the operator to insert the mandrel of the gun up into 
the tube plug and operate the mechanism to latch the mandrel to the inside 
wall of the plug. The welding gun attached to the mandrel is then actuated 
to weld the tube plug into place. 
ROTATION OF THE WELDING ELECTRODE ON GUN 4 
Gun 4 has an outer casing 10, which is effectively linked to the underside 
of tube sheet 1. A cup structure 11 is mounted on the top of casing 10, so 
the cup lips 12 will positively engage the surface of the tube sheet 1 as 
gun 4 has its mandrel inserted up into the tube plug. This positive 
engagement and latch of the entire gun to the tube plug by the mandrel, 
links the welding gun casing and the tube sheet together, through the cup 
11. 
Mounted on the casing 10 is a motor 13, which is enclosed in its own sub 
housing 14. Therefore, motor 13 is fixed in relation to casing 10. Gears 
15 connect the motor 13 to barrel 16, which is rotatable within casing 10 
of the gun. It is on this barrel 16 that the welding electrode is mounted, 
so it will follow the edge of the tube plug and tube and the hole of the 
sheet to weld them together. 
Barrel 16 is essentially a cylindrical housing. The barrel rotates with its 
longitudinal axis aligned with the axis of the mandrel. Welding electrode 
17 is offset from the axis the radial distance which will cause it to 
engage the surface to be welded. Therefore, with the gun firmly planted on 
the underside of the tube sheet 1, motor 13 is actuated to rotate barrel 
16, so the welding electrode 17, mounted on the barrel, will be 
automatically carried over the surfaces to be welded together. 
Cup 11 has at least two functions. As described, it forms a link between 
the tube sheet and the outer gun casing 10, so that the casing will be 
fixed in relation to the tube sheet while the barrel 16 is rotated by 
motor 13. Secondly, the cup forms a retention chamber about the electrode 
and welded surfaces to maintain the welding process isolated. The present 
welding system utilized is the so-called TIG process. Essentially, the 
electrode of this system has an electric arc generated between it and the 
surfaces to be welded within an inert gas atmosphere. Cup 11 forms an 
effective isolation chamber in which this welding process can be carried 
out. 
THE COOLING SYSTEM 
The welding operation with gun 4 generates a large quantity of heat. It is 
necessary that this heat be removed from the welding gun structure. 
Essential elements of this cooling system are to be traced from the inlet 
coolant conduit 20 which directs coolant to the base of the electrode. The 
coolant is then conducted by way of outlet conduit 21, and is connected up 
to coolant inlet 22 for circulation of the coolant with cavity 23 of the 
barrel 16. The majority of the heat generated by the welding electrode is 
located in heat exchange contact with this cavity, and the coolant therein 
absorbs the heat. The coolant is then conducted from this cavity by outlet 
24. The pump for the coolant, and the means for dissipating the heat of 
the coolant, are not shown. The disclosure is essentially directed to the 
cooling problem of flowing the coolant to those specific areas of the gun 
4, which require heat to be withdrawn, in order for operation of the gun 
to be carried on continuously. 
SUB-CONCLUSION 
The operation of the various elements and systems associated with the gun 4 
have been outlined in their structure and cooperation disclosed in FIG. 1. 
The overall operation is apparent in that the gun 4 is placed in the 
position shown in FIG. 1 manually. The motor 13 is energized to rotate 
barrel 16 through gears 15, with its electrode, while coolant is 
circulated to withdraw the heat generated. When the welding at position 
shown is completed, latch 8 is actuated to move plunger push rod 7 to 
disengage the mandrel from the internal wall of the tube plug. The gun is 
then dropped down and transferred to another tube plug where welding is 
required, and the operation repeated. For more detailed disclosure of the 
tube plug and its force fit into a tube 2, FIGS. 2 and 3 are provided. 
FIGS. 4 and 5 are provided to disclose, with unmistakable clarity, the 
mandrel's all-important link with the tube plug. 
TUBE PLUG 3 
FIGS. 2 and 3 are to be taken together for thorough understanding of the 
different parts of the plug in their cooperation with tubes 2 and the 
mandrel 5 under the concepts of the invention. FIG. 2 discloses the plug 3 
partially thrust up into tube 2. FIG. 3 shows the plug 3 in its final 
position within the tube 2. 
The external configuration of plug 3 is that of a bullet. The external wall 
of the plug is bevelled at 30, so there will be absolutely no hangup in 
getting the plug initially started into tube 2. From bevel 30, along the 
outside surface of the plug 3, down to about position 31, the diameter of 
the plug is uniform and approximately 0.005" smaller than the internal 
diameter of tube 2. Welding electrode 17 is mounted on the barrel and 
offset from the axis the distance which will enable it to properly engage 
the surface to be welded a radial distance from the axis. 
Initially, the plug is inserted by hand, as shown in FIG. 2. From position 
31 to the lower edge of position 32, the external sides of the plug 3 are 
given a slight flare. In an actual reduction to practice, the diameter at 
position 31 was 0.005", flaring outwardly to a diameter at position 32 of 
0.675". 
The cylindrical surface from bevel 30 to position 31 provides an extensive 
guiding portion for the plug for accurate manual insertion up into 
designated tube 2. To get the plug the rest of the way into position, a 
hammer can then strike the plug upward from its lower edge and readily 
swage the plug from position 31 to edge 32. The result is a force fit of 
the plug which will resist dislodgment by hundreds of pounds of force. The 
design contemplates at least 500 pounds of force being required to remove 
the plug. 
The internal bore 33 is sized to receive the outside diameter of the 
mandrel 5 of FIG. 1. Bore 33 is formed cylindrically from position 34 to 
position 35 to accommodate the upper portion of mandrel 5. A groove 36 is 
formed in this wall, shaped to accommodate spherical bodies mounted on 
mandrel 5. Groove 36 functions as a race for these spherical bodies. The 
cooperation between the race structure and the spherical bodies will be 
more clearly seen in connection with FIGS. 4 and 5. 
FIG. 3 shows the plug 3 hammered up into position so the lower edges at 
position 32 are flush with the lower edges of tube 2 and tube sheet 1 
surface. The force fit lodges the tube plug into position with such 
stability that the welding gun 4 can be suspended therefrom with the 
assurance that the plug will not be dislodged from its FIG. 3 position. 
THE MARRIAGE OF THE PLUG AND MANDREL 
FIGS. 4 and 5 show plug 3 in its FIG. 3 position, force fit into tube 2. 
FIGS. 4 and 5 are to be taken together in showing the two-step rape of 
plug 3 by the mandrel 5. FIG. 4 shows the male mandrel 5 partially 
inserted into female bore 33, its linking spherical elements retracted so 
as not to impede or obstruct the full engagement of mandrel 5 up to bore 
33 of plug 3. FIG. 5, of course, shows the mandrel 5 in fully inserted 
position and the spherical elements forced radially outward into 
engagement with groove-race 36. 
The external profile of mandrel 5 is that of a cylinder. This protuberance 
could be fabricated into various parts and threaded together as indicated. 
The precise parting lines, number of parts and modes of assembly are a 
matter of fabrication design which do not form a significant aspect of the 
invention. The essential elements are that the mandrel 5 includes a 
central cavity 40, in which plunger 41 reciprocates. Plunger 41 is moved 
upwardly by direct engagement with push rod 7, and is urged downwardly by 
the force of spring 42 between the top of the cavity 40 and the top of the 
plunger 41. In reciprocation, the plunger 41 actuates spherical bodies, or 
balls 43, into and out of groove-race 36. 
In FIG. 4, plunger 41 is shown in its upward position carrying its 
downwardly facing ram 44 out of contact with balls 43. Without contact 
with ramp 44, the balls are moved toward the axis of the mandrel 5, and 
out of groove-race 36. The result is that the cylindrical profile of 
mandrel 5 slides smoothly, upwardly, into position with bore 33. However, 
FIG. 5 discloses the actuation of this mechanism to link tube 3 and 
mandrel 5, so that mandrel 5 will be positively held in its upward 
position, within the bore 33, and yet be given the freedom to rotate with 
balls 43 as a bearing between the two structures. 
FIG. 5 discloses how balls 43 have been contacted by ramp 44, as plunger 41 
is moved downwardly. Contacted by the surface of the ramp, the balls are 
forced radially outward through holes 45, the sizing and arrangement is 
such that the balls are not moved entirely out of their holes, but enough 
of the balls are moved into the groove-race 36 to give the desired linkage 
between the mandrel and the plug. The balls are held in this position by 
contact with the ramp 44 and thus lodged between plunger 41 and 
groove-race 36. So wedged, the balls become a protuberance structure from 
the side of the mandrel 5, which does not permit withdrawal of the mandrel 
from the bore 33, yet mandrel 5 is free to rotate with the balls as 
rolling contacts between the mandrel and top groove. 
It is now evident that the end result of the arrangement is that the balls 
are manually actuated by the push rod and plunger to act as protuberances 
moved outwardly from the mandrel to fully engage the tube plug and thereby 
suspend the mandrel and welding equipment attached to, and part of, the 
mandrel from the underside of the tube sheet. Thus suspended, the welding 
apparatus attached to the mandrel is held in position to rotate and 
perform its welding function on the very tube plug from which it is 
suspended. 
CONCLUSION 
The invention finds embodiment in the novel form of tube plug 3, the 
mandrel 5 linkage with the tube plug and the cooperative arrangement of 
welding gun 4. Ultimately, the electrode of the gun is brought into 
effective contact with the lower edge of the plug, the ends of the tube 
into which the plug is positioned and the tube sheet to form them into a 
unitary weld, which seals the tube. The unique combination enables 
relatively unskilled personnel to position the novel tube plug into its 
force fit with the tube, so it may be efficiently welded. 
Further, relatively unskilled personnel may guide the mandrel up into the 
tube plug and linkage readily actuated by push-button to suspend the 
welding gun from the tube plug. Finally, the welding operation is reduced 
to the level of a push button, actuate the welding gun and the subsequent 
automatic operation of the gun to complete the weld. Removal of the gun 
and transfer to a second tube plug is relatively child's play, given the 
invention as embodied. Thus, the technology of plugging tubes is advanced 
into the realm of semi-automatic operation which reduces man-rem hours, 
and elevates the quality of the welding work product. 
From the foregoing, it will be seen that this invention is one well adapted 
to attain all of the ends and objects hereinabove set forth, together with 
other advantages which are obvious and inherent to the method and 
apparatus. 
It will be understood that certain features and subcombinations are of 
utility and may be employed without reference to other features and 
subcombinations. This is contemplated by and is within the scope of the 
invention. 
As many possible embodiments may be made of the invention without departing 
from the scope thereof, it is to be understood that all matter herein set 
forth or shown in the accompanying drawings is to be interpreted in an 
illustrative and not in a limiting sense.