Plugging apparatus and method using a hydraulically assisted plug expander

A plugging apparatus and method utilizing a plug expander that is hydraulically assisted. The apparatus generally comprises a plug shell having a closed end and an open end, an expander element contained within the shell which is movable between the open and closed ends thereof for wedgingly engaging the shell and radially expanding it, and an expansion mechanism including a combination pull rod and expansion mandrel that is connected to the expander element contained within the shell. A source of pressurized hydraulic fluid is connected to the combination pull rod and mandrel. The mandrel is capable of conducting pressurized hydraulic fluid between the closed end of the shell and the expander element in order to facilitate the movement of the expander element toward the open end of the shell. The invention may be used to conveniently and effectively plug heat exchanger tubes of either nuclear or fossil fuel steam generators.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention generally relates to plugging tubes by means of a radially 
expandable plug having an expander element, and specifically concerns both 
an apparatus and a method for plugging relatively small diameter heat 
exchange tubes in either a fossil fuel or nuclear steam generator. 
2. Description of the Prior Art 
Plugging devices for plugging the heat exchanger tubes of steam generators 
are known in the prior art. Often, such devices are used to seal off one 
or more of the U-shaped heat exchanger tubes contained within a nuclear 
steam generator when the walls of these tubes become degraded below 
acceptable limits. If such tubes are not plugged or repaired, they may 
crack and allow radioactive water from the primary side of the generator 
to leak into the non-radioactive water in the secondary side. This, in 
turn, could result in the radioactive contamination of the non-radioactive 
steam that Westinghouse-type nuclear steam generators provide to turn the 
turbines of the electric generators of the plant. Hence the plugging of 
potentially degraded heat exchanger tubes is an important maintenance 
operation. 
The plugs used in such prior art devices generally comprise a tubular shell 
that is open on one end and closed at the other end, and which contains a 
frustoconcially shaped expander member. In one type of prior art plug, the 
expander element is a conical wedge shaped like a common cork used to seal 
a bottle, and is disposed completely within the interior of the shell with 
its larger circular end facing the inner surface of the closed distal end 
of the plug shell. Instead of being cylindrical, the interior walls of the 
shell are slightly tapered by increasing the thickness of the shell walls 
from the distal closed end to the proximal open end. When the cork-shaped 
wedge is forcefully pulled from the closed end toward the open end of the 
shell, it will radially expand the plug into sealing engagement with the 
inner wall of a tube by a wedging action. Such a plug design is completely 
described in U.S. Pat. No. 4,390,042 invented by Harvey D. Kucherer and 
assigned to the Westinghouse Electric Corporation. In this particular plug 
design, the cork-shaped expander wedge is forcefully pulled from the 
distal to the proximal end of the plug shell by means of a pull-rod that 
is connected to the expander member on one end and to a hydraulic ram on 
the other end. 
In most instances, this particular plug design is capable of reliably and 
conveniently plugging the open ends of a potentially degraded U-shaped 
tube whose ends are surrounded by the thick steel tubesheet that divides 
the primary from the secondary side of the steam generator. The forceful 
pulling of the cork-shaped expander member along the axis of the shell not 
only radially expands the wall of the shell outwardly as the member is 
wedgingly drawn toward the proximal end of the shell, but further applies 
an extruding force to the metallic walls of the shell along the 
longitudinal axis of the tube. 
In a variation of this design, an explosive charge is used in lieu of a 
pull-rod to move the cork-shaped wedge along the longitudinal axis of the 
tube shell. In such plugs, the expansion member is situated near the open 
end of the tubeshell, and the explosive charge is disposed between the 
proximal end of the shell and the top surface of the expansion member. 
When the charge is detonated, the cork-shaped wedge is pushed along the 
longitudinal axis of the shell until it abuts the closed distal end of the 
plug. 
Unfortunately, there are certain mechanical limitations associated with 
these prior art plug designs that interfere with their usefulness in 
certain applications. For example, in plugs wherein a pull-rod is used to 
draw the cork-shaped wedge against the internally tapered walls, there is 
a limit as to the inner diameter of the tubes that such plugs can reliably 
seal. In nuclear steam generators utilizing heat exchanger tubes having 
inner diameters of approximately 0.50 inches or greater, this mechanical 
limitation usually poses no problem. On the other hand, for tubes whose 
inner diameter is less than 0.50 inches, it becomes increasingly difficult 
to design a pull-rod capable of withstanding the tensile force necessary 
to draw the cork-shaped wedge throughout the entire longitudinal axis of 
the tubeshell. Even when the pull-rod is formed from the strongest 
commercially available tool metals, such as Vascomax.RTM., it will still 
have a tendency to break off in small diameter plugs since its own 
external diameter can be no larger than the minimum internal diameter of 
the tapered interior of the plug shell, and since the tensile strength of 
any material decreases exponentially with its diameter. One way of solving 
this problem is to reduce the angle of both the cork-shaped wedge and the 
tapered walls within the plug shell. However, to obtain the same quality 
of seal, the plug must be lengthened. While the use of longer plugs poses 
no problem in tubes centrally located in the tubesheet, they are difficult 
if not impossible to use in the peripheral tubes of the tubesheet due to 
the long stroke the ram-operated pull-rod member has to make to completely 
pull the wedge through the plug shell. 
Still another limitation of this prior art design arises from the size of 
the hydraulic ram that is required to apply the tensile force necessary to 
draw down the cork-shaped wedge. Such rams typically have a minimum 
diameter of about 4.5 inches. Yet, around the periphery of the tubesheet, 
a clearance of only one half inch exists between the tube and the 
bowl-shaped wall that forms the primary side of the nuclear steam 
generator. Hence, it is difficult to provide a ram that is powerful enough 
to generate the required tensile force yet compact enough to be easily 
manipulated in the limited space surrounding the peripheral heat exchanger 
tubes. 
In an attempt to solve the foregoing problems the previously mentioned 
explosive-type plugs were developed. But while the use of explosives 
obviates the need for pull-rods and hydraulic rams, they proven in 
practice to generate at least as many problems as they solve. To minimize 
the amount of generator down-time necessary to complete the plugging 
operation, a group of explosive plugs are usually positioned and detonated 
simultaneously. However, the simultaneous detonation of a plurality of 
such plugs generates powerful mechanical shock waves that can break 
weakened sections of the U-shaped heat exchanger tubes that are not being 
plugged, thereby defeating the overall purpose of the plugging operation. 
These shock waves can also damage the sensitive monitoring instrumentation 
present on all nuclear steam generators. Additionally, the special 
arrangements that are necessary for the transportation of such explosively 
operated devices, and the necessity for licensed explosives technicians to 
install such plugs has made them substantially more expensive to use than 
plugs which are expanded by a hydraulically operated pull-rod. 
Clearly, there is a need for a new type of plugging device that is capable 
of reliably plugging small diameter as well as large diameter heat 
exchanger tubes in steam generators. Ideally, such a device should be 
capable of installing plugs even in heat exchanger tubes of limited 
access, such as the tubes situated around the periphery of the tubesheet. 
SUMMARY OF THE INVENTION 
In its broadest sense, the invention is an apparatus for plugging a 
conduit, such as an Inconel.RTM. tube, that comprises a plug shell having 
a closed end and an open end, an expander element contained within the 
shell that is movable across said shell between the open and closed ends 
thereof for wedgingly engaging and spreading the shell and thereby 
radially expanding it, and an expansion means including a source of 
pressurized hydraulic fluid for facilitating the movement of the expander 
element by hydraulically expanding the interior of the shell. 
The expansion means may include a pull-rod that is detachably connected to 
the expander element for applying a complementary pulling force to the 
expander element when the pressurized hydraulic fluid is introduced in the 
interior of the shell. The pull-rod may include a piston face in fluid 
communication with the source of pressurized fluid for generating the 
pulling force on the pull-rod. In one method of the invention, the 
expansion means may conduct the pressurized fluid in the interior of the 
shell between the expander element and the closed ends thereof in order to 
hydraulically push the expander element like a piston from the closed to 
the open end of the shell. In a variation of this method the expander 
element may be moved by the simultaneous application of a hydraulic force 
from the pressurized fluid, and a pulling force from the rod. In another 
method of the invention, the pressurized fluid may be conducted to all 
points of the interior of the shell while the rod applies a pulling force. 
When this method is used, the cross sectional area of the expander element 
facing the closed end of the shell may be made larger than the cross 
sectional area of the end of the expander element facing the closed end of 
the shell, so that a net hydraulic force is generated by the pressurized 
fluid that assists the pulling force applied by the rod in moving the 
expander element. In a variation of this method, pressurized fluid may be 
conducted only between the expander element and the open end of the shell 
in order to expand the shell, while a pulling force is applied by the rod 
means to move the expander element toward the open end of the shell. 
The pull-rod may constitute a tubular mandrel connected to the source of 
pressurized hydraulic fluid. This mandrel may be detachably connectable 
with a bore that extends completely through the expander element for 
conducting pressurized fluid between the element and the closed end of the 
shell. Additionally, both the mandrel and the bore may include mating 
threads so that the mandrel may be easily connected with the expander 
element prior to the expansion operation, and then easily disconnected 
therefrom after the plug shell has been expanded into sealing engagement 
with the tube. 
The apparatus and method of the invention provide a convenient and reliable 
way to plug both small diameter and peripherally located tubes within the 
tubesheet of a steam generator, whether fossil fuel or nuclear. The use of 
the expander element as a hydraulic piston within the plug shell, and the 
provision of a piston face on the pull-rod minimizes or eliminates the 
need for a large hydraulic ram beneath the plug shell during the plugging 
operation, and results in plugs which are reliably and easily installed in 
their respective tubes without any of the aforementioned disadvantages 
associated with prior art plugs and plugging methods.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference now to FIGS. 1A and 1B, wherein like reference numerals 
designate like components of the invention throughout all of the several 
figures, the plugging apparatus 1 of the invention is particularly adapted 
for plugging a tube 3 in the tubesheet 5 of a nuclear steam generator. 
Generally, the plugging apparatus 1 comprises a plug 7, and an expansion 
assembly 14. The plug is formed from a tapered, hollow plug-shell 9 that 
contains a cork-shaped expander element 11. The expansion assembly 14 
includes a hydraulic inlet block 16 that is connected to a source of 
pressurized fluid 18 for hydraulically expanding the shell 9, and a 
pull-rod mechanism 20 that is detachably connected to the expander element 
11 of the plug 7 for applying a tensile force onto the element 11 and 
drawing it down into the position illustrated in FIG. 1B. As will be 
described in more detail hereinafter, the pressurized hydraulic fluid 
which may be conducted to one or more regions of the interior of the shell 
9 always serves to expand the walls of the shell 9 away from the outer 
surface of the expander element 11, thereby reducing the amount of tensile 
force that the pull-rod mechanism 20 must exert onto the expander element 
11 to draw it down into the position illustrated in FIG. 1B. 
Turning now to a more detailed description of the plug 7, the shell 9 
includes a distal closed end 22 that terminates in a wall 24 having a 
chamfered end 25 for facilitating the insertion of the shell 9 into the 
open end of a tube 3. This shell 9 further includes a proximal open end 26 
that terminates in a circular opening 28 circumscribed by a flat annular 
wall 30. In the preferred embodiment, the circular opening 28 leads into a 
threaded bore 32 that in turn communicates with the interior of the shell 
9. This threaded bore 32 is matable with the threaded end of a nipple 33 
that extends out of the top face of the inlet block 16. 
Circumscribing the hollow interior of the shell 9 are tapered inner walls 
34. These walls 34 are circular in cross-section with respect to the 
longitudinal axis of the shell 9. The walls 34 converge to their minimum 
extent at the threaded bore 32 located at the proximal end of the shell 9, 
and diverge to their maximum extent at the wall 24 which is located at the 
distal closed end 22 of the shell 9. The expander element 11 is formed 
from a cork-shaped body 36, the conical taper of which is preferably equal 
to the conical taper of the inner walls 34. This substantial equivalence 
in the taper of the cork-shaped body 36 and taper of the inner walls 34 of 
the shell 9 advantageously allows a large portion of the outer surface of 
the cork-shaped body 36 to engage the tapered inner walls 34 of the shell 
9 in sealing engagement when the expander element 11 is drawn downwardly 
toward the threaded bore 32. It should be noted that the flat, circular 
distal end 38 of the cork-shaped body 36 has a larger cross-sectional area 
with respect to the longitudinal axis of the shell 9 for a purpose that 
will become evident presently. Finally, the cork-shaped body 36 includes a 
centrally disposed, threaded bore 42 circumscribed by an annular recess 
44. 
Turning now to a more detailed description of the expansion assembly 14, 
this portion of the invention includes a pull-rod member 50 that can also 
function as a hydraulic mandrel, as well as be seen shortly. Pull-rod 
member 50 has an upper section 51 that terminates in a distal end 52, and 
a lower section 53 that terminates in proximal end 54. The distal and 
proximal ends 52, 54 each terminate in threads 56, 58. The threads 58 of 
the distal end 52 are matable with the threaded bore 42 of the expander 
element 11. The threads 56 of the proximal end 54 are matable with a 
fitting (not shown) for connecting a concentrically aligned bore 60 that 
runs completely along the longitudinal axis of the pull-rod member 50 with 
the source 18 of pressurized fluid. The provision of the bore 60 allows 
the pull-rod member 50 to conduct pressurized hydraulic fluid from the 
source 18 to the space between the wall 24 that defines the closed end 22 
of the shell 9, and the flat, circular distal end 38 of the expander 
element 11 (see flow arrows). Hence, the member 50 can function as a 
hydraulic mandrel within the plugging apparatus 1, as well as a pull-rod. 
Concentrically disposed around the middle of the pull-rod member 50 is an 
integrally formed piston 62. This piston 62 is in turn circumscribed by 
one or more sealing rings 64 for preventing pressurized hydraulic fluid 
from leaking out of the inlet block 16. 
The inlet block 16 includes a vertically disposed bore 66 having an upper 
portion 68, and an enlarged lower portion 72 for slidably housing the 
upper rod section 51, and the integrally formed piston 62 of the pull-rod 
member 50. The enlarged lower portion 72 serves as a hydraulic cylinder 
that houses the piston 62, and sealingly engages the ring 64 that 
circumscribes the piston 62. The vertically disposed bore 66 includes a 
conical portion 74 that melds in with the enlarged lower bore 72. In 
addition to the vertically disposed bore 66, the inlet block 16 includes 
upper and lower horizontal bores 76 and 78, respectively. Each of these 
horizontal bores 76 and 78 includes a threaded end 80 and 82 for receiving 
a hydraulic fitting (not shown) that ultimately connects the bores 76 and 
78 with the source 18 of pressurized fluid. An O-ring 84 seated in an 
annular groove 86 circumscribes the upper section 51 of the pull-rod 
member 50 between the upper and lower horizontal bores 76 and 78. The 
O-ring 84 hydraulically isolates the upper annular space 88 defined 
between the bore 66, and the upper section 51 of the pull-rod member 50 
from the lower annular space 90 defined between the bore 66 and the 
proximal end of the upper section 51 of member 50. 
The bottom end of the inlet block 16 includes a threaded fitting 92 that is 
engageable with threads 94 present on the bottom end of the enlarged lower 
bore 72. Disposed at the center of the threaded fitting 92 is a circular 
opening 96 that is concentrically aligned with the lower section 53 of the 
pull-rod member 50. This opening 96 is circumscribed by an O-ring 98 
seated within an annular recess 99 that slidably and sealingly engages the 
lower section 53 of the pull-rod member 50. The purpose of the O-ring 98 
is to prevent any hydraulic fluid that manages to get past the sealing 
ring 64 of the piston 62 from exiting the inlet block 16. In the preferred 
embodiment, the threaded fitting 92 includes a pair of opposing dimples 
100a, 100b that allows the prongs of a wrench (not shown) to install or 
remove the fitting 92 from the bore 94. 
On the right-hand side of the inlet block 16, the threaded ends 80 and 82 
of the upper and lower horizontal bores 76 and 78 are fluidly connected in 
parallel to the source 18 of pressurized fluid, as is the concentrically 
aligned bore 60 present in the pull-rod member 50. Each of these parallel 
connections includes a pressure reducing control valve 105a, 105b, and 
105c so that the pressure of the hydraulic fluid entering the upper bore 
76, lower bore 78, and concentric bore 60 may be selectively adjusted. 
Such pressure reducing control valves are commercially available items 
well-known in the art. In the preferred embodiment, the source 18 of 
pressurized fluid is preferably a Haskel Hydroswage.RTM. brand hydraulic 
expander manufactured by Haskel, Inc. of Burbank, Calif. 
Turning finally to the top end of the inlet block 16, the block 16 includes 
the previously mentioned threaded nipple 33 (best seen in FIG. 1B). This 
nipple 33 extends out of an integrally formed, annular spacing collar 107 
that is concentrically aligned with the pull-rod member 50. Preferably, 
the outer diameter of the spacing collar 107 is no greater than the outer 
diameter of the flat annular wall 30 that circumscribes the circular 
opening 28 of the plug 7. The upper edge of the spacing collar 106 is 
chamfered as shown, and further includes a sealing ring 108 seated within 
an annular groove 110. In the preferred embodiment, the depth of the 
annular groove 110 is about 60 to 70% of the vertical height of the 
sealing ring 108. So proportioned, the annular groove 110 is deep enough 
to prevent the sealing ring from blowing out during the application of 
maximum expansion pressures, yet shallow enough so that the compressive 
force applied by the threaded nipple 30 when the plug 7 is screwed onto 
the block 16 never completely overcomes the resiliency of the ring 108, 
thus assuring that all of this compressive force will be used to sealingly 
engage the annular wall 30 of the plug 7 against the ring 108. 
In the method of the invention, the plug 7 is attached to the expansion 
assembly 14 by inserting the distal end 52 of the pull-rod member 50 
through the proximal open end 26 of the shell 9. The annular recess 44 
that circumscribes the proximal end of the threaded bore 42 of the 
expander element 11 helps the operator to properly align the threaded bore 
42 with the threads 56 present on the distal end 52 of the pull-rod member 
50. Once such proper alignment has been attained, the operator hand-screws 
the expander element 11 of the plug 7 over the distal end 52 of the 
pull-rod member 50. When the distal end 52 is about half-way screwed into 
the bore 42 of the expander element 11, the threaded nipple 33 will begin 
to screw into the threaded bore 32 present at the proximal open end 26 of 
the plug 7. The operator continues to screw the plug 7 into the expansion 
assembly 14 until the flat annular wall 30 of the plug 7 engages the 
sealing ring 108 that circumscribes the spacing collar 107 of the inlet 
block 16. Normally, no wrenches or other tools will be required to screw 
the plug 7 against the sealing ring 108; the applicants have found that 
only a hand-tight screwing together is necessary in order to contain 
pressures within the shell 9 of up to 28,000 psi. 
Once the plug 7 has been installed onto the expansion assembly 14, the 
plugging apparatus 1 is inserted into the open end of a tube 3 in the 
position illustrated in FIG. 1A. At this juncture, the operator may 
execute either one of three embodiments of the method of the invention. 
The first of these methods is illustrated in FIG. 1A. In this method, the 
operator simultaneously conducts pressurized hydraulic fluid from the 
source 18 through the bore 60 of the pull-rod member 50, as well as the 
upper and lower horizontal bores 76 and 78. Pressurized fluid from the 
bores 60 and 16 accordingly enters all of the interior regions of the 
shell 9, both in the small space between the wall 24 of the closed distal 
end 22 of the plug 7, and the circular distal end 38 of the expander 
element 11, as well as in the space between the rounded, proximal end 40 
of the expander element 11, and the circular opening 28 in the shell 9. 
The pressurized hydraulic fluid from the bores 60 and 76 has two effects. 
First, it serves to slightly expand the interior of the shell 9. Second, 
because the area of the circular distal end 38 of the expander element 11 
is larger than its rounded, proximal end 40, and because the conically 
shaped walls of the expander element 11 are sealingly engaged to the 
tapered walls 34 within the shell 9, this hydraulic fluid creates a net 
hydraulic force that urges the expander element 11 downwardly. At the same 
time, pressurized fluid from the bore 78 flows into the annular space 90, 
and applies pressure against the upper face 63 of the piston 62, thereby 
pushing the piston 62 downwardly and generating a tensile force on the 
upper section 51 of the pull-rod member 50. The end result of the radial 
expansion of the shell 9, the net hydraulic force that urges the expander 
element 11 downwardly, and the tensile force exerted onto the element 11 
by the pull-rod member 50 is that the expander element is pushed down into 
the position illustrated in FIG. 1B. 
The second preferred embodiment of the method is illuminated in FIG. 2. 
Here, the operator admits pressurized hydraulic fluid from the source 18 
only through the bore 60 of the pull-rod, thereby relying upon a 
piston-like action of the expander element to push the expander element 11 
into the final position illustrated in FIG. 1B. When this particular 
method is employed, it should be noted that the pressurized hydraulic 
fluid pushes the cork-shaped expander element 11 downwardly by applying 
both a vertically oriented force against the flat, circular distal end 38 
of the element, and a radially expansive force against the tapered inner 
walls 34 of the shell 9 that facilitates the downward movement of the 
element 11. In a variation of this embodiment, the operator may 
simultaneously conduct pressurized hydraulic fluid through the bore 78, 
thereby pushing piston 62 downwardly and creating a tensile force in the 
pull-rod member 50 that assists the pressurized hydraulic fluid bearing 
against the distal end 38 of the element 11 in moving the element 
downwardly. 
The third preferred embodiment of the method is illustrated in FIG. 3. In 
this embodiment, the operator admits pressurized fluid into bores 76 and 
78. The fluid flowing out of bore 76 serves to radially expand the 
interior of the shell 9 in the region below the rounded, proximal end 40 
of the expander element 11 as indicated. This fluid also applies a 
pressure against the rounded, proximal end 40 of the element 11 that urges 
the element upwardly. However, this force is more than counteracted by the 
tensile force applied to the element 11 by the pull-rod member 50 as a 
result of the fluid from bore 78 applying pressure onto the upper surface 
63 of the piston 62. The end result is that the element 11 is moved into 
the position illustrated in FIG. 1B. 
While all three embodiments of the method have been described as though the 
pressure-reducing valves 105a, 105b and 105c are used merely as fluid 
switches, it should be noted that the operator has the option of varying 
the pressure of the fluid he admits through the bores 60, 76 and 78. This 
feature advantageously allows the operator to empirically determine and 
use whatever balance of pressures through bores 60, 76 and 78 are 
necessary to successfully move the element 11 downwardly so that the lands 
on the exterior of the shell 9 are radially expanded into sealing 
engagement with the inside surface of the tube 3. 
When the shell 9 is formed from Inconel.RTM., the pressures of the 
hydraulic fluids flowing through the bores 60, 76 and 78 will generally 
range from between about 12,000 to 22,000 psi, and more preferably from 
between 17,000 psi and 22,000 psi. 
While the invention has been specifically described in the context of 
plugging the heat exchange tubes of a nuclear steam generator, the 
invention is equally applicable to the heat exchange tubes of a fossil 
fuel generator, and may be used to plug virtually any tube in any 
environment.