EDM crack removal tooling

A tool system features an EDM crack removal head which can be positioned within a nozzle/thermal sleeve and then oscillated in a vertical and horizontal directions to enable precise material removal, leaving the surface free of cracks and in a condition for rewelding if required. If a crack is found in a surface which is covered by a thermal sleeve, then a small specialized EDM cutting head, which can be delivered from the under side of the reactor head and has an ability to pass through the ID of the thermal sleeve, is used. The head enables the sleeve to be cut and allow a portion of the sleeve to be removed. The crack can then be removed using a crack removal type of head.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a crack removal tool. More 
specifically, this invention relates to a crack removal tool which utilize 
EDM techniques and which are suitable for removing cracks which appear 
within conduits, nozzles and the like, such as are found in nuclear 
reactor related structures. 
2. Description of the Related Art 
During inspection of certain types of nozzle penetrations in pressurized 
water nuclear reactor heads, cracks may be discovered in weld areas of one 
or more nozzles. Access to these defects is severely hindered by the 
presence of thermal sleeves which are welded in place in nozzles and which 
prevent access with tooling. Accordingly, it is extremely difficult to 
effect repairs. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide cutting and removal 
tools or heads which simplify the removal and repair of cracks which tend 
to develop in nozzle penetrations and similar types of conduiting which 
are used in nuclear reactors and the like type of environments. 
In brief, the above object is achieved through the use of EDM (electro 
discharge machining) heads which were developed so as to permit the 
cutting and partial removal of a thermal sleeve so as to expose a cracked 
area to permit defect blending within the head penetration 
In brief, the above object is achieved through the use of a tool system 
which features an EDM crack removal head which can be positioned within 
the nozzle or thermal sleeve and then oscillated in vertical and 
horizontal directions to enable precise material removal, leaving a 
surface free from cracks and in a condition for rewelding if required. 
In the event that a crack is found in a surface which is covered by a 
thermal sleeve, a small specialized EDM cutting head which can be 
delivered from an under side of the reactor head, and which has the 
ability to pass through the ID of the thermal sleeve, is used to cut the 
thermal sleeve and allow a portion of the sleeve to be removed. The crack 
can then be readily removed using the crack removal type of head. 
The use of the tooling system according the present invention enables 
repair of cracked nozzles in PWR heads from the underside, thus 
eliminating a costly need to remove a control rod drive mechanism and 
associated hardware from a reactor. 
More specifically, a first aspect of the present invention resides in a 
tool for use with conduiting, comprising: an elongated shaft structure; 
first and second support members disposed on the shaft structure which 
engage an inner wall of a conduit when actuated; cutting head means, 
supported on the shaft structure between the first and second support 
members, for performing a cutting operation on an inner wall of the 
conduit, the cutting head means including a movable cutting electrode and 
first servo means for selectively moving the electrode member laterally 
outwardly with respect the shaft structure; and second servo means, 
operatively connected with the cutting head mean for selectively 
displacing the cutting electrode in at least one of first and second 
rotational directions. 
A second aspect of the present invention resides in a crack removal tool 
comprising: an elongate shaft structure; first and second inflatable 
members disposed on the shaft structure; a crack sensor supported on the 
shaft structure at a location between the first and second inflatable 
members; a crack removal head supported on the shaft between the first and 
second inflatable members at a predetermined distance from the crack 
sensor, the crack removal head including a removal electrode and electrode 
servo means for selectively displacing the removal electrode radially with 
respect to an axis of the shaft structure; and head servo means for 
selectively displacing the crack sensor and the crack removal head with 
respect to the first and second inflatable members and for causing the 
crack removal head to undergo rotation about the axis of the shaft 
structure in at least one of first and second rotational directions. 
A third aspect of the present invention resides in a sleeve cutting tool 
comprising: an elongate shaft structure; first and second inflatable 
members disposed on the shaft structure; a cutting head supported on the 
shaft between the first and second inflatable members, the cutting head 
including a cutting electrode and cutting electrode servo means for 
selectively displacing the cutting electrode radially with respect to an 
axis of the shaft structure; and cutting head servo means for selectively 
displacing the cutting head in at least one of first and second rotational 
directions. 
A fourth aspect of the present invention resides in a crack removal system 
comprising: a crack removal tool which comprises: a first elongated shaft 
structure; first and second selectively actuatable support members 
disposed on the shaft structure; a crack sensor supported on the shaft 
structure at a location between the first and second support members; a 
crack removal head supported on the shaft between the first and second 
support members at a predetermined distance from the crack sensor, the 
crack removal head including a crack removal electrode and a first servo 
means for selectively displacing the crack removal electrode radially with 
respect to an axis of the shaft structure; and second servo means for 
selectively axially displacing the crack sensor and the crack removal head 
with respect to one of the first and second support members and for 
causing the crack removal head to undergo rotation about the axis of the 
shaft structure in at least one of first and second rotational directions. 
A fifth aspect of the present invention resides in a crack removal system 
further comprising: a sleeve cutting tool which comprises: a second 
elongate shaft structure; third and fourth selectively actuatable support 
members disposed on the second shaft structure; a cutting head supported 
on the shaft between the third and fourth support members, the cutting 
head including a cutting electrode and third servo means for selectively 
displacing the cutting electrode radially outwardly with respect to an 
axis of the second shaft structure; and fourth servo means for selectively 
causing the cutting head to undergo rotation about the axis of the shaft 
structure in at least one of first and second rotational directions. 
A further aspect of the present invention is presented in a method of 
repairing cracks in a nozzle in which a sleeve is fixedly disposed, 
comprising the steps of: inserting sleeve cutting tool into the sleeve; 
activating support means which engages the inner wall of the sleeve and 
which maintains the sleeve cutting tool in a predetermined position within 
the sleeve; cutting through the sleeve using the sleeve cutting tool in a 
manner which allows a portion of the sleeve to be removed; removing the 
portion of the sleeve; inserting a crack removing tool into the portion of 
the nozzle wherein the sleeve has been removed; activating support means 
on the crack removing tool to support the crack removing tool in the 
nozzle; using a crack detecting sensor to locate the position of a crack 
in the nozzle; moving the crack detecting sensor away from the location at 
which the crack is detected and moving a crack removal head into position 
opposite the location whereat the crack was detected; and removing portion 
of the inner wall of the nozzle using the crack removal head.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a schematic side sectional elevation showing a sleeve cutting 
tool 1 according to the present invention. This tool basically comprises 
two concentrically arranged shafts 2, 4 which are reciprocal with respect 
to one another. Both shafts 2, 4 are hollow. The outer shaft 2 supports 
the inner shaft 4 concentrically therein and in a manner which allows the 
inner shaft to rotate relative thereto. 
Selectively inflatable upper and lower bladder assemblies 6, 8 are 
supported on the shaft assembly. These bladder assemblies 6, 8 are 
connected with a source of pneumatic or hydraulic pressure via conduits. 
Note that only the conduit 7 which supplies the upper bladder assembly 
which extends all the way up the hollow inner shaft and which is 
illustrated as extending out of the top of the inner shaft 4 and curving 
back down to the upper bladder assembly 6, is shown. 
An EDM cutting head 10 is supported between the upper and lower bladder 
assemblies 6, 8. The cutting head 10 is in a drive connection with the 
inner shaft so as to be synchronously rotatable therewith. In the 
embodiments of the invention, the inner shaft 4 is connected with a 
hydraulic motor 12 which can drive the shaft in either rotational 
direction. The motor 12 is controlled by a switching control (not shown) 
which reverses the direction the motor is driving the shaft each 
360.degree. to 370.degree. rotation (for example). While it is possible to 
continuously drive the shaft 4 only in one rotational direction, it is 
preferred to induce the above type of oscillation in that it simplifies 
the electrical connection between the base 11 and the EDM cutting head. 
For example, the oscillation eliminates the need for brushes and the like 
to maintain constant electrical communication between the base of the 
cutting tool and the cutting head. 
The cutting head 10 includes a hydraulically operated motor 13 (see FIG. 7, 
for example) which allows the cutting electrode 14 to be displaced with 
respect to the axis of rotation of the inner shaft 4 and thus allows the 
eccentricity of the cutting electrode 14 to be varied. 
In the situation illustrated in FIG. 1, it is assumed that a crack has been 
detected in a portion of the nozzle 16 which is covered with a thermal 
sleeve 18. In accordance with this detection, the cutting tool 1 is 
inserted into the thermal sleeve 18 so that the cutting electrode 14 is 
located at a level which is between the crack and the site where the 
thermal sleeve 18 is welded to the nozzle. The upper and lower bladder 
assemblies 6,8 are inflated so that the tool 1 is retained in place and 
the cutting tool is temporarily secured in place. The EDB cutting process 
is then initiated. In FIG. 1, the cutting electrode 14 has been gradually 
displaced laterally until such time as the EDM cutting action has cut 
almost through the thermal sleeve 18 which is fitted within the nozzle. 
After the thermal sleeve 18 is cut all the way through, the cutting 
electrode 14 is retracted to a position of minimal projection, the upper 
and lower bladder assemblies 6, 8 are deflated and the sleeve cutting tool 
is removed. Following this, the free end portion of the thermal sleeve 18 
is pulled from the nozzle 14, thus exposing the portion of the 16 nozzle 
in which the crack is formed. 
Following the removal of the thermal sleeve, the crack removal tool 20 is 
inserted into the nozzle 16. 
As shown in FIG. 2 the crack removal tool 20 basically comprises upper and 
lower bladder assemblies 22, 24 which are larger than those provided on 
the sleeve cutting tool. In this arrangement the lower bladder assembly 24 
is supported on the outer shaft 26 while the upper bladder assembly 22 is 
slidably disposed on the inner shaft 28. The cutting head (hereinafter 
referred to as the crack removal head) 30 and a crack detection sensor 32 
are mounted on the inner shaft so as to be displaceable relative to the 
lower bladder assembly 24. Although not clear from this figure, the inner 
shaft 28 is arranged to be displaceable through a relatively large 
distance with respect to the outer shaft (see FIG. 12 for example). The 
reason for this is that, when the crack removing tool 20 is inserted into 
the nozzle 16, it is impossible to see the crack or to determine when it 
has been removed. Accordingly, the crack detector 32 is provided. In this 
instance, the detector is an eddy current type detection. 
The crack detector 32 is energized and moved both axially and rotationally, 
until such time as the crack or flaw is located. After the position of the 
crack is identified, the inner shaft 28 is displaced (upwardly as seen in 
the drawings) through a predetermined distance which locates the crack 
removal electrode 34 immediately opposite the crack. EDM cutting is then 
initiated and the metal around the crack is removed. Since the amount of 
metal which is being removed cannot be measured while the tool is in 
position, the metal removal is continued for a predetermined time. This 
time is determined by empirical data from which it is able to relatively 
accurately estimate how much metal is removed per unit time. 
After the predetermined time (for example, 1 hour) the EDM cutting is 
stopped and the inner shaft 28 retracted to return the crack sensor 32 to 
the crack site. If the crack is still detected, the EDM cutting electrode 
34 is moved back into position and metal is removed for another 
predetermined period of time. These cutting/checking steps are repeated 
until such time as the crack is no longer detected. 
However, since the accuracy of the crack detector 32 is limited, after the 
crack is detected as having been eliminated, the metal removal procedure 
is repeated once more but for a shorter period of time (e.g. 40 mins) to 
ensure total removal. 
When this last metal removal process is completed, the bladder assemblies 
22, 24 are deflated and the tool 20 is extracted from the nozzle. 
Depending on the amount of metal which has been removed, it may be 
necessary to fill the newly created void with a suitable weld material or 
the like. If desired, the crack removal tool can be reinserted and the 
surface of the weld material smoothed via EDM cutting to exactly the 
required ID. 
The cut-off portion of the thermal sleeve 18 can be reinserted and 
butt-welded to the portion still fixed within the nozzle, thus completing 
the repair. 
It will be noted that in addition to the 360.degree. to 370.degree. 
oscillation, it is possible to reciprocally move the metal removal 
electrode 34 up and down while the rotational motion is taking place to 
remove long cracks. It is also possible to use different shaped metal 
removal electrodes of the nature depicted in FIGS. 5 and 6, for example. 
The type (for example, shape) can be selected based on the width and 
length of the crack that needs be removed. 
As will be appreciated by those skilled in the art of EDM, it is necessary 
to continuously supply a flow of dielectric fluid between the interface 
defined between the electrode and the surface of work piece being cut. 
This fluid, along with pressurized fluid(s) which controls the operation 
of the hydraulic motor 36 used to determine the lateral displacement of 
the crank removal electrode 14, is supplied via conduits which are passed 
upwardly through the interior of the hollow inner shaft 28. It will be 
understood that a similar conduiting arrangement is provided in the sleeve 
cutting tool 1. 
In the case of the crack removal tool, two motors 40, 42 are required at 
the base. One motion 40 is for inducing rotational motion and the other 
motion 42 is for producing reciprocal or axial motion 42. 
The control of the hydraulic motors 12, 13, 36, 40, 42 of the cutting and 
removal tools 1, 20 is controlled by controllers (no numerals) which are 
operatively connected with the tools in the representative manner shown in 
FIGS. 1 and 2. 
In this instance, de-ionized water is used as the dielectric fluid and is 
constantly circulated through the space defined between the inflatable 
bladder assemblies. In the case of the crack removal electrodes shown in 
FIGS. 5 and 6, through bores 38 are formed therein in a manner which 
allows the dielectric fluid to be supplied to the cutting site. 
It is worth noting at this point that the motors which are used to provide 
rotational and reciprocal motion are preferably hydraulic or pneumatically 
operated types as differentiated from electrically operated motors. The 
reason for this is that even though the lower inflatable bladders provide 
a reasonable seal with the inner surfaces of the thermal sleeve or nozzle, 
still some leakage occurs and the need to hermetically seal the motors and 
the like is avoided. 
In order to establish a satisfactory electrical connection necessary for 
performing EDM, it is possible to provide a leaf spring like contacts at 
the upper ends of the tools, preferably at a location above the upper 
bladder assemblies. 
The electrodes used in the above types of sleeve cutting and crack removal 
tools can be made of materials such as copper-tungsten, tungsten and 
graphite. In the case of the thin sharp edged sleeve cutting electrode, 
the former two materials can be used. In the case of the crack removal 
electrodes, the latter two types of material can find application. 
It is of course within the scope of the invention that a number of 
different materials or composites can be used and a such the invention is 
not specifically limited to the same. 
FIG. 3 shows an example of the shape (as seen in plan) of the thin cutting 
electrode used in the sleeve cutting tool. 
FIGS. 7 and 8 show upper and lower portions respectively of a preferred 
embodiment of the sleeve cutting tool according to the present invention. 
In this figure, elements designated in FIG. 1 are designated by like 
numerals. 
FIGS. 9 to 12 show details of the crack removal tool according to a 
preferred embodiment of the device. FIGS. 9 and 10 show the crack removal 
head in its upper and lower positions. As the upper bladder member is 
slideably supported on the inner shaft, it is preferred to move the crack 
removal head to its uppermost position at the time of insertion and to 
inflate the upper bladder. The crack removal head is then lowered to its 
lowermost position and the lower bladder is then inflated. This separates 
the upper and lower bladders and improves the alignment of the tool within 
the nozzle. 
It should also be noted that it is within the scope of the invention to 
reduce the diameters of the crack removal device and adapt the same for 
use a thermal sleeve should a crack be discovered in a portion which is 
not readily removed through the use of the sleeve cutting tool.