Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
1997-10-24
2001-04-03
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C219S069200, C219S121630, C219S121640, C376S260000
Reexamination Certificate
active
06211482
ABSTRACT:
BRIEF DESCRIPTION OF THE INVENTION
This invention relates generally to the repair of thick-walled components susceptible to corrosion, such as reactor pressure vessel control rod drive mechanisms in pressurized water reactor nuclear power plants. More particularly, the present invention relates to a technique for repairing such thick-walled components through precision excavation and welding.
BACKGROUND OF THE INVENTION
A number of technologies have been developed to repair corroded or damaged thin-walled, small diameter tubes used in applications such as heat exchangers or material transport systems. U.S. Pat. Nos. 5,430,270; 5,514,849; 5,430,270; 5,656,185; 5,573,683; and 5,653,897 disclose technologies of this type. Each of these patents is owned by the assignee of the present invention and is incorporated by reference herein.
FIG. 1
illustrates an apparatus described in several of the foregoing patents. In particular, the figure illustrates a rotating apparatus
20
used to repair damaged tubes. A rotating welding head
22
is fixedly positioned at the end of a rotating sleeve
24
.
A rotating drive mechanism
25
rotates the sleeve
24
, thus the rotating sleeve
24
and the rotating welding head
22
synchronously rotate. The rotating drive mechanism
25
simultaneously rotates a filler assembly
26
that includes a filler metal receptacle
28
and a filler metal delivery system
30
. The filler metal receptacle
28
holds the filler metal to be welded. Generally, the filler metal receptacle
28
will be in the form of a reel of filler metal wire. The filler metal delivery system
30
receives the filler metal and delivers it to a filler passage within the rotating sleeve
24
. Since the rotating sleeve
24
and the filler assembly
26
rotate synchronously, the filler metal does not become tangled.
The filler metal delivery system
30
is powered through filler assembly slip rings
32
. The speed of the wire feed motor can be varied to permit different wire feed speeds, providing control of clad thickness and to allow adjustment for variations in laser output levels, travel speed, rotational pitch, and other factors.
The rotating apparatus
20
also includes a gas coupler
36
that is connected to a gas supply
38
. The rotating sleeve
24
includes a rotating fiber optic cable
40
. A laser
44
supplies energy to a fixed fiber optic cable
43
. The laser energy is transferred from the fixed fiber optic cable
43
to the rotating fiber optic cable
40
through an optical coupler
42
.
The rotating apparatus
20
is moved along its longitudinal axis by an axial drive system
50
mounted on shaft
51
. Guide rollers
49
may be used to guide the rotating sleeve
24
into position. A computer controller
53
is used to control the operation of the rotating apparatus drive mechanism
25
, the axial drive system
50
, and the filler metal delivery system
30
. In particular, the computer controller
53
is used to set the speed of the rotating apparatus drive mechanism
25
, the position for the axial drive system
50
, and the filler delivery rate for the filler metal delivery system
30
.
The operation of the rotating apparatus
20
is more fully appreciated with reference to
FIG. 2
, which provides an enlarged cross-sectional view of the rotating welding head
22
. The rotating welding head
22
includes a body
80
, which defines a filler passage
86
. The filler passage
86
, also called the wire conduit runs the length of the rotating sleeve
24
. Filler
88
is forced from the filler metal delivery system
30
through the filler passage
86
to a body aperture
94
. The laser energy is delivered through the body aperture
94
and welds the filler
88
. Gas conduit
89
delivers a shielding gas to the welding head
22
. Preferably, the gas conduit
89
terminates in distribution channels that distribute the gas to the aperture
94
at a number of locations.
FIG. 2
also depicts the rotating fiber optic cable
40
positioned within the body
80
of the rotating welding head
22
. The rotating fiber optic cable
40
runs the length of the rotating sleeve
24
and is affixed thereto.
The rotating fiber optic cable
40
terminates at a laser energy directional modification assembly
92
. Preferably, the assembly
92
is implemented as an optical assembly.
FIG. 3
discloses an assembly
92
that includes an input lens assembly
96
, a wedge prism
97
, and an output lens assembly
98
. The wedge prism
97
serves to change the direction of the laser energy. Preferably, the laser energy is directed toward the receiving surface
99
at a non-orthogonal angle &thgr;. When the laser energy is impinged upon a surface to be welded at an angle, of say 45°, as shown in
FIG. 3
, then reflective laser energy does not disrupt the incoming laser energy.
The device of
FIGS. 1-3
has been used for clad weld repair of thin-walled (e.g., 0.05 inches thick) heat exchanger tubes. The device can also be used for fusing defects by melting and re-solidifying the metal of a thin-walled heat exchanger tube.
Most corrosion in pressurized water reactors has been associated with thin-walled heat exchanger tubes. However, there have been recent reports of water stress corrosion cracking in reactor pressure vessel control rod drive mechanisms.
FIG. 4
illustrates a prior art reactor vessel dome
110
with a set of control rod drive mechanism (CRDM) nozzles
112
. A prior art repair system is positioned underneath the reactor vessel dome
110
. The prior art repair system includes a tool delivery system
114
, which supports a tool arm
116
that has a tool head
118
positioned at its end. The tool delivery system
114
executes radial motion as shown with line
120
, rotational motion as shown with arc
122
, and lift motion as shown with line
124
. These motions are used to deliver the tool head
118
to different locations in a CRDM nozzle
112
so that repairs can be effectuated.
A variety of tool heads
118
are used to effectuate repairs. A detection probe that uses eddy current techniques may be used to identify flaws in the CRDM nozzle
112
. Similarly, a detection probe that uses ultrasonic testing may be used to identify flaws in the CRDM nozzle
112
. A detection probe to execute dye penetrant examinations may also be used. Such a probe is used to verify information found from other detection techniques and to examine completed weld repairs.
An excavation tool may also be used as a tool head
118
. Prior art excavation tools generally rely upon milling, grinding, or cutting tools. Such tools typically require large motor power that is difficult to deliver to remote locations, such as CRDM nozzles. Another class of prior art excavation tools relies upon a welding mechanism to melt damaged surface areas. The problem with this approach is that it is rather difficult to handle the molten metal that is removed from the damaged surface areas. Both of the foregoing excavation techniques also share the shortcoming that they are imprecise and therefore result in relatively large and unnecessary excavations that must be reconstructed.
A cavity repair weld head may be used for reconstruction operations. Such a weld head is used to fill the excavated area with a filler material, such as weld beads. Alternately, an arc welding cavity repair weld head may be used. For example, a gas-tungsten arc welding tool may be used.
A boring tool head may also be used as a tool head
118
. A boring tool is used to bore the weld buildup after a weld repair. This allows the nozzle
112
to be returned to original design specifications.
As indicated above, one problem with prior art excavation tools is that they are imprecise and therefore produce relatively large excavations. Consequently, relatively voluminous reconstruction operations must be performed. This can result in high residual stresses and welding distortion, which may promote future cracks. Another problem arises when welding excavation operations produce a molten metal byproduct that is difficult to dispose. Finally, prior art techniques require
Baucom J. Darryl
Findlan Shane J.
Frederick Gregory J.
Peterson, Jr. Artie G.
Electric Power Research Institute Inc.
Evans Geoffrey S.
Galliani William S.
Pennie & Edmonds LLP
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