U.S. patent application number 10/278889 was filed with the patent office on 2003-12-25 for process for in-situ electroforming a structural layer of metallic material to an outside wall of a metal tube.
Invention is credited to Brooks, Iain, Gonzalez, Francisco, Palumbo, Gino, Panagiotopoulos, Konstantinos, Robertson, Andrew J., Tomantschger, Klaus.
Application Number | 20030234181 10/278889 |
Document ID | / |
Family ID | 34575398 |
Filed Date | 2003-12-25 |
United States Patent
Application |
20030234181 |
Kind Code |
A1 |
Palumbo, Gino ; et
al. |
December 25, 2003 |
Process for in-situ electroforming a structural layer of metallic
material to an outside wall of a metal tube
Abstract
A process for in situ electroforming a structural reinforcing
layer of selected metallic material for repairing an external
surface area of a degraded section of metallic workpieces,
especially of tubes and tube sections, is described. Preferably,
the metal layer coatings are made of fine-grained metals, metal
alloys or metal matrix composites. The plating system can be used
on straight tubes, tube joints to different diameter tubes or face
plates, tube elbows and other complex shapes encountered in piping
systems. A suitable apparatus is assembled on or near the degraded
site and is sealed in place to form the plating cell. Also
described is a process for plating "patches" onto degraded areas by
selective plating including brush plating.
Inventors: |
Palumbo, Gino; (Toronto,
CA) ; Brooks, Iain; (Toronto, CA) ; Robertson,
Andrew J.; (Toronto, CA) ; Panagiotopoulos,
Konstantinos; (Toronto, CA) ; Gonzalez,
Francisco; (Toronto, CA) ; Tomantschger, Klaus;
(Mississauga, CA) |
Correspondence
Address: |
BACON & THOMAS, PLLC
625 SLATERS LANE
FOURTH FLOOR
ALEXANDRIA
VA
22314
|
Family ID: |
34575398 |
Appl. No.: |
10/278889 |
Filed: |
October 24, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10278889 |
Oct 24, 2002 |
|
|
|
PCT/EP02/07023 |
Jun 25, 2002 |
|
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Current U.S.
Class: |
205/115 ;
205/224; 205/76 |
Current CPC
Class: |
C25D 5/617 20200801;
C25D 5/02 20130101; C25D 15/02 20130101; C25D 5/18 20130101; C25D
5/06 20130101; C25D 5/611 20200801; C25D 7/04 20130101; C25D 5/67
20200801 |
Class at
Publication: |
205/115 ; 205/76;
205/224 |
International
Class: |
C25D 005/02 |
Claims
1. A method for patching a degraded portion of a metallic workpiece
which comprises electroplating a reinforcing metallic patch on an
exterior surface of said workpiece wherein said patch covers said
degraded portion of said workpiece without covering at least a
portion of a non-degraded portion of said workpiece; said
electroplating being conducted under electroplating conditions
whereby electrodeposited metal of said metallic patch has an
average grain size of 1000 nm or less.
2. The method of claim 1 wherein said workpiece is a pipe.
3. The method of claim 2 wherein the pipe is connected to an
apparatus for the conveyance of fluid and said patch is formed in
situ without removing the pipe from said apparatus.
4. The method of claim 3 wherein the electroplating is performed by
surrounding the exterior degraded portion of the pipe with an
electroplating cell through which electroplating solution
containing ions of the metal to be electrodeposited is circulated
whereby said solution contacts said exterior degraded portion of
the pipe while the cell is operated to electrodeposit said metal
onto said exterior degraded portion of said pipe to thereby form
said patch; said electroplating cell comprising: a housing which
surrounds the exterior degraded portion of said pipe; at least one
anode within said housing; electrical connections which connect
said at least one anode to an electric power source required for
electroplating said metal and which connect said power source to
said pipe whereby said pipe is a cathode during said
electroplating.
5. The method of claim 4 wherein said housing comprises two
sections and said sections of said housing are assembled around
said exterior degraded portion of said pipe to form a watertight
seal around said pipe; and said housing comprises a fluid inlet for
introducing electroplating solution into said plating cell and a
fluid outlet for removing electroplating solution from said cell
whereby said electroplating solution is circulated through said
plating cell by flowing the solution from the inlet to the
outlet.
6. The method of claim 5 wherein said sections of said housing are
joined together along one side thereof by a hinge whereby said
housing can be opened and closed around said exterior degraded
portion of said pipe and said housing is assembled around said
exterior degraded portion of said pipe by closing said housing
around said pipe.
7. The method of claim 6 which further includes regulating the
temperature of said electroplating solution circulating through
said plating cell to enhance the electroplating of said reinforcing
metallic patch.
8. The method of claim 7 which further includes agitating the
electroplating solution circulating through said plating cell.
9. The method of claim 3 wherein said electroplating is conducted
under electroplating conditions whereby electrodeposited metal of
said metallic patch has an average grain size in the range of
10-750 nm.
10. The method of claim 9 wherein the average grain size is in the
range of 30-500 nm.
11. The method of claim 10 wherein the average grain size is in the
range of 50-300 nm.
12. The method of claim 11 wherein the average grain size is in the
range of 10-100 nm.
13. The method of claim 3 wherein said reinforcing metallic patch
is electroplated to an average thickness of at least 0.125 mm.
14. The method of claim 3 wherein said pipe comprises a Fe, Cu or
Ni based alloy.
15. The method of claim 3 wherein said electrodeposition provides
an equiaxed microstructure throughout the electrodeposited metal
wherein the average grain size is substantially uniform throughout
the electrodeposited metal.
16. The method of claim 13 wherein said electroplating is conducted
to produce an average grain size of said electrodeposited metal
such that the ratio of said thickness to said average grain size is
at least 1000.
17. The method of claim 3 wherein said electrodeposited metal is
selected from the group consisting of Ag, Au, Cu, Co, Cr, Ni, Fe,
Pb, Pd, Pt, Rh, Ru, Sn, Mo, Mn, W, V, and Zn, or said metal is an
alloy comprising one or more metals selected from the group
consisting of Ag, Au, Cu, Co, Cr, Ni, Fe, Pb, Pd, Pt, Rh, Ru, Sn,
Mo, Mn, W, V, and Zn alloyed with an alloying element selected from
the group consisting of B, C, P, S and Si, or said metal is an
alternative alloy comprising two or more metals selected from the
group consisting of Ag, Au, Cu, Co, Cr, Ni, Fe, Pb, Pd, Pt, Rh, Ru,
Sn, Mo, Mn, W, V, and Zn, wherein said alternative alloy optionally
further comprises an alloying element selected from the group
consisting of B, C, P, S and Si.
18. The method of claim 17 which further comprises incorporating
particulate material into said electrodeposited metal during said
electroplating to form a metal matrix composite, said particulate
material being selected from the group consisting of metal powder,
metal alloy powder, metal oxide, nitride powder, carbon powder,
carbide powder, MoS.sub.2 and organic material wherein: said metal
oxide is metal oxide of metal selected from the group consisting of
Al, Co, Cu, In, Mg, Ni, Si, Sn, V and Sn; said nitride is a nitride
of an element selected from the group consisting of Al, B, C, and
Si; said carbide is a carbide of an element selected from the group
consisting of B, Cr, Bi, Si and W; said organic material is
selected from the group consisting of polymer spheres and
particulate polytetrafluoroethylene; and said carbon is graphite or
diamond.
19. The method of claim 17 wherein said electroplating is conducted
from an electroplating solution which includes grain
refining/stress relieving agent selected from the group consisting
of saccharin, coumarin, sodium lauryl sulphate, naphthalene
trisulfonic acid and thiourea.
20. The method of claim 18 wherein said particulate material has an
average particle size of less than 10 microns.
21. The method of claim 4 wherein said electrodeposition takes
place using DC or pulse electrodeposition at a deposition rate of
at least 0.05 mm/hour.
22. The method of claim 20 wherein said electrodeposition is
accomplished by passing single or multiple DC cathodic-current
between the anode and said cathode at a cathodic-current pulse
frequency in the range of about 0 to 1000 Hz at pulsed intervals
during which the current passes for a t.sub.on-time period of at
least 0.1 msec and does not pass for a t.sub.off-time period in the
range of 0 to 500 msec, and passing single or multiple DC
anodic-current pulses between the cathode and the anode at
intervals during which the current passes for a t.sub.anodic-time
period in the range of 0 to 50 msec, the total duty cycle being in
the range of 10% to 100%.
23. The method of claim 3 wherein said electroplating comprises:
connecting said pipe to a negative outlet of an electric power
source whereby said pipe functions as a cathode during said
electroplating; supplying electroplating solution to an anode wick
which is connected to a conductive anode brush, said anode brush
being connected to a power outlet of an electric power source;
contacting said wick with said exterior portion of said pipe to be
patched and moving said wick in contact with said pipe over a
portion of said pipe which is to be covered with said reinforcing
metallic patch, whereby said electroplating solution from said wick
bathes the portion of the pipe to be patched so that said
reinforcing metallic patch is electroplated on the exterior surface
of said pipe.
24. Process for in situ electroforming a structural reinforcing
layer of a thickness of at least 0.125 mm of selected metallic
material coated on an external surface area of a degraded section
of a metallic workpiece containing Fe, Co, Cu, Ni, Mo, Mn
comprising: (i) assembling a housing in the vicinity of the
workpiece area to be plated, (ii) positioning and closing the
housing to provide a leak tight seal around the surface area of the
workpiece to be plated, (iii) connecting fluid supply inlets and
outlets to a temperature controlled reservoir to enable the
circulation of fluids to and from the workpiece to be plated, (iv)
providing electrical connections to the workpiece to be plated and
to one or several anodes forming the in-situ plating cell around
the workpiece area to be plated, so that said workpiece becomes a
cathode during said electroforming, (v) electrodepositing a
structural layer of metallic material with an average grain size of
less than 1,000 nm on the external surface area of the degraded
section of the metallic workpiece using electrodeposition at a
deposition rate of at least 0.05 mm/h, by flowing an aqueous
electrolyte containing ions of said metallic material, providing
the anode and the workpiece area to be plated in contact with said
electrolyte, passing single or multiple D.C. cathodic-current
pulses between said anode and said workpiece area to be plated at a
cathodic-current pulse frequency in a range of about 0 and 1000 Hz,
at pulsed intervals during which said current passes for a
t.sub.on-time period of at least 0.1 msec and does not pass for a
t.sub.off-time period in the range of about 0 to 500 msec, and
passing single or multiple D.C. anodic-current pulses between said
cathode and said anode at intervals during which said current
passes for a t.sub.anodic-time period in the range of 0 to 50 msec,
a total duty cycle being in a range of 10 to 100%.
25. Process for in situ electroforming a structural reinforcing
layer of a thickness of at least 0.125 mm of selected metallic
material coated on an external surface area of a degraded section
of a metallic workpiece containing Fe, Co, Cu, Ni, Mo, Mn
comprising: (i) assembling a selective plating apparatus employing
an anode brush wrapped in an absorbent separator, (ii) connecting a
fluid supply to the anode brush to enable the supply of fluids to
the absorbent separator between the anode and the workpiece area to
be plated, (iii) providing electrical connections to the workpiece
to be plated and the anode brush forming the in-situ plating cell
around the workpiece area to be plated, and (iv) electrodepositing
a structural layer of metallic material with an average grain size
of less than 1,000 nm on the external surface area of the degraded
section of the metallic workpiece using electrodeposition at a
deposition rate of at least 0.05 mm/h, by supplying an aqueous
electrolyte containing ions of said metallic material, providing
the anode and the workpiece area to be plated in contact with said
electrolyte by moving the anode brush over the workpiece area to be
plated, passing single or multiple D.C. cathodic-current pulses
between said anode and said workpiece area to be plated at a
cathodic-current pulse frequency in a range of about 0 and 1000 Hz,
at pulsed intervals during which said current passes for a
t.sub.on-time period of at least 0.1 msec and does not pass for a
t.sub.off-time period in the range of about 0 to 500 msec, and
passing single or multiple D.C. anodic-current pulses between said
cathode and said anode at intervals during which said current
passes for a t.sub.anodic-time period in the range of 0 to 50 msec,
a total duty cycle being in a range of 10 to 100%.
26. Process as claimed in claim 24 or 25, characterized in that the
single or multiple D.C. cathodic-current pulses between said anode
and said cathode have a peak current density in the range of about
0.01 to 10 A/cm.sup.2.
27. Process as claimed in claim 26, characterized in that the peak
current density of the cathodic-current pulses is in the range of
about 0.1 to 10 A/cm.sup.2.
28. Process as claimed in claim 24, characterized in that said
selected metallic material is (a) a pure metal selected from the
group consisting of Ag, Au, Cu, Co, Cr, Ni, Fe, Pb, Pd, Rt, Rh, Ru,
Mo, Mn, Sn, V, W, Zn, or (b) an alloy containing at least one of
the elements of group (a) and alloying elements selected from the
group consisting of C, P, S and Si.
29. Process as claimed in claim 24, characterized in that the
t.sub.on-time period is in the range of about 0.1 to about 50 msec,
the t.sub.off-time period is in the range of about 1 to 100 msec
and the t.sub.anodic-time period is in the range of about 1 to 10
msec.
30. Process as claimed in claim 24, characterized in that the duty
cycle is at least 25%.
31. Process as claimed in claim 24, characterized in that the
cathodic-current pulse frequency ranges from 2 Hz to 100 Hz.
32. Process as claimed in claim 24, characterized in that the
deposition rate is at least 0.075 mm/h.
33. Process as claimed in claim 24, characterized in that the
electrolyte is agitated by means of pumps, stirrers or ultrasonic
agitation at rates of 0 to 750 ml/min/A (ml solution per minute per
applied Ampere average current).
34. Process as claimed in claim 24, characterized in that said
electrolyte contains a stress relieving/grain refining agent
selected from the group of saccharin, coumarin, sodium lauryl
sulfate, naphthalene trisulfonic acid and thiourea.
35. Process as claimed in claim 24, characterized in that said
electrolyte contains particulate additives in suspension selected
from pure metal powders, metal alloy powders or metal oxide powders
of Al, Co, Cu, In, Mg, Ni, Si, Sn, V and Zn, nitrides of Al, B and
Si, carbon C (graphite or diamond), carbides of B, Bi, Si, W, or
organic materials such as PTFE and polymers spheres, whereby the
electrodeposited metallic material contains said particulate
additives.
36. Process as claimed in claim 35, characterized in that the
electrodeposited metallic material contains at least 5% by volume
of said particulate additives.
37. Process as claimed in claim 35, characterized in that the
electrodeposited metallic material contains at least 10% by volume
of said particulate additives.
38. Process as claimed in claim 35, characterized in that the
electrodeposited metallic material contains at least 20% by volume
of said particulate additives.
39. Process as claimed in claim 35, characterized in that the
particulate additives average particle size is below 10 pm.
40. Process as claimed in claim 24, characterized in that the
thickness of the reinforcing layer is at least 0.5 mm.
41. Process as claimed in claim 24, characterized in that the
average grain size of the deposited layer is equal to or smaller
than 1000 nm and that the ratio between the thickness and the
average grain size of the coated layer is greater than 1,000.
42. Process as claimed in any claim 24, characterized in that the
coated layer has an equiaxed micro structure.
43. Process as claimed in claim 24, characterized by maintaining
said electrolyte at a temperature in the range between 0 to
85.degree. C.
44. Process as claimed in claim 24, characterized by cleaning,
electropolishing or striking the workpiece.
45. Process as claimed in claim 24, characterized by electroforming
age hardenable metallic coatings and increasing the strength and
thermal stability thereof by a subsequent heat-treatment.
Description
[0001] This application is a continuation-in-part of International
Application No. PCT/EPO2/07023 filed on Jun. 25, 2002, the
specification of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] This invention relates to a process and apparatus for
electroplating a metal patch on the outside or exterior surface of
a damaged or degraded portion of a metallic workpiece, especially a
degraded or damaged portion of a metallic tube or conduit. In
particular a degraded or damaged (hereinafter referred to as
degraded) portion of a metallic pipe or conduit (hereinafter
referred to as a pipe) may be repaired in accordance with this
invention without having to remove the pipe from an apparatus or
installation in which the pipe is connected for the conveyance of
fluids (i.e., in situ repair of the pipe). The method and apparatus
is particularly suitable for the in situ repair and maintenance of
feeder pipe systems in nuclear reactors and applications where
degradation of the pipes occur by localized and general corrosion,
stress corrosion cracking, fatigue, erosion and the like. Formation
of the in situ patch uses an apparatus which is configured to form
a water tight electrolytic plating cell around the degraded portion
of the pipe. The plating cell which is advantageously confined to
the degraded portion of the pipe, is used to form a patch of fine
grained electrolytically deposited metal or metal alloy, which
optionally includes particulate material entrapped therein, wherein
the electroplated metal or metal alloy has an average grain size of
10-1000 nm, and desirably contains a portion of nanocrystalline
grain size electrodeposited metal or metal alloy. The
electrodeposition employs pulse electrodeposition with a total duty
cycle of 10-100%.
[0004] 2. Background Art
[0005] Tubes and pipes are commonly used e.g. in heat exchangers in
various applications in the chemical and nuclear industry, in
above-ground and underground pipelines for the transport of fluids
including liquid petroleum fuel, water, sewer, natural gas, etc. In
a variety of these applications the tube material locally degrades
with time and means are sought to repair a damaged section by a
convenient and cost-effective method.
[0006] A number of sleeving methods that involve welding, re-lining
with appropriate sleeves, as well as electroforming sleeves for
application to the inside of degraded pipe sections have been
disclosed in the prior art.
[0007] Malagola in U.S. Pat. No. 4,624,750 (1986) describes a
process for corrosion protection of a steam generator tube before
final assembly wherein a metallic layer is deposited on the inside
of the tube. This invention is specifically directed to applying a
protective coating to the inside of tubes. In one embodiment,
however, the outer surface of the tube, is also electroplated with
a 0.1 mm layer of electrolytic Ni before it is installed in the
tube plate. The process relies on plating a thin corrosion
resistant protective layer and is neither intended nor suitable for
the outside repair of degraded tube sections already in
service.
[0008] Erb in U.S. Pat. No. 5,352,266 (1994), and U.S. Pat. No.
5,433,797 (1995) describes a process for producing nanocrystalline
materials, particularly nanocrystalline nickel. The nanocrystalline
material is electrodeposited onto the cathode in an aqueous acidic
electrolytic cell by application of a pulsed DC current. The cell
also optionally contains stress relievers. Products of the
invention include wear resistant coatings, magnetic materials and
catalysts for hydrogen evolution.
[0009] Palumbo in U.S. Pat. No. 5,257,445 (1996), U.S. Pat. No.
5,516,415 (1996) and in U.S. Pat. No. 5,538,615 (1996) discloses a
plating process for the repair of nuclear steam generator tubes by
in-situ electroforming a structural layer on the inside of the
degraded tube section. The electrosleeve is applied by a convenient
remote process for forming a structural layer on the inside of the
affected tube section. The inner diameter of the tube to be
repaired is at least 5 mm, but typically between 1 cm and 5 cm. The
thickness of the electroformed layer is typically 0.1 to 2 mm and
its length ranges from 10 cm to 90 cm.
[0010] Michaut in U.S. Pat. No. 5,660,705 (1997) describes a thick,
non-magnetic Ni--B metal plating sleeve on the inside of a tube to
repair a steam generator tube crimped in a tube plate. The inside
diameter of the tube to be repaired is 2 cm and the coating
thickness ranges from 0.5 to 1.5 mm.
[0011] Although quite elegant, the electrosleeve process applied to
inside tube surfaces of nuclear steam generator tubes does have
limitations. Namely the thickness of the coating is limited
typically to less than 1 mm due to considerations such as probe
removal, flow restriction, coating surface finishing and need for
maintaining a non-destructive inspection capability such as eddy
current or ultrasound testing. Thin coatings inside the tube are
frequently insufficient to reestablish the original mechanical
properties. Relying on a substantial grain size reduction to enable
a complete structural repair compromises other physical properties
such as ductility. The method of handling and sealing the probe
against the inside tube wall can, at times, be challenging. The
process is neither well suited for small inner diameter tubes
(<0.5 cm) nor larger ones (>5 cm). Probe insertion/removal
may be difficult due to the location of the damaged area and the
geometry of the tubing, e.g. in long and more complex piping
systems involving elbows, tees, various inner diameter piping etc.
In some of these circumstances the damaged areas to be repaired are
more easily accessible from the outside of the tube. The
application of a suitable sleeve in regions other than straight
areas, such as bends, elbows, tees and the like can be difficult as
well. Inside diameter electrodeposition repairs provide a sleeve of
essentially uniform thickness which may not be desired/required,
e.g. in the case of larger inner diameter tubes with very localized
damaged areas, a "patch" may be a more suitable repair technique as
compared to sleeving the entire tube section, thereby minimizing
build up of additional material and minimizing heat exchange
property changes. Alternatively, an outside outer diameter repair
can be carried out without disrupting the power plant operation.
Therefore the need exists for a repair technique that can be used
in applications not currently satisfied by inside inner diameter
electrodeposition methods noted above.
SUMMARY OF THE INVENTION
[0012] It is an objective of the invention to repair corroded,
eroded, cracked or other degraded sections of a metallic workpiece
including e.g. at least a section of a tube, optionally with more
complex geometries such as elbows, tees, flanges and connections to
e.g. base plates and the like by applying a suitable metallic
coating to the outer surface of the damaged section using
electrodeposition. It is a further objective of this invention to
provide a process for plating a fine-grained metal, metal alloy or
metal matrix composite on the external surface of a tube section to
institute a full structural repair.
[0013] It is a further objective of this invention to provide an
apparatus for the in situ electrodeposition of a structural
reinforcing layer of selected metallic material on an external
surface of a degraded section of a metallic workpiece, especially a
pipe.
[0014] These and other objectives are obtained by the below
described process and apparatus for in situ electrodepositing a
structural reinforcing layer of selected metallic material on an
external surface of a degraded section of a metallic workpiece such
as a pipe. When a degraded section of pipe or tubing is repaired in
accordance with this invention, the wall of the pipe is restored to
its original mechanical design specifications, including burst
pressure, bend strength, fatigue and corrosion performance.
[0015] The process of the invention may be applied to establish a
thick corrosion resistant coating of a metal (e.g., pure metal
except for incidental impurities) selected from the group
consisting of Ag, Au, Cu, Co, Cr, Ni, Fe, Pb, Pd, Pt, Rh, Ru, Sn,
Mo, Mn, W, V, and Zn. Alternatively, the invention may be used to
establish a thick corrosion resistant coating of a metal alloy
wherein the metal alloy contains a combination of two or more of
the aforementioned metals. In addition, the metal alloy may further
comprise an alloying element selected from the group consisting of
B, C, P, S and Si. The metal alloy may also comprise one of the
above listed metals alloyed with at least one of the aforementioned
alloying elements. Furthermore, the aforementioned metal or metal
alloys may further comprise particulate additives which become
entrapped in the metal during the electroplating procedure.
Suitable particulate additives include particulates selected from
the group consisting of metal powder, metal alloy powder, metal
oxide powder, nitride powder, carbon (either graphite or diamond),
carbide powder, MoS.sub.2, and organic material such as polymer
spheres and particulate PTFE. Suitable metal oxide powders include
metal oxide of Al, Co, Cu, In, Mg, Ni, Si, Sn, V, and Zn. Suitable
nitrides include the nitrides of Al, B, C and Si. Suitable carbides
include the carbides of B, Cr, Bi, Si and W.
[0016] The process may be employed to create high strength equiaxed
coatings on the outside of degraded tubes in nuclear reactors,
industrial plants, above ground and underground pipelines, pipe
systems and related applications. The process is particularly
advantageous since the degraded portion of the metallic workpiece
may be repaired by electroplating a metal patch on the outside of
the degraded portion of the pipe without having to remove the pipe
from the apparatus or installation in which the pipe is used to
convey fluids. In other words the process provides an in situ
repair of the pipe. The invention may also be practiced on a non in
situ workpiece such as a pipe which is not connected to an
apparatus or installation.
[0017] The process may be carried out by providing a plating cell
around the degraded portion of the pipe, preferably without
removing the pipe from the environment or installation in which it
is utilized. The plating cell includes a housing which is
configured so that it may be clamped around the pipe to provide a
fluid tight or leak tight volume between the pipe and the housing
for the circulation of electrolyte or plating solution through the
volume within the plating cell. An anode is provided within the
housing. The anode is preferably located in the vicinity of the
degraded portion of the pipe within the housing. More than one
anode may be utilized. Preferably the anode or anodes surround the
degraded portion of the pipe and extend lengthwise beyond the
degraded portion of the pipe so that the electroplated metal formed
by the electroplating process forms a patch which extends slightly
beyond the degraded portion of the pipe. The plating cell also
includes appropriate electrical wiring and electrical connections
for connection to a source of electric current required for the
electroplating procedure. A wire is connected to the pipe
undergoing repair so that the pipe functions as a cathode. Thus the
cell includes at least one anode and a cathode with electrical
connections to a source of electric current. The housing of the
plating cell further includes a fluid supply inlet and a fluid
supply outlet so that the electrolyte or plating solution which
contains ions of the metal to be plated, can be circulated through
the housing of the plating cell. In addition the electrolyte or
plating solution is desirably maintained at an ideal electroplating
temperature (e.g., 0.degree. C. to 85.degree. C.) by cooling or
heating. For example the fluid supply inlet and outlet may be
connected to a temperature controlled reservoir for the regulation
of the temperature of the plating solution or other fluid which is
circulated through the plating cell. The supply inlet and outlet
may also be connected to a source of other fluids used in the
process. For example, the inlets and outlets may be connected to a
source of cleaning fluid such as surface cleaning fluid, activation
fluid, striking fluid and electrochemical polishing fluid.
Appropriate valves which are well known to those skilled in the art
may be utilized to select a particular fluid which is to be
circulated through the plating cell. For example a cleaning fluid
may be first circulated through the plating cell to clean the
exterior of the pipe prior to the circulation of the plating
solution.
[0018] In operation the housing is positioned and closed to provide
a leak tight seal around the surface of the workpiece to be plated.
The fluid supply inlets and outlets are connected to a temperature
controlled reservoir in order to enable the circulation of fluids
to and from the workpiece to be plated. Other methods for
controlling the temperature of a circulating fluid may be used
instead of a temperature controlled reservoir. For example, the
fluid supplied to the inlet may be passed through a cooling or
heating device such as a heat exchanger, which is regulated to
supply the fluid at the desired temperature.
[0019] Electrical connections are provided to the workpiece to be
plated and to one or several anodes used in the apparatus to
thereby form the in-situ plating cell around the workpiece area to
be plated. Electric current is supplied to the cathode and anode
while the plating solution is circulated through the plating cell
to thereby electroform a structural layer of metallic material. The
plating conditions are selected so that the plated material on the
external surface of the degraded section of the metallic workpiece
has an average grain size which is equal to or less than 1000 nm.
The electrodeposition takes place using DC or pulse
electrodeposition at a deposition rate of at least 0.05 mm per hour
(0.05 mm/h) while the aqueous electrolyte or plating solution which
contains ions of the metal to be plated, is circulated through the
plating cell. This is accomplished by passing single or multiple
D.C. cathodic-current pulses between the anode and the workpiece
area to be plated (i.e., the cathode) at a cathodic-current pulse
frequency in the range of about 0 to 1000 Hz at pulsed intervals
during which the current passes for a t.sub.on-time period of at
least 0.1 msec and does not pass for a t.sub.off-time period in the
range of about 0 to 500 msec, and passing single or multiple D.C.
anodic-current pulses between the cathode and the anode at
intervals during which the current passes for a t.sub.anodic-time
period in the range of 0 to 50 msec, the total duty cycle being in
the range of 10 to 100%.
[0020] According to another aspect of this invention the in situ
repair of the pipe may be carried out without enclosing the area of
the article to be coated and forming a plating bath around it. In
particular, brush or tampon plating is a suitable alternative,
particularly when only a small portion of the workpiece is to be
plated. The brush plating apparatus typically employs a soluble or
dimensionally stable anode wrapped in an absorbent separator felt
to form an anode brush. The brush is rubbed against the surface to
be plated in a manual or mechanized mode and electrolyte solution
containing ions of the metal or metal alloys to be plated is
injected into the separator felt.
[0021] The present invention provides suitable coatings which
function as a patch over the degraded portion of the workpiece by
an electroplating procedure without the need to remove the article
from the installation and without the need to submerse the entire
article to be repaired into a plating bath. Thus, a portion of the
workpiece such as a pipe is not covered by the reinforcing metallic
patch. In other words the reinforcing metallic patch is formed on
an exterior surface of the workpiece wherein the patch covers the
degraded portion of the workpiece without covering at least a
portion of a non-degraded portion of the workpiece. Thus the patch
is substantially confined to the degraded portion of the workpiece
although there may be some overlap onto non-degraded portions of
the workpiece, but it is not essential to cover the entire
workpiece with the patch. By a "non-degraded portion of the
workpiece" it is meant that this portion of the workpiece has not
been degraded to the point of needing repair which means that the
non-degraded portion of the workpiece can function as intended.
[0022] In the process of the present invention both DC and
pulse-plating processes may be utilized. Pulse-plating processes
may consist of a single cathodic on-time or multiple cathodic
on-times of different current densities and single or multiple
off-times per cycle.
[0023] A significant feature of the invention relates to the grain
size of the metal or metal alloy which is electrodeposited to form
the patch. All of the grain sizes mentioned herein are average
grain sizes unless specifically indicated otherwise. The
electroformed metal coatings of this invention have an average
grain size equal to or less than 1 micron (1000 nm), preferably in
the range of 10 to 750 nm, more preferably between 30 and 500 nm
and even more preferably between 50 and 300 nm. In instances where
ductility is not critical, the average grain size may be 100 nm or
less. A metal which has an average grain size which is less than or
equal to 100 nanometers is considered as having a nanocrystalline
structure. Ductility of the metal is diminished as the grain size
becomes smaller. Accordingly, it is generally not ideal to
electrodeposit the metal with an average grain size below 10 nm
because the ductility would be very low. The reduced grain size of
the electrodeposited metals produced in accordance with this
invention have high strength and they therefore produce a strong
patch with a minimum of thickness of the structural repair
coating.
[0024] Preferably the average grain size of the electrodeposited
coating does not vary throughout the cross-sectional thickness of
the coating. In other words the average grain size is substantially
uniform throughout the thickness of the electrodeposited metal. By
substantially uniform it is meant that the average grain size is as
uniform as humanly possible. Thus the invention preferably provides
an equiaxed microstructure throughout the plated component, which
is relatively independent of component thickness and structure. In
a non-equiaxed microstructure there is a gradual increase in the
average grain size throughout the thickness of the electrodeposited
metal because of increasing grain size as a function of time during
which electroplating takes place such that the first deposited
metal has a relatively small grain size and metal deposited thereon
has an increasingly larger grain size.
[0025] The present invention is particularly suitable for the
repair of degraded metallic workpieces containing at least part of
a tube, which are made of Fe, Cu and Ni based alloys and may be
used to repair pipe containing, for example, Fe, Co, Cu, Ni, Mo,
and Mn.
[0026] The electroformed coating layer may be a metal selected from
the group consisting of Ag, Au, Cu, Co, Cr, Ni, Fe, Pb, Pd, Pt, Rh,
Ru, Sn, Mo, Mn, W, V and Zn. In addition, the electroformed coating
layer may be an alloy as described above. For example alloys
containing two or more of the above metals may further comprise
alloying elements selected from the group consisting of B, C, P, S
and Si.
[0027] The metal and metal alloys which are deposited may further
comprise particulate additives to improve the physical
characteristics of the metal. The particulate additives are
incorporated into the metal or metal alloy during the
electroplating procedure by, for example, suspending the particles
in the plating solution so that the particles become entrapped in
the electrodeposited metal or metal alloy. Suitable particulate
additives include metal powders, metal alloy powders, metal oxide
powders, nitrides, carbon (either graphite or diamond), carbides,
MoS.sub.2, and organic materials such as polytetrafluoroethylene
(PTFE) and polymer spheres. Suitable metal oxides include oxides of
Al, Co, Cu, In, Mg, Ni, Si, Sn, V, and Zn. Suitable nitrides are
nitrides of Al, B, C and Si. Suitable carbides include carbides of
B, Cr, Bi, Si and W.
[0028] The metal or metal alloys which contain particulate
additives as described above are referred to herein as metal matrix
composites. The selection and amount of the particulates may be
used to further enhance the coating material properties.
[0029] The patch formed in accordance with this invention
preferably surrounds the degraded portion of the pipe to thereby
form a patch in the form of a sleeve. The patches or sleeves may
have a nonuniform thickness in order to enable thicker coating of
damaged sections or sections particularly prone to corrosion such
as those created by flow induced corrosion in elbows. The
nonuniform thickness of the patch or sleeve may be accomplished by
the appropriate selection and placement of consumable or inert
anodes and possible shielding in the plating apparatus. This
technique is particularly suitable to repair large outer diameter
tubes.
[0030] It is also possible in the practice of this invention to
electrodeposit age hardenable metallic coatings to form the patch.
The strength and thermal stability of such a patch may be increased
by a subsequent heat-treatment according to known procedures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] In order to better illustrate the invention by way of
examples, descriptions are provided for suitable embodiments of the
method/process/apparatus according to the invention in the case of
small outer diameter feeder tubes (<6") in a nuclear reactor
(FIGS. 1 to 3) and large outer diameter pipes (>1 ft) used in
e.g. gas pipelines (FIG. 4).
[0032] FIG. 1 is a sectional view through an axial plane of a
feeder tube joint to a base plate illustrating a housing formed of
two hinged sections sealing the degraded curved tube area to be
plated, while providing fluid supply and electrical
connections.
[0033] FIG. 2 is a sectional view through an axial plane of a
feeder tube joint to a base plate illustrating a housing containing
two hinged sections sealing the degraded curved tube area to be
plated against the base plate, while providing fluid supply and
electrical connections.
[0034] FIG. 3 is a sectional view through an axial plane of a T
illustrating a housing formed of two sections sealing the degraded
curved tube area to be plated, while providing fluid supply and
electrical connections; and
[0035] FIG. 4 shows a cross sectional view of a preferred
embodiment of a brush plating apparatus used to repair a large
outer diameter pipe.
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
[0036] According to one aspect of the present invention the housing
of the above-described plating cell is positioned and closed around
a degraded portion of a pipe to provide a leak tight seal around
the surface of the pipe which is to be plated. The fluid supply
inlets and outlets are connected to a temperature controlled
reservoir in order to enable the circulation of fluids to and from
the pipe which is to be plated. Electrical connections are provided
to the pipe and to one or several anodes which form the in-situ
plating cell around the pipe. Prior to the circulation of plating
solution through the plating cell, the pipe may be cleaned by
circulating an aqueous alkaline cleaner followed by the circulation
of rinse water through the plating cell. In addition, the surface
of the portion of the pipe which is to be patched may be
electropolished to eliminate imperfections and may then be
activated by circulating dilute mineral acid solution through the
plating cell and then circulating rinsing water through the
cell.
[0037] The plating cell is then used to electroform a structural
layer of metallic material which an average grain size of less than
1000 nm on the external surface of the degraded portion of the pipe
using electrodeposition (DC or pulse electrodeposition) at a
deposition rate of at least 0.05 mm/h (preferably at least 0.075
mm/h and more preferably at least 0.1 mm/h) by flowing an aqueous
electrolyte containing ions of the metallic material to be plated,
passing single or multiple D.C. cathodic-current pulses between the
anode and the portion of the pipe to be plated, i.e., the cathode,
at a cathodic-current pulse frequency in the range of about 0 to
1000 Hz at pulsed intervals during which the current passes for a
t.sub.on-time period of at least 0.1 msec and does not pass for a
t.sub.off-time period in the range of about 0 to 500 msec, and
passing single or multiple D.C. anodic-current pulses between the
cathode and the anode at intervals during which the current passes
for a t.sub.anodic-time period in the range of 0 to 50 msec, the
total duty cycle being in the range of 10 to 100%.
[0038] Instead of using the above-described plating cell to
practice the invention, the desired in situ repair of the pipe or
other workpiece may be accomplished by using the device described
in FIG. 4. Thus, according to another aspect of the invention, the
process comprises the steps of: assembling a selective plating
apparatus employing an anode brush wrapped in an absorbent
separator, connecting a fluid supply to the anode brush to enable
the supply of fluids to the absorbent separator between the anode
and the workpiece area to be plated, providing electrical
connections to the workpiece to be plated and the anode brush
forming the in-situ plating cell around the workpiece area to be
plated, and electroforming a structural layer of metallic material
with an average grain size which is equal to or less than 1,000 nm
on the external surface area of the degraded section of the
metallic workpiece using electrodeposition (DC or pulse
electrodeposition) at a deposition rate of at least 0.05 mm/h
(preferably at least 0.075 mm/h and more preferably at least 0.1
mm/h) by supplying an aqueous electrolyte containing ions of said
metallic material, placing the anode and the workpiece area to be
plated, i.e. the cathode, in contact with said electrolyte by
moving the anode brush over the workpiece area to be plated,
passing single or multiple D.C. cathodic-current pulses between
said anode and said workpiece area to be plated at a
cathodic-current pulse frequency in a range of about 0 and 1000 Hz,
at pulsed intervals during which said current passes for a
t.sub.on-time period of at least 0.1 msec and does not pass for a
t.sub.off-time period in the range of about 0 to 500 msec, and
passing single or multiple D.C. anodic-current pulses between said
cathode and said anode at intervals during which said current
passes for a t.sub.anodic-time period in the range of 0 to 50 msec,
the total duty cycle being in a range of 10 to 100%.
[0039] In the process of the present invention periodic pulse
reversal, a bipolar waveform alternating between cathodic pulses
and anodic pulses, can be used. The anodic pulses can be introduced
into the waveform before, after or in between the on pulse and/or
before, after or during the off time. The anodic pulse current
density is generally equal to or greater than the cathodic current
density. The anodic charge (Q.sub.anodic) of the "reverse pulse"
per cycle is always smaller than the cathodic charge
(Q.sub.cathodic). Periodic pulse reversal has been found to be
particularly effective in raising the temperature at which grain
growth occurs and for leveling of the deposit.
[0040] According to a preferred embodiment of the invention,
nanocrystalline deposits of the metals, metal alloys and metal
matrix composites are obtained when process parameters such as
current density, duty cycle, work piece temperature, plating
solution temperature and solution circulation rates were varied
over a wide range of conditions.
[0041] The following listing describes suitable operating parameter
ranges for practicing the invention:
[0042] Average current density (if determinable, anodically or
cathodically): 0.01 to 10 A/cm.sup.2, preferably 0.1 to 10
A/cm.sup.2, more preferably 1 to 10 A/cm.sup.2,
[0043] Total Duty Cycle: 10 to 100%
[0044] Frequency: 1 to 1000 Hz
[0045] Electrolyte solution temperature: 0 to 85.degree. C.
[0046] Electrolyte solution circulation/agitation rates: <10
liter per min per cm.sup.2 anode or cathode area (0.0001 to 10
l/min.cm.sup.2)
[0047] Work piece temperature: -20 to 85.degree. C.
[0048] Cathodic pulse on-times of at least 0.1 msec, typically in
the range from 0.1 to 50 msec, more preferably from 1 to 50 msec,
off-times from 0 to 500 msec, preferably from 1 to 100 msec, and
anodic pulse times range from 0 to 50 msec, preferably from 1 to 10
msec. The total duty cycle, expressed as the cathodic on-times
divided by the sum of the cathodic on-times, the off-times and the
anodic times, ranges from 10 to 100% and is at least 10%,
preferably at least 25%, more preferably at least 50% and most
preferably at least 75%. The frequency of the cathodic pulses
ranges from 0 Hz to 1 kHz, preferably from 1 Hz to 1 kHz and more
preferably from 2 Hz to 100 Hz.
[0049] In the process of the present invention the electroformed
metallic coatings optionally contain at least 5% by volume
particulates, more preferable at least 10% by volume particulates
and most preferably at least 20% by volume particulates. The
particulates can be selected from the group of metal powders; metal
alloy powders; metal oxide powders of Al, Co, Cu, In, Mg, Ni, Si,
Sn, V, and Zn; nitrides of Al, B, C and Si; C (graphite or
diamond); carbides of B, Cr, Bi, Si, W; MoS.sub.2; and organic
materials such as PTFE and polymer spheres. The particulate average
particle size is typically below 10 microns, preferably below 1,000
nm (1 mm), and more preferably below 500 nm. The metal particulate
and metal alloy particulate may be any of the metals and metal
alloys which are electroplated.
[0050] In the process of the present invention the electrolyte
preferably may be agitated by means of pumps, stirrers or
ultrasonic agitation at rates of 0 to 750 ml/min/A (ml solution per
minute per applied Ampere average current), preferably at rates of
0 to 500 ml/min/A.
[0051] In the process of the present invention optionally a grain
refining/stress relieving agent preferentially selected from the
group of saccharin, coumarin, sodium lauryl sulfate, naphthalene
trisulfonic acid and thiourea can be added to the electrolyte
plating solution.
[0052] The present invention provides thick, structural coatings,
having a thickness which is preferably at least 0.125 mm, such as
more than 0.25 mm, more preferably at least 0.5 mm, even more
preferably at least 2.5 mm, and most preferably at least 3 mm on
the outer surface of degraded tube or pipe sections, including
elbows, tees, flanges and connections to e.g. base plates.
[0053] The electroformed metallic coatings of this invention have
an average grain size equal to or less than 1 micron (1,000 nm),
preferably in the range of 10 to 750 nm, more preferably between 30
and 500 nm and even more preferably between 50 and 300 nm. In
instances where low ductility is acceptable, the average grain size
may be .ltoreq.100 nm.
[0054] To increase the part reliability, it is preferred to
maintain the ratio between average thickness and average grain size
of the coated layer of at least or greater than 1,000, preferably
greater than 5,000, and more preferably greater than 10,000.
[0055] According to this invention, patches can be formed on the
damaged areas without the need to electrodeposit an outer diameter
sleeve on an entire tube section as e.g. in the case of a localized
through-wall crack in a tube section which otherwise has no further
damage, by the appropriate selection and placement of anodes in the
plating apparatus, which is particularly suited to repair large
outer diameter tubes.
[0056] The person skilled in the art of plating, in conjunction
e.g. with U.S. Pat. No. 5,352,266 (1994) and in U.S. Pat. No.
5,433,797 (1995), the specifications of which are incorporated
herein by reference, will know how to electrodeposit selected
metals or alloys by selecting suitable plating bath formulations
and plating conditions. Optionally solid particles can be suspended
in the electrolyte and are included in the deposit to form a metal
matrix composite.
[0057] Minimizing the thickness of structural repair coatings can
be achieved by increasing the strength through grain size
reduction. Since ductility is generally required in the
electrodeposited metal patches of this invention, grain size
refinement which produces average grain size values below 10 nm do
not necessarily provide the ideal structure. It has been determined
that an average grain size of e.g. Ni-based coatings in the range
of 50 to 250 nanometers provides a coating with suitable mechanical
properties. Incorporating a sufficient volume fraction of
particulates can be used to further enhance the coating material
properties.
[0058] Depending on the requirements of the particular application,
the material properties can also be altered e.g. by the
incorporation of lubricants in the form of particulates (such as
MoS.sub.2, boron nitride and PTFE). Generally, the particulates
such as particulate lubricants may be selected from the group of
metal powders, metal alloy powders and metal oxide powders of Al,
Co, Cu, In, Mg, Ni, Si, Sn and Zn; nitrides of Al, B and Si; C
(graphite or diamond); carbides of B, Si, W; MoS.sub.2; and organic
materials such as PTFE and polymer spheres.
[0059] Embodiments of the invention which use a plating cell are
shown in FIGS. 1-3. FIG. 4 illustrates an alternative embodiment
which electroplates the metal patch without enclosing the degraded
area of the workpiece (e.g., in-situ pipe) in a plating cell.
[0060] FIG. 1 schematically shows the feeder tube (1) attached to a
base plate (2). Flexible, split ring sections forming the anode (3)
made of e.g. Ni, Co (soluble anodes) or Pt, Pt clad Nb, or Pt clad
Ti (dimensionally stable anodes) are slipped over the feeder tube
(1) and assembled to form the anode of the plating cell. A housing
(4) containing two half shells is placed over the anode (3) and the
tube section to be repaired and the housing is closed using a
sealed hinged arrangement (5). The fluid connection (6) contains
the electrolyte feed tube (7) and the electrical contact wire (19)
to the anode (3). The electrolyte exits the housing (4) through the
fluid connection port (6) and is circulated to a
temperature-controlled tank (not shown) by a pump (not shown). The
power supply (8) provides power to the anode (3) and the feeder
tube (1), which forms the cathode. Electrical contact wire (20)
connects the power supply to the feeder tube (1) which thereby
functions as the cathode which is plated in the portion surrounded
by the anode (3).
[0061] FIG. 2 schematically shows the feeder tube (1) attached to a
base plate (2). Anode-plates or -strips (3) made of e.g. Ni, Co
(soluble anodes) or Pt, Pt clad Nb or Pt clad Ti (dimensionally
stable anodes) are secured to the feeder tube (1) to form the anode
of the plating cell. A housing (4) containing two half shells is
placed over the anode (3) and the tube section to be repaired and
the housing is closed using a sealed hinged arrangement (5). After
closing the housing and inserting of a gasket (not shown) the
housing is secured to the base plate by bolts (9). The electrolyte
enters the housing (4) through the fluid inlet (10) and exits
through the outlet (11). The electrolyte is circulated to a
temperature-controlled tank (not shown) by a pump (not shown). The
power supply (8) provides power to the anode (3) and the feeder
tube (1) forming the cathode by wires (19) and (20)
respectively.
[0062] FIG. 3 schematically shows a T shaped feeder tube (1).
Flexible, strips or plates (3) made of e.g. Ni, Co (soluble anodes)
or Pt, Pt clad Nb or Pt clad Ti (dimensionally stable anodes) are
secured to the feeder tube (1) to form the anode of the plating
cell. A housing (4) containing two half shells is placed over the
anode (3) and the tube section to be repaired and the housing is
closed after inserting of a gasket (not shown) using bolts (12).
The electrolyte enters the housing (4) through the fluid inlet (10)
and exits through the outlet (11). The electrolyte circulated to a
temperature-controlled tank (not shown) by a pump (not shown). The
power supply (8) provides power to the anode arrangement (3) and
the feeder tube (1) forming the cathode by electric wires (19) and
(20) respectively.
[0063] According to a further preferred embodiment of the present
invention it is also possible to produce nanocrystalline coatings
by electroplating without the need to enclose the area of the
article to be coated and form a plating bath around it. Brush or
tampon plating is a suitable alternative, particularly when only a
small portion of the work piece is to be plated. The brush plating
apparatus typically employs a soluble or dimensionally stable anode
wrapped in an absorbent separator felt to form the anode brush. The
brush is rubbed against the surface to be plated in a manual or
mechanized mode and electrolyte solution containing ions of the
metal or metal alloys to be plated is injected into the separator
felt. An apparatus for carrying out this embodiment of the
invention is shown in FIG. 4.
[0064] FIG. 4 schematically shows the degraded area of a pipe
component (1) to be plated which is connected to the negative
outlet of the power source (8). The anode (3) consists of a handle
(13) connected to a conductive anode brush (14). The anode contains
channels (15) for supplying the electrolyte solution (16) from a
temperature controlled tank (not shown) to the anode wick
(absorbent separator) (17). The electrolyte dripping from the
absorbent separator (17) is optionally collected in a tray (18) and
recirculated to the tank. The absorbent separator (17) containing
the electrolyte (16) also electrically insulates the anode brush
(14) from the workpiece (1) and adjusts the spacing between anode
(3) and cathode (1). The anode brush handle (13) can be moved over
the workpiece (1) manually during the plating operation.
Alternatively, the motion can be motorized.
[0065] The following examples illustrate various embodiments of the
invention. The electrolyte formulations described herein and in the
examples are aqueous based.
EXAMPLE 1
[0066] An elbow of SAE106 grade B 21/2" schedule 80 pipe was fitted
with an embodiment forming the plating cell described in FIG. 1.
After sealing the apparatus appropriate fluid connections were
established. The surface of the tube was cleaned with a 10%
solution of Soak 5000, a commercial alkaline cleaner (Soak 5000)
produced by Atotech, and rinsed with water. The surface was then
subjected to an electropolishing step to eliminate imperfections,
and then activated using a dilute mineral acid solution (20% HCl or
H.sub.2SO.sub.4 for 10 minutes), followed by rinsing. Subsequently
a 4 mm thick layer of Ni (average grain size: 70 nm) was plated
onto the elbow using Pt-clad Nb ring sections as the anode material
and the formulation and conditions listed below. After the plating
was completed, the apparatus was drained, flushed with water three
times and thereafter the apparatus was removed.
[0067] Electrolyte Formulation:
[0068] 300 g/l nickel sulfate heptahydrate
[0069] 40 g/l boric acid
[0070] 0.1 g/l phosphorous acid
[0071] 4 ml/l NPA-91 (organic surfactant)
[0072] Electrolyte temperature: 60.degree. C.
[0073] pH: .about.2.5
[0074] Average cathodic current density: 0.13 A/cm.sup.2
[0075] T.sub.on/T.sub.off: 8 msec/2 msec
[0076] Duty Cycle: 80%
[0077] Plating rate: .about.0.005"/hr (0.13 mm/hr)
[0078] Time needed to plate 4 mm: 30 hrs
[0079] Characteristics of electrodeposited metal:
[0080] Composition: Ni--0.2% P (99.8 wt. % Ni; 0.2 wt. % P)
[0081] Grain Size: 70 nm
[0082] Hardness: 400 VHN (Vickers hardness)
[0083] Ratio of coating thickness to grain size: 57,143
EXAMPLE 2
[0084] An elbow of SAE106 grade B 21/2" schedule 80 pipe was fitted
with an embodiment forming the plating cell described in FIG. 2.
Alkaline cleaning, rinsing, electropolishing, activation and
rinsing were performed as indicated in Example 1. The plating cell
contained a titanium housing and a Pt-clad Nb mesh anode conforming
to the extrados enabling the selective plating of an area on the
circumference of the elbow. Electroplating produced a patch which
covered about 50% of the total pipe area enclosed by the plating
cell and the average thickness of the coating was 4 mm (average
grain size: 200 nm). The following conditions were used:
[0085] Electrolyte Formulation:
[0086] 300 g/l nickel sulfate heptahydrate
[0087] 40 g/l boric acid
[0088] 0.1 g/l phosphorous acid
[0089] 4 ml/l NPA-91 (surfactant)
[0090] Electrolyte temperature: 60.degree. C.
[0091] pH: .about.2.5
[0092] Average cathodic current density: 0.10 A/cm.sup.2
[0093] T.sub.on/T.sub.off: 8 msec/2 msec
[0094] Duty Cycle: 80%
[0095] Plating rate: .about.0.004"/hr (0.10 mm/hr)
[0096] Time needed to plate 4 mm: 40 hrs
[0097] Characteristics of electrodeposited metal:
[0098] Composition: Ni--0.15% P (99.85 wt. % Ni, 0.15 wt. % P)
[0099] Grain Size: 200 nm
[0100] Hardness: 300 VHN
[0101] Ratio of coating thickness to grain size: 20,000
EXAMPLE 3
[0102] The set up and pipe used were as described in Example 1. A
nanocrystalline Co--TiO.sub.2 nanocomposite of 0.25 mm average
coating thickness was then deposited onto the elbow section
immersed in a modified Watts bath (i.e., the electrolyte
formulation described in this example without the titania and
particle dispersant) for cobalt using a soluble anode made of a
cobalt plate and a Dynatronics (Dynanet PDPR 20-30-100) pulse power
supply. The following conditions were used:
[0103] Electrolyte Formulation:
[0104] 300 g/l cobalt sulfate heptahydrate
[0105] 45 g/l cobalt chloride hexahydate
[0106] 45 g/l boric acid
[0107] 2 g/l sodium saccharinate
[0108] 4 ml/l NPA-91 surfactant
[0109] 0-500 g/l titania (<1 mm particle size)
[0110] 0-12 g/l Niklad.TM. particle dispersant (supplied by
MacDermid Inc.) (a surfactant for dispersing the titania
particles)
[0111] Electrolyte temperature: 60.degree. C.
[0112] pH: .about.2.5
[0113] Average cathodic current density: 0.125 A/cm.sup.2
[0114] T.sub.on/T.sub.off: 2 msec/6 msec
[0115] Duty Cycle: 25%
[0116] Plating rate: .about.0.0016"/hr (0.04 mm/hr)
[0117] Time needed to plate 0.25 mm: 61/4 hrs
[0118] A series of electrodeposits were produced on a number of
tube elbow-sections using the modified Watts bath with the addition
of TiO.sub.2 particles (particle size <1 mm) ranging from 50 g/l
to 500 g/l. Table 1 illustrates the properties of the deposits. The
ratio of coating thickness to grain size is between 14,700 and
16,700.
1TABLE 1 Co-TiO.sub.2 nanocomposite properties Bath Grain Size
TiO.sub.2 Concen- Bath of Co Fraction Micro- Sam- tration
Concentration deposit in Deposit hardness ple TiO.sub.2 [g/l]
Dispersant [g/l] [nm] [Volume %] [VHN] Con- 0 0 16 0 490 trol 1 50
0 15 19 507 2 100 1.5 15 23 521 3 200 3 17 32 531 4 300 6 17 38 534
5 500 12 16 37 541
EXAMPLE 4
[0119] T-sections of an Alloy 600 (UNS N06600) tube (OD=1.9 cm)
were fitted with an embodiment forming the plating cell described
in FIG. 3. The plating cell contained two titanium housing plates
conforming to the geometry of the T-section enabling the plating of
a "reinforcement" layer on one side of the connecting tube and
around the joint area. The patch covered about 65% of the total T
area enclosed by the plating cell. A 1 mm thick layer of Co--2.5 wt
% P (97.5 wt. % Co, 2.5 wt. % P) (average grain size: 10 nm, 650
VHN) was plated onto the T-section using the formulation and
conditions listed:
[0120] Electrolyte Formulation:
[0121] 250 g/l cobalt chloride
[0122] 20 g/l phosphoric acid
[0123] 8 g/l phosphorous acid
[0124] Electrolyte temperature: 75.degree. C.
[0125] pH=1.75
[0126] Average cathodic current density: 0.150 A/cm.sup.2
[0127] T.sub.on/T.sub.off: 2 msec/6 msec
[0128] Plating rate: 0.005 "/hour
[0129] Time needed to plate 1 mm: 8 hours
[0130] Characteristics of electrodeposited metal:
[0131] Composition: Co--2.5 % P
[0132] Grain Size: 10 nm
[0133] Hardness: 650 VHN
[0134] Ratio of coating thickness to grain size: 100,000
[0135] After plating the section was heat treated at 400.degree. C.
for 5 min. The hardness of the coating was increased to 900
VHN.
EXAMPLE 5
[0136] A 6 in.sup.2 area degraded by a localized crack in a mild
steel pipe (outer diameter=3 ft) was repaired using the selective
plating set-up described in FIG. 4. A DC power supply was employed.
Standard alkaline electro cleaners were used to remove any dirt,
oil or grease from substrate (i.e., the external surface of the
pipe). Thereafter a standard activation solution was used to remove
any oxides, corrosion products or otherwise contaminated surface
material, which could adversely affect coating adhesion. Using the
anode brush with manual operation a nanocrystalline Ni.about.0.6 wt
% P (99.4 wt. % Ni, 0.6 wt. % P) (average grain size: 13 nm, 780
VHN) patch was deposited onto the degraded section until the
original thickness was restored. Plating was continued and an area
of about 10 in.sup.2 was coated to form a patch extending about
0.25 mm from the pipe surface using the following conditions:
[0137] Electrolyte Formulation:
[0138] 137 g/l nickel sulfate heptahydrate
[0139] 36 g/l nickel carbonate
[0140] 4 g/l phosphorus acid
[0141] 2 g/l sodium saccharinate
[0142] Electrolyte temperature: 65.degree. C.
[0143] Phosphoric acid to adjust pH to 1.5
[0144] Average cathodic current density: 0.1 A/cm.sup.2
[0145] Plating rate: 0.05 mm/hr
[0146] Composition: Ni--0.6% P (99.4 wt. % Ni, 0.6 wt. % P)
[0147] Grain Size: 13 nm
[0148] Hardness: 780 VHN
[0149] Ratio of coating thickness to grain size: 19,230
[0150] Anode versus cathode linear speed: 125 cm/min
[0151] Electrolyte circulation rate: 10 ml solution per min per
cm.sup.2 anode area or 440
[0152] ml solution per min per Ampere average current applied
* * * * *