The present invention relates to a plating solution, specifically, to a plating
solution for a threaded connection for pipe or tube, and a producing method of a
threaded connection for pipe or tube using the plating solution.
BACKGROUND ART
[0002]
Pipes (so called Oil Country Tubular Goods (OCTG)) used for oil fields or
natural gas fields have a unit length of ten or more meters. The pipes are connected
to each other by the treaded connections, and the connected pipes (the connected oil
country tubular goods) have an overall length as long as several thousand meters.
[0003]
Threaded connections for pipes or tubes are classified into T&C (threaded and
coupled) type threaded connections and integral type threaded connections.
[0004]
A T&C type threaded connection includes two pins formed at each end of two
pipes or two tubes, and two boxes formed at both ends of a coupling that is a short
tube and has an outer diameter larger than the pipes or tubes. Each pin has an outer
surface having male screws thereon. Each box has an inner surface having female
screws thereon. Each pin is screwed into each box to be fastened thereto.
Specifically, in a T&C type threaded connection, the pipes are connected to each
other via the coupling.
[OOOS]
Meanwhile, an integral type threaded connection includes a box formed at an
end of a first pipe, and a pin formed at an end of a second pipe. The pin of the
second pipe is screwed into the box of the first pipe, thereby connecting the first and
the second pipes to each other. This means that in the integral type threaded
connection, the first and the second pipes are directly connected to each other. A
coupling is eliminated by using an integral. type threaded connection. Hence, there
is no outward extrusion by a thickness of the coupling, and thus there is no interfere
with an inner surface of a pipe located outward. Accordingly, integral type
threaded connections are used for a special usage such as horizontal excavations.
[0006]
In general, threaded connections are required to have endurance against a
tensile forth in the axial direction due to their own weights of the connected pipes as
we1 as endurance against pressures of external and internal liquids.
[0007]
Threaded connections are further required to have galling resistance.
Specifically, a preferable galling resistance is required even after repetitive use four
or more times in a casing pipe (large-diameter size), and ten or more times in a
tubing pipe (small-diameter size). Conventionally, in order to enhance the galling
resistance, copper plating films are formed, or surface treatments, such as
phosphatizing, are applied on contact surfaces of pins or boxes of threaded
connections. A contact surface denotes a surface portion where a pin and a box
come into contact with each other, and such a contact surface includes a threaded
portion that is threaded, and a non-threaded metal contact portion that is not threaded.
A seal portion is equivalent to the non-threaded metal contact portion.
[OOOS]
For the purpose of enhancing the galling resistance, prior to fastening, dope is
applied on the contact surface of the pin or the box. The dope is a compound grease
containing heavy metals, such as Pb.
[0009]
However, heavy metals may affect the environment, and usage of dope
containing heavy metals has been increasingly restricted. For this reason, dope
(referred to as "green dope") free from heavy metals, such as Pb, Zn, and Cu, has
recently been developed. However, green dope has a lower galling resistance than
that of conventional dope.
[OO lo]
As techniques to enhance the galling resistance without using dope, there
have been proposed 1) a method of dispersingly mixing fluororesin particles in a
plating film, 2) a method of forming a lubricating protective film through spattering,
and 3) a method of using a solid lubricating film instead of using a compound grease,
and other methods. However, each of these techniques provides a poorer galling
resistance compared with that of conventional dope.
[OOl 11
Japanese Patent Application Publication No. 2003-74763 (Patent Literature 1)
and Japanese Patent Application Publication No. 2008-2 15473 (Patent Literature 2)
propose threaded connections excellent in galling resistance. In Patent Literature 1,
a Cu-Sn alloy layer is formed on a threaded portion and a non-threaded metal contact
portion of a threaded connection. In addition, in Patent Literature 2, a Cu-Zn-M1
alloy layer (M1 is one or more types of elements selected from Sn, Bi, and In) is
formed on a threaded portion and a non-threaded metal contact portion.
CITATION LIST
PATENT LITERATURE
[OO 1 21
Patent Literature 1 : Japanese Patent Application Publication No. 2003-74763
Patent Literature 2: Japanese Patent Application Publication No. 2008-2 15473
[OO 1 31
However, in Patent Literature 1, corrosion (crevice corrosion) is likely to be
caused at an interface (contact surface between a surface where a plating film is
formed and a surface where no plating film is formed) between the pin and the box.
Particularly, in the case of using green dope or a solid lubricant, crevice corrosion is
more likely to be caused. In Patent Literature 2, crevice corrosion is suppressed.
However, in the case of storing pipes in unconnected condition for long periods of
time, spot rust may be generated through defects (porosity) of plating films
depending on the environment. This means that exposure corrosion may be caused
in some cases.
SUMMARY OF INVENTION
[00 141
An object of the present invention is to provide a plating solution for a
threaded connection for forming a plating film excellent in galling resistance, crevice
corrosion resistance, and exposure corrosion resistance, and also to provide a
producing method of a threaded connection using this plating solution.
[00 1 51
A plating solution of the present embodiment is a plating solution for a
threaded connection. The plating solution contains no cyanide, but contains copper
pyrophosphate, tin pyrophosphate, zinc pyrophosphate, pyrophosphate as a metal
complexing agent, and a sulfur-containing compound of 40 g/L or less (excluding 0).
The sulfur-containing compound includes: a mercapto compound and a sulfide
compound defined by Chemical Formula (1); a dimer formed through a disulfide
bond of the mercapto compounds; and one or more types of salts thereof:
RS-(CHX')~-(CHX~)~-CHX(I~),X ~
where each of m and n is an integer of 1 or 0; each of x', X2, X3 and x4 is any
one of hydrogen, OH, NH2, and C02H, but excluding that x', x2, x3, and x4
are all hydrogen; and R is any one of hydrogen, a methyl group, and an ethyl group.
[0016]
A producing method of a threaded connection according to the present
embodiment includes: a step of preparing the above described plating solution; and a
step of subjecting a pin or a box of the threaded connection to electroplating using
the plating solution so as to form a Cu-Sn-Zn alloy plating film on the pin or the box.
[00 171
The threaded connection produced by using the plating solution of the present
embodiment is excellent in galling resistance, crevice corrosion resistance, and
exposure corrosion resistance.
DESCRIPTION OF EMBODIMENT
1001 8)
The present inventors have investigated mechanisms of generation of galling
and corrosion in threaded connections, and have studied solutions therefor. As a
result, the present inventors have attained the following findings.
[00 191
In the case of repetitively fastening and loosening a threaded connection,
contact sliding is caused between contact surfaces of a pin and a box of the
connection. In such a case, the contact surfaces are heated due to deformation
resistance. At this time, the contact surfaces may locally experience an increased
temperature equal to or more than the melting point in some cases. In the surface
portions having a temperature equal to or more than the melting point, the metals
become melted and seized to each other.
[om01
In a threaded connection, if the contact surface portion has a higher melting
point and a higher hardness, its deformation resistance becomes smaller. In such a
case, an excellent galling resistance can be attained. If a plating film formed on the
contact surface of the pin or the box is an intermetallic compound, the hardness and
the melting point of the plating film becomes greater. Accordingly, it is possible to
attain an excellent galling resistance.
[002 11
Meanwhile, in the Cu-Sn allay plating film of Patent Literature 1, crevice
corrosion is considered to be caused for the following reasons. Fe is an
electrochemically less noble metal than Cu. If the Cu-Sn alloy plating film is
formed on the steel surface of the threaded connection, micro galvanic cells are
formed between Cu in the plating film and the less noble steel (Fe) in contact with
Cn. Hence, corrosion (crevice corrosion) is caused at an unplated portion (Fe) in
contact with the plating film.
[00221
In order to suppress crevice corrosion, a metal less noble than Fe is contained
in the Cu-Sn alloy. Specifically, Zn is contained in the Cu-Sn alloy to form a Cu-
Sn-Zn alloy plating film. In this case, generation of crevice corrosion is suppressed.
[0023]
Patent Literature 2 discloses a Cu-Sn-Zn alloy plating film. However, in
Patent Literature 2, when forming the Cu-Sn-Zn alloy plating film, a plating solution
formed of a water solution containing cyanide (referred to as a cyanide plating
solution, hereinafter) is used.
[0024]
In the cyanide plating solution, Cu is complexed with cyanide into a metal
complex. By complexing Cu into a metal complex, it is possible to shift the
deposition potential of Cu to less noble potential. Hence, during the electroplating
treatment, while preventing Cu fiom being excessively electrodeposited alone, an
appropriate amount of Cu is electrodeposited along (co-precipitated) with Zn whose
deposition potential is less noble. Consequently, a Cu-Sn-Zn alloy plating film is
formed.
[0025]
However, in the case of forming a Cu-Sn-Zn alloy plating film using a plating
solution including cyanide, spot rust may be caused on the Cu-Sn-Zn alloy plating
film depending on the storage environment, the storage duration, and the others.
Specifically, such a Cu-Sn-Zn alloy plating film does not have a high exposure
corrosion resistance. Mechanisms of generating spot rust may be considered as
follows. In the case of using cyanide, current efficiency becomes deteriorated
during the electroplating. In the electroplating, hydrogen is generated along with
the precipitation reaction of metals. During the electrolytic plating using cyanide, a
large quantity of electricity is used for generating hydrogen. Consequently, fine
void defects (porosity) are formed in the plating film due to generated hydrogen. If
the porosity is combined, oxygen intrudes into the plating film from the outer surface
of the plating film through the porosity, and reaches a steel material (Fe) under the
plating film. In such a case, spot rust is caused.
[0026]
The plating solution including cyanide generates a toxic hydrocyanic acid gas
if being mixed with an acid solution. Generally, in the electroplating, an extremely
thin film (such as a Ni plating film) is formed prior to forming of the plating film.
This treatment is called as a strike plating. Formation of the thin plating film
through the strike plating enhances adhesiveness of the plating film formed through
the subsequent electroplating to the steel material. The plating solution is an acid
solution.
[0027]
In the case of a T&C type threaded connection, there are respectively
provided a strike tank where a strike solution is reserved, a water tank for water
cleaning, and a plating tank where a plating solution is reserved. A coupling for
which a box is provided is soaked in the strike tank so as to be subjected to the strike
plating. Subsequently, the box, after being subjected to the strike plating, is soaked
in the water tank to be cleaned with the water. The acid strike solution is almost
completely removed from the coupling through the water cleaning. Hence, no
hydrocyanic acid gas is generated even if the cyanide is contained in the plating tank
used in the subsequent electroplating.
[0028]
Because a coupling of a T&C type threaded connection is a short pipe, the
coupling can be soaked in each tank. To the contrary, in the case of an integral type
threaded connection, it is hard to soak a pin or a box thereof in each tank. This is
because an overall length of an integral type threaded connection is usually dozens of
meters. Hence, in the case of forming a plating film on a pin or a box of an integral
type threaded connection, the electroplating is carried out in a different manner from
the above manner.
[0029]
For example, the electroplating for an integral type threaded connection is
carried out in the following manner. A sealable capsule is fixed to the pin or the
box of the integral type threaded connection. The strike solution is supplied into the
capsule so as to perform the strike plating. Subsequently, the strike solution is
discharged from the capsule. After the discharge of the strike solution, the plating
solution is supplied into the capsule and the electroplating is performed.
[0030]
In the case of performing the electroplating in the above procedure, the
remaining strike solution and the plating solution may be mixed in the capsule in
some cases. In such a case, a hydrocyanic acid gas is likely to be generated.
Accordingly, it is not preferable to use such a plating solution that contains cyanide.
[003 11
The present inventors have studied a plating solution free from cyanide with
which a Cu-Sn-Zn alloy plating film excellent in exposure corrosion resistance can
be formed. As a result, the present inventors have attained the following findings.
LO0321
It is possible to form a Cu-Sn-Zn alloy plating film without using cyanide if
using a plating solution containing a pyrophosphate-based alkali aqueous solution
and a sulfur-containing compound having a high reducibility.
LO0331
In the case of carrying out the electroplating with the above plating solution, it
is possible to suppress generation of hydrogen. Specifically, in the case of carrying
out the electroplating with the plating solution containing cyanide, current efficiency
is approximately 30%. In this case, approximately 70% of plating current is used
for generating hydrogen. Meanwhile, in the case of carrying out the electroplating
with the above plating solution containing the pyrophosphate and the highly
reducible sulfur-containing compound, current efficiency is approximately 80%.
Accordingly, there is less porosity in the Cu-Sn-Zn alloy plating film formed with
this plating solution. As a result, it is possible to attain excellent exposure corrosion
resistance while suppressing generation of spot rust. In addition, because of less
porosity in the Cu-Sn-Zn alloy plating film, a higher hardness is attained. Hence,
the galling resistance becomes enhanced.
[0034]
The plating solution for a threaded connection accomplished based on the
aforementioned findings contains no cyanide, but contains copper pyrophosphate, tin
pyrophosphate, zinc pyrophosphate, pyrophosphate as a metal complexing agent, and
a sulfur-containing compound of 40 g/L or less (excluding 0). The sulfurcontaining
compound includes: a mercapto compound and a sulfide compound
defined by Chemical Formula (1); a dimer formed through a disulfide bond of the
mercapto compounds; and one or more types of salts thereof
RS-(CHX')~-(CHX*),-CHX~X" (I),
where each of m and n is an integer of 1 or 0; each of XI, x2, x3 and x4 is any
one of hydrogen, OH, NH2, and C02H, but excluding that x', x2, x3, and x4
are all hydrogen; and R is any one of hydrogen, a methyl group, and an ethyl group.
[003 51
In the case of carrying out the electroplating using the plating solution of the
present embodiment, generation of hydrogen is suppressed. Hence, it is possible to
suppress amount of porosity in the Cu-Sn-Zn alloy plating film formed through the
electroplating. Accordingly, generation of spot rust is suppressed, resulting in
excellent exposure corrosion resistance. The Cu-Sn-Zn alloy plating film is also
excellent in crevice corrosion resistance. Because of less amount of porosity in the
Cu-Sn-Zn alloy plating film, the Cu-Sn-Zn alloy plating film has a higher hardness,
and is excellent in galling resistance. In addition, although containing no cyanide, it
is possible to- form the Cu-Sn-Zn alloy plating film by using the plating solution of
the present embodiment. Accordingly, there is no possibility of generation of a
hydrocyanic acid gas in the plating treatment.
[0036]
The producing method of the threaded connection according to the present
embodiment includes a step of preparing the aforementioned plating solution, and a
step of subjecting the pin or the box of the threaded connection to the electroplating
using the above plating solution, thereby forming the Cu-Sn-Zn alloy plating film on
the pin or the box.
[003 71
The plating solution for the threaded connection and the producing method of
the threaded connection using this plating solution according to the present
embodiment will be described in detail, hereinafter.
[003 81
[Plating solution]
The plating solution of the present embodiment is used for electroplating on a
pin or a box of a threaded connection. The plating solution contains no cyanide, but
contains copper pyrophosphate, tin pyrophosphate, zinc pyrophosphate, a metal
cornplexing agent, and an addition agent, and a solvent. In the present embodiment,
the solvent of the plating solution is water.
[0039]
[Copper pyrophosphate, tin pyrophosphate, and zinc pyrophosphate]
Copper pyrophosphate, tin pyrophosphate, and zinc pyrophosphate are
essential compounds for forming the Cu-Sn-Zn alloy plating film. The preferable
lower limit of the copper pyrophosphate content in the plating solution is 1 g/L, and
more preferably 3 g/L in terms of copper. The preferable upper limit of the copper
pyrophosphate content is 50 gL, and more preferably 15 g/L in terms of copper.
[0040]
The preferable lower limit of the tin pyrophosphate content in the plating
solution is 0.5 g/L, and more preferably 2 glL in terms of tin. The preferable upper
limit of the tin pyrophosphate content in the plating bath is 50 g/L in terms of tin, and
more preferably 14 g/L.
[0041]
The preferable lower limit of the zinc pyrophosphate content in the plating
solution is 0.5 g/L, and more preferably 1 g/L in terms of zinc. The preferable
upper limit of the zinc pyrophosphate content in the plating solution is 50 g/L in
terms of zinc, and more preferably 20 g/L.
[0042]
[Metal complexing agent]
In order to enhance operational advantage of the addition agent, the plating
solution further contains pyrophosphate as the metal complexing agent. The
pyrophosphate as the metal complexing agent may be sodium pyrophosphate,
potassium pyrophosphate, ammonium pyrophosphate, or a mixture thereof, for
example.
[0043]
The preferable content of the pyrophosphate as the metal complexing agent in
the plating solution is 6 to 15 in terms of the P ratio. The more preferable upper
limit of the P ratio is 10, and the further more preferable upper limit thereof is 9.
The P ratio is defined by the following Formula (A).
P ratio = mass of P207 in pyrophosphate as metal salts of the metal
complexing agent, copper, tin, and zinc in the plating sohtion / mass of metals of
copper, tin, and zinc in the plating solution (A)
[0044]
[Sulfur-containing compound]
The plating solution further contains a highly reducible sulfur-containing
compound as an addition agent. The sulfur-containing compound includes: a
mercapto compound and a sulfide compound each defined by Chemical Formula (1);
a dimer formed through a disulfide bond of the mercapto compounds; and one or
more types of salts thereof as defined by Chemical Formula (1):
RS-(CHX')~-(CHX~)~-CH(XI)~, X~
where each of m and n is an integer of 1 or 0; each of XI, x2, x3 and x4 is any
one of hydrogen, OH, NH2, S03H, and C02H, but excluding that XI, x2, x3, and x4
are all hydrogen; and R is any one of hydrogen, a methyl group, and an ethyl group.
[0045]
The sulfur-containing compound may be mercaptoacetic acid, 2-
mercaptopropionic acid, 2-aminoethanethiol, 2-mercaptoethanol, l-thioglycerol,
mercaptopropane sulfonic acid, bis (3-sulfopropyl) disulfide, mercaptosuccinic acid,
cysteine, cystine, or methionine, for example. The sulfur-containing compound
may be a combination of these compounds.
[0046]
The highly reducible sulfur-containing compound enables co-precipitation
with Zn that is a less noble metal, suppresses generation of hydrogen during the
electroplating, and also reduces amount of porosity in the plating film. If the
content of the highly reducible sulfur-containing compound in the plating solution is
excessively high, the Cu-Sn-Zn alloy plating film becomes hard to be formed, which
may cause unplating. Accordingly, the preferable upper limit of the sulfurcontaining
compound in the plating solution is 40 glL. The preferable lower limit
of the sulfur-containing compound in the plating bath is 0.01 glL.
[0047]
[Surfactant]
The plating solution may further contain surfactant. The surfactant helps the
hydrogen gas generated during the electroplating to be discharged to the outside from
the surface of the steel material and the plating film. The preferable surfactant
content in the plating bath is 0.0001 g/L to 10 g/L.
[0048]
The plating solution of the present embodiment contains no cyanide.
Although containing no cyanide, the aforementioned plating solution enables
formation of the Cu-Sn-Zn alloy plating film through the electroplating.
[0049]
[Producing method of threaded connection]
The producing method of the threaded connection using the aforementioned
plating solution is as follows. First, the above described plating solution is prepared.
Subsequently, the electroplating using the above plating solution is carried out on the
contact surface of the pin or the box of the threaded connection. The electroplating
method is not limited to a specific one. If the threaded connection is of the T&C
type, the electroplating may be carried out using the aforementioned plating tank. If
the threaded connection is of the integral type, the electroplating may be carried out
using the aforementioned capsule, or using other methods. The strike plating may
be carried out prior to the electroplating. The threaded connection is produced
through the aforementioned producing procedure. Conditions of the electroplating
(bath temperature, pH of the plating solution, current density, etc.) are not limited to
specific ones if the conditions are appropriately defined by a well-known method.
A pretreatment, such as degreasing and pickling, may be performed prior to the
electrolytic plating.
[OOSO]
[Plating film formed on threaded connection]
The threaded connection produced by the aforementioned method includes the
Cu-Sn-Zn alloy plating film formed on the pin or the box. The Cu-Sn-Zn alloy
plating film contains Cu, Sn, and Zn, and a balance thereof is impurities. In the Cu-
Sn-Zn alloy plating film, the preferable Cu content is 40 to 70 mass%, the preferable
Sn content is 20 to 50 mass%, and the preferable Zn content is 2 to 20 mass%.
[005 l]
The preferable thickness of the Cu-Sn-Zn alloy plating film is 30 to 40 prn.
As aforementioned, a Ni plating film may be formed under the Cu-Sn-Zn alloy
plating film, or a Cu plating film may be formed instead of the Ni plating film.
[0052]
Compared with a Cu-Sn-Zn alloy plating film produced by using a
conventional plating solution containing cyanide, the Cu-Sn-Zn alloy plating film
produced by the above described method has a less content of porosity. Hence, in
the threaded connection including the Cu-Sn-Zn alloy plating film produced by the
above producing method, spot rust is unlikely to be generated, and excellent
exposure corrosion resistance can be attained. Because of a less content of porosity,
the Cu-Sn-Zn alloy plating film has a higher hardness, and is excellent in galling
resistance. In addition, the Cu-Sn-Zn alloy plating film is more excellent in crevice
corrosion resistance compared with that of a Cu-Sn alloy plating film.
[0053]
In the case of fastening threaded connections, each having a Cu-Sn-Zn alloy
plating film thereon, to each other, a well-known lubricating film is formed on a
contact surface of the pin or the box. The lubricating film may be a viscous l~quid
or semisolid lubricating film, or may be a solid lubricating film. The lubricating
film may be a lubricating film having a two-layer structure including a solid
lubricating film of a lower layer and a viscous liquid or semisolid lubricating film of
an upper layer, or may be a lubricating film containing solid powder. The solid
powder is not limited to specific one if the solid powder is a well-known substance
exerting a lubricating effect. The solid powder may be graphite, MoS2
(molybdenum disulfide), WS2 (tungsten disulfide), BN (boron nitride), PTFE
(polytetrafluoroethylene), CF (fluorocarbon), or CaC03 (calcium carbonate), etc.
[0054]
The threaded connection produced by the producing method of the present
embodiment exhibits an excellent galling resistance even if using the above
lubricating film instead of using conventional dope containing heavy metals.
EXAh4PLE
[0055]
Plating films were formed on the threaded connections by using respective
plating solutions of Test No. 1 to Test No. 8 as shown in Table 1. Examination was
conducted on the obtained plating films for uniformity, galling resistance, crevice
corrosion, and exposure corrosion of each plating film.
[Table 11
Test
No.
Ainphoteric 1 3 1 ~~~~~~ / Mercaptoetl~anol / 15 / Surfactant I 5 1 3
Pyrophosphate
(A-1) Solution
Pyrophosphate
(A-1) Solution
Pyrophospl~ate
None I - 1 Ainpllote" 1 Surfactant I ,,
Plating
Time
Period
(inin.)
Plating Solution
2-
aininoethanethiol
2-
aminoethanethiol
1 6 1 "Ifate I Allyltlliourea I 0.2 I Non-ionic
~olution Surfactant I ) ) 1 2
Basic
Coinposition
Pyrophosphate
(A-1) Solution
1 1 Sulfate (E-I)
Solution
None 1 - 1 None I - 1 15
Amphoteric
Surfactant
Ainphoteric
Surfactant
1 1 Cyanate (F-1)
Solution I None 1 - 1 None / - / 40
Addition Agent
2-
aminoethanethiol
I Plating Layer
5
5
Chemical
Coinposition
Cu-Sn-Zn
Concen
tration
(g/L)
3
12
45
Cu-Sn-Zn
Thickness
(I.L~)
Surfactant
Alnphoteric
Surfactant
Cu-Sn-Zn
Cu-Sn-Zn
Concen
tration
(inL/L)
Cu-Sn-Zn
Cu-Sn
5
Cu-Sn-Zn 1
12
[0057]
First, plural seamless pipes were produced. Each chemical composition of
the seamless pipes contained Cr of 13 mass%. Each seamless pipe had an outer
diameter of 244.5 mm, a thickness of 13.84 rnrn, and a length of 1200 min. In Test
No. 1 to Test No. 7, a box was formed by internally threading an inner surface of one
pipe end of each pipe, and a pin was formed by externally threading an outer surface
of the other pipe end of each pipe, thereby forming an integral type threaded
connection.
[005 81
In Test No. 8, a coupling of a T&C type threaded connection was prepared.
An inner surface at each end of the coupling was internally threaded into a box.
The coupling had an outer diameter of 267.2 mm, a thickness of 24.0 mm, and a
length of 335 mm.
[00591
[Preparation of plating solution]
The following four types of plating solutions were prepared.
(A-1) solution:
- Tin pyrophosphate: 10 g/L in terms of tin
- Copper pyrophosphate: 10 g/L in terms of copper
- Zinc pyrophosphate: 10 g/L in terms of zinc
- Sodium pyrophosphate: 300 g/L
- P ratio = 7.7
(C-1) solution:
- Tin methanesulfonate: 15 g k in terms of Sn
- Copper methanesulfonate: 15 g/L in terms of Cu
- Sulfuric acid: 180 g/L
(E-1) solution:
- Copper sulfate: 250 g/L
- Sulfuric acid: 1 10 g/L
(F-1) solution (manufactured by Nihon Kagaku Sangyo Co., Ltd.):
- Sn: 8.5 g/L
- CU: 23.0 g k
- Zn: 0.7 g/L
- Sodium cyanide: 19.0 g/L
- Caustic soda: 13.0 g/L
[0060]
The (A-1) solution bad a composition within a range of the composition of the
plating solution according to the present embodiment. The (C-1) solution and the
(E-1) solution were sulphate baths mainly composed of sulphate. The (F-1)
solution was a cyanide bath containing cyanide.
[0061]
An addition agent and a surfactant were added to each solution as shown in
Table 1. As the amphoteric surfactant, "Arnphitol 24BMw, hich is a brand name of
Kao Corporation, was used in Test No. 1 and Test No. 2, and in Test No. 4 and Test
No. 5. In Test No. 3, as the amphoteric surfactant, Softazoline LPB, which is a
brand name of Kawaken Fine Chemicals Co., Ltd., was used. In test No.6, as nonion
surfactant, polyoxyethylene dinonylphenyl ether was used. In each of Test No.
1 to Test No. 5 ((A-1) solution), the plating solution was obtained by further
adjusting pH to be 8. In the adjustment of pH, polyphosphoric acid was used in
Test No. 1 and Test No. 3 to Test No. 5, and orthophosphoric acid was used in Test
No. 2.
[0062]
[Electroplating]
In Test No. 1 to Test No. 7, the boxes of the respective integral type threaded
connections were subjected to electroplating using the respective plating solutions as
shown in Table 1. Specifically, the box of each threaded connection was covered
with a sealable capsule. The inside of the capsule was filled with the corresponding
plating solution, and the electroplating was carried out. The bath temperature was
set to be 35°C in each of Test No. 1 to Test No. 7. The respective plating time
periods were as shown in Table 1.
[0063]
In Test No. 8, the coupling of the T&C type threaded connection was
subjected to the electroplating using the plating solution as shown in Table 1.
Specifically, the coupling was soaked in the plating bath, and the electroplating was
carried out. The bath temperature was 45°C. The plating time period was as
shown in Table 1.
[0064]
Each chemical composition of the obtained plating films was measured
through EDX (energy dispersive X-ray analysis). Each chemical composition of
the respective Cu-Sn-Zn alloy plating films in Test No. 1 to Test No. 5, and in Test
No. 8 was such that Cu content: 55 mass%, Sn content: 35 mass%, and Zn content:
10 mass%. The chemical composition of the Cu-Sn alloy plating film in Test No. 6
was such that Cu content: 55 mass%, and Sn content: 45 mass%. The chemical
composition of the Cu plating film in Test No. 7 was such that Cu content: 100
mass%.
~ 0 ~ 5 1
[Unplating determination test]
On each plating film formed under the condition of each Test No., it was
visually determined whether or not unplating portion (where the plating film was not
locally formed, so that the surface of the steel material was exposed) was generated
in the plating film. Specifically, the plating film in each Test No. was visually
observed to confirm whether or not there was any "burnt deposit" therein.
Determination results are shown in Table 1. "E" (Excellent) denotes that no burnt
deposit was observed, and the plating film of interest was uniformly formed. "NA"
(Not Acceptable) denotes that "burnt deposit" was observed in the plating film of
interest.
[0066]
[Galling resistance evaluation test]
A lubricating coating was formed on the contact surface of each box on which
the plating film was formed under the condition of each Test No. by the following
method. As the lubrication agent, green dope, specifically Bestolife "3010"NM
SPECIAL, which is a brand name of Bestolife Corporation, was used. Each
thickness of the lubricating coating was 100 pm.
[0067]
Fastening and loasening were repetitively performed using each box on which
the plating film was formed under the condition of each Test No. and each pin which
was not subjected to the plating treatment. This test was carried out at a normal
temperature (25°C). A torque used for the fastening and the loosening was
4935 1.8N.m (36400ft.lbs). Every time one cycle of the fastening and the loosening
was completed, each box was subjected to solvent cleaning to remove lubricating
coating therefrom. The contact surface of each box with the lubricating coating
removed therefrom was visually observed in a manner as to examine whether or not
any galling was generated thereon. The fastening and the loosening were
repetitively carried out up to ten times at maximum, and the number of cycles
obtained by subtracting one from N cycles when the galling was observed for the
first time (i.e., N-1 cycles; this number of cycles is referred as an M&B cycle,
hereinafter) was used as an evaluation index of the galling resistance. If the M&B
cycle was "lo", this case means that no galling was observed even after 10 cycles of
the fastening and the loosening. Test results are shown in Table 1.
[0068]
[Crevice corrosion test]
A carbon steel plate material (equivalent to SPCC defined by JIS G3 141
(201 1)) was prepared. Plural test specimens were collected from the plate material.
Each test specimen was subjected to the electroplating under the above described
conditions using the plating solution of each Test No., thereby preparing a plated test
specimen on whose surface the corresponding plating film as shown in Table 1 was
formed.
[0069]
Fixed test specimens were prepared in such a manner that, of the test
specimens collected from the plate material, each of test specimens subjected to no
electroplating (referred as a non-plated test specimen, hereinafter) and each plated
test specimen in each Test No. were fixed in contact with each other with a bolt. A
contact surface between each plated test specimen and each non-plated test specimen
that were fixed to each other had a dimension of 50 rnrn x 50 mm.
[0070]
A crevice corrosion test was conducted using the fixed test specimens. Each
fixed test specimen was soaked in a boiled water containing NaCl of 20 mass% for a
month (3 1 days). Each of the fixed test specimens was taken out after a month, and
a maximum corrosion depth in the contact surface of each non-plated test specimen
in contact with the corresponding plated test specimen was measured.
[007 11
Measurement results are shown in Table 1. "E" (Excellent) denotes that the
maximum corrosion depth was less than 1 pm. "G" (Good) denotes that the
maximum corrosion depth was 1 to less than 5 pm. "A" (Acceptable) denotes that
the maximum corrosion depth was 5 to less than 10 pm. "NA" (Not Acceptable)
denotes that the maximum corrosion depth was 10 pm or more.
[0072]
[Exposure corrosion test]
Plated test specimens that were the same as those used in the above crevice
corrosion test were prepared. In surfaces of each test specimen, a surface where the
plating film was formed (referred to as an observation surface) had a dimension of 50
mm x 50 mm. Each plated test specimen was subjected to a salt spray test in
compliance with JIS 22371 (2000) for 24 hours. In each observation surface after
the test, an area where rust (spot rust) was generated was measured. Test results are
shown in Table 1. "E" in Table 1 denotes that no rust was generated on the entire
observation surface. "G" denotes the rust occurrence area ratio in the observation
surface was less than 5%. "A" denotes that the rust occurrence area ratio in the
observation surface was 5% to less than 20%. "NA" denotes that the rust
occurrence area ratio in the observation surface was 20% or more.
[0073]
[Test results]
With reference to Table 1, in each of Test No. 1 to Test No. 3, the basic
composition of the plating solution and the addition agent were both within the range
of the present embodiment. Accordingly, the produced Cu-Sn-Zn alloy plating film
exhibited no burnt deposit, and was produced uniformly. Each M&B cycle of these
Test Nos. was ten cycles, which exhibited an excellent galling resistance. In each
plating film of these Test Nos., excellent crevice corrosion resistance and excellent
exposure corrosion resistance were obtained.
[0074]-
Meanwhile, the plating solution of Test No. 4 had an appropriate basic
composition, but contained no sulfur-containing compound as the addition agent.
Hence, burnt deposit was observed in the plating film. This is thought to be the proof
of the generation af unplating portions therein. Consequently, the M&B cycle was
as small as less than 4 cycles, so that the galling resistance was poor.
[0075]
The plating solution of Test No. 5 had an appropriate basic composition, but
had an excessively high content of the sulfur-containing compound as the addition
agent. Hence, burnt deposit was observed in the plating film. This is thought to be
the proof of the generation of unplating portions therein. Consequently, the M&B
cycle was as small as less than 4 cycles, so that the galling resistance was poor.
[0076]
The film formed using the plating solution of Test No. 6 was a Cu-Sn alloy
plating film. Hence, the crevice corrosion resistance and the exposure corrosion
resistance were poor.
[0077]
The film formed using the plating solution of Test No. 7 was a Cu plating film.
Hence, the M&B cycle was as small as less than 4 cycles, so that the galling
resistance was poor.
[0078]
In the plating solution of Test No. 8, a plating solution containing cyanide was
used. In this case, a uniform Cu-Sn-Zn alloy plating film was formed. However,
the Cu-Sn-Zn alloy plating film formed using this plating solution exhibited a poor
exposure corrosion resistance. It can be considered that the plating solution
contained cyanide, and thus plenty of hydrogen was generated during the
electroplating, which resulted in a large amount of porosity in the plating film.
[(I0793
The embodiment of the present invention has been described as above;
however, the aforementioned embodiment is merely an example for carrying out the
present invention. Accordingly, the present invention is not limited to the
aforementioned embodiment, and the aforementioned embodiment may be
appropriately modified without departing from the scope of the present invention.

We claim:
1. A plating solution for a threaded connection for pipe or tube, the plating
solution containing no cyanide,
the plating solution comprising:
copper pyrophosphate;
tin pyrophosphate;
zinc pyrophosphate;
pyrophosphate as a metal complexing agent; and
a sulfur-containing compound of 40 g/L or less (excluding O), wherein
the sulfer-containing compound inc1udes:a mercapto compound and a sulfide
compound defined by Chemical Formula (1); a dimer formed through a disulfide
bond of the mercapto compounds; and one or more types of salts thereof:
RS-(CHX'),-(CHX~),-CHX~X~(I ),
where each of m and n is an integer of 1 or 0; each of XI, x2, x3 and x4 is any
one of hydrogen, OH, NH2, S03H, and C02H, but excluding that x', X2, x3, and X4
are all hydrogen; and R is any one of hydrogen, a methyl group, and an ethyl group.
2. A producing method of a threaded connection for pipe or tube comprising:
a step of preparing the plating solution according to claim 1 ; and
a step of subjecting a pin or a box of the threaded connection to electroplating
using the plating solution so as to form a Cu-Su-Zn alloy plating film on the pin or