TUBULAR THREADED JOINT AND LUBRICATING COATING FORMING
COMPOSITION FOR USE THEREIN
TECIINICAL FIELD
[OOOl]
The present invention relates to a tubular threaded joint for use in connecting
steel pipes and particularly oil country tubular goods, and a surface treatment method
thereof.
Priority is claimed on Japanese Patent Application No. 2012-1741 17, filed on
August 6, 2012, the content of which is incorporated herein by reference.
BACKGROUND ART
[0002]
Oil country tubular goods such as tubing and casing used in oil well drilling
for excavation of crude oil or gas oil are usually connected (jointed) to each other by a
tubular threaded joint. In the past, the depth of the oil wells was 2,000 to 3,000 nl,
but in deep oil wells such as recent offshore oil fields, the depth may reach 8,000 to
10,000 m. The length of the oil country tubular goods is typically several tens of
meters, and the periphery of tubing through which a fluid such as crude oil flows is
su~soundedw ith a plurality of casings, and thus the number of the oil country tubular
goods jointed by the threaded joint reaclies a vast number.
[0003]
Under a service environment, a load that is an axial tensile force caused by the
weight of the oil country tubular goods and the joint tl~eemselvesa, composite pressure
of an internal pressure and an extenial pressure, and geothermal heat are applied to the
tubular tlxcadcd joint for oil country tubular goods. Therefore, there has been a
demand for the tubular thseaded joint to maintain gastightness \vithout undergoing
dainage even iil such a severe eil\ii.oiliileilt.
[OOO4]
Atypical tubular tlxeaded joint (also, called special tlxeaded joint) used for
connecting oil coutlt~ytu bular goods has a pin-box structure. A pin, wl~ichis a joint
member having a male thread, is typically formed at both ends of the oil countty
tubular goods. A box, which is a counterpart joint member having a female thread
that is screwed to the male thread is typically formed at both-side internal surfaces of a
coupling that is a separate member As shown it1 FIG. 1, seal portions 4a and 4b are
provided at an outer peripheral portion close to an end surface on the front end side in
relation to the male thsead of the pin, and on an internal peripheral surface of the base
portion of the female thsead of the box, respectively. Shoulder portions (also called
torque shoulder) 5a and 5b are provided at the end suiface of the front end of the pill 1,
and the deepest portion of the box 2 which corresponds to the end surface. The seal
portions 4a and 4b, and the shoulder poi?ions 5a and 5b constitute an u~ltlxeadedm etal
contact portion of the tubular threaded joint, and the unthreaded metal contact portion
and a thscaded portio~c~on stitute a contact surface of the tubular threaded joint. The
following Patent Document 1 discloses an examnple of the special tlxeaded joint.
[OOO5]
To fasten the tubular tlxeaded joint, one end (pin) of an oil cou~ltrytu bular
good is inserted into a coupling (box), and the male thread and the female thread are
fastened until the shoulder portions of the pin and the box colnc into contact wit11 each
other and interfere each other with appropriate torque. According to this, the seal
portions of the pin and the box come into close contact with each other to fosnl a
metal-to-metal seal portion, and thus gastigl~tnesso f tlie threaded joint is secured.
[0006]
During o process of lowcring tubing or casing into an oil well, due to various
problems, tlie threaded joint fastened once is loosened, the joint is lifted up once from
the oil well, tlie joint is re-fastened, and the joint is lowered sonie times. API
(American Petroleum Institute) recommends seizure resistance such that seizure called
galling does not occur and gastiglitness is maintained even when fastening (make-up)
and loosening (break-out) are repeated ten times.
[0007]
A viscous liquid lubricant (grease lubricating oil) which contains heavy metal
powders called "compound grease" is applied to the contact surface of the threaded
joint in adva~icew henever the fastening is performed so as to incrcasc seizure
resistance and gastigl~tness. Such a conlpound grease is specified in API standard
BUL 5A2.
[0008]
In order to increase the retention of tlie compou~ld grease or to improve
sliding propel-ties, it has been proposed to cany out various types of surface treatments
such as a nitriding treatment, various types of plating including zinc plating atid
dispersal plating, and phosphate cheniical conversion treat~~leonnt the contact surface
of a threaded joint to form one or more layers in order to increase the retention of
compound grease or to improve sliding properties. However, as described below,
thereis a concern that the use of conipound grease has an adverse effect on the
environment and the human body.
[0009]
Tlie compound grease contains a large amount of lieavy metal powders such
as zinc, lead, and copper. When the fastening of the tlxeaded joint is carried out,
grease which has been applied is washed off or overflows to an exterior surface, and
thus there is a possibility in that patticularly, harmful heavy metals such as lead may
have an adverse effect on the environment and particularly on sea life. In addition, a
process of applying compound grease deteriorates a working enviro~unenat nd working
efficiency, and there is also a concern of harmfi~el ffects on the 11i11nan body.
[OOl 01
In recent years, as a result of the enactment in 1998 of the OSPAR Convention
(Oslo-Paris Convention) for preventing ocean pollution in the Northeast Atlantic, strict
restrictions concerning the global environment have bee11 in progress, and in some
regions, the use of compound grease has been already restricted. Accordingly, in
order to avoid adverse effects on the environment and the human during the excavatiot:
of gas wells and oil wells, there is a demand for a threaded joint which is capable of
exhibiting excellent seizure resistance without using the compound grease.
[OOll]
As a threaded joint wl~ichIn ay be used for fastening of oil country tubular
goods without application of the compound grease, the present inventors have
suggested a threaded joint for steel pipes in which a viscous liquid or semisolid
lubricating coating is fornled in Patent Document 2, and a threaded joint for steel pipes
in which a solid lubricating coating is formed in Patent Document 3, respectively.
[0012]
Patent Document 1 : Japanese Unexamined Patent Application, First
Publication No. H5-87275
Patent Document 2: Japanese Unexamined Patent Application, First
Publication No. 2002-173692
Patent Document 3: PCT International Publication No. WO20091072486
DISCLOSUPS OF THE INVENTION
[0013]
In a premium tubular threaded joint provided with seal portions 4a and 4b,
and shoulder portions 5a and 5b as shown in FIG. 1, the seal poi-tioas 4a and 4b of a
pin 1 and a box 2 form a metal-to-metal seal portion during fastening, and thus
gastightness is secured.
[0014]
A torque chart (vertical axis: torque, and horizontal axis: turns) during
fastening of this kind of threaded joint is shown in FIG. 2. As shown in the drawing,
as rotation takes place, initially, threaded portions of the pin and thc box come into
contact with each other, and torque gradually increases. Then, when seal portions of
the pin and the box come into contact with each other, and a rate of increase in torque
increases. When a shoulder portion of the front end of the pin and a shoulder portion
of the box come into contact with each other and begin to interfere each other (the
torque at the start of this interference is called a shouldering torque: Ts), the torque
abruptly increases. When the torque reaches predetermined fastening torque, the
fastening is conlpleted.
[00 151
I-Iowever, in a premium theaded joint used in wells in which a high
connpressive stress or a bending stress is applied, .the fastening takes place with torque
higlier than coininon torque in order for tlie theaded joint not to be loosened. In this
case, the shoulder portion of the end surface of the pin and the shoulder portion of the
box m~llichc onies into contact with the sl~oouldepr ortion of the pin yield (the torque at
this time is called yielding torque: Ty), and the shoulder portions may undergo plastic
defornlation as shown in FIG. 2.
1001 61
With regard to a threaded joint which is fastened with high torque, it is
advantageous for Ty-Ts (= AT: torque on shoulder resistance) to be large. However,
in the tubular tlueaded joint provided with a viscous liquid or senlisolid lubricating
coating described in Patent Document 1 and Patent Doculllent 2, Tjr decreases
compared to a case in which compound grease of the related art is applied, and thus AT
decreases. As a result, optimal fastening torque may not be determined depending on
tolerance in an amount of thread interference. In addition, the optimal torque in FIG.
2 represents torque with which an amount of interference necessary for securing
gastightness in the seal portions is accon~plishedto tennillate fastening, and the
optimal torque is deternlined in advance for each internal size of a joint or type of a
joint.
[0017]
The invention is to provide a tubular threaded joint provided with a
lubricating coating which does not contain a harmful heavy metal, is excellent in
seizure resistance, gastightness, and anticorrosive properties, and is capable of securing
a large AT, and in which yielding of a shoulder portion is not likely to occur even in
fastening with high torque.
[0018]
It has been found that even when a composition of the lubricating coating is
changed in order for the coefficient of friction to increase or decrease, generally, Ts and
Ty behave in the same mannel; and thus AT does not vary greatly. For example, ~vhen
the coeflicient of friction of the lubricating coating increases, Ty increases, but Ts also
increases (referred to as high shouldering). As a result, in the worst case, a situation
in which the shoulder portions do not come into contact with each other even in
pi-edetei-ii~iilefda stening torque, aiid the fasteiiiiig is not coiiipleted (i~cfei~retod as no
shouldering) occws.
[0019]
The present inventors have found the following. With regard to a tubular
threaded joint provided with a lubricating coating which does not contain a harmful
heavy metal imposing a load on the global environment, when a lubricating coating is
formed on a contact surface (a threaded portion and an nnthreaded metal contact
portion) of at least one member of a pin and a box using a composition which contains
melamine cyanurate (MCA, melamine cyanuric acid) and a basic metal salt of an
aromatic organic acid as an essential cotnponent, and which further contains one or
more kinds selected from the group consisting of a pine resin-based material (including
pine resin and a derivative thereof), wax, a metal soap, and a lubricating powder, a
tubular threaded joint, which has suff~cienst eizure resistance, gastightness, and
anticorrosive properties, and a large AT, and which does not have a danger of causing
no shouldering, may be obtained.
[0020]
Here, according to an elilbodi~nenot f the invention, there is provided a
composition for forming a lubricating coating to a tubular threaded joint. The
composition co~itainsa melamine cyanurate (hereinafter, abbreviated as MCA), a basic
metal salt of an aronlatic organic acid, and one or more kinds selected from the group
consisting of a pine resin-based material, a wax, a metal soap, a lubricating powder.
[0021]
It is preferable that the amount of the MCA be 0.5 % by mass to 30% by mass
011 the basis of the total amount of non-volatile components of the coiilposition. Here,
the non-volatile components represent components other than a solvent in the
It is preferable that an average particle size of the MCA contained in the
composition be 10 pm to 40 pm. Here, the average particle size is defined as a
median diameter (50% pai-ticle size: D50) of a volume-based pai-ticle size distribution
obtained by a particle size distribution measuring device using a laser diffraction
scattering method as a measure:ernent principle.
[0022]
From the viewpoint of application properties during coating formation, the
composition may contain a volatile organic solvent for low viscosity. It is preferable
that the composition substantially do not contain a heavy metal such as lead that is
harnlful to the human body (specifically, in an amount exceeding 1% by mass on the
basis of the total amount of non-volatile coinponents of the conlposition).
[0023]
According to another aspect of the invention, there is provided a tubular
threaded joint including a pin and a box, each being provided with a contact surface
including a threaded portion and an nnthreaded metal contact portion. The
lubricating coating fornled using the composition is provided on the contact surface of
at least one inenlber of the pin and the box.
[0024]
It is preferable that a film thickness of the lubricating coating be 10 pm to 500
pn1.
It is preferable that the contact surface of at least one member of the pin and
the box which is provided with the lubricating coating be subjected to a surface
treatment by blasting, pickling, a phosphate chenlical conversion treatment, an oxalate
chemical conversion treatment, a borate cl~emicacl onversion treatment, electroplating,
i~iipacpt lating, or a surface treaiiiieilt iileiliod selected fioiii two or iiiore kiiids thereof
before forming the lubricating coating.
[0025]
In addition, in a case where only the contact surface of one member of the pin
and the box is provided with the lubricating coating, it is preferable that the contact
surface of the other member of the pin and the box be subjected to the surface
treatment by the surface treatment method.
[0026]
The tubular threaded joint according to the invention is preferably suitable for
connecting oil country tubular goods.
[0027]
In addition, according to still another embodiment of the invention, there is
provided a method of connecting a plurality of oil country tubular goods using the
tubular threaded joint without applying grease lubricating oil.
[0028]
Generally, an operation nlechanism of the lubricating coating formed from tllc
composition according to the invention is considered as follows.
Fastening (make-up) of the tubular tlxeaded joint is perfornled by inserting
tlle pin into the box, and by rotating the pin or the box. First, only threaded portions
come into contact with each other to screw together, and at a final stage of the
fastening, when seal portions and shoulder portions start to conle into contact,
respectively, and thus a predetern~ineda ~nounot f interference is obtained in tlle seal
portion and the shoulder portion, the fastening is completed.
200291
In the lubricating coating, when a surface pressure is still low at an initial
period of shouldering, coeficient of fiiction is low, and accordingly, Ts decreases.
On the other hand, under a 11igl1 surface pressure (the maximum surface pressure of the
seal portions: 1 to 3 GPa) immediately before completion of fastening, the coefficient
of fsiction increases, and thus Ty increases. As a result, AT increases. As described
above, it is considered that the specific behavior in which the coefficient of friction is
different between during low surface pressure sliding and during high surface pressure
sliding is exhibited due to combination of the MCA and the basic metal salt of an
aromatic organic acid. However, chemical interactions thereof are not sufficier~tly
made clear.
[0030]
The tubular threaded joint of the itlventiorl may reliably exhibit excellent
seizure resistance during fastening of oil country tubular goods without applying
grease lubricating oil such as compound grease which has been applied to the treaded
joint. Accordingly, the tubular threaded joint of the invention may avoid an adverse
effect on the global environment and the human body which is caused by the
compound grease. In addition, it is not likely for a shoulder postion to yield during
tlie fastening at high torque, and thus a stable metal-to-metal seal portion may be
realized with a margitl.
In the tubular threaded joint according to the invention, tlie lubricating coating
formed on the contact surface tliereof exhibits as a large AT as the coating of the grease
lubricating oil such as the compound grease containing a harmfill heavy metal in tlie
related art, and thus it is possible to perfornl a fastening process without causing yield
or seizure at the slioulder portion even during fastening with high torque. h addition,
the seizure may be suppressed even under severe conditions such as unstable drilling
work in the sea. In addition, the lubricating coating substantially does not contain a
liariiifi~hl eavy metal sucl~a s lead, aild thus there is little iiilpact oil the global
environment. In the tubular threaded joint according to the invention, formation of
rust is suppressed. Accordingly, even when fastening and loosening are repeated, a
lubricating function is continuously exhibited, and gastightness may be secured after
the fastening.
BRIEF DESCRIPTION OF THE DRAWING
[0031]
FIG. 1 is a diagram schetnatically illustrating an unthreaded metal contact
portion (a shoulder portion and a seal portion) of a premium threaded joint.
FIG. 2 is a typical torque chart during fastening of a premium tubular threaded
joint;
FIG. 3 is a diagram schematically illustrating an assembling configuration of a
steel pipe at the time of shipment and a coupling.
FIG. 4 is a diagram schematically illustrating a cross-section of the premium
tubular threaded joint.
DESCRIPTION OF EMBODIMENTS
[0032]
Hereinaftel; a tubular threaded joint and a lubricating coating forming
composition according to the invention will be described in detail for illustration.
[0033]
FIG. 3 scl~ematicallys hows a state of a steel pipe for oil country tubular goods
at tlie time of sllipment and a coupling. A pin 1 having a male tlxeaded portion 3a on
an external surface is formed on both ends of a steel pipe A, and a box 2 having a
felnale threaded portion 3b oli an ititcrna! surfacc is formed on both sides of a coupling
B. The pin represents a threaded joint liiember on a side having the nlale thread, and
the box represents a threaded joint lnelnber on a side having the felnale thread. The
coupling B may be tightly fastened in advance to one end of the steel pipe A.
Although not showll, protectors for protection of threaded portions are mounted to both
of the pin in another end of the steel pipe A and the box in another end of the coupling
B each of which is not fastened, before shipment, and those protectors are detached
before using the threaded joint.
[0034]
In a typical tubular threaded joint, as shown in the drawing, t!~pci1 1 is formed
on the external surface of both ends of the steel pipe, and the box is fornled on the
i~~ternsaulr face of the coupling that is a separate component. There is also an integral
type tubular threaded joint in which one end of tlie steel pipe is formed as a pin, and
the other end is fornied as a box \vitl~outu sing the coupling. The tubular threaded
joint of the invention is applicable to any of these types.
[0035]
FIG. 4 schematicaily illustrates a configuration of a representative tubular
threaded joint (hereinafter, referred to as sinlply "threaded joint"). The threaded joint
is constituted by a pin 1 that is formed on an external surface of an end of the steel pipe
A, and a box 2 that is formed on an internal surface of the coupling B. Tlie pin 1
includes a niale threaded portion 323, a seal portion 4a that is positioned at tlie front end
of the steel pipe, and a shoulder portion 5a of an end surface. In correspondence with
this configuration, the box 2 includes a female threaded portion 3b, and a seal portion
4b and a shoulder portion 5b on an i~ulers ide of the female threaded portion 3b. The
seal portion and the shoulder pol-tion constitute an unthreaded metal contact portion.
[0036]
The threaded portions 3a and 3b, the seal portions 4a and 4b, and the shoulder
portions 5a and 5b of the pin 1 and the box 2 (in other words, untlxeaded metal contact
portions and threaded portions) become contact surfaces of the threaded joint.
Seizure resistance, gastightness, and anticorrosive properties are required for the
contact surface. Therefore, in the related art, compound grease containing a heavy
metal powder is applied to the contact surface or viscous liquid or semisolid
lubricating coating is formed on the contact surface. However, as described above,
the former has an adverse-effect on the human body or the environment, and in the
latter, AT is low during fastening wit11 high torque, atld thus there is a problem in that
the shoulder portion may yield before fastening.
[0037]
According to the invention, the contact surface of at least one member of the
pin and the box is covered with the lubricating coating. The lubricating coating
exhibits an excellent lubricating performance and an gastightness nlaintaining effect
during fastening of the threaded joint like the compound grease in the related art.
Accordingly, even xvl~enth e compound grease is not used, and fastening and loosening
are repeated with high torque, the threaded joint of the invention may prevent the
seizure of the threaded joint without yield of the shoulder portions, and gastightness
after the fastening may be secured.
[0038]
It is preferable that an underlayer (that is, the contact surface of the threaded
joint) of the lubricating coating be roughened. The roughening may be accomplished
by directly roughening a steel surface by blasting or pickling, or by forming an
underlayer coating having a rough surface on the steel surface before forming the
lubricati~igc oating.
[0039]
The lubricating coating may be formed as follows. A lubricating coating
forming conlposition that is diluted with an appropriate volatile organic solvent as
necessary is prepared, and the conipositio~ils applied by an appropriate method such as
brush application, spraying, and itnmersion, and then the solvent is vaporized and dried
according to circumstances.
[0040]
The lubricating coating may be forn~edo n both of the contact surfaces of the
pin and tlie box. However, as shown in FIG. 3, in a case where the pin and the box
are fastened at the time of shipment, it is suficient that the lubricating coating is
fornled on a contact surface of either the pin or the box. In this case, since a surface
treatment or applicatiotl work for fornling the lubricating coating in the short coupling
is easier than that in the long steel pipe, the lubricating coating is preferably formed on
the contact surface of the coupling (commonlj~t,h e contact surface of the box). In a
case where the pin and the box are not fastened at the time of shipment, it is preferable
that the lubricating coating be formed on the contact surfaces of both of the pin and the
box to add anticorrosive properties in combination with a lubricating surface.
According to this, a decrease in lubricating properties or gastightness due to fornlation
. of rust may be prevented.
[0041]
In additioa, it is necessaly for the lubricating coating to be coated on the
entirety of tlie contact surface of the pin andlor tlie box, but a case in which a part (for
exalnple, only the unthreaded metal contact portion) of the contact surface is coated is
also included in the invention.
[0042]
[Lubricating Coating]
The lubricating coating is formed on the contact surface of at least one of the
pin and the box of the theaded joint so as to prevent the seizure during fastening
between the steel pipes using the threaded joint, and formation of rust during storage.
In the invention, to form a lubricating coating in wyhich AT is large and thus the
shoulder portion does not yield even during tight fastening with 11ig11 fastening torque,
and which is capable of preventing the seizure and formation of rust during storage, the
lubricating coating contains MCA (melamiue cyanulate) and a basic metal salt of an
arolnatic organic acid.
LO0431
The MCA is an organic salt formed from melamiue and cyanuric acid, and is a
white powder which has a chemical fortnula expressed by C3H6N6.C3H3N30a3n d
which is considered to have a mica-shaped crystal stluctitre in which the melamine and
the cyanuric acid are hydrogen-bonded. The MCA has a heat-resistant temperature as
high as 250°C to 350°C, and a non-flammable gas ( N 2 ) is generated during combustion,
and thus the MCA is mainly used as a non-halogen flame retardant, and a flame
retardant promoter with respect to various kinds of tl~er~noplastoicr thermosetting
resins. Furthermore, the MCA has a mica-shaped layered crystal structure, and thus
the MCA is also used as a white lubricating oil additive.
[0044]
However, practically, a lubricating system of the MCA is not well known
except that the MCA has a cleavable layered crystal structure. In the invention, the
lubricating coating is formed on the contact surface of the tubular threaded joint in
conibination of the MCA and the basic metal salt of an aromatic organic acid.
Accordingly, a specific friciiorial behavior in which coeficieni ofrriciion during low
surface pressure sliding is low, and coefficient of friction during high surface pressure
sliding is high is exhibited. This behavior becomes apparent for the first time in the
invention, and the mechanism has not been clear yet.
[0045]
With regard to the MCA, MCA that is subjected to a surface treatment by a
coupling agent such as a silane coupling agent and a titanium coupling agent is
commercially available. Tlie surface-treated MCA has also the above-described
effect, and thus may be used in the same manner.
[0046]
The amount of the MCA in the lubricating coating (that is, the amount on the
basis of the total amount of non-volatile co~nponentsin the lubricating coating forming
comnposition) is preferably set to be within a range of 0.5% by mass to 30% by mass.
When the amount is less than 0.5% by mass, the effect of increasing AT becomes
insufficient. On the other hand, when the amount exceeds 30% by mass, flowability
as a lubricating coating decreases, and thus lubricating properties such as seizure
resistance may be deficient. More preferably, the amount of MCA is 1% by Inass or
more, and still more preferably 2% by mass or more. The upper litnit thereof is
preferably set to 20% by mass or less.
[0047]
The basic nletal salt of an aromatic organic acid increases the seizure
prevention effect and anticorrosive effect of tlie lubricating coating formed on the
contact surface of tlie tubular threaded joint, and exhibits specific frictional behavior in
wvllich the coefficient of fiiction is low during the low surface pressure sliding, and the
coeEcient of friction is high during tlie lhigh surface pressure sliding wlien being used
in combination wiili MCA, Accordingly, ihe basic nieial sali exhibits an effect of
increasing AT.
The MCA having an average particle size of approximately 0.5 pm to 5 p n is
commonly used from the viewpoint of dispersibility to a base. The MCA is
frequently classified as a solid lubricating agent. On the other hand, an effect of
improving lubricating properties is not sufficiently verified, and with regard to
conditions under which tlie operation mechanism and effect are exhibited, and the like,
there are many unclear points.
According to investigation of the present inventors, as the MCA contained in
the lubricating coating, MCA having a large average particle size is preferable so as to
obtain a more sufficient AT improving effect.
A preferable average particle size of the MCA is 10 pm to 40 pm. When the
average particle size is 10 pm or less, the AT improving effect is not sufficient. On
the other hand, when the average particle size exceeds 40 pm, the MCA is not likely to
be uniformly distributed on a frictional sliding interface during screw fastening, and
thus the AT improving effect is not sufficiently obtained. Here, the average particle
size is defined as a median diameter (50% particle size: D50) of a volunie-based
particle size distribution obtained by a particle size distribution measuring device using
a laser diffraction scattering niethod as a nieasurement principle.
A mechanism in which AT is significantly improved when MCA having a
relatively coarse average particle size is used in combination with the basic organic
metal salt is assumed as follows.
A basic organic metal salt having both of a lipophilic group and a liydrophilic
gronp, that is, a basic organic metal salt considered to have the same operation as a
surfactant is aligned on a surface of MCA having slightly high hydropllilicity, and
allows coarse MCA io be unirormly dispersed io a base ihai is an oil base. As a result,
the coarse MCA is reliably introduced to the high surface pressure sliding interface
during fastening of the threaded joint. The coarse MCA that is introduced to the
sliding interface exhibits an operation of increasing a frictional resistance of the sliding
interface during a process of being pressed and being deformed while preventing
seizure (preventing contact between metals).
[0048]
The basic metal salt of an aromatic organic acid is a salt constituted by an
aromatic organic acid and a surplus alkali (alkali metal or alkali earth metal).
Specific example thereof includes basic sulfonate, basic salicylate, basic phenate, and
basic carboxylate. All of the basic metal salts of an aromatic organic acid are
materials in which a surplus content of alkali is dispersed in oil as a metal salt of a
colloidal fine particle and which are present in a grease form or a semisolid form at
ambient temperature. The basic metal salts of an aromatic organic acid show a
significant heavy-duty anticorrosion performance, and exhibit a lubricating operation
by physical absorption of surplus metal salts in a colloidal fine particle state, 01.
chemical absorption of organic acid groups, and the like.
[0049]
Alkali that constitutes a cation portion of the basic metal salts of an aromatic
organic acid may be an alkali metal or alkali earth metal. However, the alkali is .
preferably alkali earth metal, particularly, calcium, barium, or magnesium. Even
when any of these is used, the same effect may be obtained.
[OOSO]
With regard to the basic metal salts of an aromatic organic acid, the higher a
base value thereof is, the further an amount of fine particlemetal salts that functions as
a solid lubricant increases. Accordingly, high lubricaiing properties (seizure
resistance) may be imparted due to the lubricating coating. In addition, when basicity
becomes higher to a certain degree, there is an operation of neutralizing an acid
component, and thus anticorrosive power of the lubricating coating also increases.
From this reason, it is preferable that basic oil having a base value (JIS K2501) (in a
case of using two or more kinds, a weighted average value of base values for m~llicha n
amount is taken into consideration) of 50 mgKOWg or more be used. However,
when the base value exceeds 500 mgKOWg, hydrophilicity increases, and
anticorrosive properties also begin to decreases, and thus rust may occur. A
preferable base value is 100 mgKOH1g to 500 mgKOWg, and more preferably 250
mgKOH/g to 450 mgKOWg.
[0051]
As described above, the basic metal salts of an aromatic organic acid are
grease type or semisolid materials, and may achieve a function of a base of the
lubricating coating. Accordingly, the basic metal salts may be contained as much as
75% by mass in the lubricating coating. The amount is preferably 70% by mass or
less. The lower limit of the amount is not particularly limited, but 20% by mass or
more is preferable, and more preferably 40% by mass or more.
[0052]
The total amount of the MCA and the basic metal salts of an aromatic organic
acid in the lubricating coating is preferably set to 45% by mass to 95% by mass, and
more preferably 50% by mass to 90% by mass.
[0053]
Tlie lubricating coating forlning conlposition according to to the invention
further contains one or more kinds selected from the group consisting of a pine resinbased
material, a wax, a metal soap, and a lubricaiing powder in addition to the two
kinds of essential coniponents. In the following description, these con~ponentsa re
collectively referred to as a lubricating selective con~ponent. When the lubricating
coating does not contain at least one kind of lubricating selective component selected
from the above components, adhesiveness between the lubricating coating that is
formed and a surface of a base material, or sufficient coating strength against the high
surface pressure during frictional sliding may not be obtained, and as a result, a
lubricatitlg performance, particularly, seizure resistauce becomes deficient.
[0054]
When the lubricating coating contains the pine resin-based material that is a
material selected from pine resin and a derivative thereof, the pine resin-based material
undergoes a high surface pressure in a friction surface, and becomes highly viscous,
a~tdth us the pine resin-based material is effective for increasing AT of the coating.
[OOSS]
The pine resin is a natural resin secreted from wood of genus pinus. The
pine resin is constituted by three elements of carbon, hydrogen, and oxygen. Main
components of the fine tree include resin acid (rosin acid) expressed by CzoH3002, and
colophane acid expressed by C,,I-In+jo04. Examples of a representative resin acid
include abietic acid, d-pi~narica cid, and i-pimaric acid.
[0056]s
The pine resin (rosin) is largely classified into tall rosin, gun1 rosin, and wood
rosin according to a collection ~netlioda, nd any of these may be used. In addition,
various kinds of pine rosin derivatives such as rosin ester, hydrogenated rosin,
polylnerized rosin, and disniutated rosin are connnercially available, and these pine
-rosin derivatives may also be used as the pine resin-based material.
[0057]
The amount of the pine resin-based material including the rosin and a
derivative thereof in the lubricating coating is preferably set to 30% by Inass or less.
When the anlottnt exceeds 30% by mass, the conlposition that is used for forming the
coating beconles highly viscous, and tllus there is a concern that coating forming
properties may be damaged. To sufficiently obtain the above-described effect of the
pine resin-based material, it is preferable that 5% by mass or more of rosins be
contained in the lubricating coating, and more preferably 5% by mass to 20% by mass.
[0058]
Wax not only has a seizure prevention effect due to a decrease in friction of
the lubricating coating, but also decreases flowability of the lubricating coating.
Accordingly, the wax is helpful to increase coating strength. Any of animal wax,
vegetable wax, mineral wax, and syntl~eticw ax may be used. Examples of wax that
is usable include beeswax, spernlaceti (the above, animal wax), Japan wax, carnauba
wax, candelilla wax, rice wax (the above, vegetable wax), parafin wax,
microcrystalline wax, petrolatum, montan wax, ozocerite, ceresin (the above, mineral
wax), oxidation wax, polyethylene wax, Fischer-Tropsch wax, amide wax,
hydrogenated castor oil (castor wax) (the above, synthetic wax), and the like. Among
these, the paraffin wax having a lnolecular weight of 150 to 500 is preferable.
[OOSS]
The amount of wax in the lubricating coating is preferably set to 25% by mass
or less. When the amount exceeds 25% by mass, adhesiveness or strength of the
lubricating coating may decrease. The amount is preferably 20% by mass or less.
The lower liriiit of the amount of the wax is not particularly limited, but it is preferable
that 2% by mass or more of wax be co~itaitled so as to reliably obtain the effect of the
wax.
[0060]
The metal soap that is a salt of a fatty acid with a metal other than alkali metal
may be contained in the lubricating coating so as to increase the seizure preventioll
effect and the anticoisosive effect of the lubricating coating. The amount thereof in
the coating is set to 30% by Inass or less. When the amount exceeds 30% by tnass,
adhesiveness or strength of the lubricating coating may decrease. The lower limit of
the amount of the metal soap is not particularly limited, but it is preferable that 2% by
Inass or more of metal soap be contained so as to reliably obtain the above-described
effect.
[0061]
In view of lubricating properties or anticorrosive properties, it is preferable
that the fatty acid of the metal soap be a fatty acid having 12 to 30 carbon atoms. The
fatty acid may be either a saturated fatty acid or an unsaturated fatty acid. In addition,
the fatty acid may be any of a mixed fatty acid derived from natural fat and oil such as
beef tallow, lard, wool fat, pall11 oil, rapeseed oil, and coconut oil, and a single
compound such as lauric acid, tridecylic acid, lnyristic acid, palniitic acid, lallopalmitic
acid, stearic acid, isostearic acid, oleic acid, elaidic acid, aracliic acid, behenic acid,
elucic acid, lignoceric acid, lanoceric acid, sulfonic acid, salicylic acid, and carboxylic
acid. As a type of the metal salt, a calcium salt is preferable, but other alkali earth
metal salts or zinc salts may be used. The salt may be either a neutral salt or a basic
salt.
[0062]
The lubricating powder ilnproves the strength of the lubricating coating or
suppresses flowability thereof at a high temperature while maintaining Ts of the
lubricating coating to be low, and thus the lubricating powder may improve the seizure
resistance. As the lubricating powder, a nontoxic and harmless powder which is used
as a solid lubricant is preferably used. Exatnples of a preferable lubricating powder
include graphite, tungsten disulfide (WSz), tnolybdenuln disulfide (MoS~)t,i n disulfide,
graphite fluoride, boron nitride (BN), cryolite, and PTFE (polytetrafluoroethylene).
One or more kinds thereof may be used in combination. Graphite is preferable in
view of stability in a corrosive environment, an environment aspect, and the like.
[0063]
Graphite is largely classified into natural graphite and artificial graphite.
Natural graphite is less expet~sive. Natural graphite is classified into flake graphite,
vein graphite, and amorphous graphite according to the shape thereof. Among these,
amorphous graphite having the lowest crystallinity is preferable in terins of making an
increase in AT and improvelnellt in seizure resistance compatible with each otlieet
Furthermore, when taking electrical properties or thermal propel-ties into account,
amorphous graphite in which an ash amount is 0.2% by Inass to 5.5 % by mass, and
crystallinity is 98% or less is more preferable. Particularly, atnorphous graphite in
which crystallinity is 90% to 98% is preferable. The average particle size of graphite
is preferably 1 pm to 20 pm, and Inore preferably 1 pm to 15 pm.
[0064]
In a case where the lubricating coating contains the lubricating powder, the
aniount thereof is preferably 0.5% by Inass to 20% by tnass. When the amount is less
than 0.5% by mass, the effect is not sufficient. When the amount exceeds 20% by
mass, there is a concern that the operation of other components may be deteriorated.
111 addition, uniform dispersibility of the lubricating powder or flowability of the
lubricating coating during friction may decrease. The amount of the lubricating
powder is more preferably 0.5% by ri~assio 10% by rirass. In addition, an average
particle size of the lubricating powder which improves seizure resistance is preferably
0.1 pm to 10 pm, and more preferably 1 pm to 5 pm.
[0065]
Components other than the above-described comnponents, for example, one or
more kinds of components selected from organic resins, and various kinds of oils and
additives (for example, an extreme pressure agent) that are commonly used in
lubricating oil may be mixed in the lubricating coating to increase uniform
dispersibility of the lubricating powder in tlie lubricating coating, or to improve
characteristics or properties of tlie lubricating coating. The oils represent lubricating
components (viscous liquid material (including greasy material)) which may be used in
tlie lubricating oil and which are in a liquid form at room temperature, and the oils
themselves have lubricating properties. Examples of tlie oils that may be used
include synthetic ester, natural fats and oils, mineral oil, and the like.
[0066]
An organic resin, palticularl~~a ,t hermoplastic resin fiinctions to suppress
surface tackiness of the lubricating coating, and to increase a film thickness. In
addition, wlien being introduced to a frictional interface, the organic resin functions to
increase seizure resistance, or to reduce friction even when receiving high fastening
torque (high surface pressure) when nletal portions come into contact with each other.
Accordingly, the organic resin may be contained in the lubricating coating.
[0067]
Examples of the thermoplastic resin include polyethylene resins,
polypropylene resins, polystyrene resins, poly~netliyla crylate resins, styrenelacrylic
acid ester copolyn~ere sins, polyamide resin, polybutene (polybutylene) resins, and the
like. Copolymers or blends orihese may be used, or copolymers or blends ol' these
with other thermoplastic resins may also be used. The thernloplastic resin preferably
has a density (JIS K 71 12) in a range of 0.9 to 1.2, and ther~nald eformation
temperature (JIS K 7206) is preferably in a range of 50°C to 150°C to easily deform at
a frictional surface so as to allow the lubricating properties to be exhibited. The
polybutene resins having high viscosity at a high surface pressure are preferable.
[0068]
The ther~iloplasticr esin is preferably in the fomi of powders of 0.05 pm to 30
pm, and the amount of the ther~noplasticr esin in the coating is preferably set to 10%
by mass or less.
[0069]
Examples of the natural fats and oils that may be used as oil include beef
tallow, lard, wool fat, palm oil, rapeseed oil, coconut oil, and the like. In addition,
mineral oil (including synthetic mineral oil) having viscosity of 10 cSt to 300 cSt at
40°C may also be used as oil. Examples of synthetic ester that may be used as oil
include fatty acid monoester, dibasic acid diester, and fatty acid ester of trimetliylol
propane or pentaerythritol, and the like. In a case where the oil is contained in the
lubricating coating, the amount of the oil in the lubricating coating is preferably set to
5% by mass or less.
[0070]
Exa~npleso f the extreme pressure agent include, but are not limited to,
sulfurized fats and oils, polysulfide, phosphate, phosphite, thiophospliate, and
dithiophosphoric acid metal salt, and the like. I11 a case where the extreme pressure
agent is contained, the amount thereof in the lubricating coating is preferably set within
a range of 0.05% by Inass to 5% by mass.
[0071]
It is preferable that the lubricating coating substantially do not contain a
harntful heavy metal. The conlpound grease contains a large amount of powders of a
soft heavy metal such as lead and zinc is to prevent seizure (galliug) by suppressing
contact between metals. In the invention, this function is provided in combination of
the MCA and the basic metal salt of an aronlatic organic acid which are contained in
the lubricating coating, and thus even when the heavy metal powder is not contained at
all, the coating may exhibit a sufficient lubricating performance.
100721
The iubricatiug coating is fonned as follows. A mixture of the constituen~t
components is made into liquid by solvent addition and/or heating, and the liquid
mixture is applied to the contact surface of at least one member of the pin and the box
of the threaded joint, and the coated film is dried as necessary.
100731
The application by heating may be realized by a so-called hot melt application
method. The mixture of the constituent components of the lubricating coating is
heated to a temperature at which applicable viscosity is obtained, and the mixhtre is
sprayed onto an application surface from a sprayer provided with a heat retention
function. The application surface may be preheated, for example, to approximately
the same tenlperatnre as that of a material to be applied.
100741
In a case of performing the application at an ambient temperature, the
lubricating coating forming colnposition is prepared by adding a volatile organic
solvent to the mixture of the constituent components of the lubricating coating. The
volatile orgauic solvent is different from base oil of the lubricatingoil, arld evaporates
during a coating forming process, and thus the volatile organic solveni substaniialiy
does not remain inthe lubricating coating. "Volatile" represents that there is a
tendency for the organic solvent to evaporate at a coating state at a temperature of
room temperature to 150°C. However, the lubricating coating of the invention may
be a viscous liquid or semisolid, and t h ~a~ lsitt le amount solvent is permitted to remain.
[0075]
Examples of the solvent is not pa~ticnlarlyl imited, but examples of a volatile
organic solvent which is suitable for use in the invention include petroleum solvents
such as a solvent corresponding to industrial gasoline defined by JIS K 2201, mineral
sprit, aromatic petroleum naphtha, xylene, and Cellosolve. A mixture of two or more
kinds of these may be used. A solvent having the flash point of 30°C or higher, an
initial boiling point of 150°C or higher, and a final boiling point of 210°C or higher is
preferable from the viewpoints that it is relatively easy to handle, and evaporates
rapidly, and thus the drying time may be short.
[0076]
The lubricating coating forming composition may contain an antioxidant, a
preservative, and a colorant, in addition to the above-described components.
[0077]
Viscosity (dynamic viscosity: unit is cSt, B-type viscosity fornl) of the
lubricating coating forming conlposition may be appropriately selected by adding an .
organic solvent or the like in accordance with an application method. In a case of
spray application or immersion at an ambient temperature, viscosity at 40°C is
preferably 4,000 cSt or less, and in a case of brushing, viscosity at 60°C is preferably
1,000 cSt or less.
[0078]
The film thickness of the lubricating coating is preferably set within a range
of 10 p111 to 500 pm as described later. It is preferable that the lubricating coating
have a thickness sufficiellt to buty minute gaps such as a gap between tl~eadri dges in
the contact surface. When tlie film thickness is too small, an effect provided to the
frictional surface may not be expected. From the reason, the filtn thickness of the
l~~bricatiacoga ting is preferably set to 10 pm or more.
LO0791
Contact surfaces of the box and the pin come into contact with each other
during fastening at which lubrication is necessary. Accordingly, it is sufficient that
only any one of the pin and the box is treated for lubrication. However, from tlie
viewpoint of anticorrosion of the pin or the box which is exposed to the air, particularly,
during storage, it is preferable to form the lubricating coating on both of the pin and
the box. The minimum fill11 thickt~ense~c essary for the atiticorrosion is 10 pm.
Accordingly, in a case where separate protective means for anticorrosion (for example,
previous fastening of tlie pin and the box, or mour~tingo f a protector) is not provided,
it is preferable that the coating of 10 Fun or more be formed on both of tlie pin and tlie
box.
[0080]
On the other hand, when the lubricating coating is too tluck, the lubricant
bcconles useless, and this is retrogressive against prevention of ellvironmental
pollutioll that is one object of the invention. In light of this, it is preferable that the
upper limit of the film thickness of the lubricating coating be set to approximately 500
pm. The fihn tliichless of the llubricati~igc oating is Inore preferably 15 pm to 200
pm. However, as described later, when surface roughness of an underlayer of the
contact surface is made to be large, it is preferable that the film thickness of the
lubricating coating be made io be larger ihan Rmax of ihe uncierlayel: The film
thickness in a case where the underlayer is rough is an average value of the film
thickness of the entirety of the coating which may be calculated fiom the area, mass,
and density of the coating.
[0081]
In a general tendency with regard to properties of the lubricating coating,
when oil is contained to a certain degree, the lubricating coating becomes a viscous
liquid. It1 a case where an amount of oil is small, or oil is not contained, the
lubricating coating becomes a semisolid.
[0082]
[Surface Treatment]
With regard to the tubular threaded joint in which the lubricating coating is
formed on the contact surface of the pin and/or the box according to the invention,
when the contact surface covered with the coating is subjected to a surface treatment
for roughening, and thus surface roughness is made to be larger than 3 pm to 5 pm that
is surface roughness after grinding, the seizure resistance is improved in many cases.
Accordingly, it is preferable that the contact surface be subjected to the surface
treatment for roughening before forming the lubricating coating.
LO0831
Examples of the surface treatment include blasting by sl~ootinga Lblasting
material such as spherical shot and angular grit, and pickling by immersion in a strong
acid solution such as sulfuric acid, hydrochloric acid, nitric acid, and hydrofluoric acid
for roughening the surface. In addition, the examples include a chemical conversion
treatment such as a phosphate treatment, an oxalate treatment, and a borate treatment
(roughness on a crystal surface increases along with growth of crystals that are
geiicrated), electi-oplatiiig with iiietals such as Cu, Fe, Sii, aiid Zn, or alloys thereof
(convex portions are preferentially plated, and thus the surface is slightly roughened),
impact plating capable of forming a porous plated coating. In addition, as one kind of
electroplating, coniposite plating to fonn a plated coating in which solid fine particles
are dispersed in metal is possible as a metliod of for~ilinga roughened surface in order
for the solid fine particles to project from plated coatiug.
[0084]
Ally surface treatment method of the contact surface is preferably performed
in such a manner that the surface roughness knax obtained by the roughening of the
surface treattnetlt becoiiies 5 pnl to 40 pm. When Rnlax is less than 5 pm,
adliesiveness with the lubricating coating or coating retention properties may not be
sufficieut. On the other hand, when Rmax exceeds 40 pm, friction increases, and thus
when undergoitlg a high surface pressure, the coating may not withstand a shearing
force and a conlpressive force. Therefore, the coating may be fractured or be peeled
off. The surface treatment for the roughening may be performed in combillation of
two or more kinds of the treatments, and as a treatnient method thereof, a method
known in the related art may be used.
[0085]
In view of adhesiveness of the lubricating coating, a surface treatment capable
of forming aporous coating, that is, the chemical treatment and the impact plating are
preferable. In this case, the film thickness of the porous coating is preferably set to 5
pm or more so as to allow Rniax of the porous coating to be 5 pm or more. The
upper limit of the fill11 thickness is not particularly specified, but the upper li~niits
co~mnonly5 0 pm or less, and preferably 40 pm or less. When tlie lnbricati~~cgo ating
is formed on the porous coating fornied by tlie surface treatment, adhesiveness with the
lubricating coaiing increases due io an "anchor effeci". As a resuli, even when
fastening and loosening are repeated, the solid lubricating coating is not likely to be
peeled off, and thus contact between metals is effectively prevented. As a result,
seizure resistauce, gastightness, and corrosion resistance are further inlproved.
[0086]
Examples of particularly preferable surface treatment for for~llingth e porous
coating include formation of a coating of zinc or a zinc-iron alloy (porous metal
coating) by a phosphate chemical conversion treatment (treatment using manganese
phosphate, zinc phosphate, iron niat~ganesep hosphate, or zinc calcium phosphate), and
impact plating. From the vieivpoint of adhesiveness, the manganese phosphate
coating is preferable, and from the viewpoint of corrosion resistance, the coating of
zinc or a zinc-iron alloy on which sacrificial protection due to zinc may be expected is
more preferable.
[0087]
The phosphate chemical conversion treatment may be perfor~nedb y
in~mersiono r spraying according to a common method. As a chemical treatment
solution, an acidic phosphate treatment solutiotl for use in general galvanizing material
may be used. For exatnple, a chemical conversion treatment of a zinc phosphatebased
solution containing 1 g/L to 150 g/L of phosphate ions, 3 g/L to 70 g/L of zinc
ions, 1. g/L to 100 g/L of nitrate ions, and 0 g/L to 30 g/L of nickel ions may be
exemplified. In addition, a manganese phosphate-based chemical conversion
treatment solution that is commonly used it1 the threaded joint may be used. The
tenlperature of the solution tnay be from an ambient temperature to 100°C, and a
treatment time may be up to 15 minutes depending on a desired film thickness. In
order to accelerate the formation of the coating, prior to the pl~osphatetr eatment, an
aqueous surface conditioning soluiion containing colloidal iiianiutn may be supplied to
the surface to be treated. After the phospliate treatment, the treated surface is
preferably washed with cold or warm water prior to drying.
[0088]
The impact plating may be performed by mechanical plating in wliich
particles are allowed to collide with a material to be plated inside a rotating barrel, or
by shooting plating in which particles are allowed to collide with a material to be
plated using a blasting apparatus. In the present invention, it is sufficient to perform
the plating only on the contact surface, and thus it is preferable to employ the shooting
plating capable of performing localized plating.
[0089]
For example, a material to be shot, which is constituted by a powder in which
an iron-based core is coated with zinc or a zinc alloy, is shot against a contact surface
to be coated. The amount of zinc or a zinc alloy in the pai-ticles is preferably within a
range of 20% by mass to 60% by mass, and a particle size of the particles is preferably
within a range of 0.2 inm to 1.5 mm. Only the zinc or zinc alloy that is a covering
layer of the particles adheres to the contact surface of a base body by the shooting, and
a porous coating of zinc or a zinc alloy is formed on the~contacts urface. The shooting
plating may form a porous plated metal coating with good adl~esivenesso n a steel
surface regardless of a material quality of the steel. .
[0090]
The thickness of the zinc or zinc alloy layer formed by the impact plating is
preferably 5 p111 to 40 pm from the viewpoints of both of the coi~osionre sistance and
the adhesiveness. When the thickness is less than 5 p , sufficient corrosion
resistance is not secured, and when the thickness exceeds 40 p~nt,h e adhesiveness with
the lubricatiilg coating iilay deteriorate.
[0091]
The above-described surface treatlnent may be performed in combination of
two or Illore kinds thereof.
Atthough a roughening effect is very little, when a specific single layer or
multi-layer electroplating is perfonned as anotlier surface treatment, adhesiveness
between the lubricating coating and an underlayer increases, and thus the seizure
resistance of the tubular threaded joint may be improved.
LO0921
As such a surface treatment of the lubricating coating, electroplating ormetals
such as Cu, S11, and Ni, or alloys thereof may be exertlplified. Plating may be single-'
layer plating, or multi-layer plating of two or more layers. Specific examples of this
kind of electroplating include Cu plating, Sn plating, and Ni plating, as well as Cu-Sn
alloy plating, Cu-Sn-Zn alloy plating, two-layer plating by Cu plating-Sn plating, and
three-layer plating by Ni plating-Cu plating-Sn plating which are disclosed in Japanese
Unexalnined Patent Application, First Publication No. 2003-74763. In a tubular
threaded joint formed from a steel having a Cr content more than 5%, seizure may
significantly occ~u; and thus it is preferable to perform single-layer plating of a Cu-Sn
alloy or a Cu-Sn-Zn alloy, or multi-layer metal plating in conibination of two or Inore
layer plating selected from the alloy plating, Cu plating, Sn plating, and Ni plating, for
examnple, two-layer plating of Cu plating-Sn plating, two-layer plating of Ni plating-Sn
plating, or two-layer plating of Ni plating-Cu/Sn/Za alloy plating, and three-layer
plating ofNi plating-Cu plating-Sn plating as the surface treatment.
[0093]
Such plating may be formed according to a method disclosed in Japatiese
Unexalnined Patetit Application, First Publication No. 2003-74763. in the case of tlie
multi-layer plating, a coated film (co~ilmonlj; Ni plating) of the lowest layer is
preferably formed as a very thin coated layer having a film thickness less than 1 pm
which is called strike plating. The film thickness (in a case of multi-layer plating, the
total film thickness) of the plating is preferably set within a range of 5 pm to 15 pm.
[0094]
[Surface Treatment of Coul~terpatMt ember]
When a solid coating is fornied on the contact surface of one member of the
pin and the box (for example, tlie box) of the tubular threaded joint according to the
present invention, the contact surface of the other member (for example, the pin) which
is not coated with tlie solid coating may be left in an nutreated state, but preferably, the
other member is subjected to the above-described surface treatment to roughen the
contact surface. That is, the surface roughening may be performed by employitig a
method selected from blasting, pickling, a phosphate cheli~icacl onversion treatment,
an oxalate chemical conversion treatment, a borate chemical coliversion treatment,
electroplating, impact plating, and a conibi~iationo f two or more of these methods.
As a result, when tlie one meniber is fastened to the other member covered with the
solid coating according to the invention, the~contacst urface of the other me~iibenr ot
having a solid coating exhibits a satisfactory solid coating retetition properties due to
the anchor effect produced by the surface rougliening, thereby increasing the seizure
resistance of the tubular threaded joint.
[0095]
In order to impart anticorrosive properties, a known atiticorrosive coating
such as a coating of a UV-curable resin or a thermosetting resin may be formed after
the surface treatment as required. By preventing the contact surface from being
exposed to tile air by this aniicorrosive coating, even when the contact surface is
brought into contact with water in relation to a dew point during storage, the
occurrence of rust on the contact surface is prevented.
[0096]
Since there is no particular restriction to the surface treatment of the contact
surface of the other member, the contact surface may be subjected to another surface
treatment. For example, various kinds of solid coatings (for example, solid
lubricating coating) different from that of the invention may be formed.
EXAMPLES
[0097]
The effects of the invention will be illustrated by the following Examples and
Comparative Examples. In the following description, a contact surface including a
threaded portion and an unthreaded tnetal contact portion of the pin is referred to as
"pin surface", and a contact surface including a threaded portion and an unthreaded
metal contact portion of the box is referred to as "box surface". Surface roughness is
Rmax. In addition, % represents % by mass unless othe~wises tated.
[0098]
A surface treatment shown in Table 2 was performed with respect to a pin
surface and a box surface of a premium threaded joint VAM TOP (registered
trademark) (outer diameter: 17.78 cm (7 inches), thickness: 1.036 cm (0.408 inches)
formed from Cr-Mo steel A or 13%Cr steel B shown in Table 1. Then, a lubricating
coating was formed on the pin surface and the box surface, which was subjected to the
surface treatment, by an illustrated application method using a composition shown in
Table 3 (MCA and a basic metal salt of an aromatic organic acid are illustrated as an
essential componelit, and a pine resin-based material, a wax, a metal soap, and a
lubricating powder are illustrated as a selective component). Accordingly, the
lubricating coating formed on the pin surface and the box surface had the same
composition.
[0099]
The lubricating coating were formed by the followi~~segv eral application
methods except for Conlparative Example 1 using compound grease, all of the
lubricating coatings has the same thickness of 50 pm.
[O loo]
(1) Anlbient-temperature spray method: a lubricating coating forming
composition prepared by adding 30 parts by mass of a volatile organic solvent (mineral
split: ExxsolTM D40 manufactured by ExxonMobil Chemical) to total of 100 parts by
mass of lubricating coating components having a predetermined composition to
decrease viscosity was spray-applied at an ambient temperature, and the organic
solvent was allowed to vaporize by natural drying to form a lubricating coating;
(2) Heating spray method: a lubricating coating forming composition, which
contained lubricating coatitig comporlerits having a predetermined conlposition and did
not contain a solvent, was heated to 130°C to obtain a low viscosity liquid, and was
spray-applied fi.0111 a sprayer provided with a lieat retention function onto the pin
surface or the box surface which was preheated to 130°C by inductio~lheating. Then, I
the resultant applied con~positionw as cooled to form a lubricating coating. This is a
hot melt method.
[OlOl]
Materials used for preparation of the lubricating coating fornling comnposition
are as follows.
MCA: MC-4000 manuPaciured by NISSAN CHEMICAL INDUSTRIES, LTD.
(average particle size: 14 kiln);
Pine resin-based material: rosin ester (ester gum H) manufactured by Arakawa
Chemical Industries, Ltd.;
Basic metal salt of an aronlatic organic acid: basic Ca sulfonate (Calcinate
C400CLR) (base value: 400 mgKOWg) nlanufactured by CHEMTURA Corporation.
Metal soap: Ca stearate (manufactured by DIC Corporation);
wax: parafin wax manufactured by NIPPON SEIRO CO., LTD;
Graphite: atnorphous graphite, a graphite powder tnamfactured by Nippon
Graphite Industries, Itd., blue P (an ash content: 3.79% by mass, crystallinity: 96.9%,
average particle size: 7 pnl);
Graphite fluoride: CEFBON manufactured by Central Glass Co., Ltd
[O 1021
Anlong surface treatment coatings employed in the examples, a manganese
phosphate coating is executed by itmnersion in a manganese phosphate chemical
conversion treatment solution (PALPHOS MIA nlauufactured by Nihon Parkerizing
Co., Ltd., the same shall apply hereinafter) at 80°C to 95'C for 10 minutes, and zinc
phosphate coating is executed by immersion in a chemical conversion treatment
solution for zinc phosphate (PALBOND 181X manufactured by Nihon Parkerzing Co.,
Ltd, the same shall apply hereinafter) at 75OC to 85'C for 10 minutes.
[0103]
The alloy plating used in the surface treatment was a Cu-Sn-Zn alloy plating
having a conlposition (mass ratio) of Cu:Sn:Zn = 60:35:5.
Surface ro~~gluieRss s hown in Table 2 is exactly Rz, and was measured by
Surtronic 10 manufactured by Taylor Hobson Ltd. Rz after grinding finish was 3 pm
in each case.
[Table I]
Steel composition of threaded joint (% by tnass: tlie remainder includes Fe and
unavoidable impurities)
Symbol I C I si I Mn I P I s ] Cu I Ni I Cr I Mo
A 1 0.25 1 0.25 1 0.8 1 0.02 1 0.01 1 0.04 1 0.05 1 0.95 I 0.18
B 10.19 1 0.25 1 0.8 1 0.02 1 0.01 1 0.04 I 0.1 1 13 1 0.04
[Table 21
No.
Example 1
Steel
symbol
A
Pin
1. Grinding finish (R=3)
Surface treatment
Box
1. Grinding finish (R=3)
Example 2
Example 3
Example 4
Example 5
Example 6
Comparative Example 1
Comparative Example 2
Comparative Example 3
R: Surface Roughness (pm) t: Thickness (pm)
1. Grinding finish (R=2)
1. Grinding finish (R=2)
1. Grinding finish (R=3)
2. Zn phosphate (R=8) (t-12)
1. Grinding finish (R=3)
2. Zn phosphate (R=8) (t-12)
1. Grinding finish (R=3)
2. Zn phosphate (R=8) (t-12)
1. Grinding finish (R=3)
2. Zn phosphate (R=8) (t-12)
1. Grinding finish (R=3)
2. Zn phosphate (R=8) (t=12)
1. Grinding finish (R=3)
2. Zn phosphate (R=8) (t-12)
1. Grinding finish (R=3)
2. Ni strike plating + Cu plating (t-8) (R=3)
1. Grinding finish (R=3)
2. Ni strike plating + Cu-Sn-Zn alloy plating
(t-8) (R=2)
1. Grinding finish (R=3)
2. Mn phosphate (R=12) (t-15)
1. Grinding finish (R=3)
2. Mn phosphate (R=12) (t-15)
1. Grinding finish (R=3)
2. Mn phosphate (R=12) (t=15)
1. Grinding finish (R=3)
2. Mn phosphate (R=12) (t-15)
1. Grinding finish (R=3)
2. Mn phosphate (R=10) (t-12)
1. Grinding finish (R=3)
2. Mn phosphate (R=12) (t-15)
B
B
A
A
A
A
A
A
[Table 31
No. Organic solvent
(per 100 parts o
f total amount o
f non-volatile co
mponents)
Application me
thod
Composition of non-volatile components of lubricating coating forming composition (n
umerical value in parentheses represents amount in % by mass)
Essential component Selective component
MCA Pine resinbased
mate
Basic metal salt of
aromatic organic
W&Y Metal soap Lubricating po
wder
[0108]
As can be seen from Table 2 and Table 3, the surface treatnlent and the
lubricaiing coating I'urn~ingir eaimeni in each of ihe examples and co~llparaiive
examples were as follows.
[0 1091
(Exan~ples1 ,4, and 6, and Comparative Examples 2 and 3)
With respect to tubular threaded joint for~nedfr o~nC r-Mo steel having a
composition A shown in Table 1, a manganese phosphate coating (Rz: 12 pm) having a
thickness of 15 pm was formed on a box surface after grinding finish, and then a
lubricating coating having a film thickness of 50 pm and a composition indicated in
each of Examples and Comparative Examples of Table 3 was formed thereon by
ambient temperature spray application. A zinc phosphate coating (Rz: 8 pm) having
a thickness of 12 p n w~a s fornled on a pin surface after grinding finish, and then a
lubricating coating was formed thereon in the same manner as the box surface.
[OllO]
(Example 2)
With respect to a threaded joint formed from 13%Cr steel having a
compositiotl B shown in Table 1, first, Ni strike plating was formed on the box surface
by electroplating after grinding finish, and then Cu plating having a thickness of 7 p ~ n
was formed thereon (total plating thickness: 8 pm). Rz of the plated surface was 2
m A lubricating coating having a fill11 thickness of 50 pnl and a cotnposition
indicated in Example 2 of Table 3 was formed on the plated coating by ambient
temnperatare spray application. A lubricating coating having a thickness of 50 p111 was
formed on the pin surface (Rz = 2 pmn) in the same manner as the box surface.
[Olll]
(Exan~ple3 )
With respect to a tlueaded joint formed fiom 13%Cr steel having the
cornpositio~B~ s i~owriir i Table 1, first, Ni strike plating \vas famed on ilie box surface
by electroplating after grinding finish, and then Copper-Tin-Zinc alloy plating coating
(Rz: 2 pm) was formed thereon (total plating thickness: 8 pm). Alubricating coating
having a film thickness of 50 pm and a conlposition indicated in Example 3 of Table 3
was formed on the plated coating. A lubricating coating was formed on the pin
surface (Rz = 2 pm) in the same manner as the box surface.
[0112]
(Example 5)
With respect to tubular threaded joint formed fiom Cr-Mo steel having a
composition A shown i11 Table 1, a manganese phosphate coating (RL: 12 pm) having a
thickness of 15 pm was fornled on a box surface after grinding finish, and then a
lubricating coating having a film thickness of 50 pm and a composition indicated in
Example 5 of Table 3 was formed thereon by heating spray application. A zinc
phosphate coating (Rz: 8 pm) having a thickness of 12 pm was formed on a pin
surface after grinding finish, and then a lubricating coating was formed thereon in the
same maluler as the box surface.
[OI 131
(Comparative Example 1)
With respect to a tlueaded joint formed from Cr-Mo steel having a
composition A show~iln Table 1, a manganese phosphate coating (Rz: 12 pm) having a
thickness of 15 bun was formed 011 a box surface after grinding finish. Viscous liquid
type compound grease according to API standard was applied onto the manganese
phosphate coating (a total application amount in the pin and the box was 50 g, and a
total application area was approximately 1,400 cm2). Tlle pin surface was left as it
\$as after the grinding finish, and then the above-described conlpound grease was
applied onto il~epi n surPdce.
[0114]
With respect to the tubular threaded joint in which the surface treatment was
performed with respect to the pin surface and the box surface and the lubricating
coating was formed thereon, a fastening and loosening test was repetitively perfornled
to evaluate seizure resistance. In the repetitive fastening and loosening test, the
fastening of the threaded joint was perfornled at a fastening speed of 10 rpm and
fastening torque of2 0 kN.n~a,n d a seizure situation oft he pin surface and the box
surface after being loosened was examined. In a case where a seizure scratch
generated by ilie fastening was not significant, and re-fastening was possible aftel
trimming, fastening and loosening continued after trimming. The number of times of
fastening was set to maximum 10 times. Test results (the number of times of
repetitive fastening in which fastening was possible without causing occunence of
seizure) are shown in Table 4.
[0115]
In addition, wit11 respect to another sample of respective tubular tl~eaded
joints, a torque chart was prepared as s11o\vn in FIG. 2 by an over-torque test in which
fastening was performed by applying fastening torque of 68 kNm at a fastening speed
of 2 rpm, and Ts (shouldering torque), Ty (yield torque), and AT (= Ty-Ts, torque on
shoulder resistance) were measured on the torque chart.
[0116]
Ts was torque when a shoulder portion began to interfere, specifically, torque
when a torque variation, which was exhibited after the shoulder portion interfered,
began to enter a linear region (elastic deformation region) was set as Ts. On the other
hand, Ty was torque \vhen plastic deformation began to start, specifically, torque when
lii~eai-itiyi i a torque valiatior disappeared iogeiher with roiaiion after reaching Ts, and
it began to be away from the linear region was set as Ty. With regard to AT (= Ty-Ts),
results, which were obtained by relatively evaluating values of AT in other examples
after setting AT obtained in the compound grease in the related art shown in
Comparative Example 1 of Table 3 to 100, are shown in Table 4.
[Table 41
[0118]
As shown in Table 4, in Examples 1 to 6, in the fastening and loosening test,
occurrence of seizure was not found in 10 times of fastening and loosening except
Example 2 in which the amount of MCA was as high as 30%, and very satisfactory
results were obtained. In Example 2, in the fastening loosening test, seizure occurred
during the ninth fastening, and thus the test was stopped. Howevel; generally, w11en
the number of times of fastening and looseni~lgis five or more, there is no problem in a
practical use, and thus the tubular threaded joint of Exanlple 2 is also sufficiently
useful.
[0119]
From cotnparisoil of results of Examples 1 and 2, it was confirmed that when
MCA is contained it] an atnouni more than 30% by rnass, there is a possi'oiliCy of
decreasing the seizure resistance.
[0120]
With regard to tlie value of AT in tlie over-torque test, a relative value of AT
when AT of Comparative Example 1 using the conlpound grease was set to 100
(hereinafter, referred to simply as AT relative value) was higher than 100% in each
case, and it could be understood that it1 the tubular threaded joints of examples,
fastening with high torque was possible without causing yielding of the shoulder
portion.
[0121]
The AT relative value was as very high as 124% or more except for Example
6. The small amount 0.8% of MCA may be the reason why the AT relative value in
Example 6 was 108% lower than that of other examnples. Accordingly, to improve high
torque fastening properties, it is preferable for the amount of MCA to be 1% or more,
and Inore preferably 2% or more. As can be understood fiom results of the examples,
as the amount of MCA increases, the AT relative value may increase.
[O 1221
From Example 5, it was confirtned that even wlieti the application method
during fornlation of tlie lubricating coating is either the ambient tenlperature spray
method or heating spray metl~odt,h e effect of the invention may be obtained.
[0123]
On tlie other hand, as shown in Comparative Examples 2 to 3, it could be
understood that when the lubricating coating does not contain any one of the MCA and
the basic metal salt of an aromatic organic acid, the seizure resistance significantly
deteriorates, and the AT relative value is n1t1c11 less than 100, and tlmus not only the
seizure resistance but also the high torque fastening properiies significanily deieriorate
when compared to the compound grease.
[0 1241
To investigate anticol~osivep roperties of the tubular threaded joint
manufactured in Exanlples 1 to 6, the surface treatment and formation of a lubricating
coating as shown in a box of Table 2 were performed with respect to a coupon test
specinmen (70 nnn x 150 mtn x 1.0 nlnm (thickness)) that was separately prepared.
This test specimen was provided to a salt spray test (according to JIS 22371
(corresponding to IS0 9227), temperature: 35OC, 1,000 hours), and a humidity test
(according to JIS K5 600-7-2 (corresponding to IS0 6270), temperature: 50°C,
humidity: 98%, 200 hours), and whether or not rust occurred was examined. As a
result, in the tubular threaded joints of Examples 1 to 6, it was confinned that rust did
not occur in any test.
[0 1251
In addition, the tubular threaded joints of the respective examples were
verified by an gastigl~tnesste st or an operational suitability test in an actual drilling
apparatus, all of the joints exhibited a satisfactory result. Since AT is larger than that
of the conmpound grease used in the related art, it is verified that even when the
fastening torque increases, fastening may be stably performed.
[0 1261
Hereinbefore, an embodiment considered as the most preferable enmbodi~nent
at this time has been described, but tlle invention is not limited to the disclosed
embodiment as mentioned above. Modifications nmay be made within a range not
departing fiom a technical idea that can be read out fioln the entirety of claims and
specification, and it should be understood that a threaded joint accoinpanied with the
n~odificationb e contained in thc teclx~icals cope orilie invention.
[Description of Reference Numerals and Signs]
[0127]
A: Steel pipe
B: Coupling
I: Pin
2: Box
3a: Male threaded portion
3b: Female threaded portion
4a: Pin side seal portion
4b: Box side seal portion
5a: Pin side shoulder portion
5b: Box side shoulder portion

CLAIMS
1. A conpositionfo r forming a lubricating coating to a tubular threaded joint, the
cornposition comprising:
a lnelamirie cyanurate;
a basic metal salt of an aromatic organic acid; and
one or tnore kinds selected from the group consisting of a pine resin-based
material, a wax, a metal soap, and a lubricating powder.
2. The conlposition according to claitn 1,
wherein an atnount of the melamine cyanurate is 0.5 to 30% by mass on a
basis of a total amount of non-volatile cotnponents of the conlposition.
3. The con~positiona ccording to claim 1 or 2, further comprising:
a volatile organic solvent.
4. A tubular threaded joint comprising:
a pin and a box, each of which includes a contact surface having a threaded
poltion and an unthreaded metal contact portion,
wherein the lubricating coating fornled using the composition according to
any one of claims 1 to 3 is provided on the contact surface of at least one of the pin and
the box.
5. The tubular threaded joint according to claim 4,
wherein a film thickness of the lubricating coating is 10 pm to 500 pn~.
6. The tubular ttueaded joint according to claim 4 or 5, I
wherein the contact surface of at least one of the pin and the box having the
lubricating coating is subjected to a surface treatment by a blasting, a pickling, a
phosphate cl~emicacl onversion treatment, an oxalate chemical con~lersiontr eatment, a
borate chemical conversion treatment, an electroplating, an impact plating, or a method
selected from two or more kinds thereof before forming the lubricating coating.
7. The tubular thxeaded joint according to any one of claims 4 to 6,
wherein the lubricating coating is provided on the contact surface of one of
the pin and the box, and
the contact surface of the other of the pin and the box is subjected to a surface
treatment by a blasting, a pickling, a pl~osphatec hemical conversion treatment, an
oxalate che~nicacl onversion treatment, a borate chemical conversion treatment, an
electroplating, an impact plating, or a method'perfolmed in combination of two or
more kinds thereof.
8. The tubular threaded joint according to any one of claims 4 to 7,
wherein the tubular tlxeaded joint is used to connect a plurality of oil country
tubular goods.
9. A neth hod of connecting a plurality of oil country tubular goods, the method
comprising a step of
connecting the plurality of the oil country tubular goods using the tubular
tlxeaded joint according to any one of claitns 4 to 8 without using grease lubricating
oil.