Patent Application
20120034376
This invention relates to an apparatus and method for applying a lubricant to a threaded portion of a steel pipe. More specifically, it relates to a lubricant applying apparatus and method suitable for application of a highly viscous (semidry type) lubricant to the surface of a threaded portion of a threaded joint for pipes formed on an end portion of a steel pipe, namely, to the surface of male (external) threads formed on the outer surface of the end of a pipe or to the surface of female (internal) threads formed on the inner surface of the end of a pipe.
Oil country tubular goods such as tubing and casing used for the excavation of oil wells are assembled to a necessary length in the field by successively connecting steel pipes each having a length of ten some meters by threaded joints. A threaded joint for pipes typically has a pin-box structure using a pin, which is a joint component having male threads, and a box, which is the other mating joint component having female threads. A coupling-type threaded joint which is typically used for connecting oil country tubular goods has a pin formed on the outer surface of both ends of a steel pipe constituting an oil country tubular good and a box formed on the inner surface on both sides of a separate short joint member referred to as a coupling. In some cases, an integral-type threaded joint for pipes in which a pin is formed on the outer surface of one end of a steel pipe and a box is formed on the inner surface of the other end of the pipe is used instead of a coupling-type threaded joint for pipes.
The depth of a usual oil well is 2,000-3,000 meters, but in recent years, the depth has reached 8,000-10,000 meters or more in deep wells such as marine oil wells. As a result, in the environment of use, a threaded joint used for connecting oil country tubular goods undergoes the stresses caused by an axial tensile force due to the weight of oil country tubular goods and the joint itself as well as combined internal and external pressures and heat. Therefore, it must be able to maintain gastightness without being damaged under such severe conditions of use. During the process of lowering tubing or casing into a well, a threaded joint which has once been tightened is sometimes loosened and retightened. According to API (American Petroleum Institute) standards, it is necessary for a joint to maintain gastightness without undergoing unrecoverable seizing referred to as galling even if tightening (makeup) and loosening (breakout) are carried out ten times for a threaded joint for tubing and three times for a threaded joint for casing.
There is a type of threaded joint for pipes having excellent gastightness under high stresses which is referred to as a premium joint and which can form a metal-to-metal seal. A premium joint has a threaded portion and an unthreaded metal contact portion on both a pin and a box. The unthreaded metal contact portions of the pin and the box directly contact each other and form a metal-to-metal seal having excellent gastightness. The unthreaded metal contact portion of the pin is constituted by a metal sealing surface positioned on the outer peripheral surface of the pin closer to the end than the threaded portion and a torque shoulder on the end face of the pin. Correspondingly, a metal sealing surface and a torque shoulder are also provided on the inner peripheral surface of the box. When the pin is inserted into the box and the threads are tightened until the torque shoulders of the pin and the box contact each other, the metal sealing surfaces of the pin and the box intimately contact each other with a predetermined amount of interference to form a metal-to-metal seal. A portion of the compressing load due to tightening is borne by the contacting torque shoulders, whereby the stresses acting on the threaded portions are decreased.
However, with a premium joint, galling easily takes place particularly in the unthreaded metal contact portions and particularly the metal sealing portions thereof, so lubrication is important to prevent galling. Up to now, a highly viscous greasy lubricating referred to as dope or compound grease has generally been applied prior to shipment to the threads and the unthreaded metal contact portions of a threaded joint for oil country tubular goods, which define the surfaces where the pin and the box contact each other at the time of makeup (referred to below simply as the contact surfaces of a threaded joint) with the object of increasing galling resistance and gastightness and protecting the contact surfaces against rusting up to the time of use.
In the case of a threaded joint for oil country tubular goods of the coupling type, in order to increase the roundness and the accuracy of the shape of the end surface of a long steel pipe and prevent fluid flowing inside the pipe from being disturbed at the surface where two members are joined to each other, a tapered recess (also referred to as a chamfer) is often provided on the inner surface of the pin adjacent to its end surface where it is joined to a box. Dope is also applied to the recess of the pin with the object of preventing rust.
Thus, on the end of a steel pipe which forms a pin, dope is applied not only to the outer surface and the end surface of the pipe which constitute a contact surface of the pin which contacts a box, but it is also applied to the inner surface of the steel pipe adjacent to the pipe end in which a recess is formed. A conventional dope called compound grease contains a large amount of powder of heavy metals such as Pb and Zn in order to guarantee lubricating properties and rust prevention (corrosion resistance). Application of dope is normally carried out by brush coating, namely, by putting a suitable amount of dope onto a contact surface of a threaded joint and then spreading it with a brush.
Below-listed Patent Documents 1 and 2 disclose a lubricant applying apparatus having a nozzle head which sprays a lubricant and a brush which spreads the sprayed lubricant as apparatuses for applying a lubricating such as a grease to a threaded portion of a threaded joint for pipes.
As a result of the enactment in 1998 of the OSPAR Convention (Oslo-Paris Convention) for preventing maritime pollution in the Northeast Atlantic, strict environmental regulations have been developed on a global scale. Particularly in North Sea oil fields, the use of lubricants containing heavy metals is prohibited in order to prevent marine pollution. Therefore, in the drilling of gas wells or oil wells on ocean rigs, there is a need to minimize the discharge of substances causing maritime pollution into the environment. For this purpose, it is a trend to require an assessment of the environmental impact of substances which could be discharged from rigs into the environment and prohibit the use of substances which do not satisfy the requirements of the country or region where drilling is taking place. Accordingly, in recent years, lubricants which can cope with such a demand are being developed. Such lubricants can be largely divided into solid lubricants which are not discharged into the sea at all (completely dry types) and highly viscous, high viscosity lubricants (semidry types) which have low toxicity even if they are discharged into the sea.
A completely dry type coating is typically a solid lubricating coating which comprises a lubricating powder dispersed in an inorganic or organic resin binder. This type of a lubricating coating does not have fluidity and has poor lubricating properties. This is because when it is subjected to a high pressure during makeup of a threaded joint for pipes, the coating is sometimes damaged, and galling takes place in the damaged portion. In contrast, when a lubricating coating formed from a semidry lubricant is subjected to a high pressure during makeup, the coating flows and moves around to locations where the lubricant is inadequate. As a result, it has excellent lubricating properties. However, since the lubricant which oozes out during makeup may possibly be discharged into the sea, a semidry type is inferior to a completely dry type from an environmental standpoint. Thus, a semidry type is advantageous when lubricating properties (galling resistance) are important. A semidry type which is superior with respect to galling resistance and gastightness is particularly suitable as a lubricant in the case of a premium joint which has a metal-to-metal seal having excellent gastightness but in which galling easily takes place in the metal-to-metal seal.
Patent Document 3 discloses a highly viscous lubricating coating composition having low toxicity (referred to below as “green dope”) which contains at least one basic oily lubricant selected from a basic sulfonate salt, a basic salicylate salt, a basic phenate salt, and a basic carboxylate salt and which has biodegradability (expressed as a value of BOD, biological oxygen demand) of at least 20% when measured after 28 days in sea water. Patent Document 3 also discloses that this lubricating coating composition may contain at least one other oily lubricant having higher biodegradability than the basic oily lubricant (preferably at least one substance selected from a fatty acid metal salt and a wax) and if necessary a volatile organic solvent.
The term highly viscous lubricant used herein means a lubricant having a viscosity which is too high to be sprayed as it is so that adjustment of its viscosity is necessary in order to make it sprayable.
Patent Document 1 JP 58-219964 A
Patent Document 2 JP 62-61667 A
Patent Document 3 US 2009/0264326 A1
With a conventional dope containing large amounts of heavy metal powder (compound grease and the like), only the minimum required coating weight was prescribed, and there was little need to strictly control the applied amount. Therefore, the necessary coating weight could be adequately guaranteed by brush application.
However, even though green dope has low toxicity, there is a demand to suppress the amount of lubricant which oozes out during makeup of a threaded joint for pipes as much as possible in order to minimize environmental pollution and particularly marine pollution. Reducing the amount which oozes out also improves the ease of makeup and the work environment. Therefore, the range for the coating weight of green dope is set to a considerably narrow range. Thus, when green dope is applied to the surface of a threaded joint for pipes, there is a demand that the applied amount be controlled so as to be as thin and uniform as possible within a range which can guarantee lubricating properties.
As the lubricant applying apparatuses disclosed in Patent Documents 1 and 2 both apply a lubricant to the pin and the box on the end of a pipe using a brush, there is a limit to how thinly and uniformly a highly viscous lubricant can be applied. A minute difference develops in the thickness of deposited lubricant between portions which are contacted by the hairs of a brush and those which are not contacted. In particular, the hairs of a brush strongly contact the ridge or crest of a thread so that the lubricant is worn and becomes thin. Furthermore, when performing application using a brush, there is a limit to how small the applied thickness can be made. Thus, in practice, it was impossible to apply a highly viscous lubricant like green dope to a thickness on the order of 10 μm or less, for example.
The object of the present invention is to provide an apparatus and method for applying a lubricant to a threaded portion of a steel pipe which can thinly and uniformly apply a controlled amount of a highly viscous lubricant having a high viscosity on the surfaces of a threaded portion formed on the end of a long steel pipe.
The present invention is an apparatus for applying a lubricant to a threaded portion formed on the outer or inner surface on the end of a steel pipe which constitutes a pin or a box of a threaded joint for pipes characterized by comprising (a) a steel pipe support unit which supports the steel pipe while rotating the pipe about its central axis, (b) a lubricant circulation system comprising a tank which stores a lubricant which has been adjusted so as to have a sprayable viscosity, piping through which the lubricant circulates, and a pump which forces the lubricant to circulate through the piping, (c) a metering unit comprising a metering pump in order to meter the feed of lubricant circulating through the lubricant circulation system, (d) a lubricant spraying unit comprising a lubricant feed passage for feeding the lubricant fed by the metering unit, an air feed passage designed to feed air for atomization independently of the lubricant feed passage, and at least one spray gun having a nozzle at its tip designed to spray lubricant at the outer or inner surface on the end of a steel pipe through the nozzle, the lubricant and air feed passages having a junction in the vicinity of the nozzle of the spray gun to atomize the lubricant, and (e) a spray gun support unit which supports the spray gun such that it can move in the axial and/or radial direction of the steel pipe.
Preferred embodiments of an apparatus for applying a lubricant to a threaded portion of a steel pipe according to the present invention include the following.
From another standpoint, the present invention is a method of applying a lubricant to a threaded portion formed on the outer or inner surface on the end of a steel pipe which constitutes a pin or a box of a threaded joint for pipes characterized by performing feeding lubricant and atomizing air separately to a spray gun having a nozzle at its tip, the lubricant having a viscosity adjusted so that it is sprayable and being circulating, mixing the supplied lubricant and the atomizing air in the vicinity the nozzle of the spray gun for atomization of the lubricant, and spraying the atomized lubricant at the threaded portion of the steel pipe from the nozzle of the spray gun while the spray gun is moved in the axial direction and/or the radial direction of the steel pipe and the steel pipe is rotated about its central axis.
According to the present invention, a highly viscous lubricant can be thinly and uniformly applied with a predetermined coating weight to a threaded portion of a threaded joint for pipes formed on the outer or inner surface on the end of a steel pipe, in particular to the surface of a pin which is typically formed on the end of a long steel pipe and which is difficult to coat. More specifically, a highly viscous lubricant can be uniformly applied to a thickness which is as small as 1/10 of a conventional thickness.
a) is an explanatory view schematically showing the state in which two spray guns spray a lubricant towards the surface of threads at right angles thereto, and
Below, embodiments of the present invention will be explained in detail while referring to the attached drawings. In the following description, unless otherwise specified, percent with respect to a composition means mass percent.
However, as is obvious to a skilled artisan, actually a box is not formed inside a pin at one end of a steel pipe P. A box is formed on the inner surface of a coupling, a separate member, in the case of a threaded joint of the coupling type or on the inner surface of the other end of a second steel pipe P in the case of a threaded joint of the integral type. Therefore, either pin or box is formed on one end of a steel pipe P. For the sake of convenience to show that a lubricant applying apparatus according to the present invention can be apply lubricant both to the pin and to the box of a threaded joint,
As described previously, on the inner surface of a pin of a threaded joint close to its end, namely, close to the end of a steel pipe, in place of a threaded portion as depicted in
As shown in
The steel pipe support unit 2 supports a steel pipe P having a pin 8a or a box 8b which is a threaded portion formed on the end of a pipe while rotating the pipe about its central axis in the direction shown by the arrow in
In
The lubricant circulation system 3 allows to circulate lubricant 9 which has been adjusted to have a viscosity suitable for spraying in order to stabilize the flow of the lubricant 9 and hence improve the uniformity of the discharge rate of lubricant 9 which is sprayed by the below-described lubricant spraying unit 5.
The lubricant circulation system 3 shown in
The lubricant 9 which is used is one capable of forming a highly viscous (semidry) lubricating coating. Preferably, the lubricant is a green dope which has a minimized adverse effect on the environment even if it runs out. More preferably, it is a lubricating coating composition described in Patent Document 3 listed above. Namely, the lubricant 9 comprises at least one basic oily lubricant selected from a basic sulfonate salt, a basic salicylate salt, a basic phenate salt, and a basic carboxylate salt and has a biodegradability (BOD) after 28 days in sea water of at least 20%.
A means for adjusting the viscosity of a highly viscous lubricant so that it is sprayable may be either diluting the lubricant with a volatile solvent or heating the lubricant. An example of the composition of the lubricant 9 when it is diluted with a volatile solvent is petroleum solvent: 20-30% (a diluting solvent), petroleum wax: 5-10%, rosin: 5-10%, graphite: 3-5%, remainder: petroleum-derived basic calcium sulfonate salt (as a basic oily lubricant). An example of a lubricant having such a composition is commercially available under the tradename CWSD EVS from Daido Chemical Industry Co., Ltd.
The tank 10 is equipped with a conventional stirring mechanism 10a for stirring the lubricant 9 housed in the tank 10. Stirring the lubricant 9 housed in the tank 10 with the stirring mechanism 10a serves to stabilize the composition of the lubricant 9 and hence improve the uniformity of the discharge rate of the lubricant 9 which is sprayed from the below-described lubricant spraying unit 5.
The piping 11 has a three-way valve 13, and one of the flow passages connected to the three-way valve 13 has a solenoid valve 14. By opening the cock of the three-way valve 13 and suitably switching the solenoid valve 14, the lubricant 9 which circulates through the lubricant circulating system 3 can be fed so as to apply either the pin 8a or the box 8b.
The metering unit 4 is provided for metered feed of lubricant 9 which has an adjusted viscosity and circulates through the lubricant circulation system 3. It comprises a metering pump. In the illustrated embodiment, a rotary plunger pump is used as a metering pump, but any metering pump can be used as long as metered feeding of a sprayable viscous liquid is possible.
In the illustrated embodiment, the metering unit 4 is constituted by a first metering pump 4a for metered feeding of the lubricant to a first lubricant spraying unit 5a for applying lubricant 9 to the pin 8a (or the outer surface of an end of a steel pipe) and a second metering pump 4b for metered feeding of the lubricant to a second lubricant spraying unit 5b for applying lubricant 9 to the box 8b (or the inner surface of an end of a steel pipe).
The first metering pump 4a and the second metering pump 4b are both rotary plunger pumps which control the discharge rate of lubricant 9 in proportion to the rotational speed in order to control the feed rate of lubricant 9. The discharge rate of the first metering pump 4a is controlled by a servo motor 4c and the discharge rate of the second metering pump 4b is controlled by a servo motor 4d. The uniformity of the discharge rate of the lubricant 9 which is sprayed by the below-described lubricant spraying unit 5 can be improved by controlling the discharge rate of the first metering pump 4a and that of the second metering pump 4b in this manner.
In contrast to the lubricant applying apparatus disclosed in Patent Documents 1 or 2 which applies a lubricant to a pin 8a or a box 8b by spreading it with a brush, a lubricant spraying unit 5 in the present invention sprays atomized lubricant 9 at the pin 8a or the box 8b of steel pipe P. As described above, it has a first lubricant spraying unit 5a for applying lubricant 9 to a pin 8a and a second lubricant spraying unit 5b for applying lubricant 9 to a box 8b.
The first lubricant spraying unit 5a has two spray guns 19 and 20 each having at its tip a nozzle 19a or 20a directed toward the pin 8a, lubricant feed passages 15a and 16a which send the metered lubricant 9 from the first metering pump 4a to the spray guns 19 and 20, respectively, and air feed passages 17a and 18a which send air for atomization to the spray guns 19 and 20, respectively, independently of the lubricant. The lubricant feed passage 15a or 16a and the air feed passage 17a or 18a merge at a junction (not shown) located in the vicinity of the nozzle 19a or 20a of the spray gun 19 or 20 to atomize lubricant 9, and the atomized lubricant was sprayed from the nozzles 19a, 20a towards the pin 8a of the steel pipe P.
Similarly, the second lubricant spraying unit 5b has a lubricant feed passage 21a through which metered lubricant 9 from the second metering pump 4b passes, air feed passage 22a which is independent of the lubricant feed passage 21a and through which air for atomizing passes, and a spray gun 23 which has a nozzle 23a at its tip for spraying lubricant 9 towards the box 8b of the steel pipe P. The lubricant feed passage 21a and the air feed passage 22a merge at a junction (not shown) located in the vicinity of the nozzle 23a of the spray gun 23 for atomization of lubricant and the atomized lubricant is sprayed through the nozzle 23a.
In the illustrated embodiment, the lubricant spraying unit has one or two spray guns. It is possible to install three or more spray guns in the spraying unit 5. Also in the illustrated embodiment, spray guns 19, 20 by which the lubricant is sprayed toward the pin are located in positions different only in the axial direction, but it is possible to locate spray guns in positions different in the circumferential direction or both in the axil and circumferential directions.
The first lubricant spraying unit 5a and the second lubricant spraying unit 5b both use air pressure to uniformly atomize the lubricant 9 which was adjusted in viscosity so as to be sprayable and then spray it towards the pin 8a or the box 8b, respectively, of the steel pipe P through the nozzles 19a, 20a, or 23a which all can be opened or shut by air pressure. As a result, the stability of the discharge rate of lubricant 9 which is sprayed from the lubricant spraying unit 5 can be improved.
The spray gun support unit 6 has a mechanism for supporting the spray guns 19, 20, and 23 so as to be able to move in the axial and/or radial direction of a steel pipe P. In the embodiment shown in
The spray gun support unit 6 has a first spray gun support device 24 for supporting spray guns 19 and 20 and a second spray gun support device 25 for supporting spray gun 23.
The first spray gun support device 24 comprises a ball screw 24a for axial movement which is disposed above the steel pipe P and moves a support member 24f for the spray guns 19 and 20 in the axial direction of the steel pipe P, a servo motor 24b for axial movement which drives the ball screw 24a for axial movement, a base plate 24c on which the screw 24a for axial movement ball is mounted, a ball screw 24d for radial movement which supports the base plate 24c so as to be able to move in the radial direction of the steel pipe P, and a servo motor 24e for radial movement which drives the ball screw 24d for radial movement. The ball screw 24d for radial movement is secured to the front surface of a box shaped body 27 which can be moved backwards and forwards by an air cylinder 26.
In this manner, the spray guns 19 and 20 are moveable in the axial and radial directions of the steel pipe P, and their amounts of movement and speed of movements are accurately controlled to desired values by the servo motors 24b and 24e. The positions of the nozzles 19a and 20a in the radial direction of the pin 8a of the steel pipe P, namely, the height of the spray guns 19 and 20 is set by the servo motor 24e such that the length of the major axis of the sprayed pattern of lubricant 9 on the surface of the pin 8a of the steel pipe P becomes a predetermined value L.
The second spray gun support device 25 is disposed towards the end of the steel pipe P. It has a ball screw 25a for axial movement which supports a support member 25f for the spray gun 23 in the axial direction of the steel pipe P, a servo motor 25b for axial movement which drives the ball screw 25a for axial movement, a base plate 25c on which the ball screw 25a for axial movement is mounted, a ball screw 25d for movement in the radial direction which supports the base plate 25c so as to be able to move in the radial direction of the steel pipe P, and a servo motor 25e for movement in the radial direction which drives the ball screw 25d for radial movement. The support member 25f is provided with a screw 25g which passes through it for adjusting the tilting angle of the spray gun 23 with respect to the surface of the box 8b. The ball screw 25d for movement in the radial direction is secured to the front surface of the box-shaped body 27 which can be moved forwards and backwards by the air cylinder 26.
In this manner, the spray gun 23 is movable in the axial and radial directions of the steel pipe P, and its amount of movement and speed of movement are accurately controlled to desired values by the servo motors 25b and 25e. The position of the nozzle 23a in the radial direction of the box 8b of the steel pipe P, namely, the height of the spray gun 23 is set by the servo motor 25e to a position such that the length of the major axis of the sprayed lubricant 9 on the surface of the box 8b of the steel pipe P becomes a predetermined value L.
If the distance of nozzles 19a and 20a from the pin 8a or the distance of nozzle 23a from the box 8b is too small, there is the possibility of the nozzles 19a, 20a, or 23a contacting the steel pipe P, while if the distance is too large, the sprayed lubricant 9 splatters and it may not be possible to obtain a desired coating thickness. Therefore, the distance is preferably as small as possible without producing interference of equipment. From this standpoint, the distance of nozzles 19a and 20a from the pin 8a and the distance of nozzle 23a from the box 8b are preferably 30 mm to 80 mm. The angle of spray of the lubricant discharged from the nozzles is preferably in the range of 5 to 15 degrees.
As shown in
a) is an explanatory view schematically showing the state in which spray guns 19 and 20 spray a lubricant 9 at right angles with respect to the thread crest 8d, and
As shown in
Therefore, as shown in
This will be explained below more fully. As shown in
Upon further investigation in this respect, in the case of the thread shape shown in
When two spray guns (intended for application to a P flank and an N flank of a thread, respectively) in which the spraying directions of the nozzles are different from each other are used to apply lubricant to a male thread of a pin having a flank with a negative angle of slope from both sides of the thread for the purpose of uniform application, it is not preferable that the sprayed streams discharged through the two nozzles interfere with each other. As shown in
In this manner, using the spray gun support unit 6, the lubricant 9 having its viscosity adjusted so as to be sprayable is atomized by air pressure becomes a uniform mist and it is sprayed through the nozzles 19a, 20a, or 23a which can be opened and shut by air pressure towards the pin 8a or the box 8b of the steel pipe P.
Instead of using the first spray gun support devicet 24 and the second spray gun support devicet 25, it is of course possible to support the spray guns 19, 20, and 23 using a general-purpose articulated robot, for example, whereby each spray gun can be tilted.
It is not always necessary to provide the controlling unit 7, but it is preferable to provide it to stabilize spraying of the lubricant 9.
The controlling unit 7 controls the rotational speed of the steel pipe P by the steel pipe support unit 2 and the speed of axial movement of the spray guns 19 and 20 or 23 by the spray gun support unit 6 so as to satisfy the following Equation (1):
V≦m×n×L (1)
wherein L is the length of the major axis (mm) of the sprayed pattern on the pin 8a or the box 8b (or on the surface of the steel pipe) of the lubricant 9 sprayed in a conical shape from spray gun 19, 20, or 23, n is the rotational speed (rpm) of the steel pipe P by the turning rollers 2a and 2b, m is the number of nozzles 19a, 20a, or 23a in the axial direction of the steel pipe P, and V is the speed of movement (mm/min) of the spray gun 19, 20, or 23 in the axial direction by the spray gun support unit 6.
When there exist a plurality of nozzles having the same position in the axial direction of the steel pipe P but different positions in the circumferential direction thereof, these nozzles are considered to constitute a set and the number of m is made one.
The reasons why the controlling unit 7 preferably performs this function is as follows.
The lubricant applying apparatus 1 according to the present invention applies a lubricant 9 in a helical shape on a pin 8a or a box 8b of a steel pipe P by spraying a lubricant 9 having its viscosity adjusted so as to be sprayable in a conical shape on the pin 8a from nozzles 19a and 20a of spray guns 19 and 20 which move in the axial direction of the steel pipe P or from nozzle 23a of spray gun 23 on the box 8b of a steel pipe P while the pipe P is rotated in the direction of the arrow by turning rollers 2a and 2b. Therefore, if the speed of movement V of the spray guns 19, 20, or 23 in the axial direction exceeds the above value (m×n×L), uncoated portions are intermittently formed in the axial direction of the steel pipe P between the helical coating. Conversely, if the speed of movement V of the spray guns 19, 20, or 23 in the axial direction is too slow, productivity decreases, the applied thickness of the lubricant 9 becomes too large, and the lubricant 9 which was applied to the pin 8a or the box 8b may flow away.
The speed of movement V (cm/sec) of the spray guns 19, 20, and 23 in the axial direction of the steel pipe P, the coating thickness W (cm) of the lubricant 9, the overall feed rate of lubricant q (ml/sec) from nozzles 19a, 20a, and 23a, the outer diameter D (cm) of the steel pipe P, and the adhesion efficiency n have the relationship expressed by Equation (2): q=W×nD×V/η. An example of ranges in which Equation (2) is satisfied are when the overall feed rate of lubricant q is set to 0.1-0.6 (ml/sec) and the speed of movement V is set to 4-12 (mm/sec).
As illustrated in
In contrast, the range over which lubricant 9 is sprayed on the box 8b of the steel pipe P is often so short that it can be covered by spraying with a single spray gun 23 which is moved in the axial direction of the steel pipe P. Therefore, when it is possible to perform adequate application with the sprayed pattern of a single spray gun 23, a single spray gun 23 may be provided. Of course, when application is not adequate with the sprayed pattern of a single spray gun 23 or it is desired to increase productivity, a plurality of spray guns for spraying lubricant 9 at the box 8b of the steel pipe P can be arranged in a row in the axial direction of the steel pipe P. In such cases, as described in the below-described example, a plurality of spray guns are preferably arranged in axially different positions such that the sprayed streams slightly overlap with each other on the surface of the steel pipe in order to avoid the occurrence of non-coated portions between the streams.
At the point where application is ended such as the end point of the threads of the steel pipe or to the rear of the threads on the inner surface, it is desirable to perform application in a circumferential direction instead of along a helical line in order to prevent unnecessary application. Therefore, at this point, it is preferable to stop the movement of the spray guns 19, 20, and 23 in the axial direction of the steel pipe and continue spraying for around 0.8-2.3 seconds (the time required for one rotation of the steel pipe P) before spraying is terminated.
The wet coating thickness of lubricant 9 on the pin 8a or the box 8b of a steel pipe P is preferably at least 6 μm and at most 8 μm in order to obtain good lubricating properties without oozing of the lubricant.
A lubricant applying apparatus 1 according to the present invention can form a coating of a lubricant 9 having a desired thickness, but it is preferable to satisfy the relationship given by the above-described Equation (2).
The controlling unit 7 enables the stability of discharge of lubricant 9 which is sprayed from the lubricant spraying unit 5 to be increased. The controlling unit 7 can be used to control all the movements including the movement of the main body of the applying apparatus, the movement of the nozzles in the axial and radial directions, the rotational speed of the steel pipe, the rotational speeds or other actions of pumps, and on an off of spraying.
A lubricant applying apparatus 1 according to the present invention is constituted as described above. Next, an example of a method of applying a lubricant 9 to a pin 8a on the end of a steel pipe P using this lubricant applying apparatus 1 will be explained.
First, a steel pipe P having a threaded portion in the form of a pin 8a on the end of the pipe is mounted on the turning rollers 2a and 2b, and the steel pipe P is rotated in the direction of the arrows in
A highly viscous lubricant 9 (the above-described green dope having a biodegradability (BOD) of at least 20% after 28 days in sea water) which has been diluted with a volatile solvent to adjust its viscosity so as to be sprayable (e.g., CWSD EVS manufactured by Diado Chemical Industries, Co., Ltd.) is placed in the tank 10 of the lubricant circulating system 3. The lubricant 9 in the tank 10 is then stirred by the stirring mechanism 10a.
By setting the cock of the three-way valve 13 so as to allow circulation and starting the operation of the pump 12, the lubricant 9 is circulated through the lubricant circulating system 3.
Subsequently the solenoid valve 14 is set so as to select application of lubricant 9 to the pin 8a, and the first metering pump 4a for metered feeding to the first lubricant spraying unit 5 for applying lubricant 9 to the pin 8a is started. Lubricant 9 is thereby supplied to the first metering pump 4a.
The first metering pump 4a performs metered feeding of lubricant 9 to the spray guns 19 and 20 through the lubricant feed passages 15a and 16a. At the same time, air for atomizing is fed to spray guns 19 and 20 through air feed passages 17a and 18a by an unillustrated system for feeding air for atomizing. The lubricant 9 and the atomizing air fed to the spray guns 19 and 20 are mixed together in the vicinity of the nozzles 19a and 20a at the tips of the spray guns 19 and 20, and the lubricant 9 which is atomized by mixing with the atomizing air was sprayed towards the pin 8a of the steel pipe P through nozzles 19a and 20a.
Simultaneous with the start of this spraying, the first spray gun support unit 24 is started, and the spray guns 19 and 20 which are disposed at predetermined angles with respect to the pin 8a are moved in the axial direction of the steel pipe P at a predetermined speed V (V≦m×n×L) and are moved at a predetermined speed in the radial direction of the steel pipe P.
The rotational speed of the steel pipe P by the steel pipe support unit 2 and the speed of axial movement of the spray guns 19 and 20 by the first spray gun support unit 24 are preferably controlled by the controlling unit 7.
As a result, the lubricant 9 can be sprayed towards the pin 8a of the steel pipe P which is supported while rotating about its central axis.
As described above, with an apparatus and a method for applying lubricant to the threaded portions 8a and 8b of a steel pipe P according to the present invention, the coating thickness of lubricant 9 on the pin 8a of a steel pipe P can be controlled not only so that there is no oozing but so that good lubricating properties are obtained.
Specifically, with an apparatus and method for applying lubricant to the threaded portions 8a and 8b of a steel pipe P according to the present invention, by
(i) previously adjusting the viscosity of a highly viscous lubricant so as to be suitable for spraying by diluting with a volatile solvent or by heating,
(ii) circulating the lubricant 9 having its viscosity previously adjusted so as to be sprayable through a lubricant circulation system 3,
(iii) stirring the lubricant 9 housed in a tank 10 with a stirring mechanism 10a,
(iv) feeding lubricant 9 to spray guns 19 and 20 using a first metering pump 4a which has its discharge rate controlled by a servo motor 4c,
(v) performing fine control of the speed of movement of the spray guns 19 and 20 using the first spray gun support unit 24 having servo motors 24b and 24d as drive sources,
(vi) optimally setting the spraying angles of the spray guns 19 and 20, and
(vii) using the controlling unit 7 to performed high precision control of the rotational speed of the steel pipe P by the pipe support unit 2 and the speed of movement of the spray guns 19 and 20 by the spray guns support unit 6 so that the speed of movement V (mm/min) of the spray guns 19 and 20 in the axial direction by the spray gun support unit 6 satisfies Equation (1): V≦m×n×L and so as to be in the range of 15-25 mm/min,
the coating thickness of the lubricant 9 on the pin 8a of the steel pipe P can be controlled to be in the range of 6-8 μm in which not only is there no oozing of lubricant but good lubricating properties are obtained.
In the above explanation, an example was given of applying lubricant 9 to a pin 8a on the end of a steel pipe P. When applying lubricant 9 to a box 8b of a steel pipe P, the only difference is that the application of lubricant 9 to the box 8b is selected by switching the solenoid valve 14, and other conditions are exactly the same. Therefore, an explanation of applying lubricant 9 to the box 8b of the steel pipe P will be omitted.
A lubricant applying apparatus according to the present invention can be designed so as to enable simultaneous application of a lubricant to the inner and outer surfaces of an end of a steel pipe. Therefore, it is possible to simultaneously apply a lubricant to a pin on the outer surface of an end of a steel pipe and a recess portion on the inner surface of that end of the steel pipe.
In this manner, with a lubricant applying apparatus 1 according to the present invention, a green dope which is a highly viscous lubricant can for the first time be thinly and uniformly applied with a predetermined coating weight and specifically with a low thickness of around 1/10 of the conventional thickness to the surface of a pin 8a or a box 8b of a steel pipe P and particularly to the surface of a pin 8a which is typically formed on the end of a long steel pipe P and which is difficult to coat.
In a lubricant applying apparatus 1 according to the present invention for applying lubricant to threaded portions 8a and 8b of a steel pipe P, if each of the feed rate of lubricant 9 by the first metering pump 4a and the feed rate of lubricant 9 by the second metering pump 4b, the rate of circulation of lubricant 9 by pump 12, the distance of the nozzles 19a and 20a from the pin 8a, the distance of nozzle 23 from the box 8b, and the angles of the spray guns 19, 20, and 23 at the time of spraying are maintained constant at previously determined values, lubricant 9 can be applied to a desired thickness to the pin 8a or the box 8b of the steel pipe P regardless of the outer diameter of the steel pipe P by using the controlling unit 7 so as to control the rotational speed of the steel pipe P by the steel pipe support unit 2 and the speed of movement of spray guns 19 and 20 by the first spray gun support unit 24 or the speed of movement of spray gun 23 by the second spray gun support unit 25.
Using the lubricant applying apparatus 1 according to the present invention shown in
The spray guns 19 and 20 used to apply the lubricant to the pin had their nozzles oriented perpendicular to the surface of the steel pipe (thread crest) as shown in
In this coating process, the discharge rate V from the first metering pump 4a was maintained constant at 8.65 g/min and the rotational speed of the first metering pump 4a was maintained constant at 25.44 rpm regardless of the outer diameter of the steel pipe P. Therefore, the applied amount is given by T/60×V.
The tolerance of application (Min, Max, and Median expressed in grams) was the tolerance of the overall coating weight which was obtained by actual measurement.
The results are compiled in Table 1. In Table 1, WT indicates the wall thickness of the pipe, T/R indicates the turning roller, and the pump indicates the first metering pump 4a (which was a rotary plunger pump having variable rotational speed). Pump constant indicates the volume discharged from the pump during one revolution. Pump constant and number of pump revolutions are the values in the first metering pump 4a.
As shown in Table 1, in a lubricant applying apparatus 1 according to the present invention, if the feed rate of lubricant 9 by the first metering pump 4a, the rate of circulation of lubricant 9 by pump 12, the distance of nozzles 19a and 20a from the pin 8a, and the angles of the spray guns 19 and 20 at the time of spraying are all maintained constant at previously determined values, it can be seen that a lubricant 9 can be applied to the pin 8a of the steel pipe P to a desired thickness which satisfies tolerances regardless of the outer diameter of a steel pipe by controlling by means of the controlling unit 7 only the rotational speed of the steel pipe P by the steel pipe support unit 2 and the speeds of movement of spray guns 19 and 20 by the first spray gun support unit 24.
Fine adjustment of the coating thickness can be easily carried out by varying the rotational speed of the first metering pump 4a and varying the feed rate of the lubricant 9.
In this manner, according to the present invention, a highly viscous lubricant can be thinly and uniformly applied with a predetermined coating weight to the surface of a pin or a box of a threaded joint for pipes and particularly to the surface of a pin which is typically formed on the end of a long steel pipe and which is difficult to coat. Specifically, the highly viscous lubricant can be uniformly applied to a thickness of around 1/10 of the conventional value.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-081318 | Mar 2009 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2010/055706 | Mar 2010 | US |
| Child | 13244961 | US |
