HK1173205B - A tubular joint having wedge threads with surface coating - Google Patents

Abstract

A threaded joint for pipes includes a pin member (101) and a box member (102), the pin member having an external thread (106) configured to correspond to an internal thread (107) of the box member, a thread form of the internal and external threads having generally dovetail - shaped profile with stab flanks (231,232)and load flanks (225,226) and flat roots and crests (222,291), wherein the internal threads are increasing in width in one direction on the box and the external threads are increasing in width in the other direction on the pin, so the roots, crests, and flanks of the threads move together and form seals (112) that resist the flow of fluids between the seals. The threaded joint further includes a fluoropolymer-based coating (310) applied to specific regions of the threads and a resin coating (312) disposed in regions of the threads that are devoid of the fluoropolymer-based coating, wherein the fluoropolymer-based coating and the resin coating are configured to form a layer of substantially uniform thickness on the overall surface of the threads.

Description

Tubular joint having wedge threads with surface coating

Technical Field

Embodiments disclosed herein relate generally to threaded connections having wedge threads. More particularly, embodiments disclosed herein relate to wedge threads having an improved surface coating applied thereto and methods of applying the improved surface coating.

Background

Casing joints, liners and other oilfield tubulars are often used to drill, complete and produce wells. For example, casing joints may be provided in a wellbore to stabilize and protect a formation from high wellbore pressures that can damage the formation (e.g., wellbore pressures that exceed the formation pressure). A casing joint is a portion of a pipe (e.g., steel or titanium) that may be coupled together in an end-to-end manner by a threaded connection, welding, or any connection mechanism known in the art. The connection is therefore usually designed such that at least one seal is formed between the interior of the coupled casing joint and the annulus formed between the outer wall of the casing joint and the inner wall of the wellbore (i.e. the formation). The seal may be an elastomer (e.g., an O-ring seal), a threaded seal, a metal-to-metal seal, or any other seal known to those skilled in the art.

It will be understood that certain terms used herein are to be interpreted in a generally understood manner, particularly when the threaded tubular connection is connected in a vertical orientation along its central axis, such as when making a string of tubulars for running into a wellbore. Typically, in a male-female tubular connection, the male component of the connection acts as a "pin" member and the female component acts as a "box" member. As used herein, "make-up" refers to mating a pin member into a box member and threading the members together by torque and rotation. Additionally, the term "selectively make-up" refers to threading the pin member and the box member together with a desired amount of torque or based on the relative position (axial or circumferential) of the pin member with respect to the box member. Additionally, the term "box member face" is understood to mean the end of the box member that faces outwardly from the threads, while the term "pin member nose" is understood to mean the end of the pin member that faces outwardly from the connection of the threads. Thus, upon assembly of the connection, the nose of the pin member extends or is inserted into and through the face of the box member.

The term "load flank" refers to the side wall surface of the thread facing away from the outer end of the respective pin or box member on which the thread is formed and which supports the weight (e.g., tensile load) of the lower tubular member suspended in the wellbore, depending on the geometry of the thread. Similarly, the term "stab flank" refers to the side wall surface of the threads toward the outer end of the respective pin or box member and supports the force that compresses the joints toward each other, as the weight of the upper tubular member early in the makeup of the joint, or as the force (e.g., compressive force) applied to push the lower tubular member toward the bottom of the wellbore.

One type of threaded connection that is often used in oilfield tubulars is a wedge thread. Referring initially to fig. 1A and 1B, a prior art tubular connection 100 is shown having wedge threads. As used herein, a "wedge thread" is a thread that, regardless of the particular shape of the thread, increases in width (i.e., the axial distance between the load flanks 225 and 226 and the stab flanks 232 and 231) in a direction opposite the pin member 101 and the box member 102. The rate of change of the thread across the width of the connection is determined by a variable known as the "wedge ratio". As used herein, although "wedge ratio" is not a ratio in the technical sense, it refers to the difference between the stab and load flank leads, which results in the width of the threads varying along the connection. Additionally, as used herein, thread "lead" refers to the differential distance between the components of one thread on successive threads. Thus, the "stab lead" is the distance between the stab flanks of successive thread pitches along the axial length of the connection. A detailed discussion of the wedge ratio is provided in U.S. Pat. No.6,206,436 issued to Mallis and assigned to Hydril Company, which is incorporated herein by reference in its entirety. Wedge threads are also widely disclosed in U.S. patent No. 30,647 to Blose, U.S. patent No. re34,467 to Reeves, U.S. patent No.4,703,954 to Ortloff, and U.S. patent No.5,454,605 to Mott, all of which are assigned to hydral co.

Still taking fig. 1A and 1B as an example, the pin member thread crest 222 in the wedge thread coupling is narrow toward the distal end 108 of the pin member 101, while the box member thread crest 291 is wide toward the distal end. Moving along the axis 105 (from right to left), the pin member thread crest 222 widens and the box member thread crest 291 narrows as the distal end 110 of the box member 102 is approached. As depicted in fig. 1A, the thread is tapered, meaning that the diameter of the pin member thread 106 increases from the beginning to the end, while the diameter of the internal thread 107 decreases in a complementary manner. Having a thread taper may increase the ability to insert the pin member 101 into the box member 102 and distribute stresses throughout the connection.

Generally, non-wedge (e.g., free-running) threads have difficulty achieving thread seals. However, thread shapes that do not form wedge threads in a free-run configuration may form thread seals when a wedge thread configuration is used. Those skilled in the art will appreciate that a variety of thread shapes may be used, as wedge threads do not require any particular type or geometry for thread shape. One suitable thread form is a semi-dovetail thread form, which is disclosed in U.S. Pat. No.5,360,239 to Klementich, which is incorporated herein by reference in its entirety. Another thread form includes multi-faceted load flanks or stab flanks, as disclosed in U.S. Pat. No.6,722,706 to Church, which is incorporated herein by reference in its entirety. The above thread forms are all considered to be "trap-shaped" thread forms, meaning that at least a portion of the respective load flanks and/or the respective stab flanks axially overlap.

Also exemplified in fig. 1A and 1B, in wedge threads, thread sealing may be achieved by contact pressure resulting from interference occurring at makeup on at least a portion of the connection 100 between the pin member load flank 226 and the box member load flank 225 and between the pin member stab flank 232 and the box member stab flank 231. When such flank interference occurs, the close abutment or interference between the roots 292 and 221 and crests 222 and 291 completes the thread seal. In general, higher pressures may be tolerated by increasing the interference between roots and crests (root/crest interference) on the pin member 101 and the box member 102, or by increasing the aforementioned flank interference.

While various existing wedge thread connections have a positive-torque shoulder (such as Klementich referenced above), wedge threads generally do not have a torque shoulder and therefore their make-up is "indeterminate," and therefore there is more variation in the relative positions of the pin member and the box member during make-up than connections having a positive-torque shoulder for a given applied torque range. For wedge threads designed to have flank interference and root/crest interference at selective makeup, the connection is designed such that the flank interference and root/crest interference increase (i.e., increasing torque increases flank interference and root/crest interference) when the connection is made up. For conical wedge threads with root/crest clearance, the clearance decreases when the connection is made up.

Regardless of the design of the wedge threads, the corresponding flanks are increasingly closer to each other at makeup (e.g., clearance decreases or interference increases). Non-positive make-up allows for increased flank interference and root/crest interference by increasing make-up torque on the connection. In this way, wedge threads may thread seal higher pressure gas and/or liquid by designing the connection with more flank interference and/or root/crest interference or by increasing the makeup torque on the connection. However, increasing the interference and make-up torque increases the stress on the connection at make-up, which may lead to premature failure of the connection.

Additionally, as shown, the connection 100 includes a metal-to-metal seal 112 formed by corresponding contact between sealing surfaces 103 and 104 on the pin member 101 and the box member 102, respectively. The metal-to-metal seal 112 provides an additional measure of seal integrity for the threaded connection 100 (i.e., when the wedge thread seal is inadequate) and is particularly useful when the connection 100 is used to contain high pressure gas. While the metal-to-metal seal 112 is shown as being located near the distal end 108 of the pin member 102, one of ordinary skill in the art will appreciate that the metal-to-metal seal 112 may be located anywhere along the length of the connection 100, including but not limited to near the distal end 110 of the box member 102.

In some instances, one or more "dry" surface coatings are applied to the threaded surfaces of a connection for various reasons, for example, to improve the sealing properties of the threaded connection, to resist galling of the threads, and to provide corrosion resistance. This surface coating is characterized by being dry because it permanently adheres to the thread form rather than being used like a flowing paint type lubricant. For example, U.S. publication No.2009/0033087, assigned to the assignee of the present application, discloses a threaded joint having a free-running thread and a multi-layer applied surface coating. However, wedge threads present new difficulties for surface coatings due to the complex and high tolerance sealing characteristics of their thread form itself. Accordingly, there is a need to provide a dry surface coating for wedge thread surfaces that exhibits the beneficial properties of the surface coatings currently applied to free-running threads.

Disclosure of Invention

In one aspect, embodiments disclosed herein relate to a threaded joint for a pipe including a pin member and a box member, the pin member having an external thread that correspondingly mates with the internal thread of the box member, the thread forms of the internal and external threads having a substantially dovetail profile with stab and load flanks and flat roots and crests, wherein the internal thread on the box member increases in width in one direction and the external thread on the pin member increases in width in the other direction, such that the roots, crests, and flanks of the thread move together and form a seal that resists fluid flow between the seals. The threaded joint further includes a fluoropolymer-based coating applied to specific regions of the internal and external threads, and a resin coating disposed on the internal and external threads in areas lacking the fluoropolymer-based coating, wherein the fluoropolymer-based coating and the resin coating are configured to form a coating having a substantially uniform thickness over the entire surface of the internal and external threads.

In another aspect, embodiments disclosed herein relate to a method of modifying the threaded surface of a pipe joint that includes providing a pin member having external wedge threads and a box member having internal wedge threads configured to mate with the external wedge threads of the pin member, surface treating the entire surfaces of the internal and external wedge threads, applying a fluoropolymer-based coating to specific regions of the internal and external wedge threads, applying a resin coating to the integral thread surfaces of the internal and external threads after the fluoropolymer-based coating, wherein the resin coating is configured to bond to regions that are free of the fluoropolymer-based coating.

Wherein the method further comprises providing a solvent mixture with the fluoropolymer-based coating to apply the fluoropolymer-based coating. The fluoropolymer-based coating is present in the solvent mixture in the range of 20-40% wt and the solvent is present in the range of 60-70% wt.

Other aspects and advantages of the invention will become apparent from the following description and appended claims.

Drawings

FIGS. 1A and 1B are cross-sectional views of a prior art tubular connection having wedge threads.

FIG. 2 is a cross-sectional view of a wedge thread having a thread surface coating in accordance with a disclosed embodiment of the invention.

Detailed Description

In one aspect, embodiments disclosed herein relate to a surface coating applied to wedge threads and to related methods of applying a surface coating to wedge threads. Referring to FIG. 2, a cross-sectional view of a wedge thread shape with a surface coating 300 is shown, according to a disclosed embodiment of the invention. The topcoat 300 includes a first coating 310 and a second coating 312 that together form a uniform topcoat layer 300 over the entire thread-shaped surface. While fig. 2 depicts a surface coating 300 applied to the threads of the pin member, it should be understood that the surface coating 300 may be applied to both the threads of the pin member and the box member, or only the threads of the pin member or only the threads of the box member. In certain embodiments, the surface coating 300 may be applied to the box member while another corrosion-resistant coating and/or lubricant is applied to the pin member.

In the embodiments disclosed herein, multiple coats may be required to be applied to ultimately complete the surface coating 300 as a coating layer that completely covers the entire thread surface as a single uniform coating. One method of application according to embodiments disclosed herein may be performed as follows. Initially, the entire thread surface may be subjected to a surface preparation (i.e., chemical or mechanical surface treatment) (not shown in FIG. 2) to prepare the thread surface for subsequent coating. The chemical treatment may be a preparatory coating for the threaded surface and may not have any substantial thickness. The chemical coating may include, but is not limited to, phosphate coatings, oxalate coatings, and borate coatings. The chemical coating forms a foundation on the thread surface, thereby promoting maximum adhesion of subsequent coatings to the thread surface and preventing galling and corrosion of the thread surface. For example, after application of the chemical coating, the surface finish or roughness of the threaded surface may be required to be within a certain range to allow the subsequent coating to properly bond to the threaded surface. The mechanical treatment may include sandblasting or other abrasive treatment. In certain embodiments, the average surface roughness (Ra) may be in the range of about 2.0 microns to 6.0 microns. In other embodiments, the average surface roughness (Ra) is in the range of about 2.0 microns to 4.0 microns.

After surface treatment, a first coating 310 may be applied to the threaded surface. The first coating 310 may be applied with a solvent that may reduce the viscosity of the mixture to an applicable viscosity (i.e., dilute the mixture so that it can be applied more easily to the threaded surface). Typical organic solvents that can be used in the coating mixture include, but are not limited to, 2-methoxy-1-methyl-ethyl acetate, xylene, acetone, tetrahydrofuran, methyl ethyl ketone, ethyl acetic acid, propyl acetic acid, butyl acetic acid, isobutyl acetic acid, methyl isobutyl ketone, methyl amyl acetic acid, diisobutyl ketone, ethylene glycol monomethyl ether acetic acid, ethylene glycol monomethyl ether, and mixtures of the foregoing. After application of the first coating 310 to the thread surface, these solvents typically evaporate from the mixture, leaving only the first coating 310 as a coating on the thread surface.

The first coating 310 may be applied to substantially a specific region of the thread surface, i.e., the thread top surface 304 and substantially the central region 302A of the thread root surface 302. Due to the limitations imposed by the method of application of the first coating 310 and the wedge thread configuration, the first coating 310 may only be applied to a substantially central region 302A of the thread root surface 302. The first coating 310 may be applied substantially radially of the threads (e.g., in a direction substantially perpendicular to the central axis 305). The radial direction is used because it results in a more uniform distribution over the root surface, which can require fewer subsequent coating steps.

Due to this particular application method, the configuration of the thread form may limit the area of the thread form to which the first coating 310 may be applied. As previously mentioned, in some embodiments, the wedge threads may be a trap-shaped or dovetail-shaped thread form. As shown in FIG. 2, the dovetail thread shape has a smaller axial width near the thread roots 302 and a larger axial width near the thread crests 304. As such, a portion or area of the thread root 302 is overlapped or covered by an adjacent thread crest 304. The substantially central region of the thread roots 302 is indicated by 302A in fig. 2, while the overlapping region is indicated by 302B. Thus, the first coating 310 may be applied to only the substantially central region 302A of the thread root 302, but to the entire surface of the thread crest 304. The first coating 310 may have substantially low friction and low surface tension characteristics (i.e., subsequent coatings may not readily stick to the first coating). According to embodiments disclosed herein, the low friction value may be less than about 0.08. In other embodiments, the low friction value may be less than about 0.04. The low surface tension characteristic of the first coating 310 is beneficial for application of a second coating, as described below.

After the first coating 310, a second coating 312 may be applied to the entire surface of the threads by pouring, spraying or brushing. However, due to the low surface tension properties of the first coating, the second coating 312 is repelled by the first coating 310 and moves to the uncoated regions of the thread form. The second coating 312 may be repelled by the first coating 310 due to the different surface energies between the coatings, which may be higher than the surface energy of the first coating. In certain embodiments, the second coating may have at least twice the surface energy of the first coating. According to embodiments disclosed herein, the low surface energy value may be less than about 50 dynes/cm. In other embodiments, the low surface energy value may be less than about 20 dynes/cm.

After application of the first coating 310, the uncoated region of the thread form may generally include the thread flanks 306 (including the stab flanks and the load flanks) and the outermost region 302B (axial direction) of the thread roots 302, starting from the central region 302A and extending to the transition 303 on the thread form from the thread roots 302 to the thread flanks 306. After application of the second coating 312, a single, uniform surface coating 300 (i.e., a coating of constant thickness) appears on the threaded surface at the connection. If necessary, the surface coating 300 may be cured by heat treatment. In certain embodiments, a post-coating heat treatment may be performed, and the heat treatment temperature may reach about 150 degrees celsius or more, depending on the coating.

In one example, the first coating 310 may be a fluoropolymer-based coating. The fluoropolymer-based coating may include fluoropolymer solids (e.g., powder) dispersed in a thermosetting resin, such as an epoxy resin. The epoxy resin may be formed from an epoxy compound (e.g., conventional glycidyl epoxy resins including, but not limited to, diglycidyl ethers of bisphenol a and novolac epoxy resins, as well as any other epoxy resins known in the art) and a curing agent, as is known in the art. The fluoropolymer-based coating may include a reactive epoxy resin that is capable of reacting with a curing agent to form a thermoset network having a fluoropolymer dispersed therein. The thermosetting resin may be delivered to (e.g., applied to) the desired thread surface as an unreacted, but reactive resin that cures upon application.

The fluoropolymer solids may be dispersed within the epoxy resin in a specific ratio to exhibit the desired properties of the first coating (e.g., sealability, abrasion resistance, corrosion resistance, durability, etc.). In certain embodiments, the fluoropolymer solids may comprise 20-40% wt and the epoxy resin may comprise 40-60% wt. In addition, titanium dioxide may be present in the mixture and constitute 5-15% wt. In the embodiments disclosed herein, the thickness of the first coating 310 may vary in the range of about 10-40 microns. In certain embodiments, the fluoropolymer powder may be Polytetrafluoroethylene (PTFE). Other examples of fluoropolymers that may be used in the embodiments disclosed herein include, but are not limited to, Polytetrafluoroethylene (PFA), Fluorinated Ethylene Propylene (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), polyvinyl fluoride (PVF), ethylene chlorotrifluoroethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), Polychlorotrifluoroethylene (PCTFE), and perfluoropolyether (PFPE).

The second coating 312 may be a polymer resin that is applied to cover the thread surface uncovered, or the surface not covered by the first coating 310. The second coating 312 may have elastic properties after application to the threaded surface. The polymer resin functions to fill the gap created by the first coating. This resilient characteristic is beneficial because the material will recover its shape and maintain its sealing properties intact after each installation and removal of the material. Types of resins that can be used for the second coating include, but are not limited to, epoxy, polyester, and ester type epoxy. In the embodiments disclosed herein, the thickness of the second coating 312 may vary in the range of about 10-40 microns. Due to the low friction and low surface tension characteristics of the first coating 310, the second coating 312 or resin may be selectively distributed over the threaded surface in areas where the first coating 310 is absent. In other words, the low friction characteristics of the first coating 310 can cause (e.g., by repelling) the second coating 312 to move to areas of the threaded surface that are free of the first coating 310. Thus, the first coating 310 and the second coating 312 form a single, uniform coating 300 over the entire thread surface by occupying their respective separate regions, as will be described in greater detail below.

In an alternative embodiment, a copper plating is formed on the threaded surface prior to applying the coating. In certain embodiments, the surface treatment may limit the average surface roughness (Ra) to a range of about 2.0 microns to 6.0 microns. In other embodiments, the average surface roughness is between about 2.0 and 4.0 microns. The corrosion resistant alloy may have a higher chromium content to withstand more severe or extreme downhole environments. The choice of corrosion resistant alloy will be understood by those skilled in the art.

Advantageously, the disclosed embodiments of the present invention provide a threaded surface coating having improved galling and galling resistance properties that enables threaded connections having such coatings to withstand multiple make-ups and break-downs. The life of the threaded connection is increased with multiple make-ups and break-downs, which reduces the cost of replacing a worn or damaged threaded connection. Experimental data indicates that wedge threaded connections having surface treatments in accordance with embodiments disclosed herein have been made-up at torque values between approximately 9500 and 20000ft-lbs without galling of the threads or sealing surfaces occurring at any successive make-up and break-out.

Additionally, the surface coatings in the embodiments disclosed herein may also provide lubrication properties to the threaded connection by eliminating metal-to-metal contact at make-up. In addition, the surface coating may improve the sealing properties of the threaded connection. In addition, the surface coating may provide better corrosion resistance, thereby increasing the useful life of the threaded connection. The longer the threaded connection can be maintained in service, the lower the cost of maintenance and equipment replacement. Finally, the surface coating is environmentally friendly and does not contain potentially contaminating elements.

While the present disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the disclosure as disclosed herein. Accordingly, the scope of the invention is to be limited only by the following claims.

Claims (21)

1. A threaded joint for pipes comprising:

a pin member and a box member, the pin member having an external thread that mates with the internal thread of the box member;

the thread form of the internal and external threads is generally dovetail-like in shape and has stab and load flanks and flat roots and crests;

wherein the box member internal thread increases in width in one direction of the box and the pin member external thread increases in width in another direction of the pin member such that the internal thread and the roots, crests, and flanks of the external thread move together to form a seal that resists fluid flow between the seals;

a fluoropolymer-based coating applied to specific regions of the internal and external threads; and

a resin coating disposed in the region of the external and internal threads free of the fluoropolymer-based coating;

wherein the fluoropolymer-based coating and the resin coating together form a substantially uniform coating over the entire surface of the internal and external threads.

2. The threaded joint of claim 1, wherein the fluoropolymer-based coating is applied to substantially central regions of thread crests and thread roots of the internal and external threads.

3. The threaded joint of claim 1, wherein the fluoropolymer-based coating comprises a mixture of 20 to 40% wt fluoropolymer solids and 40 to 60% wt epoxy resin, wherein the fluoropolymer solids are polytetrafluoroethylene.

4. The threaded joint of claim 1, wherein the chemical coating is applied to the entire surface of the internal and external threads prior to application of the fluoropolymer-based coating.

5. The threaded joint of claim 4, wherein the chemical coating is selected from the group consisting of a phosphate coating, an oxalate coating, and a borate coating.

6. The threaded joint of claim 1, wherein the entire surface of the internal and external threads is subjected to a mechanical surface treatment prior to application of the fluoropolymer-based coating.

7. The threaded joint of claim 1, wherein the fluoropolymer-based coating comprises a radial thickness in the range of 10 to 40 microns.

8. The threaded joint of claim 1, wherein the resin coating comprises a thickness in the range of 10 to 40 microns.

9. The threaded joint of claim 1, wherein the fluoropolymer-based coating comprises polytetrafluoroethylene.

10. The threaded joint of claim 1, wherein the resin coating does not adhere to the fluoropolymer-based coating.

11. A method of modifying a threaded surface of a pipe joint, the method comprising:

providing a pin member having external wedge threads, and a box member having internal wedge threads that correspondingly mate with the external wedge threads of the pin member, the internal wedge threads and the external wedge threads generally having a dovetail shape;

surface treating the entire surfaces of the internal and external wedge threads;

applying a fluoropolymer-based coating to specific areas of the internal and external wedge threads; and

after applying the fluoropolymer-based coating, applying a resin coating to the entire thread surface of the internal and external threads, wherein the resin coating is configured to adhere to areas free of the fluoropolymer-based coating.

12. The method of claim 11, wherein the surface treatment comprises applying a chemical treatment selected from the group consisting of a phosphate coating, an oxalate coating, and a borate coating.

13. The method of claim 11, wherein the surface treatment comprises applying a mechanical treatment.

14. The method of claim 11, further comprising applying a fluoropolymer-based coating to substantially central regions of thread crests and thread roots of the internal and external threads.

15. The method of claim 11 further comprising forming a single, uniform layer over the entire surface of the internal and external threads having the fluoropolymer-based coating and the resin coating.

16. The method of claim 11, further comprising providing the internal and external threads with a surface roughness in a range of 2 microns to 6 microns prior to applying the fluoropolymer-based coating.

17. The method of claim 11, further comprising curing the resin coating by heating after applying to the internal and external threads.

18. The method of claim 11, further comprising providing the solvent mixture with a fluoropolymer-based coating to apply the fluoropolymer-based coating.

19. The method of claim 18, wherein the solvent comprises 2-methoxy-1-methyl-ethyl acetate and xylene.

20. The method of claim 18, wherein the fluoropolymer-based coating is present in the mixture in the range of 20 to 40% wt and the solvent is present in the range of 60 to 70% wt.

21. The method of claim 11, wherein the resin coating does not adhere to the fluoropolymer-based coating.