Connecting device for cylindrical members

Abstract

The present invention relates to a connection device (1) comprising a first tubular member (3), a second tubular member (2) and a coupling sleeve (4) for connecting the first tubular member (3) and the second tubular member (2), wherein a first male portion (6) of the first tubular member (3) has a free end provided with an annular sealing lip (16), the sealing lip (16) being configured to cover an outer sealing surface (14) of the second tubular member (2), the sealing lip (16) having an outer periphery (17) on which an external thread portion (12) is formed.

Description

Technical Field

[0001] The present invention relates to a connecting device for providing a sealed connection between two cylindrical members. The present invention relates in particular to a connecting device used in a gas well or an oil well and constituting a drill string, a casing string or a production string.

Background Art

[0002] In the prior art, a connecting device configured to be used in a gas well or an oil well is known, which includes a first cylindrical member, a second cylindrical member, and a coupling sleeve for hermetically coupling the first cylindrical member and the second cylindrical member to each other. Each cylindrical member has a male portion with a thread that is screwed into a female portion with a thread of the coupling sleeve.

[0003] Regarding the above-mentioned type of connecting device, one in which a flange protruding inward is provided on the coupling sleeve is known. Such a connecting device is described, for example, in French Patent Application Publication No. 3027649. This flange has two axial abutment surfaces, and these axial abutment surfaces are configured to cooperate with each corresponding axial abutment surface provided at the free ends of the first and second cylindrical members. The sleeve further has two sealing surfaces that cooperate with each corresponding sealing surface of the first and second cylindrical members. Such a connecting device is not entirely satisfactory. The reason is particularly that the flange and the two sealing surfaces complicate the coupling sleeve and require its machining cost.

[0004] U.S. Patent Application Publication No. 2012 / 0074692 solves the above problems by providing a connection device that realizes a contact function and a sealing function between two free ends of two cylindrical members screwed into a coupling sleeve. To achieve this, axial contact surfaces are provided at the free ends of the first and second cylindrical members. Further, an annular sealing lip is provided at the free end of one of the cylindrical members, and when both axial contact surfaces come into contact with each other, the sealing lip interferes with a frustoconical sealing surface provided on the outer surface of the other cylindrical member to seal the connection. However, such a connection device is not entirely satisfactory. In fact, the axial contact surface must be large enough to withstand a considerable tightening torque applied when screwing one of the cylindrical members into the coupling sleeve until the axial contact surface of one cylindrical member contacts the axial contact surface of the other cylindrical member. Therefore, the amount of material for making the annular sealing lip must be small, which makes the lip particularly fragile and unable to guarantee the reliability of the contact between the sealing lip and the corresponding frustoconical sealing surface. SUMMARY OF THE INVENTION

[0005] One essential idea of the present invention is to provide the above type of connection device that simplifies manufacturing and guarantees highly reliable sealing of the connection.

[0006] In one embodiment, the present invention provides a connecting device including a first cylindrical member, a second cylindrical member, and a coupling sleeve for connecting the first cylindrical member and the second cylindrical member. The coupling sleeve includes a first female portion having a first internal thread and a second female portion having a second internal thread. The first cylindrical member includes a first male portion, and the second cylindrical member includes a second male portion. The first male portion has a first external thread configured to cooperate with the first internal thread of the coupling sleeve. The second male portion has a second external thread configured to cooperate with the second internal thread of the coupling sleeve to screw-engage the first male portion with the first female portion and the second male portion with the second female portion. The first male portion has a free end provided with a first axial abutting surface. The second male portion has a free end provided with a second axial abutting surface and an outer sealing surface extending between the second axial abutting surface and the second external thread. When the first male portion and the second male portion are joined at a joining position within the first female portion and the second female portion, the second axial abutting surface is configured to contact the first axial abutting surface. The free end of the first male portion further has an annular sealing lip protruding axially from the first axial abutting surface. When the first axial abutting surface and the second axial abutting surface contact each other, the sealing lip is configured to cover the outer sealing surface and make radial sealing contact therewith. The sealing lip has an outer peripheral portion, and a part of the first external thread is formed on the outer peripheral portion.

[0007] The connecting device having the above configuration is particularly advantageous in that it simplifies the manufacture of the coupling sleeve because the space between the first cylindrical member and the second cylindrical member is sealed. Further, the presence of the first external thread on the sealing lip results in a relatively large amount of material being used to form the sealing lip. Since the amount of material used to form the sealing lip is relatively large in this way, the sealing lip has sufficient rigidity to ensure sealing contact with the outer sealing surface and to ensure the sealing of the device.

[0008] The connecting device as described above can include one or more of the following configurations according to the embodiment.

[0009] In one embodiment, the first male thread portion has a conical portion and a cylindrical portion, and the cylindrical portion is located axially between the conical portion and the free end of the first male portion such that at least a part of the cylindrical portion is disposed in the sealing lip. With such a configuration, the radial thickness of the sealing lip increases, thereby increasing the rigidity of the sealing lip and improving the reliability of the sealing of the device.

[0010] In one embodiment, the first female thread portion that cooperates with the cylindrical portion of the first male thread portion is conical.

[0011] In one embodiment, the cylindrical portion of the first male thread portion and the first conical female thread portion cooperate by interference, preferably by axial interference, to provide a self-locking action.

[0012] To achieve this, in one embodiment, the first male thread portion includes a thread portion having an engagement flank surface (flanc d’engagement) on the free end side of the first male portion and a loading flank surface (flanc porteur) on the opposite side. The first male thread portion has an axial pressure zone at the coupling position. The axial pressure zone extends between a first zone where axial interference starts between the free end of the first male portion and the corresponding surface of the first female thread portion and a second zone. From the second zone, the engagement flank surface does not interfere with the corresponding surface of the first female thread portion, and from the second zone, the loading flank surface interferes with the corresponding zone of the first female thread portion.

[0013] In one embodiment, the axial pressure zone has 1 to 4 teeth.

[0014] In one embodiment, either one of the first male portion or the second male portion is a mill end, and the other is a field end, and the mill end is configured to be coupled to the coupling sleeve in front of the field end.

[0015] In an advantageous embodiment, the first male portion is the mill end and the second male portion is the field end. Alternatively, the first male portion is the field end and the second male portion is the mill end.

[0016] In one embodiment, the coupling sleeve has an additional axial abutment surface that projects radially inward from an intermediate portion located between the first female thread portion and the second female thread portion, and the sealing lip is configured to be in axial contact with the additional axial abutment surface when the first male portion is in the coupling position.

[0017] In one embodiment, the first cylindrical member includes a visual marker disposed at a predetermined distance from the first axial abutment surface. Such a visual marker can ensure that the first cylindrical member is positioned at a predetermined relative position with respect to the coupling sleeve.

[0018] In one embodiment, the teeth at the end of the first male thread portion are configured to contact the additional axial abutment surface at the coupling position. In other words, the teeth at the position closest to the free end of the sealing lip in the first male thread portion are configured to cooperate with the additional axial abutment surface. In one embodiment, the radial height of the additional abutment surface is at least half of the radial height of the teeth at the end. In one embodiment, the radial height of the additional abutment surface is not more than the radial height of the teeth at the end.

[0019] In one embodiment, the second male thread portion is frustoconical, and the second female thread portion is frustoconical.

[0020] In one embodiment, the coupling sleeve has an intermediate portion without a thread disposed between the first female thread portion and the second female thread portion. Such an intermediate portion is advantageous in that it serves as an empty space for receiving excess grease.

[0021] In one embodiment, the axial length of the intermediate portion is equal to or greater than one thread pitch of the first male thread portion, and preferably exceeds two thread pitches of the first male thread portion. The above thread pitch is, for example, the separation distance between the engaging flank surfaces or the loading flank surfaces of two consecutive teeth of the first male thread portion. By having the intermediate portion with such a length, a relatively large empty space for receiving the first male thread portion is formed.

[0022] In one embodiment, at the coupling position, one end of the intermediate portion is axially sandwiched between the free end of the sealing lip and the first axial contact surface. Preferably, the axial distance of the one end of the intermediate portion from the first axial contact surface is equal to or less than one thread pitch of the first male thread portion. With such a configuration, the stress concentrated on the R portion at the tip of the contact portion is reduced. Further, the above configuration provides excellent axial stability of the sealing lip, thereby providing a more reliable seal for the connection.

[0023] In one embodiment, the intermediate portion forms a recess, and a part of the first male thread portion is installed in the recess.

[0024] In one embodiment, the intermediate portion is arranged such that when the first axial contact surface and the second axial contact surface come into contact with each other, the sealing lip contacts the outer sealing surface radially inside the intermediate portion.

[0025] In one embodiment, the radial sealing contact between the sealing lip and the outer sealing surface when the first axial contact surface and the second axial contact surface come into contact with each other is made with a radial interference of unit millimeters that is at least twice the radial distance by which the first male thread portion and the intermediate portion of the coupling sleeve are separated. Preferably, the distance between the first male thread portion and the intermediate portion is the distance measured by the teeth at the end of the first male thread portion.

[0026] In one embodiment, the radial sealing contact between the sealing lip and the outer sealing surface when the first axial contact surface and the second axial contact surface come into contact with each other is made with a radial interference that deforms the sealing lip radially outward so that the first male thread portion contacts the intermediate portion of the coupling sleeve. Such contact provides excellent radial stability in the installation of the sealing lip with respect to the intermediate portion, thereby ensuring a highly reliable seal.

[0027] In one embodiment, the first cylindrical portion, the second cylindrical portion, and the coupling sleeve are made of steel.

[0028] In one embodiment, in the interference zone, the first male thread portion contacts the first female thread portion with a degree of interference greater than the degree of interference between the second male thread portion and the second female thread portion, preferably with a degree of interference 10% greater than the degree of such interference. The degree of such interference relates to, for example, the interference depth in unit millimeters or the measurement of the interfering surface. In this way, the tightening torque of the first male portion becomes greater than the tightening torque of the second male portion, thereby preventing the first male portion from coming off the coupling sleeve when the second male portion is screwed.

[0029] By considering the detailed description of a plurality of specific embodiments of the present invention with reference to the following attached drawings, the present invention can be better understood, and other objects, details, configurations, and advantages of the present invention will become clearer. The following specific embodiments of the present invention are merely non-limiting examples.

Brief Description of the Drawings

[0030]

Figure 1

Figure 2

Figure 3

Figure 4

[0031] In the specification and drawings, the X-axis is the screwing axis of the cylindrical member of the connection device. By convention, the "radial direction" is the direction perpendicular to the X-axis, and the axial direction is the direction parallel to the X-axis. The terms "outer" and "inner" define the relative position of the member with respect to the X-axis. Thus, when the member is close to the X-axis, it is regarded as the "inner" side, and conversely, when the member is located at the circumferential part in the radial direction, it is regarded as the "outer" side.

[0032] Hereinafter, the connection device 1 according to the first embodiment will be described with reference to FIGS. 1 and 2. The connection device 1 includes a first cylindrical member 3, a second cylindrical member 2, and a coupling sleeve 4 for hermetically connecting the two cylindrical members 2 and 3 to each other. The cylindrical members 2, 3 and the coupling sleeve 4 are typically made of steel.

[0033] Each of the cylindrical members 2 and 3 has two ends, and only one of the ends is shown in FIG. 1. Male portions 5 and 6 are provided at each end, and these male portions 5 and 6 are configured to be screwed into the female portions 7 and 8 of the coupling sleeve 4. Thereby, a plurality of cylindrical members 2 and 3 can be sequentially hermetically connected to each other, thereby constituting, for example, a drill string, a casing string, or a production string for a gas well or an oil well.

[0034] Each male part 5, 6 is provided with male screw parts 11, 12 configured to cooperate with the female screw parts 9, 10 of each female part 7, 8 of the coupling sleeve 4. More specifically, the male part 6 of the first cylindrical member 3 is provided with a first male screw part 12 configured to cooperate with the first female screw part 10 of the coupling sleeve 4, and the male part 5 of the second cylindrical member 2 is provided with a second male screw part 11 configured to cooperate with the second female screw part 9 of the coupling sleeve 4. Advantageously, the coupling sleeve 4 has an intermediate part 18 arranged between the first female screw part 10 and the second female screw part 9, whereby an empty space for receiving excess grease is formed. In the illustrated example, the diameter of the intermediate part 18 is substantially equal to the diameter at the root of the first adjacent thread of the first and second female screw parts 9, 10 of the coupling sleeve 4. In a variant form, the diameter of the intermediate part can also be made slightly smaller than the diameter at the root of the first adjacent thread of the first female screw part 10 of the coupling sleeve 4, which helps to further enhance the self-locking action (described later) of the male part 6 of the first cylindrical member 3 of the coupling sleeve 4.

[0035] In the embodiment described below, the male portion 6 of the first cylindrical member 3 is configured to be screwed into the coupling sleeve 4 before the male portion 5 of the second cylindrical member 2 is screwed into the coupling sleeve. In this way, for example, the coupling sleeve 4 can be pre-assembled to the male portion 6 of the first cylindrical member 3 at the factory, and then, at a later time, the coupling sleeve 4 can be assembled to the male portion 5 of the second cylindrical member 2 at the installation site of the gas well or oil well. In this case, the male portion 6 of the first cylindrical member 3 is usually referred to as the "mill end", and the male portion 5 of the second cylindrical member 2 is referred to as the "field end". In order to prevent the first cylindrical member 3 from coming off the coupling sleeve 4 when the second cylindrical member 2 is screwed together, the tightening torque of the first cylindrical member 3 on the coupling sleeve 4 generated by the cooperation of the first male thread portion 12 and the first female thread portion 10 of the coupling sleeve 4 is made larger than the tightening torque of the second cylindrical member 2 generated by the cooperation of the second male thread portion 11 and the second female thread portion 9 of the coupling sleeve 4, and preferably made 10% or more larger. In order to ensure this, the surface area of the interference zone where the thread portion of the first male thread portion 12 contacts the thread portion of the first female thread portion 10 when in the contact position (also referred to as the "coupling position") is made larger than the surface area of the interference zone between the thread portion of the second male thread portion 11 and the thread portion of the second female thread portion 9, and preferably made 10% or more larger. Alternatively or additionally to the above configuration, the degree of interference per millimeter where the thread portion of the first male thread portion 12 contacts the thread portion of the first female thread portion 10 when in the coupling position is made larger than the degree of interference per millimeter between the thread portion of the second male thread portion 11 and the thread portion of the second female thread portion 9, and preferably made 10% or more larger.

[0036] In the embodiment shown in FIGS. 1 and 2, the first female screw portion 10 of the coupling sleeve 4 is formed in a frustum of a cone shape, whereby the first female screw portion 10 is inclined with respect to the X-axis. In other words, the diameter of the screw portion of the first female screw portion 10 of the coupling sleeve 4 expands from the intermediate portion 18 of the coupling sleeve 4 toward the end portion on the first female screw portion 10 side in the coupling sleeve 4. The first male screw portion 12 of the first cylindrical member 3 has a shape combining a cylinder and a cone (hereinafter referred to as "cylindrical and conical shape"). Specifically, the first male screw portion 12 includes a frustum of a cone portion where the diameter of the screw portion decreases toward the free end of the male portion 6 of the first cylindrical member 3, and a subsequent cylindrical portion where the diameter of the screw portion is maintained constant up to the free end of the male portion 6.

[0037] In an advantageous embodiment, the cylindrical portion of the first male screw portion 12 has a length sufficient to achieve a self-locking action, that is, a length sufficient to increase the tightening torque due to interference when the first male screw portion 12 is coupled to the first female screw portion 10. Therefore, in order to obtain a predetermined tightening torque, the relative position of the male portion 6 in the coupling sleeve 4 as a function of torque can be determined within the range of manufacturing tolerances. In practice, the male portion 6 of the first cylindrical member 3 is screwed into the coupling sleeve 4 until the coupling torque threshold is reached, whereby it is guaranteed that the first member with respect to the coupling sleeve 4 is positioned at a predetermined relative position.

[0038] As shown in FIG. 2, each screw portion of the first and second male screw portions 11, 12 is constituted by an engagement flank surface 19 and a loading flank surface 20. The engagement flank surface 19 is disposed upstream of the loading flank surface 20. In other words, the engagement flank surface 19 of the first male screw portion 12 is on the free end side of the first cylindrical member 3, while the loading flank surface 20 is on the side opposite to the free end.

[0039] Referring to the embodiment of FIG. 3, in order to realize the above-described self-locking action by utilizing the frustum-conical and cylindrical frustum-conical shapes of the first female thread portion 10 and the first male thread portion 12, the first male thread portion 12 has an axial pressure zone 21. This axial pressure zone extends downstream and extends between a first zone 22 where interference starts between the engagement flange surface 19 and the corresponding surface of the first female thread portion 10, and a second zone 23. From the second zone 23, the engagement flange surface 19 does not interfere with the corresponding surface of the first female thread portion 10, and from the second zone 23, the loading flange surface 20 interferes with the corresponding zone of the first female thread portion 10. Preferably, the axial pressure zone 21 has 1 to 4 teeth, and each tooth is a portion that extends 360° around the X-axis among the thread portions. In other words, the axial pressure zone 21 corresponds to a portion of the thread portion of the first male thread portion 12 that extends in an angular range of 360° to 1440° around the X-axis. Thereby, it is guaranteed that a satisfactory self-locking action is realized, especially when screwing the mill end portion. Further, due to the configuration of the above-described axial pressure zone 21, the axial stability of the sealing lip 16 described later is also enhanced.

[0040] In other embodiments, the first female thread portion 10 and the first male thread portion 12 do not have a structure that provides the above-described self-locking action. In this case, a visual marker can be provided on the first cylindrical member 3 at a predetermined distance from the free end of the male portion 6 of the first cylindrical member 3, thereby ensuring that the first cylindrical member 3 is positioned at a predetermined relative position with respect to the coupling sleeve 4.

[0041] Furthermore, the second female thread portion 9 of the coupling sleeve 4 and the second male thread portion 11 of the second cylindrical member 2 are frustum-conical. Also, the diameter of the thread portion of the second female thread portion 9 of the coupling sleeve 4 expands from the intermediate portion 18 of the coupling sleeve 4 toward one end of the coupling sleeve 4, and the diameter of the thread portion of the second male thread portion 11 of the second cylindrical member 2 shrinks toward the free end of the second cylindrical member 2.

[0042] As shown in the detailed view of FIG. 2, a first axial contact surface 15 is provided at the free end of the male part 6, and an annular sealing lip 16 that axially protrudes from the first axial contact surface 15 and is located radially outside the first axial contact surface 15 is provided. At the free end of the male part 5 of the second cylindrical member 2, an axial contact surface 13 of the coupling sleeve 42 and an outer sealing surface 14 extending between the second axial contact surface 13 and the second male thread portion 11 are provided. The outer sealing surface 14 extends obliquely with respect to the X-axis, so that the diameter of the male part 5 decreases from the second male thread portion 11 toward the second axial contact surface 13.

[0043] Thereby, when the male part 5 of the second cylindrical member 2 is screwed into the coupling sleeve 4, it can be seen that the second axial contact surface 13 axially contacts the first axial contact surface 15, whereby the second cylindrical member 2 has reached the desired predetermined position.

[0044] Furthermore, the sealing lip 16 contacts the outer sealing surface 14, thereby ensuring the sealing between the first cylindrical member 3 and the second cylindrical member 2.

[0045] More specifically, the sealing lip 16 has an inner surface having a seal seat portion, which is also referred to as the sealing surface of the sealing lip 16. The inner surface of the sealing lip 16 is machined such that when the second cylindrical member 2 is screwed into the coupling sleeve 4, the outer sealing surface 14 contacts the seal seat portion of the inner surface of the sealing lip 16 and elastically deforms the seal seat portion of the sealing lip 16. Such interference contact ensures the sealing between the outer sealing surface 14 and the sealing lip 16.

[0046] In the illustrated embodiment, the first axial abutment surface 15 and the second axial abutment surface 13 have a frustoconical shape that coincides with each other. More specifically, the first axial abutment surface 15 has a frustoconical shape in which the radial cross-section of the first axial abutment surface 15 decreases toward the end of the first male portion 6, while the second axial abutment surface 13 has a frustoconical shape in which the radial cross-section of the second axial abutment surface 13 decreases toward the end of the second male portion 5. In an advantageous embodiment, the semi-apex angle of the above-described frustoconical shape that coincides with each other is less than 90°, preferably more than 70°, for example about 75°. The above-described inclination of the first and second axial abutment surfaces 13, 15 has a tendency to press the outer sealing surface 14 against the sealing lip 16 when the two axial abutment surfaces 13, 15 cooperate, thereby ensuring satisfactory sealing contact.

[0047] As shown in FIGS. 1 and 2, the sealing lip 16 has an outer peripheral portion 17, and a part of the first male thread portion 12 is formed on the outer peripheral portion 17. Such a configuration is particularly advantageous in that the sealing lip 16 is strengthened by increasing the amount of material constituting the sealing lip 16. Advantageously, the amount of material constituting the sealing lip 16 is also increased by the fact that the shape of the first male thread portion 12 at the end of the first male portion 6 is cylindrical.

[0048] In an alternative embodiment, the structure of the free ends of the first and second male portions 5, 6 is reversed such that the sealing lip 16 is provided on the male portion 5 and the outer sealing surface 14 is provided on the male portion 6.

[0049] FIG. 4 shows another embodiment, in which an additional axial abutting surface 24 is formed in the middle portion 18 of the coupling sleeve 4, and when the first cylindrical member 3 is screwed onto the coupling sleeve 4, the end of the sealing lip 16 abuts against the additional axial abutting surface 24. With such an additional axial abutting surface 24, even when the first male screw portion 12 and the first female screw portion 10 do not provide a self-locking action, it is ensured that the first cylindrical member 3 is positioned at a predetermined relative position with respect to the coupling sleeve 4. In the illustrated embodiment, the additional axial abutting surface 24 is formed by the flank surface of an annular flange 25 that projects radially inward of the coupling sleeve 4.

[0050] The present invention has been described with reference to a plurality of specific embodiments, but the present invention is by no means limited to these embodiments, and it is obvious that all technical equivalents of the means described in this application and combinations thereof are included when they belong to the scope of the present invention.

[0051] When using the verb "comprise" or "include", including when using its conjugated forms, it does not exclude the existence of other elements or steps in addition to the elements or steps described in the claims.

[0052] In the claims, reference signs in parentheses shall not be construed as limiting the claims.

Claims

1. A connecting device (1) comprising a first cylindrical member (3), a second cylindrical member (2), and a coupling sleeve (4) for connecting the first cylindrical member (3) and the second cylindrical member (2), wherein the coupling sleeve (4) comprises a first female part (8) having a first female thread portion (10) and a second female part (7) having a second female thread portion (9), the first cylindrical member (3) comprises a first male part (6), and the second cylindrical member (2) comprises a second male part (5), the first male part (6) has a first male thread portion (12) configured to cooperate with the first female thread portion (10) of the coupling sleeve (4), the second male part (5) has a second male thread portion (11) configured to cooperate with the second female thread portion (9) of the coupling sleeve (4) to screw-connect the first male part (6) to the first female part (8) and the second male part (5) to the second female part (7), the first male part (6) has a free end provided with a first axial contact surface (15), the second male part (5) has a free end provided with a second axial contact surface (13) and an outer sealing surface (14) extending between the second axial contact surface (13) and the second male thread portion (11), when the first male part (6) is in a coupling position within the first female part (8) and the second male part (5) is in a coupling position within the second female part (7), the second axial contact surface (13) is configured to contact the first axial contact surface (15), the free end of the first male part (6) further has an annular sealing lip (16) protruding axially from the first axial contact surface (15), when the first axial contact surface (15) and the second axial contact surface (13) are in contact with each other, the sealing lip (16) is configured to cover the outer sealing surface (14) and make radial sealing contact with the outer sealing surface (14), the sealing lip (16) has an outer peripheral portion (17), a part of the first male thread portion (12) is formed on the outer peripheral portion (17), the first male thread portion (12) has a conical portion and a cylindrical portion, the cylindrical portion is located axially between the conical portion of the first male thread portion (12) and the free end of the first male part (6) such that at least a part of the cylindrical portion is arranged on the sealing lip A connecting device (1), characterized in that...

2. The first male thread portion (12) comprises a thread portion having an engaging flange surface (19) on the free end side of the first male portion (6) and a loading flange surface (20) on the reverse side. The first or second male thread portion (11, 12) has an axial pressure zone (21). The axial pressure zone (21) extends between a first zone (22) where axial interference starts between the free end of the first male portion (6) and the corresponding surface of the engaging flange surface (19) and the first female thread portion (10), and a second zone (23). From the second zone (23), the engaging flange surface (19) does not interfere with the corresponding surface of the first female thread portion (10), and from the second zone (23), the loading flange surface (20) interferes with the corresponding zone of the first female thread portion (10). The connecting device (1) according to claim 1.

3. The axial pressure zone (21) has 1 to 4 teeth. The connecting device (1) according to claim 2.

4. The coupling sleeve (4) has an additional axial abutment surface (24) that projects radially inward from an intermediate portion (18) located between the first female thread portion (10) and the second female thread portion (9) towards the inside of the coupling sleeve (4). The sealing lip (16) is configured to contact the additional axial abutment surface (24) at the coupling position. The connecting device (1) according to any one of claims 1 to 3.

5. At the coupling position, the teeth at the end of the first male thread portion (12) are configured to contact the additional axial abutment surface (24). The radial height of the additional abutment surface (24) is at least half of the radial height of the teeth at the end. The connecting device (1) according to claim 4.

6. The second male thread portion (11) is frustoconical, and the second female thread portion (9) is frustoconical. The connecting device (1) according to claim 1 or 2.

7. The coupling sleeve (4) has a threadless intermediate portion (18) arranged between the first female thread portion (10) and the second female thread portion (9). The connecting device (1) according to claim 1.

8. The axial length of the intermediate portion (18) is at least one thread pitch of the first male thread portion (12). The connecting device (1) according to claim 7.

9. At the coupling position, one end of the intermediate portion (18) is axially sandwiched between the free end of the sealing lip (16) and the first axial contact surface (15). The connecting device (1) according to claim 7 or 8.

10. At the coupling position, when the first axial contact surface (15) and the second axial contact surface (13) are in contact with each other, the intermediate portion (18) is arranged such that the sealing lip (16) is in radial contact with the outer sealing surface (14) on the radially inner side of the intermediate portion (18). The connecting device (1) according to claim 7.

11. The first cylindrical member (3), the second cylindrical member (2), and the coupling sleeve (4) are made of steel. The connecting device (1) according to claim 1 or 2.

12. The first male thread portion (12) contacts the first female thread portion (10) with a degree of interference greater than the degree of interference between the second male thread portion (11) and the second female thread portion (9) in the interference zone. The connecting device (1) according to claim 1 or 2.

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