JP2914197B2 - Threaded fittings for oil country tubular goods - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the exploration of oil and natural gas.
The present invention relates to a threaded joint used for connecting oil country tubular goods used for production and the like, and particularly to a face-sealing type threaded joint.

[0002]

2. Description of the Related Art Generally, an API standard round screw joint or a buttress screw joint is used as a threaded joint for connecting an oil country tubular good. However, the depths of oil and gas wells are increasing year by year, and due to the severer mining conditions, the threaded joints are subjected to large three-dimensional loads and are exposed to severe stress. In particular, in a production well, a circumferential stress from inside the pipe acts to maintain the airtight performance under triaxial stress.

[0003] In response to such demands, round screw joints and buttress screw joints have become insufficient.
Therefore, a face-sealing type screw joint having a metal sealing surface as disclosed in Japanese Patent Application Laid-Open No. 5-87275 has been developed, and has already begun to be used in many wells. The schematic configuration of the face seal type screw joint will be described with reference to FIGS.

Here, the oil country tubular goods P, P are coupled C
Connected by Reference numeral 10 denotes an end portion of the oil country tubular good P inserted into the coupling C, which is a pin portion. Reference numeral 20 denotes a box formed in the coupling C to receive the pin 10. A screw joint connects the pin portion 10 and the box portion 20 by screwing.

In the face-sealing type threaded joint, the pin portion 10 has a tapered male thread portion 11 whose diameter gradually decreases toward the tip.
On the outer surface. At the end of the male screw part 11, a tapered seal part 12 whose diameter is gradually reduced toward the tip is provided. The tip of the pin portion 10 is a shoulder portion 13 that is steeply inclined in a direction opposite to the external thread portion 11 and the seal portion 12. The box part 20 has a female screw part 21 corresponding to the male screw part 11 on the inner surface, a seal part 22 corresponding to the seal part 12 is provided in the back, and a shoulder part 13 further in the back. A corresponding shoulder portion 23 is provided.

When the male screw 11 is screwed into the female screw 21, the seals 12, 22 come into contact with each other, and the shoulders 13, 23 abut against each other, thereby forming the pin 10.
And the box part 20 is face-sealed. In order to generate a sufficient surface pressure on the sealing surface, a diameter difference called an interference amount is provided between the sealing portion 12 on the pin side and the sealing portion 22 on the box side.

The amount of interference S is represented by S = D _PX −D _BX D _PX : the apex diameter of the pin side seal portion (apex point) D _BX : the apex diameter of the box side seal portion (apex point), where S> 0 That is, D _PX > D _BX . By providing the interference amount, the sealing portions 12
2 begins [FIG. 2 (a)], and the shoulder portions 13,
23 come into contact with each other to complete the connection [FIG. 2 (b)]. The axial stroke from the start of the interference between the seal portions 12 and 22 to the completion of the connection is herein referred to as a tightening amount MOS (make-up on seal).

[0008]

In such a threaded joint for oil country tubular goods of the metal surface seal type, seizure is liable to occur on the seal portions 12, 22 due to the difference in diameter between the seal portions 12, 22. When this seizure occurs, the sealing surface is roughened, a gap is locally formed, or a portion of excessive interference is formed, and the sealing performance is impaired. In particular, the joint used in a relatively large oil well pipe having a diameter which is said casing size, long sliding distance L _S of the seal portion 12 and 22 which will be described later, and to the contact surface pressure P is large, seizure occurs Cheap. Also, when the oil country tubular goods are made of stainless steel, which is an alloy of nickel or chrome, or pure titanium / titanium alloy, the thermal conductivity is lower than that of steel, and the heat accumulation in the sliding part is large. But seizures often occur.

It is an object of the present invention to provide a face-sealing type threaded joint for an oil country tubular good, which suppresses seizure of a sealing face.

[0010]

In order to prevent the seizure of the sealing surface, the present inventors have conducted investigations on the occurrence of the seizure and found the following facts.

1) In a face-sealed oil country tubular good threaded joint having a tapered metal seal surface as shown in FIGS. 1 and 2, the pin-side seal is screwed in due to a difference in diameter between the seal portions 12 and 22. The tip 12 ′ of the part 12 collides with the entrance 22 ′ of the box-side seal part 22, and that part is easily scratched. If the screwing is further continued, seizure occurs in the seal portions 12, 22 with the flaw as a starting point. In the drill pipe, the pipes are sequentially discharged to the outside of the well while performing a so-called break for breaking a drill bit for replacement or the like. Since many flaws are induced on 22, seizure is likely to occur.

2) With respect to the seizure caused by the stab type contact, the tip of the pin-side seal portion 12 is completely inserted into the inside of the box-side seal portion 22.
As the seal section 12, 22 starts to interference, determining the length L _B of the box side sealing portion 22 becomes an effective measure.

3) In the face-sealing type threaded joint for oil country tubular goods, the sealing portions 12, 22 are also used until the interference between the sealing portions 12, 22 starts and the coupling is completed, that is, while the tightening amount MOS is screwed. Performs relative spiral sliding while maintaining high surface pressure. Assuming that the sliding amount is a sliding distance L _S , the sliding distance L _S is generally expressed by the following equation. _{L S = D S × π ×} (MOS / l) = D S × π × (S × T S / l) where S: the amount of interference _{(= D PX -D BX) MOS} : tightening amount 1 / T _S: Tilt (taper) of seal part π: Pi ratio D _S : Diameter of seal part l: Pitch of thread part

[0014] Incidentally, D described above the sealing portion diameter D _S
It is a diameter representative of the seal portion, such as _PX (apex diameter of pin side seal portion), D _BX (apex diameter of box side seal portion), and DB (maximum diameter of pin side seal portion).

[0015] 4) According to a survey conducted by the inventors of the present invention, W = P (surface pressure) × L _S (W seizure is likely to occur the larger represented by the sliding distance). Here, if the surface pressure P is within the elastic range, the interference amount S (= D _PX −
D _BX ), but the interference amount S cannot be reduced in order to ensure good sealing performance. Therefore, reducing the sliding distance L _S is effective for preventing image sticking.

5) The relationship between the sliding distance L _S and the seizure was investigated for various tube outer diameters, and the relationship shown in FIG. 3 was obtained. That is, sliding distance L _S / outside diameter OD ≦ −0.0093 × (outside diameter OD)
When the sliding distance L _S satisfies the relationship of +4.73, seizure caused by the sliding distance L _S is prevented. This is because, when the pipe outer diameter OD is the same, it is necessary to make the sliding distance L _S smaller than the upper limit determined by the pipe outer diameter OD.
Means that it decreases as becomes smaller.

6) In a thread seal for oil country tubular goods of the face seal type, a dope is used to lubricate the seal portions 12 and 22. If the seal parts 12 and 22 interfere during screwing,
The dope existing between the tip of the male screw portion 11 on the pin side and the interference point is confined in the space shown by hatching in FIG. The confined dope is compressed as the tightening progresses to generate a dope pressure. This doping pressure also contributes to improving the lubricity of the seal portions 12 and 22. However, if the dope pressure is too high, it lowers the surface pressure P of the seal portions 12 and 22 and causes a reduction in the sealability. In the conventional threaded joint, the imperfect thread portion existing between the female thread portion 21 on the box side and the seal portion 22 is left, and the dope confined in the narrow space is like a piston by the male thread portion 11 on the pin side. It was in the form of high pressure compression. For this reason, the dope pressure significantly increases, and a decrease in the surface pressure P may decrease the sealing performance.

7) It is effective to provide a circumferential groove in an incompletely threaded portion between the female screw portion 21 and the seal portion 22 on the box side in order to reduce the sealing performance due to the increase in the dope pressure. Becomes

The threaded joint for oil country tubular goods according to the present invention, based on these findings, effectively suppresses seizure of the seal portion without deteriorating the sealability. I do.

The length L _P of the seal portion 12 on the pin side is made larger than the length L _B of the seal portion 22 on the box side.

The length L _B of the box-side seal portion 22 is set such that the seal portions 12 and 22 start to interfere with each other when the tip of the pin-side seal portion 12 enters the inside of the box-side seal portion 12. Set.

[0022] so that the sliding distance L _S ≦ -0.0093 × (outer diameter) ² + 4.73 × sliding distance L _S a (outer diameter) is satisfied.

A peripheral groove 24 having a width of 0.5 to 1.5 pitches, which is expressed by a screw pitch, is provided between the female screw portion 21 on the box side and the seal portion 22 as a space for containing the dope .

[0024]

FIG. 4 shows a threaded joint for oil country tubular goods according to the present invention.
Here is an example. The above four components will be described in detail with reference to FIG.

If the length L _{P of the} pin-side seal portion 12 is shorter than the length L _{B of the} box-side seal portion 22, the shoulder portions 13, 14 will be provided when the tightening is completed.
Do not contact, so-called shouldering is not performed. Therefore, the L _P ≧ L _B.

According to [Requirements], the length L _P of the sealing portion 12 on the pin side normally satisfies the relationship of L _P = L _B + 2-4 mm. The tip portion of the sealing portion 12 of the pin side receives the R processing radius R _P, box side of the seal portion 2
2 of the inlet portion is under R processing of radius R _B.

The taper of the seal portions 12, 22 is a (= 1).
/ T _S ), a value obtained by multiplying a by the tightening amount MOS (a
× MOS) becomes the interference amount S (D _PX −D _BX ) for obtaining the interference between the seal portions 12 and 22. Maximum value S of interference amount S
_{When MAX} is determined, the maximum value MOS _MAX of the fastening amount MOS is determined by the following equation. MOS _MAX = S _MAX / a

Here, a = 1/10, S _MAX = 0.4 mm
Then, the MOS _MAX becomes 4 mm.

If the length L _B of the box-side seal portion 22 is made larger than this MOS _MAX , the seal portion is formed in a state where the tip of the pin-side seal portion 12 enters the inside of the box-side seal portion 22. Interferences 12 and 22 start to prevent seizure due to the above-mentioned slash type contact.

Actually, as described above, there is a tip R (R _P ) at the tip of the pin-side seal portion 12. Considering this, L _B ≧ R _P + MOS _MAX indicates that a slash type contact This is a condition for preventing image sticking.

When the interference amount S is small, MOS <MOS
_MAX , and since the tightening amount MOS is small, seizure tends to be less likely to occur.

The seal outer diameter D _S such as a pin-side seal apex diameter D _PX increases as [of requirements] tube outer diameter OD becomes larger. Therefore, when the taper a of the seal portions 12 and 22 is the same, the sliding distance L _S increases with an increase in the tube outer diameter OD. If the sliding distance L _S is set to a certain value or less irrespective of the tube outer diameter OD, it is apt to be considered that seizure is prevented. However, as shown in FIG. The distance L _S is affected by the tube outer diameter OD. Therefore, the conditions shown in FIG. 3, ie, the sliding distance L _S / outside diameter OD ≦ −0.0093 × (outside diameter OD)
+4.73 Sliding distance L _S ≦ −0.0093 × (outside diameter OD) ² +4.73
× (outer diameter OD) is required. That is, the sliding distance L _S is made smaller than the upper limit value (the right side of the lower equation) determined by the pipe outer diameter OD.

In order to reduce the sliding distance L _S , the tightening amount MOS is reduced. That is, if the amount of interference is the same, the taper of the seal portions 12 and 22 is increased. Thereby, seizure caused by the sliding distance L _S is prevented.

The sliding distance L _S required to prevent seizure is equal to the tube outer diameter.
The following are possible reasons for being affected by OD. As the tube outer diameter increases, the amount of ellipse increases,
The influence of the ellipse occurs when the seal portion interferes. When the elliptical amount is large, seizure is likely to occur. Therefore, the outer diameter of the tube is involved in the seizure limit.

The taper a of the seal portions 12 and 22 is 1/20 (gradient 1.432 °) to 1/4 (gradient 7.125).
°). If it is less than 1.432 °, the sliding distance L _S becomes large even with a small diameter size, and it approaches the seizure limit. If it exceeds 7.125 °, the reduction in surface pressure under axial force increases, which is not good from the viewpoint of leak resistance.

The end face angles of the shoulder portions 13 and 23 are expressed by angles θ _{P and} θ _B with respect to the tube axis _{, and} are preferably 85 to 90 °. If the angle is less than 85 °, the deformation of the inner surface of the shoulder during shouldering increases, which is not preferable. 90 °
If it exceeds, the shape of the shoulder bites into the inner surface of the pipe and the shape does not support the metal seal portion, which is not preferable.

[Construction Requirements] When the interference between the seal portions 12 and 22 starts, the dope confined in front of the male screw portion 11 on the pin side is compressed by subsequent tightening. The volume of the space in which the dope is confined,
Assuming that V is V at the start of the interference and V 'at the completion of the tightening, the compression ratio of the dope is V / V'.

As the compression ratio increases, the dope pressure increases due to the piston effect, causing a decrease in the surface pressure P.

In the conventional threaded joint, since the incompletely threaded portion between the female screw portion 21 on the box side and the seal portion 22 was left undisturbed, the compression ratio was large. , The compression ratio decreases.

Because V in the conventional threaded joint is V
Let o and V 'be Vo', let Vn be the volume of the peripheral groove 24 when the interference of the seal portions 12 and 22 starts, and Vn 'the volume of the peripheral groove 24 when the tightening is completed. 24
The compression ratio changes as follows: Vo / Vo '→ (Vo + Vn) / (Vo' + Vn '). Here, since VnｎVn ', Vo / Vo'> (Vo + Vn) / (Vo '+ Vn'). As a result, the dope pressure at the time of completion of tightening is reduced, and an adverse effect on the surface pressure P is avoided. The dope pressure at the completion of the tightening is desirably 400 kg / cm ² or less.

The width W of the circumferential groove 24 is expressed as the pitch of the threaded portion and is 1.5 to 2 pitches. When the pitch is less than 1.5 pitches, the use of a two-piece chaser cannot complete the cutting of the screw in the groove. If the pitch exceeds 2 pitches, the engagement length of the pin and the screw of the box decreases, so that the transmission efficiency of the axial force decreases.

The depth of the circumferential groove 24 is determined by the diameter D of the groove bottom.
Expressed as _A , the thread cut-up diameter D of the female thread on the box side
_B + 0.2 to 0.5 mm is desirable. If B _B is less than +0.2 mm, there is a possibility that the screw bottom and the groove bottom may interfere with each other when the box screw cheser is worn. If D _B +0.5 mm is exceeded, the cross-sectional area of the groove decreases from the cross-sectional area of the pipe, and the strength of the joint decreases.

[0043]

EXAMPLES Examples of the present invention will be shown below, and the effects of the present invention will be clarified by comparison with comparative examples.

31/2 "(88.9 mm) x 0.254"
(6.45mm), 7 "(177.8mm) x 0.408"
(10.36 mm), 13.3 / 8 "(339.7 mm) x
For surface oil well pipes of three sizes of 0.514 "(13.06 mm), various face-sealed threaded joints with the specifications shown in Table 1 were trial-produced. The break was repeated, and the number of repetitions is shown in Table 1.

[0045]

[Table 1]

[0046] Having greater than the length L _B of the sealing portion of the length L _P of the box side sealing portion of any of the threaded joint is also pin-side, No. 1, 4, 7 are box side sealing portion length L _B
But because it does not satisfy the _{L B ≧ R P + MOS MAX} , seizing due to contact of the Clog type occurs in the early stage. Nos. 2, 5, and 8 have a sliding distance of L _S ≦ −0.0093 × (outside diameter OD) ² +4.73.
X (outer diameter of the tube) was not satisfied, so that seizure due to the sliding distance L _S occurred early.

On the other hand, since Nos. 3, 6, and 9 satisfy all the conditions, the seizure due to the slash-type contact and the seizure due to the sliding distance L _S are suppressed, and Nos.
The number of repetitions was dramatically increased as compared to 2,4,5,7,8.

Next, in No. 6 medium-diameter threaded joint, a circumferential groove was provided in an incomplete thread portion between the female thread portion on the box side and the seal portion. The width is expressed by the pitch of the thread.
The 1.5 pitch and the depth were represented by the diameter of the groove bottom, and the thread cut-up diameter was +0.3 mm.

The doping amount was 40 g, 70 g, 140 g, 2
The dope pressure after completion of tightening was examined for each of the four stages of 00 grams. The measurement of the dope pressure was performed by a transducer through a tapped hole with a screw installed in the joint. FIG. 5 shows the results of the investigation.

By providing a circumferential groove in the incomplete screw portion on the box side, the doping pressure can be reduced. The effect is more remarkable as the doping amount increases.

[0051]

As described above, the threaded joint for oil country tubular goods according to the present invention can prevent seizure of the seal portion, which is a problem in the face seal type, from seizure due to stab type contact and seizure due to sliding distance. In both cases, it is possible to suppress effectively, and thereby the number of times of repeated use can be greatly increased. In addition, there is no need to reduce the amount of interference necessary for ensuring the sealing performance, and there is no possibility that the sealing performance will be reduced.

[0052] Further, since a space for containing the dope between the female screw portion and the sealing portion of the box side is provided a circumferential groove,
The dope pressure at the time of completion of the tightening can be reduced, whereby the reduction in the surface pressure of the seal portion can be suppressed and the sealing performance can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a face seal type screw joint.

FIG. 2 is a schematic sectional view showing the vicinity of a seal portion of the threaded joint.

FIG. 3 is a table showing an effect of a sliding distance of a seal portion on image sticking.

FIG. 4 is a schematic sectional view showing one example of a threaded joint embodying the present invention.

FIG. 5 is a table showing the influence of the presence or absence of a circumferential groove on the doping pressure.

[Explanation of symbols]

 10 Pin portion 20 Box portion 11, 21 Screw portion 12, 22 Seal portion 13, 23 Shoulder portion 24 Circumferential groove

Continuation of front page (56) References JP-A-61-286688 (JP, A) JP-A-3-234996 (JP, A) JP-A-63-172080 (JP, A) JP-A-2-80886 (JP) , A) JP-A-60-104882 (JP, A) JP-A-48-17125 (JP, A) JP-A-62-102086 (JP, U) JP-A-5-62789 (JP, U) 61-501411 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F16L 15/00 E21B 17/02

Claims (1)

(57) [Claims] 1. A pin portion (10) having a tapered seal portion (12) provided at a tip of a tapered male screw portion (11) and a shoulder portion (13) provided at a tip, and a tapered female thread portion (11). A tapered seal portion (22) is provided at the back of 21), and a box portion (20) provided with a shoulder portion (23) at the innermost portion is screwed and connected to bring the seal portions into contact with each other and to connect the shoulder portions to each other. in the surface-sealing oil well pipe threaded joint of matching, the sealing portion of the length L _P of the box side sealing portion of the pin side (12) with larger than the length L _B of the (22), the sealing portion of the pin side ( In the state where the tip of (12) has entered the inside of the sealing part (22) on the box side, the sealing parts (12, 2)
The box-side seal portion (2) is set so that 2) starts interference.
Set the length _{L B} of 2), the sealing portion during tightening period from the start interference of the seal portion (12, 22) until the shoulder portions (13, 23) abuts the (12, 22) when the relative spiral sliding amount and sliding distance _{L S,} sliding distance _{L S} ≦ -0.0093 × (outer ^diameter) 2 + 4.73 × (outer diameter) sliding distance _{L S} is satisfied And the female screw part (21) on the box side and the seal part (2)
2) As a space to contain the dope,
A circumferential groove (24) having a width of 1.5 to 2 pitches
A threaded joint for oil country tubular goods characterized by being provided .