RU2521123C2 - Threaded connection of drill pipes - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention relates to drilling engineering and refers mainly to threaded connection of drill pipe joints used for geological surveying and oil well drilling. The threaded connection consists of a sleeve, a nipple and a slotted spring installed between the sleeve lip and thrust face of the nipple. At that a gap is formed between the sleeve lip and the nipple thrust face, this gap is liquidated in process of the connection tightening and spring compression and it is equal to the spring pitch and according to its parameters it corresponds exactly to the preset axial load to the inner thrust joint. Upon tightening of the connection the exact axial loads is provided to the outer thrust joint. Reliable functioning of both thrust joints allows increasing axial force of the threaded connection 1.5 times and improving its statistical strength and cyclic life.

EFFECT: provision of the exact preset loads to the inner and outer thrust joints, maintenance of their ratio within the whole operational period.

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Description

The invention relates to drilling equipment and relates mainly to threaded joints of drill pipe locks of oil and exploration assortment.

The closest analogue adopted for the prototype is known, a threaded connection with a tapered thread of a Haidril drill lock / 1 /, which has two thrust joints - an external and an internal one, and, as studies have shown, the presence of an additional internal thrust joint allows 1.5 times increase the tightening torque of the connection / 2 /.

However, such a connection has a significant drawback, namely, that it is practically impossible to provide reliable contact and specified loads simultaneously on three surfaces — tapered threads, external and internal thrust joints, despite the very tight tolerance set to the distance between the external and internal persistent ends and persistent ledges of the nipple and coupling of the connection.

As a result, one of the stubborn joints is underloaded, and the other, on the contrary, is overloaded. Of particular danger is the case when, due to slight deviations from the specified tolerances, the external thrust joint appears to be underloaded, or even completely open, since this leads to accelerated fatigue fracture of the thread and, as a result, to breakage and accident with a drill string. Bench fatigue tests during alternating cantilever bending of full-scale drill pipe SSK-59 with such joints showed that depending on the accuracy of the parameters forming their thrust joints, the cyclic durability of the joint may differ by an order of magnitude / 2 /.

It is this drawback that explains the fact that, despite the proposals of individual firms, threaded joints with two thrust joints are not reflected in both domestic (GOST 27834; GOST 7918) and international (7API) standards for drill joints

The only exceptions are the connections of thin-walled casing and drill pipes used when drilling with a removable core receiver, the functionality of which, especially in terms of the torque transmitted to the rock cutting tool of the latter without additional internal thrust joint, is very limited.

The objective of the invention is to create a threaded connection in which a given load on the internal thrust joint is provided and maintained during the entire period of its functioning, and is not caused by a tight tolerance on the distance between the thrust ends and the thrust ledges of the parts to be joined, forming the outer and inner thrust joints, and also their wear

To solve this problem, in the threaded connection of the drill pipe, including the sleeve and the nipple, forming the outer and inner thrust joints when screwing and tightening, a slotted spring is installed between the thrust shoulder of the coupling and the thrust end of the nipple so that a liquidable is formed between the thrust shoulder of the nipple and the thrust end of the sleeve in the process of tightening the connection and compressing the spring, a gap whose size is equal to the spring travel and, according to its parameters, strictly corresponds to the specified axial load on the internal thrust joint, thanks to y, after tightening the compound is provided as a strictly predetermined axial load on the outer joint, as the difference between the total tightening force of the threaded joint and the force of the spring to the inner contact ball joint.

The invention is illustrated in the drawing (figure 1), which shows the proposed threaded connection in the form of a drill lock, including a nipple 1, a sleeve 2 and a slotted spring 5, which is installed between the thrust ledge 3 of the coupling and the thrust end 4 of the nipple. In this case, between the stop shoulder 6 of the nipple and the stop face 7 of the clutch, a gap h is formed, which is eliminated by tightening the connection and compressing the spring. The size of the gap h is equal to the stroke of the spring h ₀ and, according to its parameters, strictly corresponds to the specified axial load on the internal thrust joint. Due to this, after tightening the connection, a strictly defined axial load on the external thrust joint is also provided, as the difference between the total tightening force of the threaded connection and the force created by the spring on the internal thrust joint.

The inventive device allows to solve the problem.

Indeed, the slotted spring installed in the threaded joint of the drill pipe between the thrust shoulder of the coupling and the thrust end of the nipple has parameters that provide, when it is compressed by the stroke value h = h ₀ , the specified axial torque of the inner thrust joint. As a result of this, a strictly specified axial tightening force of the external thrust joint is simultaneously provided, since it represents the difference between the strictly specified total axial tightening force of the threaded joint and the axial force strictly provided by the spring at the internal thrust joint.

In a conventional threaded connection, the tightening force of the outer and inner thrust joint is ensured by the deformation of the supporting surfaces of the parts to be joined, which is only 0.10-0.15 mm, which on the one hand determines the corresponding very tight tolerance on the distance between the thrust joints. On the other hand, in the process of multiple assembly-disassembly of the joint during tripping operations, this precisely specified distance is violated due to wear of the bearing surfaces, which leads to significant changes in the specified ratios of axial forces at both thrust joints and a decrease in the functionality of the threaded joint.

In the proposed threaded connection using a slotted spring, the deformation of which is an order of magnitude higher than that of the material of the connection parts, the requirements for the accuracy of the distance between the abutment joints are sharply reduced, and the wear of the bearing surfaces does not significantly affect the preset axial force of the connection to the inner joint, so as its value is also an order of magnitude less than the stroke of the spring.

An example implementation of the proposed threaded connection of drill pipes.

As an example, we take a welded drill joint ZP-95-32 according to GOST 27834 to a drill pipe PV 73 × 9 according to GOST 50278.

Total tightening force Q of the threaded connection

Where:

M = 4700 Nm - optimal tightening torque for thread 3-73 / 1 /;

d _cp = 0,0667 m - the average outer diameter of the locking thread 3-73 in the middle of its length;

µ = 0.16 - coefficient of friction in a thread subjected to phosphating or plating / 3 /.

Q = 4700 / 0.0667.106 = 440000 H

The surface area of the thrust joints, mm ² : outer - 2118; internal - 1280, total 3398. Accepting the forces at the joints proportional to the area of the corresponding supporting surface, we find the axial force that must be set for the internal joint

P = Q1280 / 3398 = 440000.376 = 165000 H

The selection and calculation of the strength of the slotted spring is carried out in accordance with the recommendations set forth in / 4 /.

In accordance with the diameter of the thread 3-73 at the larger base of the cone, we take the outer diameter of the slotted spring equal to 60 mm. Its internal diameter cannot be less than the diameter of the connecting passage channel, we take it equal to 32 mm, whence the average spring radius is R = 23 mm, and its width is b = 14 mm.

By preliminary calculations, taking into account the length of the turnkey coupling housing I _m = 204 mm (see Fig. 1), we establish the thickness (height) of the rings formed when milling the grooves t = 25 mm, the number of rings i = 4 and jumpers on one of the ends of the ring n = 2. Taking the slot height equal to 3 mm, we get the height (length) of the spring: 25 · 4 + 3 · 3 = 109 mm (see figure 1).

The course (draft) of the spring is determined from the expression:

Where:

ε is the dimensionless coefficient;

P is the axial force;

R is the average radius of the spring ring;

n is the number of jumpers on one of the ends of the spring ring;

B is the stiffness of the bending section of the ring;

B = b · t ³ · E / 12;

b is the width of the spring ring;

t is the thickness (height) of the spring ring;

E is the elastic modulus of the spring material in bending;

i is the number of working rings of the spring;

ε = ν (β-χ · sinβ);

ν is the coefficient;

ν = B / C;

C is the stiffness of the torsion section of the ring;

C = J

J is the polar moment of inertia of the spring during torsion;

G - modulus of elasticity of the spring material during torsion

β - half the angle between the jumpers of the spring;

β = 0.5 π / n;

χ is the coefficient;

χ = 2ν · sinβ / | β (1 + ν) -0.5 ((1-ν) sin2β |

In addition to those established above, we determine the values of the remaining initial quantities included in expression (2)

E = 2.06 · 10 ⁵ N / mm ² ; B = 14 × 25 ³ × 2.06 · 10 ^5/12 = 0.38 × 10 ¹⁰ N · mm ^2; J = 0.1 (60 ⁴ -32 ⁴ ) = 0.119 · 10 ⁷ mm ⁴ ; G = 7.8 · 10 ⁴ N / mm ² ; G = 0.119 · 10 ⁷ · 7.8 · 10 ⁴ = 0.93 · 10 ¹¹ N · mm ² ; ν = B / C = 0.04; β = 0.5 · 180/2 = 45 °; χ = 2 · 0.04 · 0.7 / 45 (1 + 0.04) -0.5 (1-0.04) · 1 = 0.001; ε = 0.04 (45-0.001 0.7) = 1.8

Substituting the obtained values in expression (2), we obtain the stroke of the split spring

h ₀ = 1.8 · 165000 · 23 ³ · 4/2 · 0.38 · 10 ¹⁰ = 1.90 mm

Determine the maximum reduced voltage at the spring jumpers

Where:

ξ is a coefficient depending on the ratio t / b. According to the table given in (4), for t / b = 25/14 = 1.78, ξ = 1.34 and then

σ = 1.34 · 165000 · 23/14 · 25 ² = 581 N / mm ²

As a material for a slotted spring, we take, according to GOST 14959, spring-spring steel grade 60C2A with a yield strength of 1372 N / mm ² . Safety margin of spring from this steel will be

ϑ = 1372/581 = 2.4.

The axial tightening force and, accordingly, the static and cyclic strength of the threaded connection with two thrust joints can be increased by 1.5 times / 2 /, i.e. accept her equal

165000 1.5 = 247500 H.

Then the spring travel according to expression (2) will also increase by 1.5 times and will be equal to

h ₀ = 1.95 · 1.5 = 2.85 mm.

Therefore, in this case (see Fig. 1), the values h = h ₀ should be taken equal to 2.85 mm, and the safety factor of the spring will accordingly decrease by 1.5 times and amount to

2.4 / 1.5 = 1.6,

which is enough.

The total axial tightening force of such a threaded joint will be

Q = 440 · 1.5 = 660 kN,

and the tightening torque according to the expression (1)

660.0667.0.16 = 7.04 kNm = 7040 Nm.

Thus, the presence of a slotted spring in the proposed threaded connection provides the creation of strictly defined axial loads on the internal, and, as a result, on the external thrust joint and preserves their ratio for the entire period of operation, since it practically does not depend on the tolerance on the distance between them and from wear of their supporting surfaces. Reliable functioning of both thrust joints allows to increase the total axial tightening force of the threaded connection by 1.5 times and, accordingly, increase its static strength and cyclic durability.

Literature:

1. Oil pipes. Handbook / Under the General Ed. A.E. Saroyan. - 3rd ed., Revised. and add. - M .: Nedra, 1987.488 s.

2. Lachinyan L.A. The work of the drill string. - 2nd ed., Revised. and add. - M .: Nedra, 1992 .-- 214 p.: Ill.

3. Birger I. A., Iosilevich G. B. Threaded and flange connections. - M.: Mechanical Engineering, 1990. - 368 p.: Ill.

4. Birger I.A. et al. Strength calculation of machine parts: Handbook / I.A. Birger, B.F. Shorr, G.B. Iosilevich. - 4th ed., Revised. and add. - M.: Mechanical Engineering, 1993. - 640 p.: Ill.

Claims (1)

A threaded connection of drill pipes, including a sleeve and a nipple, which, when screwing and tightening, forms external and internal thrust joints, characterized in that a slotted spring is installed between the thrust shoulder of the coupling and the thrust end of the nipple so that it is formed between the thrust shoulder of the nipple and the thrust end of the sleeve the process of tightening the connection and compressing the spring, a gap whose value is equal to the spring travel and, according to its parameters, strictly corresponds to the specified axial load on the internal thrust joint, due to which after tightening the connection, a strictly defined axial load on the external joint is also provided, as the difference between the set total tightening force of the threaded joint and the force created by the spring on the internal thrust joint.

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