JP2017072187A - Screw joint for oil well pipe casing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screw joint for oil well pipe casing capable of contributing to resource saving of components of a screw joint for oil well pipe.SOLUTION: By making an inner diameter Dbid of a box larger than an inner diameter Dpid of a nose of a pin, a joint structure has the following relationship of a nose thickness tb of the box and a nose thickness tp of the pin: 0.70<tb/tp<1.00. Consequently, a wall thickness of a box member can be reduced without deteriorating leak resistance performance and galling resistance performance, which can contribute to energy saving thanks to thinning of a screw joint material.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a threaded joint for an oil well pipe casing.

  Threaded joints for pipes are widely used for connecting steel pipes used in oil industry equipment such as oil well pipes. Conventionally, a standard threaded joint specified in the API (American Petroleum Institute) standard has been typically used for connecting steel pipes used for oil and gas exploration and production. However, in recent years, the wells for crude oil and natural gas have been deepened, and the number of vertical wells, horizontal wells, inclined wells, etc. has increased, and the drilling and production environment has become severe. In addition, the demand for screw joints such as compression resistance, bending resistance, and external pressure seal performance (external pressure resistance) has diversified due to the increased development of wells in poor environments such as the ocean and polar regions. ing. For this reason, the use of high-performance special threaded joints called premium joints is increasing, and the demands on the performance are also increasing.

  A premium joint usually has a male screw member (hereinafter referred to as a pin) and a pin formed on a pipe end portion each having a taper screw, a seal portion (specifically, a metal touch seal portion), and a shoulder portion (specifically, a torque shoulder portion). Coupling in which female screw members (hereinafter referred to as boxes) are connected to each other, and coupling is provided with pins at both ends of the oil well pipe and boxes at both ends of the connecting cylinder (called coupling). There are two types: an integral type with a pin at one end of the oil well pipe and a box at the other end. The taper screw is important for firmly fixing the pipe joint, and the seal part plays a role of securing the sealing performance by metal contact between the box and the pin at this part, and the shoulder part is a stopper of the joint during tightening. It becomes the shoulder side that plays the role.

  FIG. 3 is a schematic explanatory view of a conventional premium joint for oil well pipes, and these are sectional views in the pipe axis direction of a threaded joint of a circular pipe. The threaded joint includes a pin 3 and a box 1 corresponding to the pin 3, and the pin 3 has a male screw portion 7 on the outer surface thereof, and has no screw provided adjacent to the male screw portion 7 on the tip end side of the pin 3. It has a nose portion 8 (pin nose 8) which is a length portion. The nose portion 8 has a seal portion 11 on its outer peripheral surface and a torque shoulder portion 12 on its end surface. The opposing box 1 has a female screw part 5, a seal part 13, and a part that can be screwed or brought into contact with the male screw part 7, the seal part 11, and the shoulder part 12 of the pin 3, respectively. And it has the shoulder part 14.

  In the conventional example of FIG. 3, the seal portion is at the tip of the pin nose 8, and a desired sealing performance (leak resistance) can be realized by applying an appropriate tightening torque.

  Since the tightening torque is affected by lubrication conditions, surface properties, etc., a design that does not depend greatly on this is a radial seal method in which the radial component of the seal contact pressure is relatively strong. For example, Patent Literature 1 discloses an example of a radial seal method having a large pin seal R shape and a small seal taper angle. However, the problem with the radial seal method with such a small seal taper angle is that goling is likely to occur during tightening, and in particular, the amount of seal interference for the purpose of ensuring seal performance and sealing stability. When a large value is set, the ease of occurrence of goling is remarkably increased.

  Here, the seal interference amount is a seal point that is a portion on the outer peripheral surface of the nose portion on the pin side that first comes into contact with the inner peripheral surface of the nose portion on the box side at the time of screw connection (screw tightening) of the pin and the box. This is the amount of diameter reduction when the diameter is reduced by a box. This amount of seal interference is the tube axis direction of the pipe radial dimension in the overlapping area of the pin nose and the box inner periphery formed when the drawing of the pin and box are overlapped so as to be in the arrangement state at the time of screw connection This corresponds to the maximum value of the distribution data (the pipe diameter direction dimension at the seal point of the overlapping region).

  The seals 11 and 13 in FIG. 3 or the seals of the above-described radial seal method (hereinafter also referred to as radial seal type) are subjected to a sufficient pressure so that no leaks or galling occurs. Is formed. Reference numeral 18 denotes a load surface of the screw and 19 denotes an insertion surface of the screw. The load flank angle, which is the angle formed by the screw load surface 18 and the tube axis orthogonal surface, is negative when the screw bottom side of the screw load surface 18 is located closer to the screw tip side than the screw top side, and vice versa. Positive, the case where the screw bottom side and the screw top side are at the same screw shaft (tube axis) direction position is set to zero. The stub flank angle, which is the angle formed by the screw insertion surface 19 and the tube axis orthogonal surface, is positive when the screw bottom side of the screw insertion surface 19 is located closer to the screw tip side than the screw top side, and vice versa. Negative, 0 when the screw bottom side and the screw top side are at the same screw shaft (tube axis) direction position.

Japanese Utility Model Publication No. 61-44068

  The premium joint is applied not only to tubing in an oil well pipe (pipe for passing a production fluid such as crude oil or natural gas), but also to a casing (pipe that surrounds the installation space of the tubing). In the threaded joint for tubing, in order to prevent the production fluid in the pipe from being turbulent as much as possible, the inner diameters of the shoulder portions of the pin and the box are made to coincide with each other so as not to cause a step on the inner surface of the joint. Also in the threaded joint for the casing, the inner diameters of the shoulder portions of the pin and the box are usually matched as in the case of the tubing.

  However, there is no production fluid in the space between the casing and the tubing, and there is no flow of production fluid. Therefore, in the threaded joint for casing, as long as there is no problem with leakage resistance and galling resistance There is no problem even if there is a step on the inner surface of the joint. On the contrary, it may be possible to reduce the wall thickness of the box material and contribute to resource saving by actively providing steps.

  In view of the above circumstances, an object of the present invention is to provide a threaded joint for an oil well pipe casing that can contribute to resource saving of a member of the threaded joint for an oil well pipe.

  In order to solve the above-mentioned problems, the present inventors examined the allowable range of the step on the inner surface side of the threaded joint for casing, and as a result, the inner diameter of the box was made larger than the inner diameter of the pin, and the nose thickness of the box By using a joint structure that has a specific relationship with the nose thickness of the pin, the thickness of the box member can be reduced without degrading the leakage resistance and galling resistance, and the thickness of the threaded joint material can be reduced. The present invention was made by finding that it can contribute to resource recycling.

That is, the present invention includes a male screw part, a pin provided with a nose part extending from the male screw part to the tube end side, and a shoulder part provided at the tip of the nose part,
A female screw part that is screw-coupled with the male screw part to form a screw part, a seal surface that faces the outer peripheral surface of the nose part of the pin, and a box that includes a shoulder part that contacts the shoulder part of the pin; A screw joint for an oil well pipe casing in which the pin and the box are coupled by the screw coupling, and the outer peripheral surface of the pin and the seal surface of the box are in metal-metal contact to form a seal portion,
An inner diameter Dbid of the box is larger than a nose inner diameter Dpid of the pin, and a nose thickness tb = (Dp−Dbid) / 2 determined from the nose outer diameter Dp and the Dbid at the seal point of the pin is An oil well pipe casing having a relationship of nose thickness tp = (Dp−Dpid) / 2 determined by Dp and Dpid and 0.70 <tb / tp <1.00 Thread joint.

  According to the present invention, it is possible to reduce the thickness of a threaded joint for an oil well pipe casing, thereby realizing resource saving. In addition, there is an effect that the processing efficiency of the box of the threaded joint for oil well pipe casing is improved.

It is a pipe axis direction sectional view of a threaded joint for oil country tubular goods casing showing one embodiment of the present invention. It is an example of an isostrain diagram which shows the equivalent strain distribution near the nose part at the time of completion of tightening of the series A test obtained by FEA calculation, (a) shows a conventional example, and (b) shows an example of the present invention. It is a pipe axial direction sectional view showing the conventional threaded joint for pipes, (a) is a general view, (b) is an enlarged view of a thread part in (a), (c) is an enlarged view near a pin nose in (a). is there.

  For example, as shown in FIG. 1, the threaded joint for an oil well pipe casing of the present invention is provided at a male screw part 7, a nose part 8 extending from the male screw part 7 to the pipe end side, and a tip of the nose part 8. A female screw part 5 having a pin 3 with a shoulder part 12 and screwed to the male screw part 7 to form a screw part; a seal surface facing the outer peripheral surface of the nose part of the pin 3; and the pin A box 1 having a shoulder portion 14 that abuts against the shoulder portion 12, the pin 3 and the box 1 are coupled by the screw coupling, and the nose portion outer peripheral surface of the pin 3 and the seal surface of the box 1 It is assumed that the seal portions 11 and 13 are made in metal-metal contact.

  Under the premise, the inner diameter Dbid of the box 1 is larger than the nose inner diameter Dpid of the pin 3, and the nose of the box 1 determined from the nose outer diameter Dp and the Dbid at the seal point sp of the pin 3 The thickness tb = (Dp−Dbid) / 2 is related to the nose thickness tp = (Dp−Dpid) / 2 of the pin 3 determined from the Dp and the Dpid, and 0.70 <tb / tp <1.00. It was set as the structure which has. Here, the seal point sp is a point that first contacts the inner peripheral surface of the box 1 during screw tightening among points on the outer peripheral surface of the nose portion of the pin 3.

  As a result, it is possible to reduce the thickness of the box of the casing joint while maintaining leak resistance and galling resistance, thereby realizing resource saving and improving the processing efficiency of the box as the thickness is reduced.

  When the inner diameter Dbid of the box is equal to or less than the nose inner diameter Dpid of the pin, the box cannot be thinned, so that Dbid is larger than Dpid. Further, when the ratio tb / tp of the nose thickness tb of the box to the nose thickness tp of the pin is 1.00 or more, the box cannot be thinned, so tb / tp is less than 1.00, but tb / tp is reduced. If it is too much, the leak-proof performance is lowered, so tb / tp is set to exceed 0.70. In addition, Preferably, it is tb / tp = 0.80-1.00.

  In addition, from the viewpoint of keeping leakage resistance and galling resistance at a high level, the threaded joint is preferably a radial seal type. Further, as a suitable range of joint shape specifications other than the above tb / tp and tp, the seal part of the pin nose outer peripheral surface is in a toroid shape (conical curve rotation surface shape), and the curve in the tube axis direction cross section of this toroidal surface is An arc having a radius of 25 to 105 mm is preferable. Further, the seal portion on the inner peripheral surface of the box is preferably a tapered surface that forms an angle (seal taper angle) within 10 ° with respect to the tube axis. The seal interference amount (denoted as δ) is preferably set such that the ratio (δ / Dp) to the nose outer diameter Dp at the seal point sp of the pin is 0.002 to 0.02.

  Moreover, about a thread part, it is preferable to set it as a screw taper angle = 1.5-5.0 degrees, a load flank angle = -5-5 degrees, and a stub flank angle = 0-30 degrees.

  A threaded joint for connecting a steel pipe having an outer diameter of 244.5 mm and a thickness of 13.8 mm for an oil well pipe casing was prepared. The material of the steel pipe is a steel type Q125 having a yield strength of 125 ksi specified by API. In the threaded joint, the inner diameter Dbid of the box, the nose inner diameter Dpid of the pin, the nose thickness tb of the box, and the nose thickness tp of the pin were made different as shown in Table 1. The nose outer diameter Dp at the seal point of the pin was as shown in Table 1.

  Shape specifications other than those shown in Table 1 are common to all of the plurality of threaded joints. Mainly, the seal part on the outer peripheral surface of the nose part of the pin has a toroidal shape (conical curve rotation surface shape), and the curve in the cross section in the tube axis direction of this toroidal surface is an arc having a radius of 50 mm. The seal portion on the peripheral surface is a radial seal type threaded joint that is a tapered surface having an angle of 3 ° (seal taper angle) with respect to the tube axis, and the seal interference amount (δ / Dp) is 0.004. In addition, about the thread part, it was set as the screw taper angle = 1.8 degrees, the load flank angle = -3 degrees, and the stub flank angle = 20 degrees.

  For these threaded joints, the M & B (Make and Break) test defined in ISO 13679 and the series A test for evaluating airtightness (leak resistance) were performed.

  The M & B test evaluates galling resistance (galling resistance), and it is good when lubricant is applied to the seal part and thread part in advance and seizure does not occur after tightening and tightening more than 20 times (◎). Applicable when seizure occurs after 10 to 19 times of tightening and tightening (O), not possible when seizure occurs after 5 to 9 times of tightening and rewinding (△), and tightening up to 4 times The case where seizure occurred during rewinding was evaluated as bad (x).

  The series A test was carried out after one tightening, and the evaluation was made with “X” indicating that the seal expired and “◯” indicating that the seal was not expired. The seal expiration is determined based on the reference value of fluid leakage defined in ISO 13679. In this series A test, the load schedule is defined by VME 95% and API Collapse pressure. However, the maximum compressibility (ratio of the load compressive stress to the yield stress YS) is arbitrarily set by the manufacturer, and is determined according to the performance of the threaded joint and customer requirements. In this test, the maximum compression rate of the test was 80%.

  Table 1 also shows the evaluation of leakage resistance and galling resistance, and whether the effect of thinning is (○) or not (×).

  As shown in Table 1, the present invention example (Dbid <Dpid and tb / tp = 0.70 to less than 1.00) has high leakage resistance and galling resistance equivalent to the conventional example (Dbid = Dpid). It can be seen that, according to the present invention, it is possible to achieve a reduction in the thickness of the box without deteriorating leakage resistance and galling resistance.

  FIG. 2 is an example of an isostrain diagram obtained by FEA (finite element analysis) calculation and showing an equivalent strain distribution in the vicinity of the nose portion at the completion of tightening of the series A test, (a) is a conventional example, (B) shows an example of the present invention (No. 3). From FIG. 2, it can be seen that the example of the present invention exhibits substantially the same equivalent strain distribution as the conventional example.

1 Box 3 Pin 5 Female thread 7 Male thread 8 Nose (pin nose)
11, 13 Seal part 12, 14 Shoulder part 18 Thread load surface 19 Thread insertion surface

Claims (1)

A pin provided with a male screw part, a nose part extending from the male screw part to the tube end side, and a shoulder part provided at the tip of the nose part;
A female screw part that is screw-coupled with the male screw part to form a screw part, a seal surface that faces the outer peripheral surface of the nose part of the pin, and a box that includes a shoulder part that contacts the shoulder part of the pin; A screw joint for an oil well pipe casing in which the pin and the box are coupled by the screw coupling, and the outer peripheral surface of the pin and the seal surface of the box are in metal-metal contact to form a seal portion,
An inner diameter Dbid of the box is larger than a nose inner diameter Dpid of the pin, and a nose thickness tb = (Dp−Dbid) / 2 determined from the nose outer diameter Dp and the Dbid at the seal point of the pin is An oil well pipe casing having a relationship of nose thickness tp = (Dp−Dpid) / 2 determined by Dp and Dpid and 0.70 <tb / tp <1.00 Threaded joint.

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