JP2015055296A

JP2015055296A - Screw joint for oil well pipe with superior anti-seizure characteristics

Info

Publication number: JP2015055296A
Application number: JP2013188937A
Authority: JP
Inventors: 順高野; Jun Takano; 高橋　一成; Kazunari Takahashi; 一成高橋; 博近常; Hiroshi Chikatsune; 吉川　正樹; Masaki Yoshikawa; 正樹吉川; 孝将川井; Takamasa Kawai; 拓也長濱; Takuya Nagahama; 植田　正輝; Masateru Ueda; 正輝植田
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2013-09-12
Filing date: 2013-09-12
Publication date: 2015-03-23
Anticipated expiration: 2033-09-12
Also published as: JP5915608B2

Abstract

PROBLEM TO BE SOLVED: To provide a screw joint for an oil well pipe in which seizure is hardly produced at its pre-seal part and sub-seal part and a prescribed sealing characteristic can be assured.SOLUTION: There is provided a salient 7 that interferes with a concavity 6 at the time of fastening work and causes the concavity to be slid toward an outer diameter of a pipe, shapes of the salient 7 and the concavity 6 are set such that the end part at the outer diameter side of a pin 1 continuous with the concavity 6 at the time of completion of fastening work is closely contacted with a box 2, and a screw interference amount δ0 is negative (δ0<0) and 1|δ0|<|δ| within a specified length area 10 that is a length area where a pipe axial length A ranging from the deepest end of the box to the insertion port for the pin 1 becomes A≥50×|δ1| in respect to a seal interference amount δ1.

Description

本発明は、耐焼付き性に優れた油井管用ねじ継手に関し、特に、優れた耐オーバートルク性能（締めすぎてもシールが保てる性能）及び耐圧縮性能（管長手方向の圧縮に耐える性能）を兼備した、耐焼付き性に優れた油井管用ねじ継手に関する。 The present invention relates to a threaded joint for oil well pipes having excellent seizure resistance, and in particular, has excellent over-torque resistance (performance that can keep a seal even if overtightened) and compression resistance (performance that can withstand compression in the longitudinal direction of the pipe). The present invention relates to a threaded joint for an oil well pipe having excellent seizure resistance.

天然ガス田や油田等の探査・生産に使用される油井管を接続する技術として、雌雄のテーパねじの先端に連なる非ねじ部にメタル-メタルシールを有するねじ継手（プレミアムジョイントと呼ばれる）が広く用いられている。前記ねじ継手には、(ａ)油井管の一端部に雄ねじを設けてピンとし、他端部に雌ねじを設けてボックスとし、該ボックスの雌ねじと前記ピンの雄ねじが螺合するインテグラル方式のものと、（ｂ）油井管の両端部に雄ねじを設けてピンとし、別の管の両端部に雌ねじを設けてボックスとし、該ボックスの一端側の雌ねじと一の油井管のピン部の雄ねじが螺合し、同ボックスの他端側の雌ねじと他の油井管のピンの雄ねじが螺合するカップリング方式のものとの２種類がある。 As a technology for connecting oil well pipes used for exploration and production in natural gas fields, oil fields, etc., threaded joints (called premium joints) that have a metal-metal seal at the non-threaded portion connected to the tips of male and female taper screws are widely used. It is used. In the threaded joint, (a) an integral type in which a male screw is provided at one end of the oil well pipe as a pin, a female screw is provided at the other end as a box, and the female screw of the box and the male screw of the pin are screwed together. (B) A male screw is provided at both ends of the oil well pipe to form a pin, a female screw is provided to both ends of another pipe to form a box, and a female screw at one end of the box and a male screw at the pin part of the one oil well pipe There are two types: a coupling type in which a female screw on the other end side of the box and a male screw of another oil well pipe pin are screwed together.

ピンおよびボックスのねじ設置部分を夫々ねじ部、ピンの最先端部からねじ部の１番目のねじ山にかけての非ねじの部分、及びボックスの最奥端部（ピンの最先端部を当接させる部分）からねじ部の１番目のねじ谷にかけての非ねじの部分を夫々ノーズ部、ピンの最先端部とボックスの最奥端部を夫々ショルダ部（詳しくは、トルクショルダ部）という。ねじ継手を締付けると、ピンとボックスのノーズ部同士が局所的にメタル‐メタル接触し、該接触した箇所がシールの役割を担う。 The screw installation part of the pin and the box is the screw part, the non-screw part from the tip of the pin to the first thread of the screw part, and the innermost end of the box (the tip of the pin is abutted) The non-threaded portion from the portion) to the first thread valley of the threaded portion is referred to as a nose portion, and the most distal end portion of the pin and the innermost end portion of the box are referred to as a shoulder portion (specifically, a torque shoulder portion). When the threaded joint is tightened, the nose portions of the pin and the box locally make metal-metal contact, and the contacted portion plays a role of a seal.

前記ねじ継手に設けるねじ山の軸方向断面形状は、ＡＰＩ（米国石油協会）規格に規定されたロードフランク角３°、スタビングフランク角１０°の台形が一般的である。ロードフランク角とは、ねじ軸直交線に対するねじ荷重面の傾斜角であり、ねじ荷重面の基端からみてその先端がねじ軸の先端側にある場合を正（＋）、その逆側にある場合を負（−）とする。スタビングフランク角とは、ねじ軸直交線に対するねじ挿入面の傾斜角であり、ねじ挿入面の基端からみてその先端がねじ軸の先端側にある場合を負、その逆側にある場合を正とする。 The axial cross-sectional shape of the thread provided in the threaded joint is generally a trapezoid having a load flank angle of 3 ° and a stubbing flank angle of 10 ° as defined in API (American Petroleum Institute) standards. The load flank angle is the angle of inclination of the screw load surface with respect to the screw axis orthogonal line. When the tip is on the tip side of the screw shaft when viewed from the base end of the screw load surface, it is positive (+) and on the opposite side. The case is negative (-). The stubbing flank angle is the inclination angle of the screw insertion surface with respect to the screw axis orthogonal line, and is negative when the tip is on the tip side of the screw shaft when viewed from the base end of the screw insertion surface, and on the opposite side. Positive.

尚、上記ねじ形状では、油井管の軸方向に圧縮力がかかったとき、ねじ山が浮いてシールが不完全となる問題に対して、ロードフランク角を負にする解決策が知られている（特許文献１、２）。
又、ロードフランク角を負にすると、油井管の接続作業時に雄ねじと雌ねじの荷重面が強接触し、過度の応力集中によりねじの角部が損傷してシールが不完全となる問題に対しては、ねじの荷重面を雄ねじの高さ方向で上下に二分し、上側のロードフランク角を下側よりも小さくする解決策が知られている（特許文献３）。 In addition, with the above screw shape, there is a known solution that makes the load flank angle negative for the problem that when the compressive force is applied in the axial direction of the oil well pipe, the thread rises and the seal becomes incomplete. (Patent Documents 1 and 2).
Also, if the load flank angle is negative, the load surface of the male screw and female screw will be in strong contact during oil well pipe connection work, and the corner of the screw will be damaged due to excessive stress concentration, resulting in an incomplete seal. Is known to divide the load surface of the screw vertically into the height direction of the male screw and make the upper load flank angle smaller than the lower side (Patent Document 3).

一方、ねじ継手では、シール干渉量を適正に設計・製作することによりシール性が確保される。シール干渉量とは、ピンとボックスの対応し合う管軸方向の各位置（原点はピン側ではピン最先端を通る管軸直交線と管軸との交点であり、ボックス側ではボックス最奥端を通る管軸直交線と管軸線との交点である。）における両者のノーズ部直径差（＝ピンノーズ部直径（外径）−ボックスノーズ部直径（内径））である。又、締付け状態を保持する為に適宜設定されるねじ干渉量とは、ピンとボックスの対応し合う管軸方向の各位置における両者のねじ部直径差（＝ピンねじ部直径(外径)−ボックスねじ部直径（内径））である。 On the other hand, in a threaded joint, sealing performance is ensured by appropriately designing and manufacturing the amount of seal interference. The amount of seal interference refers to each position in the tube axis direction where the pin and the box correspond (the origin is the intersection of the tube axis perpendicular line passing through the pin tip and the tube axis on the pin side, and The nose portion diameter difference (= pin nose portion diameter (outer diameter) −box nose portion diameter (inner diameter)) at the intersection of the tube axis orthogonal line and the tube axis line. Also, the amount of screw interference that is set appropriately to maintain the tightening state is the difference between the screw diameters of the pin and box at each position in the corresponding tube axis direction (= pin screw diameter (outer diameter) −box Thread diameter (inner diameter)).

特許文献１〜３に開示されるねじ継手では、ピンのノーズ部直径（外径）がボックスのノーズ部直径（内径）よりも大きく設計・製造されていた。即ちシール干渉量は正（＋）である。斯かるねじ継手を「従来ねじ継手Ｉ」と称する。
従来ねじ継手Ｉの締付け過程を図２に示す。締付けの進行に伴い、先ずねじ部３の干渉が開始し（図２（ａ））、次いで、シール干渉量が正であることがら、ノーズ部４の干渉が開始し（図２（ｂ））、この干渉によりピン１のノーズ部４は管内径側へ変形する。最後にショルダ部５の干渉が開始し、その後締付けが完了する（図２（ｃ））。 In the threaded joint disclosed in Patent Literatures 1 to 3, the pin nose diameter (outer diameter) is designed and manufactured larger than the nose diameter (inner diameter) of the box. That is, the seal interference amount is positive (+). Such a threaded joint is referred to as “conventional threaded joint I”.
The tightening process of the conventional threaded joint I is shown in FIG. As the tightening progresses, first, the interference of the screw portion 3 starts (FIG. 2A), and then the interference of the nose portion 4 starts because the amount of seal interference is positive (FIG. 2B). Due to this interference, the nose portion 4 of the pin 1 is deformed toward the inner diameter side of the tube. Finally, the interference of the shoulder portion 5 starts, and then the tightening is completed (FIG. 2 (c)).

然し、最近の油井あるいはガス井では、その坑路が直線的でなく、途中で曲がったものもある。斯かる油井あるいはガス井においては、油井管を接続しているねじ継手に過大な締め付けトルク（オーバートルク）や、管軸方向の強い圧縮力がかかる場合がある。その場合、図３に示すように、ピン１のノーズ部４はさらに管内径側に変形する。
これに対しては、ショルダ部を管内面側へ厚くすることにより、ショルダ部の面積を増大させ、耐圧縮性能とオーバートルク性能を高めている。さらに大幅な性能向上のために、ノーズ部の内径をねじ部の内径よりも小さくする場合がある。しかし、このようなねじ継手では、オーバートルクや圧縮が加わったときに、ドリフトゲージ（パイプの内部を貫通させ、曲がりを含んだパイプ内径が規定値以上あることを検査するためのゲージ）が通過しない程度にまでシール部の内径が大幅に変形する。よって、管内にさらにケーシングやチュービングを挿入できないという問題が発生する。 However, in recent oil wells or gas wells, the mine channel is not straight and some of them are bent in the middle. In such an oil well or gas well, an excessive tightening torque (over torque) or a strong compressive force in the tube axis direction may be applied to the threaded joint connecting the oil well pipes. In that case, as shown in FIG. 3, the nose portion 4 of the pin 1 is further deformed to the inner diameter side of the tube.
For this, by increasing the thickness of the shoulder portion toward the inner surface of the pipe, the area of the shoulder portion is increased, and the compression resistance performance and the overtorque performance are enhanced. In order to further improve performance, the inner diameter of the nose portion may be made smaller than the inner diameter of the screw portion. However, in such a threaded joint, when overtorque or compression is applied, a drift gauge (a gauge that passes through the inside of the pipe and inspects that the pipe inner diameter including the bend exceeds a specified value) passes. The inner diameter of the seal is greatly deformed to such an extent that it does not. Therefore, there arises a problem that a casing or tubing cannot be further inserted into the tube.

斯かる問題の解決手段として、図４に示される処の、雌雄のテーパねじにてねじ結合される雄側のピン１と雌側のボックス２とからなり、これらの双方が互いに対応する部位に、ねじ部３と、該ねじ部３の先端側に順次連なるノーズ部４および該ノーズ部４端のショルダ部５とを有する油井管用ねじ継手において、前記ノーズ部４のシール干渉量を負とし、さらに前記ピン１のショルダ部５に凹部６を設けると共に、前記ボックス２のショルダ部５に、締付け時前記凹部６と干渉してこれを管外径側に摺動させる凸部７を設けた油井管用ねじ継手が知られている（特許文献４）。これを「従来ねじ継手ＩＩ」と称する。 As a means for solving such a problem, it is composed of a male pin 1 and a female box 2 which are screw-coupled by male and female taper screws as shown in FIG. In the oil well pipe threaded joint having the screw portion 3, the nose portion 4 successively connected to the tip end side of the screw portion 3, and the shoulder portion 5 at the end of the nose portion 4, the seal interference amount of the nose portion 4 is set to be negative. Further, the well 5 is provided with a recess 6 in the shoulder portion 5 of the pin 1 and the well 5 provided with a protrusion 7 that interferes with the recess 6 and slides toward the outer diameter side of the tube when tightened. A threaded joint for pipes is known (Patent Document 4). This is referred to as “conventional threaded joint II”.

従来ねじ継手ＩＩでは、凹部６と凸部７夫々の外径側の傾斜部がプレシール部８を成し、該プレシール部８からショルダ部５最外径端までがサブシール部９を成している。締付け時に凹部６が凸部７に沿って管外径側へ摺動すると、先ずプレシール部８同士が干渉し、次いでサブシール部９同士が干渉して、これらの干渉により締付け完了時に２つのシールが形成される。この２つのシールはノーズ部４、４間への流体の侵入を防止する。 In the conventional threaded joint II, the inclined portion on the outer diameter side of each of the concave portion 6 and the convex portion 7 forms a pre-seal portion 8, and from the pre-seal portion 8 to the outermost diameter end of the shoulder portion 5 forms a sub-seal portion 9. . When the concave portion 6 slides along the convex portion 7 toward the tube outer diameter side during tightening, the pre-seal portions 8 first interfere with each other, and then the sub seal portions 9 interfere with each other. It is formed. The two seals prevent fluid from entering between the nose portions 4 and 4.

これにより、図５に示されるように、オーバートルクおよび/または管軸方向の圧縮（オーバートルク・圧縮と略記）が加わっても、シール干渉量を負としているからピン１とボックス２のノーズ部４、４間には隙間が形成されており、この隙間がピン１のノーズ部４の管外径側への変位を容易化しているので、ピン１のノーズ部４の管内径側への変形が抑制される。 As a result, as shown in FIG. 5, the nose portion of the pin 1 and the box 2 because the seal interference amount is negative even when over torque and / or compression in the tube axis direction (abbreviated as over torque / compression) is applied. A gap is formed between the pins 4 and 4, and this gap facilitates displacement of the nose portion 4 of the pin 1 toward the tube outer diameter side. Is suppressed.

特開平６−２８１０５９号公報JP-A-6-28059 特開平６−２８１０６１号公報JP-A-6-281061 再公表特許ＷＯ００/０６９３７Republished patent WO00 / 06937 特開平２００５−２４０８８８号公報Japanese Patent Laid-Open No. 2005-240888

然しながら、発明者らの更なる検討により、従来ねじ継手ＩＩでは、一般的な設計のねじ部（ねじ部の先端側からねじ部全長の１/２以上の長さ領域内のねじ干渉量が正とされる）と組合わせると、締付け過程でプレシール部８が相互接触する前にねじ部３の径方向の干渉が発生している場合があり、この状態のままプレシール部８が相互接触すると、プレシール部８更にはサブシール部９の相互摺動時の接触力が過大となって、焼付きが発生するリスクが高いことが分った。斯かる焼付きが発生すると、所定のシール性を保つのが困難である。 However, as a result of further studies by the inventors, in the conventional threaded joint II, the thread interference amount within a length region that is 1/2 or more of the entire length of the threaded portion from the tip side of the threaded portion is normal. When the pre-seal part 8 is in mutual contact in this state, there is a case where the radial interference of the screw part 3 occurs before the pre-seal part 8 contacts with each other in the tightening process. It has been found that the contact force at the time of mutual sliding of the pre-seal part 8 and the sub-seal part 9 becomes excessive, and there is a high risk of seizure. When such seizure occurs, it is difficult to maintain a predetermined sealing property.

以上の様に、従来ねじ継手ＩＩでは、プレシール部８更にはサブシール部９に焼付きが発生し易く、所定のシール性を保ち難いと云う課題があった。 As described above, in the conventional threaded joint II, there is a problem that seizure is likely to occur in the pre-seal portion 8 and the sub-seal portion 9 and it is difficult to maintain a predetermined sealing property.

本発明者らは、前記課題を解決する手段について鋭意検討し、その結果、従来ねじ継手ＩＩにおいて、ノーズ部端からねじ部にかけての或る管軸方向長さ領域内でシール干渉量とねじ干渉量の関係を規定する事が前記課題の解決に繋がると云う知見を得るに至り、この知見に基づいて。以下の要旨構成になる本発明を成した。
（１）雌雄のテーパねじにてねじ結合される雄側のピンと雌側のボックスとからなり、これらの双方が互いに対応する部位に、ねじ部と、該ねじ部の先端側に順次連なるノーズ部および該ノーズ部端のショルダ部とを有し、前記ノーズ部はシール干渉量δ１を負とし、更に、前記ピンのショルダ部には凹部を設け、且つ前記ボックスのショルダ部には、締付け時前記凹部と干渉してこれを管外径側に摺動させる凸部を設け、前記凸部及び前記凹部の形状を、締付け完了時には前記凹部に連なるピン外径側の端部が前記ボックスに密着する形状としてなる油井管用ねじ継手において、前記ボックスの最奥端からピン挿入口側への管軸方向長さＡが前記δ１に対し、Ａ≧５０×｜δ１｜になる長さ領域である特定長さ領域内で、ねじ干渉量δ０を負で且つ｜δ０｜＜｜δ１｜としたことを特徴とする耐焼付き性に優れた油井管用ねじ継手。 The present inventors have intensively studied the means for solving the above-mentioned problems, and as a result, in the conventional threaded joint II, the amount of seal interference and thread interference within a certain tube axial direction length region from the nose end to the threaded portion. Based on this knowledge, we have obtained the knowledge that prescribing the quantity relationship leads to the solution of the above-mentioned problems. The present invention has the following summary.
(1) A male-side pin and a female-side box that are screw-coupled by male and female taper screws, a screw part, and a nose part that is successively connected to the tip side of the screw part at a position where both of them correspond to each other And a shoulder portion at the end of the nose portion, the nose portion has a negative seal interference amount δ1, a recess portion is provided in the shoulder portion of the pin, and the shoulder portion of the box is Provided with a convex portion that interferes with the concave portion and slides it toward the outer diameter side of the tube, and the end portion on the outer diameter side of the pin connected to the concave portion closely contacts the box when tightening is completed. In the oil well pipe threaded joint having a shape, a specific length which is a length region in which the length A in the pipe axis direction from the innermost end of the box to the pin insertion port side is A ≧ 50 × | δ1 | Within the region, the screw interference amount δ0 is negative. And | δ0 | <| δ1 | and to seizure excellent in oil well pipe threaded joint, characterized in that the.

本発明によれば、前記構成を採用したから、優れた耐オーバートルク性能及び耐圧縮性能を兼備した、耐焼付き性に優れた油井管用ねじ継手が得られる。 According to this invention, since the said structure was employ | adopted, the threaded joint for oil well pipes which was excellent in the seizure resistance which combined the outstanding over-torque-proof performance and the compression-proof performance is obtained.

本発明の実施形態の一例を示す管軸方向断面図である。It is a pipe axis direction sectional view showing an example of an embodiment of the present invention. 従来ねじ継手Ｉのオーバートルク・圧縮時のピン側シール部の変形を示す管軸方向断面図である。It is a pipe axis direction sectional view showing modification of a pin side seal part at the time of overtorque and compression of conventional screw joint I. 従来ねじ継手Ｉのオーバートルク・圧縮時のピン側ノーズ部の変形を示す管軸方向断面図である。It is a pipe axis direction sectional view showing modification of a pin side nose part at the time of overtorque and compression of conventional screw joint I. 従来ねじ継手ＩＩの一例とその締付け過程を示す管軸方向断面図である。It is a pipe axis direction sectional view showing an example of the conventional screw joint II and its tightening process. 図４のねじ継手のオーバートルク・圧縮時のピン側ノーズ部の変形を示す管軸方向断面図である。FIG. 5 is a cross-sectional view in the tube axis direction showing the deformation of the pin side nose portion during over torque / compression of the threaded joint of FIG. 4.

本発明は、図１に実施形態の一例を示す通り、雌雄のテーパねじにてねじ結合される雄側のピン１と雌側のボックス２とからなり、これらの双方が互いに対応する部位に、ねじ部３と、該ねじ部３の先端側に順次連なるノーズ部４および該ノーズ部４端のショルダ部５とを有し、前記ノーズ部４はシール干渉量δ１を負とされ、更に、前記ピン１のショルダ部５には凹部６を設け、且つ前記ボックス２のショルダ部５には、締付け時前記凹部６と干渉してこれを管外径側に摺動させる凸部７を設け、前記凸部７及び前記凹部６の形状を、締付け完了時には前記凹部６に連なるピン１外径側の端部が前記ボックス２に密着する（ピン１とボックス２のプレシール部８同士及びサブシール部９同士が互いに密着する）形状としてなる油井管用ねじ継手（これは従来ねじ継手ＩＩに該当する）である事を前提としている。 As shown in FIG. 1, the present invention includes a male pin 1 and a female box 2 that are screw-coupled with male and female taper screws, and both of them correspond to each other at a portion corresponding to each other. A screw part 3, a nose part 4 successively connected to the tip side of the screw part 3, and a shoulder part 5 at the end of the nose part 4, wherein the nose part 4 has a negative seal interference amount δ 1, and The shoulder portion 5 of the pin 1 is provided with a concave portion 6, and the shoulder portion 5 of the box 2 is provided with a convex portion 7 that interferes with the concave portion 6 at the time of tightening and slides it toward the pipe outer diameter side, The ends of the pin 1 and the outer diameter side of the pin 1 connected to the recess 6 are in close contact with the box 2 when tightening is completed (the pin 1 and the pre-seal portion 8 and the sub seal portion 9 of the box 2 are in contact with each other). Oil well pipe screws with a shape that adheres to each other) Hand (which conventionally corresponds to the threaded joint II) assumes it is.

本発明は、前記前提の下で、前記ボックス２の最奥端からピン１挿入口側への管軸方向長さＡが前記δ１に対し、Ａ≧５０×｜δ１｜になる長さ領域である特定長さ領域１０内で、ねじ干渉量δ０を負（δ０＜０）で且つ｜δ０｜＜｜δ１｜としたことを特徴とする耐焼付き性に優れた油井管用ねじ継手である。
尚、特定長さ領域１０外の管軸方向長さ領域内ではねじ干渉量は正とする。 Under the above assumption, the present invention is a length region in which the tube axis length A from the innermost end of the box 2 to the pin 1 insertion port side is A ≧ 50 × | δ1 | This is a threaded joint for oil well pipes excellent in seizure resistance, characterized in that the screw interference amount δ0 is negative (δ0 <0) and | δ0 | <| δ1 | within a specific length region 10.
It should be noted that the screw interference amount is positive in the tube axis direction length region outside the specific length region 10.

これにより、ねじ継手締付け時のピン１のノーズ部４の過度の縮径を防止でき、以て、プレシール部８及びサブシール部９に過大な接触力が生じるのを防止できる。
従来ねじ継手ＩＩを前提とするものであっても、特定長さ領域１０の長さＡが５０×｜δ１｜未満であると云う条件、及び特定長さ領域１０内でδ０≧０であると云う条件、及び特定長さ領域１０内で｜δ０｜≧｜δ１｜であると云う条件の何れか一つ以上が成り立つ場合は、ねじ継手締付け時のプレシール部８及びサブシール部９の接触力を有効に低減できず焼付き発生の防止効果に乏しい。 Thereby, the excessive diameter reduction of the nose part 4 of the pin 1 at the time of screw joint fastening can be prevented, and it can prevent that an excessive contact force arises in the pre-seal part 8 and the sub seal part 9 by this.
Even if the conventional threaded joint II is assumed, the condition that the length A of the specific length region 10 is less than 50 × | δ1 | and that δ0 ≧ 0 in the specific length region 10 When one or more of the above conditions and the condition that | δ0 | ≧ | δ1 | is satisfied in the specific length region 10, the contact force between the pre-seal portion 8 and the sub seal portion 9 at the time of tightening the threaded joint is determined. It cannot be effectively reduced and is poor in preventing seizure.

尚、特定長さ領域１０の長さＡを大きくとり過ぎると、ねじ干渉量δ０が正になる長さ領域が過小となって、締付け完了（締付けトルク解除）後にその締付け状態を保持するのが困難となる為、前記長さＡは、ねじ部３の全長の５０％以下とするのが好ましい。 If the length A of the specific length region 10 is too large, the length region in which the screw interference amount δ0 is positive becomes too small, and the tightening state is maintained after the tightening is completed (tightening torque is released). Since it becomes difficult, the length A is preferably 50% or less of the entire length of the screw portion 3.

ＡＰＩ−Ｌ８０相当鋼種の外径２４４．５ｍｍ×肉厚１１．９９ｍｍの油井管用鋼管の管端部をねじ切削加工してなるピンと、これに対応するボックスとからなるカップリング方式で、図１に例示した形態とされ、表１に設計条件の水準を示す処の、種々の油井管用ねじ継手を製作し、これらを供試材として、ＩＳＯ１３６７９に準拠した締付け試験において通常の締付け完了時の所定トルクの１．５倍のオーバートルクをかける締付け実験を行って、リーク発生の有無を調査すると共に、実験後のねじ継手を管軸方向に切断し、その断面を観察して、プレシール部及びサブシール部における焼付き発生の有無を調査した。 A coupling method comprising a pin formed by threading a pipe end of an oil well pipe of an API-L80 equivalent steel type with an outer diameter of 244.5 mm and a wall thickness of 11.99 mm, and a box corresponding thereto, as shown in FIG. Various types of threaded joints for oil well pipes, which are in the illustrated form and whose levels of design conditions are shown in Table 1, were manufactured, and these were used as test materials, with a predetermined torque when a normal tightening was completed in a tightening test according to ISO 13679. A tightening experiment with 1.5 times the overtorque was conducted to investigate the presence or absence of leakage, and the threaded joint after the experiment was cut in the direction of the tube axis, and the cross section was observed, and the pre-seal part and sub-seal part The presence or absence of seizure occurrence was investigated.

前記調査の結果を表１に示す。表１に示す通り、本発明例では、焼付き発生は無く、リーク発生も無い良好な継手性能が得られた。 The results of the investigation are shown in Table 1. As shown in Table 1, in the example of the present invention, there was no seizure occurrence, and good joint performance without leak occurrence was obtained.

１ピン
２ボックス
３ねじ部
４ノーズ部
５ショルダ部
６凹部（ピンのショルダ部の凹部）
７凸部（ボックスのショルダ部の凸部）
８プレシール部
９サブシール部
１０特定長さ領域 1 Pin 2 Box 3 Threaded part 4 Nose part 5 Shoulder part 6 Recessed part (Recessed part of the shoulder part of the pin)
7 Convex part (Convex part of the shoulder part of the box)
8 Pre-seal part 9 Sub-seal part 10 Specific length region

Claims

雌雄のテーパねじにてねじ結合される雄側のピンと雌側のボックスとからなり、これらの双方が互いに対応する部位に、ねじ部と、該ねじ部の先端側に順次連なるノーズ部および該ノーズ部端のショルダ部とを有し、前記ノーズ部はシール干渉量δ１を負とし、更に、前記ピンのショルダ部には凹部を設け、且つ前記ボックスのショルダ部には、締付け時前記凹部と干渉してこれを管外径側に摺動させる凸部を設け、前記凸部及び前記凹部の形状を、締付け完了時には前記凹部に連なるピン外径側の端部が前記ボックスに密着する形状としてなる油井管用ねじ継手において、前記ボックスの最奥端からピン挿入口側への管軸方向長さＡが前記δ１に対し、Ａ≧５０×｜δ１｜になる長さ領域である特定長さ領域内で、ねじ干渉量δ０を負で且つ｜δ０｜＜｜δ１｜としたことを特徴とする耐焼付き性に優れた油井管用ねじ継手。 The male side pin and the female side box that are screw-coupled by male and female taper screws, the screw part, the nose part that is successively connected to the tip side of the screw part, and the nose, both of which correspond to each other The nose portion has a negative seal interference amount δ1, a recess is provided in the shoulder portion of the pin, and the shoulder portion of the box interferes with the recess when tightened. Then, a convex portion is provided for sliding the tube toward the outer diameter side of the tube, and the shape of the convex portion and the concave portion is such that the end portion on the outer diameter side of the pin connected to the concave portion is in close contact with the box when tightening is completed. In the oil joint pipe threaded joint, the length A in the pipe axis direction from the innermost end of the box to the pin insertion port side is a length area where A ≧ 50 × | δ1 | And the screw interference amount δ0 is negative and | A threaded joint for oil country tubular goods excellent in seizure resistance, characterized in that δ0 | <| δ1 |.