JP3767668B2

JP3767668B2 - Threaded joint for oil well pipe

Info

Publication number: JP3767668B2
Application number: JP24189299A
Authority: JP
Inventors: 秀男山本; 和行中筋
Original assignee: Sumitomo Metal Industries Ltd
Current assignee: Nippon Steel Corp
Priority date: 1999-08-27
Filing date: 1999-08-27
Publication date: 2006-04-19
Anticipated expiration: 2019-08-27
Also published as: JP2001065754A

Description

【０００１】
【発明の属する技術分野】
本発明は、耐焼付き性に優れた炭素鋼製またはＣｒ含有量が１０重量％未満の低合金鋼製の油井管用ねじ継手に関し、更に詳しくは高深度、高温油井等の劣悪環境下の原油採掘において繰り返しの締め付け・緩め戻しに対して焼き付きことなく、かつ、気密性が保たれ、繰り返し使用できる油井管継手に関する。
【０００２】
【従来の技術】
通常、油井の深さは２０００ｍ〜３０００ｍであるが、近年の海洋油田などの深油井では８０００ｍ〜１００００ｍにも達する。このような油井に竪て込まれるチュービングやケーシングなどの油井管の連結には、一般的にねじ継手が用いられる。すなわち、油井管外面に形成した雄ねじとねじ継手内面に形成した雌ねじをはめ合わせ、締め付けることにより連結がおこなわれる。
【０００３】
ねじ継手には使用環境下で軸方向の引張力や内外面圧力などの複合した圧力や熱が作用するため、このような環境下においてもねじ継手の気密性が維持されること、ねじ継手が破損しないことが要求される。一方、チュービングやケーシングの降下作業時には、一度締め込んだ継手を緩め、再度締め直すことがあり、ＡＰＩ（米国石油協会）ではチュービングで１０回、ケーシングで３回の締め付け（メイクアップ）−締め戻し（ブレークアウト）を行ってもゴーリングと呼ばれる焼付きの発生がなく、気密性が維持されることが要求されている。ゴーリングが発生すると、気密性が不完全となり、繰り返し使用回数が低下する。
【０００４】
ところで、ねじ継手としては、通常、油井管の端部に形成した雄ねじの先端にねじ無し金属接触部を形成し、これと、ねじ継手の内面の雌ねじの基部に形成したねじ無し金属接触部とをはめ合わせ、締め付けることによりねじ無し金属接触部同士を当接してメタルシール部を形成した構造のねじ継手が使用される。
【０００５】
しかし、メタルシール部およびねじ部には高面圧が作用するため、特に、高温条件下ではゴーリングが発生しやすく、ＡＰＩの規格には、継手締結後に１７７℃×２４Ｈｒの耐熱試験を実施した後、締め戻し−再度締め付けを行っても気密性が保たれていることが要求されている。
【０００６】
そこで、上記要求に応じるため、従来より種々の対策案が提示されている。
例えば、特開平５−１１７８７０公報にはねじ継手の表面に平均粗さ２０〜６０μｍの凹凸加工を施した後、燐酸塩化成処理被膜を形成する方法が、また、特開平６−１０１５４公報にはメタルシール部の表面最大粗さと表面処理被膜層の厚さを規定して表面処理する方法が、特開平５−１４９４８５公報にはピンまたはボックス表面に分散めっき層を形成したねじ継手が、特開平２−８８５５９３公報には表面粗さを２０〜５０μｍに加工したメタルシール部にセラミックス塗装を施す方法が、特開平８−２３３１６４公報や特開平９−７２４６７公報にはボックスまたはピンの接触表面に二硫化モリブデン粉末を分散混合した樹脂被膜を形成したねじ継手が、それぞれ提示されている。
【０００７】
【発明が解決しようとする課題】
近年、従来より高温の２５０〜３００℃の使用環境下で用いる高温油井用や、原油回収効率を高めるため、臨界温度にも達する高温蒸気（３５０℃）を注入する蒸気注入油井用の耐熱性継手が要求されている。したがって、ねじ継手には、継手締結後に３５０℃を越す温度で耐熱試験を実施した後、締め戻し−再締結の処理を行っても気密性が保持される性能が要求される。
【０００８】
しかしながら、上記公報などに開示された従来の技術では、上記性能を確保することが難しい。即ち、ねじ継手を締結する際に、ＡＰＩの規格ＢＵＬ５Ａ２に規定されるようなコンパウンドグリスを使用する場合は、高温のためグリス成分が蒸発して潤滑性が低下するため、締め戻し後の再締め付け時において所定の気密性が得られないという問題がある。従って、コンパウンドグリスの塗布を念頭に置いた特開平５−１１７８７０公報、特開平６−１０１５４公報、特開平５−１４９４８５公報および特開平２−８８５５９３公報などに開示された技術では高温時の気密性の確保に問題がある。
【０００９】
また、コンパウンドグリスを使用しないことを特徴とする特開平８−２３３１６４公報や特開平９−７２４６７公報に開示された技術では、４００℃にも達する高温に長時間曝されると樹脂が変質するため、二硫化モリブデンなどの固体潤滑剤を保持するバインダー機能が喪失し、潤滑性が低下し、締付け不良や焼付きが発生し、更には気密性が悪化するという問題がある。
【００１０】
以上のように、４００℃にも達する高温環境下で繰り返し使用できる耐ゴーリング性に優れたねじ継手は得られていないのが現状である。
【００１１】
本発明の課題は、炭素鋼製またはＣｒ含有量が１０重量％未満の低合金製の耐ゴーリング性に優れた油井管用ねじ継手を提供することにある。更に詳しくは高深度、高温油井、あるいは蒸気注入油井等の高温環境下の原油採掘において繰り返しの締め付け・緩め戻しに対してゴーリングの発生を抑制し、気密性に優れた油井管用ねじ継手を提供することにある。
【００１２】
【課題を解決するための手段】
本発明者らは上記課題を解決するため、高温環境下における耐ゴーリング性に優れた潤滑被膜の形成に注視し、固体潤滑剤とバインダー（結合剤）の耐熱性、潤滑性、被膜処理性などに関して基礎的検討を行い、以下の知見を得た。
【００１３】
（イ）二硫化モリブデンや黒鉛等の固体潤滑剤は４００℃程度の温度でも熱による変質・分解もなく、常温と変わらない潤滑性を示す。
【００１４】
（ロ）固体潤滑剤のバインダーとして樹脂を用いると、２４Ｈｒを越える長時間の高温環境下では変質、分解、あるいは炭化が進み、固体潤滑剤を継手表面に被覆するバインダーとしての機能が失われ、潤滑性が低下する。
【００１５】
（ハ）Ｓｉ、Ｔｉ、Ａｌ等の酸化物、炭化物、窒化物等の無機化合物は、熱的に安定しているが、固体潤滑剤を被覆するバインダーとしての機能が全くない。従って、被膜形成ができないため、固体潤滑剤を混合しても潤滑性が低い。
【００１６】
（ニ）チタンアルコキシド（Ｔｉ（ＯＲ）₄、Ｒ＝アルキル基）はアルキル基を有するため、有機物的な特性を示し、バインダーとしての機能がある。この物質は大気中では不安定で、水分を吸収して共加水分解が起こり、分解物はお互いに結合して網目構造を有したＴｉ−Ｏを骨格とし熱的に安定な無機高分子化合物に変化する。（１）式に代表的な無機高分子化合物の分子構造式を例示する。
【００１７】
【化１】

【００１８】
（ホ）上記無機高分子化合物は硬質であり耐摩耗性に優れる。
（ヘ）従って、二硫化モリブデンや黒鉛などの固体潤滑剤にバインダーとしてチタンアルコキシドを混合して塗布し、加湿処理を施すことにより、二硫化モリブデンや黒鉛を含有し、潤滑性と耐熱性に優れたＴｉ−Ｏを骨格とする無機系の潤滑被膜を形成させることができる。
【００１９】
以上の基礎的検討結果を基に上記潤滑被膜を炭素鋼製またはＣｒ含有量が１０重量％未満の低合金鋼製のねじ継手に形成するための適正条件を検討し、以下の知見を得た。
【００２０】
（ト）少なくともピンあるいはボックスのいずれか一方のねじ無し金属接触部に燐酸塩化成処理被膜を形成し、更にその上に上記Ｔｉ−Ｏを骨格とする無機高分子化合物の被膜を形成することにより焼き付きが抑制される。
【００２１】
（チ）潤滑被膜を構成する固体潤滑剤は、二硫化モリブデンの粉末または黒鉛の粉末あるいは二硫化モリブデンと黒鉛の混合粉末で、無機高分子化合物の含有量Ａと上記固体潤滑剤の含有量Ｂとの重量比（Ｂ／Ａ）は０．３〜９．０の範囲とするとよい。
【００２２】
（リ）燐酸塩化成処理被膜を形成するねじ無し金属接触部の表面粗さはＲmax で３〜１５μｍとし、潤滑被膜の膜厚は５〜３０μｍとすることにより耐焼付き性が向上する。
【００２３】
本発明は、上記の知見に基づいて完成されたもので、その要旨は以下の通りである。
（１）ねじ部とねじ無し金属接触部をそれぞれ有するピンとボックスとから構成され、炭素鋼製またはＣｒ含有量が１０重量％未満の低合金鋼製のねじ継手において、ボックスとピンの少なくともいずれか一方のねじ無し金属接触部に燐酸塩化成処理被膜を形成させ、更に、該燐酸塩化成処理被膜上に二硫化モリブデンおよび／または黒鉛を分散混合したＴｉ−Ｏを骨格とする無機高分子化合物の潤滑被膜を形成したことを特徴とする油井管用ねじ継手。
【００２４】
（２）上記燐酸塩化成処理被膜が燐酸マンガン化成処理被膜であることを特徴とする上記（１）項に記載の油井管用ねじ継手。
【００２５】
（３）上記無機高分子化合物の含有量（Ａ）と、二硫化モリブデンと黒鉛の合計の含有量（Ｂ）との重量比（Ｂ／Ａ）が０．３〜９．０であることを特徴とする上記（１）項または（２）項に記載の油井管用ねじ継手。
【００２６】
（４）上記燐酸塩化成処理被膜を形成するねじ無し金属接触部の表面粗さがＲmax で３〜１５μｍであることを特徴とする上記（１）項ないし（３）項のいずれかに記載の油井管用ねじ継手。
【００２７】
（５）上記潤滑被膜の膜厚が５〜３０μｍであることを特徴とする上記（１）項ないし（４）項のいずれかに記載の油井管用ねじ継手。
【００２８】
【発明の実施の形態】
本発明は、高炭素鋼製やＣｒ含有量が１０重量％未満の低合金鋼製のねじ継手に関するものである。
【００２９】
図１は本発明の油井管用ねじ継手の構成を模式的に示す概要図である。符号１はボックス、２はピン、３はねじ部、４はねじ無し金属接触部、５はショルダー部を示す。
【００３０】
図２は本発明に係る潤滑被膜の形成状況の一例を示すピンのねじ無し金属接触部の断面拡大図である。符号６は潤滑被膜、７は無機高分子化合物、８は固体潤滑剤、９は燐酸塩化成処理被膜で、図１と同じ要素は同一の符号で示す。
【００３１】
図１に示すように、本発明の油井管用ねじ継手（以下、ねじ継手ともいう）は、油井管の内面に形成されるねじ部３とねじ無し金属接触部４からなるボックス１と、ねじ継手部材の外面に形成されるねじ部３とねじ無し金属接触部４からなるピン２とで構成される。更に、図２に示すように、ピンのねじ無し金属部の表面に燐酸塩化成処理被膜を形成し、更にその上に固体潤滑剤８を分散混合したＴｉ−Ｏを骨格とする無機高分子化合物７の潤滑被膜６を形成する。上記固体潤滑剤は、二硫化モリブデンまたは黒鉛を単独であるいは二硫化モリブデンと黒鉛とを混合して用いる。なお、図２は、ピンのねじ無し金属部に燐酸系化成処理層を形成する場合を示したが、少なくともピンとボックスのいずれか一方のねじ無し金属部に形成すればよい。
【００３２】
ねじ無し金属接触部（以下、単に金属接触部ともいう）はねじ部に比べ接触面圧が高く過酷な潤滑状態にあり、また、ねじ継手はピンとボックスとを相互にねじ込んで締結するため、少なくともピンとボックスのいずれかの一方の金属接触部に潤滑被膜を形成することにより耐焼付き性を向上させることができる。なお、材料強度が高く、ねじ部にも高い接触面圧が作用するねじ継手では、焼付きが発生しやすくなるため、金属接触部に加え更にねじ部にも潤滑被膜を形成することが望ましい。
【００３３】
Ｔｉ−Ｏを骨格とする無機高分子化合物（以下、単に無機高分子化合物ともいう）は、前記（１）式に例示する分子構造を備えており、二硫化モリブデンや黒鉛などの固体潤滑剤のバインダーとしての機能を有し潤滑被膜を形成する。例えば、無機高分子化合物として、（１）式のアルキル基がメチル、エチル、イソプロピル、プロピル、イソブチル、ブチルなどのアルキル基を備えたチタン化合物を挙げることができる。
【００３４】
二硫化モリブデンおよび黒鉛はいずれも締め付け作業の際の締め付け圧力で薄く伸ばされるため、潤滑被膜の潤滑性を高め、耐焼き付き性を向上させる作用がある。なお、二硫化モリブデンは黒鉛に比べ特に高面圧下において潤滑性が高いので、材料強度の高いねじ継手には二硫化モリブデンを単独で用いるのが望ましい。
【００３５】
無機高分子化合物の含有量（Ａ）と、二硫化モリブデンと黒鉛の合計の含有量（Ｂ）との重量比（Ｂ／Ａ）は０．３以上、９．０以下とするのが望ましい。重量比が０．３未満では形成される潤滑被膜の潤滑性向上の効果が少なく、耐焼き付き性の改善が不十分であり、また、重量比が９．０より大きくなると、潤滑被膜の密着性が低下し、特に潤滑被膜からの固体潤滑剤の剥離が著しいなどの問題が生じる。より好ましくは、重量比は０．５以上、７．０以下であり、更に好ましくは３．０以上、６．５以下である。
【００３６】
潤滑被膜の厚さは５μｍ以上、３０μｍ以下とすることが望ましい。潤滑被膜の厚さが５μｍ未満では潤滑性向上の効果が少なく、一方、３０μｍより大きくなると潤滑被膜形成の処理コストが嵩むとともに潤滑性向上の効果が飽和するため経済的に不利といった問題や潤滑被膜が剥離しやすくなるといった欠点がある。より好ましくは、潤滑被膜の膜厚は５μｍ以上、１５μｍ以下であり、更に好ましくは６μｍ以上、１０μｍ以下である。
【００３７】
上記潤滑被膜を形成する際の下地処理として、燐酸塩化成処理被膜を形成する。燐酸塩化成処理被膜は継手の材料表面に化学反応により形成された反応層で、、その表面は微細な結晶粒子が林立した構造をなす。従って、その層の下側の材料との密着性は極めて高く、また、その層の上に形成される潤滑被膜を繋ぎ止めるいわゆるアンカー効果が高まり、潤滑被膜の密着性が向上する。
【００３８】
燐酸塩化成処理被膜として、燐酸マンガン、燐酸亜鉛、燐酸カルシウムおよび燐酸亜鉛カルシウムなどの化成処理層を挙げることができる。これらの結晶の幾何学的形態はそれぞれ異なり、燐酸マンガンの結晶が最も微細で絨毯のように林立している。従って、アンカー効果の向上の観点から燐酸マンガン系化成処理層とするのが望ましい。
【００３９】
燐酸塩化成処理被膜の厚さについては特に限定していないが、薄すぎると潤滑被膜の剥離を抑制する効果が少なく、厚すぎると化成処理被膜の内部に亀裂が入り潤滑被膜とともに脱落する。従って、膜厚は３μｍ以上、１０μｍ以下とするのが望ましい。
【００４０】
上記燐酸塩化成処理被膜を形成するねじ無し金属接触部（下地）の表面粗さはＲmax で３μｍ以上、１５μｍ以下であることが望ましい。化成処理被膜を形成する際の下地処理として適正な表面粗さを付与することにより、その上に形成される燐酸塩化成処理被膜を物理的に捕捉するいわゆるアンカー効果が高まり、化成処理層の剥離が阻止される。表面粗さがＲmax で３μｍ未満ではアンカー効果が小さく化成処理層が剥離しやすい。一方、表面粗さが１５μｍを越えると締め付け・締め戻し時に粗さの凸部に形成された化成処理被膜上の潤滑被膜が破れて焼き付きが発生しやすい。より好ましい表面粗さは４μｍ以上、１０μｍ以下である。なお、本発明の処理を一方の面にのみ施す場合には、燐酸塩被膜を形成しない相対する面の表面粗さは上記下地の表面粗さ未満にするのがよい。
【００４１】
本発明のねじ継手は、従来、メークアップ前に塗布していたコンパウンドグリスなどの潤滑剤を一切使用することなく耐ゴーリング性を著しく改善することができる。
【００４２】
なお、本発明のねじ継手は、潤滑被膜中に防錆添加剤や腐食防止剤を添加し、耐焼き付き性を維持しながら錆の発生を防止することができる。防錆添加剤や腐食防止剤は公知のものを使用することができる。
【００４３】
次ぎに、本発明に係る被膜の形成方法を説明する。
本発明の方法は、燐酸塩系の溶液を用いてピンとボックスの少なくともいずれか一方の金属接触部の表面に化成処理を施して燐酸塩被膜を形成し、次いでチタンアルコキシド（Ｔｉ（ＯＲ）₄、Ｒ：アルキル基）と二硫化モリブデン粉末および／または黒鉛粉末とに分散媒を加えて混合し、これらを上記燐酸塩被膜の上にに塗布し、加湿処理を施して共加水分解させて、Ｔｉ−Ｏを骨格とする無機高分子化合物の潤滑被膜を形成する。
【００４４】
チタンアルコキシドとしては、アルキル基がメチル、エチル、イソプロピル、プロピル、イソブチル、ブチルなどのアルキル基を備えたチタンアルコキシドを用いることができる。
【００４５】
チタンアルコキシドと二硫化モリブデン、黒鉛の混合割合は、潤滑被膜を形成した後の乾燥した状態で、無機高分子化合物の含有量（Ａ）と、二硫化モリブデンと黒鉛の合計の含有量（Ｂ）との重量比が０．３以上９．０以下となるように決定される。
【００４６】
分散剤としては、キシレン、塩化メチレン、ブチルアルコールおよびメチルエチルケトンなどの低沸点液を単独にあるいは２種類以上組み合わせて用いることができる。
【００４７】
加湿処理は、大気中に所定時間放置することにより行うことができるが、湿度が７０％以上の雰囲気下で行うのが望ましい。更に、加湿処理後に加熱処理を行うことが望ましい。加熱処理により共加水分解が促進され、加水分解物であるアルキル物質の潤滑被膜内からの排出を促進することができ、潤滑被膜の密着性が強固となり、耐焼付き性が向上する。また、加熱は分散媒が蒸発した後に行うことが好ましい。加熱温度はアルキル物質の沸点に近い１００〜２００℃の温度とするのがよく、熱風を当てるとより効果的である。
【００４８】
また、本発明は、燐酸塩の被膜を形成する際に、予め下地処理としてブラスティング加工を施し、下地の表面粗さをＲmax で３〜１５μｍにするのが望ましい。ブラスティング加工を施すことにより、表面に活性な新生面が現れ、燐酸塩被膜の密着性が強固になり燐酸塩被膜の耐剥離性が向上する。ブラスティング加工は、公知のサンドブラスト法、ショットブラスト法やグリッドブラスト法などでよく、サンド、ショット、グリッドやカットワイヤーなどの硬質材を高速で吹き付ける方法により行うことができる。
【００４９】
【実施例】
表１に示す成分組成の炭素鋼製、Ｃｒ−Ｍｏ鋼製および５Ｃｒ鋼製のねじ継手（外径：７インチ、肉厚：０．４０８インチ）のボックスやピンのねじ部と金属接触部の双方に各種の下地処理や被膜形成などの表面処理を施した。表２、３に表面処理条件を示す。なお、同表に示す比較例は樹脂被膜を形成した、あるいはコンパウンドグリスを塗布したものである。
【００５０】
【表１】

【００５１】
【表２】

【００５２】
【表３】

【００５３】
次いで、上記表面処理を施したねじ継手を用い、表４に示す要領で最大２５回の締め付け・締め戻しの繰り返し作業を行い、焼き付きの発生状況を調査した。
【００５４】
【表４】

【００５５】
すなわち、表４に示すように、１〜１０回目、１２〜１５回目、１７〜２０回目、２２〜２５回目は常温にて締め付け・締め戻しを行い、一方、１１回目、１６回目および２１回目は常温にて締め付け後４００℃で２４時間の加熱処理を行い、その後冷却して常温で締め戻しを実施した。締め付け速度と締め付けトルクの条件を表５に示す。
【００５６】
【表５】

【００５７】
表６に焼き付き発生状況ならびに締め付け状況を示す。なお、以下、ピンのねじ部と金属接触部の双方の表面をピン表面といい、ボックスのねじ部と金属接触部の双方の表面をボックス表面という。また、表面粗さはＲmax 値で示す。
【００５８】
【表６】

【００５９】
（本発明例１）
表１に示す炭素鋼製のねじ継手に以下の表面処理を施した。ピン表面は機械仕上げのままで表面粗さを３μｍとした。ボックス表面は機械研削仕上げで表面粗さを３μｍとし、そのボックス表面に化成処理で厚さ５μｍの燐酸亜鉛被膜を形成した。更にその上面にアルキル基がメチルのチタンアルコキシドと、平均粒径が１．５μｍの二硫化モリブデンの粉末と平均粒径が３．５μｍの黒鉛の粉末をチタンアルコキシド１に対し二硫化モリブデン０．７７、黒鉛０．７７の重量割合で混合し、キシレン、塩化メチレンおよびブチルアルコールの混液を分散媒として塗布した。次いで、大気中で６時間放置した後、乾燥状態で燐酸亜鉛被膜の上面に形成された被膜の組成を測定したところ、含有量は重量の相対値でＴｉ−Ｏを骨格とする無機高分子化合物を１とすると、二硫化モリブデンが１、黒鉛が１であり、被膜厚さは４０μｍであった。
【００６０】
表６に示すように、表３の２０回目の締め付け・締め戻し作業までは焼き付きの発生が無く良好であった。しかし、２１回目の加熱処理後の締め戻し時に焼付きが発生した
（本発明例２）
表１に示す炭素鋼製のねじ継手に以下の表面処理を施した。ピン表面は機械研削仕上げで表面粗さを２μｍとした。ボックス表面は＃８０番のサンドを吹き付け、表面粗さを１０μｍとし、そのボックス表面に化成処理で厚さ１０μｍの燐酸亜鉛被膜を形成した。更にその上面にアルキル基がエチルのチタンアルコキシドと、平均粒径が１．８μｍの二硫化モリブデンの粉末と平均粒径が２．８μｍの黒鉛の粉末をチタンアルコキシド１に対し二硫化モリブデン２、黒鉛１．３３の重量割合で混合し、キシレン、塩化メチレンおよびブチルアルコールの混液を分散媒として塗布した。次いで、大気中で３時間放置後に１６５℃の熱風を３０分間吹き付けた。乾燥状態で燐酸亜鉛被膜の上面に形成された被膜の組成を測定したところ、含有量は重量割合でＴｉ−Ｏを骨格とする無機高分子１に対し二硫化モリブデン３、黒鉛２であり、被膜厚さは１０μｍであった。
【００６１】
表６に示すように、表３の２２回目の締め付け・締め戻し作業までは焼き付きの発生が無く良好であった。しかし、２３回目の締め付け時に焼付きが発生した。なお、締め付け時の締め込み量ならびに締め込みトルクは適正であった。
【００６２】
（本発明例３）
表１に示す５％Ｃｒ鋼製のねじ継手に以下の表面処理を施した。ボックス表面は機械研削仕上げで表面粗さを２μｍとした。ピン表面は＃８０番のサンドを吹き付け表面粗さを１０μｍとし、そのピン表面に化成処理で厚さ５μｍの燐酸カルシウム被膜を形成した。更にその上面にアルキル基がイソプロピルのチタンアルコキシドと、平均粒径が１．８μｍの二硫化モリブデンの粉末と平均粒径が２．５μｍの黒鉛の粉末をチタンアルコキシド１に対し二硫化モリブデン３．０６、黒鉛１．９４の重量割合で混合し、メチルエチルケトン、塩化メチレンおよびブチルアルコールの混液を分散媒として塗布した。次いで、大気中で２時間放置後に加湿した１５０℃の熱風を１５分間吹き付け、更に乾燥した１５０℃の熱風を吹き付けた。乾燥状態で燐酸カルシウム被膜の上面に形成された被膜の組成を測定したところ、含有量は重量割合でＴｉ−Ｏを骨格とする無機高分子１に対し二硫化モリブデン５．５、黒鉛３．５であり、被膜厚さは２０μｍであった。
【００６３】
表６に示すように、表３の２５回の締め付け・締め戻しにおいて、焼き付きの発生が無く極めて良好であった。また、締め付け時の締め込み量ならびに締め込みトルクも適正であった。
【００６４】
（本発明例４）
表１に示す炭素鋼製のねじ継手に以下の表面処理を施した。ボックス表面は機械研削仕上げで表面粗さを２μｍとした。ピン表面は＃８０番のショットを吹き付け表面粗さを１５μｍとし、そのピン表面に化成処理で厚さ１０μｍの燐酸マンガン被膜を形成した。更にその上面にアルキル基がプロピルのチタンアルコキシドと、平均粒径が４．６μｍの二硫化モリブデンの粉末と平均粒径が１．３μｍの黒鉛の粉末をチタンアルコキシド１に対し二硫化モリブデン２．７８、黒鉛０．８３の重量割合で混合し、メチルエチルケトン、塩化メチレンおよびブチルアルコールの混液を分散媒として塗布した。次いで、大気中で３時間放置後に加湿した１５０℃の熱風を１０分間吹き付けた。乾燥状態で燐酸カルシウム被膜の上面に形成された被膜の組成を測定したところ、含有量は重量割合でＴｉ−Ｏを骨格とする無機高分子１に対し二硫化モリブデン５．０、黒鉛１．５であり、被膜厚さは２０μｍであった。
【００６５】
表６に示すように、表３の２５回の締め付け・締め戻しにおいて、焼き付きの発生が無く極めて良好であった。また、締め付け時の締め込み量ならびに締め込みトルクも適正であった。
【００６６】
（本発明例５）
表１に示すＣｒ−Ｍｏ鋼製のねじ継手に以下の表面処理を施した。ピン表面とボックス表面に＃１８０番のサンドを吹き付け、双方とも表面粗さを３μｍとした。その双方の表面に化成処理で厚さ５μｍの燐酸マンガン被膜を形成した。更にその双方の上面にアルキル基がメチルのチタンアルコキシドと、平均粒径が１．２μｍの二硫化モリブデンの粉末をチタンアルコキシド１に対し二硫化モリブデン２．３１の重量割合で混合し、キシレン、塩化メチレンおよびブチルアルコールの混液を分散媒として塗布した。次いで、大気中で２時間放置後に加湿した１６５℃の熱風を３０分間吹き付けた。乾燥状態で燐酸マンガン被膜の上面に形成された被膜の組成を測定したところ、含有量は重量割合でＴｉ−Ｏを骨格とする無機高分子１に対し二硫化モリブデン３．０であり、被膜厚さはピン側、ボックス側とも８μｍであった。
【００６７】
表６に示すように、表３の２５回の締め付け・締め戻しにおいて、焼き付きの発生が無く極めて良好であった。また、締め付け時の締め込み量ならびに締め込みトルクも適正であった。
【００６８】
（本発明例６）
表１に示すＣｒ−Ｍｏ鋼製のねじ継手に以下の表面処理を施した。ピン表面は機械研削仕上げで表面粗さを２μｍとした。ボックス表面は機械研削仕上げで表面粗さを２μｍとし、そのボックス表面に化成処理で厚さ３μｍの燐酸マンガン被膜を形成した。更にその上面にアルキル基がイソブチルのチタンアルコキシドと、平均粒径が３．１μｍの二硫化モリブデンの粉末と平均粒径が３．５μｍの黒鉛の粉末をチタンアルコキシド１に対し二硫化モリブデン１．３９、黒鉛０．８３の重量割合で混合し、キシレン、塩化メチレンおよびイソブチルアルコールの混液を分散媒として塗布した。次いで、大気中で６時間放置し、乾燥状態で燐酸マンガン被膜の上面に形成された被膜の組成を測定したところ、含有量は重量割合でＴｉ−Ｏを骨格とする無機高分子１に対し二硫化モリブデン２．５、黒鉛１．５であり、被膜厚さは３０μｍであった。
【００６９】
表６に示すように、表３の２４回目の締め付け・締め戻し作業までは焼き付きの発生が無く良好であった。しかし、２５回目の締め付け時に焼付きが発生した。なお、締め付け時の締め込み量ならびに締め込みトルクも適正であった。
【００７０】
（本発明例７）
表１に示す５％Ｃｒ鋼製のねじ継手に以下の表面処理を施した。ピン表面とボックス表面に＃１２０番のサンドを吹き付け、双方とも表面粗さを５μｍとした。その双方の表面に化成処理で厚さ５μｍの燐酸マンガン被膜を形成した。更にその双方の上面にアルキル基がエチルのチタンアルコキシドと、平均粒径が１．０μｍの二硫化モリブデンの粉末をチタンアルコキシド１に対し二硫化モリブデン０．２３の重量割合で混合し、キシレン、塩化メチレンおよびブチルアルコールの混液を分散媒として塗布した。次いで、大気中で４時間放置後に１５０℃の熱風を１５分間吹き付けた。乾燥状態で燐酸マンガン被膜の上面に形成された被膜の組成を測定したところ、含有量は重量割合でＴｉ−Ｏを骨格とする無機高分子１に対し二硫化モリブデン０．３５であり、被膜厚さはピン側、ボックス側とも２０μｍであった。
【００７１】
表６に示すように、表３の２５回の締め付け・締め戻しにおいて、焼き付きの発生が無く極めて良好であった。また、締め付け時の締め込み量ならびに締め込みトルクも適正であった。
【００７２】
（本発明例８）
表１に示すＣｒ−Ｍｏ鋼製のねじ継手に以下の表面処理を施した。ピン表面とボックス表面に＃１８０番のサンドを吹き付け、双方とも表面粗さを４μｍとした。その双方の表面に化成処理で厚さ５μｍの燐酸亜鉛被膜を形成した。更にその双方の上面にアルキル基がイソプロピルのチタンアルコキシドと、平均粒径が１．２μｍの二硫化モリブデンの粉末と平均粒径が１．５μｍの黒鉛の粉末をチタンアルコキシド１に対し二硫化モリブデン２．７７、黒鉛０．８３の重量割合で混合し、キシレン、塩化メチレンおよびブチルアルコールの混液を分散媒として塗布した。次いで、大気中で３時間放置後に加湿した１４０℃の熱風を２０分間吹き付けた。乾燥状態で燐酸亜鉛被膜の上面に形成された被膜の組成を測定したところ、含有量は重量割合でＴｉ−Ｏを骨格とする無機高分子１に対し二硫化モリブデン５．０、黒鉛１．５であり、被膜厚さはピン側、ボックス側とも１０μｍであった。
【００７３】
表６に示すように、表３の２５回の締め付け・締め戻しにおいて、焼き付きの発生が無く極めて良好であった。また、締め付け時の締め込み量ならびに締め込みトルクも適正であった。
【００７４】
（本発明例９）
表１に示す炭素鋼製のねじ継手に以下の表面処理を施した。ピン表面は機械研削仕上げで表面粗さを２μｍとした。ボックス表面は＃１８０番のサンドを吹き付け、表面粗さを５μｍとし、そのボックス表面に化成処理で厚さ５μｍの燐酸マンガン被膜を形成した。更に、ピン表面と燐酸マンガン被膜の上面にアルキル基がエチルのチタンアルコキシドと、平均粒径が１．２μｍの二硫化モリブデンの粉末と平均粒径が１．５μｍの黒鉛の粉末をチタンアルコキシド１に対し二硫化モリブデン１．３３、黒鉛１．０の重量割合で混合し、キシレン、塩化メチレンおよびブチルアルコールの混液を分散媒として塗布した。次いで、大気中で６時間放置し、乾燥状態でピン表面ならびに燐酸亜鉛被膜の上面に形成された被膜の組成を測定したところ、双方とも含有量は重量割合でＴｉ−Ｏを骨格とする無機高分子１に対し二硫化モリブデン２、黒鉛１．５であり、被膜厚さは５μｍであった。
【００７５】
表６に示すように、表３の２５回の締め付け・締め戻しにおいて、焼き付きの発生が無く極めて良好であった。また、締め付け時の締め込み量ならびに締め込みトルクも適正であった。
【００７６】
（本発明例１０）
表１に示すＣｒ−Ｍｏ鋼製のねじ継手に以下の表面処理を施した。ピン表面は機械仕上げのままで表面粗さを３μｍとした。ボックス表面は機械研削仕上げで表面粗さを３μｍとし、そのボックス表面に化成処理で厚さ１０μｍの燐酸亜鉛被膜を形成した。更にその上面にアルキル基がエチルのチタンアルコキシドと、平均粒径が３．５μｍの二硫化モリブデンの粉末と平均粒径が３．１μｍの黒鉛の粉末をチタンアルコキシド１に対し二硫化モリブデン４．０、黒鉛２．３３の重量割合で混合し、キシレン、塩化メチレンおよびブチルアルコールの混液を分散媒として塗布した。次いで、大気中で６時間放置した後、乾燥状態で燐酸亜鉛被膜の上面に形成された被膜の組成を測定したところ、含有量は重量の相対値でＴｉ−Ｏを骨格とする無機高分子化合物を１とすると、二硫化モリブデンが６、黒鉛が３．５であり、被膜厚さは２０μｍであった。
【００７７】
表６に示すように、表３の１５回目の締め付け・締め戻し作業までは焼き付きの発生が無く良好であった。しかし、１６回目の締め付け時に焼付きが発生した。なお、締め付け時の締め込み量ならびに締め込みトルクは適正であった。
【００７８】
（本発明例１１）
表１に示す炭素鋼製のねじ継手に以下の表面処理を施した。ボックス表面は機械研削仕上げで表面粗さを２μｍとした。ピン表面は＃１８０番のサンドを吹き付け表面粗さを１０μｍとし、そのピン表面に化成処理で厚さ１０μｍの燐酸カルシウム被膜を形成した。更にその上面にアルキル基がプロピルのチタンアルコキシドと、平均粒径が４．６μｍの二硫化モリブデンの粉末をチタンアルコキシド１に対し二硫化モリブデン０．１４の重量割合で混合し、メチルエチルケトン、塩化メチレンおよびイソブチルアルコールの混液を分散媒として塗布した。次いで、大気中で３時間放置後に加湿した１５０℃の熱風を３０分間吹き付けた。乾燥状態で燐酸カルシウム被膜の上面に形成された被膜の組成を測定したところ、含有量は重量割合でＴｉ−Ｏを骨格とする無機高分子１に対し二硫化モリブデン０．２５であり、被膜厚さは２５μｍであった。
【００７９】
表６に示すように、表３の１６回目の締め付け・締め戻し作業までは焼き付きの発生が無く良好であった。しかし、１７回目の締め付け時に焼付きが発生した。なお、締め付け時の締め込み量ならびに締め込みトルクは適正であった。
【００８０】
（比較例１）
表１に示す５％Ｃｒ鋼製のねじ継手に以下の表面処理を施した。ピン表面とボックス表面に＃８０番のサンドを吹き付け、双方とも表面粗さを１０μｍとした。その双方の表面にエポキシ樹脂と平均粒径が１．８μｍ粉末をエポキシ樹脂１に対して二硫化モリブデン１の重量割合で、トルエン、イソプロピルアルコールなどの混液を分散媒として混合し塗布した。次いで、乾燥後１８０℃で３０分間の加熱処理を実施した。加熱処理後の被膜の組成を測定したところ、ピン側及びボックス側のいずれも、含有量は重量割合でエポキシ樹脂１に対し二硫化モリブデン１であり、被膜厚は２０μｍであった。
【００８１】
表６に示すように、１２回目の締め付けで軽度の焼き付きが認められ、また、締め付け量が不足してショルダー部に所定の面圧を負荷することができなかった。そこで、所定位置まで締め込むように締め付けトルクを高めたところ、１３回目の締め付けで焼き付きが発生した。
【００８２】
（比較例２）
表１に示す炭素鋼製のねじ継手に下記の表面処理を施した。ピン表面は機械研削仕上げで表面粗さを２μｍとした。ボックス表面は機械研削仕上げで表面粗さを２μｍとし、そのボックス表面に厚さ２μｍの溶融塩窒化層を形成し、その上に厚さ１５μｍの燐酸マンガン層を形成した。次いで、ポリアミドイミド樹脂と平均粒径が３．５μｍの二硫化タングステン粉末をポリアミドイミド樹脂１に対し二硫化タングステン１の重量割合でキシレン、トルエンおよびイソプロピルアルコールの混液を分散剤として混合し、上記燐酸マンガン層の上面に塗布した。次いで、乾燥後１８０℃で３０分の加熱処理を実施した。加熱処理後の燐酸マンガン層の上面に形成された被膜の組成を測定したところ、含有量は重量割合でポリアミドイミド樹脂１に対して二硫化タングステン１であり、被膜厚は３５μｍであった。
【００８３】
表６に示すように、１２回目の締め付けで焼き付きは認められなかったが、締付け量が不足して、ショルダー部に所定の面圧がかからなかった。そこで、所定位置まで締込むよう締付けトルクを高めたところ、１４回目の締付けで焼付きが発生した。
【００８４】
（比較例３）
表１に示す炭素鋼製のねじ継手に下記の表面処理を施した。ボックス表面は機械研削仕上げで表面粗さを２μｍとした。ピン表面は＃８０番のサンドを吹き付けて表面粗さを１０μｍとし、そのピン表面に厚さ１５μｍの燐酸マンガン層を形成し、その上にエポキシ樹脂と平均粒径が１．８μｍの二硫化モリブデン粉末をエポキシ樹脂１に対して二硫化モリブデン１の重量割合でトルエン、イソプロピルアルコール等の混液を分散媒として混合し塗布した。次いで、乾燥後１８０℃で３０分の加熱処理を実施した。加熱処理後の燐酸マンガン層の上面に形成された被膜の組成を測定したところ、含有量は重量割合でエポキシ樹脂１に対して二硫化モリブデン１であり、被膜厚は３０μｍであった。
【００８５】
表６に示すように、１２回目の締め付けで焼き付きが認められ、しかも、締付け量が不足して、ショルダー部に所定の面圧を負荷することができなかった。
【００８６】
（比較例４）
表１に示す５％Ｃｒ鋼製のねじ継手に下記の表面処理を施した。ピン表面は機械研削仕上げで表面粗さを２μｍとした。表面粗さ２μｍに機械研削仕上げを施したボックス表面に厚さ１０μｍのＣｕメッキ処理を施した。次いで、ピン表面とボックス表面の双方にＡＰＩ−Ｂｕｌ５Ａ２に相当するコンパウンドグリスを単位面積（１ｄｍ²）当たり約２０ｇの割合で塗布した。
【００８７】
表６に示すように、１２回目の締め付けで軽度の焼き付きが認められ、また、締め付け量が不足してショルダー部に所定の面圧を負荷することができなかった。そこで、所定位置まで締込むよう締付けトルクを高めたところ、１３回目の締付けで焼付きが発生した。
【００８８】
（比較例５）
表１に示す炭素鋼製の継手に下記の表面処理を施した。ピン表面は機械研削仕上げで表面粗さを２μｍとした。＃８０番のサンドを吹き付け表面粗さを１０μｍとしたボックス表面に化成処理を施し厚さ１５μｍの燐酸マンガン被膜を形成した。次いで、ピン表面と燐酸マンガン被膜の上面の双方にＡＰＩ−Ｂｕｌ５Ａ２に相当するコンパウンドグリスを単位面積（１ｄｍ²）当たり約２０ｇの割合で塗布した。
【００８９】
表６に示すように、８回目の締め付けから軽度の焼付きが発生したが手入れを実施して試験を継続した。しかし、１１回目の締め戻し時に焼付きが認められ、１２回目の締付けで焼付きが著しくなるとともに、締付け量が不足して、ショルダー部に所定の面圧を負荷することができなかった
以上のように、本発明の燐酸系化成処理被膜の上にＴ−Ｏを骨格とする無機系潤滑被膜を形成したねじ継手は、従来の樹脂をバインダーとした継手やコンパウンドグリスを使用した継手に比べ、高温履歴時の耐焼付き性に優れることが判った。
【００９０】
【発明の効果】
本発明による炭素鋼製あるいは低合金鋼製のねじ継手は高深度、高温油井、あるいは蒸気注入油井等の４００℃にも達する高温環境下の原油採掘における繰り返しの締め付け、緩め戻しの際の耐焼き付き性を著しく向上させることができる。
【図面の簡単な説明】
【図１】本発明の油井管用ねじ継手の構成を模式的に示す概要図である。
【図２】本発明に係る潤滑被膜の形成状況の一例を示す模式的断面図である。
【符号の説明】
１：ボックス、２：ピン、
３：ねじ部、４：ねじ無し金属接触部、
５：ショルダー部、６：潤滑被膜、
７：無機系高分子化合物、８：固体潤滑剤
９：燐酸塩化成処理被膜。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a threaded joint for oil well pipes made of carbon steel having excellent seizure resistance or a low alloy steel having a Cr content of less than 10% by weight, and more specifically, crude oil mining in a poor environment such as high depth and high temperature oil wells. It is related with the oil well pipe joint which can be used repeatedly, without being seized with repeated tightening / relaxing and maintaining airtightness.
[0002]
[Prior art]
Usually, the depth of the oil well is 2000 m to 3000 m, but in a deep oil well such as a recent offshore oil field, it reaches 8000 m to 10,000 m. In general, a threaded joint is used to connect oil well pipes such as a tubing and a casing that are inserted into the oil well. That is, the connection is performed by fitting the male screw formed on the outer surface of the oil well pipe with the female screw formed on the inner surface of the threaded joint and tightening.
[0003]
Since combined pressure and heat, such as axial tensile force and inner / outer surface pressure, act on the threaded joint in the operating environment, the tightness of the threaded joint is maintained even in such an environment, It is required not to break. On the other hand, when lowering the tubing or casing, the joint once tightened may be loosened and retightened. API (American Petroleum Institute) tightens 10 times with tubing and 3 times with casing (make-up)-tightening back Even when (breakout) is performed, there is no occurrence of seizure called goling, and airtightness is required to be maintained. When goling occurs, the airtightness becomes incomplete and the number of repeated uses decreases.
[0004]
By the way, as a threaded joint, an unthreaded metal contact portion is usually formed at the tip of a male thread formed at the end of an oil well pipe, and an unthreaded metal contact portion formed at the base of a female thread on the inner surface of the threaded joint. A threaded joint having a structure in which a metal seal portion is formed by abutting and tightening the screw-free metal contact portions to each other is used.
[0005]
However, since high surface pressure acts on the metal seal part and the screw part, goling is likely to occur particularly under high temperature conditions, and the API standard is that after a heat resistance test of 177 ° C. × 24 Hr is performed after the joint is fastened. , Retightening—It is required that airtightness is maintained even after retightening.
[0006]
Therefore, various countermeasures have been proposed to meet the above requirements.
For example, Japanese Patent Laid-Open No. 5-117870 discloses a method of forming a phosphate chemical conversion coating film after subjecting the surface of a threaded joint to irregularities with an average roughness of 20-60 μm, and Japanese Patent Laid-Open No. 6-10154 A method for surface treatment by defining the maximum surface roughness of the metal seal portion and the thickness of the surface treatment coating layer is disclosed in JP-A-5-149485, and a threaded joint in which a dispersion plating layer is formed on the surface of a pin or box is disclosed in Japanese Patent No. 2-885933 discloses a method of applying a ceramic coating to a metal seal portion having a surface roughness of 20 to 50 μm, and Japanese Patent Application Laid-Open No. 8-233164 and Japanese Patent Application Laid-Open No. 9-72467 have two methods for forming a contact surface of a box or a pin. Each of the threaded joints formed with a resin film in which molybdenum sulfide powder is dispersed and mixed is presented.
[0007]
[Problems to be solved by the invention]
In recent years, heat-resistant joints for high-temperature oil wells used in a higher temperature environment of 250-300 ° C. and steam injection wells for injecting high-temperature steam (350 ° C.) that reaches the critical temperature in order to increase crude oil recovery efficiency. Is required. Therefore, a threaded joint is required to have a performance that maintains airtightness even after a tightening-refastening process is performed after a heat resistance test is performed at a temperature exceeding 350 ° C. after the joint is fastened.
[0008]
However, it is difficult to ensure the above performance with the conventional techniques disclosed in the above publications. That is, when using a compound grease as defined in API standard BUL5A2 when fastening the threaded joint, the grease component evaporates due to the high temperature and the lubricity deteriorates. There is a problem that a predetermined airtightness cannot be obtained. Therefore, the techniques disclosed in JP-A-5-117870, JP-A-6-10154, JP-A-5-149485, JP-A-2-885933 and the like with the application of compound grease in mind are airtight at high temperatures. There is a problem in securing.
[0009]
In addition, in the techniques disclosed in Japanese Patent Laid-Open Nos. 8-233164 and 9-72467, which do not use compound grease, the resin changes in quality when exposed to a high temperature as high as 400 ° C. for a long time. There is a problem that a binder function for holding a solid lubricant such as molybdenum disulfide is lost, lubricity is lowered, tightening failure or seizure occurs, and airtightness is further deteriorated.
[0010]
As described above, the present situation is that a threaded joint excellent in galling resistance that can be repeatedly used in a high temperature environment as high as 400 ° C. has not been obtained.
[0011]
An object of the present invention is to provide a threaded joint for oil country tubular goods excellent in galling resistance, made of carbon steel or made of a low alloy having a Cr content of less than 10% by weight. More specifically, it provides a threaded joint for oil well pipes that suppresses the occurrence of galling against repeated tightening and loosening in crude oil mining in high-temperature environments such as deep, high-temperature oil wells, or steam injection wells, and has excellent airtightness. There is.
[0012]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have focused on the formation of a lubricating coating excellent in galling resistance in a high-temperature environment, and the heat resistance, lubricity, coating processability of a solid lubricant and a binder (binder), etc. A basic study was conducted and the following findings were obtained.
[0013]
(A) Solid lubricants such as molybdenum disulfide and graphite are not altered or decomposed by heat even at a temperature of about 400 ° C., and exhibit a lubricity that is not different from that at room temperature.
[0014]
(B) When a resin is used as a binder for a solid lubricant, the transformation, decomposition, or carbonization proceeds in a high temperature environment over 24 hours, and the function as a binder for coating the surface of the joint with the solid lubricant is lost. Lubricity decreases.
[0015]
(C) Inorganic compounds such as oxides such as Si, Ti, and Al, carbides, and nitrides are thermally stable, but have no function as a binder for coating the solid lubricant. Therefore, since a film cannot be formed, the lubricity is low even if a solid lubricant is mixed.
[0016]
(D) Titanium alkoxide (Ti (OR) _Four , R = alkyl group) has an alkyl group and therefore exhibits organic properties and functions as a binder. This substance is unstable in the atmosphere, and co-hydrolysis occurs by absorbing moisture, and the decomposition products are bonded to each other to form a thermally stable inorganic polymer compound with a network structure of Ti-O. Change. The formula (1) illustrates a typical molecular structural formula of an inorganic polymer compound.
[0017]
[Chemical 1]

[0018]
(E) The inorganic polymer compound is hard and has excellent wear resistance.
(F) Therefore, by mixing titanium alkoxide as a binder with a solid lubricant such as molybdenum disulfide and graphite, and applying a humidification treatment, it contains molybdenum disulfide and graphite and is excellent in lubricity and heat resistance. In addition, an inorganic lubricating film having Ti—O as a skeleton can be formed.
[0019]
Based on the above basic study results, we examined the appropriate conditions for forming the above lubricating coating on a threaded joint made of carbon steel or low alloy steel with a Cr content of less than 10% by weight, and obtained the following knowledge .
[0020]
(G) By forming a phosphate chemical conversion coating on at least one of the pins and the unthreaded metal contact portion of the box, and further forming a coating of the inorganic polymer compound having the Ti-O skeleton thereon. Burn-in is suppressed.
[0021]
(H) The solid lubricant constituting the lubricating coating is a powder of molybdenum disulfide, a powder of graphite, or a mixed powder of molybdenum disulfide and graphite. The content A of the inorganic polymer compound and the content B of the solid lubricant The weight ratio (B / A) is preferably in the range of 0.3 to 9.0.
[0022]
(I) The surface roughness of the unthreaded metal contact portion for forming the phosphate chemical conversion coating is 3 to 15 μm in Rmax, and the film thickness of the lubricating coating is 5 to 30 μm to improve the seizure resistance.
[0023]
The present invention has been completed based on the above findings, and the gist thereof is as follows.
(1) In a threaded joint made of carbon steel or a low alloy steel having a Cr content of less than 10% by weight, each of the box and the pin is composed of a pin and a box each having a threaded portion and an unthreaded metal contact portion. An inorganic polymer compound having a skeleton of Ti-O in which a phosphate chemical conversion coating film is formed on one screwless metal contact portion and molybdenum disulfide and / or graphite is dispersed and mixed on the phosphate chemical conversion coating film. A threaded joint for oil well pipes, characterized in that a lubricating coating is formed.
[0024]
(2) The threaded joint for oil country tubular goods according to (1) above, wherein the phosphate chemical conversion coating is a manganese phosphate chemical conversion coating.
[0025]
(3) The weight ratio (B / A) between the content (A) of the inorganic polymer compound and the total content (B) of molybdenum disulfide and graphite is 0.3 to 9.0. The threaded joint for oil country tubular goods as described in the above item (1) or (2).
[0026]
(4) The surface roughness of the unthreaded metal contact portion forming the phosphate chemical conversion coating film is 3 to 15 μm in Rmax, as described in any one of (1) to (3) above Threaded joint for oil well pipes.
[0027]
(5) The threaded joint for oil country tubular goods according to any one of (1) to (4) above, wherein the lubricating coating has a thickness of 5 to 30 μm.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a threaded joint made of high carbon steel or low alloy steel having a Cr content of less than 10% by weight.
[0029]
FIG. 1 is a schematic diagram schematically showing the configuration of a threaded joint for oil country tubular goods according to the present invention. Reference numeral 1 denotes a box, 2 denotes a pin, 3 denotes a threaded portion, 4 denotes an unthreaded metal contact portion, and 5 denotes a shoulder portion.
[0030]
FIG. 2 is an enlarged cross-sectional view of the unthreaded metal contact portion of the pin showing an example of the formation state of the lubricating coating according to the present invention. Reference numeral 6 is a lubricating coating, 7 is an inorganic polymer compound, 8 is a solid lubricant, 9 is a phosphate chemical conversion coating, and the same elements as those in FIG.
[0031]
As shown in FIG. 1, a threaded joint for oil country tubular goods (hereinafter also referred to as a threaded joint) of the present invention includes a box 1 including a threaded part 3 and an unthreaded metal contact part 4 formed on the inner surface of the oil country tubular goods, and a threaded joint. It is comprised by the screw part 3 formed in the outer surface of a member, and the pin 2 which consists of a screwless metal contact part 4. FIG. Further, as shown in FIG. 2, an inorganic polymer compound having a skeleton of Ti—O in which a phosphate chemical conversion coating film is formed on the surface of the unthreaded metal portion of the pin and solid lubricant 8 is dispersed and mixed thereon. 7 is formed. As the solid lubricant, molybdenum disulfide or graphite is used alone or in a mixture of molybdenum disulfide and graphite. FIG. 2 shows the case where the phosphoric acid-based chemical conversion treatment layer is formed on the unthreaded metal portion of the pin, but it may be formed on at least one of the unthreaded metal portion of the pin or the box.
[0032]
The unthreaded metal contact portion (hereinafter also simply referred to as the metal contact portion) has a higher contact surface pressure than the threaded portion and is in a severely lubricated state, and the threaded joint is fastened by screwing the pin and the box into each other. The seizure resistance can be improved by forming a lubricant film on one of the metal contact portions of the pin and the box. Note that in a threaded joint having high material strength and high contact surface pressure acting on the threaded portion, seizure is likely to occur. Therefore, it is desirable to form a lubricant film on the threaded portion in addition to the metal contacted portion.
[0033]
An inorganic polymer compound having a skeleton of Ti-O (hereinafter also simply referred to as an inorganic polymer compound) has a molecular structure exemplified in the above formula (1), and is a solid lubricant such as molybdenum disulfide and graphite. It has a function as a binder and forms a lubricating coating. For example, examples of the inorganic polymer compound include titanium compounds in which the alkyl group represented by the formula (1) has an alkyl group such as methyl, ethyl, isopropyl, propyl, isobutyl, and butyl.
[0034]
Since both molybdenum disulfide and graphite are thinly stretched by the tightening pressure during the tightening operation, they have the effect of improving the lubricity of the lubricating coating and improving the seizure resistance. Since molybdenum disulfide has higher lubricity than graphite, particularly under high surface pressure, it is desirable to use molybdenum disulfide alone for a threaded joint with high material strength.
[0035]
The weight ratio (B / A) between the content (A) of the inorganic polymer compound and the total content (B) of molybdenum disulfide and graphite is preferably 0.3 or more and 9.0 or less. When the weight ratio is less than 0.3, the effect of improving the lubricity of the formed lubricating film is small, and the improvement of the seizure resistance is insufficient. When the weight ratio is larger than 9.0, the adhesion of the lubricating film is increased. In particular, problems such as significant peeling of the solid lubricant from the lubricating coating occur. More preferably, the weight ratio is 0.5 or more and 7.0 or less, and further preferably 3.0 or more and 6.5 or less.
[0036]
The thickness of the lubricating coating is desirably 5 μm or more and 30 μm or less. If the thickness of the lubricating coating is less than 5 μm, the effect of improving the lubricity is small. On the other hand, if the thickness is larger than 30 μm, the processing cost for forming the lubricating coating increases and the effect of improving the lubricity is saturated. Has the disadvantage that it is easy to peel off. More preferably, the thickness of the lubricating coating is 5 μm or more and 15 μm or less, and more preferably 6 μm or more and 10 μm or less.
[0037]
As a base treatment for forming the lubricating coating, a phosphate chemical conversion coating is formed. The phosphate chemical conversion coating is a reaction layer formed by chemical reaction on the surface of the joint material, and the surface has a structure in which fine crystal particles are forested. Therefore, the adhesiveness with the material under the layer is extremely high, and the so-called anchor effect for securing the lubricating coating formed on the layer is increased, and the adhesiveness of the lubricating coating is improved.
[0038]
Examples of the phosphate chemical conversion coating include chemical conversion treatment layers such as manganese phosphate, zinc phosphate, calcium phosphate, and zinc calcium phosphate. These crystals have different geometrical forms, and the crystals of manganese phosphate are the finest and stand like a carpet. Therefore, it is desirable to use a manganese phosphate-based chemical conversion treatment layer from the viewpoint of improving the anchor effect.
[0039]
The thickness of the phosphate chemical conversion coating is not particularly limited, but if it is too thin, the effect of suppressing the peeling of the lubricating coating is small, and if it is too thick, the chemical conversion coating will crack inside and fall off with the lubricating coating. Therefore, the film thickness is desirably 3 μm or more and 10 μm or less.
[0040]
The surface roughness of the unthreaded metal contact portion (underlying) for forming the phosphate chemical conversion coating is preferably 3 μm or more and 15 μm or less in terms of Rmax. By imparting an appropriate surface roughness as a base treatment when forming a chemical conversion coating, the so-called anchor effect that physically captures the phosphate chemical conversion coating formed thereon is enhanced, and the chemical conversion layer is peeled off. Is blocked. When the surface roughness is less than 3 μm in Rmax, the anchor effect is small and the chemical conversion treatment layer is easy to peel off. On the other hand, when the surface roughness exceeds 15 μm, the lubricating coating on the chemical conversion coating formed on the convex portion of the roughness is broken at the time of tightening / tightening, and seizure is likely to occur. A more preferable surface roughness is 4 μm or more and 10 μm or less. When the treatment of the present invention is performed only on one surface, the surface roughness of the opposing surface on which the phosphate coating is not formed should be less than the surface roughness of the base.
[0041]
The threaded joint of the present invention can remarkably improve the galling resistance without using any lubricant such as compound grease that has been applied before the make-up.
[0042]
In addition, the screw joint of this invention can prevent generation | occurrence | production of rust, adding a rust preventive additive and a corrosion inhibitor in a lubricating film, and maintaining seizure resistance. A well-known thing can be used for a rust inhibitor and a corrosion inhibitor.
[0043]
Next, a method for forming a film according to the present invention will be described.
In the method of the present invention, a phosphate coating is formed by subjecting the surface of the metal contact portion of at least one of the pin and the box to a phosphate coating using a phosphate-based solution, and then titanium alkoxide (Ti (OR)). _Four , R: alkyl group) and molybdenum disulfide powder and / or graphite powder are mixed with a dispersion medium, and these are applied on the phosphate coating and subjected to humidification to co-hydrolyze, A lubricating coating of an inorganic polymer compound having Ti—O as a skeleton is formed.
[0044]
As the titanium alkoxide, a titanium alkoxide in which an alkyl group is provided with an alkyl group such as methyl, ethyl, isopropyl, propyl, isobutyl, and butyl can be used.
[0045]
The mixing ratio of titanium alkoxide, molybdenum disulfide, and graphite is the content of the inorganic polymer compound (A) and the total content of molybdenum disulfide and graphite (B) in the dry state after the formation of the lubricating coating. The weight ratio is determined to be not less than 0.3 and not more than 9.0.
[0046]
As the dispersant, low boiling point liquids such as xylene, methylene chloride, butyl alcohol and methyl ethyl ketone can be used alone or in combination of two or more.
[0047]
The humidification treatment can be performed by leaving it in the air for a predetermined time, but it is desirable to perform it in an atmosphere with a humidity of 70% or more. Furthermore, it is desirable to perform heat treatment after the humidification treatment. The co-hydrolysis is promoted by the heat treatment, the discharge of the hydrolyzate alkyl substance from the lubricating coating can be promoted, the adhesion of the lubricating coating is strengthened, and the seizure resistance is improved. The heating is preferably performed after the dispersion medium has evaporated. The heating temperature is preferably a temperature of 100 to 200 ° C. close to the boiling point of the alkyl substance, and is more effective when hot air is applied.
[0048]
Further, in the present invention, when forming the phosphate film, it is desirable to perform blasting as a base treatment in advance, so that the surface roughness of the base is 3 to 15 μm in terms of Rmax. By performing blasting, an active new surface appears on the surface, the adhesion of the phosphate coating is strengthened, and the peel resistance of the phosphate coating is improved. The blasting process may be performed by a known sand blasting method, shot blasting method, grid blasting method, or the like, and can be performed by a method of spraying a hard material such as sand, shot, grid or cut wire at high speed.
[0049]
【Example】
Threaded joints of carbon steel, Cr-Mo steel, and 5Cr steel screw joints (outer diameter: 7 inches, wall thickness: 0.408 inches) and metal contact portions of the component compositions shown in Table 1 Both were subjected to various surface treatments such as various base treatments and film formation. Tables 2 and 3 show the surface treatment conditions. In addition, the comparative example shown to the same table formed the resin film, or apply | coated compound grease.
[0050]
[Table 1]

[0051]
[Table 2]

[0052]
[Table 3]

[0053]
Next, using the threaded joint subjected to the above surface treatment, a maximum of 25 tightening / rewinding operations were repeated in the manner shown in Table 4, and the occurrence of seizure was investigated.
[0054]
[Table 4]

[0055]
That is, as shown in Table 4, the 1st to 10th, the 12th to 15th, the 17th to 20th, the 22nd to 25th are tightened and retightened at room temperature, while the 11th, 16th and 21st are After tightening at normal temperature, a heat treatment was performed at 400 ° C. for 24 hours, and then cooled and tightened at normal temperature. Table 5 shows the conditions of the fastening speed and the fastening torque.
[0056]
[Table 5]

[0057]
Table 6 shows the seizure occurrence and tightening conditions. Hereinafter, the surfaces of both the screw portion of the pin and the metal contact portion are referred to as the pin surface, and the surfaces of both the screw portion of the box and the metal contact portion are referred to as the box surface. The surface roughness is indicated by Rmax value.
[0058]
[Table 6]

[0059]
(Invention Example 1)
The following surface treatments were applied to the carbon steel threaded joint shown in Table 1. The pin surface was machine finished and the surface roughness was 3 μm. The surface of the box was mechanically ground to a surface roughness of 3 μm, and a 5 μm thick zinc phosphate coating was formed on the box surface by chemical conversion treatment. Further, a titanium alkoxide having an alkyl group of methyl on its upper surface, a molybdenum disulfide powder having an average particle diameter of 1.5 μm, and a graphite powder having an average particle diameter of 3.5 μm are added to the titanium alkoxide 1 by 0.77 of molybdenum disulfide. Then, graphite was mixed at a weight ratio of 0.77, and a mixed liquid of xylene, methylene chloride and butyl alcohol was applied as a dispersion medium. Next, after standing in the air for 6 hours, the composition of the coating formed on the upper surface of the zinc phosphate coating in a dry state was measured, and the content was a relative value of weight, and the inorganic polymer compound having a skeleton of Ti-O Was 1, molybdenum disulfide was 1, graphite was 1, and the film thickness was 40 μm.
[0060]
As shown in Table 6, there was no occurrence of seizure until the 20th tightening / tightening operation in Table 3 and it was good. However, seizure occurred at the time of tightening after the 21st heat treatment.
(Invention Example 2)
The following surface treatments were applied to the carbon steel threaded joint shown in Table 1. The pin surface was mechanically ground and the surface roughness was 2 μm. # 80 sand was sprayed onto the surface of the box to make the surface roughness 10 μm, and a 10 μm thick zinc phosphate coating was formed on the box surface by chemical conversion treatment. Further, titanium alkoxide having an alkyl group of ethyl, molybdenum disulfide powder having an average particle diameter of 1.8 μm, and graphite powder having an average particle diameter of 2.8 μm on the upper surface thereof, molybdenum disulfide 2 and graphite with respect to titanium alkoxide 1. The mixture was mixed at a weight ratio of 1.33, and a mixed liquid of xylene, methylene chloride and butyl alcohol was applied as a dispersion medium. Next, after being left in the atmosphere for 3 hours, hot air of 165 ° C. was blown for 30 minutes. When the composition of the film formed on the upper surface of the zinc phosphate film in a dry state was measured, the content was molybdenum disulfide 3 and graphite 2 with respect to the inorganic polymer 1 having a skeleton of Ti—O by weight. The thickness was 10 μm.
[0061]
As shown in Table 6, there was no occurrence of seizure until the 22nd tightening / tightening operation in Table 3 and it was good. However, seizure occurred during the 23rd tightening. The tightening amount and tightening torque at the time of tightening were appropriate.
[0062]
(Invention Example 3)
The following surface treatment was applied to a threaded joint made of 5% Cr steel shown in Table 1. The box surface was mechanically ground and the surface roughness was 2 μm. The pin surface was sprayed with # 80 sand to make the surface roughness 10 μm, and a 5 μm thick calcium phosphate coating was formed on the pin surface by chemical conversion treatment. Further, a titanium alkoxide having an alkyl group of isopropyl, a molybdenum disulfide powder having an average particle size of 1.8 μm, and a graphite powder having an average particle size of 2.5 μm on the upper surface of the titanium alkoxide 1 and molybdenum disulfide 3.06. Then, graphite was mixed at a weight ratio of 1.94, and a mixed solution of methyl ethyl ketone, methylene chloride and butyl alcohol was applied as a dispersion medium. Next, a hot air of 150 ° C. which was humidified after being left in the atmosphere for 2 hours was blown for 15 minutes, and further a hot air of 150 ° C. which was dried was blown. When the composition of the coating formed on the upper surface of the calcium phosphate coating in a dry state was measured, the content was 5.5 wt% molybdenum disulfide and 3.5 wt% graphite relative to the inorganic polymer 1 having Ti-O as a skeleton. The film thickness was 20 μm.
[0063]
As shown in Table 6, there was no occurrence of seizure in the 25 tightening / tightening operations shown in Table 3, which was very good. The tightening amount and tightening torque at the time of tightening were also appropriate.
[0064]
(Invention Example 4)
The following surface treatments were applied to the carbon steel threaded joint shown in Table 1. The box surface was mechanically ground and the surface roughness was 2 μm. The pin surface was sprayed with # 80 shot to make the surface roughness 15 μm, and a 10 μm thick manganese phosphate coating was formed on the pin surface by chemical conversion treatment. Further, a titanium alkoxide having an alkyl group of propyl, a molybdenum disulfide powder having an average particle diameter of 4.6 μm, and a graphite powder having an average particle diameter of 1.3 μm on the upper surface of the titanium alkoxide 1 is 2.78 molybdenum disulfide. Then, graphite 0.83 was mixed at a weight ratio, and a mixed liquid of methyl ethyl ketone, methylene chloride and butyl alcohol was applied as a dispersion medium. Subsequently, hot air at 150 ° C. which was humidified after being left in the atmosphere for 3 hours was blown for 10 minutes. When the composition of the film formed on the upper surface of the calcium phosphate film in a dry state was measured, the content was 5.0% by weight, molybdenum disulfide 5.0, and graphite 1.5 with respect to the inorganic polymer 1 having Ti—O as a skeleton. The film thickness was 20 μm.
[0065]
As shown in Table 6, there was no occurrence of seizure in the 25 tightening / tightening operations shown in Table 3, which was very good. The tightening amount and tightening torque at the time of tightening were also appropriate.
[0066]
(Invention Example 5)
The following surface treatment was applied to the threaded joint made of Cr-Mo steel shown in Table 1. # 180 sand was sprayed onto the pin surface and the box surface, and the surface roughness of both was 3 μm. A manganese phosphate coating having a thickness of 5 μm was formed on both surfaces by chemical conversion treatment. Further, a titanium alkoxide having a methyl alkyl group and a molybdenum disulfide powder having an average particle diameter of 1.2 μm are mixed on the upper surface of both in a weight ratio of 2.31 to molybdenum alkoxide 1, and xylene, chloride. A mixed solution of methylene and butyl alcohol was applied as a dispersion medium. Subsequently, hot air of 165 ° C. which was humidified after being left in the atmosphere for 2 hours was blown for 30 minutes. When the composition of the film formed on the upper surface of the manganese phosphate film in a dry state was measured, the content was 3.0 by weight with respect to the inorganic polymer 1 having Ti—O as a skeleton, and the film thickness. The pin side and box side were 8 μm.
[0067]
As shown in Table 6, there was no occurrence of seizure in the 25 tightening / tightening operations shown in Table 3, which was very good. The tightening amount and tightening torque at the time of tightening were also appropriate.
[0068]
(Invention Example 6)
The following surface treatment was applied to the threaded joint made of Cr-Mo steel shown in Table 1. The pin surface was mechanically ground and the surface roughness was 2 μm. The surface of the box was mechanically ground to a surface roughness of 2 μm, and a 3 μm thick manganese phosphate coating was formed on the box surface by chemical conversion treatment. Further, a titanium alkoxide having an isobutyl alkyl group, a molybdenum disulfide powder having an average particle size of 3.1 μm, and a graphite powder having an average particle size of 3.5 μm on the upper surface of the titanium alkoxide 1 are obtained by using 1.39 molybdenum disulfide. Then, graphite 0.83 was mixed at a weight ratio, and a mixed liquid of xylene, methylene chloride and isobutyl alcohol was applied as a dispersion medium. Next, the composition of the coating formed on the upper surface of the manganese phosphate coating in a dry state was measured for 6 hours, and the content was 2% by weight relative to the inorganic polymer 1 having Ti—O as a skeleton. It was molybdenum sulfide 2.5 and graphite 1.5, and the film thickness was 30 μm.
[0069]
As shown in Table 6, there was no occurrence of seizure until the 24th tightening / tightening operation shown in Table 3 and it was good. However, seizure occurred during the 25th tightening. The tightening amount and tightening torque at the time of tightening were also appropriate.
[0070]
(Invention Example 7)
The following surface treatment was applied to a threaded joint made of 5% Cr steel shown in Table 1. # 120 sand was sprayed on the pin surface and the box surface, and both had a surface roughness of 5 μm. A manganese phosphate coating having a thickness of 5 μm was formed on both surfaces by chemical conversion treatment. Further, titanium alkoxide having an alkyl group of ethyl and molybdenum disulfide powder having an average particle size of 1.0 μm are mixed on the upper surface of both in a weight ratio of 0.23 molybdenum disulfide to titanium alkoxide 1, and xylene, chloride A mixed solution of methylene and butyl alcohol was applied as a dispersion medium. Subsequently, hot air at 150 ° C. was blown for 15 minutes after being left in the atmosphere for 4 hours. When the composition of the coating formed on the upper surface of the manganese phosphate coating in a dry state was measured, the content was 0.35 molybdenum disulfide with respect to the inorganic polymer 1 having a skeleton of Ti-O by weight, and the film thickness was The pin side and the box side were 20 μm.
[0071]
As shown in Table 6, there was no occurrence of seizure in the 25 tightening / tightening operations shown in Table 3, which was very good. The tightening amount and tightening torque at the time of tightening were also appropriate.
[0072]
(Invention Example 8)
The following surface treatment was applied to the threaded joint made of Cr-Mo steel shown in Table 1. # 180 sand was sprayed on the pin surface and the box surface, and both had a surface roughness of 4 μm. A zinc phosphate coating having a thickness of 5 μm was formed on both surfaces by chemical conversion treatment. Further, titanium alkoxide having an alkyl group of isopropyl, molybdenum disulfide powder having an average particle diameter of 1.2 μm, and graphite powder having an average particle diameter of 1.5 μm on the upper surface of both of them are molybdenum disulfide 2 with respect to titanium alkoxide 1. .77 and graphite at a weight ratio of 0.83, and a mixed solution of xylene, methylene chloride and butyl alcohol was applied as a dispersion medium. Subsequently, hot air at 140 ° C. that was humidified after being left in the atmosphere for 3 hours was blown for 20 minutes. When the composition of the film formed on the upper surface of the zinc phosphate film in a dry state was measured, the content was 5.0 by weight, molybdenum disulfide 5.0, and graphite 1.5. The film thickness was 10 μm on both the pin side and the box side.
[0073]
As shown in Table 6, there was no occurrence of seizure in the 25 tightening / tightening operations shown in Table 3, which was very good. The tightening amount and tightening torque at the time of tightening were also appropriate.
[0074]
(Invention Example 9)
The following surface treatments were applied to the carbon steel threaded joint shown in Table 1. The pin surface was mechanically ground and the surface roughness was 2 μm. A # 180 sand was sprayed on the surface of the box to make the surface roughness 5 μm, and a manganese phosphate coating having a thickness of 5 μm was formed on the surface of the box by chemical conversion treatment. Further, titanium alkoxide having an alkyl group of ethyl on the pin surface and the upper surface of the manganese phosphate coating, molybdenum disulfide powder having an average particle diameter of 1.2 μm, and graphite powder having an average particle diameter of 1.5 μm are used as titanium alkoxide 1. In contrast, molybdenum disulfide 1.33 and graphite 1.0 were mixed at a weight ratio, and a mixed liquid of xylene, methylene chloride and butyl alcohol was applied as a dispersion medium. Next, the composition of the film formed on the pin surface and the upper surface of the zinc phosphate film was measured by leaving it in the air for 6 hours and in a dry state. The molecule 1 was molybdenum disulfide 2 and graphite 1.5, and the film thickness was 5 μm.
[0075]
As shown in Table 6, there was no occurrence of seizure in the 25 tightening / tightening operations shown in Table 3, which was very good. The tightening amount and tightening torque at the time of tightening were also appropriate.
[0076]
(Invention Example 10)
The following surface treatment was applied to the threaded joint made of Cr-Mo steel shown in Table 1. The pin surface was machine finished and the surface roughness was 3 μm. The surface of the box was mechanically ground to a surface roughness of 3 μm, and a 10 μm thick zinc phosphate coating was formed on the box surface by chemical conversion treatment. Further, titanium alkoxide having an alkyl group of ethyl, molybdenum disulfide powder having an average particle diameter of 3.5 μm, and graphite powder having an average particle diameter of 3.1 μm on the upper surface thereof are molybdenum disulfide 4.0 to titanium alkoxide 1. Then, 2.33 by weight of graphite was mixed, and a mixed solution of xylene, methylene chloride and butyl alcohol was applied as a dispersion medium. Next, after standing in the air for 6 hours, the composition of the coating formed on the upper surface of the zinc phosphate coating in a dry state was measured, and the content was a relative value of weight, and the inorganic polymer compound having a skeleton of Ti-O Was 1, molybdenum disulfide was 6, graphite was 3.5, and the film thickness was 20 μm.
[0077]
As shown in Table 6, there was no occurrence of seizure until the 15th tightening / tightening operation in Table 3 and it was good. However, seizure occurred during the 16th tightening. The tightening amount and tightening torque at the time of tightening were appropriate.
[0078]
(Invention Example 11)
The following surface treatments were applied to the carbon steel threaded joint shown in Table 1. The box surface was mechanically ground and the surface roughness was 2 μm. The surface of the pin was sprayed with # 180 sand to a surface roughness of 10 μm, and a 10 μm thick calcium phosphate coating was formed on the pin surface by chemical conversion treatment. Furthermore, titanium alkoxide having an alkyl group of propyl and molybdenum disulfide powder having an average particle size of 4.6 μm are mixed on the upper surface thereof in a weight ratio of 0.14 molybdenum disulfide to titanium alkoxide 1, and methyl ethyl ketone, methylene chloride and A mixed liquid of isobutyl alcohol was applied as a dispersion medium. Subsequently, hot air at 150 ° C. which was humidified after being left in the atmosphere for 3 hours was blown for 30 minutes. When the composition of the coating formed on the upper surface of the calcium phosphate coating in a dry state was measured, the content was 0.25 molybdenum disulfide with respect to the inorganic polymer 1 having a skeleton of Ti-O by weight, and the film thickness was The thickness was 25 μm.
[0079]
As shown in Table 6, there was no occurrence of seizure until the 16th tightening / rewinding operation in Table 3 and it was good. However, seizure occurred during the 17th tightening. The tightening amount and tightening torque at the time of tightening were appropriate.
[0080]
(Comparative Example 1)
The following surface treatment was applied to a threaded joint made of 5% Cr steel shown in Table 1. # 80 sand was sprayed onto the pin surface and the box surface, and the surface roughness of both was 10 μm. An epoxy resin and a powder having an average particle size of 1.8 μm were mixed on both surfaces with a weight ratio of molybdenum disulfide 1 to the epoxy resin 1 and mixed with a mixed liquid such as toluene and isopropyl alcohol as a dispersion medium. Next, after drying, a heat treatment was performed at 180 ° C. for 30 minutes. When the composition of the film after the heat treatment was measured, the content on both the pin side and the box side was molybdenum disulfide 1 with respect to the epoxy resin 1 by weight ratio, and the film thickness was 20 μm.
[0081]
As shown in Table 6, a slight seizure was observed in the 12th tightening, and the tightening amount was insufficient, so that a predetermined surface pressure could not be applied to the shoulder portion. Therefore, when the tightening torque was increased so as to tighten to a predetermined position, seizure occurred in the thirteenth tightening.
[0082]
(Comparative Example 2)
The following surface treatment was applied to the threaded joint made of carbon steel shown in Table 1. The pin surface was mechanically ground and the surface roughness was 2 μm. The box surface was mechanically ground to a surface roughness of 2 μm, a 2 μm thick molten chloronitride layer was formed on the box surface, and a 15 μm thick manganese phosphate layer was formed thereon. Next, a polyamideimide resin and a tungsten disulfide powder having an average particle size of 3.5 μm are mixed as a dispersant with a mixed solution of xylene, toluene and isopropyl alcohol in a weight ratio of tungsten disulfide 1 to the polyamideimide resin 1, and the above phosphoric acid. It was applied to the upper surface of the manganese layer. Then, after drying, a heat treatment was performed at 180 ° C. for 30 minutes. When the composition of the film formed on the upper surface of the manganese phosphate layer after the heat treatment was measured, the content was tungsten disulfide 1 with respect to the polyamideimide resin 1 by weight, and the film thickness was 35 μm.
[0083]
As shown in Table 6, no seizure was observed in the 12th tightening, but the tightening amount was insufficient and a predetermined surface pressure was not applied to the shoulder portion. Therefore, when the tightening torque was increased to tighten to a predetermined position, seizure occurred at the 14th tightening.
[0084]
(Comparative Example 3)
The following surface treatment was applied to the threaded joint made of carbon steel shown in Table 1. The box surface was mechanically ground and the surface roughness was 2 μm. The surface of the pin is sprayed with # 80 sand to a surface roughness of 10 μm, and a 15 μm thick manganese phosphate layer is formed on the surface of the pin, on which an epoxy resin and molybdenum disulfide having an average particle size of 1.8 μm are formed. The powder was mixed with a mixture of toluene, isopropyl alcohol and the like at a weight ratio of molybdenum disulfide 1 to the epoxy resin 1 as a dispersion medium and applied. Then, after drying, a heat treatment was performed at 180 ° C. for 30 minutes. When the composition of the film formed on the upper surface of the manganese phosphate layer after the heat treatment was measured, the content was molybdenum disulfide 1 with respect to the epoxy resin 1 by weight, and the film thickness was 30 μm.
[0085]
As shown in Table 6, seizure was recognized by the 12th tightening, and the tightening amount was insufficient, so that a predetermined surface pressure could not be applied to the shoulder portion.
[0086]
(Comparative Example 4)
The following surface treatment was applied to a threaded joint made of 5% Cr steel shown in Table 1. The pin surface was mechanically ground and the surface roughness was 2 μm. A 10 μm thick Cu plating treatment was applied to the surface of the box having a surface roughness of 2 μm and a mechanical grinding finish. Next, compound grease corresponding to API-Bul5A2 is applied to both the pin surface and the box surface with a unit area (1 dm). ² ) About 20 g.
[0087]
As shown in Table 6, a slight seizure was observed in the 12th tightening, and the tightening amount was insufficient, so that a predetermined surface pressure could not be applied to the shoulder portion. Therefore, when the tightening torque was increased to tighten to a predetermined position, seizure occurred at the thirteenth tightening.
[0088]
(Comparative Example 5)
The following surface treatment was applied to the carbon steel joint shown in Table 1. The pin surface was mechanically ground and the surface roughness was 2 μm. A # 80 sand was sprayed on the surface of the box with a surface roughness of 10 μm to form a 15 μm thick manganese phosphate coating. Next, compound grease corresponding to API-Bul5A2 is applied to both the pin surface and the upper surface of the manganese phosphate coating in a unit area (1 dm). ² ) About 20 g.
[0089]
As shown in Table 6, although slight seizure occurred from the 8th tightening, the test was continued with care taken. However, seizure was recognized at the time of the 11th tightening, the seizure became remarkable at the 12th tightening, the tightening amount was insufficient, and a predetermined surface pressure could not be applied to the shoulder portion.
As described above, a threaded joint in which an inorganic lubricating coating having a skeleton of TO is formed on the phosphoric acid-based chemical conversion coating of the present invention is a joint using a conventional resin resin binder or a joint using compound grease. In comparison, it was found that the seizure resistance at high temperature history was excellent.
[0090]
【The invention's effect】
The screw joint made of carbon steel or low alloy steel according to the present invention has seizure resistance during repeated tightening and loosening in high-temperature crude oil mining in a high temperature environment as high as 400 ° C. such as a high depth, high temperature oil well or steam injection well. Property can be remarkably improved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram schematically showing the configuration of a threaded joint for oil country tubular goods according to the present invention.
FIG. 2 is a schematic cross-sectional view showing an example of a formation state of a lubricating coating according to the present invention.
[Explanation of symbols]
1: Box, 2: Pin,
3: Screw part, 4: Unthreaded metal contact part,
5: Shoulder portion, 6: Lubricating film,
7: Inorganic polymer compound, 8: Solid lubricant
9: Phosphate chemical conversion coating.

Claims

In a threaded joint made of carbon steel or low alloy steel with a Cr content of less than 10% by weight, which is composed of a pin and a box each having a threaded portion and an unthreaded metal contact portion, the thread of at least one of the box and the pin A phosphate chemical conversion coating is formed on the metal contact portion, and a lubricating coating of an inorganic polymer compound having a skeleton of Ti-O in which molybdenum disulfide and / or graphite is dispersed and mixed is formed on the phosphate chemical conversion coating. A threaded joint for high-temperature oil well pipes characterized by being humidified .

The threaded joint for high-temperature oil country tubular goods according to claim 1, wherein the phosphate chemical conversion coating is a manganese phosphate chemical conversion coating.

The weight ratio (B / A) between the content (A) of the inorganic polymer compound and the total content (B) of molybdenum disulfide and graphite is 0.3 to 9.0, or 2. A threaded joint for high temperature oil country tubular goods according to 2.

4. The threaded joint for high-temperature oil country tubular goods according to claim 1, wherein the surface roughness of the unthreaded metal contact portion forming the phosphate chemical conversion coating film is 3 to 15 [mu] m in Rmax.

The threaded joint for high temperature oil country tubular goods according to any one of claims 1 to 4, wherein the lubricating coating has a thickness of 5 to 30 µm.