JP2009167476A - Stainless steel pipe for oil well having excellent pipe expandability, and its manufacturing method - Google Patents
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Abstract
Description
この発明は、原油あるいは天然ガスの油井、ガス井に使用される油井管用として好適な油井用ステンレス鋼管に係り、特に、拡管性の改善に関する。 The present invention relates to oil well stainless steel pipes suitable for oil well pipes used for oil wells and gas wells for crude oil or natural gas, and more particularly to improvement of pipe expandability.
地表から地下の油田まで油井管を敷設するには、まず地表から所定の深さまで掘削し、その中にケーシングと呼ばれる鋼管を埋設し壁の崩壊を防止する。その後、ケーシングの先端からさらに地下を掘削してより深い井戸とし、先に埋設したケーシング内を通して新たなケーシングを埋設する。この作業を繰り返して、最終的に油田に到達する油井管（チュービング）が敷設される。深度の深い井戸を掘削する場合には、直径の異なる多種類のケーシングを必要とする。原油やガスを通す油井管（チュービング）の径は定められているため、深度の深い井戸を掘削する場合には、径方向における掘削面積を広くする必要があり、掘削に要する費用は増大することになる。このため、油井の掘削費を低減することが強く要望されている。 In order to lay an oil well pipe from the ground surface to an underground oil field, first, excavation from the ground surface to a predetermined depth is carried out, and a steel pipe called a casing is buried therein to prevent the collapse of the wall. Thereafter, the basement is further excavated from the tip of the casing to form a deeper well, and a new casing is buried through the previously buried casing. By repeating this operation, an oil well pipe (tubing) that finally reaches the oil field is laid. When excavating deep wells, many types of casings with different diameters are required. Since the diameter of the oil well pipe (tubing) through which crude oil and gas pass is determined, when drilling deep wells, it is necessary to increase the drilling area in the radial direction, and the cost required for drilling will increase become. For this reason, it is strongly desired to reduce the drilling cost of oil wells.
このような要望に対し、例えば特許文献１、特許文献２には、井戸中でケーシング（鋼管）を、押拡げ加工等により拡管する方法が記載されている。特許文献１、特許文献２に記載された技術によれば、井戸中でケーシング（鋼管）を、半径方向に膨張させることにより、多段構造になったケーシング毎の直径を小さく抑えることができ、井戸上部のケーシングサイズを小さく抑えて、油井の掘削費を低減することが可能となるとしている。 In response to such a request, for example, Patent Document 1 and Patent Document 2 describe a method of expanding a casing (steel pipe) in a well by means of expansion or the like. According to the techniques described in Patent Document 1 and Patent Document 2, the diameter of each casing having a multistage structure can be kept small by expanding the casing (steel pipe) in the radial direction in the well. It is said that it is possible to reduce the well drilling cost by keeping the upper casing size small.
しかし、特許文献１、特許文献２に記載された技術を利用したケーシング（鋼管）は、拡管による加工を受けた状態のままで、原油やガスに晒されるため、井戸中で拡管加工を施される使途に用いられる油井用鋼管には、冷間加工ままで耐食性に優れることが要求されることになる。
近年、原油価格の高騰や、近い将来に予想される石油資源の枯渇化に対処するため、従来、省みられなかったような深層油田や、一旦は開発が放棄されていた腐食性の強いサワーガス田等に対する開発が、世界的規模で盛んになっている。このような油田、ガス田は一般に深度が極めて深く、またその雰囲気は高温でかつ、CO2、Cl−等を含む厳しい腐食環境となっている。したがってこのような油田、ガス田の採掘に使用される油井用鋼管としては、高強度で、しかも耐食性を兼ね備えた鋼管が要求されている。従来から、このような環境下で使用される油井用鋼管として、耐CO2腐食性に優れた13％Crマルテンサイト系ステンレス鋼管が使用されてきた。
However, casings (steel pipes) using the techniques described in Patent Literature 1 and Patent Literature 2 are exposed to crude oil and gas while being subjected to processing by pipe expansion. Therefore, oil well steel pipes used for various purposes are required to have excellent corrosion resistance while being cold worked.
In recent years, in order to cope with soaring crude oil prices and the depletion of petroleum resources expected in the near future, deep oil fields that have not been excluded in the past, or highly corrosive sour gas that had been abandoned once Developments for rice fields etc. are flourishing on a global scale. Such oil fields and gas fields are generally extremely deep, and the atmosphere is high in temperature and has a severe corrosive environment containing CO 2 , Cl −, and the like. Therefore, as steel pipes for oil wells used for mining such oil fields and gas fields, steel pipes having high strength and corrosion resistance are required. Conventionally, 13% Cr martensitic stainless steel pipes excellent in CO 2 corrosion resistance have been used as oil well steel pipes used in such an environment.
しかし、更なる油井環境の厳しさのため、従来の13％Crマルテンサイト系ステンレス鋼管では、耐食性が不足するという問題があった。このような問題に対し、特許文献３には、CO2、Cl−等を含む180℃を超える高温の腐食雰囲気下においても優れた耐CO2腐食性を有する油井用ステンレス鋼管が提案されている。特許文献３に記載されたステンレス鋼管は、Cr：14〜18％、Ni：5.0〜8.0％、Mo：1.5〜3.5％、Cu：0.5〜3.5％、を含み、かつCr、Ni、Mo、Cu、Ｃからなる特定関係およびCr、Mo、Si、Ｃ、Mn、Ni、Cu、Ｎからなる特定関係を満足するように含有する組成を有する鋼管であり、降伏強さ654MPa以上の高強度を確保でき、耐CO2腐食性に優れるとしている。
しかし、通常の焼入れ焼戻処理を施されて製造された13％Crマルテンサイト系ステンレス鋼管は、高強度であり、深層油田開発用として要求されるような十分な拡管性を具備していないという問題があった。このため、油井中の拡管という新技術を適用するためには、耐CO2腐食性、および拡管性がともに優れた油井用ステンレス鋼管が強く望まれていた。 However, the 13% Cr martensitic stainless steel pipe manufactured by ordinary quenching and tempering treatment has high strength and does not have sufficient pipe expansion as required for deep oil field development. There was a problem. For this reason, in order to apply the new technology of expanding pipes in oil wells, there has been a strong demand for stainless steel pipes for oil wells that are excellent in both CO 2 corrosion resistance and pipe expanding properties.
またさらに油井では、例えば特許文献３に記載されたような油井用ステンレス鋼管同士をねじ継手で接続して使用している。このため、ねじ継手で接続した油井用ステンレス鋼管を、井戸中で拡管すると、ねじ継手部も拡管されることになる。しかし、高拡管性を有するねじ継手は、現状ではまだ開発されておらず、そのため、ねじ継手部を含めて高い拡管率で拡管した場合には、ねじ継手部からガスや原油が漏れ出すことが懸念されている。 Furthermore, in an oil well, for example, stainless steel pipes for oil wells as described in Patent Document 3 are connected by a threaded joint. For this reason, if the stainless steel pipe for oil wells connected by the threaded joint is expanded in the well, the threaded joint part is also expanded. However, screw joints with high pipe expandability have not been developed at present, so that when pipes are expanded at a high pipe expansion rate, including screw joint parts, gas and crude oil may leak from the screw joint parts. There are concerns.
本発明は、上記したような従来技術の問題に鑑みてなされたものであり、炭酸ガス（CO2）、塩素イオン（Cl−）等を含む苛酷な腐食環境下においても優れた耐CO2腐食性と、さらに厳しい拡管加工にも耐えられる優れた拡管性とを兼備し、さらに鋼管端部同士を接合し拡管した後の継手部からのガスや原油等の漏れをも防止できる、安価な、油井用ステンレス鋼管およびその製造方法を提供することを目的とする。 The present invention has been made in view of the above-described problems of the prior art, and has excellent CO 2 corrosion resistance even in a severe corrosive environment containing carbon dioxide (CO 2 ), chlorine ions (Cl − ), and the like. In addition, it has excellent pipe expandability that can withstand even more severe pipe expansion processing, and can prevent leakage of gas and crude oil from the joint after the pipe ends are joined and expanded. An object of the present invention is to provide a stainless steel pipe for oil wells and a method for producing the same.
本発明者らは、上記した目的を達成するために、まず、油井用ステンレス鋼管のねじ継手部からの漏れを防止する手段について鋭意研究した。その結果、ねじ継手部の拡管を不要とするか、あるいはねじ継手部以外の部位（母管部）に比べて、拡管量を少なくすることに思い至った。そして、ねじ継手部を母管部より少ない拡管量とするために、拡管性に優れたステンレス鋼管（母管）としたうえで、鋼管製造後に、予め、ねじが形成される鋼管の両端部を拡管し、その後、該両端部にねじを形成することに想到した。 In order to achieve the above-mentioned object, the present inventors first conducted intensive research on means for preventing leakage from the threaded joint portion of the oil well stainless steel pipe. As a result, it has been thought that pipe expansion of the threaded joint portion is not required or that the amount of pipe expansion is reduced as compared with a portion other than the threaded joint portion (host pipe portion). And, in order to make the threaded joint part less than the mother pipe part, after making the stainless steel pipe (mother pipe) excellent in pipe expandability, both ends of the steel pipe where the screw is formed in advance after manufacturing the steel pipe. The idea was to expand the tube, and then to form screws at both ends.
さらに本発明者らは、拡管性を向上したステンレス鋼管（母管）とするために、13％Cr系鋼を基本組成として、母管の拡管性に及ぼす各種要因の影響について鋭意研究した。その結果、さらに優れた拡管性を確保するためには、材料因子として、所望の範囲内の降伏強さを有するとともに、所定値以上のｎ値を有することが重要であるという知見を得た。
また、所望の強度、耐食性（耐CO2腐食性等）さらには靭性を確保するために、Ｃ，Si，Mn，Cr，あるいはさらにCu，Ni，Mo，Ｖ，Nb、および／または、Ti，Zr，Ｂ，Ｗ、および／または、Caを適正含有量範囲内に調整し、さらに適正な組織とすることにより、所望の強度を有し、優れた耐食性、とくに優れた耐CO2腐食性と優れた拡管性とを兼備する油井用ステンレス鋼管とすることができることを知見した。
Furthermore, in order to obtain a stainless steel pipe (base pipe) with improved pipe expandability, the present inventors have intensively studied the influence of various factors on the pipe pipe expandability using 13% Cr steel as a basic composition. As a result, in order to secure further excellent tube expandability, it has been found that it is important to have a yield strength within a desired range and an n value equal to or greater than a predetermined value as a material factor.
Further, in order to ensure desired strength, corrosion resistance (CO 2 corrosion resistance, etc.) and toughness, C, Si, Mn, Cr, or even Cu, Ni, Mo, V, Nb, and / or Ti, By adjusting Zr, B, W, and / or Ca within the appropriate content range, and further forming a proper structure, it has the desired strength, excellent corrosion resistance, particularly excellent CO 2 corrosion resistance, It has been found that it can be a stainless steel pipe for oil wells that combines excellent pipe expandability.
なお、ここで「拡管性に優れる」とは、限界拡管率が25％以上である場合をいい、また「耐CO2腐食性に優れる」とは、0.1MPa以上のCO2を含む100℃以上の苛酷な腐食環境下で問題なく使用可能である場合をいう。
本発明は、上記した知見に基づき、さらに検討を加えて完成されたものである。すなわち、本発明の要旨は、次のとおりである。
Here, “excellent tube expansion” refers to the case where the limit tube expansion rate is 25% or more, and “excellent CO 2 corrosion resistance” refers to 100 ° C. or more containing CO 2 of 0.1 MPa or more. The case where it can be used without any problem in a severe corrosive environment.
The present invention has been completed based on the above findings and further studies. That is, the gist of the present invention is as follows.
（１）油井内に挿入された状態で拡管される油井用ステンレス鋼管であって、該油井用ステンレス鋼管の端面側が拡管加工され、該拡管加工された部位にねじを形成してなることを特徴とする拡管性に優れた油井用ステンレス鋼管。
（２）（１）において、前記拡管加工の量が、次（１）式
拡管率＝［｛（プラグ外径）−（素管内径）｝／（素管内径）］×100（％）‥（１）
（ここで、プラグ外径：拡管用工具（プラグ）の外径（mm）、素管内径：鋼管端面部の加工前内径（mm））
で定義される拡管率で３％以上であることを特徴とする油井用ステンレス鋼管。
(1) A stainless steel pipe for an oil well that is expanded in a state of being inserted into an oil well, wherein the end surface side of the stainless steel pipe for the oil well is expanded and a screw is formed at the expanded portion. Stainless steel pipe for oil wells with excellent pipe expandability.
(2) In (1), the amount of the tube expansion processing is the following (1) equation: tube expansion ratio = [{(plug outer diameter) − (element tube inner diameter)} / (element tube inner diameter)] × 100 (%). (1)
(Here, the outer diameter of the plug: the outer diameter (mm) of the tube expansion tool (plug), the inner diameter of the raw pipe: the inner diameter of the steel pipe end face before processing (mm))
An oil well stainless steel pipe characterized by having a pipe expansion rate of 3% or more as defined in 1.
（３）（１）または（２）において、前記油井用ステンレス鋼管が、降伏強さ：350MPa以上、ｎ値：0.08以上を有し、かつｎ値と均一伸びu-Elとが次（２）式を満足することを特徴とする油井用ステンレス鋼管。
ｎ＞0.007×（25−u-El）‥（２）
(ここで、ｎ：ｎ値、u-El：均一伸び（％））
（４）（１）ないし（３）のいずれかにおいて、 前記油井用ステンレス鋼管が、質量％で、Ｃ：0.25％以下、Si：1.0％以下、Mn：0.10〜2.50％、Ｐ：0.05％以下、Ｓ：0.005％以下、Al：0.05％以下、Cr：10.5〜18.0％、Ｎ：0.09％以下を含有し、残部Feおよび不可避的不純物からなる組成を有し、耐CO２腐食性に優れることを特徴とする油井用ステンレス鋼管。
(3) In (1) or (2), the stainless steel pipe for oil well has yield strength: 350 MPa or more, n value: 0.08 or more, and n value and uniform elongation u-El are the following (2) Stainless steel pipe for oil wells characterized by satisfying the formula.
n> 0.007 × (25−u-El) (2)
(Where n: n value, u-El: uniform elongation (%))
(4) In any one of (1) to (3), the stainless steel pipe for oil well is in% by mass, C: 0.25% or less, Si: 1.0% or less, Mn: 0.10 to 2.50%, P: 0.05% or less , S: 0.005% or less, Al: 0.05% or less, Cr: 10.5 to 18.0%, N: 0.09% or less, having a composition composed of the balance Fe and inevitable impurities, and having excellent resistance to CO 2 corrosion Stainless steel pipe for oil wells.
（５）（４）において、前記組成に加えてさらに、質量％で、次Ａ群〜Ｄ群
Ａ群：Cu：3.5％以下、
Ｂ群：Ni：7.0％以下、Mo：3.0％以下、Ｖ：0.20％以下、Nb：0.20％以下のうちから選ばれた１種または２種以上、
Ｃ群：Ti：0.3％以下、Zr：0.2％以下、Ｂ：0.01％以下、Ｗ：3.0％以下のうちから選ばれた１種または２種以上、
Ｄ群：Ca：0.0005〜0.01％
のうちから選ばれた１群または２群以上を含有する組成とすることを特徴とする油井用ステンレス鋼管。
(5) In (4), in addition to the above-mentioned composition, in mass%, the following group A to group D group A: Cu: 3.5% or less,
Group B: Ni: 7.0% or less, Mo: 3.0% or less, V: 0.20% or less, Nb: one or more selected from 0.20% or less,
Group C: Ti: 0.3% or less, Zr: 0.2% or less, B: 0.01% or less, W: 3.0% or less selected from one or more,
Group D: Ca: 0.0005 to 0.01%
A stainless steel pipe for oil wells, wherein the composition contains one group or two or more groups selected from among the above.
（６）（４）または（５）において、前記油井用ステンレス鋼管が、前記組成を有し、かつ焼戻マルテンサイト相を主相とし、第二相として体積率で、５％以上のオーステナイト相と、あるいはさらに５％以下のフェライト相を含む組織を有することを特徴とする油井用ステンレス鋼管。
（７）ステンレス鋼管を素管として、該素管に、熱処理として、焼入れ処理および焼戻処理、または焼戻処理を施したのち、前記素管の端面側に拡管加工を施し、ついで該拡管加工を施された部位にねじ加工を施すことを特徴とする拡管性に優れた油井用ステンレス鋼管の製造方法。
(6) In (4) or (5), the stainless steel pipe for oil well has the above composition, and has a tempered martensite phase as a main phase and a volume ratio of 5% or more as an austenite phase as a second phase. Or a stainless steel pipe for oil wells characterized by having a structure containing 5% or less of a ferrite phase.
(7) Using a stainless steel pipe as a raw pipe, the pipe is subjected to quenching treatment and tempering treatment or tempering treatment as a heat treatment, and then subjected to pipe expansion processing on the end face side of the raw pipe, and then the pipe expansion processing A method for producing a stainless steel pipe for oil wells having excellent pipe expandability, characterized in that a threaded portion is threaded.
（８）（７）において、前記焼入れ処理を、800℃以上の加熱温度に再加熱し、引き続いて空冷以上の冷却速度で冷却する処理とし、前記焼戻処理を、Ａc1変態点を超える温度に加熱し冷却する処理とすることを特徴とする油井用ステンレス鋼管の製造方法。
（９）（８）において、前記焼戻処理が、Ac1変態点超え700℃以下の二相温度域に加熱し、冷却する処理であることを特徴とする油井用ステンレス鋼管の製造方法。
(8) In (7), the quenching treatment is reheated to a heating temperature of 800 ° C. or higher and subsequently cooled at a cooling rate of air cooling or higher, and the tempering treatment is performed at a temperature exceeding the Ac 1 transformation point. A method for producing a stainless steel pipe for oil wells, characterized in that it is heated and cooled.
(9) The method for producing a stainless steel pipe for oil wells according to (8), wherein the tempering process is a process of heating and cooling to a two-phase temperature range of 700 ° C. or more exceeding the Ac1 transformation point.
（１０）（７）ないし（９）のいずれかにおいて、前記拡管加工の量が、次（１）式
拡管率＝［｛（プラグ外径）−（素管内径）｝／（素管内径）］×100（％）‥（１）
（ここで、プラグ外径：拡管用工具（プラグ）の外径（mm）、素管内径：鋼管端面側の加工前内径（mm））
で定義される拡管率で３％以上であることを特徴とする油井用ステンレス鋼管の製造方法。（１１）（７）ないし（１０）のいずれかにおいて、前記ステンレス鋼管が、質量％
で、Ｃ：0.25％以下、Si：1.0％以下、Mn：0.10〜2.50％、Ｐ：0.05％以下、Ｓ：
0.005％以下、Al：0.05％以下、Cr：10.5〜18.0％、Ｎ：0.09％以下を含有し、残部Fe
および不可避的不純物からなる組成を有することを特徴とする油井用ステンレス鋼管の製
造方法。
(10) In any one of (7) to (9), the amount of the tube expansion processing is the following equation (1): tube expansion ratio = [{(plug outer diameter) − (element tube inner diameter)} / (element tube inner diameter) ] X 100 (%) (1)
(Here, the outer diameter of the plug: the outer diameter (mm) of the tool for expanding the pipe (plug), the inner diameter of the raw pipe: the inner diameter of the steel pipe end face before processing (mm))
A method for producing a stainless steel pipe for oil wells, characterized in that the expansion ratio defined by is 3% or more. (11) In any one of (7) to (10), the stainless steel pipe is mass%.
C: 0.25% or less, Si: 1.0% or less, Mn: 0.10 to 2.50%, P: 0.05% or less, S:
Contains 0.005% or less, Al: 0.05% or less, Cr: 10.5 to 18.0%, N: 0.09% or less, and the balance Fe
And a method for producing a stainless steel pipe for oil wells, which has a composition comprising inevitable impurities.
（１２）（１１）において、前記組成に加えてさらに、質量％で、次Ａ群〜Ｄ群
Ａ群：Cu：3.5％以下、
Ｂ群：Ni：7.0％以下、Mo：3.0％以下、Ｖ：0.20％以下、Nb：0.20％以下のうちから選ばれた１種または２種以上、
Ｃ群：Ti：0.30％以下、Zr：0.20％以下、Ｂ：0.0005〜0.01％、Ｗ：1.0％以下のうちから選ばれた１種または２種以上、
Ｄ群：Ca：0.0005〜0.01％
のうちから選ばれた１群または２群以上を含有する組成とすることを特徴とする油井用ステンレス鋼管の製造方法。
(12) In (11), in addition to the above-mentioned composition, the following group A to group D group A: Cu: 3.5% or less in mass%,
Group B: Ni: 7.0% or less, Mo: 3.0% or less, V: 0.20% or less, Nb: one or more selected from 0.20% or less,
Group C: Ti: 0.30% or less, Zr: 0.20% or less, B: 0.0005-0.01%, W: 1.0% or less selected from 1.0% or less,
Group D: Ca: 0.0005 to 0.01%
The manufacturing method of the stainless steel pipe for oil wells characterized by setting it as the composition containing 1 group or 2 groups or more selected from these.
本発明によれば、CO2、Cl−を含む高温の厳しい腐食環境下においても、十分な耐食性、とくに優れた耐CO2腐食性を有し、かつ母管および継手部を含めて、油井における厳しい拡管加工にも耐えうる、優れた拡管性を有する、油井用ステンレス鋼管を安価に製造でき、産業上格段の効果を奏する。 According to the present invention, even in a high temperature severe corrosive environment containing CO 2 , Cl − , it has sufficient corrosion resistance, particularly excellent CO 2 corrosion resistance, and includes oil pipes and joints in oil wells. Stainless steel pipes for oil wells with excellent pipe expandability that can withstand severe pipe expansion processing can be manufactured at low cost, and there are remarkable industrial effects.
本発明の油井用ステンレス鋼管は、両端面側が拡管加工され、該拡管加工された部位（拡管部）にねじを形成してなる、図１に示すような鋼管である。本発明では、ステンレス鋼管（素管）の両端面側に素管内径より大きい各種外径を有するプラグをそれぞれ押し込み、所定の拡管率となるように予め拡管して拡管部を形成し、該拡管部にはさらにねじ加工を施し、ねじ加工部を形成する。これにより、ねじ継手部における油井内での拡管量を低減することができるとともに、油井内での拡管作業を軽減することが可能となるうえ、油井内における拡管によるねじ継手部の特性劣化を防止あるいは軽減でき、ねじ継手部からの漏れを防止できることになる。なお、拡管加工が施される領域は、ステンレス鋼管の端面から管軸方向に所定の長さとする。ここでいう「所定の長さ」とは、鋼管の端部同士を適正にねじ接合するのに必要な長さのねじを、端面側に加工できる長さを意味する。 The stainless steel pipe for oil wells of the present invention is a steel pipe as shown in FIG. 1 in which both end surfaces are expanded and a screw is formed at the expanded portion (expanded portion). In the present invention, plugs having various outer diameters larger than the inner diameter of the pipe are respectively pushed into both end surfaces of the stainless steel pipe (element pipe), and expanded in advance so as to obtain a predetermined expansion ratio, thereby forming the expanded section. The part is further threaded to form a threaded part. As a result, the amount of pipe expansion in the oil well at the threaded joint can be reduced, and the pipe expansion work in the oil well can be reduced, and the characteristic deterioration of the threaded joint due to pipe expansion in the oil well can be prevented. Or it can reduce, and the leak from a threaded joint part can be prevented. In addition, the area | region where a pipe expansion process is performed is taken as predetermined | prescribed length in a pipe-axis direction from the end surface of a stainless steel pipe. Here, the “predetermined length” means a length capable of processing a screw having a length necessary for properly joining the ends of the steel pipes to the end face side.
また、両端面側に形成するねじの形状はとくに限定する必要はないが、内容物（原油、ガス等）が漏れないような構造、例えばテーパーねじとすることが好ましい。また、一方の端面側を雄ねじ、他方の端面側を雌ねじとし、ステンレス鋼管同士を管軸方向にねじ接合可能とすることは言うまでもない。
また、ステンレス鋼管両端面側における拡管加工は、拡管率で３％以上とすることが好ましい。なお、拡管率は、下記（１）式
拡管率＝［｛（プラグ外径）−（素管内径）｝／（素管内径）］×100（％）‥（１）
（ここで、プラグ外径：拡管用工具（プラグ）の外径（mm）、素管内径：鋼管端面部の加工前内径（mm））
で定義される。拡管率が３％未満では、油井内での高拡管に対応することが難しくなる。
Further, the shape of the screw formed on both end surfaces is not particularly limited, but a structure that does not leak the contents (crude oil, gas, etc.), for example, a taper screw is preferable. Further, it goes without saying that one end face side is a male screw and the other end face side is a female screw, and the stainless steel pipes can be screwed together in the pipe axis direction.
Moreover, it is preferable that the pipe expansion process in the both end surface side of a stainless steel pipe shall be 3% or more by a pipe expansion rate. The tube expansion rate is the following (1) equation tube expansion rate = [{(plug outer diameter) − (element tube inner diameter)} / (element tube inner diameter)] × 100 (%) (1)
(Here, the outer diameter of the plug: the outer diameter (mm) of the tube expansion tool (plug), the inner diameter of the raw pipe: the inner diameter of the steel pipe end face before processing (mm))
Defined by If the pipe expansion rate is less than 3%, it becomes difficult to cope with high pipe expansion in the oil well.
本発明の油井用ステンレス鋼管は、好ましくは降伏強さ：350MPa以上を有する鋼管である。油井用鋼管を油井内に挿入した状態で行う拡管は、通常、当該ステンレス鋼管内に拡管用プラグを通して行う。油井用ステンレス鋼管の降伏強さが350MPa未満では、拡管用プラグを通す際に、座屈等の問題が生じ、適正な拡管を行うことができない場合がある。このため、十分な拡管性を確保するために、本発明では油井用ステンレス鋼管の降伏強さを350MPa以上に限定することが好ましい。なお、より好ましくは350〜550MPaである。 The oil well stainless steel pipe of the present invention is preferably a steel pipe having a yield strength of 350 MPa or more. The pipe expansion performed in a state where the oil well steel pipe is inserted into the oil well is usually performed through the pipe for expansion into the stainless steel pipe. If the yield strength of the stainless steel pipe for oil wells is less than 350 MPa, problems such as buckling may occur when the pipe for pipe expansion is passed, and proper pipe expansion may not be performed. For this reason, in order to ensure sufficient pipe expandability, in the present invention, it is preferable to limit the yield strength of the oil well stainless steel pipe to 350 MPa or more. More preferably, it is 350 to 550 MPa.
また、本発明の油井用ステンレス鋼管は、0.08以上のｎ値を有する鋼管とすることが、高拡管性を確保するうえで好ましい。ｎ値は、本発明者らの検討によれば、鋼管の拡管性に影響する重要な材料因子であり、優れた拡管性を確保するために、本発明ではｎ値を0.08以上に限定することが好ましい。ｎ値が0.08未満では、所望の拡管性を確保することが難しくなる。なお、好ましくは0.10以上である。なお、ここでいう「ｎ値」は、管軸方向を引張方向とする引張試験片をAPI規定または、JIS規定に準拠して採取し、該引張試験片を用いてJIS規定（JIS Z 2253）に準拠して測定した値とする。 In addition, the oil well stainless steel pipe of the present invention is preferably a steel pipe having an n value of 0.08 or more in order to ensure high pipe expandability. The n value is an important material factor that affects the pipe expandability of the steel pipe according to the study by the present inventors. In order to ensure excellent pipe expandability, the n value is limited to 0.08 or more in the present invention. Is preferred. If the n value is less than 0.08, it is difficult to ensure the desired tube expandability. In addition, Preferably it is 0.10 or more. The “n value” here refers to a tensile test piece with the tube axis direction as the tensile direction, sampled in accordance with API regulations or JIS regulations, and using these tensile test specimens (JIS Z 2253) The value measured in accordance with
また、油井用鋼管の均一伸びu-Elが十分に大きければ、ｎ値が低くても、高い拡管率の拡管が可能であるが、しかし、均一伸びu-Elが小さいと、十分な拡管性を確保できなくなる。本発明者らの検討によれば、優れた拡管性を確保するためには、上記した範囲のｎ値を有するとともに、均一伸びu-Elに関連した所定値、すなわち次（２）式
ｎ＞0.007×（25−u-El）‥‥‥（２）
（ここで、ｎ：ｎ値、u-El：均一伸び（％））
を満足するｎ値を有することが好ましいという知見を得ている。ｎ値が（２）式を満足できない場合には、所望の優れた拡管性を確保することが難しくなる。なお、均一伸びu-Elは、管軸方向を引張方向とするAPI規定またはJIS規定（JIS Z 2241）に準拠して採取した引張試験片を用いてAPI規定または、JIS規定（JIS Z 2241）に準拠して引張試験を実施して測定した値を用いるものとする。
In addition, if the uniform elongation u-El of the oil well steel pipe is sufficiently large, it is possible to expand the tube with a high expansion ratio even if the n value is low. However, if the uniform elongation u-El is small, sufficient expansion is possible. Cannot be secured. According to the study by the present inventors, in order to ensure excellent tube expandability, it has an n value in the above range and a predetermined value related to the uniform elongation u-El, that is, the following equation (2):
n> 0.007 × (25−u-El) (2)
(Where n: n value, u-El: uniform elongation (%))
It has been found that it is preferable to have an n value that satisfies the above. If the n value cannot satisfy the formula (2), it becomes difficult to ensure the desired excellent tube expandability. Uniform elongation u-El is determined by API regulations or JIS regulations (JIS Z 2241) using tensile test specimens collected according to API regulations or JIS regulations (JIS Z 2241) with the tube axis direction as the tensile direction. The value measured by carrying out a tensile test according to the above shall be used.
つぎに、本発明の油井用ステンレス鋼管の好ましい組成範囲およびその限定理由について説明する。以下、とくに断らないかぎり、質量％は単に％と記す。
Ｃ：0.25％以下
Ｃは、マルテンサイト系ステンレス鋼管の強度に関係する重要な元素であるが、0.25％を超えて多量に含有すると、鋼管製造時に焼割れを発生する恐れが増大する。また、Ｃの多量含有は、耐食性を低下させる。このため、Ｃは0.25％以下に限定した。なお、好ましくは0.005〜0.22％の範囲である。
Next, the preferable composition range of the stainless steel pipe for oil well of the present invention and the reason for limitation thereof will be described. Hereinafter, unless otherwise specified, mass% is simply expressed as%.
C: 0.25% or less C is an important element related to the strength of the martensitic stainless steel pipe, but if it is contained in a large amount exceeding 0.25%, there is an increased risk of causing cracking during the production of the steel pipe. In addition, a large amount of C decreases the corrosion resistance. For this reason, C was limited to 0.25% or less. In addition, Preferably it is 0.005 to 0.22% of range.
Si：1.0％以下
Siは、通常の製鋼過程において脱酸剤として有用な元素である。このような効果を得るために0.05％以上含有することが望ましいが、1.0％を超える含有は、熱間加工性、さらには靭性を低下させる。このため、Siは1.0％以下に限定することが好ましい。なお、より好ましくは0.05〜0.50％である。
Si: 1.0% or less
Si is an element useful as a deoxidizer in a normal steelmaking process. In order to acquire such an effect, it is desirable to contain 0.05% or more, but inclusion exceeding 1.0% reduces hot workability and further toughness. For this reason, it is preferable to limit Si to 1.0% or less. In addition, More preferably, it is 0.05 to 0.50%.
Mn：0.10〜2.50％
Mnは、固溶して鋼管強度を増加させる作用を有するとともに、ｎ値向上に有効に寄与する元素である。油井用マルテンサイト系ステンレス鋼管として所望の強度を確保するために0.10％以上含有することが好ましいが、2.50％を超える多量の含有は、靭性に悪影響を及ぼすとともに、鋼管製造時に焼割れを発生する恐れを増大させる。このため、Mnは0.10〜2.50％の範囲に限定することが好ましい。なお、より好ましくは0.10〜1.00％である。
Mn: 0.10-2.50%
Mn is an element that has the effect of increasing the steel pipe strength by solid solution and contributes effectively to the improvement of the n value. In order to ensure the desired strength as a martensitic stainless steel pipe for oil wells, it is preferable to contain 0.10% or more, but a large content exceeding 2.50% adversely affects toughness and causes cracking during steel pipe production. Increase fear. For this reason, it is preferable to limit Mn to the range of 0.10 to 2.50%. In addition, More preferably, it is 0.10 to 1.00%.
Ｐ：0.05％以下
Ｐは、熱間加工性を低下させるとともに、耐CO2腐食性、耐CO2応力腐食割れ性、耐孔食性および耐硫化物応力腐食割れ性をともに劣化させる元素であり、本発明ではその含有量は可及的に少ないことが望ましいが、極端な低減は製造コストの高騰を招く。そのため、本発明ではＰは、工業的に比較的安価に実施可能でかつ、熱間加工性、耐CO2腐食性、耐CO2応力腐食割れ性、耐孔食性および耐硫化物応力腐食割れ性を低下させない範囲である、0.05％以下に限定することが好ましい。なお、より好ましくは0.02％以下である。
P: 0.05% or less P is an element that decreases hot workability and deteriorates both CO 2 corrosion resistance, CO 2 stress corrosion cracking resistance, pitting corrosion resistance and sulfide stress corrosion cracking resistance. In the present invention, the content is desirably as small as possible, but an extreme reduction leads to an increase in manufacturing cost. Therefore, in the present invention, P can be implemented industrially at a relatively low cost and is hot workability, CO 2 corrosion resistance, CO 2 stress corrosion crack resistance, pitting corrosion resistance and sulfide stress corrosion crack resistance. It is preferable to limit the amount to 0.05% or less, which is a range that does not reduce the amount of water. In addition, More preferably, it is 0.02% or less.
Ｓ：0.005％以下
Ｓは、パイプ造管過程における熱間加工性を著しく劣化させる元素であり、本発明ではその含有量は可及的に少ないことが望ましいが、極端な低減は製造コストの高騰を招く。そのため、本発明ではＳは、通常の工程でのパイプ製造が可能な範囲である0.005％以下に限定することが好ましい。なお、より好ましくは0.003％以下である。
S: 0.005% or less S is an element that remarkably deteriorates the hot workability in the pipe making process. In the present invention, its content is preferably as low as possible, but extreme reduction increases the manufacturing cost. Invite. Therefore, in the present invention, S is preferably limited to 0.005% or less, which is a range in which pipe production in a normal process is possible. More preferably, it is 0.003% or less.
Al：0.05％以下
Alは、強力な脱酸剤として作用するとともに、Ｎと結合し結晶粒を微細化する作用をも有する元素である。このような効果を安定して確保するために0.005％以上含有することが望ましいが、0.05％を超える含有は、靭性に悪影響を及ぼす。このため、Alは0.05％以下に限定することが好ましい。なお、より好ましくは0.005〜0.03％である。
Al: 0.05% or less
Al is an element that acts as a strong deoxidizer and also has an effect of combining with N to refine crystal grains. In order to ensure such an effect stably, it is desirable to contain 0.005% or more, but inclusion exceeding 0.05% adversely affects toughness. For this reason, Al is preferably limited to 0.05% or less. In addition, More preferably, it is 0.005-0.03%.
Cr：10.5〜18.0％
Crは、所望の耐CO2腐食性、耐CO2応力腐食割れ性を保持するために重要な元素であり、本発明が対象としている環境下における耐食性確保の観点からは、10.5％以上含有することが好ましいが、18.0％を超える含有は、フェライトが安定となり所望の鋼管強度を確保できなくなる。このため、Crは10.5〜18.0％の範囲に限定することが好ましい。なお、より好ましくは11.0〜15.0％である。
Cr: 10.5 to 18.0%
Cr is an important element for maintaining desired CO 2 corrosion resistance and CO 2 stress corrosion cracking resistance, and is contained in an amount of 10.5% or more from the viewpoint of ensuring corrosion resistance under the environment targeted by the present invention. However, if the content exceeds 18.0%, the ferrite becomes stable and the desired steel pipe strength cannot be secured. For this reason, it is preferable to limit Cr to the range of 10.5 to 18.0%. In addition, More preferably, it is 11.0 to 15.0%.
Ｎ：0.09％以下
Ｎは、オーステナイト生成元素であり、鋼管強度の向上に有効に寄与する。また、耐孔食性を向上させる作用をも有する。このような効果を得るためには、0.005％以上含有することが望ましいが、0.09％を超えて含有すると、Cr窒化物等の種々の窒化物を多量に形成して靭性、耐食性を低下させる。このため、Ｎは0.09％以下に限定することが好ましい。なお、より好ましくは0.01〜0.06％である。
N: 0.09% or less N is an austenite generating element and contributes effectively to the improvement of steel pipe strength. It also has the effect of improving pitting corrosion resistance. In order to acquire such an effect, it is desirable to contain 0.005% or more. However, if it contains more than 0.09%, a large amount of various nitrides such as Cr nitrides are formed to reduce toughness and corrosion resistance. For this reason, it is preferable to limit N to 0.09% or less. In addition, More preferably, it is 0.01 to 0.06%.
上記した成分が基本の成分であるが、この基本の組成に加えて、さらに次Ａ群〜Ｄ群のうちから選ばれた１群または２群以上を選択して含有できる。
Ａ群：Cu：3.5％以下
Ａ群：Cuは、保護皮膜を強固にして鋼中への水素の侵入を抑制し、耐硫化物応力腐食割れ性を向上させる作用を有する元素であり、必要に応じて含有できる。このような効果は0.2％以上の含有で顕著となるが、3.5％を超える含有は、高温で粒界にCuSが析出し、熱間加工性を低下させる。このため、Cuは3.5％以下に限定することが好ましい。なお、より好ましくは0.5〜2.5％である。
Although the above-mentioned components are basic components, in addition to this basic composition, one or more groups selected from the following groups A to D can be selected and contained.
Group A: Cu: 3.5% or less Group A: Cu is an element having an action of strengthening a protective film to suppress the penetration of hydrogen into steel and improving the resistance to sulfide stress corrosion cracking. Can be contained depending on the case. Such an effect becomes remarkable when the content is 0.2% or more. However, when the content exceeds 3.5%, CuS precipitates at the grain boundary at a high temperature, thereby reducing the hot workability. For this reason, it is preferable to limit Cu to 3.5% or less. In addition, More preferably, it is 0.5 to 2.5%.
Ｂ群：Ni：7.0％以下、Mo：3.0％以下、Ｖ：0.20％以下、Nb：0.20％以下のうちから選ばれた１種または２種以上
Ｂ群：Ni、Mo、Ｖ、Nbはいずれも、鋼管強度を増加させる作用を有し、必要に応じて選択して１種または２種以上含有できる。
Niは、靭性の向上に有効に寄与する元素であるが、Crを多量に含む場合には、マルテンサイト相を安定化して鋼管強度の増加に有効に寄与する。このような効果を得るためには0.1％以上含有することが望ましいが、7.0％を超えて含有すると、変態点が低下しすぎて、鋼管強度の著しい低下を招く。このため、Niは7.0％以下とすることが好ましい。なお、より好ましくは0.1〜6.5％である。
Group B: Ni: 7.0% or less, Mo: 3.0% or less, V: 0.20% or less, Nb: One or more selected from 0.20% or less Group B: Any of Ni, Mo, V, and Nb Has the effect of increasing the strength of the steel pipe, and can be selected as necessary and contained in one or more kinds.
Ni is an element that contributes effectively to improving toughness. However, when it contains a large amount of Cr, it stabilizes the martensite phase and contributes effectively to an increase in steel pipe strength. In order to acquire such an effect, it is desirable to contain 0.1% or more. However, if it exceeds 7.0%, the transformation point is excessively lowered, and the steel pipe strength is significantly reduced. For this reason, Ni is preferably 7.0% or less. In addition, More preferably, it is 0.1 to 6.5%.
Moは、焼入れ性の向上を介して、鋼管強度の増加に寄与する元素であるが、硫化水素が存在する環境下では耐硫化物応力腐食割れ性を向上させる元素でもある。このような効果を得るためには、0.5％以上含有することが望ましいが、3.0％を超えて含有しても、効果が飽和し含有量に見合う効果が期待できなくなる。このため、Moは3.0％以下に限定することが好ましい。なお、より好ましくは0.5〜2.5％である。 Mo is an element that contributes to an increase in steel pipe strength through improvement of hardenability, but is also an element that improves resistance to sulfide stress corrosion cracking in an environment where hydrogen sulfide is present. In order to acquire such an effect, it is desirable to contain 0.5% or more, but even if it contains more than 3.0%, the effect is saturated and an effect commensurate with the content cannot be expected. For this reason, it is preferable to limit Mo to 3.0% or less. In addition, More preferably, it is 0.5 to 2.5%.
Ｖは、焼入れ性の向上を介して、鋼管強度の増加に寄与する元素であるが、耐硫化物応力腐食割れ性を向上させる元素でもある。このような効果を得るためには、0.01％以上含有することが望ましいが、0.20％を超える含有は、靭性を低下させる。このため、Ｖは0.20％以下に限定することが好ましい。なお、より好ましくは0.02〜0.15％である。
Nbは、鋼の強度増加、靱性向上に有効に寄与する元素である。このような効果は0.01％以上の含有で顕著となるが、0.20％を超える含有は、靱性を低下させる。このため、Nbは0.20％以下とすることが好ましい。なお、より好ましくは0.02〜0.12％である。
V is an element that contributes to an increase in steel pipe strength through an improvement in hardenability, but is also an element that improves the resistance to sulfide stress corrosion cracking. In order to acquire such an effect, it is desirable to contain 0.01% or more, but inclusion exceeding 0.20% reduces toughness. For this reason, it is preferable to limit V to 0.20% or less. In addition, More preferably, it is 0.02 to 0.15%.
Nb is an element that contributes effectively to increasing the strength and toughness of steel. Such an effect becomes remarkable when the content is 0.01% or more, but when the content exceeds 0.20%, the toughness is lowered. For this reason, Nb is preferably 0.20% or less. In addition, More preferably, it is 0.02 to 0.12%.
Ｃ群：Ti：0.3％以下、Zr：0.2％以下、Ｂ：0.01％以下、Ｗ：3.0％以下のうちから選ばれた１種または２種以上
Ｃ群：Ti、Zr、Ｂ、Ｗはいずれも、鋼管強度を増加させ、耐応力腐食割れ性を改善する作用を有する元素であり、必要に応じて選択して１種または２種以上含有できる。このような効果は、Ti：0.01％以上、Zr：0.01％以上、Ｂ：0.0005％以上、Ｗ：0.1％以上の含有で顕著となる。一方、Ti：0.3％、Zr：0.2％、Ｂ：0.01％、Ｗ：3.0％、をそれぞれ超える含有は、靱性を劣化させる。このため、Ti：0.3％以下、Zr：0.2％以下、Ｂ：0.01％以下、Ｗ：3.0％以下にそれぞれ限定することが好ましい。
Group C: Ti: 0.3% or less, Zr: 0.2% or less, B: 0.01% or less, W: 3.0% or less selected from one or more types C Group: Ti, Zr, B, W are any Is an element having an action of increasing the strength of the steel pipe and improving the resistance to stress corrosion cracking, and can be selected as necessary and contained in one or more kinds. Such an effect becomes significant when Ti: 0.01% or more, Zr: 0.01% or more, B: 0.0005% or more, and W: 0.1% or more. On the other hand, the contents exceeding Ti: 0.3%, Zr: 0.2%, B: 0.01%, W: 3.0% respectively deteriorate the toughness. For this reason, it is preferable to limit to Ti: 0.3% or less, Zr: 0.2% or less, B: 0.01% or less, and W: 3.0% or less, respectively.
Ｄ群：Ca：0.0005〜0.01％
Ｄ群：Caは、ＳをCaSとして固定しＳ系介在物を球状化する作用により、介在物の周囲のマトリックスの格子歪を小さくして、水素のトラップ能を下げる作用を有する元素である。このような効果は0.0005％以上の含有で顕著となるが、0.01％を超える含有は、CaOの増加を招き、耐CO2腐食性、耐孔食性を低下させる。このため、Caは0.0005〜0.01％の範囲に限定することが好ましい。なお、より好ましくは0.001〜0.005％である。
Group D: Ca: 0.0005 to 0.01%
Group D: Ca is an element having an effect of reducing the trapping ability of hydrogen by reducing the lattice strain of the matrix around the inclusions by fixing S as CaS and making the S-based inclusions spherical. Such an effect becomes remarkable when the content is 0.0005% or more. However, when the content exceeds 0.01%, CaO increases, and the resistance to CO 2 corrosion and pitting corrosion decreases. For this reason, it is preferable to limit Ca to 0.0005 to 0.01% of range. In addition, More preferably, it is 0.001 to 0.005%.
上記した成分以外の残部は、Feおよび不可避的不純物からなる。
つぎに、本発明ステンレス鋼管の好ましい組織について説明する。
本発明ステンレス鋼管は、上記した組成を有し、焼戻マルテンサイト相を主相とし、第二相として体積率で、５％以上のオーステナイト相と、あるいはさらに５％以下のフェライト相を含む組織を有することが好ましい。ここでいう「主相」とは、体積率で50％以上の組織分率を有する相をいう。
焼戻マルテンサイト相を主相とする組織とすることにより、所望の高強度を確保することができる。焼戻マルテンサイト相が体積率で50％未満では、鋼管強度が低下し、所望の鋼管強度を確保できなくなる。そして主相に加えてさらに、第二相としてオーステナイト相を含む組織に限定することが好ましい。オーステナイト相の含有量は、体積率で５％以上となるように調整することが好ましい。これにより、所望の高い拡管性を兼備させることができる。オーステナイト相含有量の調整は、組成および熱処理の調整により行うことができる。また、第二相として上記したオーステナイト相に加えて、体積率で０〜５％のフェライト相を含有してもよい。フェライト相が５％を超えて多量になると、拡管性低下の原因となる。このようなことから、焼戻マルテンサイト相を主相とし、第二相を、体積率で、５％以上のオーステナイト相と、あるいはさらに、５％以下のフェライト相とを含む組織に限定することが好ましい。なお、それ以外の第二相としては、体積率で20％以下の焼入れマルテンサイトが許容される。
The balance other than the components described above consists of Fe and inevitable impurities.
Next, a preferred structure of the stainless steel pipe of the present invention will be described.
The stainless steel pipe of the present invention has the above-described composition, and has a structure containing a tempered martensite phase as a main phase and a volume ratio of 5% or more of an austenite phase as a second phase, or a ferrite phase of 5% or less. It is preferable to have. The “main phase” here refers to a phase having a structure fraction of 50% or more by volume.
A desired high strength can be ensured by using a tempered martensite phase as the main phase. If the tempered martensite phase is less than 50% by volume, the steel pipe strength is lowered and the desired steel pipe strength cannot be ensured. In addition to the main phase, the second phase is preferably limited to a structure containing an austenite phase. The content of the austenite phase is preferably adjusted to be 5% or more by volume ratio. Thereby, desired high tube expansion property can be combined. The austenite phase content can be adjusted by adjusting the composition and heat treatment. Moreover, in addition to the austenite phase described above as the second phase, a ferrite phase of 0 to 5% by volume may be contained. When the ferrite phase exceeds 5% and becomes a large amount, it causes a decrease in tube expandability. For this reason, the tempered martensite phase is the main phase, and the second phase is limited to a structure containing an austenite phase of 5% or more by volume, or a ferrite phase of 5% or less. Is preferred. In addition, as the second phase other than that, quenched martensite having a volume ratio of 20% or less is allowed.
上記した組成と、上記した組織を有することにより、耐食性、とくに優れた耐CO2腐食性と、拡管性に優れた油井用ステンレス鋼管となる。
つぎに、本発明ステンレス鋼管の好ましい製造方法を、継目無鋼管を例にして説明する。なお、本発明では鋼管は、継目無鋼管に限定されるものではなく、熱延鋼板を素材とした溶接鋼管（電縫鋼管）としてもよいのは言うまでもない。
上記した組成を有する溶鋼を、転炉、電気炉、真空溶解炉等の通常の溶製方法で溶製し、連続鋳造法、造塊−分塊圧延法等の通常の方法でビレット等の鋼管素材とすることが好ましい。ついで、これら鋼管素材を加熱し、通常のマンネスマン−プラグミル方式、あるいはマンネスマン−マンドレルミル方式の製造工程を用いて熱間加工し造管して、所望の寸法の継目無鋼管とする。造管後、継目無鋼管は、通常工程と同様に、空冷程度の冷却速度で室温程度の温度まで冷却することが好ましい。
By having the above-described composition and the above-described structure, it becomes an oil well stainless steel pipe excellent in corrosion resistance, particularly excellent CO 2 corrosion resistance, and pipe expandability.
Next, a preferred method for producing the stainless steel pipe of the present invention will be described using a seamless steel pipe as an example. In the present invention, the steel pipe is not limited to a seamless steel pipe, and needless to say, it may be a welded steel pipe (electrically welded steel pipe) made of a hot-rolled steel sheet.
Molten steel having the above composition is melted by a normal melting method such as a converter, an electric furnace, a vacuum melting furnace, etc., and a steel pipe such as a billet by a normal method such as a continuous casting method or an ingot-bundling rolling method. It is preferable to use a raw material. Subsequently, these steel pipe materials are heated and hot-worked and piped using a normal Mannesmann-plug mill system or Mannesmann-Mandrel mill system manufacturing process to obtain seamless steel pipes of desired dimensions. After the pipe making, the seamless steel pipe is preferably cooled to a temperature of about room temperature at a cooling rate of about air cooling, as in the normal process.
上記した本発明範囲の組成を有する継目無鋼管（ステンレス鋼管）であれば、熱間加工後、空冷程度の冷却速度で室温程度の温度まで冷却することにより、マルテンサイト相を主体とする組織とすることができるが、本発明では、造管ままのステンレス鋼管（素管）に、さらに熱処理を施すことが好ましい。熱処理としては、焼入れ焼戻処理、あるいは焼戻処理を施すことが好ましい。 If it is a seamless steel pipe (stainless steel pipe) having the composition of the present invention as described above, after hot working, it is cooled to a temperature of about room temperature at a cooling rate of about air cooling, and a structure mainly composed of a martensite phase; However, in the present invention, it is preferable to further heat-treat the as-made stainless steel pipe (base pipe). As the heat treatment, it is preferable to perform quenching and tempering treatment or tempering treatment.
焼入れ処理は、800℃以上の加熱温度に再加熱し続いて空冷以上の冷却速度で200℃以下の温度、好ましくは室温まで冷却する処理とすることが好ましい。なお、加熱温度での保持は５min以上とすることが好ましい。加熱温度が800℃未満では、組織を焼戻マルテンサイト相を主相とする組織とすることができない。
また、焼戻処理は、Ａc1変態点を超える温度に加熱し、好ましくは空冷程度あるいは空冷以上の冷却速度で冷却する処理とすることが好ましい。焼戻温度をＡc1変態点を超える温度とすることにより、オーステナイト相の析出、あるいは焼入れマルテンサイト相の生成が生じる。なお、焼入れ焼戻処理に代えて、上記した焼戻処理のみの熱処理としてもよい。このような熱処理を鋼管（ステンレス鋼管）に施すことにより、上記した組織を安定して確保できる。
The quenching process is preferably a process of reheating to a heating temperature of 800 ° C. or higher followed by cooling to a temperature of 200 ° C. or lower, preferably room temperature, at a cooling rate of air cooling or higher. The holding at the heating temperature is preferably 5 min or more. If the heating temperature is less than 800 ° C., the structure cannot be a structure whose main phase is a tempered martensite phase.
Further, the tempering treatment is preferably performed by heating to a temperature exceeding the Ac 1 transformation point and preferably cooling at a cooling rate of about the air cooling or air cooling. By setting the tempering temperature to a temperature exceeding the Ac 1 transformation point, precipitation of the austenite phase or formation of a quenched martensite phase occurs. In place of the quenching and tempering process, the above-described tempering process alone may be used. By applying such heat treatment to the steel pipe (stainless steel pipe), the above-described structure can be stably secured.
また、上記した焼戻処理を、Ａc1変態点超え700℃以下の二相域の温度に加熱し、冷却する処理としてもよい。
上記したように、熱処理を施された継目無鋼管（素管）は、ついで、両端面側に拡管を施される。拡管は、通常、当該鋼管内に拡管用プラグを挿入して行う。本発明では、素管の両端面側に素管内径より大きい各種外径を有するプラグをそれぞれプレス等で押し込み、好ましくは３％以上の、所定の拡管率となるように予め拡管加工して拡管部を形成する。なお、拡管加工が施される領域（拡管部）は、素管（ステンレス鋼管）の端面から管軸方向に、適正長さのねじが加工できる長さとする。
Further, the tempering process described above may be a process of heating and cooling to a temperature in a two-phase region exceeding the Ac 1 transformation point and 700 ° C. or less.
As described above, the heat-treated seamless steel pipe (base pipe) is then subjected to pipe expansion on both end surfaces. The pipe expansion is usually performed by inserting a pipe expansion pipe into the steel pipe. In the present invention, plugs having various outer diameters larger than the inner diameter of the raw tube are respectively pushed into the both end surfaces of the raw tube with a press or the like, and are preferably expanded in advance to obtain a predetermined expansion rate of 3% or more. Forming part. In addition, let the area | region (expansion part) to which a pipe expansion process is performed be the length which can process the screw | thread of an appropriate length from the end surface of a raw pipe (stainless steel pipe) to a pipe-axis direction.
ついで、該拡管部に、適正長さのねじを加工し、ねじ加工部を形成し、本発明の油井用ステンレス鋼管を得る。
さらに、本発明を実施例に基づき詳細に説明する。
Next, a screw having an appropriate length is processed on the expanded portion to form a threaded portion, thereby obtaining the oil well stainless steel tube of the present invention.
Further, the present invention will be described in detail based on examples.
表１に示す組成の溶鋼を、真空溶解炉で溶製し、十分に脱ガスした後、100キロ鋼塊とし、研究用モデルシームレス圧延機により造管し、継目無鋼管（外径73mmφ×肉厚7.0mm）とした。なお、造管後、室温まで空冷とした。
次いで各鋼管に、表２に示す条件で、熱処理を施した。
ついで、上記した鋼管から、組織観察用試片を採取し、管軸方向断面を研磨して、腐食し組織観察に供した。組織観察は、走査型電子顕微鏡を用いて行った。組織を撮像（各５視野以上）し、各相の組織分率（体積％）を画像解析装置を用いて算出した。なお、オーステナイト相の組織分率は、Ｘ線回析により測定した。
Molten steel with the composition shown in Table 1 was melted in a vacuum melting furnace, fully degassed, and then made into a 100 kg steel ingot, which was then piped by a model seamless rolling mill for research, and seamless steel pipe (outer diameter 73 mmφ x meat The thickness was 7.0 mm. In addition, it was made to air-cool to room temperature after pipe making.
Next, each steel pipe was subjected to heat treatment under the conditions shown in Table 2.
Next, a specimen for observing the structure was taken from the above-described steel pipe, the cross section in the tube axis direction was polished, corroded, and subjected to the structure observation. Tissue observation was performed using a scanning electron microscope. The tissue was imaged (5 visual fields or more), and the tissue fraction (volume%) of each phase was calculated using an image analyzer. The structural fraction of the austenite phase was measured by X-ray diffraction.
また、上記した鋼管から、APIの規定に準拠して、管軸方向を引張方向とする引張試験片（弧状試験片：GL：25.4mm）を切り出し、APIの規定に準拠して、引張試験を実施し、引張特性（降伏強さYS、引張強さTS、均一伸びu-El）を求めた。また、同時に、JIS Z 2253の規定に準拠してｎ値を求めた。
また、上記した鋼管から、拡管試験片（鋼管：長さ300mm）を採取した。これら拡管試験片（鋼管）に、拡管試験片（鋼管）の内径より大きい各種外径を有するプラグを順次、プレスにより押し込み、亀裂が発生した時点のプラグ径を求め、次式
限界拡管率＝［｛（亀裂が発生したときのプラグ外径）−（試験材内径）｝／（試験材内径）］×100（％）
で限界拡管率を算出した。なお、使用したプラグの外径は、拡管率が５％刻みとなるように配慮した。
In addition, a tensile test piece (arc-shaped test piece: GL: 25.4mm) with the pipe axis direction as the tensile direction is cut out from the above steel pipe in accordance with the API regulations, and a tensile test is conducted in accordance with the API regulations. The tensile properties (yield strength YS, tensile strength TS, uniform elongation u-El) were determined. At the same time, the n value was determined in accordance with JIS Z 2253.
Further, a pipe expansion test piece (steel pipe: length 300 mm) was collected from the above steel pipe. Plugs with various outer diameters larger than the inner diameter of the expanded test specimen (steel pipe) are sequentially pressed into these expanded test specimens (steel pipe), and the plug diameter when the crack occurs is obtained. {(Plug outer diameter when crack occurred)-(Test material inner diameter)} / (Test material inner diameter)] × 100 (%)
The critical expansion rate was calculated at In addition, the outer diameter of the used plug was considered so that the expansion ratio might be 5%.
また、上記した鋼管から試験材（管状）を採取し、拡管率：30％の拡管加工を施した。該拡管加工を施された試験片（管状）から、腐食試験片（厚さ３mm×幅30mm×長さ40mm）を機械加工により採取した。腐食試験は、オートクレーブ中に保持された試験液：20％NaCl水溶液（液温：100℃、30気圧のCO2ガス雰囲気）に腐食試験片を浸漬し、浸漬期間を２週間として実施した。腐食試験後の試験片重量を測定し、腐食試験による試験片の重量減を求め、腐食速度を算出した。また、腐食試験後の試験片表面について10倍のルーペ観察を行い、孔食発生の有無も調査した。得られた腐食速度および孔食発生の有無で、耐CO2腐食性を評価した。 Moreover, the test material (tubular) was extract | collected from the above-mentioned steel pipe, and the pipe expansion process of 30% was given. A corrosion test piece (thickness 3 mm × width 30 mm × length 40 mm) was sampled from the test piece (tubular) subjected to the tube expansion process by machining. The corrosion test was performed by immersing the corrosion test piece in a test solution: 20% NaCl aqueous solution (liquid temperature: 100 ° C., CO 2 gas atmosphere of 30 atm) held in the autoclave, and setting the immersion period to 2 weeks. The weight of the test piece after the corrosion test was measured, the weight loss of the test piece by the corrosion test was determined, and the corrosion rate was calculated. In addition, the surface of the test piece after the corrosion test was observed with a magnifying glass 10 times, and the presence or absence of pitting corrosion was investigated. The CO 2 corrosion resistance was evaluated based on the obtained corrosion rate and the presence or absence of pitting corrosion.
得られた結果を表２に示す。 The obtained results are shown in Table 2.
本発明の好適範囲を満足する鋼管はいずれも、降伏強さ：350MPa以上の高強度を有し、限界拡管率が25％以上と優れた拡管性を有するとともに、腐食速度も0.127mm／y以下であり優れた耐CO2腐食性を有し、また孔食の発生もなく、優れた耐CO2腐食性を有する鋼管となっている。一方、本発明の好適範囲を外れる鋼管は、降伏強さが350MPa未満であるか、限界拡管率が低く拡管性が若干低下しているか、あるいは腐食速度が0.127mm／yを超えて大きくなっているか、あるいは孔食が発生し、耐CO2腐食性が若干低下している。 All of the steel pipes satisfying the preferred range of the present invention have a high yield strength of 350 MPa or more, an excellent tube expansion ratio of 25% or more, and a corrosion rate of 0.127 mm / y or less. The steel pipe has excellent CO 2 corrosion resistance, no pitting corrosion, and excellent CO 2 corrosion resistance. On the other hand, a steel pipe that is outside the preferred range of the present invention has a yield strength of less than 350 MPa, a low critical expansion rate and a slight decrease in expandability, or a corrosion rate greater than 0.127 mm / y. Or pitting corrosion has occurred, and the CO 2 corrosion resistance is slightly reduced.
ついで、表２に示す特性を有する継目無鋼管（素管）の両端面部に、表３に示す拡管率となるように、各種外径を有するプラグをプレスで押し込み、端面側拡管加工を施した。この端面側拡管加工は、鋼管同士をねじ接合可能なように、同一条件で少なくとも２本の鋼管について行った。なお、拡管率は次（１）式
拡管率＝［｛（プラグ外径）−（素管内径）｝／（素管内径）］×100（％）‥（１）
（ここで、プラグ外径：拡管用工具（プラグ）の外径（mm）、素管内径：鋼管端面部の加工前内径（mm））
を用いて算出した。
Next, plugs having various outer diameters were pressed into the both end faces of the seamless steel pipe (elementary pipe) having the characteristics shown in Table 2 with a press so as to achieve the pipe expansion ratio shown in Table 3, and subjected to end face side pipe expansion processing. . This end face side pipe expansion process was performed on at least two steel pipes under the same conditions so that the steel pipes could be screwed together. The tube expansion rate is the following equation (1): tube expansion rate = [{(plug outer diameter) − (element tube inner diameter)} / (element tube inner diameter)] × 100 (%) (1)
(Here, the outer diameter of the plug: the outer diameter (mm) of the tube expansion tool (plug), the inner diameter of the raw pipe: the inner diameter of the steel pipe end face before processing (mm))
It calculated using.
ついで拡管加工を施された拡管加工部に、ねじ加工を施した。加工されたねじは、テーパねじ（テーパ：１／8、ピッチ：1／6 inch、長さ：4.715 inch）とし、鋼管の一方の端部を雄ねじ、他方を雌ねじとした。なお、一部の鋼管は、ねじ加工を施した後、表３に示す拡管率の端面側拡管加工を行った。
得られた同一条件の鋼管同士をねじ接合したのち、さらに、所定の内径となるように、母管およびねじ継手部に接合後の拡管加工を施した。なお、拡管加工は、ねじ加工前の端面側拡管加工を含め、合計で20％の拡管率となるように施した。接合後の拡管加工を施された鋼管について、水圧試験（圧力：8MPa）を実施し、ねじ継手部からの漏れの有無を確認した。
Next, the thread expansion was applied to the tube expansion processing portion that had been subjected to the tube expansion processing. The processed screw was a taper screw (taper: 1/8, pitch: 1/6 inch, length: 4.715 inch), and one end of the steel pipe was a male screw and the other was a female screw. In addition, some steel pipes performed the end face side pipe expansion process of the pipe expansion rate shown in Table 3 after giving a thread process.
After the obtained steel pipes having the same conditions were screwed together, the mother pipe and the threaded joint were subjected to pipe expansion after joining so as to have a predetermined inner diameter. In addition, pipe expansion processing was performed so that the total pipe expansion ratio would be 20%, including end face side pipe expansion before threading. A water pressure test (pressure: 8 MPa) was performed on the steel pipe that had been subjected to pipe expansion after joining, and the presence or absence of leakage from the threaded joint was confirmed.
得られた結果を表３に示す。 The obtained results are shown in Table 3.
本発明例はいずれも、ねじ継手部からの漏れは認められなかった。一方、本発明の範囲を外れる比較例は、ねじ継手部からの漏れが認められた。 In any of the inventive examples, no leakage from the threaded joint was observed. On the other hand, in the comparative example outside the scope of the present invention, leakage from the threaded joint was observed.
Claims (12)
記
拡管率＝［｛（プラグ外径）−（素管内径）｝／（素管内径）］×100（％）‥‥（１）
ここで、プラグ外径：拡管用工具（プラグ）の外径（mm）
素管内径：鋼管端面部の加工前内径（mm） 2. The oil well stainless steel pipe according to claim 1, wherein an amount of the pipe expansion processing is 3% or more as a pipe expansion rate defined by the following formula (1).
Tube expansion rate = [{(plug outer diameter)-(element tube inner diameter)} / (element tube inner diameter)] x 100 (%) (1)
Here, plug outer diameter: outer diameter of pipe expansion tool (plug) (mm)
Base tube inner diameter: Inner diameter of steel pipe end face before processing (mm)
記
ｎ＞0.007×（25−u-El）‥‥‥（２）
ここで、ｎ：ｎ値、
u-El：均一伸び（％） 2. The oil well stainless steel pipe has a yield strength of 350 MPa or more, an n value of 0.08 or more, and an n value and uniform elongation u-El satisfy the following expression (2): Or the stainless steel pipe for oil wells of 2.
Record
n> 0.007 × (25−u-El) (2)
Where n: n value,
u-El: Uniform elongation (%)
Ｃ：0.25％以下、 Si：1.0％以下、
Mn：0.10〜2.50％、 Ｐ：0.05％以下、
Ｓ：0.005％以下、 Al：0.05％以下、
Cr：10.5〜18.0％、 Ｎ：0.09％以下
を含有し、残部Feおよび不可避的不純物からなる組成を有し、耐CO２腐食性に優れることを特徴とする請求項１ないし３のいずれか１項に記載の油井用ステンレス鋼管。 The oil well stainless steel pipe is in mass%,
C: 0.25% or less, Si: 1.0% or less,
Mn: 0.10 to 2.50%, P: 0.05% or less,
S: 0.005% or less, Al: 0.05% or less,
4. The composition according to claim 1, comprising Cr: 10.5 to 18.0%, N: 0.09% or less, having a composition comprising the balance Fe and inevitable impurities, and being excellent in CO 2 corrosion resistance. The stainless steel pipe for oil wells as described in the item.
記
Ａ群：Cu：3.5％以下、
Ｂ群：Ni：7.0％以下、Mo：3.0％以下、Ｖ：0.20％以下、Nb：0.20％以下のうちから選ばれた１種または２種以上、
Ｃ群：Ti：0.3％以下、Zr：0.2％以下、Ｂ：0.01％以下、Ｗ：3.0％以下のうちから選ばれた１種または２種以上、
Ｄ群：Ca：0.0005〜0.01％ The stainless steel pipe for oil wells according to claim 4, further comprising, in addition to the composition, a composition containing one group or two or more groups selected from the following groups A to D in mass%. .
Group A: Cu: 3.5% or less,
Group B: Ni: 7.0% or less, Mo: 3.0% or less, V: 0.20% or less, Nb: one or more selected from 0.20% or less,
Group C: Ti: 0.3% or less, Zr: 0.2% or less, B: 0.01% or less, W: 3.0% or less selected from one or more,
Group D: Ca: 0.0005 to 0.01%
記
拡管率＝［｛（プラグ外径）−（素管内径）｝／（素管内径）］×100（％） ‥‥（１）
ここで、プラグ外径：拡管用工具（プラグ）の外径（mm）
素管内径：鋼管端面側の加工前内径（mm） 10. The method for producing a stainless steel pipe for an oil well according to claim 7, wherein the amount of the pipe expansion processing is 3% or more as a pipe expansion rate defined by the following formula (1).
Expansion rate = [{(Plug outer diameter)-(Base tube inner diameter)} / (Base tube inner diameter)] x 100 (%) (1)
Here, plug outer diameter: outer diameter of pipe expansion tool (plug) (mm)
Base tube inner diameter: Inner diameter before processing of steel pipe end face (mm)
Ｃ：0.25％以下、 Si：1.0％以下、
Mn：0.10〜2.50％、 Ｐ：0.05％以下、
Ｓ：0.005％以下、 Al：0.05％以下、
Cr：10.5〜18.0％、 Ｎ：0.09％以下
を含有し、残部Feおよび不可避的不純物からなる組成を有することを特徴とする請求項７ないし１０のいずれか１項に記載の油井用ステンレス鋼管の製造方法。 The stainless steel pipe is in mass%,
C: 0.25% or less, Si: 1.0% or less,
Mn: 0.10 to 2.50%, P: 0.05% or less,
S: 0.005% or less, Al: 0.05% or less,
The stainless steel pipe for oil wells according to any one of claims 7 to 10, comprising Cr: 10.5 to 18.0%, N: 0.09% or less, and having a composition comprising balance Fe and inevitable impurities. Production method.
記
Ａ群：Cu：3.5％以下、
Ｂ群：Ni：7.0％以下、Mo：3.0％以下、Ｖ：0.20％以下、Nb：0.20％以下のうちから選ばれた１種または２種以上、
Ｃ群：Ti：0.30％以下、Zr：0.20％以下、Ｂ：0.0005〜0.01％、Ｗ：1.0％以下のうちから選ばれた１種または２種以上、
Ｄ群：Ca：0.0005〜0.01％ The stainless steel pipe for oil wells according to claim 11, further comprising, in addition to the composition, a composition containing one group or two or more groups selected from the following groups A to D in mass%. Manufacturing method.
Group A: Cu: 3.5% or less,
Group B: Ni: 7.0% or less, Mo: 3.0% or less, V: 0.20% or less, Nb: one or more selected from 0.20% or less,
Group C: Ti: 0.30% or less, Zr: 0.20% or less, B: 0.0005-0.01%, W: 1.0% or less selected from 1.0% or less,
Group D: Ca: 0.0005 to 0.01%
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