JP2016029368A - Steep product sulfide stress corrosion cracking test method and seamless steel pipe excellent in sulfide stress corrosion cracking resistance - Google Patents
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Abstract
Description
本発明は、湿潤硫化水素環境（サワー環境ともいう）下で使用される油井管やラインパイプなどに用いて好適な、継目無鋼管等の鋼材の、耐硫化物応力腐食割れ性（耐SSC性）を評価する試験方法に係り、とくに、降伏強さ：758MPa（110ksi）級以上の高強度鋼材の耐硫化物応力腐食割れ性（耐SSC性）評価に関する。 The present invention is a sulfide stress corrosion cracking resistance (SSC resistance) of steel materials such as seamless steel pipes suitable for oil well pipes and line pipes used in a wet hydrogen sulfide environment (also called sour environment). In particular, the present invention relates to the sulfide stress corrosion cracking resistance (SSC resistance) evaluation of high strength steel materials with yield strength of 758 MPa (110 ksi) class or higher.
近年、石油や天然ガスの資源枯渇にともない、従来、見合わせてきたような高深度でかつ硫化水素（H2S）を含み腐食性が強いサワー環境となる油井およびガス井の開発が進められるようになってきた。このような油井、ガス井の高深度化に伴い、掘削用の油井管および輸送用のラインパイプに対しては、硫化水素（H2S）を含むサワー環境下での耐SSC性に優れているとともに、降伏強さ：758MPa （110ksi）級以上の高強度を保持することが要求されている。 In recent years, with the depletion of oil and natural gas resources, the development of oil wells and gas wells that have a deep sour environment that includes hydrogen sulfide (H 2 S) and is highly corrosive has been promoted. It has become. As oil wells and gas wells become deeper, excavating oil well pipes and transportation line pipes have excellent SSC resistance in sour environments containing hydrogen sulfide (H 2 S). At the same time, yield strength is required to maintain a high strength of 758 MPa (110 ksi) or higher.
一般的には、耐SSC性の評価は、例えば、非特許文献１に準拠して、NACE TM0177に規定されるMethod Aで行っている。この方法は、鋼材から機械加工により採取した棒状引張試験片（図２参照）を用い、標準溶液（例えばH2S飽和5％NaCl（食塩）＋0.5％CH3COOH（酢酸））中で所定の応力を負荷し、720時間経過後までに、破断するか否かを、評価する試験方法である。なお、使用する棒状引張試験片は、図２に示すように、平行部、肩部、つかみ部からなる。 In general, the evaluation of SSC resistance is performed by Method A defined in NACE TM0177, for example, in accordance with Non-Patent Document 1. This method uses rod-shaped tensile specimens (see Fig. 2) taken from steel by machining, and in a standard solution (for example, H 2 S saturated 5% NaCl (sodium chloride) + 0.5% CH 3 COOH (acetic acid)). This is a test method for evaluating whether or not a fracture occurs by applying a predetermined stress and lapse of 720 hours. In addition, the rod-shaped tensile test piece to be used consists of a parallel part, a shoulder part, and a grip part as shown in FIG.
評価対象は平行部とし、試験時には、平行部に、例えば、鋼材の規格降伏強さの下限値（SMYS：Specified Minimum Yield Strength）の80〜95％の応力を、負荷する。平行部は、棒状引張試験片の中で最も径が小さく、負荷される応力は他の箇所に比べ高くなる。そのため、硫化物応力腐食割れ（SSC）起因の破断が発生する場合は、平行部の中央付近で破断し、平行部での正当な評価が可能となるとしている。 The evaluation object is a parallel part, and at the time of testing, a stress of 80 to 95% of the lower limit value (SMYS: Specified Minimum Yield Strength) of the steel material is applied to the parallel part, for example. The parallel portion has the smallest diameter among the rod-like tensile test pieces, and the stress applied is higher than in other places. For this reason, when a rupture due to sulfide stress corrosion cracking (SSC) occurs, the rupture occurs near the center of the parallel portion, and a proper evaluation at the parallel portion is possible.
NACE TM0177 に規定されるMethod Aは、鋼材の耐SSC性を評価するために、一般的に広く用いられる方法である。しかし、この方法を用いて、鋼材の耐SSC性を評価する場合、平行部で破断せずに、応力的には本来破断しないはずの肩部や上つかみ部で破断する場合がある。とくに、SMYSに対する負荷応力の比率（応力比）が高い場合や、応力比が一定であっても、鋼材の高強度化に伴いSMYSが高くなり、負荷応力そのものが高くなる場合などに、その発生頻度が高くなるという問題があった。 Method A defined in NACE TM0177 is a widely used method for evaluating the SSC resistance of steel materials. However, when this method is used to evaluate the SSC resistance of a steel material, it may break at the shoulder portion or upper grip portion that should not break in terms of stress without breaking at the parallel portion. This occurs especially when the ratio of stress to SMYS (stress ratio) is high, or even when the stress ratio is constant, SMYS increases as the strength of steel increases, and the load stress itself increases. There was a problem of high frequency.
肩部やつかみ部で破断すると、平行部での評価ができていないため、鋼材の耐SSC性の正当な評価でないとして、試験が無効と判断される場合がある。その場合は、再試験を行う必要がある。再試験を行うと、試験用の鋼材や溶液および試験費用に無駄が生じるばかりでなく、長時間の試験であるため、大きな時間的損失を伴うという問題があった。 If the shoulder portion or the grip portion is broken, the parallel portion cannot be evaluated, and therefore the test may be judged invalid if it is not a valid evaluation of the SSC resistance of the steel material. In that case, it is necessary to retest. When the retest is performed, not only is the test steel material and solution and the test cost was wasted, but there is a problem that a large time loss is caused because the test is a long time.
そこで、本発明は、上記した従来技術の問題を解決し、とくに鋼材の強度や負荷応力の大きさに関係なく、鋼材の耐SSC性を適正に評価できる、鋼材の硫化物応力腐食割れ試験方法を提供することを目的とする。なお、ここでいう「硫化物応力腐食割れ試験」とは、NACE TM0177 Method Aに準じた定荷重試験をいう。 Therefore, the present invention solves the above-described problems of the prior art, and can particularly appropriately evaluate the SSC resistance of a steel material regardless of the strength of the steel material or the magnitude of load stress, and a sulfide stress corrosion cracking test method for steel materials. The purpose is to provide. The “sulfide stress corrosion cracking test” here refers to a constant load test according to NACE TM0177 Method A.
本発明者らは、上記した目的を達成するため、鋼材の硫化物応力腐食割れ試験における破断原因について、鋭意研究した。 In order to achieve the above-described object, the present inventors diligently studied the cause of breakage in the sulfide stress corrosion cracking test of steel materials.
NACE TM0177に規定されるMethod Aでは、図３に示すように、平行部、肩部、つかみ部を有する棒状引張試験片を、図１に示すように、試験セル内の試験溶液中に浸漬し、上下方向に引張負荷荷重を負荷し、試験片に引張応力（負荷応力）を負荷して、所定時間（720時間）保持する。そして、所定時間経過までに、破断が生じるか否かを、測定し、耐SSC性を評価する。使用する試験溶液は、通常、H2S飽和5％NaCl（食塩）＋0.5％CH3COOH（酢酸）を用いる。硫化物応力腐食割れ試験中の試験セル内では、気相と液相（試験溶液）との界面（気液界面）が必然的に生じ、棒状引張試験片の上つかみ部の特定の位置がその気液界面と接触する。 In Method A defined in NACE TM0177, as shown in FIG. 3, a rod-shaped tensile test piece having a parallel part, a shoulder part, and a grip part is immersed in a test solution in a test cell as shown in FIG. A tensile load is applied in the vertical direction, a tensile stress (load stress) is applied to the test piece, and the test piece is held for a predetermined time (720 hours). Then, it is measured whether or not the fracture occurs before the predetermined time elapses, and the SSC resistance is evaluated. As a test solution to be used, H 2 S saturated 5% NaCl (salt) + 0.5% CH 3 COOH (acetic acid) is usually used. In the test cell during the sulfide stress corrosion cracking test, an interface (gas-liquid interface) between the gas phase and the liquid phase (test solution) inevitably occurs, and the specific position of the upper grip of the bar-shaped tensile test piece Contact with gas-liquid interface.
このような、鋼材の硫化物応力腐食割れ試験について、とくに試験片の腐食状況を中心に、種々観察した結果、つぎのような知見を得た。 As a result of various observations about the sulfide stress corrosion cracking test of steel materials, particularly focusing on the corrosion state of the test pieces, the following knowledge was obtained.
（１）硫化物応力腐食割れ試験の進行とともに、腐食生成物が試験片全体に一様に付着し、それにより腐食の進行は緩やかになること、しかし、
（２）試験片の上つかみ部の、気液界面と接する位置では、乾湿繰り返し環境となるため、平行部に比べ不均一な腐食が進行しやすいこと、そして不均一腐食が生じた箇所では、破断を生じ易いこと、
（３）試験片の肩部では、試験中に試験片表面に付着した腐食生成物にき裂が発生しやすいこと、そしてき裂が発生した箇所では、試験片の新生面が露出し、それにより平行部に比べ不均一な腐食が進行しやすいこと、
（４）不均一な腐食が進行した箇所における深さが、耐SSC性に対する臨界サイズを超えると、そこが起点となり、試験片が破断すること、
を知見した。
(1) With the progress of the sulfide stress corrosion cracking test, the corrosion product adheres uniformly to the entire specimen, which slows the progress of corrosion,
(2) At the position where the top grip part of the test piece comes into contact with the gas-liquid interface, it becomes a wet and dry repeated environment, so that non-uniform corrosion tends to proceed compared to the parallel part, and in places where non-uniform corrosion occurs, Easy to break,
(3) At the shoulder portion of the test piece, cracks are likely to occur in the corrosion products adhered to the surface of the test piece during the test, and the new surface of the test piece is exposed at the place where the crack occurred, thereby Non-uniform corrosion is likely to proceed compared to parallel parts,
(4) If the depth at the location where the non-uniform corrosion has progressed exceeds the critical size for SSC resistance, that will be the starting point, and the specimen will break.
I found out.
このような知見から、平行部では硫化物応力腐食割れ（SSC）が発生しない場合でも、上つかみ部や肩部ではSSCが発生し、試験片が破断することがありうることを新規に見出した。このような知見に基づき、本発明者らは、棒状引張試験片の上つかみ部および肩部における破断を抑制するためには、不均一腐食を抑制することが肝要であり、そのために、図２に示すように、上つかみ部の特定領域および肩部全域に、耐食性樹脂を塗布して、試験片における不均一腐食の生成を抑制すれば、試験片の不適正な破断を防止でき、適正な耐硫化物応力腐食試験を安定して行うことができることを見出した。 From such knowledge, it was newly found that even when no sulfide stress corrosion cracking (SSC) occurs in the parallel part, SSC occurs in the upper grip part or shoulder part, and the specimen may break. . Based on such knowledge, the present inventors need to suppress non-uniform corrosion in order to suppress breakage at the upper gripping portion and shoulder portion of the rod-shaped tensile test piece. As shown in Fig. 3, if a corrosion-resistant resin is applied to the specific area of the upper grip and the entire shoulder area to suppress the generation of uneven corrosion in the test piece, it is possible to prevent improper breakage of the test piece. It was found that the sulfide stress corrosion test can be performed stably.
本発明は、かかる知見に基づき、さらに検討を加えて完成されたものである。すなわち、本発明の要旨はつぎのとおりである。
（１）被試験材である鋼材から採取した棒状引張試験片を、試験セルに保持した試験溶液中に浸漬し、前記棒状引張試験片の長手方向に所定の負荷応力を負荷して鋼材の耐硫化物応力腐食割れ性を評価する鋼材の耐硫化物応力腐食割れ試験方法であって、前記棒状引張試験片として、平行部と、該平行部を挟み上側の肩部および下側の肩部と、前記上側の肩部に続く上側のつかみ部および前記下側の肩部に続く下側のつかみ部とを有し、かつ前記上側および前記下側の肩部全域、および前記上側のつかみ部で試験開始時の前記試験溶液の初期気液界面と接する位置を中心として所定の幅にわたり、耐食性樹脂を塗布した棒状引張試験片を使用することを特徴とする、鋼材の硫化物応力腐食割れ試験方法。
（２）（１）において、前記所定の幅が、3.0mm以上であることを特徴とする鋼材の硫化物応力腐食割れ試験方法。
（３）（１）または（２）において、前記耐食性樹脂が、タールエポキシ樹脂、シリコン樹脂のうちのいずれかであることを特徴とする鋼材の硫化物応力腐食割れ試験方法。
（４）（１）ないし（３）のいずれかにおいて、前記鋼材が、降伏強さ：758MPa以上を有する高強度鋼材であることを特徴とする鋼材の硫化物応力腐食割れ試験方法。
（５）継目無鋼管について、（１）ないし（４）のいずれかに記載の鋼材の硫化物応力腐食割れ試験方法を用いて試験を行い、破断無しであるとの評価が付加されたことを特徴とする耐硫化物応力腐食割れ性に優れた継目無鋼管。
The present invention has been completed based on such findings and further studies. That is, the gist of the present invention is as follows.
(1) A rod-shaped tensile test piece taken from a steel material to be tested is immersed in a test solution held in a test cell, and a predetermined load stress is applied in the longitudinal direction of the rod-shaped tensile test piece to resist the steel material. A method for testing sulfide stress corrosion cracking resistance of a steel material for evaluating sulfide stress corrosion cracking properties, comprising: a parallel part as the rod-shaped tensile test piece; an upper shoulder part and a lower shoulder part sandwiching the parallel part; An upper grip portion that follows the upper shoulder portion and a lower grip portion that continues to the lower shoulder portion, and the entire upper and lower shoulder portions, and the upper grip portion. A sulfide stress corrosion cracking test method for steel, characterized by using a rod-shaped tensile test piece coated with a corrosion-resistant resin over a predetermined width centered on a position in contact with the initial gas-liquid interface of the test solution at the start of the test. .
(2) The sulfide stress corrosion cracking test method for steel according to (1), wherein the predetermined width is 3.0 mm or more.
(3) The sulfide stress corrosion cracking test method for steel according to (1) or (2), wherein the corrosion-resistant resin is one of a tar epoxy resin and a silicon resin.
(4) The sulfide stress corrosion cracking test method for a steel material according to any one of (1) to (3), wherein the steel material is a high-strength steel material having a yield strength of 758 MPa or more.
(5) The seamless steel pipe was tested using the sulfide stress corrosion cracking test method for steel materials described in any of (1) to (4), and the evaluation that there was no break was added. A seamless steel pipe with excellent resistance to sulfide stress corrosion cracking.
本発明によれば、油井管用鋼管やラインパイプ用鋼管などの鋼材、特に降伏強さ：758MPa（110ksi）級以上の鋼材であっても、鋼材の耐硫化物応力腐食割れ性を適正に評価でき、再試験の実施等の必要がなくなり、産業上格段の効果を奏する。例えば、NACE TM0177 Method Aに準拠する定荷重試験において、負荷応力がSMYSの80％以上となる試験条件においても、試験片肩部や上つかみ部での破断を抑制でき、試験工程を短縮できるという効果もある。 According to the present invention, it is possible to appropriately evaluate the resistance to sulfide stress corrosion cracking of steel materials, such as steel pipes for oil well pipes and steel pipes for line pipes, particularly steel materials having a yield strength of 758 MPa (110 ksi) or higher. This eliminates the need for re-examination and provides a remarkable industrial effect. For example, in a constant load test conforming to NACE TM0177 Method A, it is possible to suppress breakage at the test piece shoulder and upper grip even under test conditions where the load stress is 80% or more of SMYS, thereby shortening the test process. There is also an effect.
本発明で対象とする鋼材の硫化物応力腐食割れ試験は、NACE TM0177 Method Aに準拠する定荷重試験とし、平行部と、平行部を挟み上側の肩部および下側の肩部と、上側の肩部に続く上側のつかみ部および下側の肩部に続く下側のつかみ部とを有し、図３に示す寸法形状の棒状引張試験片を使用する。さらに加えて、本発明では、図２に示すように、上側の肩部および下側の肩部の全域、および、つかみ部のうち上側のつかみ部の特定領域に、耐食性樹脂を塗布した棒状引張試験片を使用する。耐食性樹脂としては、鋼材との密着性や、試験環境での耐食性に優れた材料を使用することが好ましい。そのような耐食性樹脂としては、例えば、タールエポキシ樹脂、シリコン樹脂、ポリウレタン樹脂、フッ素樹脂等が例示できるが、なかでもタールエポキシ樹脂、シリコン樹脂が好ましい。 The sulfide stress corrosion cracking test of the steel material which is the subject of the present invention is a constant load test in accordance with NACE TM0177 Method A. The parallel part, the upper shoulder part and the lower shoulder part across the parallel part, and the upper part A bar-shaped tensile test piece having the shape shown in FIG. 3 is used, which has an upper grip portion that follows the shoulder portion and a lower grip portion that continues to the lower shoulder portion. In addition, in the present invention, as shown in FIG. 2, a rod-like tension in which a corrosion-resistant resin is applied to the entire area of the upper shoulder portion and the lower shoulder portion, and a specific region of the upper grip portion among the grip portions. Use specimens. As the corrosion resistant resin, it is preferable to use a material having excellent adhesion to a steel material and corrosion resistance in a test environment. Examples of such a corrosion resistant resin include a tar epoxy resin, a silicon resin, a polyurethane resin, and a fluororesin. Among these, a tar epoxy resin and a silicon resin are preferable.
ここでいう「上側のつかみ部の特定領域」とは、「試験開始時の試験溶液の初期気液界面と接する位置を中心として所定の幅」を意味する。試験中に、試験片と気液界面が接する位置は、液面の微小なゆれによって乾湿が繰り返される環境に晒されるため、他の部位よりも腐食環境が厳しい。そのため、上側のつかみ部における試験溶液の気液界面と接する位置では、不均一な腐食が発生し、破断の起点となりやすい。本発明では、試験開始時の試験溶液の気液界面（以下、初期気液界面ともいう）と接する位置を中心として所定の幅に、耐食性樹脂を塗布する。「所定の幅」としては、気液界面のゆれや蒸発による液量減少を考慮して、3mm以上とすることが好ましい。 Here, the “specific region of the upper grip portion” means “a predetermined width centered on a position in contact with the initial gas-liquid interface of the test solution at the start of the test”. During the test, the position where the test piece and the gas-liquid interface come into contact with each other is exposed to an environment in which drying and wetting are repeated due to minute fluctuations in the liquid level, and therefore, the corrosive environment is severer than other parts. For this reason, non-uniform corrosion occurs at the position where the upper grip portion is in contact with the gas-liquid interface of the test solution, which is likely to be the starting point of fracture. In the present invention, the corrosion-resistant resin is applied to a predetermined width around a position in contact with the gas-liquid interface (hereinafter also referred to as initial gas-liquid interface) of the test solution at the start of the test. The “predetermined width” is preferably 3 mm or more in consideration of the fluctuation of the gas-liquid interface and the decrease in the liquid volume due to evaporation.
また、本発明では、上側の肩部および下側の肩部の全域、に耐食性樹脂を塗布する。 In the present invention, the corrosion resistant resin is applied to the entire area of the upper shoulder and the lower shoulder.
試験を開始した後の初期には、試験表面は、腐食されて一様に腐食生成物に覆われる。しかし、時間の経過とともに、応力勾配を有する肩部では腐食生成物にき裂が発生する。腐食生成物にき裂が発生した箇所では、新生面が露出するため、さらに腐食が進行して、不均一な腐食となる。そのため、不均一な腐食が生成した箇所では、硫化物応力腐食割れ起因の破断が起こりやすい。本発明では、試験片の上側および下側の肩部全域に、耐食性樹脂を塗布する。これにより、肩部における腐食の進行を防止し、不均一腐食の発生による、試験片の異常破断を防止することができる。 Initially after starting the test, the test surface is eroded and uniformly covered with corrosion products. However, over time, cracks occur in the corrosion products at the shoulders having a stress gradient. Since the new surface is exposed at a portion where a crack is generated in the corrosion product, the corrosion further proceeds and non-uniform corrosion occurs. Therefore, breakage due to sulfide stress corrosion cracking is likely to occur at a location where non-uniform corrosion occurs. In the present invention, the corrosion resistant resin is applied to the entire upper and lower shoulder portions of the test piece. Thereby, the progress of the corrosion in the shoulder portion can be prevented, and the abnormal fracture of the test piece due to the occurrence of the uneven corrosion can be prevented.
このように、上側の肩部および下側の肩部の全域、および上側のつかみ部の特定領域に、耐食性樹脂を塗布することにより、塗布された箇所においては、不均一な腐食の進行はもちろん、腐食が進行しなくなり、上記した領域における硫化物応力腐食割れの発生、すなわち、平行部以外での破断がなくなり、適正な耐硫化物応力腐食割れ性の評価が安定して可能になる。 In this way, by applying the corrosion-resistant resin to the entire area of the upper shoulder portion and the lower shoulder portion, and the specific region of the upper grip portion, the progress of non-uniform corrosion is, of course, at the applied location. Corrosion does not proceed, and the occurrence of sulfide stress corrosion cracking in the above-described region, that is, breakage at portions other than the parallel portion is eliminated, and proper evaluation of resistance to sulfide stress corrosion cracking becomes possible stably.
なお、本発明が対象とする鋼材の一つである油井用高強度継目無鋼管の好ましい組成としては、つぎのような組成が例示できる。 In addition, the following composition can be illustrated as a preferable composition of the high strength seamless steel pipe for oil wells which is one of the steel materials which this invention makes object.
例えば、質量％で、Ｃ：0.20〜0.50％、Si：0.05〜0.40％、Mn：0.3〜1.5％、Ｐ：0.015％以下、Ｓ：0.005％以下、Al：0.0005〜0.10％、Ｎ：0.006％以下、Cr：0.1〜1.5％、Mo：0.5〜3.0％、Ｖ：0.01〜0.3％、Nb：0.002〜0.05％、Ti：0.001〜0.03％、Ｂ：0.0003〜0.0030％、Ｏ（酸素）：0.0040％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とすることが好ましい。なお、Ti：0.001〜0.03％に代えて、Ti：0.003〜0.025％でかつTi、ＮをTi/Ｎ：2.0〜5.0を満足するように調整して含有することが好ましい。 For example, in mass%, C: 0.20 to 0.50%, Si: 0.05 to 0.40%, Mn: 0.3 to 1.5%, P: 0.015% or less, S: 0.005% or less, Al: 0.0005 to 0.10%, N: 0.006% Hereinafter, Cr: 0.1 to 1.5%, Mo: 0.5 to 3.0%, V: 0.01 to 0.3%, Nb: 0.002 to 0.05%, Ti: 0.001 to 0.03%, B: 0.0003 to 0.0030%, O (oxygen): 0.0040 % Or less, and the composition is preferably composed of the remaining Fe and inevitable impurities. In place of Ti: 0.001 to 0.03%, Ti is preferably 0.003 to 0.025%, and Ti and N are preferably contained so as to satisfy Ti / N: 2.0 to 5.0.
また、上記した組成に加えてさらに、必要に応じて、質量％で、Cu：1.0％以下、Ni：0.5％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、および／または、Ca：0.0005〜0.050％、Zr：0.0005〜0.03％、Mg：0.0005〜0.0025％のうちから選ばれた１種または２種以上、を選択して含有できる。 Further, in addition to the above-described composition, if necessary, by mass%, Cu: 1.0% or less, Ni: 0.5% or less, W: 3.0% or less, and one or more selected from / Or Ca: 0.0005 to 0.050%, Zr: 0.0005 to 0.03%, Mg: 0.0005 to 0.0025% can be selected and contained.
そして、上記した組成を有する油井用高強度継目無鋼管の好ましい製造方法は、つぎのとおりである。 And the preferable manufacturing method of the high strength seamless steel pipe for oil wells which has the above-mentioned composition is as follows.
上記した組成の鋼素材を、加熱して、好ましくはマンネスマン方式の熱間加工を施し、継目無鋼管としたのち、空冷以上の冷却速度で、表面温度が200℃以下になるまで冷却し、しかるのちに、焼戻温度：600〜740℃に加熱する焼戻処理を施すことが好ましい。 The steel material having the above composition is heated, preferably subjected to Mannesmann's hot working to form a seamless steel pipe, and then cooled at a cooling rate higher than air cooling until the surface temperature becomes 200 ° C. or lower. After that, it is preferable to perform a tempering treatment by heating to a tempering temperature of 600 to 740 ° C.
なお、空冷以上の冷却速度で、表面温度が200℃以下になるまで冷却したのち、さらに、焼入れ温度：Ａc3変態点以上1000℃以下に再加熱したのち、表面温度が200℃以下になるまで、急冷する焼入れ処理を１回以上施したのち、さらに上記した焼戻処理を施してもよい。 After cooling at a cooling rate of air cooling or higher until the surface temperature becomes 200 ° C. or lower, after further re-heating to a quenching temperature: Ac 3 transformation point or higher and 1000 ° C. or lower, until the surface temperature becomes 200 ° C. or lower, The quenching treatment for quenching may be performed once or more, and then the above-described tempering treatment may be performed.
つぎに、実施例に基づきさらに、本発明について説明する。 Next, the present invention will be further described based on examples.
表１に示す組成を有する油井用高張力鋼管から、機械加工により、NACE TM0177 Method Aに準拠して、図３に示す寸法形状の棒状引張試験片を採取した。なお、肩部Rは20mmとした。また、引張試験片は、API SPECIFICATION 5CT Annex Ｄに準じて、当該継目無鋼管の内面、外面、板厚中央部でのそれぞれの平均硬さのうち、最も硬さが大きい位置を試験片の採取位置とし、試験片の長手方向が、鋼管の長手方向（管軸方向）と一致するように採取した。 According to NACE TM0177 Method A, rod-shaped tensile test pieces having the dimensions shown in FIG. 3 were collected from high-strength steel pipes for oil wells having the compositions shown in Table 1 by machining. The shoulder R was 20 mm. In addition, according to API SPECIFICATION 5CT Annex D, the tensile test specimen should be sampled at the position where the hardness is the highest among the average hardness of the inner surface, outer surface, and center of the thickness of the seamless steel pipe. The sample was taken so that the longitudinal direction of the test piece coincided with the longitudinal direction of the steel pipe (tube axis direction).
そして、採取した棒状引張試験片の上側および下側の肩部全域、および／または、上側のつかみ部における試験溶液の初期気液界面と接する位置を中心とした所定の幅に耐食性樹脂を刷毛で塗布した。塗布箇所は、表２に示す箇所とした。なお、塗布した耐食性樹脂は、タールエポキシ樹脂（大日本塗料（株）製「SDCコート#402Tエコ」（商品名））、またはシリコン樹脂（信越化学工業（株）製「KE-45-W」（商品名））を用いた。塗布後、室温（大気中）に放置して乾燥させ、試験に供した。なお、比較として、耐食性樹脂を塗布しなかった試験片も用いた。 Then, brush the anti-corrosion resin to a predetermined width centered on the position of the upper and lower shoulders of the collected bar-shaped tensile test piece and / or the position of the upper gripping portion in contact with the initial gas-liquid interface. Applied. The application locations were those shown in Table 2. The applied corrosion-resistant resin is tar epoxy resin ("SDC Coat # 402T Eco" (trade name) manufactured by Dainippon Paint Co., Ltd.) or silicon resin ("KE-45-W" manufactured by Shin-Etsu Chemical Co., Ltd.). (Trade name)) was used. After coating, it was left to dry at room temperature (in the air) and used for the test. For comparison, a test piece to which the corrosion resistant resin was not applied was also used.
上記したように準備された棒状引張試験片を用いて、硫化物応力腐食試験を実施した。試験は、NACE TM0177 Method Aに準拠し、25℃のNACE溶液（硫化水素飽和5％NaCl＋0.5％CH3COOH溶液）を用いて、表２に示す定荷重（負荷応力）を負荷し、最大720ｈまで継続した。なお、試験片は、ばらつきを考慮して各３本とした。 A sulfide stress corrosion test was performed using the rod-shaped tensile test piece prepared as described above. In accordance with NACE TM0177 Method A, the test was performed using a NACE solution (hydrogen sulfide saturated 5% NaCl + 0.5% CH 3 COOH solution) at 25 ° C and the constant load (load stress) shown in Table 2 was applied. It continued until 720h. Three test pieces were used in consideration of variations.
720ｈまで破断しなかったものは、評価は「○（適合）」とした。また、720ｈ経過前に破断した試験片については、破断位置を確認し、平行部で破断した場合は、適正な評価ができているため評価は「○（適合）」とし、肩部またはつかみ部で破断した場合は、適正な評価ができておらず評価は「×不適合」とした。試験片３本とも評価が「○（適合）」であった場合に、判定は「○（合格）」とした。３本のうち１本でも評価が「×不適合」であった場合には、「×（不合格）」と判定した。 Those that did not break until 720h were evaluated as “◯ (conformity)”. In addition, for the test piece that broke before 720h, if the break position was confirmed, and the fracture occurred at the parallel part, the evaluation was “○ (conformity)” because the proper evaluation was made, and the shoulder or grip part In the case of breaking at, proper evaluation was not made and the evaluation was “non-conforming”. When the evaluation of all three test pieces was “◯ (conformity)”, the determination was “◯ (pass)”. If even one of the three was “x nonconforming”, it was determined as “x (failed)”.
得られた結果を表２に示す。 The obtained results are shown in Table 2.
本発明範囲の棒状引張試験片を用いた本発明例（試験No.1、No.2、No.6、No.9、No.10、No.11）はいずれも、破断が生じておらず、評価は「○」で、適正な耐硫化物応力腐食割れ性の評価を行うことができ、判定は合格（「○」）であった。 None of the inventive examples (test No.1, No.2, No.6, No.9, No.10, No.11) using rod-shaped tensile specimens within the scope of the present invention were not broken. The evaluation was “◯”, and proper sulfide stress corrosion cracking resistance could be evaluated, and the determination was acceptable (“◯”).
一方、上つかみ部で気液界面と接する位置に耐食性樹脂を塗布していないため、本発明範囲を外れる試験No.3、No.5、No.8は、上つかみ部での破断が発生し、また、肩部に耐食性樹脂を塗布していないため本発明範囲を外れる試験No.3、No.4、No.7は、肩部での破断が発生して、適正な評価を行うことができず、評価は「×」となり、判定は「×」となっている。 On the other hand, because no corrosion-resistant resin is applied to the position of the upper grip where the gas-liquid interface is in contact, tests No. 3, No. 5, and No. 8 that are outside the scope of the present invention cause breakage at the upper grip. In addition, tests No.3, No.4, and No.7, which do not fall within the scope of the present invention because no corrosion-resistant resin is applied to the shoulders, may cause a breakage at the shoulders and perform an appropriate evaluation. The evaluation is “x” and the determination is “x”.
なお、試験No.11、No.12は、鋼管（鋼材）の降伏強さが758MPa未満と強度が低いため、試験No.11のように本発明範囲を満足する引張試験片を用いた場合はもちろん、試験No.12のように本発明範囲を外れる引張試験片を用いた場合でも、破断は発生せず、適正な評価ができており、評価は「○」となっている。 Test No. 11 and No. 12 are low in yield strength of steel pipes (steel materials) less than 758 MPa, so when using a tensile test piece that satisfies the scope of the present invention as in test No. 11 Of course, even when a tensile test piece outside the scope of the present invention was used as in Test No. 12, the fracture did not occur and proper evaluation was made, and the evaluation was “◯”.
このようなことから、本発明によれば、とくに、降伏強さが758MPa（110ksi）以上の高強度である鋼材について、耐硫化物応力腐食割れ性の適正な評価が可能となることがわかる。 From this, it can be seen that according to the present invention, it is possible to appropriately evaluate the resistance to sulfide stress corrosion cracking particularly for a steel material having a yield strength of 758 MPa (110 ksi) or higher.
したがって、本発明になる鋼材の硫化物応力腐食割れ試験方法を用いて試験した結果、「破断無し」と評価された鋼材には、「本発明鋼材の硫化物応力腐食割れ試験方法を用いて試験を行い、破断無しである」との評価を付加できる。この評価の付加は、ミルシートに記載したり、当該鋼材にラベルを貼付したりして、行うことが好ましい。 Therefore, as a result of testing using the sulfide stress corrosion cracking test method for steels according to the present invention, the steel materials evaluated as “no break” were tested using the sulfide stress corrosion cracking test method for steel materials according to the present invention. It is possible to add an evaluation of “no breakage”. It is preferable to add this evaluation by writing on a mill sheet or attaching a label to the steel material.
Claims (5)
前記棒状引張試験片として、平行部と、該平行部を挟み上側の肩部および下側の肩部と、前記上側の肩部に続く上側のつかみ部および前記下側の肩部に続く下側のつかみ部とを有し、かつ前記上側および前記下側の肩部全域、および前記上側のつかみ部で試験開始時の前記試験溶液の初期気液界面と接する位置を中心として所定の幅にわたり、耐食性樹脂を塗布した棒状引張試験片を使用することを特徴とする、鋼材の硫化物応力腐食割れ試験方法。 A rod-shaped tensile test piece taken from a steel material to be tested is immersed in a test solution held in a test cell, and a predetermined load stress is applied in the longitudinal direction of the rod-shaped tensile test piece to thereby prevent sulfide stress of the steel material. It is a sulfide stress corrosion cracking test method for steel materials for evaluating corrosion cracking properties,
As the rod-shaped tensile test piece, a parallel part, an upper shoulder part and a lower shoulder part sandwiching the parallel part, an upper grip part following the upper shoulder part, and a lower side following the lower shoulder part The upper and lower shoulders, and the upper grip part over a predetermined width centered on a position in contact with the initial gas-liquid interface of the test solution at the start of the test, A sulfide stress corrosion cracking test method for steel, characterized by using a rod-shaped tensile test piece coated with a corrosion-resistant resin.
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