WO2016013197A1 - 鋼材の硫化物応力腐食割れ試験方法および耐硫化物応力腐食割れ性に優れた継目無鋼管 - Google Patents
鋼材の硫化物応力腐食割れ試験方法および耐硫化物応力腐食割れ性に優れた継目無鋼管 Download PDFInfo
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- G01N17/00—Investigating resistance of materials to the weather, to corrosion, or to light
- G01N17/006—Investigating resistance of materials to the weather, to corrosion, or to light of metals
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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- C—CHEMISTRY; METALLURGY
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T436/00—Chemistry: analytical and immunological testing
- Y10T436/18—Sulfur containing
- Y10T436/182—Organic or sulfhydryl containing [e.g., mercaptan, hydrogen, sulfide, etc.]
- Y10T436/184—Only hydrogen sulfide
Definitions
- the present invention relates to a test method for evaluating the resistance to sulfide stress corrosion cracking (SSC resistance) of steel materials such as steel pipes for oil well pipes and steel pipes for line pipes in a wet hydrogen sulfide environment (also referred to as sour environment) and sulfide resistance.
- SSC resistance sulfide stress corrosion cracking
- the present invention relates to seamless steel pipes with excellent stress corrosion cracking properties, and in particular, with regard to SSC resistance evaluation of high strength steel materials with yield strength of 110 ksi class (758 MPa class) or higher and seamless steel pipes with excellent sulfide stress corrosion cracking resistance. .
- Evaluation of SSC resistance is generally performed by a method (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)).
- 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 applying a predetermined stress and evaluating whether or not it breaks after 720 hours.
- the rod-shaped tensile test piece to be used consists of a parallel part, a shoulder part, and a grip part.
- the evaluation object is a parallel part, and during the test, for example, a stress of 80 to 95% of the lower limit value (SMYS; Specified Minimum Yield Strength) of the standard yield stress of steel is applied to the parallel part.
- 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 an SSC break occurs, it breaks near the center of the parallel part, and a valid evaluation at the parallel part becomes possible.
- Method A specified in NACE TM0177, is a widely used method for evaluating the SSC resistance of steel materials.
- this method is used to evaluate the SSC resistance of a high strength steel material having a yield strength YS of 110 ksi or more, there is a case where it does not break at the parallel portion but breaks at the shoulder portion which does not break originally.
- the higher the load stress the higher the frequency of occurrence.
- the test may be judged invalid because it is not a valid evaluation of the SSC resistance of the steel. In that case, it is necessary to retest.
- the retest is performed, there is a problem that not only the steel material and solution for the test and the cost of the test are wasted, but also a large time loss occurs because the test is a long time.
- the present invention solves the above-mentioned problems of the prior art, and can particularly evaluate the SSC resistance of a steel material, even if it is a high-strength steel material having a yield strength YS of 110 ksi or more.
- An object is to provide a crack test method.
- the “sulfide stress corrosion cracking test” here refers to a test in a constant load test according to NACE TM TM0177 Method A.
- the present inventors have studied various factors affecting the occurrence of fracture at the test piece shoulder in the sulfide stress corrosion cracking test of steel materials. Paying careful attention to the load stress, we have studied diligently. As a result, the following knowledge was obtained.
- the shape of the shoulder portion of the test piece for suppressing breakage at the shoulder portion in the present invention has a plurality of radii of curvature, and the radius of curvature of the shoulder portion closest to the parallel portion is large and becomes closer to the grip portion side. I came up with a shape with a smaller radius of curvature. That is, in order to prevent breakage at the shoulder, it has been found that the radius of curvature of the shoulder of the test piece needs to be a radius of curvature corresponding to the load stress during the test and the diameter of the parallel part of the test piece. It has also been found that it is important to increase the stress change by reducing the radius of curvature at the shoulder near the grip portion of the specimen in order to prevent breakage near the grip portion.
- the “curvature radius of the shoulder portion of the test piece” as used herein refers to a curve (curve in a longitudinal section including the central axis) that forms a shoulder portion in a bar-shaped tensile test piece having a parallel portion, a shoulder portion, and a grip portion. It means the radius of curvature.
- 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 for a sulfide stress corrosion cracking test of a steel material, which has a parallel part, a shoulder part, and a grip part, and the cross-sectional shape of the shoulder part has two or more kinds of curvature radii.
- the curvature radius R1 (mm) of the curve on the side in contact with the parallel part is 15 mm or more and the following equation (1) (0.22 ⁇ ) according to the load stress ⁇ (MPa) of the sulfide stress corrosion cracking test 119) ⁇ R1 ⁇ 100 (1) (Where ⁇ is the applied stress (MPa) during the sulfide stress corrosion cracking test) Satisfied, further the curvature of the test piece longitudinal curved portion having a radius R1 length X1 (mm) The following (2) formula X1 ⁇ ⁇ ⁇ (r / 8 ) ⁇ (R1-r 2/4) ⁇ (2) (Where r is the radius of the tensile test piece parallel part (mm)) And the other curvature radius of the curve is smaller than the curvature radius R1, a bar-shaped tensile specimen for sulfide stress corrosion cracking test of steel.
- a constant tensile stress ⁇ (MPa) is applied to a rod-shaped tensile test piece immersed in the test solution, and the resistance to sulfide stress corrosion cracking is evaluated based on the presence or absence of breakage up to a predetermined time.
- a sulfide stress corrosion cracking test method for steels characterized in that the rod-like tensile test piece described in (1) is used as the rod-like tensile test piece.
- the present invention it is possible to properly 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 with yield strength of 110 ksi class (758 MPa class) or higher.
- steel materials such as steel pipes for oil well pipes and steel pipes for line pipes, particularly steel materials with yield strength of 110 ksi class (758 MPa class) or higher.
- This eliminates the need for re-testing, etc., and has a remarkable industrial effect.
- NACE TM TM0177 Method A even under test conditions where the load stress is 85% or more of SMYS, it is possible to suppress breakage at the shoulder of the specimen and shorten the test process.
- FIG. 1 is an explanatory view schematically showing the shape of the rod-shaped tensile test piece of the present invention.
- FIG. 2 is an explanatory view showing the dimensional shape of a conventional bar-shaped tensile test piece.
- the sulfide stress corrosion cracking test of the steel material that is the subject of the present invention is a constant load test according to NACE TM0177 ⁇ Method A. Is used.
- the shoulder portion is formed by a curve having two or more kinds of curvature radii R1, R2, R3, and the like.
- the curvature radius R1 (mm) of the curve on the side in contact with the parallel part is 15 mm or more and satisfies the expression (1).
- the curvature radius R1 is set to 15 mm or more so that a stress concentration portion is not formed near the boundary between the parallel portion and the shoulder portion.
- the radius of curvature R1 of the shoulder on the side in contact with the parallel portion is limited to (0.22 ⁇ 119) mm or more in relation to the load stress ⁇ .
- the curvature radius R1 is (0.22 ⁇ 119) mm or more, it is possible to prevent breakage at the shoulder.
- the radius of curvature R1 is too large, the increase in the cross-sectional area of the test piece at the shoulder is small, that is, the decrease in the load stress at the shoulder is small, and the region where the load stress close to the parallel part is applied becomes large. Induces breakage at the part. Therefore, the curvature radius R1 is limited to 100 mm or less. In addition, Preferably, it is 80 mm or less. For this reason, the curvature radius R1 (mm) of the shoulder curve on the side in contact with the parallel part is limited to a value that is 15 mm or more and satisfies the expression (1).
- the length X1 (mm) in the longitudinal direction of the test piece of the curved portion having the curvature radius R1 is related to the parallel portion radius r (mm) and the curvature radius R1 (mm). r / 8) ⁇ (R1- ( r 2/4)) ⁇ .... (2) (Where r is the radius of the parallel part (mm)) Adjust to satisfy.
- Curvature radius of shoulder curve two or more types
- the shoulder portion is formed by a curve having two or more types of curvature radii.
- the curvature radius of the shoulder portion is made smaller than the curvature radius R1 of the shoulder curve on the side in contact with the parallel portion, and the curve forming the shoulder portion is a curve having at least two types of curvature radii.
- the types of curvature radii of the curve forming the shoulder increase, the processing of the test piece becomes complicated, and even if the types of curvature radii are increased beyond three, a remarkable effect cannot be expected. For this reason, it is preferably up to three types.
- the radius of curvature at the shoulder near the gripping portion is made smaller than the radius of curvature R1 of the shoulder at the side in contact with the parallel portion.
- the radius of curvature other than R1 is preferably 15 mm or more and 40 mm or less.
- yield strength a high strength seamless steel pipe for oil wells used in a wet hydrogen sulfide environment (sour environment) of 110 ksi class (758 MPa class) or higher, which is one of the steel materials to be tested by the present invention.
- the composition is as follows.
- a high-strength seamless steel pipe for oil wells containing one or more types For example, after forming the material (billet) having the above components into a seamless steel pipe by hot working, The seamless steel pipe is cooled to a temperature at which the surface temperature becomes 200 ° C. or lower at a cooling rate higher than that of air cooling, and then tempered by heating to a temperature in the range of 600 to 740 ° C. Further, after the cooling, and before the tempering treatment, the steel is reheated to a temperature in the range of Ac3 transformation point to 1000 ° C and rapidly quenched to a temperature of 200 ° C or less at the surface temperature. Thereafter, the tempering treatment may be performed.
- Test pieces were collected from high-strength seamless steel pipes for oil wells having the compositions shown in Table 1, and machined to obtain various rod-shaped tensile test pieces for sulfide stress corrosion tests having the dimensions shown in Table 2.
- the method for collecting the test piece is as follows according to API SPECIFICATION 5CT, but is not limited if there is an agreement between the manufacturer and the purchaser. That is, as described in API SPECIFICATION 5CT Annex D, the sampling frequency of the test piece is set for each heat treatment heat, and the hardness value is the largest among the average hardnesses at the inner surface, outer surface, and central portion of the seamless steel pipe. The position is taken as the specimen collection position, and the specimen is collected from the longitudinal direction of the steel pipe.
- test Nos. 1 to 12 the total length of all test pieces was 115.0 mm, the length of the parallel part was 25.4 mm, and the radius of the grip part was determined by the test. No. 1 to 3, 5 to 7, 9, 11, and 12 are 4.0 mm, test No. 4, 8, and 10 were 5.55 mm.
- Steel pipe Nos. A, B, and C are steel pipes having a yield strength of 758 MPa (110 ksi) or more, and steel pipe No. D is a steel pipe having a yield strength of less than 758 MPa.
- a sulfide stress corrosion test was performed using the obtained rod-shaped tensile test piece.
- the test is based on NACE TM0177 Method A, using a NACE solution (hydrogen sulfide saturated 5% NaCl + 0.5% CH 3 COOH solution) at 25 ° C, with a constant load, up to 720h, some more severe The evaluation continued until 840h.
- Three test pieces were used in consideration of variations. Table 3 shows the test results. 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 “x (nonconformity)”. When the evaluation of all three test pieces was “ ⁇ (conformity)”, it was determined as “ ⁇ (pass)”. If even one of the three was “ ⁇ (nonconforming)”, it was determined to be “ ⁇ (failed)”.
- Test No.1 the shape of the test piece satisfies the scope of the present invention (Equation (1) and (2) meet ( ⁇ ) Or R3 is specified), and the shoulder does not break.
- Equation (1) and (2) meet ( ⁇ ) Or R3 is specified)
- the shoulder does not break.
- the curvature radius R1 of the shoulder part in contact with the parallel part is out of the range of the present invention, and the shoulder part is broken.
- Test No. 6 the length X1 of the shoulder that is the radius of curvature R1 in contact with the parallel portion deviates from the range of the present invention, and the shoulder is broken.
- the curvature radius of the shoulder portion is one type, which is outside the scope of the present invention, and the shoulder portion or the grip portion is broken.
- the radius of curvature R1 of the shoulder in contact with the parallel part deviates from the scope of the present invention, and the shoulder is broken.
- Test No. 11 and No. 12 have a steel pipe yield strength of less than 758 MPa (110 ksi) and low strength, so the test piece shape satisfies the scope of the present invention (Test No. 11). Even when outside the scope of the present invention (Test No. 12), proper evaluation can be made. Thus, according to the present invention, when the yield strength of the steel pipe is a high strength of 758 MPa (110 ksi) or higher, it is possible to properly evaluate particularly the resistance to sulfide stress corrosion cracking. . In addition, No. 1 of the invention example completed the test without breaking even if it continued up to 840 hours, but No. 2 and 6 of the comparative example continued further for the test piece that did not break in 720 hours.
- test No. 1, No. 3, No. 4, No. 9, No. 10, No. 11 all three are predetermined High-strength seamless steel pipes for steel wells (steel pipe No. 1) from which rod-shaped tensile test pieces (test No. 1, No. 9, No. 10, No. 11) that did not break until time (here, 720 hours) were collected.
- a test result indicating that “no breakage occurred until a predetermined time (for example, 720 hours) in the sulfide stress corrosion cracking test of the present invention” was added.
- the test result may be described on the mill sheet of the oil well high-strength seamless steel pipe, or a label describing the test result may be attached to the oil well high-strength seamless steel pipe.
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Abstract
Description
(2)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、また、とくに負荷応力が高いほどその傾向が強いこと、
(3)肩部における腐食生成物のき裂の発生は、肩部における荷重負荷方向(試験片軸方向)の応力勾配が大きい位置で発生し、肩部と平行部の境界付近の応力集中部で必ずしも発生するものではないこと、
(4)腐食生成物に、き裂が発生すると試験片の新生面が露出し、その箇所では、さらに不均一な腐食が進行すること、
(5)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。このような知見から、平行部ではSSCが発生しない場合でも、肩部でSSCが発生し、試験片が破断することがありうることを新たに見出した。
すなわち、肩部における破断を防止するためには、試験片肩部の曲率半径を、試験時の負荷応力と試験片平行部径に対応した曲率半径とする必要があることを見出した。なお、試験片つかみ部近傍の肩部では、つかみ部近傍での破断を防止するために、曲率半径を小さくして応力変化を大きくすることが肝要であることも知見した。
(1)鋼材の硫化物応力腐食割れ試験用の棒状引張試験片であって、平行部、肩部およびつかみ部を有し、前記肩部の断面形状が、2種類以上の曲率半径を有する曲線で形成され、前記平行部に接する側の前記曲線の曲率半径R1(mm)が15mm以上でかつ硫化物応力腐食割れ試験の負荷応力σ(MPa)に応じて次(1)式
(0.22σ-119)≦ R1 ≦ 100 ‥‥(1)
(ここで、σ:硫化物応力腐食割れ試験時の負荷応力(MPa))
を満足し、さらに前記曲率半径R1を有する曲線部分の試験片長手方向の長さX1(mm)が次(2)式
X1 ≧ √{(r/8)×(R1-r2/4)} ‥‥(2)
(ここで、r:引張試験片平行部半径(mm))
を満足し、かつ、前記曲線の他の曲率半径が前記曲率半径R1より小さいことを特徴とする、鋼材の硫化物応力腐食割れ試験用棒状引張試験片。
(2)試験液中に浸漬した棒状引張試験片に、一定の負荷応力σ(MPa)を負荷し、所定時間経過までの破断の有無で、耐硫化物応力腐食割れ性を評価する、鋼材の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、(1)に記載の棒状引張試験片を用い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)(2)において、前記鋼材が、降伏強さ:110ksi級(758MPa級)以上の強度を有する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。
(4)評価対象となる継目無鋼管から採取された(1)に記載の硫化物応力腐食割れ試験用棒状引張試験片を用いた(2)または(3)に記載の硫化物応力腐食割れ試験方法による試験結果が、破断無しという結果が付加されたことを特徴とする継目無鋼管。
(0.22σ-119)≦ R1 ≦ 100 ‥‥(1)
(ここで、σ:試験時の負荷応力(MPa))
平行部と肩部の境界付近に応力集中部を形成することがないように、曲率半径R1は15mm以上とする。また、肩部での破断と試験時の負荷応力σとは相関があり、試験時の負荷応力σが大きいほど、肩部の曲率半径を大きくし、肩部の応力勾配を小さくして、肩部での破断を防止する必要がある。このため、平行部に接する側の肩部の曲率半径R1は、負荷応力σに関連して(0.22σ-119)mm以上に限定した。曲率半径R1が(0.22σ-119)mm以上であれば、肩部での破断を防止できる。一方、曲率半径R1が大きすぎると、肩部での試験片断面積の増加が小さく、つまり、肩部の負荷応力の減少が小さく、平行部に近い負荷応力がかかる領域が大きくなるため、かえって肩部での破断を誘発する。そのため、曲率半径R1は100mm以下に限定した。なお、好ましくは、80mm以下である。このようなことから、平行部に接する側の肩部曲線の曲率半径R1(mm)は15mm以上でかつ(1)式を満足する値に限定した。
X1 ≧ √{(r/8)×(R1-(r2/4))} ‥‥(2)
(ここで、r:平行部半径(mm))
を満足するように調整する。
肩部は、2種類以上の曲率半径を有する曲線で形成する。つかみ部に近い肩部領域では、肩部の曲率半径を、平行部に接する側の肩部曲線の曲率半径R1より小さくし、肩部を形成する曲線は、少なくとも2種類の曲率半径を有する曲線とする。肩部を形成する曲線の曲率半径の種類が増えると、試験片加工が煩雑となることに加え、曲率半径の種類を3種類を超えて増やしても、顕著な効果を期待できなくなる。このため、好ましくは3種類までである。
なお、本発明が試験対象とする鋼材の一つである、降伏強さ:110ksi級(758MPa級)以上の湿潤硫化水素環境(サワー環境)下で使用される油井用高強度継目無鋼管の好ましい組成としては、例えば、以下のとおりである。
(a)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:0.005~0.10%、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%、B :0.0003~0.0030%、 O(酸素):0.0040%以下、Ti:0.001~0.025%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油井用高強度継目無鋼管。
(b)前記(a)の組成に加えてさらに、質量%で、Ti:0.003~0.025%を含み、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油井用高強度継目無鋼管。
(c)前記(a)または(b)の組成に加えてさらに、質量%で、Cu:1.0%以下、Ni:0.10%以下、W:3.0%以下のうちから選ばれた1種または2種以上を含有する油井用高強度継目無鋼管。
(d)前記(a)~(c)のいずれかの組成に加えてさらに、質量%で、Ca:0.0005~0.0050%、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種以上を含有する油井用高強度継目無鋼管。
そして、前記(a)~(d)の油井用高強度継目無鋼管を製造する際には、例えば、前記成分を有する素材(ビレット)を熱間加工にて継目無鋼管に成形した後、その継目無鋼管に空冷以上の冷却速度で表面温度が200℃以下となる温度まで冷却を施し、しかるのち、600~740℃の範囲の温度に加熱する焼戻処理を施すようにする。
さらに、前記冷却後で、前記焼戻処理の前に、Ac3変態点以上1000℃以下の範囲の温度に再加熱し、表面温度で200℃以下となる温度まで急冷する焼入れ処理を1回以上施し、しかる後に前記焼戻処理を施すこともある。
試験片の採取方法はAPI SPECIFICATION 5CTに準じて以下のとおりとするが、製造者と購入者の合意があればその限りではない。すなわち、API SPECIFICATION 5CT Annex Dに記載の通り、試験片の採取頻度は熱処理ヒート毎とし、当該継目無鋼管の内面、外面、中央部でのそれぞれの平均硬さのうち最も硬さの値が大きい位置を試験片の採取位置とし、鋼管の長手方向から試験片を採取する。
そして、表2には記載していないが、全ての試験片(試験No.1~12)について、全長は115.0mm、平行部の長さは25.4mmとし、つかみ部の半径は、試験No.1~3、5~7、9、11、12は4.0mm、試験No.4、8、10は5.55mmとした。
なお、鋼管No.A、B、Cは、降伏強さ:758MPa(110ksi)以上を有する鋼管であり、鋼管No.Dは降伏強さ:758MPa未満の鋼管である。得ら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、定荷重を負荷し、最大720h、一部はより過酷な評価として840h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。表3に試験結果を示す。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、「○(合格)」と判定した。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。
また、発明例のNo.1は、840時間まで継続しても未破断で試験を満了したが、比較例であるNo.2、6は720時間で破断しなかった試験片についても、さらに継続すると840時間に到達前に肩部での破断が発生した。
そして、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.3、No.4、No.9、No.10、No.11)のうちで、3本とも所定時間(ここでは、720時間)経過まで破断しなかった棒状引張試験片(試験No.1、No.9、No.10、No.11)を採取した油井用高張力継目無鋼管(鋼管No.A、No.C、No.D)については、「本発明の硫化物応力腐食割れ試験では所定時間(例えば、720時間)経過まで破断は生じ無かった」旨の試験結果を付加する。試験結果を付加する方法としては、試験結果を当該油井用高張力継目無鋼管のミルシートに記載したり、当該油井用高張力継目無鋼管に試験結果を記載したラベルを貼ったりすればよい。
Claims (4)
- 鋼材の硫化物応力腐食割れ試験用の棒状引張試験片であって、平行部、肩部およびつかみ部を有し、
前記肩部の断面形状が、2種類以上の曲率半径を有する曲線で形成され、前記平行部に接する側の前記曲線の曲率半径R1(mm)が15mm以上でかつ硫化物応力腐食割れ試験の負荷応力σ(MPa)に応じて下記(1)式を満足し、さらに前記曲率半径R1を有する曲線部分の試験片長手方向の長さX1(mm)が下記(2)式を満足し、かつ、
前記曲線の他の曲率半径が前記曲率半径R1より小さいこと
を特徴とする、鋼材の硫化物応力腐食割れ試験用棒状引張試験片。
記
(0.22σ-119)≦ R1 ≦ 100 ‥‥(1)
ここで、σ:硫化物応力腐食割れ試験時の負荷応力(MPa)
X1 ≧ √{(r/8)×(R1-r2/4)} ‥‥(2)
ここで、r:引張試験片平行部半径(mm) - 試験液中に浸漬した棒状引張試験片に、一定の負荷応力σ(MPa)を負荷し、所定時間経過までの破断の有無で、耐硫化物応力腐食割れ性を評価する、鋼材の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、請求項1に記載の棒状引張試験片を用い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。 - 前記鋼材が、降伏強さ:110ksi級(758MPa級)以上の強度を有する鋼材であることを特徴とする請求項2に記載の鋼材の硫化物応力腐食割れ試験方法。
- 評価対象となる継目無鋼管から採取された請求項1に記載の硫化物応力腐食割れ試験用棒状引張試験片を用いた請求項2または3に記載の硫化物応力腐食割れ試験方法による試験結果が、破断無しという結果が付加されたことを特徴とする継目無鋼管。
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