WO2018074433A1 - 圧潰強度予測方法 - Google Patents
圧潰強度予測方法 Download PDFInfo
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- WO2018074433A1 WO2018074433A1 PCT/JP2017/037425 JP2017037425W WO2018074433A1 WO 2018074433 A1 WO2018074433 A1 WO 2018074433A1 JP 2017037425 W JP2017037425 W JP 2017037425W WO 2018074433 A1 WO2018074433 A1 WO 2018074433A1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
- B21C51/00—Measuring, gauging, indicating, counting, or marking devices specially adapted for use in the production or manipulation of material in accordance with subclasses B21B - B21F
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F17/00—Digital computing or data processing equipment or methods, specially adapted for specific functions
- G06F17/10—Complex mathematical operations
- G06F17/11—Complex mathematical operations for solving equations, e.g. nonlinear equations, general mathematical optimization problems
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/20—Design optimisation, verification or simulation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
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- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
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- G06F30/17—Mechanical parametric or variational design
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- G06F30/20—Design optimisation, verification or simulation
- G06F30/23—Design optimisation, verification or simulation using finite element methods [FEM] or finite difference methods [FDM]
Definitions
- the present invention relates to a crushing strength prediction method.
- This application claims priority based on Japanese Patent Application No. 2016-204404 filed in Japan on October 18, 2016, the contents of which are incorporated herein by reference.
- the crushing value is measured by a crushing test for a steel pipe having a diameter of 16 inches or less.
- FEA finite element analysis
- Non-Patent Document 1 proposes a method for calculating the biaxial crushing strength of a seamless steel pipe for oil wells. Such a seamless steel pipe is quenched and tempered, and has the same strength in the L direction (the length direction of the steel pipe) and the C direction (the circumferential direction).
- Non-Patent Document 1 Although the crushing strength in a biaxial stress field of a small-diameter oil well pipe to which a seamless steel pipe is applied can be estimated, it cannot be applied to a large-diameter oil well pipe to which a welded pipe is applied. is there. In Non-Patent Document 1, no consideration is given to the crushing mode and the effect on the crushing strength.
- the yield elongation type SS curve as shown in FIG. 1A is a diagram showing a yield elongation type SS curve described in Non-Patent Document 1.
- FIG. 1A the crushing strength can be predicted with a certain accuracy by using 0.20% proof stress.
- the seamless steel pipe described in Non-Patent Document 1 is heat-treated, it exhibits such a yield elongation type SS curve.
- the tendency of the SS curve varies depending on the method of forming the steel pipe and the presence or absence of heat treatment.
- an ERW steel pipe without heat treatment shows a round SS curve as shown in FIG.
- a clear yield phenomenon does not appear, and when the prediction calculation of the crushing strength is performed using 0.20% proof stress as in the conventional case, the crushing strength is affected by the round shape of the SS curve.
- the crushing strength cannot be predicted with high accuracy.
- a welded pipe other than an ERW steel pipe such as a UO steel pipe
- the present inventors diligently studied a crushing strength prediction method applicable to steel pipes having various dimensions, and obtained the following knowledge.
- the crushing phenomenon of a steel pipe changes with the increase in D / t, such as yield crushing, plastic crushing, transition crushing, and elastic crushing (see Non-Patent Document 2). At this time, the higher the D / t, the lower the crushing strength.
- the crushing dominant yield strength used a value of stress that produces a permanent strain of 0.20%, which is generally defined as the yield strength.
- the yield stress is not clear for a steel pipe that draws a stress-strain curve (SS curve) showing a gradual increase in stress as the strain increases or a complicated SS curve. Therefore, the yield strain value of the steel pipe varies depending on the shape of the SS curve, and it may not be appropriate to use a permanent strain of 0.20%.
- the present inventors can provide a crushing strength prediction formula applicable to steel pipes of various dimensions by adopting a numerical value corresponding to the permanent strain value of the compression SS curve in the circumferential direction of the steel pipe as the crushing dominant strength. I found. Depending on the selection of the permanent strain value, the crushing dominant strength will vary greatly.
- the study by the present inventors revealed that the stress having a high correlation with the crushing strength, that is, the crushing dominant strength changes with D / t. That is, the present inventors have found that the crushing strength can be predicted with high accuracy by setting an appropriate crushing control strength according to the value of D / t.
- the present invention has been made based on the above findings.
- An object of the present invention is to provide a crushing strength prediction method capable of accurately predicting the crushing strength of steel pipes having various dimensions.
- the crushing strength prediction method is a method for predicting the crushing strength of a steel pipe, and using a plurality of reference steel pipes whose crushing strength is required in advance, the outer diameter D (mm) of the steel pipe. Deriving a prediction formula indicating the relationship between D / t, material characteristics, crush strength controlling factor and crush controlling strength, and predicted crush strength divided by wall thickness t (mm); A step of obtaining D / t obtained by dividing the outer diameter D (mm) by a wall thickness t (mm), a material characteristic and a crushing strength controlling factor; a step of obtaining a compressive stress strain curve in a circumferential direction of the steel pipe to be evaluated And obtaining the stress that causes permanent strain in the steel pipe to be evaluated as the crushing dominant strength based on the compressive stress strain curve; and the obtained D / t, the material characteristics, and the crushing strength.
- Dominant factors and previous Calculating a predicted crushing strength of the steel pipe to be evaluated based on the prediction formula from a crushing proof stress, and the permanent strain is in accordance with the value of D / t of the steel pipe to be evaluated. It is characterized by being set.
- the crushing strength prediction capable of accurately predicting the crushing strength of the steel pipe having various dimensions. Can provide a method.
- the stress applied when X% permanent set is generated is defined as “X% proof stress”.
- the X% proof stress is expressed as “ ⁇ X ”.
- the permanent strain used when determining the crushing control strength is expressed as “CDOS”, and the crushing control strength is expressed as “ ⁇ CDOS ”.
- the crushing dominant strength is such that the value of D / t of the steel pipe to be evaluated is in the yield crushing region. It may be 0.50% yield strength in some cases, 0.10% yield strength in the plastic crush region, and 0.05% yield strength in the transition crush region or elastic crush region. .
- the crushing dominant strength is a value of D / t of the steel pipe to be evaluated, 10 is 0.50% yield strength, 19 is 0.10% yield strength, In the case of 28 to 48, it is 0.05% proof stress, and in the case of exceeding 10 and less than 19, it is obtained by interpolation calculation of 0.50% proof strength and 0.10% proof strength, If it exceeds 19 and less than 28, it may be obtained by interpolation calculation of 0.10% proof stress and 0.05% proof strength.
- the permanent strain in the crushing strength prediction method according to the above (1), may be represented by the following (Formula 1) or (Formula 2).
- the material characteristics are the Young's modulus of the steel pipe to be evaluated and
- the crushing strength controlling factor may include one or more selected from the roundness, thickness deviation, and residual stress in the circumferential direction of the steel pipe.
- the prediction formula may be expressed by the following (Formula 3).
- P C in the equation (3) is the predicted crush strength
- H is H
- ⁇ is a correction term, the following (Equation 4 ) To (Equation 15).
- E Young's modulus
- ⁇ Poisson's ratio
- u roundness represented by the following (Formula 11)
- e is uneven thickness represented by the following (Formula 12).
- ⁇ R ⁇ is the residual stress in the circumferential direction
- ⁇ CDOS is the crushing dominant strength
- the values represented by h ⁇ , h ⁇ , h ⁇ , ⁇ , ⁇ , ⁇ and ⁇ are coefficients determined in advance.
- (Formula 7) is: Represented by Said (Equation 8) is Represented by Said (Equation 9) is Represented by Said (Equation 10) is Represented by Said (Equation 14) is Represented by Said (Formula 15) is It may be represented by
- FIG.1 (a) is a figure which shows an example of a yield elongation type SS curve
- FIG.1 (b) is a figure which shows an example of a round type SS curve
- FIG. 2 is a diagram illustrating comparison of prediction errors between the case where the prediction method according to the embodiment of the present invention is used and the case where the conventional prediction method is used.
- FIG. 3 is a diagram for comparing the crushing strength obtained in each of the crushing test and the FEA.
- FIG. 4 is a diagram showing a comparison between an example (crushing strength prediction method according to the present invention) and a comparative example (crushing strength prediction method according to the prior art) for experimental values of crushing strength.
- the crushing strength prediction method is a method for predicting the crushing strength of a steel pipe, and uses a plurality of reference steel pipes whose crushing strength is required in advance, and determines the outer diameter D (mm) of the steel pipe.
- the crushing strength prediction method according to the present embodiment is a step of obtaining D / t, material characteristics, and crushing strength controlling factor obtained by dividing the outer diameter D (mm) by the wall thickness t (mm) for the steel pipe to be evaluated. Is provided.
- the crushing strength prediction method according to the present embodiment includes a step of obtaining a compressive stress strain curve in the circumferential direction of the steel pipe to be evaluated.
- the crushing strength prediction method includes a step of obtaining, as the crushing dominant strength, a stress that causes permanent deformation in the steel pipe to be evaluated based on the compressive stress strain curve.
- the crushing strength prediction method predicts the steel pipe to be evaluated based on the prediction formula from the obtained D / t, the material characteristics, the crushing strength controlling factor, and the crushing controlling strength.
- the step of calculating the crushing strength is further provided.
- the permanent strain is set according to the value of D / t of the steel pipe to be evaluated.
- a prediction formula for predicting the crushing strength of a steel pipe is derived using a plurality of reference steel pipes whose crushing strength is required in advance.
- a formula incorporating a parameter indicating the relationship between the ratio D / t of the outer diameter D and the wall thickness t of the steel pipe, the material characteristics, the crush strength controlling factor, the crush controlling strength, and the predicted crush strength is used. It is preferable. The prediction formula will be described later.
- the ratio D / t between the outer diameter D and the wall thickness t, the material characteristics, the crushing strength controlling factor, etc. are obtained for the steel pipe to be evaluated.
- D / t is the ratio of the outer diameter D (mm) to the wall thickness t (mm). According to the crushing strength prediction method according to the present embodiment, it is possible to predict with high accuracy even for a steel pipe having a D / t in the range of about 10 to 48.
- the roundness which is a factor controlling the crushing strength, is obtained, for example, by measuring the diameter of the steel pipe at four positions at 45 ° intervals and calculating the roundness from the result by (Equation 11) described later.
- the thickness deviation that is a factor controlling the crushing strength is obtained, for example, by measuring the wall thickness of the steel pipe at 8 positions at 45 ° intervals, and obtaining from the result (Formula 12) described later.
- the residual stress in the circumferential direction which is a factor controlling the crushing strength, is obtained by the Clampton method represented by the following (Equation 22).
- the Clampton method is a method of releasing residual stress by cutting a steel pipe in the longitudinal direction and obtaining the residual stress from the amount of change in outer diameter before and after cutting.
- D0 is the average outer shape before cutting
- D1 is the average outer shape after cutting. Note that the length of the specimen of the clampton method satisfies L / D (ratio of the specimen length L to the outer diameter D) ⁇ 2.
- the material characteristics may include the Young's modulus and Poisson's ratio of the steel pipe to be evaluated.
- the crushing strength controlling factor may include one or more selected from the roundness, uneven thickness, and residual stress in the circumferential direction of the steel pipe.
- a compressive stress strain curve (SS curve) in the circumferential direction (C direction) of the steel pipe is obtained.
- the compressive stress-strain curve is obtained by collecting a cylindrical test piece from the circumferential direction and performing a compression test. For example, it can be obtained by performing a compression test using a cylindrical test piece having a diameter of 70% of the steel pipe wall thickness and a length twice the diameter (140% of the steel pipe wall thickness). it can.
- the collection position of the cylindrical specimen may be any position such as 22.5 °, 45 °, and 90 ° intervals.
- the crushing dominant strength is obtained.
- the crushing dominant strength which is a stress highly correlated with the crushing strength, changes. Therefore, the value of the permanent strain corresponding to the value of D / t of the steel pipe is appropriately selected, and the yield strength at that permanent strain is obtained as the crushing dominant strength.
- the permanent strain value is set according to the value of D / t of the steel pipe to be evaluated. Then, based on the compressive stress-strain curve, a stress corresponding to the permanent strain set according to the value of D / t of the steel pipe to be evaluated is obtained, and this yield strength is used as the crushing dominant yield strength.
- the crushing dominant strength is 0.50% proof strength when the D / t value of the steel pipe to be evaluated is in the yield crushing region, and the crushing strength in the plastic crushing region. In some cases, it may be 0.10% yield strength, and in the transition collapse region or elastic collapse region, it may be 0.05% yield strength.
- 0.50% proof stress means a stress applied when a permanent strain of 0.50% is generated.
- the above-mentioned crushing region is based on the classification of Document A (American Petroleum Institute: API BUL 5C3, 1985.).
- the area is defined as a yield crush area, a plastic crush area, a transition crush area, and an elastic crush area, and by adopting the crushing proof strength corresponding to these areas, it is possible to predict crush strength with higher accuracy .
- the crushing dominant proof stress is 0.50% proof stress when the D / t value of the steel pipe to be evaluated is 10, and the D / t of the steel pipe to be evaluated.
- the strength is 0.10%, and when the value of D / t of the steel pipe to be evaluated is 28 to 48, the strength may be 0.05%.
- the steel pipe to be evaluated is obtained by interpolation calculation of 0.50% proof strength and 0.10% proof strength.
- the value of D / t exceeds 19 and is less than 28, it may be obtained by interpolation calculation of 0.10% proof stress and 0.05% proof strength.
- the interpolation calculation method is not particularly limited, and may be interpolated with a straight line of a linear function, or may be interpolated with a curve such as an n-order function, a logarithmic function, or an exponential function.
- the permanent strain (%) for obtaining the crushing dominant strength may be expressed by the following (formula 1) when D / t ⁇ 28.
- D / t when D / t> 28, it may be expressed by the following (formula 2).
- the material properties used in the prediction formula are the Young's modulus and Poisson's ratio of the steel pipe.
- the crushing strength controlling factor is a factor affecting the crushing strength such as the shape of the steel pipe, and specifically includes roundness, uneven thickness and residual stress in the circumferential direction of the steel pipe. All of these factors may be used in the prediction formula, or one or two of them may be used. For example, when predicting the crushing strength of an ERW steel pipe, the unevenness degree of the ERW steel pipe is extremely small, and therefore the factor can be omitted.
- P E , P Y , H and ⁇ are calculated by the following (formula 4) to (formula 15).
- E Young's modulus
- ⁇ Poisson's ratio
- u roundness represented by the following (formula 11)
- e the thickness deviation represented by the following (formula 12)
- ⁇ R ⁇ the residual in the circumferential direction.
- Stress, ⁇ CDOS is the crushing dominant strength.
- the values represented by h ⁇ , h ⁇ , h ⁇ , h ⁇ , ⁇ , ⁇ , ⁇ , and ⁇ are coefficients obtained in advance.
- the calculation method of these coefficients is not particularly limited. For example, it is possible to determine a plurality of reference steel pipes whose crushing strength is obtained in advance by a least square method based on an error between an actual measurement value and a predicted value.
- coefficients ⁇ , ⁇ , ⁇ , and ⁇ in the above formula are coefficients obtained in advance.
- the calculation method of these coefficients is not particularly limited. For example, it is possible to determine a plurality of reference steel pipes whose crushing strength is obtained in advance by a least square method based on an error between an actual measurement value and a predicted value.
- the crushing strength can be predicted with higher accuracy by using (Formula 3) as the prediction formula.
- the prediction formula is not limited to (Formula 3), and the following prediction formula can also be adopted.
- the coefficients of (Expression 4) to (Expression 15) may be obtained separately.
- Equation 23 is a prediction equation in the yield crush region
- Equation 24 is a prediction equation in the plastic crush region
- Equation 25 is a transition crush.
- a prediction formula in the region, (Formula 26) is a prediction formula in the elastic crush region.
- Document A describes a crushing strength prediction formula used at the time of oil well design and a crushing mode with respect to D / t for each grade of steel pipe.
- the crushing mode is classified into elastic crushing, transition crushing, plastic crushing, and yield crushing according to the steel pipe strength and D / t.
- the elastic crush equation gives a crushing strength of 71.25% of the theoretical solution in consideration of the safety factor.
- the yield crush is defined as the external pressure at the time when the inner surface of the steel pipe reaches the yield stress.
- the plastic crush formula is derived by regression analysis from the crush test results of about 2500 times of K55, N80, and P110 seamless steel pipes.
- the transition crush formula is constructed to compensate for the occurrence of a D / t range in which the prediction diagrams of the elastic crush formula and the plastic crush formula do not intersect.
- the type of steel pipe to which the prediction method of the above embodiment can be applied is not particularly limited, and examples thereof include seamless steel pipes, ERW steel pipes, and arc welded steel pipes.
- the measurement of the residual stress in the roundness, thickness deviation, and circumferential direction of a steel pipe, which is a crushing strength controlling factor, can be performed by the following method, for example.
- Example 1 The steel pipes having the shapes shown in Tables 1 to 4 were compared with the crushing strength obtained by finite element analysis (FEA) and the estimated crushing strength estimated using the conventional method and the prediction method according to the present invention.
- the steel pipe has a D / t value of 10, 19, 28, 32 or 48.
- FEA finite element analysis
- the prediction formula described in Non-Patent Document 1 was used. That is, in all the comparative examples, 0.20% yield strength was adopted as the crushing dominant strength.
- the prediction formula expressed by (Expression 3) is used, and as the crushing control strength, when the value of D / t is 10, 0.50% strength is adopted. In the case of 0.10% proof stress was adopted, and in the case of 28 to 48, 0.05% proof stress was adopted.
- the Young's modulus of the steel pipe is 205800 MPa and the Poisson's ratio is 0.3.
- FEA is a calculation method with extremely high accuracy with respect to actual measurement values because various factors can be taken in. Since it is very difficult to perform a crush test on a large-diameter steel pipe, in this experimental example, the crushing strength obtained by FEA and the predicted crushing strength estimated using the conventional method and the prediction method according to the present invention are used. Comparing.
- Table 7 shows a comparison between the crushing strength by FEA and the experimental values of crushing strength for the test bodies A to C.
- the crushing strength calculated based on the stress-strain curve at each of the seam portion and 45 °, 90 °, 135 °, and 180 ° from the seam portion in the cross section perpendicular to the length direction of the steel pipe is shown.
- the crushing strength calculated based on the seam portion and the stress strain curve based on the average values of the 45 °, 90 °, 135 °, and 180 ° portions from the seam portion is shown.
- FIG. 4 shows prediction values (examples) obtained by the crushing strength prediction method according to the present invention with respect to the experimental values of crushing strength for samples A-1 to D-3 and predictions obtained by the conventional prediction formula.
- the graph of a comparison with a value (comparative example) is shown.
- the crushing strength prediction method according to the present invention has higher accuracy than the predicted value obtained by the conventional prediction formula.
- the crushing strength prediction method of the present invention it is possible to provide a method that can be applied to steel pipes having various dimensions, that is, various outside diameters and wall thicknesses, and that can accurately predict crushing strength.
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Abstract
Description
本願は、2016年10月18日に、日本に出願された特願2016-204404号に基づき優先権を主張し、その内容をここに援用する。
有限要素解析(FEA)を用いて圧潰値を推定する方法もあり、圧潰値を正確に推定できるが、これには手間がかかる。そのため、推定式を用いた、高精度の圧潰値の予測方法が望まれていた。
このようなシームレス鋼管は、焼入れ・焼きもどしがされ、L方向(鋼管の長さ方向)とC方向(周方向)の強度が等しい。
また、非特許文献1では、圧潰様式とこれによる圧潰強度への影響に関する考察などはされていない。
このような降伏伸び型SS曲線を有する鋼管の場合、0.20%耐力を用いることで、圧潰強度を一定の精度で予測することができる。例えば、非特許文献1に記載されているシームレス鋼管は熱処理をするため、このような降伏伸び型SS曲線を示す。
例えば、UO鋼管など電縫鋼管以外の溶接管の場合にも、複雑なSS曲線を示し、精度の高い圧潰強度の予測計算ができないという同様の問題がある。
しかし、ひずみ増加に伴い緩やかな応力増加を示す応力ひずみ曲線(SS曲線)や複雑なSS曲線を描く鋼管に関しては、降伏応力が明瞭でない。そのため、SS曲線の形状によって、鋼管の降伏ひずみの値が変わり、0.20%の永久ひずみを用いることが適切ではない場合がある。
本発明は上記の知見に基づいてなされたものである。
また、圧潰支配耐力を求めるときに用いる永久ひずみを「CDOS」と表記し、圧潰支配耐力を「σCDOS」と表記する。
10の場合には0.50%耐力であり、19の場合には0.10%耐力であり、
28~48の場合には0.05%耐力であり、10を超えて19未満の場合には、0.50%耐力と0.10%耐力との内挿計算により求め、
19を超えて28未満の場合には、0.10%耐力と0.05%耐力との内挿計算により求めるようにしてもよい。
また、本実施形態に係る圧潰強度予測方法は、評価対象となる鋼管について、外径D(mm)を肉厚t(mm)で除算したD/t、材料特性および圧潰強度支配因子を求める工程を備える。また、本実施形態に係る圧潰強度予測方法は、前記評価対象となる鋼管の円周方向における圧縮応力ひずみ曲線を求める工程を備える。
本実施形態に係る圧潰強度予測方法は、求められた、前記D/t、前記材料特性、前記圧潰強度支配因子および前記圧潰支配耐力から、前記予測式に基づき、前記評価対象となる鋼管の予測圧潰強度を算出する工程を、さらに備える。
D/tは、外径D(mm)と肉厚t(mm)との比である。本実施形態に係る圧潰強度予測方法によれば、D/tが10~48程度の範囲の鋼管についても、精度の高い予測が可能である。
圧潰強度支配因子である真円度は、例えば、鋼管の直径を45°間隔で4か所について測定し、その結果から、後述する(式11)により求める。
次に、鋼管の周方向(C方向)における圧縮応力ひずみ曲線(SS曲線)を求める。圧縮応力ひずみ曲線は、周方向から円柱試験片を採取して、圧縮試験を行うことで得られる。
例えば、直径が鋼管肉厚の70%であり、長さが直径の2倍(鋼管肉厚の140%)となるような寸法の円柱試験片を用いて、圧縮試験を行うことにより求めることができる。円柱試験片の採取位置は、22.5°、45°、90°間隔など、任意の位置でよい。
次いで、得られた圧縮応力ひずみ曲線に基づき、圧潰支配耐力を求める。上述のように、D/tにより、圧潰強度と相関の高い応力である圧潰支配耐力が変化する。そのため、鋼管のD/tの値に応じた永久ひずみの値を適切に選択し、その永久ひずみでの耐力を、圧潰支配耐力として求める。
本実施形態に係る圧潰強度予測方法においては、評価対象となる鋼管のD/tの値に応じて、永久ひずみの値を設定する。そして、圧縮応力ひずみ曲線に基づき、評価対象となる鋼管のD/tの値に応じて設定された永久ひずみと対応する応力を求め、この耐力を圧潰支配耐力とする。
ここで、例えば0.50%耐力とは、0.50%の永久ひずみを生じる際に付与される応力を意味する。
このとき、評価対象となる鋼管のD/tの値が10を超えて19未満の場合には、0.50%耐力と0.10%耐力との内挿計算により求め、評価対象となる鋼管のD/tの値が19を超えて28未満の場合には、0.10%耐力と0.05%耐力との内挿計算により求めるようにしてもよい。
求められたD/t、材料特性、圧潰強度支配因子および圧潰支配耐力から、下記(式3)で表わされる予測式を用いて、鋼管の予測圧潰強度を算出する。
予測式には、これらの因子の全てを用いてもよいし、そのうちの1種または2種を用いてもよい。例えば、電縫鋼管の圧潰強度を予測する場合、電縫鋼管の偏肉度は極めて小さいため、その因子を省略することができる。
なお、上記式中の係数α、β、ξおよびηは、予め求められる係数である。これら係数の算出方法については特に制限はないが、例えば、予め圧潰強度が求められている複数の基準鋼管について、実測値と予測値との誤差から最小二乗法により決定することが可能である。
また、(式8)が、
また、(式9)が、
また、(式10)が、
また、(式14)が、
また、(式15)が、
係数α、β、ξおよびηを算出する際のNの好ましい値は5である。
弾性圧潰式は、安全係数を考慮し、理論解の71.25%の圧潰強度を与えるものである。APIでは、降伏圧潰は、鋼管内面が降伏応力に到達した時点の外圧と定めている。塑性圧潰式は、K55、N80、P110シームレス鋼管の約2500回の圧潰試験結果から回帰分析で導出している。遷移圧潰式は、弾性圧潰式と塑性圧潰式の予測線図が交差しないD/t範囲が生じることから、それを補うために構築している。
以下に、本発明の圧潰強度予測方法に関する実験例を記載する。
表1~4に示す形状の鋼管について、有限要素解析(FEA)で得られた圧潰強度と、従来方法および本発明に係る予測方法を用いて推定された予測圧潰強度との比較を行った。鋼管のD/tの値は、10、19、28、32または48のいずれかである。
従来方法としては、非特許文献1に記載の予測式を用いた。すなわち、全ての比較例において、圧潰支配耐力として、0.20%耐力を採用した。
図4に、試料A-1からD-3について、圧潰強度の実験値に対する、本発明に係る圧潰強度予測方法によって得られた予測値(実施例)と、従来の予測式によって得られた予測値(比較例)との比較のグラフを示す。
この結果からわかるように、本発明に係る圧潰強度予測方法は、従来の予測式によって得られた予測値よりも精度が高い。
Claims (7)
- 鋼管の圧潰強度を予測する方法であって、
予め圧潰強度が求められている複数の基準鋼管を用いて、鋼管の、外径D(mm)を肉厚t(mm)で除算したD/t、材料特性、圧潰強度支配因子および圧潰支配耐力と、予測圧潰強度との関係を示す予測式を導出する工程と;
評価対象となる鋼管について、外径D(mm)を肉厚t(mm)で除算したD/t、材料特性および圧潰強度支配因子を求める工程と;
前記評価対象となる鋼管の円周方向における圧縮応力ひずみ曲線を求める工程と;
前記圧縮応力ひずみ曲線に基づき、前記評価対象となる鋼管に永久ひずみを生じさせる応力を、前記圧潰支配耐力として求める工程と;
求められた、前記D/t、前記材料特性、前記圧潰強度支配因子および前記圧潰支配耐力から、前記予測式に基づき、前記評価対象となる鋼管の予測圧潰強度を算出する工程と;
を備え、
前記永久ひずみは、前記評価対象となる鋼管の前記D/tの値に応じて設定される、
ことを特徴とする圧潰強度予測方法。 - 前記圧潰支配耐力は、前記評価対象となる鋼管のD/tの値が、降伏圧潰領域にある場合には0.50%耐力であり、塑性圧潰領域にある場合には0.10%耐力であり、遷移圧潰領域または弾性圧潰領域にある場合には0.05%耐力である、
ことを特徴とする請求項1に記載の圧潰強度予測方法。 - 前記圧潰支配耐力は、前記評価対象となる鋼管のD/tの値が、
10の場合には0.50%耐力であり、19の場合には0.10%耐力であり、28~48の場合には0.05%耐力であり、
10を超えて19未満の場合には、0.50%耐力と0.10%耐力との内挿計算により求め、
19を超えて28未満の場合には、0.10%耐力と0.05%耐力との内挿計算により求める、
ことを特徴とする請求項1に記載の圧潰強度予測方法。 - 前記材料特性は、前記評価対象となる鋼管のヤング率およびポアソン比を含み;
前記圧潰強度支配因子は、前記鋼管の真円度、偏肉度および円周方向における残留応力から選択される1種以上を含む;
ことを特徴とする請求項1から4のいずれか一項に記載の圧潰強度予測方法。
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JP6969713B1 (ja) * | 2020-09-11 | 2021-11-24 | Jfeスチール株式会社 | 鋼管圧潰強度予測モデルの生成方法、鋼管の圧潰強度予測方法、鋼管の製造特性決定方法、及び鋼管の製造方法 |
JPWO2021240900A1 (ja) * | 2020-05-26 | 2021-12-02 | ||
WO2022054336A1 (ja) * | 2020-09-11 | 2022-03-17 | Jfeスチール株式会社 | 鋼管圧潰強度予測モデルの生成方法、鋼管の圧潰強度予測方法、鋼管の製造特性決定方法、及び鋼管の製造方法 |
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WO2021240900A1 (ja) * | 2020-05-26 | 2021-12-02 | Jfeスチール株式会社 | 鋼管圧潰強度予測モデルの生成方法、鋼管の圧潰強度予測方法、鋼管の製造特性決定方法、及び鋼管の製造方法 |
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