JP3985481B2 - Steel pipe with excellent cold bendability - Google Patents
Steel pipe with excellent cold bendability Download PDFInfo
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- JP3985481B2 JP3985481B2 JP2001282626A JP2001282626A JP3985481B2 JP 3985481 B2 JP3985481 B2 JP 3985481B2 JP 2001282626 A JP2001282626 A JP 2001282626A JP 2001282626 A JP2001282626 A JP 2001282626A JP 3985481 B2 JP3985481 B2 JP 3985481B2
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Description
【０００１】
【発明の属する技術分野】
本発明は、海底ラインパイプ等に用いられる鋼管に係り、特に、敷設時に行われる冷間曲げ加工において必要なエネルギーを低減することができる冷間曲げ加工性に優れた、リールバージ法に用いられる鋼管に関する。
【０００２】
【従来の技術】
配管の敷設現場において、敷設ルート等の条件によっては冷間のまま鋼管に曲げ加工を実施する場合がある。また、近年、海底ラインパイプ等の敷設においては、敷設作業の効率化を図るべく、予め地上において周溶接したパイプを船上の巨大なリールに巻き取り、このパイプを海底に敷設する、いわゆるリールバージ法を適用する場合も多くなってきている。
【０００３】
リールバージ法による敷設では、例えば、外径が406.4mmの鋼管の場合には、スプール径が約20ｍのリールが使用されている。しかし、昨今のエネルギー枯渇化等の事情から、海底ラインパイプは、より深海域に敷設されるようになってきており、高強度化や厚肉化の要請がますます強くなってきている。パイプの高強度化や厚肉化が進められると、曲げ加工に必要なエネルギーが上昇し、これに伴う冷間加工設備の大規模化が余儀なくされる。
【０００４】
【発明が解決しようとする課題】
鋼管に冷間曲げ加工を施す際に必要なエネルギーを低減できれば、現有の冷間加工設備を改造することなく、高強度化や厚肉化した製品に冷間曲げ加工を実施することができ、また、今後、製造される冷間加工設備のコンパクト化を図ることができる。
【０００５】
本発明は、このような観点からなされたものであって、鋼管に冷間曲げ加工を施す際に必要なエネルギーを低減して、冷間加工性に優れた、リールバージ法に用いられる鋼管を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明は、下記の（１）式で表される鋼管の内面側の平均硬さＡと下記の（２）式で表される鋼管の外面側の平均硬さＢとが下記の（３）式で表される関係を有することを特徴とする冷間曲げ性に優れた、リールバージ法に用いられる鋼管を要旨とする。
但し、（１）式および（２）式中のＤは外径（ｍｍ）を示し、ｔは肉厚（ｍｍ）を示し、Ｈ（ｎ）は鋼管の肉厚を２ｍ等分した際に、中心側からｎ番目の位置におけるビッカース硬度（Ｈｖ）を示し、ｒ（ｎ）は鋼管の肉厚を２ｍ等分した際に、中心側からｎ番目の位置における半径（ｍｍ）を示す。
【０００７】
【数４】
【数５】
【数６】
【発明の実施の形態】
高強度継目無鋼管を製造する場合には、熱処理として、焼入れ焼戻し処理が実施される。一般に適用されている連続焼入れ方式では、リングの内側からリング中心方向に向かって高圧の冷却水を噴射するスプレーを使用し、そのリング内に鋼管を通過させることによって、焼入れが実施される。即ち、設備上、内面側の冷却を行うのは困難であり、焼入れ時の冷却水の水量（以下、焼入れ水量という）は、内面側より外面側の方が多いのが一般的である。従って、従来の高強度継目無鋼管は、外面側の硬さが内面側の硬さより高いものであった。
【００１１】
しかし、鋼管の冷間曲げに必要なエネルギーは、外面近傍の強度の影響を受けることになるため、外面側の強度レベルが内面側のそれより低くすることができれば、塑性変形域までの冷間曲げに必要なエネルギーを低く抑えることができると考えられる。
【００１２】
そこで、本発明者らは、鋼管全体の強度レベルを下げることなく、鋼管の外面側の硬さを内面側の硬さより低減すべく研究を重ねた結果、本発明を完成した。
【００１３】
ここで、本件明細書において、内面側の硬さは、下記の（１）式で示される内面側の平均硬さＡと定義し、外面側の硬さは、下記の（２）式で示される外面側の平均硬さＢと定義する。但し、（１）式および（２）式中のＤは外径（ｍｍ）を示し、ｔは肉厚（ｍｍ）を示し、Ｈ（ｎ）は鋼管の肉厚を２ｍ等分した際に、中心側からｎ番目の位置におけるビッカース硬度（Ｈｖ）を示し、ｒ（ｎ）は鋼管の肉厚を２ｍ等分した際に、中心側からｎ番目の位置における半径（ｍｍ）を示す。
【００１４】
【数７】
【数８】
これは、内面側および外面側のそれぞれの平均硬さを同心円分布を仮定した面積平均で表したものである。ｍが５である場合を例にとって説明すると、まず、測定対象となる鋼管を肉厚方向に同心円で10等分し、この等分したそれぞれの領域の硬さＨ(ｒ)をビッカース硬さで測定する。一方で、下記の(4)式によって10等分したそれぞれの領域の半径ｒ(ｎ)を求め、円周長さ２πｒ(ｎ)を算出する。
【００１７】
【数９】
【００１８】
10等分したそれぞれの領域について「Ｈ(n)・２πｒ(n)・(ｔ/10)」を計算し、内面側平均硬さＡについては、鋼管の内表面の位置から肉厚方向中心の位置までの和に所定の係数をかけることによって求め、外面側平均硬さＢについては、鋼管の肉厚方向中心の位置から外表面の位置までの和に所定の係数をかけることによって求める。
【００１９】
このようにして求めた内面側平均硬さＡおよび外面側平均硬さＢとの差が０を超える、即ち、下記の(3)式を満たす場合に、冷間曲げ加工時の曲げエネルギーを低減することができる。
【００２０】
【数１０】
本発明の鋼管の製造方法については、特に限定しないが、例えば、製管後に熱処理を実施する際に、内面側の焼入れ水量を外面側の焼入れ水量より多くすることで、本発明の硬さ条件を具備する鋼管を製造することができる。
【００２２】
【実施例】
表１に示す化学組成を有する鋳片から、マンネスマン製管法によって、外径が60.3mmであり、肉厚が5.0mm、10.0mmおよび15.0mmの３種類の継目無鋼管にした後、焼入れ焼戻し処理（焼入れ温度：900℃、焼戻し温度：600℃）を実施して、API5LX60の鋼管を作製し、これを供試材とした。
【００２３】
【表１】
上記の供試材の寸法および焼入れ水量、ならびに、下記の要領で求めた断面平均硬さおよび曲げエネルギーを表２に示す。
【００２５】
内面側および外面側の平均硬さの測定は、各供試材の任意の位置から管軸方向と垂直な断面を含む試験片を切り出し、この試験片について、管の肉厚方向を10等分（ｍ＝５）したそれぞれの位置のビッカース硬さ（試験力：98.07Ｎ）を測定し、この結果を下記の(1)式および(2)式に代入することによって算出した。更に、内面側平均硬さと外面側平均硬さの差も算出した。
【００２６】
【数１１】
【数１２】
但し、(1)式および(2)式中のＤは外径（mm）を示し、ｔは肉厚（mm）を示し、ａは外半径（mm）を示し、Ｈ(ｎ)は鋼管の肉厚を２ｍ等分した際に、中心側からｎ番目の位置におけるビッカース硬度（Ｈｖ）を示し、ｒ(ｎ)は鋼管の肉厚を２ｍ等分した際に、中心側からｎ番目の位置における半径（mm）を示す。
【００２９】
曲げエネルギーは、図１に示す三点曲げ試験機（支持スパンＬ１：250mm）を使って、各供試材に曲げ荷重を負荷し、図１中のｙで示した変位量が60mmに達するまでの曲げ荷重積分値を求め、各供試材の断面積で除した値を示す。なお、図２に示すとおり、変位量が60mmに達するときに、曲げ荷重積分値が最大になるため、変位量が60mmに達するまでの曲げ荷重積分値を求めることとした。
また、評価は、同様の化学組成を有する供試材のうち、内面側と外面側でほぼ均一な硬さ分布を持つ供試材と比較し、その曲げエネルギーの差が−120N-mm/mm２以下の場合を「◎」、−120N-mm/mm２を超え０N-mm/mm２未満の場合を「○」、０N-mm/mm２以上の場合を「×」として評価した結果を示す。
【００３０】
【表２】
表２に示したとおり、本発明例1〜3、比較例1、4および5は、その化学組成および寸法が同一の鋼である。しかし、内面側の硬さと外面側の硬さがほぼ均一の比較例１と比較すると、本発明例1〜3は、曲げエネルギーが101〜191N-mm/mm２低くなっており、比較例4および5は、曲げエネルギーが9〜23N-mm/mm２高くなっている。
【００３２】
同様に、本発明例4〜6、比較例2、6および7は、その化学組成および寸法が同一の鋼である。内面側の硬さと外面側の硬さがほぼ均一の比較例2と比較すると、本発明例4〜6は、曲げエネルギーが110〜182N-mm/mm２低くなっており、比較例6および7は、曲げエネルギーが80〜113N-mm/mm２高くなっている。
【００３３】
同様に、本発明例7〜9、比較例3、8および9は、その化学組成および寸法が同一の鋼である。内面側の硬さと外面側の硬さがほぼ均一の比較例3と比較すると、本発明例7〜9は、曲げエネルギーが103〜149N-mm/mm２低くなっており、比較例6および7は、曲げエネルギーが62〜95N-mm/mm２高くなっている。
【００３４】
以上のとおり、本発明例として示したいずれの鋼管も、内面側平均硬さが外面側平均硬さより大きくなっており、これによって、曲げエネルギーが低く抑えられることが判明した。
【００３５】
【発明の効果】
本発明によれば、冷間曲げ加工時の曲げエネルギーを低く抑えることができるので、鋼管にリールバージ法を適用して冷間曲げ加工を施す際に必要なエネルギーを低減でき、現有の冷間加工設備を改造することなく、高強度化や厚肉化した製品に冷間曲げ加工を実施することができ、また、今後、製造される冷間加工設備のコンパクト化を図ることができる。
【図面の簡単な説明】
【図１】実施例で使用した三点曲げ試験機を示す模式図である。
【図２】三点曲げ試験機を使用して鋼管に曲げ荷重を負荷した際の変位量と荷重積分値との関係を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel pipe used for a submarine line pipe or the like, and in particular, is used for a reel barge method excellent in cold bending workability capable of reducing energy required in cold bending work performed at the time of laying. It relates to steel pipes.
[0002]
[Prior art]
Depending on the conditions such as the laying route at the pipe laying site, the steel pipe may be bent while it is cold. In recent years, in order to improve the efficiency of laying work such as submarine line pipes, a so-called reel barge that winds a pipe that has been circumferentially welded in advance on a huge reel on board and lays this pipe on the sea floor. In many cases, the law is applied.
[0003]
In laying by the reel barge method, for example, in the case of a steel pipe having an outer diameter of 406.4 mm, a reel having a spool diameter of about 20 m is used. However, under recent circumstances such as energy depletion, submarine line pipes have been laid more deeply, and demands for higher strength and thickness have become stronger. As pipes are made stronger and thicker, the energy required for bending increases, which necessitates an increase in the size of cold working equipment.
[0004]
[Problems to be solved by the invention]
If we can reduce the energy required for cold bending of steel pipes, we can carry out cold bending on high-strength and thickened products without remodeling existing cold-processing equipment. Further, it is possible to reduce the size of the cold working equipment to be manufactured in the future.
[0005]
The present invention has been made from such a viewpoint, and reduces the energy required for cold bending of a steel pipe, and is excellent in cold workability and is used for a reel barge method. The purpose is to provide.
[0006]
[Means for Solving the Problems]
In the present invention, the average hardness A on the inner surface side of the steel pipe represented by the following formula (1) and the average hardness B on the outer surface side of the steel pipe represented by the following formula (2) are the following (3): excellent cold bending properties characterized by having a relationship expressed by the formula, and the gist of the steel tubes used in the reel barge method.
However, D in (1) type | formula and (2) type | formula shows an outer diameter (mm), t shows wall thickness (mm), H (n) is when the wall thickness of a steel pipe is equally divided into 2m, The Vickers hardness (Hv) at the nth position from the center side is shown, and r (n) shows the radius (mm) at the nth position from the center side when the thickness of the steel pipe is equally divided by 2 m.
[0007]
[Expression 4]
[Equation 5]
[Formula 6]
DETAILED DESCRIPTION OF THE INVENTION
When manufacturing a high-strength seamless steel pipe, a quenching and tempering process is performed as a heat treatment. In a continuous quenching method that is generally applied, quenching is performed by using a spray that injects high-pressure cooling water from the inside of the ring toward the center of the ring and passing a steel pipe through the ring. That is, it is difficult to cool the inner surface from the viewpoint of equipment, and the amount of cooling water during quenching (hereinafter referred to as the quenching water amount) is generally larger on the outer surface than on the inner surface. Therefore, the conventional high-strength seamless steel pipe has a higher hardness on the outer surface side than that on the inner surface side.
[0011]
However, the energy required for cold bending of the steel pipe will be affected by the strength near the outer surface, so if the strength level on the outer surface side can be made lower than that on the inner surface side, It is considered that the energy required for bending can be kept low.
[0012]
Therefore, the present inventors have completed the present invention as a result of repeated studies to reduce the hardness of the outer surface side of the steel pipe from the hardness of the inner surface side without reducing the strength level of the entire steel pipe.
[0013]
Here, in this specification, the hardness on the inner surface side is defined as the average hardness A on the inner surface side represented by the following equation (1), and the hardness on the outer surface side is represented by the following equation (2). It is defined as the average hardness B on the outer surface side. However, D in (1) type | formula and (2) type | formula shows an outer diameter (mm), t shows wall thickness (mm), H (n) is when the wall thickness of a steel pipe is equally divided into 2m, shows the Vickers hardness (Hv) in the n-th position from the center side, r (n) is in the thickness of the steel pipe was 2m aliquoted, shows the radius (mm) in the n-th position from the center side.
[0014]
[Expression 7]
[Equation 8]
This represents the average hardness of each of the inner surface side and the outer surface side as an area average assuming a concentric distribution. The case where m is 5 will be described as an example. First, the steel pipe to be measured is divided into 10 concentric circles in the thickness direction, and the hardness H (r) of each equally divided area is expressed as Vickers hardness. taking measurement. On the other hand, the radius r (n) of each region divided into 10 by the following equation (4) is obtained, and the circumferential length 2πr (n) is calculated.
[0017]
[Equation 9]
[0018]
“H (n) · 2πr (n) · (t / 10)” is calculated for each region divided into 10 parts, and the inner surface side average hardness A is calculated from the position of the inner surface of the steel pipe to the center in the thickness direction. The outer surface side average hardness B is obtained by multiplying the sum from the position in the thickness direction of the steel pipe to the position of the outer surface by multiplying the sum up to the position by a predetermined coefficient.
[0019]
When the difference between the inner surface average hardness A and the outer surface average hardness B obtained in this way exceeds 0, that is, when the following equation (3) is satisfied, the bending energy during cold bending is reduced. can do.
[0020]
[Expression 10]
The method for producing the steel pipe of the present invention is not particularly limited. For example, when the heat treatment is performed after the pipe making, the amount of quenching water on the inner surface side is made larger than the amount of quenching water on the outer surface side, so The steel pipe which comprises can be manufactured.
[0022]
【Example】
After slabs with the chemical composition shown in Table 1 were made into three types of seamless steel pipes with outer diameter of 60.3mm and wall thickness of 5.0mm, 10.0mm and 15.0mm by Mannesmann pipe manufacturing method, quenching and tempering Processing (quenching temperature: 900 ° C., tempering temperature: 600 ° C.) was performed to prepare a steel pipe of API5LX60, which was used as a test material.
[0023]
[Table 1]
Table 2 shows the dimensions and the quenching water amount of the test material, and the cross-sectional average hardness and bending energy determined in the following manner.
[0025]
To measure the average hardness on the inner and outer surfaces, cut out a test piece including a cross section perpendicular to the tube axis direction from any position of each specimen, and divide the tube thickness direction into 10 equal parts. Vickers hardness (test force: 98.07 N) at each position (m = 5) was measured, and the result was calculated by substituting the results into the following formulas (1) and (2). Further, the difference between the inner surface side average hardness and the outer surface side average hardness was also calculated.
[0026]
[Expression 11]
[Expression 12]
In the equations (1) and (2), D represents the outer diameter (mm), t represents the wall thickness (mm), a represents the outer radius (mm), and H (n) represents the steel pipe Indicates the Vickers hardness (Hv) at the nth position from the center side when the wall thickness is divided into 2 m, and r (n) is the nth position from the center side when the wall thickness of the steel pipe is divided into 2 m. The radius (mm) is shown.
[0029]
Bending energy is applied to each specimen using a three-point bending tester (supporting span L 1 : 250 mm) shown in FIG. 1, and the displacement indicated by y in FIG. 1 reaches 60 mm. The bending load integral value up to is obtained, and the value divided by the cross-sectional area of each specimen is shown. As shown in FIG. 2, since the bending load integrated value becomes maximum when the displacement reaches 60 mm, the bending load integrated value until the displacement reaches 60 mm is obtained.
In addition, the evaluation was made with a difference in bending energy of -120 N-mm / mm compared to a test material having a substantially uniform hardness distribution on the inner surface side and outer surface side among the test materials having the same chemical composition. in the case of 2 or less "◎", - 120N-mm / mm 2 beyond the case of less than 0N-mm / mm 2 "○", the results of the evaluation 0N-mm / mm 2 or more of the case as "×" Show.
[0030]
[Table 2]
As shown in Table 2, Examples 1 to 3 of the present invention and Comparative Examples 1, 4 and 5 are steels having the same chemical composition and dimensions. However, compared with Comparative Example 1 in which the hardness on the inner surface side and the hardness on the outer surface side are substantially uniform, the inventive examples 1 to 3 have lower bending energy of 101 to 191 N-mm / mm 2 , and Comparative Example 4 And 5, the bending energy is 9 to 23 N-mm / mm 2 higher.
[0032]
Similarly, Invention Examples 4-6 and Comparative Examples 2, 6 and 7 are steels having the same chemical composition and dimensions. Compared with Comparative Example 2 in which the hardness on the inner surface side and the hardness on the outer surface side are substantially uniform, Inventive Examples 4 to 6 have lower bending energy of 110 to 182 N-mm / mm 2 , and Comparative Examples 6 and 7 The bending energy is 80 to 113 N-mm / mm 2 higher.
[0033]
Similarly, Invention Examples 7-9 and Comparative Examples 3, 8 and 9 are steels having the same chemical composition and dimensions. Compared with Comparative Example 3 in which the hardness on the inner surface side and the hardness on the outer surface side are substantially uniform, the inventive examples 7 to 9 have a bending energy of 103 to 149 N-mm / mm 2 lower, and Comparative Examples 6 and 7 The bending energy is 62-95 N-mm / mm 2 higher.
[0034]
As described above, it has been found that any of the steel pipes shown as examples of the present invention has an inner surface side average hardness larger than the outer surface side average hardness, whereby the bending energy can be kept low.
[0035]
【The invention's effect】
According to the present invention, since the bending energy at the time of cold bending can be kept low, it is possible to reduce the energy required when performing cold bending by applying the reel barge method to the steel pipe. Cold bending can be performed on products with increased strength and thickness without modifying the processing equipment, and the cold processing equipment to be manufactured can be made more compact in the future.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a three-point bending tester used in Examples.
FIG. 2 is a diagram showing a relationship between a displacement amount and a load integral value when a bending load is applied to a steel pipe using a three-point bending tester.
Claims (1)
Ｄ：外径（ｍｍ）
ｔ：肉厚（ｍｍ）
Ｈ（ｎ）：鋼管の肉厚を２ｍ等分した際に、中心側からｎ番目の位置におけるビッカース硬度（Ｈｖ）
ｒ（ｎ）：鋼管の肉厚を２ｍ等分した際に、中心側からｎ番目の位置における半径（ｍｍ）The average hardness A on the inner surface side of the steel pipe represented by the following formula (1) and the average hardness B on the outer surface side of the steel pipe represented by the following formula (2) are represented by the following formula (3). that it has excellent cold bending properties, characterized in having a relationship, steel pipes for use in the reel barge method.
D: Outer diameter (mm)
t: Wall thickness (mm)
H (n): Vickers hardness (Hv) at the nth position from the center side when the thickness of the steel pipe is equally divided by 2 m
r (n): radius (mm) at the nth position from the center side when the thickness of the steel pipe is equally divided by 2 m
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2001282626A JP3985481B2 (en) | 2001-09-18 | 2001-09-18 | Steel pipe with excellent cold bendability |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2001282626A JP3985481B2 (en) | 2001-09-18 | 2001-09-18 | Steel pipe with excellent cold bendability |
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| Publication Number | Publication Date |
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| JP2003089850A JP2003089850A (en) | 2003-03-28 |
| JP3985481B2 true JP3985481B2 (en) | 2007-10-03 |
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