JP4975354B2 - Manufacturing method of high strength welded steel pipe - Google Patents

Manufacturing method of high strength welded steel pipe Download PDF

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JP4975354B2
JP4975354B2 JP2006107229A JP2006107229A JP4975354B2 JP 4975354 B2 JP4975354 B2 JP 4975354B2 JP 2006107229 A JP2006107229 A JP 2006107229A JP 2006107229 A JP2006107229 A JP 2006107229A JP 4975354 B2 JP4975354 B2 JP 4975354B2
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steel pipe
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friction coefficient
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JP2007275953A (en
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英司 津留
淳 阿形
達哉 吉田
崇 寺澤
豪 鈴木
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Nippon Steel Corp
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本発明は、天然ガス・原油輸送用ラインパイプ等に用いられる、引張強度が850MPa以上の高強度溶接鋼管の製造方法に関する。   The present invention relates to a method for producing a high-strength welded steel pipe having a tensile strength of 850 MPa or more, which is used for a natural gas / crude oil transportation line pipe or the like.

天然ガスを輸送する長距離パイプラインにおいて輸送の効率化、付帯設備のコスト削減の観点から引張強度が850MPaを超えるような超高強度な大径ラインパイプの敷設が検討されている。このようなラインパイプは通常、UOE方式により造管され、つなぎ目となるシーム溶接部はサブマージアーク溶接により、内外面から溶接が行われる。その後、鋼管の真円度を整えるために拡管による矯正が行われる。   In the long-distance pipeline for transporting natural gas, the laying of an ultra-high-strength large-diameter line pipe having a tensile strength exceeding 850 MPa has been studied from the viewpoint of improving transportation efficiency and reducing the cost of incidental facilities. Such a line pipe is usually formed by the UOE method, and the seam welded portion that becomes a joint is welded from the inner and outer surfaces by submerged arc welding. Thereafter, in order to adjust the roundness of the steel pipe, correction by pipe expansion is performed.

UOE造管プロセスによる高強度溶接鋼管の製造における重要な課題は、拡管時のシーム溶接部からの割れ(拡管割れ)及び最大肉厚と最小肉厚の差が大きくなること(偏肉)である。しかし、これまで拡管割れ及び偏肉を防止する目的から拡管工程を工夫した発明はほとんどなかった。拡管工程に関する提案は汎用材に対して、鋼管の真円度、真直性を高めたものであり(例えば、特許文献1〜3)、高強度材に対して拡管割れ及び偏肉を防止できる技術ではなかった。   Important issues in the manufacture of high-strength welded steel pipes by the UOE pipe making process are cracks from the seam welds during pipe expansion (expansion cracks) and the difference between the maximum and minimum thicknesses (uneven thickness). . However, there have been few inventions that have devised the tube expansion process for the purpose of preventing the tube expansion crack and uneven thickness. The proposal concerning the pipe expansion process is a technique that can improve the roundness and straightness of the steel pipe with respect to the general-purpose material (for example, Patent Documents 1 to 3), and can prevent the pipe expansion crack and uneven thickness for the high-strength material. It wasn't.

特許文献1及び2は、高摩擦係数を有したセグメントによって拡管する方法であり、高摩擦による真円度、直度の向上については記載されている。しかし、拡管割れ、偏肉度、拡管率との相互関係については記載されておらず、高強度鋼管で偏肉度を確保しながら拡管割れを防止することについては記載されていない。
Patent Documents 1 and 2 is a method for tube expansion by a segment having a high coefficient of friction, roundness due to high friction, it is described for improving the true Jikado. However, there is no description about the interrelationship between the pipe expansion crack, the thickness deviation, and the pipe expansion ratio, and there is no description about preventing the pipe expansion crack while securing the thickness deviation with a high-strength steel pipe.

特許文献3には、拡管時の周方向位置で摩擦係数を変化させる方法が開示されており、鋼管の真直度を確保する目的から複数の相対的に異なった摩擦係数のセグメントを用いることが記載されている。しかし、鋼管の内面とセグメントとの摩擦係数を高めることにより拡管割れが防止できること、偏肉度を考慮したとき、摩擦係数、及び、摩擦係数を高くすべき部位に最適範囲が存在することについては記載されていない。   Patent Document 3 discloses a method of changing the friction coefficient at the circumferential position at the time of pipe expansion, and describes that a plurality of segments having relatively different friction coefficients are used for the purpose of ensuring the straightness of the steel pipe. Has been. However, it is possible to prevent expansion cracking by increasing the friction coefficient between the inner surface of the steel pipe and the segment, and when considering the uneven thickness, there is an optimum range in the part where the friction coefficient and the friction coefficient should be increased. Not listed.

特開昭57−94434号公報JP 57-94434 A 特開昭57−94433号公報JP-A-57-94433 特開平9−182924号公報JP-A-9-182924

本発明は、シーム溶接後の高強度鋼管を機械的に拡管矯正する際に、シーム溶接部に生じる拡管割れ及び偏肉を防止し得る、高強度溶接鋼管の製造方法を提供するものである。   The present invention provides a method for manufacturing a high-strength welded steel pipe that can prevent pipe expansion cracks and uneven thickness that occur in a seam weld when a high-strength steel pipe after seam welding is mechanically expanded and straightened.

本発明は上記課題を解決するためになされたもので、溶接部近傍の鋼管内面及びその他の部位の鋼管内面と拡管セグメントとの摩擦係数を特定の値とすることによって、溶接部に発生する歪みを抑制し、拡管割れ及び偏肉の発生を防止する高強度鋼管の製造方法であり、その要旨は、引張強度が850MPa以上の鋼板を筒状に成形し、鋼板端部同士を突き合わせてシーム溶接して鋼管とした後、該鋼管を拡管するにあたり、鋼管内面と拡管セグメントとの摩擦係数が0.15以上である高摩擦係数適用領域を、シーム溶接部を周方向の中央として鋼管中心角が25゜以上180゜以下の範囲とし、該高摩擦係数適用領域以外の部位における鋼管内面とセグメントとの摩擦係数を0.15未満として拡管し、シーム溶接部に生じる拡管割れ及び偏肉を防止することを特徴とする高強度溶接鋼管の製造方法である。 The present invention has been made in order to solve the above-described problems. By setting the coefficient of friction between the inner surface of the steel pipe near the welded portion and the inner surface of the steel pipe and the expanded portion of the other portion to a specific value, the distortion generated in the welded portion Is a method of manufacturing a high-strength steel pipe that prevents the occurrence of expansion cracks and uneven wall thickness, the gist of which is to form a steel sheet having a tensile strength of 850 MPa or more into a cylindrical shape, and seam welds by abutting the ends of the steel sheets After the steel pipe is expanded, when expanding the steel pipe, the high friction coefficient application area where the friction coefficient between the inner surface of the steel pipe and the expanded segment is 0.15 or more is used. in the range below 25 ° more than 180 °, the coefficient of friction between the steel pipe inner surface and the segments in the portion other than the high friction coefficient application areas tube expansion as less than 0.15, the tube expansion cracking及occurring seam weld A process for producing a high strength welded steel pipe, characterized in that to prevent uneven thickness.

本発明によれば、天然ガス・原油輸送用ラインパイプ等に用いられる引張強度が850MPa以上の高強度鋼管を、拡管割れ及び偏肉を発生することなく製造することができ、産業上の貢献が極めて顕著である。   According to the present invention, a high-strength steel pipe having a tensile strength of 850 MPa or more used for a natural gas / crude oil transportation line pipe or the like can be produced without causing expansion cracking and uneven thickness, which contributes to the industry. Extremely prominent.

UOE造管プロセスでは、Cプレスで鋼板のエッジ近傍を曲げ、UプレスでU字形状に曲げ、次いでOプレスにより鋼管状に成形し、その後、通常、外面からの仮付け溶接後、サブマージ溶接による内面溶接、続いて外面溶接を行い、さらに拡管により真円度が整えられ、UOE鋼管となる。拡管は通常、周方向に1%程度の塑性変形を与えることで行われる。しかし、引張強度が850MPaを超えるような鋼管では1%の塑性歪みを与える前にシーム溶接部止端部から破断する、いわゆる拡管割れが生産性を大きく損ねる結果となっていた。拡管割れは拡管率を低下させることで防止できるが、製品の真円度は著しく悪化することとなる。   In the UOE pipe making process, the edge of a steel plate is bent with a C press, bent into a U shape with a U press, then formed into a steel tube with an O press, and then usually by tack welding from the outer surface and then by submerged welding. Inner surface welding is performed, followed by outer surface welding, and the roundness is further adjusted by pipe expansion to form a UOE steel pipe. The pipe expansion is usually performed by giving a plastic deformation of about 1% in the circumferential direction. However, in steel pipes having a tensile strength exceeding 850 MPa, so-called expanded cracks that break from the seam weld toe before giving 1% plastic strain have resulted in a significant loss of productivity. Tube expansion cracks can be prevented by reducing the tube expansion rate, but the roundness of the product is significantly deteriorated.

本発明者らは、シーム溶接部近傍の鋼管内面とセグメントとの摩擦係数を高くし、それ以外の部位では鋼管内面とセグメントとの摩擦係数を低くすることにより、拡管割れの発生を防止する方法について検討を行った。   The inventors of the present invention provide a method for preventing the occurrence of expansion cracking by increasing the friction coefficient between the inner surface of the steel pipe and the segment in the vicinity of the seam weld, and lowering the friction coefficient between the inner surface of the steel pipe and the segment in other portions. Was examined.

図1は、鋼管内面とセグメントとの摩擦係数を0.15〜0.40と高くする範囲(高摩擦係数適用領域という。)を周方向位置で変化させた時の止端部への歪み集中をFEAにより解析したものである。高摩擦係数適用領域以外の部位の摩擦係数は0.15未満とした。ここで横軸は高摩擦係数適用領域を鋼管の中心角の角度で示し、シーム溶接部の中央を0°としている。歪みは高摩擦係数適用領域が40゜を下回ると上昇し始め、25゜を下回ると急速に増加し、拡管割れを生じることがわかった。すなわち、シーム溶接部を周方向の中央部(中心角0°)とし、それを挟んで中心角が25゜以上である部位を高摩擦係数適用領域とすれば、顕著な歪み低減効果が得られ、拡管割れを防止できることを図1は示している。   FIG. 1 shows strain concentration at the toe when the friction coefficient between the inner surface of the steel pipe and the segment is increased to 0.15 to 0.40 (referred to as a high friction coefficient application region) at the circumferential position. Is analyzed by FEA. The friction coefficient of the part other than the high friction coefficient application area was less than 0.15. Here, the horizontal axis indicates the high friction coefficient application area by the angle of the central angle of the steel pipe, and the center of the seam weld is 0 °. It was found that the strain began to rise when the high friction coefficient application area was less than 40 °, and increased rapidly when it fell below 25 °, resulting in a pipe expansion crack. That is, if the seam welded portion is a central portion in the circumferential direction (center angle 0 °) and a portion having a central angle of 25 ° or more with the seam welded portion as a high friction coefficient application region, a remarkable distortion reduction effect can be obtained. FIG. 1 shows that pipe expansion cracking can be prevented.

次に高摩擦係数適用領域の上限を検討するため、高摩擦係数適用領域の範囲と偏肉度との関係を検討した。鋼管の偏肉度は、(最大肉厚―最小肉厚)/平均肉厚の値を百分率で示したものである。結果を図2に示すが、これにより、摩擦係数が0.4の場合、高摩擦係数適用領域がシーム溶接部を周方向の中央部(中心角0°)とし、それを挟んで中心角が180゜(鋼管の半周)を超えると偏肉が顕著になることがわかる。   Next, in order to examine the upper limit of the high friction coefficient application range, the relationship between the range of the high friction coefficient application range and the thickness deviation was examined. The thickness deviation of a steel pipe is expressed as a percentage of (maximum wall thickness-minimum wall thickness) / average wall thickness. The result is shown in FIG. 2. As a result, when the friction coefficient is 0.4, the high friction coefficient application area makes the seam welded portion the central portion (center angle 0 °) in the circumferential direction, and the center angle is sandwiched between them. It can be seen that if the angle exceeds 180 ° (half the circumference of the steel pipe), uneven thickness becomes significant.

この解析結果を実証するためにUOE鋼管の拡管試験を行い、シーム部の割れ発生を評価した。高摩擦係数適用領域の範囲は、シーム溶接部を周方向の中央として、鋼管中心角25°とし、高摩擦係数適用領域以外の摩擦係数は0.1とした。拡管試験による拡管割れ発生と摩擦係数の関係を図3に示す。ここで試験は各摩擦条件に対して10本行い、度数は周方向歪みを1.5%まで加えたときの割れ本数を意味する。摩擦係数が0.12以下では割れが発生し、発生部位はシーム部からで溶接止端部が起点となっていた。これに対し、摩擦係数を0.15以上にすると割れは発生しなかった。   In order to verify this analysis result, a pipe expansion test was performed on the UOE steel pipe, and the occurrence of cracks in the seam portion was evaluated. The range of the high friction coefficient application region was a steel pipe center angle of 25 ° with the seam weld in the center in the circumferential direction, and the friction coefficient other than the high friction coefficient application region was 0.1. FIG. 3 shows the relationship between the expansion cracking caused by the expansion test and the friction coefficient. Here, 10 tests are performed for each friction condition, and the frequency means the number of cracks when the circumferential strain is added to 1.5%. When the friction coefficient was 0.12 or less, cracking occurred, and the generation site started from the seam portion and started from the weld toe. On the other hand, when the friction coefficient was 0.15 or more, no crack was generated.

以上の結果を基に、本発明では、少なくとも、シーム溶接部を周方向の中央として中心角が少なくとも25゜以上、多くとも180゜以下の範囲内の鋼管内面とセグメントとの摩擦係数を0.15以上にし、それ以外の部位の鋼管内面とセグメントとの摩擦係数を0.15未満にして、機械的に拡管矯正を行うこととした。これにより、拡管割れを発生させず、かつ、偏肉度も著しく悪化させずに拡管できることがわかった。   Based on the above results, in the present invention, at least the friction coefficient between the inner surface of the steel pipe and the segment within the range where the center angle is at least 25 ° and at most 180 ° with the seam welded portion as the center in the circumferential direction is set to 0. The coefficient of friction between the inner surface of the steel pipe and the segment in other parts was set to less than 0.15, and the pipe expansion was mechanically corrected. As a result, it has been found that pipe expansion can be performed without causing pipe expansion cracks and without significantly deteriorating the uneven thickness.

本発明は拡管時のセグメントの数を特定するものではないが、全周で8〜14分割されることが鋼管の多角形化を効率よく軽減するには望ましい。   Although the present invention does not specify the number of segments at the time of pipe expansion, it is desirable to divide the entire circumference by 8 to 14 in order to efficiently reduce the polygonalization of the steel pipe.

本発明では、シーム溶接部を周方向の中央とし、鋼管の中心角が少なくとも25゜以上、多くとも180゜以下の部位の鋼管内面を高摩擦係数適用領域とすることが重要であり、その部位に対応するセグメントの数を特定するものではない。12等分割のセグメント使用時にはシーム部に相当するセグメント、すなわち30゜分の摩擦係数を0.15以上とし、その他の摩擦係数を0.15未満にしても、3セグメント分、シーム溶接位置を含み90゜分の摩擦係数を0.15以上とし、その他の摩擦係数を0.15未満にしても本発明に含まれる。   In the present invention, it is important that the seam welded portion is the center in the circumferential direction, and the inner surface of the steel pipe where the central angle of the steel pipe is at least 25 ° or more and 180 ° or less is the high friction coefficient application region. It does not specify the number of segments corresponding to. When using 12 equally divided segments, the segment corresponding to the seam part, that is, if the friction coefficient for 30 ° is 0.15 or more and the other friction coefficient is less than 0.15, the seam welding position is included for 3 segments. Even if the friction coefficient for 90 ° is 0.15 or more and other friction coefficients are less than 0.15, it is included in the present invention.

なお、本発明において、鋼板の引張強度が850MPa未満であると拡管割れが発生しないことから、引張強度を850MPa以上の鋼板を母材とする鋼管に限定した。鋼板の引張強度の上限は限定しないが、現状では、1200MPaを超える引張強度を有する鋼板から鋼管を製造することは困難である。   In the present invention, when the tensile strength of the steel sheet is less than 850 MPa, pipe expansion cracking does not occur, so the steel sheet is limited to a steel pipe having a tensile strength of 850 MPa or more as a base material. The upper limit of the tensile strength of the steel sheet is not limited, but at present, it is difficult to manufacture a steel pipe from a steel sheet having a tensile strength exceeding 1200 MPa.

UOE鋼管の素材となる厚鋼板(母材)は、その鋼組成が、質量%で、C:0.02〜0.10%、Si:0.01〜0.6%、Mn:1.5〜2.5%、P:0.015%以下、S:0.003%以下、Ni:0.1〜2.0%、Mo:0.15〜0.60%、Nb:0.001〜0.10%、Ti:0.005〜0.030%、Al:0.06%以下を含有し、さらに、必要に応じてB:0.0001〜0.005%、N:0.0001〜0.006%、V:0.001〜0.10%、Cu:0.01〜1.0%、Cr:0.01〜1.0%、Zr:0.0001〜0.005%、Ta:0.0001〜0.005%、Ca:0.0001〜0.01%、REM:0.0001〜0.01%、Mg:0.0001〜0.006%の1種または2種類以上を含有し、残部Feおよび不可避的不純物からなる鋼を溶製し、鋳造した鋼片を熱間制御圧延して製造すれば良い。   The thick steel plate (base material) that is the material of the UOE steel pipe has a steel composition of mass%, C: 0.02-0.10%, Si: 0.01-0.6%, Mn: 1.5 -2.5%, P: 0.015% or less, S: 0.003% or less, Ni: 0.1-2.0%, Mo: 0.15-0.60%, Nb: 0.001- 0.10%, Ti: 0.005 to 0.030%, Al: 0.06% or less, and further, B: 0.0001 to 0.005%, N: 0.0001 to 0.006%, V: 0.001 to 0.10%, Cu: 0.01 to 1.0%, Cr: 0.01 to 1.0%, Zr: 0.0001 to 0.005%, Ta : 0.0001 to 0.005%, Ca: 0.0001 to 0.01%, REM: 0.0001 to 0.01%, Mg: 0.0001 to 0.006% It contains two or more kinds, and Steels balance consisting of Fe and unavoidable impurities, the cast steel strip may be produced by hot controlled rolling.

また、鋼板から鋼管を製造する方法は主にUOE造管プロセスであるが、ベンディングロールで成形した鋼管を内面から機械的に矯正する場合にも適用可能である。鋼管のシーム溶接は、質量%で、C:0.01〜0.12%、Si:0.3%以下、Mn:1.2〜2.4%、Ni:4.0〜8.5%、Cr+Mo+V:3.0〜5.0%、Ti:0.005〜0.15%、Al:0.02%以下からなる溶接ワイヤーを用いて、入熱を1.5kJ/mm〜6.3kJ/mmとし、サブマージアーク溶接によって行えば良い。   Moreover, although the method of manufacturing a steel pipe from a steel plate is mainly a UOE pipe making process, it is applicable also when the steel pipe shape | molded with the bending roll is mechanically corrected from an inner surface. Seam welding of steel pipes is mass%, C: 0.01 to 0.12%, Si: 0.3% or less, Mn: 1.2 to 2.4%, Ni: 4.0 to 8.5% , Cr + Mo + V: 3.0 to 5.0%, Ti: 0.005 to 0.15%, Al: 0.02% or less, heat input is 1.5 kJ / mm to 6.3 kJ / Mm and may be performed by submerged arc welding.

このようにして得られた溶接金属については、成分が、質量%で、C:0.04〜0.14%、Si:0.05〜0.4%、Mn:1.2〜2.2%、P:0.01%以下、S:0.010%以下、Ni:1.3〜3.2%、Cr+Mo+V:1.0〜2.5%、Ti:0.003〜0.050%、Al:0.02%以下、B:0.005%以下、O:0.01〜0.03%を含有し、残部Feおよび不可避的不純物からなるものである。   About the weld metal obtained in this way, a component is the mass%, C: 0.04-0.14%, Si: 0.05-0.4%, Mn: 1.2-2.2 %, P: 0.01% or less, S: 0.010% or less, Ni: 1.3 to 3.2%, Cr + Mo + V: 1.0 to 2.5%, Ti: 0.003 to 0.050% Al: 0.02% or less, B: 0.005% or less, O: 0.01 to 0.03%, and the balance is Fe and inevitable impurities.

本発明の方法によって製造した高強度鋼管はシーム溶接止端部への歪み集中が従来技術で製造した鋼管に比べ、相対的に低くなっているため、内圧を負荷した時のバースト強度についてもシーム部からの破断を回避でき、有利であると考えられる。   The high-strength steel pipe manufactured by the method of the present invention has a relatively low strain concentration at the seam weld toe, compared to the steel pipe manufactured by the prior art, so the burst strength when the internal pressure is applied is also seam. It is possible to avoid breakage from the part, which is advantageous.

以下に本発明例と比較例により本発明の実施による効果を説明する。   The effects of the implementation of the present invention will be described below with reference to the present invention examples and comparative examples.

表1は鋼管サイズφ914×12t、φ914×16t、φ1016×19t、φ1219×20t、鋼管強度850〜1040MPaのUOE鋼管の拡管を、図4の領域Aに示すシーム溶接部を含んだ周方向領域の角度を変化させ、また、領域A及び領域A以外の鋼管内部とセグメントとの摩擦係数を変化させて行った結果であり、拡管割れの発生と偏肉度を示す。摩擦係数を領域毎に変化させる方法としては表2に示したように、異なった表面性状を有したセグメントを部分的に配置する方法、及び潤滑剤種類、あるいは塗布の有無を周方向位置で変えることで実現した。   Table 1 shows the expansion of a UOE steel pipe having a steel pipe size of φ914 × 12t, φ914 × 16t, φ1016 × 19t, φ1219 × 20t, steel pipe strength of 850 to 1040 MPa, in the circumferential region including the seam weld shown in region A of FIG. This is a result obtained by changing the angle and changing the friction coefficient between the inside of the steel pipe other than the region A and the region A and the segment, and shows the occurrence of the expansion crack and the thickness deviation. As shown in Table 2, as a method of changing the coefficient of friction for each region, a method in which segments having different surface properties are partially arranged, and the type of lubricant or the presence / absence of application are changed in the circumferential position. That was realized.

摩擦係数は、図5に示すように、管状に成形する前の鋼板から切り出したサンプルを、セグメントの表面と同等の加工を施した金型を用いて、拡管と同等の潤滑を行い、面圧100MPaで両側から挟みつけ、引張試験機で片方から引き抜き、そのときの引き抜き荷重、Pと挟み付け荷重、Wの比の1/2を摩擦係数μとして求めた(下記(1)式)。   As shown in FIG. 5, the friction coefficient is obtained by performing lubrication equivalent to pipe expansion on a sample cut out from a steel plate before being formed into a tubular shape using a die that has been processed in the same manner as the surface of the segment. The sample was sandwiched from both sides at 100 MPa and pulled out from one side by a tensile tester, and the half of the ratio between the pulling load, P and the sandwiching load, and W at that time was determined as the friction coefficient μ (the following formula (1)).

この試験法の試験条件と得られた摩擦係数を表2に示す。なお、表2のセグメントの表面性状の欄には、金型の表面の加工方法を示した。ショットブラストでは表面粗さをRmax=20μmとし、目立てでは引き抜き荷重方向と45゜方向に深さ0.1mmで溝を与えた。また、潤滑剤のコンパウンドグリス及びソリュブル油はサンプルに塗布したが、固体潤滑剤は、金型の表面にリン酸塩皮膜を施し、二硫化モリブデンを含有させたポリアミドイミド樹脂を吹き付け、焼き固めたものである。   Table 2 shows the test conditions of this test method and the obtained friction coefficient. In the column of the surface property of the segment in Table 2, a method for processing the surface of the mold is shown. In shot blasting, the surface roughness was Rmax = 20 μm, and in sharpening, grooves were provided at a depth of 0.1 mm in the direction of the drawing load and 45 °. In addition, lubricant compound grease and soluble oil were applied to the sample, but the solid lubricant was coated with a phosphate film on the mold surface and sprayed with polyamideimide resin containing molybdenum disulfide and baked. Is.

実施例1〜13は領域Aが25゜以上、180゜以下であり、摩擦係数が0.15以上であり、尚かつ、領域A以外では摩擦係数が0.15未満であったため、拡管割れは起こさず、偏肉度も3%以下であった。   In Examples 1 to 13, the region A is 25 ° or more and 180 ° or less, the friction coefficient is 0.15 or more, and the friction coefficient is less than 0.15 except in the region A. The uneven thickness was 3% or less.

鋼管の偏肉度は、(最大肉厚―最小肉厚)/平均肉厚の値を百分率で示したものであり、各摩擦条件で10本ずつ拡管した結果の平均である。拡管割れの数値は、各摩擦条件による拡管を10本ずつ行ったときの拡管割れが発生した本数から、割れが発生した率を算出し、百分率で示したものである。なお、拡管は、周方向歪みを1.0%として行った。   The thickness deviation of the steel pipe is expressed as a percentage of (maximum wall thickness−minimum wall thickness) / average wall thickness, and is the average of the results of expanding 10 pipes under each friction condition. The numerical value of the pipe expansion crack is a percentage obtained by calculating the rate of occurrence of cracks from the number of pipe expansion cracks when ten pipe expansions were performed under each friction condition. The tube expansion was performed with the circumferential strain set at 1.0%.

比較例1、3,5,6は、領域Aが25゜未満であり、摩擦係数が0.15以上である高摩擦係数適用領域が本発明の範囲よりも小さかったため、拡管割れを起こした。比較例3は、更に領域A以外の摩擦係数が0.15超であるため、偏肉度も3%を超えている。比較例2は摩擦係数が0.15以上である高摩擦係数適用領域が180゜を超えており、偏肉度が3%を超えた。比較例4及び8は領域Aの範囲が広く、しかも摩擦係数が0.15未満であるため、即ち、高摩擦係数適用領域とすべき部位の摩擦係数が0.15未満であるため、拡管割れを生じた。比較例7は領域Aの範囲は25゜以上であったが、摩擦係数が0.15未満であったため、拡管割れを生じた。   In Comparative Examples 1, 3, 5, and 6, since the region A was less than 25 ° and the high friction coefficient application region having a friction coefficient of 0.15 or more was smaller than the range of the present invention, pipe expansion cracking occurred. In Comparative Example 3, since the friction coefficient other than the region A is more than 0.15, the thickness deviation is more than 3%. In Comparative Example 2, the high friction coefficient application region where the friction coefficient was 0.15 or more exceeded 180 °, and the uneven thickness degree exceeded 3%. In Comparative Examples 4 and 8, since the range of the region A is wide and the friction coefficient is less than 0.15, that is, the friction coefficient of the portion to be a high friction coefficient application region is less than 0.15, the pipe expansion crack Produced. In Comparative Example 7, the range of the region A was 25 ° or more, but the coefficient of friction was less than 0.15, so that a pipe expansion crack occurred.

高摩擦係数適用領域とシーム溶接止端部への塑性歪みの関係を示す図。The figure which shows the relationship of the plastic strain to a high-friction coefficient application area | region and a seam weld toe part. 高摩擦係数適用領域と偏肉度の関係を示す図。The figure which shows the relationship between a high friction coefficient application area | region and thickness deviation. 鋼管内面−セグメント間の摩擦係数に対する拡管割れのヒストグラム。Histogram of pipe cracking against coefficient of friction between steel pipe inner surface and segment. 摩擦係数を特定した領域を示す図。The figure which shows the area | region which specified the friction coefficient. 摩擦係数の測定方法を示す図。The figure which shows the measuring method of a friction coefficient.

符号の説明Explanation of symbols

1 拡管までの鋼管
2 シーム溶接部
3 拡管セグメント
1 Steel pipe up to pipe expansion 2 Seam weld 3 Pipe expansion segment

Claims (1)

引張強度が850MPa以上の鋼板を筒状に成形し、鋼板端部同士を突き合わせてシーム溶接して鋼管とした後、該鋼管を拡管するにあたり、鋼管内面と拡管セグメントとの摩擦係数が0.15以上である高摩擦係数適用領域を、シーム溶接部を周方向の中央として鋼管中心角が25゜以上180゜以下の範囲とし、該高摩擦係数適用領域以外の部位における鋼管内面とセグメントとの摩擦係数を0.15未満として拡管し、シーム溶接部に生じる拡管割れ及び偏肉を防止することを特徴とする高強度溶接鋼管の製造方法。 A steel plate having a tensile strength of 850 MPa or more is formed into a cylindrical shape, end portions of the steel plates are butted together and seam welded to form a steel pipe. Then , when the steel pipe is expanded, the coefficient of friction between the inner surface of the steel pipe and the expanded segment is 0.15. The above-described high friction coefficient application area is a steel pipe center angle in the range of 25 ° to 180 ° with the seam weld in the center in the circumferential direction, and the friction between the inner surface of the steel pipe and the segment in the area other than the high friction coefficient application area. A method for producing a high-strength welded steel pipe, characterized in that the pipe is expanded with a coefficient of less than 0.15 to prevent pipe cracking and uneven thickness occurring in a seam weld .
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