JP2007307607A - Method of manufacturing electric resistance welded tube which is excellent in property of weld zone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an electric resistance welded tube which is excellent in the properties of a weld zone by which the properties of the weld zone (especially low-temperature toughness) can be improved surely than a conventional level. <P>SOLUTION: In a process where a tube is made by forming a band material 1, butting end parts and performing the electric resistance welding of the end parts, after imparting a tapered shape to the end parts before the electric resistance welding, non-oxidizing gas is blown to the end parts receiving the heating by the electric resistance welding. Preferably, the environment of the end parts is held in non-oxidizing gas atmosphere. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は、溶接部特性の良好な電縫管の製造方法に関し、特に、油井ラインパイプ向けなどの溶接部の靭性が要求される管あるいは油井のケーシングパイプなどの溶接部強度が要求される管の製造に好ましく用いうる、溶接部特性の良好な電縫管の製造方法に関する。   TECHNICAL FIELD The present invention relates to a method for manufacturing an electric resistance welded tube having good welded portion characteristics, and in particular, a tube that requires toughness of a welded portion such as for oil well line pipes or a tube that requires welded portion strength such as an oil well casing pipe. The present invention relates to a method for manufacturing an electric resistance welded tube that can be preferably used for manufacturing a welded part and has good welded portion characteristics.

通常、管は溶接管と継目無管に大別される。溶接管は、電縫鋼管を例とするように、板（帯材の意。以下同じ）を丸めて端部を突き合わせて溶接して製造し、継目無管は、材料の塊を高温で穿孔しマンドレルミル等で圧延して製造する。溶接管の場合、一般に溶接部の特性は母材より劣ると言われ、管の適用に当たって、用途ごとに溶接部の靭性や強度の保証が常に議論されて問題となってきた。   Usually, pipes are roughly classified into welded pipes and seamless pipes. Welded pipes are manufactured by rolling plates (meaning strips; the same shall apply hereinafter) and welding the ends together, as in the case of ERW steel pipes. It is manufactured by rolling with a mandrel mill or the like. In the case of a welded pipe, it is generally said that the properties of the welded part are inferior to that of the base metal, and in the application of the pipe, guarantees of toughness and strength of the welded part have always been discussed for each application.

例えば、原油や天然ガスなどを輸送するラインパイプでは、管を寒冷地に敷設することが多いため低温靭性が重要であり、また、原油採掘の油井では採掘管を保護するためのケーシングパイプが必要とされ、管の強度が重要視される。
また、通常、管の母材となる熱延板は、管製造後の母材特性を考慮して成分設計や熱処理等が行われて、母材の靭性や強度等の特性が確保される。 For example, in line pipes that transport crude oil, natural gas, etc., low temperature toughness is important because pipes are often laid in cold regions, and casing pipes are required to protect mining pipes in oil wells for crude oil mining. The strength of the tube is regarded as important.
In general, a hot-rolled sheet serving as a base material for a pipe is subjected to component design, heat treatment, and the like in consideration of the base material characteristics after the pipe is manufactured, and characteristics such as toughness and strength of the base material are ensured.

しかし、溶接部の特性は、母材の成分設計や熱処理等以上に、電縫溶接方法によって大きく左右されるため、溶接技術の開発が重要であった。
電縫溶接の不良原因としては、ペネトレータと呼ばれる溶接板材の端面に生成する酸化物が、電縫溶接時に溶鋼とともに端面から排出されずに残留し、この残留したペネトレータを原因として靭性が低下したり強度不足になる例が多かった。 However, since the characteristics of the welded part are greatly influenced by the electric resistance welding method more than the component design and heat treatment of the base metal, development of the welding technique has been important.
The reason for the failure of ERW welding is that the oxide generated on the end face of the welded plate material called penetrator remains without being discharged from the end face together with the molten steel during ERW welding, and the toughness decreases due to this residual penetrator. There were many examples of insufficient strength.

そこで、従来技術として電縫溶接不良の主原因であるペネトレータを溶接部から除くため、溶接部の板端面から積極的に溶鋼を排出する技術が鋭意検討されてきた。例えば、特許文献１〜４などに、板端面の形状について検討した例が記載されている。
また、特許文献５には、電縫管の溶接時における板材の両側縁部の突き合わせ圧力の調整を容易にし、溶接信頼性を高める目的で、板幅端部を種々の形状に面取り加工する旨記載されている。
特開昭57-31485号公報 特開昭63-317212号公報 特開2001-170779号公報 特開2003-164909号公報 特開2001-259733号公報 Therefore, as a conventional technique, in order to remove the penetrator, which is the main cause of ERW welding failure, from the welded portion, a technique for actively discharging molten steel from the plate end surface of the welded portion has been intensively studied. For example, Patent Documents 1 to 4 describe examples of examining the shape of the plate end surface.
Patent Document 5 discloses that the width end of the plate is chamfered into various shapes for the purpose of facilitating adjustment of the butting pressure at both side edges of the plate material during welding of the ERW pipe and enhancing welding reliability. Are listed.
Japanese Unexamined Patent Publication No. 57-31485 JP 63-317212 A JP 2001-170779 JP 2003-164909 JP 2001-259733 A

特許文献１〜４は、いずれも板端面にテーパを付与して、溶鋼とともにペネトレータを排出することを意図している。テーパを付与する理由は、板端面に容易に形状を与えやすいためと考えられる。しかし、単に、直線あるいは平面状のテーパを与えるのでは、溶接部特性（特に低温靭性）の改善効果が充分でない場合があり、さらに詳細な検討が必要であった。   Patent Documents 1 to 4 all intend to give a taper to the plate end surface and discharge the penetrator together with the molten steel. The reason for imparting the taper is considered to be because the shape is easily given to the end face of the plate. However, simply giving a linear or flat taper may not be sufficient in improving the welded portion characteristics (particularly, low temperature toughness), and further detailed examination is required.

また、特許文献５には、突き合わせ圧力の調整を容易にする種々の面取り形状が開示されているものの、溶鋼とともにペネトレータを排出する点、およびそれにより溶接部特性（特に低温靭性）を改善する点については、一切記載がないから、そこに開示されている多種多様な面取り形状のうち、いずれの形状が溶接部特性（特に低温靭性）を改善しうるものなのか、全く不明である。   Patent Document 5 discloses various chamfering shapes that facilitate adjustment of the butt pressure, but also discharges the penetrator together with the molten steel, and thereby improves the weld properties (particularly low temperature toughness). Is not described at all, it is completely unknown which of the various chamfered shapes disclosed therein can improve the welded portion characteristics (particularly low temperature toughness).

そこで、本発明は、溶接部特性（特に低温靭性）を確実かつ充分に向上させうる、溶接部特性の良好な電縫管の製造方法を提供することを目的とする。   Therefore, an object of the present invention is to provide a method for producing an electric resistance welded tube having good welded part characteristics, which can reliably and sufficiently improve welded part characteristics (particularly low temperature toughness).

発明者らは、前記目的を達成するために鋭意検討し、以下の要旨構成になる本発明に想到した。
１． 帯材を成形して端部を突き合わせ、該端部を電縫溶接して管とする過程の中で、電縫溶接前の前記端部にテーパ形状を付与しておき、電縫溶接の加熱を受けつつある前記端部に非酸化性ガスを吹き付けることを特徴とする溶接部特性の良好な電縫管の製造方法。 The inventors diligently studied to achieve the above-mentioned object and arrived at the present invention having the following gist configuration.
1. In the process of forming the strip material, butting the ends, and electro-welding the ends to make a pipe, a taper shape is given to the end before the ERW welding, and heating of the ERW welding is performed. A method of manufacturing an electric resistance welded tube with good welded portion characteristics, characterized in that a non-oxidizing gas is sprayed on the end portion that is being subjected to welding.

２． 帯材を成形して端部を突き合わせ、該端部を電縫溶接して管とする過程の中で、電縫溶接前の前記端部にテーパ形状を付与しておき、電縫溶接の加熱を受けつつある前記端部の周囲を非酸化性ガス雰囲気に保つことを特徴とする溶接部特性の良好な電縫管の製造方法。
３． 前記非酸化性ガスとして、還元性ガスを含むガスを用いることを特徴とする前項１または２に記載の溶接部特性の良好な電縫管の製造方法。 2. In the process of forming the strip material, butting the ends, and electro-welding the ends to make a pipe, a taper shape is given to the end before the ERW welding, and heating of the ERW welding is performed. A method of manufacturing an electric resistance welded tube having good welded portion characteristics, wherein the periphery of the end portion that is being subjected to heat treatment is maintained in a non-oxidizing gas atmosphere.
3. 3. The method of manufacturing an electric resistance welded tube having good welded portion characteristics according to item 1 or 2, wherein a gas containing a reducing gas is used as the non-oxidizing gas.

４． 前記テーパ形状を、テーパ面の帯材幅方向端面に対する角度が25〜50度、テーパ面の帯材厚み方向長さが帯材厚みの20〜40％であるテーパ形状とすることを特徴とする前項１〜３のいずれかに記載の溶接部特性の良好な電縫管の製造方法。   4). The taper shape is a taper shape in which the angle of the taper surface with respect to the end surface in the width direction of the strip is 25 to 50 degrees, and the length of the taper surface in the thickness direction of the strip is 20 to 40% of the thickness of the strip. 4. A method for producing an electric resistance welded tube having good weld joint characteristics according to any one of items 1 to 3.

本発明によれば、電縫管の溶接部特性（特に低温靭性）を確実に従来レベルよりも向上させることができる。   According to the present invention, the welded portion characteristics (especially low temperature toughness) of the ERW pipe can be reliably improved from the conventional level.

以下、従来技術と対比して、本発明を詳しく説明する。従来技術では、板（帯材）の端部（幅方向端部）に、単に、直線あるいは平面状のテーパを与えている。このテーパ加工により次のような作用効果が得られるとされている。すなわち、電縫溶接中、板端部が加熱されていく段階で、溶接欠陥であるペネトレータの原因となる酸化物が板端面に形成される。この酸化物は、板端部が溶融する段階で該溶融した溶鋼表面に浮き、圧接の段階で、一部は溶鋼とともに排出される。この際に、板端面にテーパ形状が付与されていると、溶鋼が容易に排出されて、同時にペネトレータも有効に排出できるわけである。   Hereinafter, the present invention will be described in detail in comparison with the prior art. In the prior art, a straight or flat taper is simply given to the end (width direction end) of the plate (strip). It is said that the following effects can be obtained by this taper processing. That is, during the electric resistance welding, at the stage where the plate end is heated, an oxide that causes a penetrator, which is a welding defect, is formed on the plate end surface. This oxide floats on the surface of the molten steel at the stage where the plate end melts, and a part of the oxide is discharged together with the molten steel at the stage of pressure welding. At this time, if the end face of the plate is tapered, the molten steel is easily discharged, and at the same time, the penetrator can be effectively discharged.

しかし、ペネトレータの元になる板端面の酸化物は、電縫溶接の加熱とともに順次生成してくるため、溶接条件によっては、板端部のテーパ形状のみでは、溶接後の靭性または強度を充分に向上できない場合が生じた。
そこで、本発明者らは電縫溶接現象を詳細に観察し直した結果、ペネトレータの原因となる酸化物の生成に着目した。すなわち、板端部のテーパ形状によるペネトレータの排出だけでなく、ペネトレータの原因となる酸化物の生成を防止する方法を検討した。 However, since the oxide on the plate end surface that becomes the basis of the penetrator is generated sequentially with the heating of ERW welding, depending on the welding conditions, the toughness or strength after welding is sufficient with only the taper shape of the plate end. There was a case where it could not be improved.
Therefore, the present inventors have re-observed the electric resistance welding phenomenon in detail, and as a result, have focused on the generation of oxides that cause penetrators. That is, a method for preventing not only the discharge of the penetrator due to the taper shape at the end of the plate but also the generation of oxides causing the penetrator was studied.

その結果、電縫溶接の加熱（すなわち圧接前に被圧接端部を溶融させるための加熱）を受けつつある板端部に向かって、非酸化性ガスを吹き付けると、酸化物の生成を抑制できることを把握した。ここで、非酸化性ガスとは、不活性ガス（窒素ガス、ヘリウムガス、アルゴンガス、ネオンガス、キセノンガス等、もしくはこれらの２種以上を混合してなる混合ガス）、還元性ガス（水素ガス、一酸化炭素ガス、メタンガス、プロパンガス等、もしくはこれらの２種以上を混合してなる混合ガス）、またはこれらを混合してなる混合ガスを意味する。   As a result, when non-oxidizing gas is blown toward the end of the plate that is undergoing heating by electro-resistance welding (that is, heating for melting the pressed end before pressing), generation of oxide can be suppressed. I figured out. Here, the non-oxidizing gas is an inert gas (nitrogen gas, helium gas, argon gas, neon gas, xenon gas, or a mixed gas obtained by mixing two or more of these), a reducing gas (hydrogen gas). , Carbon monoxide gas, methane gas, propane gas, etc., or a mixed gas formed by mixing two or more of these), or a mixed gas formed by mixing these.

つまり、本発明では、電縫溶接前の板端部にテーパ形状を付与しておくことで、ペネトレータの排出を促進し、それとともに、電縫溶接中の加熱を受けつつある板端部に非酸化性ガスを吹き付けることで、ペネトレータの原因となる酸化物の生成を抑制する。これにより、溶接部の靭性または強度を確実に従来レベルよりも向上させることができる。
もっとも、非酸化性ガスを吹き付けるだけでは、周辺の空気を巻き込むために、板端部での酸化物生成を抑制する効果が多かれ少なかれ弱められる。そこで、周辺の空気の巻き込みをなくすことが好ましく、それには、電縫溶接の加熱を受けつつある板端部を囲ってその囲いの内部を非酸化性ガス雰囲気に保つのがよい。 In other words, in the present invention, by providing a taper shape to the plate end portion before the ERW welding, the penetration of the penetrator is promoted, and at the same time, the plate end portion being subjected to the heating during the ERW welding is not used. By blowing the oxidizing gas, the generation of oxide that causes the penetrator is suppressed. Thereby, the toughness or strength of the welded portion can be reliably improved from the conventional level.
Of course, simply blowing non-oxidizing gas can weaken the effect of suppressing oxide generation at the edge of the plate more or less because the surrounding air is entrained. Therefore, it is preferable to eliminate the entrainment of the surrounding air. For this purpose, it is preferable to surround the end of the plate that is being heated by the electric resistance welding and keep the inside of the enclosure in a non-oxidizing gas atmosphere.

また、非酸化性ガスのうちでも、還元性ガスを含むガスを用いる方が、ペネトレータの原因となる酸化物の生成を抑制する効果がより強くなり、溶接部の靭性または強度を、より大きく向上させることができる。
また、入手容易性および廉価性の点からは、非酸化性ガスとして、次のガスを用いることが好ましい。
・不活性ガス単独使用の場合：（Ａ）窒素ガス、ヘリウムガス、アルゴンガスのいずれかもしくはこれらの２種以上の混合ガス
・還元性ガス単独使用の場合：（Ｂ）水素ガス、一酸化炭素ガスのいずれかもしくはこれら２種の混合ガス
・不活性ガスと還元性ガスの混合ガス使用の場合：前記（Ａ）と（Ｂ）の混合ガス
なお、特に、水素ガスおよび／または一酸化炭素ガスを含むガスを使用する場合、遺漏なき安全対策をとるべきことはいうまでもない。 In addition, among non-oxidizing gases, the use of a gas containing a reducing gas has a stronger effect of suppressing the formation of oxides that cause penetrators, and greatly improves the toughness or strength of the weld. Can be made.
From the viewpoint of availability and low cost, it is preferable to use the following gas as the non-oxidizing gas.
-When using inert gas alone: (A) When using nitrogen gas, helium gas, argon gas or a mixture of two or more of these or reducing gas alone: (B) Hydrogen gas, carbon monoxide In the case of using any one of these gases or a mixed gas of these two kinds of mixed gas / inert gas and reducing gas: mixed gas of the above (A) and (B) In particular, hydrogen gas and / or carbon monoxide gas Needless to say, safety measures should be taken when using gas containing gas.

また、テーパ形状について最適化を図った結果、板幅端面に対するテーパ面の角度（傾き角度；図３のθ_１、θ_２）を25〜50度の範囲とし、テーパ面の板厚方向長さ（図３のδ_１、δ_２）を板厚の20〜40％の範囲とすると良いことを把握した。
すなわち、テーパ面の角度を25度未満とすると板厚中央部からの溶鋼排出が不十分となってペネトレータが残留して、電縫溶接後の靭性や強度が低下しやすく、一方、テーパ面の角度を50度超えとすると、電縫溶接後にそのテーパ形状が製品管の疵として残留しやすい。また、テーパ面の板厚方向長さを板厚の20％未満とすると、板厚中央部の溶鋼排出が不十分となってペネトレータが残留しやすくなり、一方、テーパ面の板厚方向長さを板厚の40％超とすると、電縫溶接後にそのテーパ形状が製品管の疵として残留しやすくなる。 Further, as a result of optimization of the taper shape, the angle of the taper surface with respect to the end surface of the plate width (inclination angle; θ ₁ , θ _{2 in} FIG. 3) is in the range of 25 to 50 degrees, and the length of the taper surface in the thickness direction It was understood that (δ ₁ , δ _{2 in} FIG. 3) should be in the range of 20 to 40% of the plate thickness.
That is, if the angle of the taper surface is less than 25 degrees, the molten steel discharge from the central portion of the plate thickness is insufficient and the penetrator remains, and the toughness and strength after ERW welding tend to decrease, while the taper surface If the angle exceeds 50 degrees, the taper shape tends to remain as a flaw in the product pipe after ERW welding. If the length of the taper surface in the plate thickness direction is less than 20% of the plate thickness, the molten steel discharge at the center of the plate thickness is insufficient and the penetrator tends to remain, whereas the length of the taper surface in the plate thickness direction If the thickness is more than 40% of the plate thickness, the taper shape tends to remain as a flaw in the product tube after ERW welding.

以下、実施例に基づいて説明する。この実施例では、板幅1920ｍｍ×板厚19.1ｍｍの鋼帯からなる帯材を、アンコイラー、レベラー、ロール成形機、電縫溶接機、サイザーからなる造管機に通して、外径600ｍｍの鋼管を製造するにあたり、製造条件を以下の４通りに違えて製造した。
（No.１） 本発明例として、ロール成形の最終段であるフィンパス圧延を活用して帯材端部にほぼ直線状のテーパ形状を付与（図３のパラメータは表１に示す値に設定）し、図１に示す実施形態で、電縫溶接の加熱（コンタクトチップ２からの通電加熱）を受けつつある帯材端部に、ガス供給ノズル３から窒素ガスを吹き付けた。 Hereinafter, a description will be given based on examples. In this example, a steel strip having a plate width of 1920 mm and a plate thickness of 19.1 mm is passed through a pipe making machine comprising an uncoiler, leveler, roll forming machine, electric welding machine, and sizer, and a steel pipe having an outer diameter of 600 mm. In manufacturing, the manufacturing conditions were changed in the following four ways.
(No. 1) As an example of the present invention, utilizing the fin pass rolling which is the final stage of roll forming, a substantially linear taper shape is given to the end of the strip (parameters in FIG. 3 are set to values shown in Table 1). In the embodiment shown in FIG. 1, nitrogen gas was blown from the gas supply nozzle 3 to the end portion of the strip material that was being subjected to the heating of the electric seam welding (the energization heating from the contact tip 2).

（No.２） 本発明例として、ロール成形機入側に配置した孔型ロールを活用して帯材端部にほぼ直線状のテーパ形状を付与（図３のパラメータは表１に示す値に設定）し、図２に示す実施形態で、電縫溶接の加熱（コンタクトチップ２からの通電加熱）を受けつつある帯材端部を、ガス雰囲気ボックス５で囲い、該ボックス内を、３％水素ガス＋残部アルゴンガスの雰囲気に保った。   (No. 2) As an example of the present invention, a substantially linear taper shape is imparted to the end of the strip using a perforated roll placed on the roll forming machine entrance side (parameters in FIG. 3 are set to values shown in Table 1). 2), in the embodiment shown in FIG. 2, the end portion of the strip material that is being subjected to the heating of the electric resistance welding (electric current heating from the contact tip 2) is surrounded by the gas atmosphere box 5, and the inside of the box is 3% An atmosphere of hydrogen gas + balance argon gas was kept.

（No.３） 比較例として、ロール成形の最終段であるフィンパス圧延を活用して帯材端部にほぼ直線状のテーパ形状を付与（図３のパラメータは表１に示す値に設定）し、電縫溶接の加熱を受けつつある帯材端部は大気中にさらしたままとした。
（No.４） 従来例として、帯材端部形状は矩形状（長方形の長さ端部形状）とし、電縫溶接の加熱を受けつつある帯材端部は大気中にさらしたままとした。 (No. 3) As a comparative example, a fin tape rolling which is the final stage of roll forming is utilized to give a substantially linear taper shape to the end of the strip (parameters in FIG. 3 are set to values shown in Table 1). The end of the strip that was being heated by the electric resistance welding was left exposed to the atmosphere.
(No. 4) As a conventional example, the end of the strip is rectangular (rectangular length end), and the end of the strip that is being heated by ERW welding is left exposed to the atmosphere. .

上記４通りの条件で製造した鋼管の溶接部から試験片を切り出してシャルピー試験を行い、性能を評価した。シャルピー試験片は、管長手方向の相違する10点から１本ずつ、試験片長さ方向を管円周方向にとり、ノッチ長さ中心を溶接部肉厚中心位置にとって採取した、JIS ５号の２mmＶノッチ衝撃試験片を用いて、試験片温度−46℃で衝撃試験を行い、吸収エネルギー、脆性破面率を測定した。なお、吸収エネルギー：125Ｊ以上、脆性破面率：35％以下を性能許容範囲とした。その結果を表１に示す。   A test piece was cut out from a welded portion of a steel pipe manufactured under the above four conditions and a Charpy test was performed to evaluate the performance. Each Charpy test piece was taken from 10 points with different pipe lengths, and the test piece length direction was taken in the pipe circumferential direction, and the notch length center was taken at the weld thickness center position. Using the impact test piece, an impact test was conducted at a test piece temperature of −46 ° C., and the absorbed energy and the brittle fracture surface ratio were measured. In addition, the absorbed energy: 125 J or more and the brittle fracture surface ratio: 35% or less were set as the allowable performance range. The results are shown in Table 1.

表１より、本発明例では、溶接部の衝撃強度（吸収エネルギー）が著しく高く脆性破面率が小さくて、靭性が良好であって製品の信頼性が高いが、これに比べて、比較例および従来例では、溶接部の衝撃強度（吸収エネルギー）が低く脆性破面率が大きくて、靭性が低下しており、製品の信頼性に乏しかった。   From Table 1, in the present invention example, the impact strength (absorbed energy) of the welded portion is remarkably high, the brittle fracture surface ratio is small, the toughness is good, and the reliability of the product is high. In the conventional example, the impact strength (absorbed energy) of the welded portion is low, the brittle fracture surface ratio is large, the toughness is lowered, and the reliability of the product is poor.

本発明の実施形態の１例を示す模式図である。It is a schematic diagram which shows one example of embodiment of this invention. 本発明の実施形態の１例（既出例とは異なる）を示す模式図である。It is a schematic diagram which shows one example (different from the previous example) of embodiment of this invention. テーパ形状のパラメータの定義説明図である。It is a definition explanatory drawing of the parameter of a taper shape.

符号の説明Explanation of symbols

１ 帯材（板；幅を丸めた状態の板）
２ コンタクトチップ
３ ガス供給ノズル
４ テーパ面
５ ガス雰囲気ボックス
６ 通材方向 1 Band material (board; board with rounded width)
2 Contact Tip 3 Gas Supply Nozzle 4 Tapered Surface 5 Gas Atmosphere Box 6 Feeding Direction

Claims (4)

帯材を成形して端部を突き合わせ、該端部を電縫溶接して管とする過程の中で、電縫溶接前の前記端部にテーパ形状を付与しておき、電縫溶接の加熱を受けつつある前記端部に非酸化性ガスを吹き付けることを特徴とする溶接部特性の良好な電縫管の製造方法。   In the process of forming the strip material, butting the ends, and electro-welding the ends to make a pipe, a taper shape is given to the end before the ERW welding, and heating of the ERW welding is performed. A method of manufacturing an electric resistance welded tube with good welded portion characteristics, characterized in that a non-oxidizing gas is sprayed on the end portion that is being subjected to welding. 帯材を成形して端部を突き合わせ、該端部を電縫溶接して管とする過程の中で、電縫溶接前の前記端部にテーパ形状を付与しておき、電縫溶接の加熱を受けつつある前記端部の周囲を非酸化性ガス雰囲気に保つことを特徴とする溶接部特性の良好な電縫管の製造方法。   In the process of forming the strip material, butting the ends, and electro-welding the ends to make a pipe, a taper shape is given to the end before the ERW welding, and heating of the ERW welding is performed. A method of manufacturing an electric resistance welded tube having good welded portion characteristics, wherein the periphery of the end portion that is being subjected to heat treatment is maintained in a non-oxidizing gas atmosphere. 前記非酸化性ガスとして、還元性ガスを含むガスを用いることを特徴とする請求項１または２に記載の溶接部特性の良好な電縫管の製造方法。   The method for manufacturing an electric resistance welded tube with good weldability characteristics according to claim 1 or 2, wherein a gas containing a reducing gas is used as the non-oxidizing gas. 前記テーパ形状を、テーパ面の帯材幅方向端面に対する角度が25〜50度、テーパ面の帯材厚み方向長さが帯材厚みの20〜40％であるテーパ形状とすることを特徴とする請求項１〜３のいずれかに記載の溶接部特性の良好な電縫管の製造方法。   The taper shape is a taper shape in which the angle of the taper surface with respect to the end surface in the width direction of the strip is 25 to 50 degrees, and the length of the taper surface in the thickness direction of the strip is 20 to 40% of the thickness of the strip. The manufacturing method of the electric-welded pipe with the favorable weld-part characteristic in any one of Claims 1-3.