JP2004105994A

JP2004105994A - Welding method for tube and infusing nozzle for shielding gas for welding

Info

Publication number: JP2004105994A
Application number: JP2002269358A
Authority: JP
Inventors: Korehisa Fukuda; 福田　是寿; Masayuki Ishiwatari; 石渡　雅幸; Yasukazu Shiraishi; 白石　八州一; Kazuhiko Mogaki; 藻垣　和彦; Shunichi Sudo; 須藤　俊一
Original assignee: Hitachi Engineering and Services Co Ltd; Hitachi Ltd
Current assignee: Hitachi Engineering and Services Co Ltd; Hitachi Ltd
Priority date: 2002-09-17
Filing date: 2002-09-17
Publication date: 2004-04-08
Anticipated expiration: 2022-09-17
Also published as: JP3996825B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for locally sealing a shielding gas for welding into a tube near a butt welding zone of piping, in a system structure in which sealing of a shielding gas is difficult at the time of welding piping or in which no water soluble film can be used. <P>SOLUTION: In butt welding of a pair of pipes in piping 12, columnar dry ice 11 having an outer diameter equal to the inner diameter of the piping is inserted into the piping, forming a wall inside the piping 12 for the purpose of a purge dam of the shielding gas for welding, thereby suppressing air flow in the air space 13 on the non-welding side inside the piping as well as in the air space 14 inside the piping near the welding back bead. A nozzle 16 for infusing the shielding gas is inserted into the piping 12 from a hole drilled in the groove abutting part in the butt welding zone of the piping 12, with the shielding gas 18 infused into space 14 inside the piping to lower the oxygen concentration, to prevent oxidation in the welding back bead on the piping inner face at the time of the welding. In addition, the outer periphery of the piping in which the dry ice is installed is wrapped with a freezing jacket 10 utilizing liquefied carbon dioxide, suppressing vaporization of the dry ice. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、ステンレス製配管を含む金属製配管の溶接方法及び溶接用シールドガス注入用ノズルに関する。
【０００２】
【従来の技術】
従来、ステンレス製の配管同士を突合せ溶接する際には、空気中の酸素や窒素などが溶接部裏波ビードに侵入することによる金属の機械的，化学的劣化防止の観点から、アルゴン（Ａｒ），ヘリウム（Ｈｅ），炭酸ガス（ＣＯ_２　）などの溶接用シールドガスを配管内に注入して配管内の酸素濃度を低下させている。
【０００３】
その配管内の溶接用シールドガスが溶接部近傍から移動しないように溶接用シールドガスを溶接部近傍に封入する必要があるが、その封入技術として、気化時に溶接用シールドガスとなるドライアイスと、そのドライアイスを配管内に固定するための固定用の水溶性固形物を併用して、パージダム生成とシールドガス注入を同時に可能とした公知例が特許文献１に挙げられる。
【０００４】
また、配管の突合せ溶接開先部分から配管内に溶接用シールドガスを注入し、注入した溶接用シールドガスが抜けないように配管内面に水溶性フィルムによる袋を配管内で膨らませて溶接用シールドガスを封入する方法が特許文献２にて公知である。
【０００５】
また、配管内に溶接開先部から差し込んだ溶接用シールドガス注入用ノズルを通じて溶接用シールドガスを注入する技術が特許文献３で公知である。
【０００６】
【特許文献１】
特開平６−３０７５８６号公報
【特許文献２】
特開平５−２４５６３３号公報
【特許文献３】
特開平９−２９５１４７号公報
【０００７】
【発明が解決しようとする課題】
特開平６−３０７５８６号公報の技術は、配管とドライアイスの接触面でドライアイスが気化蒸発するので、溶接用シールドガスを配管内に封入するのに水溶性固形物が必要である。特開平５−２４５６３３号公報に記載の技術も配管内に水溶性フィルムによる袋が必要である。
【０００８】
いずれの場合にも、水溶性材料が溶接後の配管内に残留するので、水洗にて水溶性材料を洗い流す必要がある。水洗する際には、多量の水と水の勢いとが必要であるから、配管に接続されたタンクや配管に水が残留したり排水しにくい配管系統では従来技術が利用しにくいという課題を有する。
【０００９】
また、配管内に溶接用シールドガスを注入する際に従来の溶接用シールドガス注入用ノズルでは、ノズル周囲に均等にガスの流出用細孔が開いているので、溶接用シールドガスを配管の溶接開先に重点的に行き渡らせることが出来ない。
【００１０】
また、ドライアイスのみで配管内を閉鎖して溶接用シールドガスを溶接開先部の局所において局部的に配管内に封じ込めることが思いつくが、この場合には、配管とドライアイスとが接する部分でドライアイスが気化蒸発して前述の封じ込めの機能が喪失されれるとともに、配管が傾斜乃至は垂直の場合には、ドライアイスが配管と接する部分で気化蒸発するので、ドライアイスが傾斜下降方向又は垂直下方へずれ動いて希望する領域での溶接用シールドガスの局部的封じ込め状態が達成できないという課題を負うことになる。
【００１１】
したがって、本発明の目的は、水溶性材料による溶接用シールドガスの局部的封じ込めが利用できない場合や配管が傾斜乃至は垂直である場合にも溶接用シールドガスの局部的封じ込めを達成して配管溶接が可能な溶接方法を提供することである。
【００１２】
また、本発明の他の目的は、配管の溶接開先近傍の配管内の酸素濃度を効率よく低下させることのできる溶接用シールドガス注入用ノズルを提供することにある。
【００１３】
【課題を解決するための手段】
課題を解決するための手段は、ドライアイスを配管内を塞ぐように設置して、溶接用シールドガスが抜けにくい壁を配管内に作り、そのドライアイスの壁を配管の外周から配管とともに冷却し、さらには配管内に溶接用シールドガスを注入する溶接用シールドガスのバックパージ方法を採用し、このような溶接用シールドガスのバックパージ方法により溶接個所近傍の配管内の局所的な空間の雰囲気の酸素濃度を溶接用シールドガスを注入する以前よりも低下させ、その後に配管の溶接個所を溶接する溶接方法を採用している。
【００１４】
また、配管内に溶接用シールドガスを注入するシールドガス注入用ノズルは、ノズルに開けたシールドガスの噴出用の孔を、シールドガス注入ノズルの径の中心を通る線上と、前記線から前記径の周方向±４５度の角度の線上とに設け、これら各孔をシールドガス注入ノズルの軸心方向に千鳥配置で備えて前記孔を不均一に分布させてあることに特徴がある。
【００１５】
【発明の実施の形態】
本発明の実施例は以下のとおりである。即ち、図１に示すように、互いに突合せ溶接されるステンレス製の一対の配管１２の溶接取合端部１７を合わせる。溶接取合端部１７には配管１２の端部を加工して溶接開先を形成し、図１のように配管１２同士を突き合わせた状態では溶接取合端部１７には外側に開かれたＶ字型の断面の溶接開先の部分が表れる。
【００１６】
そして、その溶接開先が合わされた溶接取合端部１７を配管１２の外周囲側からＴＩＧ（タングステン　イナート　ガス）溶接によって突合せ溶接する。ＴＩＧ溶接するに際しては、アルゴン（Ａｒ），ヘリウム（Ｈｅ），炭酸ガス（ＣＯ_２）などの溶接用シールドガスを配管１２の外周から溶接部に吹き付けながら行う。その突合せ溶接を行う際に、あらかじめ溶接を行う当該配管１２の内径と等しい外径に成型した円柱状ドライアイス１１を、突合せ溶接部を行う各々の配管１２の突合せ溶接部にて溶接時の熱影響が無視できる距離を確保した溶接部近傍にそれぞれ挿入して配管１２内に円柱状ドライアイス１１を壁とした溶接用シールドガスのパージダムを生成する。
【００１７】
このようにして、円柱状ドライアイス１１の壁を境に溶接取合端部１７から遠い方の配管１２内部空間である非溶接側空間１３と、円柱状ドライアイス１１の壁を境に溶接取合端部１７に近い方の空間である配管内部空間１４との空気の流れを遮断する。ここで言う遮断とは、配管１２とドライアイス１１の接触部１５は、自然に空気の流れを生ずることを遮断する程度の密着で良く、気密という意味ではない。
【００１８】
溶接作業中にドライアイス１１の気化蒸発を抑制するために、ドライアイス設置部の配管１２外周を、液化炭酸ガスを通したフリージングジャケット１０にて包み込みドライアイス１１を配管１２に挿入後は配管１２外周をフリージングジャケット１０を冷却手段に用いて常に冷却させておく。
【００１９】
その後、溶接取合端部１７に加工した孔よりシールドガス注入用ノズル１６を配管１２の内部１４に挿入し、アルゴン（Ａｒ），ヘリウム（Ｈｅ），炭酸ガス（ＣＯ_２　）或いはそれらのいずれかの混合ガスによる溶接用シールドガス１８を配管内部空間１４へ注入することで配管内に供給し、配管内部１４空間の空気を溶接用シールドガス１８により置換する。この置換で配管内部１４の酸素濃度を低下させつつ、溶接取合端部１７の溶接開先同士を溶接し、この溶接時の配管内面溶接裏波部の酸化防止を図る。
【００２０】
更に詳細に説明すれば以下のとおりである。即ち、図１におけるシールドガス注入用ノズル１６の先端部であるＡ部の詳細を図２に示す。シールドガス注入用ノズル１６は、ガス用ホース１９の一端に接続され、ガス用ホース１９の他端は溶接用シールドガス１８が配管内部空間１４よりも高圧に貯蔵してあるガスボンベに接続されている。好ましくは、ガス用ホース１９と前述のガスボンベとは流量及び圧力調整機構を通じて接続され、配管内部空間１４内の圧力よりも溶接用シールドガス１８の圧力が高圧となるように、及び予め決められた流量の溶接用シールドガス１８が配管内部空間１４内に注入されるように制御することが好ましい。
【００２１】
ドライアイス１１の壁と配管１２内面とはドライアイス設定時の若干の気化減容とドライアイスの加工精度からドライアイス１１の壁と配管１２内面全周囲が完全には閉鎖されず、高圧な溶接用シールドガス１８が配管内部空間１４内に入ると、配管内部空間１４内が非溶接側空間１３内よりも高圧となって、配管内部空間１４内の空気が非溶接側空間１３内側へドライアイス１１の壁と配管１２内面との不完全閉鎖部から抜けて配管内部空間１４内が溶接用シールドガス１８に置換される。
【００２２】
配管内部空間１４内と非溶接側空間１３内との間で、差圧が生じていなければ、容易には配管内部空間１４内と非溶接側空間１３内との間で雰囲気の通り抜けは発生しない。実際には、溶接作業中は、溶接用シールドガス１８を配管内部空間１４内へ注入し続けて配管内部空間１４内の圧力が高く非溶接側空間１３内の圧力が低い状態の差圧が常に生じるようにする。
【００２３】
このシールドガス注入用ノズル１６の配管内部空間１４内へ挿入される先端部の側面には、図２の（ａ），（ｂ）で表示されているように、溶接取合端部１７の溶接開先合わせ部方向と、その方向を基準にシールドガス注入用ノズル１６の円周方向へ振り角４５度にて６方向、且つノズル軸方向（ノズル長手方向）では千鳥配置として微細な孔加工を施し、この微細な孔２０から溶接取合端部１７の溶接開先合わせ部方向に集中的にシールドガスを噴射させ、効率良く図１に示す溶接取合端部１７の内側の配管内部空間１４を溶接用シールドガスで置換し、また溶接時の溶接裏波部への効率的な溶接用シールドガス供給の為の配管内部空間１４内でのガス流を生成する機能を有する。
【００２４】
このように、シールドガス注入用ノズル１６の孔２０は、シールドガス注入用ノズル１６の軸心を示す線Ｃと直交する第１の断面（Ｘ−Ｘ断面）でシールドガス注入用ノズル１６の径の中心を通る線Ａ上と、前記第１の断面の位置と異なる位置におけるシールドガス注入ノズルの軸心示す線Ｃと直交する第２の断面（Ｙ−Ｙ断面）で前記線Ａから前記径の周方向±４５度の角度の線Ｂ上とに配置して、前記孔を不均一に分布させてある。
【００２５】
この図２（ａ）（ｂ）に示す本発明のシールドガス注入用ノズル１６の微細な孔２０の配置の効果を確認するために、図３（ａ）（ｂ）に示す様にノズル側面に周方向に均等に微細な孔３０を加工した従来型のシールドガス注入用ノズル
１６ａとの比較検証結果を図４に示す。
【００２６】
図４では、長さ５００ｍｍ、内径が１０６．３ｍｍ、外径が１１４．３ｍｍの端部開放の二本の配管１２を突合せたものに対して、ノズルＡを図３（ａ）（ｂ）に示す従来型をノズルとして、ノズルＢを図２（ａ）（ｂ）に示す今回発明のノズルとして、流量１０Ｌ／ｍｉｎ　で不活性ガスであるアルゴン（Ａｒ）ガスを注入して５分後のそれぞれの酸素濃度計（図中４１〜４３）の値を示したものである。本図から明らかなように、同じ溶接用シールドガス注入流量にて、従来型に比較して本発明のノズルでは、効率的に溶接取合端部１７周辺を０．１％　まで酸素濃度を低下させることが確認出来た。この際、ノズルＢは図３（ａ）（ｂ）に示すように線Ｂの向きが溶接取合端部１７の溶接開先合わせ部方向に向くようにした。
【００２７】
次に、図１に示す本発明の方法での適用配管口径の最大径を確定するため、実機の配管溶接を想定した図５に示す試験体にて、配管１２内部の酸素濃度測定によるバックパージの状況確認を行った。図５に示す水平に設置した溶接対象と仮定した配管１２に対し、中央部を溶接取合端部１７の溶接開先合わせ位置に仮定し、図２（ａ）（ｂ）に示すシールドガス注入用ノズル１６を設定、溶接取合端部１７の溶接開先合わせ部を中心に、酸素濃度計５１−５６を配管内部中央部に設定し、配管内部空間１４の酸素濃度分布を管軸方向の分布として測定できるようにした。
【００２８】
また、水平設置の配管１２の両端部には、円柱状の配管１２内径に外径を合わせたドライアイス１１を設定した。その設定位置は、図５に示すように、溶接取合端部１７の溶接開先合わせ位置から５００ｍｍにドライアイス１１の壁の溶接取合端部１７側の面が位置するようにされる。この配管１２は配管呼び径１００Ａ（管内径１０６．２ｍｍ）のＳＵＳ３０４ＴＰステンレス製配管である。
【００２９】
このドライアイス１１の設定箇所における配管１２の外周面には、液化炭酸ガスを通したフリージングジャケット１０を覆いかぶせて実機で必要な溶接作業時間の間、十分にパージダムとしての機能を果たせる様にドライアイス１１の気化減容を抑制させた。
【００３０】
表１は、図５に示す試験体にて、バックパージの経過時間と各酸素濃度測定値を示した表である。経過時間４ｍｉｎ　にて酸素濃度が低下して配管溶接が可能な状態にバックパージが達成され、以後２４０ｍｉｎ　の間、安定的に溶接用シールドガスによるバックシールドが確保され、実機での配管溶接に適用できることが確認された。なお、ドライアイス設定後、溶接用シールドガス噴射開始時間を０ｍｉｎ　とし、以後、溶接用シールドガスは常にシールドガス注入用ノズル１６を通じて配管内部空間１４内に噴射させてある。この際の溶接用シールドガスはアルゴン（Ａｒ）ガスであり、その流量は１０Ｌ／ｍｉｎ　である。
【００３１】
【表１】

【００３２】
本発明を利用した、実機での配管溶接の作業手順を図６に示す。配管溶接作業場所の安全確認６００を実施した後、溶接取合端部１７の溶接開先合わせ位置である配管溶接部からの熱影響が無視できる距離を確保した位置に、フリージングジャケット１０を設定６０１する。これにより、フリージングを開始６０２して、配管１２自体を予め冷却してドライアイス１１の配管１２内への設定時のドライアイス１１の配管接触面での滑りと気化減容を抑制する。
【００３３】
次に、配管１２に勾配が有るか否か判断し、配管１２に勾配がある場合には、配管１２内に配管１２の内径に外径を合わせた円柱状の氷７０を設定６０４し、配管１２に勾配が無い場合には円柱状の氷７０の配管１２内への設定は行わない。この氷の設定要否は、配管勾配有り６０３の判定により決定し、氷を設定することで、氷７０で勾配下降方向にずれ動くドライアイス１１を受け止めてドライアイス１１の配管１２内の滑りを防止することが出来る。次に、配管１２内に配管１２の内径に外径を合わせた円柱状のドライアイス１１を設定６０５する。
【００３４】
図７は、配管１２の勾配が９０度の垂直配管へのドライアイス１１と氷７０の設置状態を示したものである。垂直に設置された配管１２に対してドライアイス１１の落下方向に配管１２の内径に合わせた円柱上の氷７０を設定する。その設定の際に氷との接点となる配管内面７１は、予め配管外周面からフリージングジャケット１０にて十分に冷却されており、空気中の水蒸気による霜が発生するため、氷７０が配管１２の内面に接着される。接着されにくい場合は配管内面７１へ向けての霧吹きなどで、配管内面７１に水分を与えて接着を達成させる。
【００３５】
このようにして配管１２内にドライアイス１１の設定６０５を突合せ溶接を行う対象の一対の各々の配管１２に行った後、溶接取合端部１７の溶接開先合わせとしての配管組立作業６０６を行う。その後に、一対の配管の溶接取合端部１７の溶接開先合わせ部に配管穴開作業６０６にて小穴を開け、その小穴にシールドガス注入用ノズル１６を挿入して溶接取合端部１７にセットする作業６０８を行う。
【００３６】
また、配管溶接時の品質保証として、酸素濃度計を配管１２に差し込んでセットする酸素濃度測定用ノズルセット作業６０９も合わせて行い、溶接時の酸素濃度の変動を確認できるようにする。その後、シールドガス注入用ノズル１６から溶接用シールドガスをシールドガス注入用ノズルを通して配管内部空間１４に注入すること、即ちバックパージ用ガス注入６１１を行い、溶接に悪影響を及ぼさない所望の酸素濃度になったことを確認する酸素濃度低下６１２確認が実施される。
【００３７】
所望の酸素濃度になったことを確認した場合には、次に溶接取合端部１７の溶接開先合わせ部に対してＴＩＧ溶接で配管１２の外周側から周溶接６１３を行う。周溶接６１３を行っている間は、溶接用シールドガスは配管内部空間１４内に注入し続けて酸素濃度の上昇を極力抑制する。フリージングジャケット１０による配管１２の冷却も溶接中においても継続して氷７０の液化やドライアイス１１の気化蒸発を極力抑制して配管内部空間１４内の酸素濃度の上昇を少ない溶接用シールドガス流量で抑制する。
【００３８】
酸素濃度低下６１２の判定で希望の酸素濃度に下がらなかった場合には、図６に示すフリージングジャケット設定６０１以降酸素濃度低下６１２までの各ステップを繰り返して、溶接開先合せ部周溶接６１３が行えるようにする。
【００３９】
図７のように氷７０を配管１２内に設定した例の場合にも、ドライアイス１１の設定時の若干の気化減容と、氷７０の加工精度から配管１２内全周面に対してドライアイス１１と氷７０が気密に密着しているわけではなく、部分部分に気密で無い部分が生じ、ドライアイス１１と氷７０で完全には配管１２を閉鎖出来ず、したがって、シールドガス注入用ノズルから溶接用シールドガスを配管内部空間１４内に注入すると、配管内部空間１４とその外部との差圧で配管内部１４内の空気が前述の気密で無い部分から流出し、溶接用シールドガスによる配管内部空間１４内が置換できる。
【００４０】
希望する酸素濃度に溶接用シールドガスによる配管内部空間１４内が置換出来たか否かは、酸素濃度計で測定して知ることもできるが、予め溶接用シールドガスの注入時間と配管内部空間１４内の酸素濃度との関係を表１のように知っておけば、酸素濃度計の採用を必須のものでは無くなる。
【００４１】
図６で溶接開先合せ部周溶接６１３が進んで終了直前になったら、シールドガス注入用ノズルや酸素濃度計を配管１２から抜いて撤去し、直ちにＴＩＧ溶接でシールドガス注入用ノズルや酸素濃度計を抜いた後に配管１２に残った穴とシールドガス注入用ノズルの有った周辺の溶接開先部を塞ぐ。
【００４２】
その後に、フリージングジャケット１０を配管１２から撤去して、ドライアイス１１を自然に気化させ、氷７０も併用してある場合には、その氷７０も自然にとかして液体に戻す。その氷７０を採用する場合には、ドライアイス１１との併用によって氷７０の量は少なくて済み、とけて生じた液体の量も配管内を水フラッシングして生じる排水に比較して極端に少なくて済む。
【００４３】
以上のように、ドライアイス１１又はドライアイス１１と氷７０とを使用して溶接用シールドガスが溶接部近傍から抜けないように配管１２内に壁を作る際に、突合せ溶接される一対の各配管１２全部に対してその壁を作ってもよく、溶接近傍に弁が存在して弁を閉めることで壁の役割を果たすことや配管が垂直であるとか、何らかの原因で一対の各配管１２の一方の配管１２に対してのみドライアイス１１又はドライアイス１１と氷７０とを使用して壁を配管内に設定するようにしても良い。また、溶接用シールドガスを溶接取合端部１７から配管内に注入するようにしても良いが、図７のように溶接用シールドガス１８を配管１２の端部から図７に表示した矢印方向に注入して溶接取合端部１７の配管内側の雰囲気の酸素濃度を低下するようにしても良い。
【００４４】
また、酸素濃度計を配管１２内に差し込む位置を配管の溶接取合端部１７にしても良い。この場合には、配管同士を突き合せた状態の溶接取り合い端部１７に穴をあけて、その穴を通じて酸素濃度計を配管１２内に差し込むことであても良い。この場合にも、溶接取合端部１７の配管内側の空間における酸素濃度を酸素濃度計で計測して確認し、溶接しても溶接裏波に大きな悪影響を及ぼさない酸素濃度になった時点で溶接取合端部１７を溶接する。その穴は最終的には、酸素濃度計を配管から抜き去った後に溶接で穴埋めされる。
【００４５】
以上、説明してきたように、本発明の実施例では、自然に気化・蒸発するドライアイスを配管溶接時のバックパージダムの壁として使用するため、配管溶接後の水フラッシングを行う必要は無く、水フラッシングの適用出来ない配管溶接部へのバックパージ方法が可能となる。また、本発明の実施例では、局所的なバックパージ方法を提供するものであり、配管系統全体をバックパージして溶接するのに比して極少量の溶接用シールドガスにて配管溶接が可能となり、経済性も良くなる。
【００４６】
【発明の効果】
以上のように、本発明によれば、自然に気化・蒸発するドライアイスを配管溶接時の溶接用シールドガスを配管内に貯留させるための壁として使用するため、配管溶接後の水洗が適用できない配管溶接部に対しても溶接用シールドガスを配管溶接部に対応した配管の局所において充填することができる。
【図面の簡単な説明】
【図１】本発明の実施例による配管突合せ溶接時のパックパージ方法を説明する配管断面図である。
【図２】本発明の実施例で用いられるシールドガス注入用ノズルの拡大断面図であり、（ａ）図はそのノズルの長手方向の断面図であり、（ｂ）図は（ａ）図のＸ−Ｘ断面図であり、（ｃ）図は（ａ）図のＹ−Ｙ断面図である。
【図３】従来のシールドガス注入用ノズルの拡大断面図であり、（ａ）図はそのノズルの長手方向の断面図であり、（ｂ）図は（ａ）図のＸ−Ｘ断面図であり、（ｃ）図は（ａ）図のＹ−Ｙ断面図である。
【図４】従来型と本発明のシールドガス注入ノズルを用いた配管内酸素濃度低減効果の比較説明図である。
【図５】本発明を実機適用へ模擬した試験体を示した図である。
【図６】本発明による突合せ溶接作業の流れを示した図である。
【図７】本発明を垂直配管に適用した場合の図である。
【符号の説明】
１０…フリージングジャケット、１１…ドライアイス、１２…配管、１６…シールドガス注入用ノズル、７０…氷。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for welding metal piping including stainless steel piping and a nozzle for injecting a shielding gas for welding.
[0002]
[Prior art]
Conventionally, when stainless steel pipes are butt-welded to each other, argon (Ar) is used to prevent mechanical and chemical deterioration of the metal due to oxygen and nitrogen in the air penetrating into the weld backside bead. , Helium (He), carbon dioxide gas (CO ₂ ), or other welding shielding gas is injected into the pipe to reduce the oxygen concentration in the pipe.
[0003]
It is necessary to seal the welding shield gas in the vicinity of the welded portion so that the welding shield gas in the pipe does not move from the vicinity of the welded portion, but as the sealing technology, dry ice that becomes the shielding gas for welding during vaporization, Patent Document 1 discloses a known example in which a water-soluble solid for fixing for fixing the dry ice in a pipe is used in combination to simultaneously generate a purge dam and inject a shield gas.
[0004]
In addition, a welding gas is injected into the pipe from the butt weld groove of the pipe, and a bag made of a water-soluble film is inflated in the pipe so that the injected welding gas does not escape. A method for encapsulating is disclosed in Patent Document 2.
[0005]
Patent Document 3 discloses a technique for injecting a welding shield gas through a welding shield gas injection nozzle inserted into a pipe from a welding groove.
[0006]
[Patent Document 1]
JP-A-6-307586 [Patent Document 2]
JP-A-5-245633 [Patent Document 3]
JP-A-9-295147
[Problems to be solved by the invention]
In the technique disclosed in JP-A-6-307586, since dry ice is vaporized and evaporated at the contact surface between the pipe and the dry ice, a water-soluble solid is required to seal the welding shielding gas into the pipe. The technique described in JP-A-5-245633 also requires a bag made of a water-soluble film in the piping.
[0008]
In any case, since the water-soluble material remains in the pipe after welding, it is necessary to wash away the water-soluble material with water. When washing with water, a large amount of water and the momentum of the water are required, so there is a problem that the conventional technology is difficult to use in a piping system in which water remains or is difficult to drain in a tank or piping connected to the piping. .
[0009]
In addition, when the welding shield gas is injected into the pipe, the conventional welding shield gas injection nozzle has a gas outflow opening evenly around the nozzle, so that the welding shield gas is used to weld the pipe. I can't focus on the bevel.
[0010]
In addition, it is conceivable that the pipe is closed only with dry ice and the shielding gas for welding is locally confined in the pipe at a local portion of the welding groove, but in this case, the pipe is in contact with dry ice. When the dry ice is vaporized and evaporated, the above-mentioned function of the containment is lost, and when the pipe is inclined or vertical, the dry ice is vaporized and evaporated at a portion in contact with the pipe, so that the dry ice is inclined downward or vertically. This poses the problem that it moves downward and cannot achieve the local containment of the welding shielding gas in the desired area.
[0011]
Therefore, an object of the present invention is to achieve the local containment of the welding shield gas even when the local containment of the welding shield gas by the water-soluble material is not available or the pipe is inclined or vertical, and to perform pipe welding. It is to provide a welding method that is possible.
[0012]
Another object of the present invention is to provide a welding shield gas injection nozzle capable of efficiently reducing the oxygen concentration in the pipe near the welding groove of the pipe.
[0013]
[Means for Solving the Problems]
The means to solve the problem is to install dry ice so as to close the inside of the pipe, create a wall in the pipe where the welding shield gas is difficult to escape, and cool the dry ice wall together with the pipe from the outer circumference of the pipe. In addition, a welding shield gas back-purge method of injecting a welding shield gas into the pipe is adopted. By such a back-purging method of the welding shield gas, a local space atmosphere in the pipe near the welding point is adopted. The welding method of lowering the oxygen concentration of the pipe than before injecting the shielding gas for welding, and then welding the welding portion of the pipe is adopted.
[0014]
Further, the shield gas injection nozzle for injecting the shield gas for welding into the pipe is provided with a hole for ejecting the shield gas opened in the nozzle on a line passing through the center of the diameter of the shield gas injection nozzle and the diameter from the line. The holes are provided on a line having an angle of ± 45 degrees in the circumferential direction, and the holes are provided in a staggered arrangement in the axial direction of the shield gas injection nozzle so that the holes are unevenly distributed.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Examples of the present invention are as follows. That is, as shown in FIG. 1, the welded end portions 17 of a pair of stainless steel pipes 12 to be butt-welded to each other are joined. The end of the pipe 12 was machined at the welded end 17 to form a weld groove, and the pipe 12 was opened outward at the welded end 17 when the pipes 12 were butted together as shown in FIG. The welding groove portion of the V-shaped cross section appears.
[0016]
Then, the welded joint portion 17 with the weld groove joined is butt-welded from the outer peripheral side of the pipe 12 by TIG (tungsten inert gas) welding. TIG welding is performed while spraying a welding shielding gas such as argon (Ar), helium (He), or carbon dioxide (CO ₂ ) from the outer periphery of the pipe 12 to the welding portion. When performing the butt welding, the cylindrical dry ice 11 molded in advance to the outer diameter equal to the inner diameter of the pipe 12 to be welded is heated by the butt welding portion of each pipe 12 for performing the butt welding. A purge dam of a shield gas for welding is formed in the pipe 12 by inserting the dry ice 11 as a wall in the pipe 12 by inserting the same in the vicinity of the welded portion where the influence is negligible.
[0017]
Thus, the non-welding side space 13 which is the internal space of the pipe 12 far from the welding end portion 17 at the boundary of the wall of the cylindrical dry ice 11, and the welding at the boundary of the wall of the cylindrical dry ice 11. The flow of air to the pipe inner space 14 which is a space closer to the joint end 17 is blocked. Here, the term “blocking” means that the contact portion 15 between the pipe 12 and the dry ice 11 only needs to be close enough to block the flow of air naturally, and does not mean airtight.
[0018]
In order to suppress the vaporization and evaporation of the dry ice 11 during the welding operation, the outer periphery of the pipe 12 of the dry ice installation part is wrapped in a freezing jacket 10 through which liquefied carbon dioxide gas is passed, and after the dry ice 11 is inserted into the pipe 12, the pipe 12 The outer circumference is always cooled by using the freezing jacket 10 as a cooling means.
[0019]
Thereafter, a shielding gas injection nozzle 16 is inserted into the inside 14 of the pipe 12 through a hole formed in the welding joint end portion 17, and argon (Ar), helium (He), carbon dioxide (CO ₂ ), or one of them is used. Is supplied into the pipe by injecting the welding shield gas 18 into the pipe interior space 14 with the mixed gas of the above, and the air in the pipe interior 14 space is replaced by the welding shield gas 18. This replacement lowers the oxygen concentration in the pipe interior 14 and welds the welding grooves of the welded end portions 17 to prevent oxidation of the weld fins on the inner surface of the pipe during this welding.
[0020]
This will be described in more detail below. That is, FIG. 2 shows the details of the portion A which is the tip of the shielding gas injection nozzle 16 in FIG. The shield gas injection nozzle 16 is connected to one end of a gas hose 19, and the other end of the gas hose 19 is connected to a gas cylinder in which the welding shield gas 18 is stored at a higher pressure than the piping internal space 14. . Preferably, the gas hose 19 and the above-mentioned gas cylinder are connected through a flow rate and pressure adjusting mechanism, and the pressure of the welding shielding gas 18 is higher than the pressure in the pipe internal space 14 and is predetermined. It is preferable to control so that the welding shield gas 18 at a flow rate is injected into the pipe internal space 14.
[0021]
The wall of the dry ice 11 and the inner surface of the pipe 12 are not completely closed due to a slight volume reduction in dry ice setting and the processing accuracy of the dry ice, and the entire periphery of the wall of the dry ice 11 and the inner surface of the pipe 12 are not completely closed. When the shielding gas 18 enters the pipe interior space 14, the interior of the pipe interior space 14 has a higher pressure than the interior of the non-welding side space 13, and the air in the piping interior space 14 flows into the non-welding side space 13 to dry ice. Through the imperfectly closed portion between the wall of the pipe 11 and the inner surface of the pipe 12, the inside of the pipe internal space 14 is replaced with the shielding gas 18 for welding.
[0022]
If there is no pressure difference between the inside of the pipe interior space 14 and the inside of the non-weld side space 13, the atmosphere does not easily pass through between the inside of the pipe interior space 14 and the inside of the non-weld side space 13. . Actually, during the welding operation, the welding shield gas 18 is continuously injected into the pipe internal space 14 so that the pressure difference in the state where the pressure in the pipe internal space 14 is high and the pressure in the non-weld side space 13 is low is always maintained. To occur.
[0023]
As shown in FIGS. 2 (a) and 2 (b), the side of the tip of the shield gas injection nozzle 16 which is inserted into the pipe interior space 14 has the welded end 17 welded. In the groove alignment direction and the circumferential direction of the shield gas injection nozzle 16 based on the groove alignment direction, there are six directions at a swing angle of 45 degrees, and fine hole processing is performed in a staggered arrangement in the nozzle axis direction (nozzle longitudinal direction). The shielding gas is intensively injected from the fine hole 20 in the direction of the welding groove at the welding end portion 17 so that the pipe internal space 14 inside the welding end portion 17 shown in FIG. Is replaced with a shielding gas for welding, and a function of generating a gas flow in the pipe interior space 14 for efficient supply of the shielding gas for welding to the welding back seam portion at the time of welding.
[0024]
As described above, the hole 20 of the shield gas injection nozzle 16 has the diameter of the shield gas injection nozzle 16 in the first section (XX section) orthogonal to the line C indicating the axis of the shield gas injection nozzle 16. And a second cross section (Y-Y cross section) orthogonal to a line C indicating the axis of the shield gas injection nozzle at a position different from the position of the first cross section at a position different from the position of the first cross section. The holes are arranged unevenly on the line B at an angle of ± 45 degrees in the circumferential direction.
[0025]
In order to confirm the effect of the arrangement of the fine holes 20 of the shield gas injection nozzle 16 of the present invention shown in FIGS. 2 (a) and 2 (b), as shown in FIGS. FIG. 4 shows the results of comparison and verification with a conventional shield gas injection nozzle 16a in which fine holes 30 are uniformly processed in the circumferential direction.
[0026]
In FIG. 4, the nozzle A is shown in FIGS. 3 (a) and 3 (b) with two pipes 12 having a length of 500 mm, an inner diameter of 106.3 mm, and an outer diameter of 114.3 mm open at the end. The conventional type shown in FIG. 2 is used as a nozzle, the nozzle B is used as a nozzle of the present invention shown in FIGS. 2A and 2B, and argon (Ar) gas, which is an inert gas, is injected at a flow rate of 10 L / min. Of the oxygen concentration meter (41-43 in the figure). As is apparent from this figure, at the same welding shield gas injection flow rate, the nozzle of the present invention efficiently reduces the oxygen concentration around the welding end portion 17 to 0.1% as compared with the conventional type. It was confirmed that it was done. At this time, as shown in FIGS. 3A and 3B, the direction of the line B of the nozzle B was directed to the direction of the welding groove alignment portion of the welding end portion 17.
[0027]
Next, in order to determine the maximum diameter of the applicable pipe diameter in the method of the present invention shown in FIG. 1, a back purge by measuring the oxygen concentration inside the pipe 12 was performed using a test body shown in FIG. Was confirmed. With respect to the pipe 12 supposed to be a horizontally installed welding target shown in FIG. 5, the center is assumed to be a welding groove alignment position of the welding joint end portion 17, and the shielding gas injection shown in FIGS. The nozzle 16 is set, the oxygen concentration meter 51-56 is set at the center of the pipe centering on the welding groove at the welding end portion 17, and the oxygen concentration distribution in the pipe inner space 14 is measured in the pipe axis direction. It can be measured as a distribution.
[0028]
Further, dry ice 11 whose outer diameter was adjusted to the inner diameter of the cylindrical pipe 12 was set at both ends of the horizontally installed pipe 12. As shown in FIG. 5, the set position is such that the surface of the wall of the dry ice 11 on the side of the welding end 17 is located 500 mm from the position of the welding groove at the welding end 17. The pipe 12 is a SUS304TP stainless steel pipe having a nominal pipe diameter of 100A (inner diameter of 106.2 mm).
[0029]
The outer peripheral surface of the pipe 12 at the set point of the dry ice 11 is covered with a freezing jacket 10 through which liquefied carbon dioxide gas is passed, so that the dry ice 11 can sufficiently function as a purge dam during the welding operation time required by the actual machine. The evaporation and volume reduction of the ice 11 were suppressed.
[0030]
Table 1 is a table showing the elapsed time of the back purge and the measured value of each oxygen concentration in the test specimen shown in FIG. Back purge was achieved in a state where oxygen concentration was reduced and pipe welding was possible at an elapsed time of 4 min, and a back shield with a welding shield gas was secured stably for 240 min thereafter, and applied to pipe welding in actual equipment It was confirmed that it was possible. After setting the dry ice, the welding shield gas injection start time was set to 0 min. Thereafter, the welding shield gas was always injected into the pipe interior space 14 through the shielding gas injection nozzle 16. The shielding gas for welding at this time is argon (Ar) gas, and the flow rate is 10 L / min.
[0031]
[Table 1]

[0032]
FIG. 6 shows an operation procedure of pipe welding in an actual machine using the present invention. After the safety check 600 of the pipe welding work place is performed, the freezing jacket 10 is set 601 at a position where the heat influence from the pipe welded portion, which is the welding groove alignment position of the welding end portion 17, is negligible. I do. Thus, the freezing is started 602, and the pipe 12 itself is cooled in advance to suppress the slipping of the dry ice 11 on the pipe contact surface and the vaporization volume reduction when the dry ice 11 is set in the pipe 12.
[0033]
Next, it is determined whether or not the pipe 12 has a gradient. If the pipe 12 has a gradient, a columnar ice 70 having an outer diameter equal to the inner diameter of the pipe 12 is set 604 in the pipe 12, and If there is no gradient in 12, the setting of the columnar ice 70 in the pipe 12 is not performed. The necessity of setting the ice is determined by the determination that the pipe slope is present 603, and by setting the ice, the ice 70 receives the dry ice 11 which is displaced in the gradient descending direction and slides in the pipe 12 of the dry ice 11. Can be prevented. Next, a cylindrical dry ice 11 whose outer diameter is adjusted to the inner diameter of the pipe 12 is set 605 in the pipe 12.
[0034]
FIG. 7 shows a state where the dry ice 11 and the ice 70 are installed in a vertical pipe having a pipe 12 having a gradient of 90 degrees. An ice 70 on a cylinder is set in the vertical direction of the pipe 12 in the direction in which the dry ice 11 falls so as to match the inner diameter of the pipe 12. The inner surface 71 of the pipe, which serves as a contact point with ice at the time of the setting, is sufficiently cooled in advance by the freezing jacket 10 from the outer peripheral surface of the pipe, and frost is generated by water vapor in the air. Glued to the inner surface. When it is difficult to adhere, moisture is given to the inner surface 71 of the pipe by spraying or the like toward the inner surface 71 of the pipe to achieve the adhesion.
[0035]
After the setting 605 of the dry ice 11 in the pipe 12 is performed on each of the pair of pipes 12 to be subjected to the butt welding in this manner, the pipe assembling work 606 as the welding groove alignment of the welding joint end 17 is performed. Do. After that, a small hole is made in a welding groove fitting portion of the welding joint end portion 17 of the pair of pipes by a pipe hole opening work 606, and a shield gas injection nozzle 16 is inserted into the small hole to form a welding joint end portion 17. 608 is performed.
[0036]
Further, as a quality assurance at the time of pipe welding, an oxygen concentration measurement nozzle setting work 609 for inserting and setting an oxygen concentration meter into the pipe 12 is also performed so that a change in the oxygen concentration at the time of welding can be confirmed. Thereafter, the welding shield gas is injected from the shielding gas injection nozzle 16 into the pipe interior space 14 through the shielding gas injection nozzle, that is, the back purge gas injection 611 is performed to achieve a desired oxygen concentration that does not adversely affect welding. An oxygen concentration drop 612 confirmation is performed to confirm that it has become no longer.
[0037]
When it is confirmed that the desired oxygen concentration has been obtained, next, circumferential welding 613 is performed from the outer circumferential side of the pipe 12 by TIG welding to the welding groove alignment portion of the welding end portion 17. While the girth welding 613 is performed, the welding shielding gas is continuously injected into the pipe internal space 14 to suppress the increase in the oxygen concentration as much as possible. The cooling of the pipe 12 by the freezing jacket 10 is continued even during welding, and the liquefaction of the ice 70 and the vaporization and evaporation of the dry ice 11 are suppressed as much as possible, so that the increase in the oxygen concentration in the pipe internal space 14 is reduced with a small shielding gas flow rate for welding. Suppress.
[0038]
If the oxygen concentration does not drop to the desired oxygen concentration in the determination of the oxygen concentration decrease 612, the steps from the freezing jacket setting 601 to the oxygen concentration decrease 612 shown in FIG. To do.
[0039]
In the case where the ice 70 is set in the pipe 12 as shown in FIG. 7, even when the dry ice 11 is set, a small amount of vaporization occurs and the processing accuracy of the ice 70 causes The ice 11 and the ice 70 are not in close contact with each other in an airtight manner, and a non-hermetic portion is generated in the portion, and the pipe 12 cannot be completely closed by the dry ice 11 and the ice 70. When the welding shielding gas is injected into the piping interior space 14 from above, the air in the piping interior 14 flows out of the above-mentioned non-airtight portion due to the pressure difference between the piping interior space 14 and the outside, and the piping by the welding shielding gas is used. The inside of the internal space 14 can be replaced.
[0040]
Whether or not the inside of the pipe inner space 14 can be replaced with the desired oxygen concentration by the welding shield gas can be known by measuring with an oxygen concentration meter. If the relationship between the oxygen concentration and the oxygen concentration is known as shown in Table 1, the use of an oxygen concentration meter is not essential.
[0041]
In FIG. 6, when the welding groove circumferential welding 613 proceeds and immediately before the end, the shield gas injection nozzle and the oxygen concentration meter are pulled out from the pipe 12 and removed, and immediately the shield gas injection nozzle and the oxygen concentration are removed by TIG welding. After removing the gauge, the welding groove around the hole remaining in the pipe 12 and the shield gas injection nozzle is closed.
[0042]
Thereafter, the freezing jacket 10 is removed from the pipe 12, and the dry ice 11 is naturally vaporized. If the ice 70 is also used, the ice 70 is naturally melted and returned to the liquid. When the ice 70 is used, the amount of the ice 70 can be reduced by using the ice 70 together with the dry ice 11, and the amount of the melted liquid is extremely small as compared with the drainage generated by flushing the piping. Do it.
[0043]
As described above, when a wall is formed in the pipe 12 using the dry ice 11 or the dry ice 11 and the ice 70 so that the welding shield gas does not escape from the vicinity of the welded portion, a pair of butt-welded parts is formed. A wall may be formed for the entire pipe 12, and a valve may be present near the weld to serve as a wall by closing the valve, the pipe may be vertical, or for some reason, a pair of pipes 12 may be formed. The wall may be set in the pipe by using dry ice 11 or dry ice 11 and ice 70 only for one pipe 12. Further, the welding shield gas may be injected into the pipe from the welding end 17, but the welding shield gas 18 may be injected from the end of the pipe 12 in the direction of the arrow shown in FIG. To lower the oxygen concentration of the atmosphere inside the pipe at the welding connection end portion 17.
[0044]
Further, the position where the oxygen concentration meter is inserted into the pipe 12 may be the welded end 17 of the pipe. In this case, a hole may be made in the welding joint end portion 17 where the pipes are butted with each other, and the oxygen concentration meter may be inserted into the pipe 12 through the hole. Also in this case, the oxygen concentration in the space inside the pipe at the welding end portion 17 is measured and confirmed with an oxygen concentration meter, and when the oxygen concentration does not significantly affect the welding backwash even when welding is performed, The welded end 17 is welded. The hole is finally filled by welding after removing the oximeter from the pipe.
[0045]
As described above, in the embodiment of the present invention, since dry ice that evaporates and evaporates naturally is used as the wall of the back purge dam at the time of pipe welding, there is no need to perform water flushing after pipe welding. A back-purging method for piping welds to which water flushing cannot be applied becomes possible. Further, in the embodiment of the present invention, a local back-purge method is provided, and pipe welding can be performed with a very small amount of welding shielding gas as compared with back-purging and welding the entire pipe system. And the economy is improved.
[0046]
【The invention's effect】
As described above, according to the present invention, since dry ice that evaporates and evaporates naturally is used as a wall for storing the welding shielding gas in the pipe during pipe welding, water washing after pipe welding cannot be applied. The welding shield gas can also be filled into the pipe weld at the local portion of the pipe corresponding to the pipe weld.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a pipe for explaining a pack purging method at the time of pipe butt welding according to an embodiment of the present invention.
FIGS. 2A and 2B are enlarged sectional views of a shielding gas injection nozzle used in an embodiment of the present invention, FIG. 2A is a longitudinal sectional view of the nozzle, and FIG. 2B is a sectional view of FIG. It is XX sectional drawing, (c) drawing is YY sectional drawing of (a) drawing.
3A and 3B are enlarged cross-sectional views of a conventional shielding gas injection nozzle, in which FIG. 3A is a cross-sectional view in the longitudinal direction of the nozzle, and FIG. 3B is a cross-sectional view taken along line XX of FIG. FIG. 3C is a sectional view taken along line YY of FIG.
FIG. 4 is a comparative explanatory view of the effect of reducing the oxygen concentration in a pipe using the conventional type and the shield gas injection nozzle of the present invention.
FIG. 5 is a diagram showing a test body simulating the present invention for application to an actual machine.
FIG. 6 is a diagram showing a flow of a butt welding operation according to the present invention.
FIG. 7 is a diagram when the present invention is applied to a vertical pipe.
[Explanation of symbols]
10: Freezing jacket, 11: Dry ice, 12: Piping, 16: Shield gas injection nozzle, 70: Ice.

Claims

Dry ice is installed inside at least one of the two pipes that are welded to each other, away from a welding point, and the pipe part surrounding the dry ice is cooled from the outer circumference of the pipe while a welding shield is provided in the pipe. A welding method of supplying a gas, replacing air in a pipe inside the welding location with the shielding gas for welding, and welding the welding location in the replaced state.

Prior to performing butt welding of two pipes, a cylindrical dry ice is installed inside the pipe, the pipe portion surrounding the dry ice is cooled from the outer circumference of the pipe, and a shielding gas for welding is provided in the pipe. It is supplied from a welding joint end of the pipe via a shielding gas injection nozzle inserted into the pipe, and replaces air in the pipe inside the welding joint end of the pipe with the welding shield gas, A welding method for welding a welding joint end of the pipe in a replaced state.

The welding method according to claim 1 or 2, wherein the dry ice is stopped by the ice adhered to the inner surface of the pipe.

In a shielding gas injection nozzle having a plurality of holes for supplying a welding shielding gas in a pipe,
The hole is formed on a line passing through the center of the diameter of the shield gas injection nozzle in a first cross section orthogonal to the axis of the shield gas injection nozzle, and the axis of the shield gas injection nozzle at a position different from the position of the first cross section. A shield gas injection nozzle in which the holes are non-uniformly arranged at a second cross section orthogonal to the above and on a line at an angle of ± 45 degrees in the circumferential direction of the diameter from the line.