JP3825213B2

JP3825213B2 - Ultrasonic flaw detection method for pipe welded joints

Info

Publication number: JP3825213B2
Application number: JP32164899A
Authority: JP
Inventors: 新二野口; 宗昭芝山; 正純岩田
Original assignee: Shikoku Research Institute Inc; Shikoku Electric Power Co Inc
Current assignee: Shikoku Research Institute Inc; Shikoku Electric Power Co Inc
Priority date: 1999-11-11
Filing date: 1999-11-11
Publication date: 2006-09-27
Anticipated expiration: 2019-11-11
Also published as: JP2001141705A

Description

【０００１】
【発明の属する技術分野】
この発明は、配管の溶接継手のように、内表面の凹凸や引張残留応力や冶金的な変質に起因して、溶接継手近傍の内面から発生する振動疲労割れや応力腐食割れを外部から推定し、製造者においては出荷の可否を、使用者においては取り替えの要否を判断するための情報を得られるようにした配管溶接継手の超音波探傷方法に関するものである。
【０００２】
【従来の技術】
配管に生じる割れは、その深さが管厚の１／１０以上に達すると、それまでに費やした期間よりも短い期間で急激に成長し、配管を貫通するおそれがあることが知られている。そのため、深さが管厚の１／１０程度以下の比較的浅い割れを検出し得るようにすることが望まれている。
【０００３】
配管の内面の割れに対しては、現在、超音波を入射して割れからの反射波（エコー）を検知する超音波探傷法が主流となっている。具体的には、図１５（ａ）に示すように、超音波探触子１を配管２の割れ３が存在する可能性の高い位置に押し当て、２０゜〜３０゜の拡がり（発散角）で超音波４を入射し、割れ３によって反射された反射波５の音圧の変化を図１５（ｂ）に示すような電気信号に変え、そのピーク値を計測する。そして、予め確認しておいた割れ３の深さと電気信号のピーク値との関係を参照して、上記位置における割れ３の深さを推定する。その後、上記計測を位置を変えて多数回行い、割れ３の深さと拡がりを求めて行くようにする。なお、図１５中、符号６は溶接継手である。
【０００４】
【発明が解決しようとする課題】
しかしながら、このような従来の超音波探傷手段では、超音波４の発散角が２０゜〜３０゜の標準的な超音波探触子１が使用されているが、管厚の１／１０相当の浅い割れ３、或いは、０．５ｍｍ以下の浅い割れ３から得られる音圧は低いため、信号とノイズとの判別が難しかった。
【０００５】
そのため、図１６（ａ）に示すように、発散角が５゜〜１０゜と狭い集束型の超音波探触子７を使用して、割れ３から強い反射音圧を得ることも行われたが、視野が狭いため、管厚相当の距離で溶接線に近付いたり遠ざかったりする、いわゆる位置の揺らぎがある現実の割れ３を見落すことがあった。また、発散角が狭いため、多数の凹凸面を有してジグザグ状を呈している現実の割れ３から安定した反射音圧を得ることが難しいなどの問題があり、広くは用いられなかった。
【０００６】
そこで、本発明の目的は、上記の問題点を解消し、配管の内面に発生する微小な割れを精度良く計測することのできる配管溶接継手の超音波探傷方法を提供することにある。
【０００７】
【課題を解決するための手段】
上記課題を解決するために、請求項１に記載された発明では、配管の円周方向へ延びる溶接継手に対し、溶接継手に沿って円周方向へ位置を移動しつつ配管の外面側から超音波を入射して割れからの反射波を検知し割れを計測する配管溶接継手の超音波探傷方法において、溶接継手近傍の割れが推測される位置と超音波の入射角とに基づき溶接継手に対し超音波探触子を置くべき基点までの距離を定め、超音波の発散角が５゜〜１０゜と狭い集束型超音波探触子を配管外面の溶接継手から管軸方向へ上記距離を有した基点位置に配置し、前記集束型超音波探触子を円周方向へ１゜〜５゜の微小ピッチずつ位置を移動しつつ全周に亘り走査させ、溶接継手に対し管軸方向から超音波を入射することにより得られた反射波と、溶接継手に対し管軸方向から５゜〜１５゜傾斜させて超音波を入射することにより得られた反射波と、溶接継手に対し管軸方向から−５゜〜−１５゜傾斜させて超音波を入射することにより得られた反射波との３種類の反射波を計測し、同一の到達位置からの上記３種類の反射波のうちの最大値を採用して割れの形状を推定することを特徴としている。
【０００８】
このように構成された請求項１にかかる発明によれば、集束型超音波探触子を用いることにより、割れから高い反射音圧が得られるので、信号とノイズとを確実に判別して深さが管厚の１／１０程度以下の微小な割れを検知することができるようになる。
【０００９】
集束型超音波探触子を円周方向へ１゜〜５゜の微小ピッチずつ位置を移動しつつ全周に亘り走査させることにより、全周を漏れなく計測することが可能となる。
【００１０】
超音波を管軸方向から入射した反射波と、管軸方向から５゜〜１５゜傾斜させて入射した反射波と、管軸方向から−５゜〜−１５゜傾斜させて入射した反射波との３種類の反射波のうちの最大値を採用することにより、ジグザグ状を呈している現実の割れから安定した反射音圧を得ることができるようになる。
【００１１】
以上により、配管の内面に発生する微小な割れを確実且つ精度良く計測することが可能となる。
【００１２】
請求項２に記載された発明では、配管の管軸方向へ延びる溶接継手に対し、溶接継手に沿って管軸方向へ位置を移動しつつ配管の外面側から超音波を入射して割れからの反射波を検知し割れを計測する配管溶接継手の超音波探傷方法において、溶接継手近傍の割れが推測される位置と超音波の入射角とに基づき溶接継手に対し超音波探触子を置くべき基点までの距離を定め、超音波の発散角が５゜〜１０゜と狭い集束型超音波探触子を配管外面の溶接継手から円周方向へ上記距離を有した基点位置に配置し、前記集束型超音波探触子を管軸方向へ１ｍｍ〜２ｍｍの微小ピッチずつ位置を移動しつつ溶接継手の全長に亘り走査させ、溶接継手に対し円周方向から超音波を入射することにより得られた反射波と、溶接継手に対し円周方向から５゜〜１５゜傾斜させて超音波を入射することにより得られた反射波と、溶接継手に対し円周方向から−５゜〜−１５゜傾斜させて超音波を入射することにより得られた反射波との３種類の反射波を計測し、同一の到達位置からの上記３種類の反射波のうちの最大値を採用して割れの形状を推定することを特徴としている。
【００１３】
このように構成された請求項２にかかる発明によれば、集束型超音波探触子を用いることにより、割れから高い反射音圧が得られるので、信号とノイズとを確実に判別して深さが管厚の１／１０程度以下の微小な割れを検知することができるようになる。
【００１４】
集束型超音波探触子を管軸方向へ所要のピッチずつ位置を移動しつつ溶接継手の全長に亘り走査させることにより、溶接継手の全長を漏れなく計測することが可能となる。
【００１５】
超音波を円周方向から入射した反射波と、円周方向から５゜〜１５゜傾斜させて入射した反射波と、円周方向から−５゜〜−１５゜傾斜させて入射した反射波との３種類の反射波のうちの最大値を採用することにより、ジグザグ状を呈している現実の割れから安定した反射音圧を得ることができるようになる。
【００１６】
以上により、配管の内面に発生する微小な割れを確実且つ精度良く計測することが可能となる。
【００１７】
請求項３に記載された発明では、前記基点位置に対し管厚の０．１〜０．３倍の距離だけ溶接継手に近付けた位置と、前記基点位置に対し管厚の０．１〜０．３倍の距離だけ溶接継手に遠ざけた位置とを新たな基点位置として上記請求項１または請求項２の操作を行い、上記３つの基点位置から得られた３種類の最大値の反射波のうちの更に最大値を採用して割れの形状を推定するか、または、上記に加えて、最初の基点位置に対し管厚の０．４〜０．６倍の距離だけ溶接継手に近付けた位置と、最初の基点位置に対し管厚の０．４〜０．６倍の距離だけ溶接継手に遠ざけた位置とを新たな基点位置として上記請求項１または請求項２の操作を行い、上記５つの基点位置から得られた５種類の最大値の反射波のうちの更に最大値を採用して割れの形状を推定することを特徴としている。
【００１８】
このように構成された請求項３にかかる発明によれば、基点位置を管軸方向へ変えて上記請求項１または請求項２の操作を行うことにより、管厚相当の範囲に対し、計測を行うことが可能となる。よって、溶接線に近付いたり遠ざかったりする、いわゆる位置の揺らぎがある現実の割れを漏れなく計測することが可能となる。
【００１９】
【発明の実施の形態】
以下、本発明の具体的な実施の形態について、図示例と共に説明する。
【００２０】
図１〜図５は、この発明の実施の形態を示すものである。なお、前記従来例と同一ないし均等な部分については、同一の符号を付すことにより説明を省略する。
【００２１】
この実施の形態に使用する配管溶接継手の超音波探傷装置は、超音波４の発散角が狭い集束型超音波探触子１１と、特に図示しないが、該集束型超音波探触子１１を溶接継手１２に沿って移動する移動用駆動部と、該移動用駆動部を制御する移動部制御部と、前記集束型超音波探触子１１を溶接継手１２に対して傾斜させる回転駆動部と、該回転駆動部を制御する駆動部制御部と、反射波５の最大値を求める音圧信号ピーク値Ａ／Ｄ変換部と、反射波５の音圧信号と集束型超音波探触子１１の傾斜角１３とを記録する記録部と、反射波５の音圧信号と集束型超音波探触子１１の傾斜角１３とをプロットするプロット部と、各種設定パネルなどとを備えている。
【００２２】
そして、配管２の円周方向３３へ延びる溶接継手１２に対し、溶接継手１２に沿って円周方向３３へ位置を移動しつつ配管２の外面側から超音波４を入射して割れ３からの反射波５を検知し割れ３を計測する場合に、図２（ａ）に示すように、溶接継手１２近傍の割れ３が推測される位置と超音波４の入射角とに基づき溶接継手１２に対し超音波探触子１を置くべき基点位置１４までの距離１５を定める。
【００２３】
次に、超音波４の発散角が狭い集束型超音波探触子１１を配管２外面の溶接継手１２から管軸方向１６へ上記距離１５を有した基点位置１４に配置し、前記集束型超音波探触子１１を円周方向３３へ１゜〜５゜の微小ピッチずつ位置を移動しつつ全周に亘り走査させる。
【００２４】
そして、図１（ｂ）に示すように、溶接継手１２に対し管軸方向１６（溶接継ぎ手１２垂直な方向）から超音波４を入射し、反射波５を得る。また、図１（ｃ）に示すように、溶接継手１２に対し管軸方向１６から５゜〜１５゜傾斜させて超音波４を入射し、反射波５を得る。更に、図１（ｄ）に示すように、溶接継手１２に対し管軸方向１６から−５゜〜−１５゜傾斜させて超音波４を入射し、反射波５を得る。以上により、ほぼ同一の到達位置からの上記３種類の反射波５を計測する。
【００２５】
この場合、一箇所で、管軸方向１６から超音波４を入射する操作と、管軸方向１６から５゜〜１５゜傾斜させて超音波４を入射する操作と、管軸方向１６から−５゜〜−１５゜傾斜させて超音波４を入射する操作との全てを行ってから、集束型超音波探触子１１を円周方向３３へ走査させるようにしても良い。
【００２６】
或いは、管軸方向１６から超音波４を入射する操作を行いつつ集束型超音波探触子１１を円周方向３３へ走査した後、管軸方向１６から５゜〜１５゜傾斜させて超音波４を入射する操作を行いつつ集束型超音波探触子１１を円周方向３３へ走査させ、最後に、管軸方向１６から−５゜〜−１５゜傾斜させて超音波４を入射する操作を行いつつ集束型超音波探触子１１を円周方向３３へ走査させるようにしても良い。
【００２７】
なお、集束型超音波探触子１１を傾斜させた場合の集束型超音波探触子１１の位置は、集束型超音波探触子１１を傾斜させたことによる超音波４の到達位置に修正しておく。
【００２８】
但し、集束型超音波探触子１１の傾斜角１３が小さい場合や、集束型超音波探触子１１の入射角が４５゜以下の場合には、集束型超音波探触子１１の傾斜による超音波４の到達位置と集束型超音波探触子１１の位置とのズレ量は小さいので、位置の修正操作は省略しても良い。また、比較的深い割れ３を対照とする場合には、割れ３の長さの計測誤差の許容範囲が大きいので、位置の修正操作は省略できる。
【００２９】
そして、最後に、図１（ｅ）に示すように、ほぼ同一の到達位置からの上記３種類の反射波５のうちの最大値を採用して、割れ３と位置との関係をプロットすることにより、割れ３の形状を推定する。
【００３０】
更に、上記に加えて、前記基点位置１４に対し管厚の０．１〜０．３倍の距離だけ溶接継手１２に近付けた位置１７と、前記基点位置１４に対し管厚の０．１〜０．３倍の距離だけ溶接継手１２から遠ざけた位置１８とを新たな基点位置としてそれぞれ上記操作を行う。
【００３１】
必要に応じて更に、最初の基点位置１４に対し管厚の０．４〜０．６倍の距離だけ溶接継手１２に近付けた位置１９と、最初の基点位置１４に対し管厚の０．４〜０．６倍の距離だけ溶接継手１２から遠ざけた位置２０とを新たな基点位置としてそれぞれ上記操作を行う。
【００３２】
そして、同一の位置から得られた３種類または５種類の反射波５のうちの最大値を採用して割れ３の形状を推定する。
【００３３】
次に、この実施の形態の作用について説明する。
【００３４】
配管溶接継手１２の超音波探傷装置は、図１、図２に示すように、集束型超音波探触子１１が発散角の狭い超音波４を配管２へ入射し、溶接継手１２近傍に発生した割れ３からの反射波５を受信する。集束型超音波探触子１１は、ビームの拡がりがほぼ一定しており、図３に示すように、約±１０゜の指向性を有している。移動部制御部は移動用駆動部へ制御信号を送って集束型超音波探触子１１を溶接継手１２に沿って所要のピッチずつ移動させる。駆動部制御部は回転駆動部へ制御信号を送って集束型超音波探触子１１を傾斜させる。
【００３５】
そして、音圧信号ピーク値Ａ／Ｄ変換部が、同一位置についての反射波５のうちの最大値を求める。更に、記録部が反射波５の音圧信号と集束型超音波探触子１１の傾斜角１３とを記録し、プロット部がこれをプロットする。
【００３６】
このように、集束型超音波探触子１１を用いることにより、割れ３から高い反射音圧が得られるので、信号とノイズとを確実に判別して微小な割れ３を検知することができるようになる。
【００３７】
集束型超音波探触子１１を円周方向３３へ１゜〜５゜の微小ピッチずつ位置を移動しつつ全周に亘り走査させることにより、全周を漏れなく計測することが可能となる。
【００３８】
超音波４を管軸方向１６から入射した反射波５と、管軸方向１６から５゜〜１５゜傾斜させて入射した反射波５と、管軸方向１６から−５゜〜−１５゜傾斜させて入射した反射波５との３種類の反射波５のうちの最大値を採用することにより、多数の凹凸面を有してジグザグ状を呈している現実の割れ３から安定した反射音圧を得ることができるようになる。
【００３９】
即ち、現実の割れ３は、図１に示すように、直径１ｍｍ〜５ｍｍの小平面２１〜２３の集合体となっており、約半数は、溶接継手１２に対し１０゜以上の傾きを有しているが、そのほとんどは２０゜以内の傾きとなっているので、超音波４を管軸方向１６から±５゜〜±１５゜傾斜させて入射させることにより、ほとんどの割れ３を計測することが可能となる。なお、図４に示すように、超音波４を傾斜させずに入射させるのみであると、１０゜以上の傾きを有する割れ３から十分な反射音圧を得ることができない。
【００４０】
以上により、配管２の内面に発生する微小な割れ３を確実且つ精度良く計測することが可能となる。
【００４１】
また、基点位置１４を、管厚の±０．１〜±０．３倍、或いは更に、管厚の±０．４〜±０．６倍管軸方向１６へ変えて上記の操作を行うことにより、管厚相当の範囲に対し、計測を行うことが可能となる。よって、図５に示すように、溶接弱点部の軸方向のバラツキに依存して溶接線（溶接継手１２）に近付いたり遠ざかったりする、いわゆる位置の揺らぎ（イ≠ロ≠ハ≠ニ）がある現実の割れ３を漏れなく計測することが可能となる。なお、溶接弱点部とは、開先の溶け込み不足や、溶接止端部の突出や、溶接中に４００℃〜６００℃の温度域に長時間保たれたことにより生じた変質部などである。
【００４２】
なお、本発明の他の実施の形態として、配管２の管軸方向１６へ延びる溶接継手１２に対し、溶接継手１２に沿って管軸方向１６へ位置を移動しつつ配管２の外面側から超音波４を入射して割れ３からの反射波５を検知し割れ３を計測する場合に適用することが可能である。
【００４３】
この場合には、溶接継手１２近傍の割れ３が推測される位置と超音波４の入射角とに基づき溶接継手１２に対し超音波探触子１を置くべき基点位置１４までの距離１５を定め、超音波４の発散角が狭い集束型超音波探触子１１を配管２外面の溶接継手１２から円周方向３３へ上記距離１５を有した基点位置１４に配置し、前記集束型超音波探触子１１を管軸方向１６へ微小ピッチ、例えば、１ｍｍ〜２ｍｍずつ位置を移動しつつ溶接継手１２の全長に亘り走査させ、溶接継手１２に対し円周方向３３から超音波４を入射することにより得られた反射波５と、溶接継手１２に対し円周方向３３から５゜〜１５゜傾斜させて超音波４を入射することにより得られた反射波５と、溶接継手１２に対し円周方向３３から−５゜〜−１５゜傾斜させて超音波４を入射することにより得られた反射波５との３種類の反射波５を計測し、ほぼ同一の到達位置からの上記３種類の反射波５のうちの最大値を採用して、割れ３と位置との関係をプロットすることにより、割れ３の形状を推定するようにする。
【００４４】
このように、配管２の管軸方向１６へ延びる溶接継手１２に対して適用した場合でも、集束型超音波探触子１１を用いることにより、割れ３から高い反射音圧が得られるので、信号とノイズとを確実に判別して微小な割れ３を検知することができるようになる。
【００４５】
集束型超音波探触子１１を管軸方向１６へ微小ピッチずつ位置を移動しつつ溶接継手１２の全長に亘り走査させることにより、溶接継手１２の全長を漏れなく計測することが可能となる。
【００４６】
超音波４を円周方向３３から入射した反射波５と、円周方向３３から５゜〜１５゜傾斜させて入射した反射波５と、円周方向３３から−５゜〜−１５゜傾斜させて入射した反射波５との３種類の反射波５のうちの最大値を採用することにより、ジグザグ状を呈している現実の割れ３から安定した反射音圧を得ることができるようになる。
【００４７】
以上により、配管２の内面に発生する微小な割れ３を確実且つ精度良く計測することが可能となる。
【００４８】
【実施例】
以下に、本発明の実施例を説明する。
（実施例１）
呼び径が２０ｍｍ、耐圧が１６０キロの配管２の内面に深さが、それぞれ、
０．５ｍｍ、１．０ｍｍ、１．５ｍｍ、２．０ｍｍ、２．５ｍｍ、３．０ｍｍ、幅が０．５ｍｍのスリット状の人工欠陥を設け、配管２の外面に対し、入射角が７０゜、焦点直径が２ｍｍ、深さ方向表現の焦点距離が２ｍｍ〜８ｍｍの集束型超音波探触子１１を押し当てて、配管２の円周上を１゜おきに移動させ、上記スリットを狙って超音波４を送受信して、反射波５の音圧信号のピーク値を記録した。
【００４９】
その結果、図６に示すように、ノイズが数％であり、０．５ｍｍの深さのスリットが明確に認識できることが確認された。
【００５０】
一方、比較例として、発散角の広い標準の超音波探触子１を用いた場合には、図７に示すように、ｄＢ表示のＣＲＴ画面上で２０％高さのノイズが見られ、０．５ｍｍの深さのスリットは、ノイズに隠されて検出できないことが確認された。
（実施例２）
呼び径が２０ｍｍ、耐圧が１６０キロのステンレスパイプとソケットとで溶接継手１２を作り、濃度が４２％で沸騰状態の塩化マグネシウム水溶液に１．５時間浸漬した。この配管２に対し、実施例１で用いた集束型超音波探触子１１を用い、集束型超音波探触子１１の傾斜角１３が±１０゜、円周方向３３の移動距離（角）が１０゜の条件で走査させた。
【００５１】
その結果、図８に示すように、円周角１０゜〜１００゜の位置で比較的高い反射波５を得た。割れ３の最大深さは２．０ｍｍ（１００％の位置が２ｍｍに相当する）、応力腐食割れ３の長さは角度表示で７５゜となった。これは、図９に示すように、配管２を切断し顕微鏡観察して得られた割れ３の深さとほぼ一致した。一方、集束型超音波探触子１１を傾斜させずに用いた場合には、図１０に示すように、十分な反射音圧が得られず、しかも、６０゜や８０゜の位置で割れ３が検出されなかった。
（実施例３）
呼び径が２０ｍｍ、耐圧が１６０キロのステンレスパイプとソケットとで溶接継手１２を作り、濃度が４２％で沸騰状態の塩化マグネシウム水溶液に１．０時間浸漬した。この配管２に対し、実施例１で用いた集束型超音波探触子１１を用い、集束型超音波探触子１１の傾斜角１３が±１０゜、円周方向３３の移動距離（角）が１゜の条件で走査させた。
【００５２】
その結果、図１１に示すように、円周角２７０゜〜３６０゜の位置でノイズの２倍となる反射波５を得た。校正線図より、割れ３の最大深さは０．６ｍｍ（１００％の位置が２ｍｍに相当する）となった。これは、図１２に示すように、配管２を切断し顕微鏡観察して得られた割れ３の深さ０．２５ｍｍと比較的近いものであった。
【００５３】
一方、比較実施例として、集束型超音波探触子１１を傾斜させずに計測した場合には、図１３に示すように、割れ３の存在が示唆される程度であり、発散角の広い標準の超音波探触子１を用いた場合には、図１４に示すように、ノイズに埋もれていた。
【００５４】
【発明の効果】
以上説明してきたように、請求項１の発明によれば、集束型超音波探触子を用いることにより、割れから高い反射音圧が得られるので、信号とノイズとを確実に判別して深さが管厚の１／１０程度以下の微小な割れを検知することができるようになる。
【００５５】
集束型超音波探触子を円周方向へ１゜〜５゜の微小ピッチずつ位置を移動しつつ全周に亘り走査させることにより、全周を漏れなく計測することが可能となる。
【００５６】
超音波を管軸方向から入射した反射波と、管軸方向から５゜〜１５゜傾斜させて入射した反射波と、管軸方向から−５゜〜−１５゜傾斜させて入射した反射波との３種類の反射波のうちの最大値を採用することにより、ジグザグ状を呈している現実の割れから安定した反射音圧を得ることができるようになる。
【００５７】
以上により、配管の内面に発生する微小な割れを確実且つ精度良く計測することが可能となる。
【００５８】
請求項２の発明によれば、集束型超音波探触子を用いることにより、割れから高い反射音圧が得られるので、信号とノイズとを確実に判別して深さが管厚の１／１０程度以下の微小な割れを検知することができるようになる。
【００５９】
集束型超音波探触子を管軸方向へ所要のピッチずつ位置を移動しつつ溶接継手の全長に亘り走査させることにより、溶接継手の全長を漏れなく計測することが可能となる。
【００６０】
超音波を円周方向から入射した反射波と、円周方向から５゜〜１５゜傾斜させて入射した反射波と、円周方向から−５゜〜−１５゜傾斜させて入射した反射波との３種類の反射波のうちの最大値を採用することにより、ジグザグ状を呈している現実の割れから安定した反射音圧を得ることができるようになる。
【００６１】
以上により、配管の内面に発生する微小な割れを確実且つ精度良く計測することが可能となる。
【００６２】
請求項３の発明によれば、基点位置を管軸方向へ変えて上記請求項１または請求項２の操作を行うことにより、管厚相当の範囲に対し、計測を行うことが可能となる。よって、溶接線に近付いたり遠ざかったりする、いわゆる位置の揺らぎがある現実の割れを漏れなく計測することが可能となる、という実用上有益な効果を発揮し得る。
【図面の簡単な説明】
【図１】（ａ）〜（ｅ）は本発明の実施の形態にかかる集束型超音波探触子を用いた探傷方法を示す図である。
【図２】（ａ）は本発明の実施の形態にかかる集束型超音波探触子を用いて配管溶接継手の割れを計測している状態を示す部分拡大側方断面図、（ｂ）は（ａ）の超音波と反射波の波形を示すグラフである。
【図３】集束型超音波探触子の指向性を示すグラフである。
【図４】（ａ）（ｂ）は比較例として集束型超音波探触子を傾斜させない場合の図１と同様の図である。
【図５】溶接継手近傍の割れの位置の揺らぎを示す斜視図である。
【図６】実施例１にかかるスリット状人工欠陥からの反射波を示すグラフである。
【図７】実施例１の比較例にかかるスリット状人工欠陥からの反射波を示すグラフである。
【図８】実施例２にかかる典型的な応力腐食割れからの反射波を示すグラフである。
【図９】典型的な応力腐食割れの顕微鏡観察による形状を示すグラフである。
【図１０】実施例２の比較例にかかる典型的な応力腐食割れからの反射波を示すグラフである。
【図１１】実施例３にかかる微小な応力腐食割れからの反射波を示すグラフである。
【図１２】微小な応力腐食割れの顕微鏡観察による形状を示すグラフである。
【図１３】実施例３の比較例にかかる集束型超音波探触子を傾斜させない場合の微小な応力腐食割れからの反射波を示すグラフである。
【図１４】実施例３の比較例にかかる標準的な超音波探触子を用いた場合の微小な応力腐食割れからの反射波を示すグラフである。
【図１５】（ａ）は標準的な超音波探触子を用いて配管溶接継手の割れを計測している状態を示す従来例の部分拡大側方断面図、（ｂ）は（ａ）の超音波と反射波の波形を示すグラフである。
【図１６】（ａ）は集束型の超音波探触子を用いて配管溶接継手の割れを計測している状態を示す従来例の部分拡大側方断面図、（ｂ）は（ａ）の超音波と反射波の波形を示すグラフである。
【符号の説明】
２配管
３割れ
４超音波
５反射波
１１集束型超音波探触子
１２溶接継手
１３傾斜角
１４基点位置
１５距離
１６管軸方向
１７位置
１８位置
１９位置
２０位置
３３円周方向[0001]
BACKGROUND OF THE INVENTION
This invention estimates from the outside the vibration fatigue cracks and stress corrosion cracks that occur on the inner surface near the welded joint due to unevenness on the inner surface, tensile residual stress, and metallurgical alteration, such as welded joints in pipes. Further, the present invention relates to an ultrasonic flaw detection method for a pipe-welded joint in which information for determining whether or not shipment is possible for a manufacturer and whether replacement is necessary for a user is obtained.
[0002]
[Prior art]
It is known that cracks that occur in pipes may grow rapidly and penetrate through pipes when the depth reaches 1/10 or more of the pipe thickness, in a period shorter than the period spent so far. . Therefore, it is desired to detect a relatively shallow crack whose depth is about 1/10 or less of the tube thickness.
[0003]
For cracking of the inner surface of a pipe, an ultrasonic flaw detection method in which an ultrasonic wave is incident and a reflected wave (echo) from the crack is detected is currently mainstream. Specifically, as shown in FIG. 15A, the ultrasonic probe 1 is pressed against a position where there is a high possibility that the crack 3 of the pipe 2 is present, and the spread is 20 ° to 30 ° (divergence angle). Then, the ultrasonic wave 4 is incident and the change in the sound pressure of the reflected wave 5 reflected by the crack 3 is changed to an electric signal as shown in FIG. 15B, and the peak value is measured. And the depth of the crack 3 in the said position is estimated with reference to the relationship between the depth of the crack 3 and the peak value of the electric signal which were confirmed beforehand. Thereafter, the above measurement is performed many times at different positions, and the depth and spread of the crack 3 are obtained. In FIG. 15, reference numeral 6 denotes a welded joint.
[0004]
[Problems to be solved by the invention]
However, in such conventional ultrasonic flaw detection means, the standard ultrasonic probe 1 having a divergence angle of the ultrasonic wave 20 of 20 ° to 30 ° is used, which is equivalent to 1/10 of the tube thickness. Since the sound pressure obtained from the shallow crack 3 or the shallow crack 3 of 0.5 mm or less is low, it is difficult to distinguish between a signal and noise.
[0005]
Therefore, as shown in FIG. 16A, a strong reflected sound pressure was obtained from the crack 3 by using a focusing type ultrasonic probe 7 having a narrow divergence angle of 5 ° to 10 °. However, since the field of view is narrow, the actual crack 3 having a so-called position fluctuation that approaches or moves away from the weld line at a distance corresponding to the tube thickness may be overlooked. Further, since the divergence angle is narrow, there is a problem that it is difficult to obtain a stable reflected sound pressure from the actual crack 3 having a large number of uneven surfaces and presenting a zigzag shape, and it has not been widely used.
[0006]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an ultrasonic flaw detection method for a pipe welded joint that can solve the above-described problems and can accurately measure a minute crack generated on the inner surface of the pipe.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, in the invention described in claim 1, with respect to the welded joint extending in the circumferential direction of the pipe, the position is moved in the circumferential direction along the welded joint while moving from the outer surface side of the pipe. In an ultrasonic flaw detection method for pipe welded joints, in which reflected waves from cracks are detected by measuring the incidence of sound waves, the cracks are detected. Determine the distance to the base point where the ultrasonic probe should be placed, and set the ultrasonic divergence angle as narrow as 5 ° to 10 ° between the welded joint on the pipe outer surface and the above-mentioned distance in the tube axis direction. The focused ultrasonic probe is scanned over the entire circumference while moving the position by a fine pitch of 1 ° to 5 ° in the circumferential direction, and the welded joint is superposed from the tube axis direction. The reflected wave obtained by the incident sound wave and the pipe axis against the welded joint Reflected waves obtained by injecting ultrasonic waves at an angle of 5 ° to 15 ° from the direction and obtained by injecting ultrasonic waves at an angle of −5 ° to −15 ° from the tube axis direction with respect to the weld joint. It is characterized in that three types of reflected waves with the reflected wave are measured and the shape of the crack is estimated by adopting the maximum value of the three types of reflected waves from the same arrival position.
[0008]
According to the invention according to claim 1 configured as described above, since the high reflected sound pressure can be obtained from the crack by using the focusing type ultrasonic probe, the signal and the noise are reliably discriminated and the depth is determined. It becomes possible to detect minute cracks of about 1/10 or less of the tube thickness .
[0009]
By scanning the focus type ultrasonic probe over the entire circumference while moving the position in the circumferential direction by a minute pitch of 1 ° to 5 °, the entire circumference can be measured without omission.
[0010]
A reflected wave incident from the tube axis direction, a reflected wave incident at an angle of 5 ° to 15 ° from the tube axis direction, and a reflected wave incident at an angle of −5 ° to −15 ° from the tube axis direction By adopting the maximum value among the three kinds of reflected waves, it is possible to obtain a stable reflected sound pressure from an actual crack presenting a zigzag shape.
[0011]
As described above, it is possible to reliably and accurately measure a minute crack generated on the inner surface of the pipe.
[0012]
In the invention described in claim 2, with respect to the weld joint extending in the pipe axis direction of the pipe, the ultrasonic wave is incident from the outer surface side of the pipe while moving the position in the pipe axis direction along the weld joint from the crack. In an ultrasonic flaw detection method for pipe welded joints that detects reflected waves and measures cracks, an ultrasonic probe should be placed on the welded joint based on the position where cracks are estimated near the welded joint and the incident angle of the ultrasonic wave. The distance to the base point is determined, and a focused ultrasonic probe having a narrow ultrasonic divergence angle of 5 ° to 10 ° is arranged at the base point position having the above distance in the circumferential direction from the welded joint on the outer surface of the pipe, It is obtained by scanning the entire length of the welded joint while moving the position of the focused ultrasonic probe in the pipe axis direction by a minute pitch of 1 mm to 2 mm, and injecting ultrasonic waves from the circumferential direction to the welded joint. 5 ° from the circumferential direction with respect to the reflected wave and the welded joint A reflected wave obtained by injecting ultrasonic waves at an angle of 15 °, and a reflected wave obtained by injecting ultrasonic waves at an angle of −5 ° to −15 ° from the circumferential direction with respect to the weld joint; The three types of reflected waves are measured, and the shape of the crack is estimated by adopting the maximum value of the three types of reflected waves from the same arrival position.
[0013]
According to the invention according to claim 2 configured as described above, since a high reflected sound pressure can be obtained from the crack by using the focusing type ultrasonic probe, the signal and noise are reliably discriminated and the depth is determined. It becomes possible to detect minute cracks of about 1/10 or less of the tube thickness .
[0014]
By scanning the focused ultrasonic probe over the entire length of the welded joint while moving the position in the pipe axis direction by a required pitch, the entire length of the welded joint can be measured without leakage.
[0015]
A reflected wave incident from the circumferential direction, a reflected wave incident at an angle of 5 ° to 15 ° from the circumferential direction, and a reflected wave incident at an angle of −5 ° to −15 ° from the circumferential direction By adopting the maximum value among the three kinds of reflected waves, it is possible to obtain a stable reflected sound pressure from an actual crack presenting a zigzag shape.
[0016]
As described above, it is possible to reliably and accurately measure a minute crack generated on the inner surface of the pipe.
[0017]
In the invention described in claim 3, the position close to the weld joint by a distance of 0.1 to 0.3 times the pipe thickness with respect to the base position, and the pipe thickness of 0.1 to 0 with respect to the base position. The operation according to claim 1 or 2 is performed with the position away from the weld joint by a distance of 3 times as a new base position, and the three kinds of maximum reflected waves obtained from the three base positions are Estimate the shape of the crack by adopting the maximum value of them, or in addition to the above, the position close to the welded joint by a distance 0.4 to 0.6 times the tube thickness relative to the initial base point position Then, the operation according to claim 1 or 2 is performed with the position away from the welded joint by a distance 0.4 to 0.6 times the tube thickness as the new base position, and the above 5 further employs a maximum split of the five kinds of the reflected wave of the maximum values obtained from one base point position It is characterized by estimating the shape.
[0018]
According to the invention according to claim 3 configured as described above, the base point position is changed in the tube axis direction, and the operation according to claim 1 or 2 is performed, thereby measuring the range corresponding to the tube thickness. Can be done. Therefore, it is possible to measure an actual crack with a so-called position fluctuation that approaches or moves away from the weld line without omission.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of the present invention will be described together with illustrated examples.
[0020]
1 to 5 show an embodiment of the present invention. Note that the same or equivalent parts as those in the conventional example are denoted by the same reference numerals and the description thereof is omitted.
[0021]
An ultrasonic flaw detector for a pipe welded joint used in this embodiment includes a focused ultrasonic probe 11 having a narrow divergence angle of the ultrasonic wave 4 and a focused ultrasonic probe 11 that is not particularly illustrated. A moving drive unit that moves along the welded joint 12; a moving unit control unit that controls the moving drive unit; and a rotary drive unit that tilts the focusing ultrasonic probe 11 with respect to the welded joint 12; A drive unit control unit for controlling the rotation drive unit, a sound pressure signal peak value A / D conversion unit for obtaining the maximum value of the reflected wave 5, a sound pressure signal of the reflected wave 5, and the focusing ultrasonic probe 11. Are provided with a recording section for recording the inclination angle 13, a plot section for plotting the sound pressure signal of the reflected wave 5 and the inclination angle 13 of the focusing ultrasonic probe 11, various setting panels, and the like.
[0022]
Then, with respect to the welded joint 12 extending in the circumferential direction 33 of the pipe 2, the ultrasonic wave 4 is incident from the outer surface side of the pipe 2 while moving the position in the circumferential direction 33 along the welded joint 12 and from the crack 3. When detecting the reflected wave 5 and measuring the crack 3, as shown in FIG. 2A, the weld joint 12 is applied to the weld joint 12 based on the position where the crack 3 near the weld joint 12 is estimated and the incident angle of the ultrasonic wave 4. On the other hand, a distance 15 to the base point position 14 where the ultrasonic probe 1 is to be placed is determined.
[0023]
Next, the focusing type ultrasonic probe 11 having a narrow divergence angle of the ultrasonic wave 4 is disposed at the base point position 14 having the distance 15 from the welded joint 12 on the outer surface of the pipe 2 to the pipe axis direction 16, and the focusing type ultrasonic probe 11. The acoustic probe 11 is scanned over the entire circumference while moving the position in the circumferential direction 33 by a minute pitch of 1 ° to 5 °.
[0024]
Then, as shown in FIG. 1 (b), the ultrasonic wave 4 is incident on the welded joint 12 from the pipe axis direction 16 (direction perpendicular to the weld joint 12) to obtain a reflected wave 5. Further, as shown in FIG. 1C, the ultrasonic wave 4 is incident on the welded joint 12 with an inclination of 5 ° to 15 ° from the tube axis direction 16 to obtain a reflected wave 5. Further, as shown in FIG. 1 (d), the ultrasonic wave 4 is incident on the welded joint 12 with an inclination of −5 ° to −15 ° from the tube axis direction 16 to obtain a reflected wave 5. As described above, the three kinds of reflected waves 5 from almost the same arrival position are measured.
[0025]
In this case, the operation of injecting the ultrasonic wave 4 from the tube axis direction 16 at one place, the operation of injecting the ultrasonic wave 4 with an inclination of 5 ° to 15 ° from the tube axis direction 16, and −5 from the tube axis direction 16 It is also possible to scan the focusing ultrasonic probe 11 in the circumferential direction 33 after performing all operations of injecting the ultrasonic wave 4 with an inclination of -15 °.
[0026]
Alternatively, after performing the operation of making the ultrasonic wave 4 incident from the tube axis direction 16, the focused ultrasonic probe 11 is scanned in the circumferential direction 33, and then the ultrasonic wave is inclined by 5 ° to 15 ° from the tube axis direction 16. 4, the focusing-type ultrasonic probe 11 is scanned in the circumferential direction 33 while the operation of injecting 4 is performed, and finally the operation of injecting the ultrasonic wave 4 by tilting by −5 ° to −15 ° from the tube axis direction 16. The focusing type ultrasonic probe 11 may be scanned in the circumferential direction 33 while performing the above.
[0027]
The position of the focused ultrasonic probe 11 when the focused ultrasonic probe 11 is tilted is corrected to the arrival position of the ultrasonic wave 4 by tilting the focused ultrasonic probe 11. Keep it.
[0028]
However, when the inclination angle 13 of the focusing type ultrasonic probe 11 is small or when the incident angle of the focusing type ultrasonic probe 11 is 45 ° or less, the inclination of the focusing type ultrasonic probe 11 depends on the inclination. Since the amount of deviation between the arrival position of the ultrasonic wave 4 and the position of the focusing ultrasonic probe 11 is small, the position correcting operation may be omitted. Further, when the comparatively deep crack 3 is used as a control, the tolerance of the measurement error of the length of the crack 3 is large, so that the position correcting operation can be omitted.
[0029]
Finally, as shown in FIG. 1 (e), the maximum value of the three kinds of reflected waves 5 from almost the same arrival position is adopted, and the relationship between the crack 3 and the position is plotted. Thus, the shape of the crack 3 is estimated.
[0030]
Further, in addition to the above, a position 17 that is close to the welded joint 12 by a distance of 0.1 to 0.3 times the pipe thickness with respect to the base position 14 and a pipe thickness of 0.1 to 0.1 with respect to the base position 14. The above operation is performed with the position 18 away from the weld joint 12 by a distance of 0.3 times as a new base point position.
[0031]
Further, if necessary, a position 19 that is close to the weld joint 12 by a distance 0.4 to 0.6 times the tube thickness with respect to the first base point position 14 and a tube thickness of 0.4 with respect to the first base point position 14. The above operations are performed with the position 20 away from the weld joint 12 by a distance of ~ 0.6 times as a new base point position.
[0032]
And the shape of the crack 3 is estimated by adopting the maximum value of the three or five kinds of reflected waves 5 obtained from the same position.
[0033]
Next, the operation of this embodiment will be described.
[0034]
As shown in FIGS. 1 and 2, the ultrasonic flaw detector for the pipe welded joint 12 is generated in the vicinity of the welded joint 12 when the focused ultrasonic probe 11 enters the ultrasonic wave 4 with a narrow divergence angle into the pipe 2. The reflected wave 5 from the broken crack 3 is received. The focused ultrasonic probe 11 has a substantially constant beam divergence and has a directivity of about ± 10 ° as shown in FIG. The moving unit control unit sends a control signal to the moving drive unit to move the focusing type ultrasonic probe 11 along the weld joint 12 by a predetermined pitch. The driving unit control unit sends a control signal to the rotation driving unit to incline the focusing type ultrasonic probe 11.
[0035]
Then, the sound pressure signal peak value A / D converter determines the maximum value of the reflected waves 5 for the same position. Further, the recording unit records the sound pressure signal of the reflected wave 5 and the inclination angle 13 of the focusing ultrasonic probe 11, and the plotting unit plots this.
[0036]
Thus, since the high reflected sound pressure can be obtained from the crack 3 by using the focusing type ultrasonic probe 11, it is possible to detect the minute crack 3 by reliably distinguishing the signal and the noise. become.
[0037]
By scanning the focus type ultrasonic probe 11 over the entire circumference while moving the position in the circumferential direction 33 by a minute pitch of 1 ° to 5 °, the entire circumference can be measured without omission.
[0038]
The ultrasonic wave 4 is reflected from the tube axis direction 16, the reflected wave 5 is inclined from the tube axis direction 16 by 5 ° to 15 °, and the reflected wave 5 is inclined from the tube axis direction 16 by −5 ° to −15 °. By adopting the maximum value of the three kinds of reflected waves 5 with the incident reflected wave 5, a stable reflected sound pressure can be obtained from an actual crack 3 having a large number of uneven surfaces and having a zigzag shape. Be able to get.
[0039]
That is, as shown in FIG. 1, the actual crack 3 is an aggregate of small planes 21 to 23 having a diameter of 1 mm to 5 mm, and about half of them have an inclination of 10 ° or more with respect to the welded joint 12. However, most of them have an inclination of 20 ° or less, so most of the cracks 3 can be measured by making the ultrasonic wave 4 incident at an angle of ± 5 ° to ± 15 ° from the tube axis direction 16. Is possible. As shown in FIG. 4, if only the ultrasonic wave 4 is incident without being inclined, sufficient reflected sound pressure cannot be obtained from the crack 3 having an inclination of 10 ° or more.
[0040]
As described above, the minute crack 3 generated on the inner surface of the pipe 2 can be reliably and accurately measured.
[0041]
Further, the above operation is performed by changing the base point position 14 to ± 0.1 to ± 0.3 times the tube thickness, or further ± 0.4 to ± 0.6 times the tube thickness, and to the tube axis direction 16. Thus, it is possible to perform measurement on a range corresponding to the tube thickness. Therefore, as shown in FIG. 5, there is a so-called position fluctuation (i ≠ ro ≠ ha ≠ ni) that approaches or moves away from the weld line (welded joint 12) depending on the axial variation of the weld weak point. It is possible to measure the actual crack 3 without omission. In addition, a weld weak point part is a quality change part etc. which arose due to insufficient penetration of a groove | channel, a protrusion of a welding toe part, or being kept in a 400 to 600 degreeC temperature range for a long time during welding.
[0042]
As another embodiment of the present invention, with respect to the welded joint 12 extending in the pipe axis direction 16 of the pipe 2, the position of the pipe 2 in the pipe axis direction 16 is moved along the welded joint 12 from the outer surface side of the pipe 2. It can be applied to the case where the sound wave 4 is incident to detect the reflected wave 5 from the crack 3 and the crack 3 is measured.
[0043]
In this case, a distance 15 to the base position 14 where the ultrasonic probe 1 is to be placed is determined with respect to the weld joint 12 based on the position where the crack 3 near the weld joint 12 is estimated and the incident angle of the ultrasonic wave 4. The focusing type ultrasonic probe 11 having a narrow divergence angle of the ultrasonic wave 4 is disposed at the base point position 14 having the distance 15 in the circumferential direction 33 from the welded joint 12 on the outer surface of the pipe 2, and the focusing type ultrasonic probe is arranged. Scanning the entire length of the welded joint 12 while moving the position of the contactor 11 in the tube axis direction 16 by a minute pitch, for example, 1 mm to 2 mm, and making the ultrasonic wave 4 enter the welded joint 12 from the circumferential direction 33. The reflected wave 5 obtained by the above and the reflected wave 5 obtained by making the ultrasonic wave 4 incident on the welded joint 12 with an inclination of 5 ° to 15 ° from the circumferential direction 33 and the welded joint 12 are circumferential. Tilt from -5 ° to -15 ° from direction 33 Three kinds of reflected waves 5 with the reflected wave 5 obtained by making the wave 4 incident are measured, and the maximum value of the above three kinds of reflected waves 5 from almost the same arrival position is adopted to crack. The shape of the crack 3 is estimated by plotting the relationship between 3 and position.
[0044]
Thus, even when applied to the welded joint 12 extending in the pipe axial direction 16 of the pipe 2, a high reflected sound pressure can be obtained from the crack 3 by using the converging ultrasonic probe 11. It is possible to detect minute cracks 3 by reliably discriminating between noise and noise.
[0045]
By scanning the focused ultrasonic probe 11 over the entire length of the weld joint 12 while moving the position in the tube axis direction 16 by a small pitch, the entire length of the weld joint 12 can be measured without omission.
[0046]
The ultrasonic wave 4 is reflected from the circumferential direction 33, the reflected wave 5 is inclined from the circumferential direction 33 by 5 ° to 15 °, and the reflected wave 5 is inclined from the circumferential direction 33 by −5 ° to −15 °. By adopting the maximum value of the three kinds of reflected waves 5 with the incident reflected wave 5, a stable reflected sound pressure can be obtained from the actual crack 3 having a zigzag shape.
[0047]
As described above, the minute crack 3 generated on the inner surface of the pipe 2 can be reliably and accurately measured.
[0048]
【Example】
Examples of the present invention will be described below.
Example 1
The depth on the inner surface of the pipe 2 having a nominal diameter of 20 mm and a pressure resistance of 160 kg,
A slit-shaped artificial defect of 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm and a width of 0.5 mm is provided, and the incident angle is 70 ° with respect to the outer surface of the pipe 2. The focused ultrasonic probe 11 having a focal diameter of 2 mm and a focal length expressed in the depth direction of 2 mm to 8 mm is pressed and moved on the circumference of the pipe 2 every 1 ° to aim at the slit. The ultrasonic wave 4 was transmitted and received, and the peak value of the sound pressure signal of the reflected wave 5 was recorded.
[0049]
As a result, as shown in FIG. 6, it was confirmed that the noise was several percent and a slit having a depth of 0.5 mm could be clearly recognized.
[0050]
On the other hand, when a standard ultrasonic probe 1 having a wide divergence angle is used as a comparative example, as shown in FIG. 7, 20% high noise is seen on the CRT screen of dB display. It was confirmed that a slit with a depth of 5 mm was hidden by noise and could not be detected.
(Example 2)
A welded joint 12 was made of a stainless steel pipe and socket having a nominal diameter of 20 mm and a pressure resistance of 160 kg, and immersed in an aqueous magnesium chloride solution having a concentration of 42% and boiling for 1.5 hours. The focusing ultrasonic probe 11 used in the first embodiment is used for the pipe 2, and the inclination angle 13 of the focusing ultrasonic probe 11 is ± 10 ° and the moving distance (angle) in the circumferential direction 33. Was scanned under the condition of 10 °.
[0051]
As a result, as shown in FIG. 8, a relatively high reflected wave 5 was obtained at a circumferential angle of 10 ° to 100 °. The maximum depth of the crack 3 was 2.0 mm (100% position corresponds to 2 mm), and the length of the stress corrosion crack 3 was 75 ° in angle display. As shown in FIG. 9, this substantially coincided with the depth of the crack 3 obtained by cutting the pipe 2 and observing under a microscope. On the other hand, when the focusing-type ultrasonic probe 11 is used without being tilted, sufficient reflected sound pressure cannot be obtained as shown in FIG. 10, and cracks 3 are formed at positions of 60 ° and 80 °. Was not detected.
Example 3
A welded joint 12 was made of a stainless steel pipe and socket having a nominal diameter of 20 mm and a pressure resistance of 160 kg, and immersed in a boiling magnesium chloride aqueous solution at a concentration of 42% for 1.0 hour. The focusing ultrasonic probe 11 used in the first embodiment is used for the pipe 2, and the inclination angle 13 of the focusing ultrasonic probe 11 is ± 10 ° and the moving distance (angle) in the circumferential direction 33. Was scanned under the condition of 1 °.
[0052]
As a result, as shown in FIG. 11, a reflected wave 5 having twice the noise was obtained at a circumferential angle of 270 ° to 360 °. From the calibration diagram, the maximum depth of the crack 3 was 0.6 mm (100% position corresponds to 2 mm). As shown in FIG. 12, this was relatively close to the depth of 0.25 mm of the crack 3 obtained by cutting the pipe 2 and observing under a microscope.
[0053]
On the other hand, as a comparative example, when the focused ultrasonic probe 11 is measured without being tilted, as shown in FIG. 13, the presence of the crack 3 is suggested and a standard with a wide divergence angle is provided. When the ultrasonic probe 1 was used, it was buried in noise as shown in FIG.
[0054]
【The invention's effect】
As has been described, according to the first aspect of the present invention, by using a focused ultrasonic probe, since the high reflection sound pressure from cracking resulting, deep and reliably distinguish the signal and the noise It becomes possible to detect minute cracks of about 1/10 or less of the tube thickness .
[0055]
By scanning the focus type ultrasonic probe over the entire circumference while moving the position in the circumferential direction by a minute pitch of 1 ° to 5 °, the entire circumference can be measured without omission.
[0056]
A reflected wave incident from the tube axis direction, a reflected wave incident at an angle of 5 ° to 15 ° from the tube axis direction, and a reflected wave incident at an angle of −5 ° to −15 ° from the tube axis direction By adopting the maximum value among the three kinds of reflected waves, it is possible to obtain a stable reflected sound pressure from an actual crack presenting a zigzag shape.
[0057]
As described above, it is possible to reliably and accurately measure a minute crack generated on the inner surface of the pipe.
[0058]
According to the second aspect of the present invention, since a high reflected sound pressure can be obtained from the crack by using the focusing type ultrasonic probe, it is possible to reliably discriminate between the signal and the noise and the depth is 1 / th of the tube thickness. A minute crack of about 10 or less can be detected.
[0059]
By scanning the focused ultrasonic probe over the entire length of the welded joint while moving the position in the pipe axis direction by a required pitch, the entire length of the welded joint can be measured without leakage.
[0060]
A reflected wave incident from the circumferential direction, a reflected wave incident at an angle of 5 ° to 15 ° from the circumferential direction, and a reflected wave incident at an angle of −5 ° to −15 ° from the circumferential direction By adopting the maximum value among the three kinds of reflected waves, it is possible to obtain a stable reflected sound pressure from an actual crack presenting a zigzag shape.
[0061]
As described above, it is possible to reliably and accurately measure a minute crack generated on the inner surface of the pipe.
[0062]
According to the invention of claim 3, by changing the base point position in the tube axis direction and performing the operation of claim 1 or claim 2, it is possible to measure the range corresponding to the tube thickness. Therefore, it is possible to exert a practically beneficial effect that it is possible to measure an actual crack with a so-called position fluctuation that approaches or moves away from the weld line without omission.
[Brief description of the drawings]
FIGS. 1A to 1E are diagrams showing a flaw detection method using a focused ultrasonic probe according to an embodiment of the present invention.
FIG. 2A is a partially enlarged side cross-sectional view showing a state in which cracks in a pipe welded joint are measured using the focused ultrasonic probe according to the embodiment of the present invention, and FIG. It is a graph which shows the waveform of the ultrasonic wave and reflected wave of (a).
FIG. 3 is a graph showing the directivity of a focused ultrasonic probe.
FIGS. 4A and 4B are views similar to FIG. 1 in a case where the focusing ultrasonic probe is not tilted as a comparative example. FIGS.
FIG. 5 is a perspective view showing fluctuation of a crack position in the vicinity of a welded joint.
6 is a graph showing a reflected wave from a slit-like artificial defect according to Example 1. FIG.
7 is a graph showing a reflected wave from a slit-like artificial defect according to a comparative example of Example 1. FIG.
FIG. 8 is a graph showing reflected waves from a typical stress corrosion cracking according to Example 2.
FIG. 9 is a graph showing the shape of typical stress corrosion cracking observed with a microscope.
10 is a graph showing a reflected wave from a typical stress corrosion cracking according to a comparative example of Example 2. FIG.
11 is a graph showing a reflected wave from a minute stress corrosion crack according to Example 3. FIG.
FIG. 12 is a graph showing the shape of microscopic stress corrosion cracking observed with a microscope.
13 is a graph showing reflected waves from a minute stress corrosion crack when the focusing type ultrasonic probe according to the comparative example of Example 3 is not tilted. FIG.
14 is a graph showing reflected waves from a minute stress corrosion crack when a standard ultrasonic probe according to a comparative example of Example 3 is used. FIG.
15 (a) is a partially enlarged side sectional view of a conventional example showing a state in which a crack of a pipe welded joint is measured using a standard ultrasonic probe, and FIG. 15 (b) is a diagram of (a). It is a graph which shows the waveform of an ultrasonic wave and a reflected wave.
16 (a) is a partially enlarged side sectional view of a conventional example showing a state in which cracks of a pipe welded joint are measured using a focusing type ultrasonic probe, and FIG. 16 (b) is a diagram of (a). It is a graph which shows the waveform of an ultrasonic wave and a reflected wave.
[Explanation of symbols]
2 Piping 3 Crack 4 Ultrasonic wave 5 Reflected wave 11 Focusing ultrasonic probe 12 Weld joint 13 Inclination angle 14 Base point position 15 Distance 16 Pipe axis direction 17 Position 18 Position 19 Position 20 Position 33 Circumferential direction

Claims

Pipes that detect cracks by detecting reflected waves from cracks by entering ultrasonic waves from the outer surface side of the pipe while moving the position along the weld joint in the circumferential direction against the weld joint extending in the circumferential direction of the pipe In the ultrasonic inspection method for welded joints,
Based on the position where cracks in the vicinity of the welded joint are estimated and the incident angle of the ultrasonic wave, the distance to the base point where the ultrasonic probe should be placed on the welded joint is determined.
A focusing type ultrasonic probe having a narrow ultrasonic divergence angle of 5 ° to 10 ° is arranged at the base point position having the above distance from the welded joint on the outer surface of the pipe to the pipe axis direction.
The focused ultrasonic probe is scanned over the entire circumference while moving the position by a minute pitch of 1 ° to 5 ° in the circumferential direction,
Reflected waves obtained by injecting ultrasonic waves into the welded joint from the pipe axis direction and reflected waves obtained by injecting ultrasonic waves into the welded joint at an angle of 5 ° to 15 ° from the pipe axis direction And three kinds of reflected waves, that is, the reflected wave obtained by making the ultrasonic wave incident on the welded joint with an inclination of −5 ° to −15 ° from the tube axis direction,
An ultrasonic flaw detection method for a pipe-welded joint, wherein the crack shape is estimated by adopting the maximum value of the above three kinds of reflected waves from the same arrival position.

Piping that detects cracks by detecting reflected waves from cracks by entering ultrasonic waves from the outer surface side of the pipe while moving the position in the pipe axis direction along the weld joint to the weld joint extending in the pipe axis direction of the pipe In the ultrasonic inspection method for welded joints,
Based on the position where cracks in the vicinity of the welded joint are estimated and the incident angle of the ultrasonic wave, the distance to the base point where the ultrasonic probe should be placed on the welded joint is determined.
A focusing type ultrasonic probe having a narrow ultrasonic divergence angle of 5 ° to 10 ° is arranged at the base point position having the above distance in the circumferential direction from the weld joint on the outer surface of the pipe,
Scanning the entire length of the welded joint while moving the position of the focused ultrasonic probe by a minute pitch of 1 mm to 2 mm in the tube axis direction;
A reflected wave obtained by injecting ultrasonic waves into the welded joint from the circumferential direction and a reflected wave obtained by injecting ultrasonic waves into the welded joint at an angle of 5 ° to 15 ° from the circumferential direction. And three kinds of reflected waves, that is, the reflected wave obtained by making the ultrasonic wave incident on the welded joint with an inclination of −5 ° to −15 ° from the circumferential direction,
An ultrasonic flaw detection method for a pipe-welded joint, wherein the crack shape is estimated by adopting the maximum value of the above three kinds of reflected waves from the same arrival position.

A position close to the welded joint by a distance of 0.1 to 0.3 times the pipe thickness relative to the base position, and a distance of 0.1 to 0.3 times the pipe thickness from the base position to the welded joint. The operation of claim 1 or claim 2 is performed with the new position as a new base position,
Estimate the shape of the crack by adopting the maximum value among the three types of maximum reflected waves obtained from the three base positions,
Alternatively, in addition to the above, a position close to the weld joint by a distance 0.4 to 0.6 times the tube thickness with respect to the initial base point position, and a tube thickness of 0.4 to 0.00 mm with respect to the initial base point position. The operation according to claim 1 or claim 2 is performed with the position away from the weld joint by a distance of 6 times as a new base position,
3. The pipe welding according to claim 1, wherein the shape of the crack is estimated by further adopting a maximum value among the five kinds of reflected waves having the maximum value obtained from the five base point positions. Ultrasonic flaw detection method for joints.