JP3764616B2 - Turbine rotor crack growth prediction method - Google Patents

Description

として与えられる。
【００３１】
ここで、ａ_ｘはタービンロータ表層部からの亀裂深さ、Ｈ_１はタービンロータ表層部硬さ、Ｈ_０は、例えばタービンロータ表層部から深さ２００〜３００μｍにおける硬さ、Ｃは定数をそれぞれ示す。
【００３２】
上式（１）は、タービンロータ表層部の硬さＨ_１と亀裂深さａ_ｘ、例えば表層部から２００〜３００μｍの深さにおける硬さＨ_０との二点間の範囲に亘ってテスト材で実測して作成したマスターカーブである。このマスターカーブは、タービンロータ表層部が軟質層と硬質層とに混在した組織層になっていて、ある程度の深さから硬さを求めることが必要な場合に適用される。
【００３３】
なお、亀裂深さａ_ｘは、以下に示す非破壊的検査法を用いて求めることができる。
【００３４】
第１の亀裂深さａ_ｘの測定方法は、図４に示すように、亀裂部分を跨いで配置した電極１４ａ，１４ｂを介して亀裂から一定の距離に離れた部位における電位差を用いて測定する方法である。電極１４ａ，１４ｂ間を一定の電位差Ｖ_０（照合電極）にしたとき、計測電極間の電位差Ｖは、関数Ｖ＝Ｖ（ａ_ｘ，Ｖ_０）として与えられる。したがって、電位差Ｖを計測すれば、亀裂深さａ_ｘは求めることかできる。
【００３５】
また、第２の亀裂深さａ_ｘの測定方法は、図５に示すように、亀裂部分にビオデンフィルム（プラスチックフィルム）を貼付してもよい。ビデオフィルムは、酢酸メチルにより軟化し、この酢酸メチルの気化とともに硬化して亀裂の形状をレプリカすることができる。また、ビオデンフィルムに代えて紫外線により硬化するプラスチック材を用いてもよい。
【００３６】
また、他の亀裂深さａ_ｘを求める場合、例えば図６に示すように、予めデータベース化した亀裂深さ−亀裂長さ線図、図７に示すように、予めデータベース化した等応力分布線図、あるいは図８に示すように、予めデータベース化した亀裂深さ−亀裂開口量（開口幅）線図を用いてもよい。
【００３７】
また、本実施形態は、上述応力−硬さ線図に限らず、例えば図９および図１０に示すように、バルクハウゼンノイズ法から硬さを求めてもよい。
【００３８】
このバルクハウゼンノイズ法による実施形態は、図９に示すように、被検体１５にパルス発生器１６からのパルスを増幅器１７、センサ１８を介して与え、被検体１５に発生する磁気変化をセンサ１８で検出し、その検出信号を増幅器１９、フィルタ２０を介して周波数解析装置２１で演算し、その演算信号に基づくバルクハウゼンノイズ出力から図１０に示すように、タービンロータ表層部の硬さを求めることができるようになっている。
【００３９】
このバルクハウゼンノイズ法は、強磁性体が磁化される過程で磁壁が不連続に発生、移動する際に生じる磁気ノイズの増減変化が材料の硬さの高低変化に対応する関係にあることに着目したものである。したがって、バルクハウゼンノイズ法は、強磁性体の表層部の硬さを求める場合、有効である。
【００４０】
図１１は、第２ステップ（ＳＴ２）において、各負荷帯の振動応力を求めるに先立ち、その前提となる蒸気タービンの負荷出力と運用モード１，２との関係からタービン動翼を介してタービンロータのフック部に加えられる加振力を算出する蒸気タービン負荷出力−加振力線図である。
【００４１】
蒸気による加振力は、蒸気タービンの負荷出力が一定でも運用モードが異なれば著しく変動する。特に、運転モード１、具体的には３アドミッション方式は、運用モード２、具体的には２アドミッション方式に較べて加振力が高い。また、３アドミッション方式は、蒸気タービンの負荷出力が所定領域の負荷出力になると、高加振力になり、タービンロータに亀裂を発生させる危険域に入る。
【００４２】
このように、運用モード１，２により加振力が変動する中で、変動する加振力を考慮して第２ステップ（ＳＴ２）では、振動応力（応力振幅）σを求める（平均応力でもよい）。
【００４３】
タービンロータの振動応力（応力振幅）σは、図１２に示すように、動翼カバー２２、テノン２３、タービン動翼７、植込み部９、タービンロータ５、フック部１１で構成した実機の蒸気タービンをモデル化し、そのモデルを用いて有限要素法により求める。
【００４４】
このようにして有限要素法によって求めた振動応力σは、図１３に示すように、蒸気タービン負荷に対応させてプロットし、振動応力線図をマスターカーブとして作成する。
【００４５】
一方、第５ステップ（ＳＴ５）で亀裂進展負荷帯を決定するにあたり、応力拡大係数範囲ΔＫと亀裂進展下限界値ΔＫ_ｔｈとが関係するので、先ず、応力拡大係数範囲ΔＫと亀裂進展下限界値ΔＫ_ｔｈは、タービンロータの亀裂進展の開始点となるので、明確に定めておくことが大切であり、図１５を用いて説明する。
【００４６】
図１５は、亀裂進展下限界値ΔＫ_ｔｈと応力拡大係数範囲ΔＫとの大小関係を示す亀裂深さ−応力拡大係数範囲線図の例示である。また、この図において、予め定められた亀裂深さａを基点に亀裂深さ領域１と亀裂深さ領域２とに区分けされる。
【００４７】
今、亀裂深さ領域１において、蒸気タービンが、例えばモード１、具体的には３アドミッション方式で運転していると、応力拡大係数範囲ΔＫは、亀裂進展下限界値ΔＫｔｈを超えているので危険域に入っている。このため、危険域を避ける必要上、蒸気タービンは、その運用モードを３アドミッション方式から２アドミッション方式に変更させるか、あるいは図１１で示した高加振力域を避けるために、蒸気量を急激に増加させ、高加振力域に相当する蒸気タービン出力負荷を迅速に通過させる。
【００４８】
また、亀裂深さ領域１において、蒸気タービンが、例えばモード２、具体的には２アドミッション方式で運転していると、応力拡大係数範囲ΔＫは、亀裂進展下限界値ΔＫ_ｔｈを超えていないので、蒸気タービンの運転はそのまま継続される。
【００４９】
しかし、蒸気タービンは、その運転が亀裂深さ領域２になると、亀裂が進展する危険域に入る。このため、蒸気タービンは亀裂部分を補修するか、新規なタービンロータに交換するかの措置が講じられる。
【００５０】
このように、亀裂進展下限界値ΔＫｔｈが応力拡大係数範囲ΔＫとの関係では、タービンロータの亀裂進展開始点になるので、亀裂進展下限界値ΔＫｔｈおよび応力拡大係数範囲ΔＫともに明確に定めておくことが必要とされる。
【００５１】
応力拡大係数範囲ΔＫは、ΔＫ＝Ｋ_ｓ−Ｋ_ｃとしてあらわすことができる。ここで、Ｋ_ｓは最大応力拡大係数であり、Ｋｃは、最小応力拡大係数である。この応力拡大係数範囲ΔＫは、第２ステップ（ＳＴ２）で作成した振動応力線図における加振力負荷時および加振力除荷時の振動応力および亀裂深さａ_ｘに基づいて影響関数法で算出される。
【００５２】
また、亀裂進展下限界値ΔＫ_ｔｈは、亀裂深さａ_ｘおよび応力比Ｒの設定如何によって第６ステップ（ＳＴ６）で求める亀裂進展特性評価が不正確になるので、予めテスト材等を用いて第４ステップ（ＳＴ４）において定める。
【００５３】
第４ステップ（ＳＴ４）で定める亀裂進展下限界値△Ｋ_ｔｈは、図１４で示す亀裂進展下限界値を定める線図のうち、図１４（ａ）の応力比依存性の下限界値線図から求めた亀裂進展下限界値Ｋ_ｔｈ１、図１４（ｂ）の亀裂長さ依存性の下限界値線図から求めた亀裂進展下限界値Ｋ_ｔｈ２、および図１４（ｃ）の硬さ依存性の下限界値線図から求めた亀裂進展下限界値Ｋ_ｔｈ３を算出し、算出した各値を乗算し、△Ｋ_ｔｈ＝Ｋ_ｔｈ１×Ｋ_ｔｈ２×Ｋ_ｔｈ３として算出する。
【００５４】
このようにして亀裂進展下限界値△Ｋ_ｔｈを算出すると、第５ステップ（ＳＴ５）では、図１３に示すように、亀裂進展下限界値△Ｋ_ｔｈに相当する亀裂進展最小応力値σ_ｍｉｎを振動応力線にプロットし、振動応力線との交点Ｘを亀裂進展最小負荷Ｌ_ｍｉｎとし、交点Ｙを亀裂進展最大負荷Ｌ_ｍａｘとする。この亀裂進展最小負荷Ｌ_ｍｉｎから亀裂進展最大負荷Ｌ_ｍａｘまでの範囲を亀裂進展領域ＣＲとして定められる。なお、この亀裂進展領域ＣＲの前後領域は、亀裂の進展が停止している範囲である。
【００５５】
第５ステップ（ＳＴ５）で亀裂進展負荷帯（Ｌ_ｍｉｎ〜Ｌ_ｍａｘ）が定められると、蒸気タービンは、図１３に示すように、上述影響関数法で求めた応力拡大係数範囲△Ｋと第４ステップ（ＳＴ４）で求めた亀裂進展下限界値△Ｋ_ｔｈとを突き合わせ、△Ｋ_ｔｈ＞△Ｋの場合、実負荷Ｌ（ｘ）がまだ亀裂進展領域ＣＲに入っていないと認定し、実負荷Ｌ（ｘ）に増加負荷分△Ｌを加えて運転を継続する。
【００５６】
また、蒸気タービンは、応力拡大係数範囲△Ｋと亀裂進展下限界値△Ｋ_ｔｈとを突き合わせ、△Ｋ_ｔｈ＜△Ｋの場合、実負荷Ｌ（ｘ）が亀裂進展領域ＣＲに入っていると認定し、第６ステップ（ＳＴ６）で亀裂進展特性評価、具体的には亀裂進展速度ｄｌ／ｄＮ，許容亀裂長さまでの亀裂進展寿命Ｎ_ｆを求め、さらにステップ７で許容亀裂長さまでの寿命消費率φＬをそれぞれ求める。
【００５７】
まず、亀裂進展速度ｄｌ／ｄ_Ｎは、応力拡大係数範囲△Ｋ、亀裂長さｌ、応力比Ｒ（Ｋｃ／Ｋｓ）、亀裂進展下限界値△Ｋ_ｔｈの依存性を考慮して次式で求められる。
【００５８】
【数２】

【００５９】
次に、許容亀裂長さまでの亀裂進展寿命Ｎ_ｆは、実亀裂長さｌ_０から予め定められた許容亀裂長さｌ_１までを次式で求められる。
【００６０】
【数３】

【００６１】
なお、予め定められた許容亀裂長さｌ_１は、例えば運転上、支障のない範囲で運転できる最大限の亀裂長さ等の経験則から定められる。
【００６２】
第７ステップ（ＳＴ７）では、上述の許容亀裂長さまでの亀裂進展寿命Ｎ_ｆにおける単位時間ｎ_０あたりの寿命消費率φＬを次式で算出する。
【００６３】
【数４】
φＬ＝ｎ_０／Ｎ_ｆ ……（４）
次に、寿命消費率φＬと亀裂進展負荷帯（Ｌ_ｍｉｎ〜Ｌ_ｍａｘ）における運転時間ｔＬとから総合亀裂進展寿命Ｔを次式で算出する。
【００６４】
【数５】

【００６５】
式（５）で、総合亀裂進展寿命Ｔが算出されると、第８ステップ（ＳＴ８）では、許容亀裂長さに至るまでの亀裂進展時間評価が行われる。亀裂進展時間評価の際、残っている運転時間が次回の定期検査まで維持できる場合、第９ステップ（ＳＴ９）では引き続き運転を継続させる。
【００６６】
また、残っている運転時間が次回の定期検査まで維持できない場合、第９ステップ（ＳＴ９）では、タービンロータの補修、交換または亀裂進展負荷帯（Ｌ_ｍｉｎ〜Ｌ_ｍａｘ）を避ける運転（例えば、蒸気量を急激に増して高加振力に相当する蒸気タービン出力負荷を迅速に通過させる）のうち、いずれかが応急対策として選択される。
【００６７】
タービンロータの材料劣化層や亀裂発生部の除去などの補修を選択する場合、蒸気タービンは、図１６に示すように、斜線で示す補修幅領域を一方のタービン動翼のフック部Ａと隣のタービン動翼のフック部Ｂとに跨がって削除する。補修幅領域を一方のタービン動翼のフック部Ａとなりのタービン動翼のフック部Ｂとに跨がって削除するのは、タービン動翼の接触端間距離が削除前に較べて大きくなって接触端間の近接効果が小さくなり、疲労強度が向上することと相まってタービン動翼間の隙間分だけ両圧増加が抑えられるからである。
【００６８】
また、タービンロータの補修後、タービン動翼を植設する際、タービン動翼は亀裂発生部が再び接触部分にならないように、円周上の位置をずらすか、あるいは植設位置を元の位置にし、タービンロータの削除した部分をフック接触部分にしてもよい。ともに、フレッティング疲労強度を向上させることができる。
【００６９】
このように、本実施形態に係るタービンロータの亀裂進展予測方法は、第１ステップ（ＳＴ１）から求めた負荷、運転時間を基に有限要素法で振動応力を算出するとともに、算出した振動応力等から影響関数法を用いて算出した応力拡大係数範囲△Ｋと亀裂硬さ等から算出した亀裂進展下限界値△Ｋ_ｔｈとにより亀裂進展負荷帯を設定する一方、蒸気タービンが亀裂進展負荷帯内で運転する時、亀裂進展特性評価として亀裂進展速度、亀裂進展寿命等を求めた後、亀裂寿命消費率および総合亀裂進展寿命を算出し、その算出した総合亀裂進展寿命から許容亀裂長さに至までの残りの運転時間を求め、残りの運転時間が次回の定期検査まで維持できない場合、タービンロータに適切な措置を講じるので、タービンロータに安全かつ安定運転を行わせることができる。
【００７０】
図１７は、タービンロータ材を変更した場合、応力拡大係数範囲△Ｋから亀裂進展速度ｄｌ／ｄＮを求めるにあたり、本発明に係るタービンロータの亀裂進展予測方法に適用する亀裂進展速度線図である。
【００７１】
最近の蒸気タービンは、タービン駆動蒸気を超高圧・超高温化する研究が進められており、従来からタービンロータ材として用いられているＣ_ｒＭ_ｏＶ材を、１２Ｃ_ｒ材に変更する検討が行われている。
【００７２】
本実施形態は、タービンロータ材が１２Ｃ_ｒ材に変更されてもその１２Ｃ_ｒ材の応力拡大係数範囲△Ｋに対する亀裂進展速度ｄｌ／ｄＮを容易に算出することができるようにしたものである。
【００７３】
したがって、本実施形態は、タービンロータ材が１２Ｃ_ｒ材に変更になっても亀裂進展速度ｄｌ／ｄＮを容易に算出できるようにしたので、タービンロータの亀裂進展を容易に予測することができる。
【００７４】
また、Ｃ_ｒＭ_ｏＶ材から１２Ｃ_ｒ材に変更したタービンロータの亀裂進展を予測するにあたり、本実施形態では、図１８に示すように、予めマスターカーブとして作成した応力−硬さ線図を用い、使用温度および運転時間に対するタービンロータの表層部の硬さを求め、求めた硬さが予め定めた許容硬さ限界値よりも下廻った場合、タービンロータの軟化層除去等の補修開始条件として活用してもよい。タービンロータの補修の有無を検討する場合に有効である。
【００７５】
図１９は、タービン動翼への加振力を算出するにあたり、本発明に係るタービンロータの亀裂進展予測方法に適用するタービン動翼加振力線図である。
【００７６】
従来、タービン駆動蒸気には、酸化スケール等の異物微粒子が含まれることが多い。このためタービン動翼の上流側に位置するタービンノズルは、酸化スケール等の衝突で長年の使用の結果、浸食を受ける。
【００７７】
また、蒸気タービンは、タービン駆動蒸気が膨張仕事をする際、熱を失って水滴（ドレン）を発生させることがあり、この水滴によりタービンノズルを浸食させている。このため、タービン動翼に与えられる加振力は、タービンノズルの浸食度合の大小により変動する。
【００７８】
本実施形態は、タービンノズルの浸食度合の大小に応じてタービン動翼に与えられる加振力を修正し、修正した加振力から亀裂進展負荷帯を求めることができるようにしたものである。
【００７９】
本実施形態では、タービンノズルが浸食している場合、タービン動翼加振力線図を用いてタービンロータに発生した亀裂が進展しているかの有無を判定できるようにしたので、亀裂が進展している場合、迅速に補修対策を行うことができる。
【００８０】
【発明の効果】
以上の説明のとおり、本発明に係るタービンロータの亀裂進展予測方法は、タービンロータの亀裂発生の有無および亀裂進展量を予測するにあたり、硬さ、加振力、振動応力を基に応力拡大係数範囲および亀裂進展下限界値を算出し、算出した応力拡大係数範囲および亀裂進展下限界値から亀裂進展負荷帯を決定するとともに、亀裂進展負荷帯における亀裂進展量を予測し、予測した亀裂進展量と許容亀裂量との差分からタービンロータの補修等の有無を判定するので、蒸気タービンに安全かつ安定な運転を行わせることができる。
【図面の簡単な説明】
【図１】本発明に係るタービンロータの亀裂進展予測方法の実施形態の手順を示すブロック図。
【図２】本発明に係るタービンロータの亀裂進展予測方法に用いる応力−硬さを示すグラフ。
【図３】本発明に係るタービンロータの亀裂進展予測方法に用いるタービンロータ表層部硬さ変化曲線を示すグラフ。
【図４】亀裂深さを測定する際に電気的に測定することを説明するために用いた概念図。
【図５】亀裂深さを測定する際、レプリカ方式で測定することを説明するために用いた概念図。
【図６】亀裂深さを測定する際、予めデータベース化した亀裂深さ−亀裂長さ線図から求めることを説明するために用いたグラフ。
【図７】亀裂深さを測定する際、予めデータベース化した等応力分布線図から求めることを説明するために用いたグラフ。
【図８】亀裂深さを測定する際、予めデータベース化した亀裂開口量（開口幅）線図から求めることを説明するために用いたグラフ。
【図９】バルクハウゼンノイズ法で表層部の硬さを求める場合の実施形態を示すブロック図。
【図１０】図９に示す構成で求めたバルクハウゼンノイズ出力から表層部の硬さを求めることを説明するために用いたグラフ。
【図１１】タービンロータに亀裂が発生した場合、その亀裂を除去して応急的に手当をすることを説明するために用いたグラフ。
【図１２】蒸気タービンをモデル化する前の組立状態を示す一部切欠斜視図。
【図１３】本発明に係るタービンロータの亀裂進展予測方法の各ステップを細かく説明するために用いたグラフ。
【図１４】本発明に係るタービンロータの亀裂進展予測方法に用いる亀裂進展下限界値を求める線図で、（ａ）は応力比依存性の下限界値線図、（ｂ）は亀裂長さ依存性の下限界値線図、（ｃ）は硬さ依存性の下限界値線図。
【図１５】本発明に係るタービンロータの亀裂進展予測方法に用いる亀裂深さ−応力拡大係数範囲を示す線図。
【図１６】本発明に係るタービンロータの亀裂進展予測方法において、タービンロータの補修を必要とした場合、その補修状況を説明するために用いた図。
【図１７】本発明に係るタービンロータの亀裂進展予測方法において、ＣｒＭｏＶ鋼の応力拡大係数範囲ΔＫおよび１２Ｃｒ鋼の応力拡大係数範囲ΔＫのそれぞれから亀裂進展速度を求めることを説明するために用いたグラフ。
【図１８】本発明に係るタービンロータの亀裂進展予測方法において、ＣｒＭｏＶ鋼の応力・硬さと１２Ｃｒ鋼の応力・硬さとを示すグラフ。
【図１９】本発明に係るタービンロータの亀裂進展予測方法において、タービン動翼の上流側に配置したタービンノズルの、そのタービンノズルが浸食を受けている場合にタービン動翼に加えられた加振力に基づく亀裂進展負荷帯と、タービンノズルが浸食を受けていない場合にタービン動翼に加えられた加振力に基づく亀裂進展負荷帯を示すグラフ。
【図２０】従来の蒸気タービンを示す一部切欠断面図。
【図２１】タービン動翼とタービンノズルとの位置関係を示す概略図。
【図２２】図２１のＡ−Ａ矢視方向から切断した断面図。
【図２３】タービンノズルからタービン動翼に流れる蒸気によりタービン動翼に加振力が加えられることを説明するために用いた図。
【図２４】蒸気加減弁の弁開度順序を説明するために用いた図。
【図２５】タービンロータのフック部に亀裂が発生したことを説明するために用いた図。
【図２６】基台部に隣接して部材を設置した場合、加振力により亀裂が発生したことを説明するために用いた図。
【図２７】材料に加振力が繰り返し与えられた場合、通常の疲労強度とフレッティング疲労強度とを比較する図。
【符号の説明】
１ 外部ケーシング
２ 内部ケーシング
３ タービンケーシング
４ 軸受
５ タービンロータ
６ タービンノズル
７ タービン動翼
８ タービン段落
９ 植込み部
１０ 植込み溝
１１ フック部
１２ ノズルボックス
１３ 蒸気入口
１４ａ，１４ｂ 電極
１５ 被検体
１６ パルス発生器
１７ 増幅器
１８ センサ
１９ 増幅器
２０ フィルタ
２１ 周波数解析装置
２２ 動翼カバー
２３ テノン[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a method for predicting crack propagation in a turbine rotor, and more particularly, a turbine rotor crack for predicting a life based on a crack generated in a contact portion between a implanted portion of a turbine rotor blade implanted in a turbine rotor and the turbine rotor. It relates to progress prediction methods.
[0002]
[Prior art]
In general, a steam turbine accommodates a turbine rotor 5 pivotally supported by a bearing 4 in a turbine casing 3 divided into an outer casing 1 and an inner casing 2 as shown in FIG. The turbine stage 6 is formed by combining the turbine nozzle 6 and the turbine rotor blade 7 implanted in the turbine rotor 5, and the turbine stage 8 is arranged in multiple stages along the axial direction.
[0003]
As shown in FIG. 21, the turbine rotor blade 7 is implanted in an annular row along the circumferential direction by engaging the implanted portion 9 with the hook portion 11 of the implanted groove 10 of the turbine rotor 5.
[0004]
Further, as shown in FIGS. 21 and 22, the turbine nozzle 6 is arranged in an annular row along the circumferential direction of the turbine rotor 5 so as to correspond to the turbine rotor blade 7, and includes a nozzle box 12 on the inlet side thereof. At the same time, the steam inlet 13 communicating with the nozzle box 12 is usually provided with a four-valve steam control valve (not shown).
[0005]
The steam control valve, as shown in FIG. 24, opens the first valve and the second valve almost simultaneously as the turbine output increases, and further sequentially opens the third valve and the fourth valve sequentially. The so-called three-admission method, or the so-called two-admission method, which is not shown, but the first valve, the second valve and the third valve are simultaneously opened and the remaining fourth valve is opened next, or the first Any one of the so-called one-admission system operation modes is adopted in which all the valves from the valve to the fourth valve are simultaneously opened.
[0006]
For example, when the steam control valve adopts the 3-admission system operation mode during the start-up operation, the turbine rotor blade 7 is configured so that the turbine nozzle 5 is rotated while the turbine rotor 5 makes one rotation (360 °) as shown in FIG. The steam guided from 6 is received twice. For this reason, the turbine rotor blade 7 has a steam pressure fluctuation force based on whether steam is received or not. In addition, the turbine rotor blade 7 has a pressure difference between the ventral side and the back side, and the steam flow based on this pressure difference fluctuates. As shown in FIG. 23, a strong excitation force F is received in the same direction as the rotation direction of the turbine rotor 5.
[0007]
When such an exciting force F is repeatedly received, the turbine rotor 5 is cracked in the hook portion 11 of the implantation groove 10 to be engaged with the implantation portion 9 of the turbine rotor blade 7 as shown in FIG. was there. Since the occurrence of cracks in the turbine rotor 5 inevitably impairs the stable operation of the steam turbine, recently, many inventions for predicting the progress of cracks have been proposed.
[0008]
However, the prediction of crack growth involves many factors such as steam conditions, such as operating conditions such as pressure, temperature, steam flow rate, and the number of start-ups, making the solution difficult. This is the exploration stage.
[0009]
[Problems to be solved by the invention]
Conventionally, the turbine rotor blade 7 uses 12Cr alloy steel having excellent high-temperature strength, whereas the turbine rotor 5 has a relatively low high-temperature strength Cr—Mo— compared with the turbine blade material. V alloy steel is used. The reason why the turbine rotor 5 is made of Cr-Mo-V alloy steel having a low high-temperature strength compared to the turbine blade material is that the seizure of the bearing 4 is reduced, but the high-temperature strength is low. Therefore, the hook portion 11 of the implantation groove 10 of the turbine rotor 5 is affected by the above-described excitation force F, and as a result of use for many years, a crack C may occur as shown in FIG. This crack C develops even with a very small excitation force if the metallographic structure has changed as a result of years of use of the turbine rotor material. Such fatigue failure is called fretting fatigue.
[0010]
  As shown in FIG. 26, this fretting fatigue is considered to occur due to vibration stress σa. That is, when the members Y and Z are in contact with the base portion X with a distance δ, the excitation force F is repeatedly applied to the base portion X from the outside.Once added,A vibration stress (stress amplitude) σa is applied to the base portion X. The vibration stress σa is applied in a direction intersecting the surface pressure applied to the base portion X from the end portions of the members Y and Z, so that the strength is reduced and the crack C is considered to occur. In particular, when the members Y and Z are installed within a certain distance δ with respect to the base portion X, this tendency is strong. Incidentally, when the base part X and the members Y and Z are installed adjacent to each other, the vibration stress σa is larger than that when the members Y and Z are not installed (no fretting) as shown in FIG. It has been confirmed through experiments that the value is significantly lower.
[0011]
It is considered that the crack C due to fretting fatigue is generated in the hook portion 11 of the implantation groove 10 of the turbine rotor 5 due to the planting of the turbine rotor blade 7 adjacent to the annular row. The implanted portion 9 of the turbine rotor blade 7 has no high fretting fatigue due to its high material strength.
[0012]
The crack C generated in the hook portion 11 of the implantation groove 10 of the turbine rotor 5 cannot be observed from the outside for many minutes, and is only during the periodic inspection. If the crack C develops during the operation of the steam turbine, safe and stable operation is impaired, so an accurate crack growth prediction technique is required.
[0013]
The present invention has been made based on such circumstances, and the hardness of the hook portion of the implantation groove in the turbine rotor engaged with the implantation portion of the turbine rotor blade is determined based on the vibration stress and hardness generated during operation. An object of the present invention is to provide a method for predicting crack growth in a turbine rotor that predicts the amount of crack growth for future operation, and that can appropriately deal with replacement or repair of the turbine rotor under an accurate crack growth prediction. To do.
[0014]
[Means for Solving the Problems]
  In order to achieve the above object, the method for predicting crack growth in a turbine rotor according to the present invention provides a first step of recording an operation result as described in claim 1.When,Determination of vibration stress by finite element method from modeled steam turbine.Together with the vibration stress diagram corresponding to the steam turbine loadSecond stepWhen, ax The crack depth from the turbine surface, H1 The turbine surface layer hardness, H0 When the hardness is 200 to 300 μm from the turbine surface layer, H ( ax ) = H0 − ( H0 − H1 ) exp ( -cXa Using the turbine rotor surface layer hardness change curveThird step for determining the hardness of the surface layer of the turbine rotorWhen,4th step of finding the lower limit of crack growth by multiplying the hardness, crack length and stress ratio of the turbine rotorAnd the crack growth minimum stress value corresponding to the crack growth lower limit value obtained in the fourth step is plotted on the vibration stress line obtained in the second step, and the steam turbine low load side on the vibration stress line is plotted on the vibration stress line. The intersection is the minimum crack growth load, the intersection with the steam turbine high load side at this vibration stress line is the crack growth maximum load, and the range from the crack growth minimum load to the crack growth maximum load is the crack growth load band. The stress intensity factor range obtained using the influence function method based on the vibration stress and crack depth obtained in the second step and the crack growth lower limit value obtained in the fourth step, and If the lower limit value is larger than the stress intensity factor range, it is recognized that the actual load of the steam turbine has not yet entered the crack growth region, and the operation is continued by adding the increased load ΔL to the actual load. On the other hand, if the crack growth lower limit value is smaller than the stress intensity factor range, it is determined that the actual load of the steam turbine is in the crack growth region, and the fifth step proceeds to the next step; ,In the crack propagation load zone determined in this fifth stepThe crack growth rate determined from the function consisting of the stress intensity factor range, crack length, the stress ratio determined by the ratio of the minimum stress intensity factor and the maximum stress intensity factor, and the crack growth lower limit value, and determined in the fifth step The allowable crack length obtained by integrating the stress intensity factor range, the stress ratio obtained by the ratio between the minimum stress intensity factor and the maximum stress intensity factor, the crack growth lower limit, and the reciprocal of the crack length function As the crack growth characteristics6th stepWhen,From the crack propagation characteristics in the crack propagation load zone obtained in this sixth stepConvert the crack growth life up to a predetermined allowable crack length into unit timeSeventh step of calculating the life consumption rateWhen,The life consumption rate calculated in the seventh step andBased on the total crack growth life determined from the operation time in the crack growth load zone determined in the fifth step,Eighth step of calculating a time from the actual crack length to a predetermined allowable crack lengthAnd thisWhen the time to reach the allowable crack length determined in the 8th step cannot be maintained until the next periodic inspection, repair and replacement of the turbine rotorOr, while selecting the operation to avoid the crack propagation load zone, if the time to reach the allowable crack length can be maintained until the next periodic inspection, the operation is continued to be selected as it is9th stepWhen,Is provided.
[0017]
  In order to achieve the above object, the crack propagation prediction method for a turbine rotor according to the present invention provides:Claim 2As described inIn the third stepCrack depth is the potential difference detection method for detecting the potential difference of the corresponding part, the method of detecting with a replica, the crack depth-crack length diagram created in advance in the database, the iso-stress distribution diagram created in the database in advance, and the database created in advance. Select one of the crack depth and crack opening diagramsAskIs.
[0018]
  In order to achieve the above object, the crack propagation prediction method for a turbine rotor according to the present invention provides:Claim 3As described above, the replica selects either a video film or a plastic material that is cured by ultraviolet rays.
[0019]
  In order to achieve the above object, the crack propagation prediction method for a turbine rotor according to the present invention provides:Claim 4As described above, the hardness of the surface layer portion of the turbine rotor in the third step applies a pulse to the corresponding part, calculates Barkhausen noise from the generated magnetic change, and obtains the surface layer hardness from the calculated signal Barkhausen noise methodUseIs.
[0024]
  In order to achieve the above object, the crack propagation prediction method for a turbine rotor according to the present invention provides:Claim 5As described above, when repairing the turbine rotor in the ninth step, the repair width region is deleted across the hook portion of one turbine blade and the hook portion of the adjacent turbine blade.
[0025]
  In order to achieve the above object, the crack propagation prediction method for a turbine rotor according to the present invention provides:Claim 6As described above, the turbine rotor repair in the ninth step is to obtain the hardness from the operating temperature and the operation time, plot the hardness on a stress-hardness diagram prepared in advance, and the hardness is the allowable hardness. It starts when it falls below the limit value.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment of a crack propagation prediction method for a turbine rotor according to the present invention will be described with reference to the drawings and the reference numerals attached to the drawings.
[0027]
FIG. 1 is a block diagram showing a procedure in an embodiment of a crack propagation prediction method for a turbine rotor according to the present invention.
[0028]
The crack propagation prediction method for the turbine rotor according to the present embodiment includes, for example, a first step (ST1) for recording operation results such as load and operation time, and a second step (ST2) for obtaining vibration stress for each load band during operation. ), The third step (ST3) for determining the hardness of the surface layer portion of the turbine rotor, the fourth step (ST4) for determining the crack growth lower limit value from the hardness of the turbine rotor, and the vibration stress obtained in the second step Fifth step (ST5) for determining a load zone (load range from the lowest load to the highest load) where the crack propagates from the stress intensity factor range calculated by the influence function method and the lower limit value of crack growth obtained in the fourth step The sixth step (ST6) for determining the crack growth characteristics in the crack growth load zone determined in the fifth step, specifically the crack growth rate, the crack growth life up to the allowable crack length, etc. The seventh step (ST7) for calculating the life consumption rate from the crack growth characteristics in the crack growth load zone obtained in 6 steps, from the life consumption rate calculated in the seventh step and the actual crack length to a predetermined allowable crack length The 8th step (ST8) for calculating the time to reach the 9th step, and if the time to reach the allowable crack length obtained in the 8th step cannot be maintained until the next periodic inspection, the 9th step to consider measures for repairing or replacing the turbine rotor The procedure goes through (ST9).
[0029]
The hardness of the turbine rotor obtained in the third step (ST3) can be obtained from a stress-hardness diagram prepared in advance as shown in FIG. This stress-hardness diagram shows the hardness of the surface layer of the turbine rotor on the vertical axis, and the temperature and operating time of the turbine rotor on the horizontal axis. The stress value of the turbine rotor at each operating temperature and operating time ( The hardness of the surface layer according to the stress 2 is larger than the stress 1 is plotted. In addition, although this embodiment calculated | required the hardness of the surface layer of a turbine rotor from the stress-hardness diagram, it calculates | requires from not only this but a turbine rotor surface layer part hardness change curve as shown, for example in FIG. May be.
[0030]
This turbine rotor surface layer hardness change curve H (a_x)
[Expression 1]

As given.
[0031]
Where a_xIs the crack depth from the turbine rotor surface layer, H₁Is the turbine rotor surface layer hardness, H₀Is, for example, the hardness at a depth of 200 to 300 μm from the turbine rotor surface layer, and C is a constant.
[0032]
The above formula (1) is the hardness H of the turbine rotor surface layer.₁And crack depth a_xFor example, hardness H at a depth of 200 to 300 μm from the surface layer portion₀And a master curve created by actual measurement with a test material over a range between two points. This master curve is applied when the surface layer of the turbine rotor is a texture layer in which a soft layer and a hard layer are mixed, and it is necessary to obtain the hardness from a certain depth.
[0033]
In addition, crack depth a_xCan be determined using the following non-destructive testing method.
[0034]
First crack depth a_xAs shown in FIG. 4, this measurement method is a method of measuring using a potential difference at a part away from the crack by a certain distance via the electrodes 14 a and 14 b arranged across the crack part. A constant potential difference V between the electrodes 14a and 14b.₀(Reference electrode), the potential difference V between the measurement electrodes is the function V = V (a_x, V₀). Therefore, if the potential difference V is measured, the crack depth a_xCan be asked.
[0035]
The second crack depth a_xAs shown in FIG. 5, a bioden film (plastic film) may be attached to the cracked portion. The video film can be softened with methyl acetate and harden with the evaporation of the methyl acetate to replicate the crack shape. Further, a plastic material that is cured by ultraviolet rays may be used instead of the bioden film.
[0036]
Other crack depths a_xFor example, as shown in FIG. 6, a crack depth-crack length diagram created in advance as a database, as shown in FIG. 7, an iso-stress distribution diagram created in a database as shown in FIG. 7, or as shown in FIG. In addition, a crack depth-crack opening amount (opening width) diagram that has been databased in advance may be used.
[0037]
Further, the present embodiment is not limited to the above-described stress-hardness diagram, and the hardness may be obtained from the Barkhausen noise method, for example, as shown in FIGS.
[0038]
In the embodiment using the Barkhausen noise method, as shown in FIG. 9, the pulse from the pulse generator 16 is given to the subject 15 via the amplifier 17 and the sensor 18, and the magnetic change generated in the subject 15 is detected by the sensor 18. And the detected signal is calculated by the frequency analyzer 21 through the amplifier 19 and the filter 20, and the hardness of the turbine rotor surface layer is obtained from the Barkhausen noise output based on the calculated signal as shown in FIG. Be able to.
[0039]
In the Barkhausen noise method, attention is paid to the fact that the change in magnetic noise that occurs when the domain wall is discontinuously generated and moved in the process of magnetizing the ferromagnetic material corresponds to the change in hardness of the material. It is a thing. Therefore, the Barkhausen noise method is effective in obtaining the hardness of the surface layer portion of the ferromagnetic material.
[0040]
FIG. 11 shows the turbine rotor through the turbine rotor blade from the relationship between the load output of the steam turbine and the operation modes 1 and 2, which are the prerequisites, before obtaining the vibration stress of each load band in the second step (ST2). It is a steam turbine load output-excitation force diagram which calculates the excitation force applied to the hook part of.
[0041]
The excitation force due to steam varies significantly if the operation mode is different even if the load output of the steam turbine is constant. In particular, the driving mode 1, specifically the 3 admission method, has a higher excitation force than the operation mode 2, specifically the 2 admission method. Further, in the three-admission system, when the load output of the steam turbine becomes a load output in a predetermined region, a high excitation force is applied, and a danger zone that causes a crack in the turbine rotor is entered.
[0042]
Thus, in the second step (ST2), the vibration stress (stress amplitude) σ is obtained in consideration of the fluctuating vibration force while the vibration force fluctuates depending on the operation modes 1 and 2. ).
[0043]
As shown in FIG. 12, the vibration stress (stress amplitude) σ of the turbine rotor is an actual steam turbine composed of a moving blade cover 22, a tenon 23, a turbine moving blade 7, an implanted portion 9, a turbine rotor 5, and a hook portion 11. Is obtained by a finite element method using the model.
[0044]
As shown in FIG. 13, the vibration stress σ obtained by the finite element method is plotted in correspondence with the steam turbine load, and a vibration stress diagram is created as a master curve.
[0045]
On the other hand, in determining the crack growth load zone in the fifth step (ST5), the stress intensity factor range ΔK and the crack growth lower limit value ΔK_thFirst, the stress intensity factor range ΔK and the crack growth lower limit value ΔK_thIs the starting point of crack propagation in the turbine rotor, so it is important to define it clearly and will be described with reference to FIG.
[0046]
FIG. 15 shows a crack growth lower limit value ΔK._th3 is an illustration of a crack depth-stress intensity factor range diagram showing a magnitude relationship between the stress intensity factor range ΔK and the stress intensity factor range ΔK. Further, in this figure, the crack is divided into a crack depth region 1 and a crack depth region 2 based on a predetermined crack depth a.
[0047]
  Now, in the crack depth region 1, when the steam turbine is operated in, for example, mode 1, specifically, the 3-admission system, the stress intensity factor range ΔK exceeds the crack growth lower limit value ΔKth. You are in a danger zone. Therefore, in order to avoid the danger zone, the steam turbine changes its operation mode from the 3-admission system to the 2-admission system, or the high excitation force area shown in FIG.To avoidThe amount of steam is increased rapidly, and the steam turbine output load corresponding to the high excitation force region is passed quickly.
[0048]
In the crack depth region 1, when the steam turbine is operated in, for example, mode 2, specifically, the 2-admission system, the stress intensity factor range ΔK is the crack growth lower limit value ΔK._thTherefore, the operation of the steam turbine is continued as it is.
[0049]
However, when the operation of the steam turbine is in the crack depth region 2, the steam turbine enters a risk region where the cracks progress. For this reason, measures are taken to repair the cracked part of the steam turbine or replace it with a new turbine rotor.
[0050]
  Thus, since the crack progress lower limit value ΔKth is the starting point of crack growth of the turbine rotor in relation to the stress intensity factor range ΔK, the crack progress lower limit valueΔKthThe stress intensity factor range ΔK must be clearly defined.
[0051]
The stress intensity factor range ΔK is ΔK = K_s-K_cCan be represented as: Where K_sIs the maximum stress intensity factor, and Kc is the minimum stress intensity factor. This stress intensity factor range ΔK is the vibration stress and crack depth a when the excitation force is loaded and when the excitation force is unloaded in the vibration stress diagram created in the second step (ST2)._xIs calculated by the influence function method.
[0052]
  In addition, the crack growth lower limit ΔK_thIs the crack depth a_xSince the crack growth characteristic evaluation obtained in the sixth step (ST6) becomes inaccurate depending on the setting of the stress ratio R and the stress ratio R, the fourth step (ST4) using a test material or the like in advance.InDetermine.
[0053]
Crack propagation lower limit value ΔK determined in the fourth step (ST4)_thIs the crack growth lower limit value K determined from the stress ratio dependence lower limit value diagram of FIG. 14A among the diagrams defining the crack growth lower limit value shown in FIG._th114B, the crack growth lower limit value K obtained from the lower limit value diagram of the crack length dependency in FIG._th2, And the lower limit value K of crack growth obtained from the lower limit value diagram of the hardness dependence in FIG._th3And multiply each calculated value by ΔK_th= K_th1× K_th2× K_th3Calculate as
[0054]
In this way, crack growth lower limit value ΔK_thIs calculated, in the fifth step (ST5), as shown in FIG._thMinimum crack growth stress value σ_minIs plotted on the vibration stress line, and the intersection point X with the vibration stress line is the crack propagation minimum load L_minAnd the intersection Y is the crack growth maximum load L_maxAnd This crack growth minimum load L_minTo crack growth maximum load L_maxThe range up to is defined as the crack propagation region CR. Note that the region before and after the crack propagation region CR is a range in which the growth of the crack is stopped.
[0055]
  In the fifth step (ST5), the crack growth load zone (L_min~ L_max) Is determined, the steam turbine, as shown in FIG. 13, has a stress intensity factor range ΔK determined by the influence function method and a crack growth lower limit value ΔK determined in the fourth step (ST4)._thAndMatch,△ K_thWhen> ΔK, it is recognized that the actual load L (x) is not yet in the crack propagation region CR, and the operation is continued by adding the increased load ΔL to the actual load L (x).
[0056]
The steam turbine also has a stress intensity factor range ΔK and a crack growth lower limit value ΔK._th△ K_thIn the case of <ΔK, it is recognized that the actual load L (x) is in the crack propagation region CR, and the crack propagation characteristic is evaluated in the sixth step (ST6), specifically, the crack propagation speed dl / dN, the allowable crack Crack growth life up to length N_fFurther, in step 7, the lifetime consumption rate φL up to the allowable crack length is obtained.
[0057]
First, crack growth rate dl / d_NIs stress intensity factor range ΔK, crack length l, stress ratio R (Kc / Ks), crack growth lower limit value ΔK_thTaking into account the dependency of
[0058]
[Expression 2]

[0059]
Next, the crack growth life N up to the allowable crack length_fIs the actual crack length l₀From a predetermined allowable crack length l₁Is obtained by the following equation.
[0060]
[Equation 3]

[0061]
Note that a predetermined allowable crack length l₁Is determined from an empirical rule such as the maximum crack length that can be operated within a range that does not hinder the operation.
[0062]
In the seventh step (ST7), the crack growth life N up to the allowable crack length described above._fUnit time n₀The per-life consumption rate φL is calculated by the following equation.
[0063]
[Expression 4]
φL = n₀/ N_f      ...... (4)
Next, life consumption rate φL and crack propagation load zone (L_min~ L_maxThe total crack growth life T is calculated from the operation time tL in the following equation.
[0064]
[Equation 5]

[0065]
When the total crack growth life T is calculated by the equation (5), in the eighth step (ST8), the crack growth time until reaching the allowable crack length is evaluated. If the remaining operation time can be maintained until the next periodic inspection during the crack growth time evaluation, the operation is continued in the ninth step (ST9).
[0066]
  If the remaining operating time cannot be maintained until the next periodic inspection, the ninth step (ST9)ThenTurbine rotor repair, replacement or crack propagation load zone (L_min~ L_max) (For example, rapidly increasing the amount of steam and allowing a steam turbine output load corresponding to a high excitation force to pass quickly) is selected as an emergency measure.
[0067]
When repair such as removal of a material deterioration layer or crack generation part of the turbine rotor is selected, the steam turbine has a repair width region indicated by hatching adjacent to the hook part A of one turbine blade as shown in FIG. Delete over the hook B of the turbine blade. The reason why the repair width region is deleted across the hook portion B of the turbine blade that becomes the hook portion A of one turbine blade is that the distance between the contact ends of the turbine blade is larger than before the deletion. This is because the proximity effect between the contact ends is reduced, and the increase in both pressures is suppressed by the gap between the turbine rotor blades coupled with the improvement in fatigue strength.
[0068]
In addition, when the turbine rotor blade is implanted after repairing the turbine rotor, the turbine rotor blade is shifted on the circumference so that the cracked portion does not become a contact portion again, or the implantation position is changed to the original position. In addition, the deleted portion of the turbine rotor may be used as a hook contact portion. Both can improve fretting fatigue strength.
[0069]
Thus, the crack propagation prediction method of the turbine rotor according to the present embodiment calculates the vibration stress by the finite element method based on the load and operation time obtained from the first step (ST1), and calculates the calculated vibration stress and the like. From the stress intensity factor range ΔK calculated using the influence function method from the above and the crack growth lower limit value ΔK calculated from crack hardness, etc._thWhile the crack growth load zone is set by the Calculate the life, find the remaining operating time from the calculated total crack growth life to the allowable crack length, and take appropriate measures for the turbine rotor if the remaining operating time cannot be maintained until the next periodic inspection Therefore, the turbine rotor can be operated safely and stably.
[0070]
FIG. 17 is a crack growth rate diagram applied to the crack propagation prediction method for a turbine rotor according to the present invention when the crack growth rate dl / dN is obtained from the stress intensity factor range ΔK when the turbine rotor material is changed. .
[0071]
Recent steam turbines have been researched to increase turbine-driven steam to ultra-high pressure and ultra-high temperature._rM_oV material, 12C_rConsideration is being made to change the material.
[0072]
In this embodiment, the turbine rotor material is 12C._rEven if it is changed to wood, its 12C_rThe crack growth rate dl / dN with respect to the stress intensity factor range ΔK of the material can be easily calculated.
[0073]
Therefore, in this embodiment, the turbine rotor material is 12C._rSince the crack growth rate dl / dN can be easily calculated even when the material is changed, the crack growth of the turbine rotor can be easily predicted.
[0074]
C_rM_o12C from V material_rIn predicting crack growth of a turbine rotor changed to a material, in the present embodiment, as shown in FIG. 18, a stress-hardness diagram created in advance as a master curve is used, and the turbine rotor with respect to operating temperature and operating time is used. When the hardness of the surface layer portion is obtained and the obtained hardness falls below a predetermined allowable hardness limit value, it may be used as a repair start condition such as removal of the softened layer of the turbine rotor. This is effective when examining whether or not turbine rotors are repaired.
[0075]
FIG. 19 is a turbine rotor blade excitation force diagram applied to the turbine rotor crack growth prediction method according to the present invention in calculating the excitation force to the turbine rotor blade.
[0076]
Conventionally, turbine-driven steam often contains foreign particles such as oxide scale. For this reason, the turbine nozzle located on the upstream side of the turbine rotor blade is eroded as a result of many years of use due to collisions of oxide scales and the like.
[0077]
Further, when the turbine-driven steam performs expansion work, the steam turbine may lose heat and generate water droplets (drain), and the water droplets erode the turbine nozzle. For this reason, the exciting force applied to the turbine rotor blade varies depending on the degree of erosion of the turbine nozzle.
[0078]
In the present embodiment, the excitation force applied to the turbine rotor blade is corrected according to the degree of erosion of the turbine nozzle, and the crack propagation load zone can be obtained from the corrected excitation force.
[0079]
In this embodiment, when the turbine nozzle is eroded, it is possible to determine whether or not the crack generated in the turbine rotor has progressed using the turbine rotor blade excitation force diagram. If so, repair measures can be taken quickly.
[0080]
【The invention's effect】
As described above, the method of predicting crack growth of a turbine rotor according to the present invention is based on the stress intensity factor based on the hardness, excitation force, and vibration stress in predicting the occurrence of cracks and the amount of crack growth in the turbine rotor. The crack growth load zone is determined from the calculated stress intensity factor range and the crack growth lower limit value, and the crack growth amount in the crack growth load zone is predicted. Since the presence or absence of repair of the turbine rotor or the like is determined from the difference between the allowable crack amount and the allowable crack amount, the steam turbine can be operated safely and stably.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a procedure of an embodiment of a method for predicting crack growth in a turbine rotor according to the present invention.
FIG. 2 is a graph showing the stress-hardness used in the crack propagation prediction method for a turbine rotor according to the present invention.
FIG. 3 is a graph showing a hardness change curve of a turbine rotor surface layer portion used in a method for predicting crack growth of a turbine rotor according to the present invention.
FIG. 4 is a conceptual diagram used to explain electrical measurement when measuring crack depth.
FIG. 5 is a conceptual diagram used for explaining the measurement by the replica method when measuring the crack depth.
FIG. 6 is a graph used for explaining that a crack depth is obtained from a crack depth-crack length diagram created in advance in a database when measuring the crack depth.
FIG. 7 is a graph used for explaining that a crack depth is obtained from an iso-stress distribution diagram stored in a database in advance.
FIG. 8 is a graph used for explaining that a crack depth is calculated from a crack opening amount (opening width) diagram stored in a database in advance when measuring the crack depth.
FIG. 9 is a block diagram showing an embodiment in the case where the hardness of the surface layer portion is obtained by the Barkhausen noise method.
10 is a graph used for explaining the determination of the hardness of the surface layer portion from the Barkhausen noise output obtained with the configuration shown in FIG. 9;
FIG. 11 is a graph used for explaining that when a crack occurs in the turbine rotor, the crack is removed and emergency treatment is performed.
FIG. 12 is a partially cutaway perspective view showing an assembled state before modeling the steam turbine.
FIG. 13 is a graph used for finely explaining each step of the crack propagation prediction method for a turbine rotor according to the present invention.
FIGS. 14A and 14B are diagrams for determining a crack growth lower limit value used in the method for predicting crack growth of a turbine rotor according to the present invention, wherein FIG. 14A is a lower limit value diagram depending on a stress ratio, and FIG. 14B is a crack length; Lower limit value diagram of dependence, (c) is a lower limit value diagram of hardness dependence.
FIG. 15 is a diagram showing a crack depth-stress intensity factor range used in a crack propagation prediction method for a turbine rotor according to the present invention.
FIG. 16 is a diagram used for explaining the repair status of the turbine rotor in the crack propagation prediction method according to the present invention when the turbine rotor needs to be repaired.
FIG. 17 is used to explain the determination of crack growth rate from each of the stress intensity factor range ΔK of CrMoV steel and the stress intensity factor range ΔK of 12Cr steel in the crack propagation prediction method of the turbine rotor according to the present invention. Graph.
FIG. 18 is a graph showing stress / hardness of CrMoV steel and stress / hardness of 12Cr steel in the method of predicting crack growth of a turbine rotor according to the present invention.
FIG. 19 shows a method of predicting crack growth in a turbine rotor according to the present invention, in which a vibration applied to a turbine blade when the turbine nozzle is eroded in a turbine nozzle arranged on the upstream side of the turbine blade. The graph which shows the crack progress load zone based on the force and the crack progress load zone based on the excitation force added to the turbine rotor blade when the turbine nozzle is not eroded.
FIG. 20 is a partially cutaway sectional view showing a conventional steam turbine.
FIG. 21 is a schematic view showing a positional relationship between a turbine rotor blade and a turbine nozzle.
22 is a cross-sectional view taken from the direction of arrows AA in FIG. 21. FIG.
FIG. 23 is a diagram used for explaining that an exciting force is applied to the turbine rotor blade by steam flowing from the turbine nozzle to the turbine rotor blade.
FIG. 24 is a diagram used for explaining the valve opening order of the steam control valves.
FIG. 25 is a view used for explaining that a crack has occurred in the hook portion of the turbine rotor.
FIG. 26 is a diagram used for explaining that a crack is generated by an excitation force when a member is installed adjacent to a base portion.
FIG. 27 is a diagram comparing normal fatigue strength and fretting fatigue strength when an excitation force is repeatedly applied to a material.
[Explanation of symbols]
1 External casing
2 Inner casing
3 Turbine casing
4 Bearing
5 Turbine rotor
6 Turbine nozzle
7 Turbine blade
8 Turbine paragraph
9 Implanting part
10 Implantation groove
11 Hook part
12 Nozzle box
13 Steam inlet
14a, 14b electrode
15 Subject
16 Pulse generator
17 Amplifier
18 sensors
19 Amplifier
20 filters
21 Frequency analyzer
22 Rotor cover
23 Tenon

Claims (6)

A first step of recording driving performance ;
A second step of obtaining vibration stress from a modeled steam turbine by a finite element method and obtaining a vibration stress diagram corresponding to the steam turbine load ;
ax crack depth from the turbine surface portion, H1 turbine surface layer portion hardness, H0 a when the hardness at 200~300μm from the turbine surface part, H (ax) = H0 - (H0 - H1) exp (- cXa ) a third step of determining the hardness of the turbine rotor surface layer using a turbine rotor surface layer hardness change curve ;
A fourth step of determining the crack growth lower limit by multiplying the hardness, crack length, and stress ratio of the turbine rotor ;
The crack growth minimum stress value corresponding to the crack growth lower limit value obtained in the fourth step is plotted on the vibration stress line obtained in the second step, and the intersection with the steam turbine low load side on the vibration stress line is indicated. The crack propagation minimum load is set, and the intersection with the steam turbine high load side at this vibration stress line is the crack growth maximum load, and the range from the crack growth minimum load to the crack growth maximum load is defined as a crack growth load zone. The stress intensity factor range obtained using the influence function method based on the vibration stress and crack depth obtained in the second step is matched with the lower limit value of crack growth obtained in the fourth step, and the lower limit of crack growth is determined. If the value is larger than the stress intensity factor range, it is determined that the actual load of the steam turbine has not yet entered the crack propagation region, and the operation is continued by adding the increased load ΔL to the actual load. While the determination, when the crack propagation lower limit value is smaller than the stress intensity factor range, a fifth step of the actual load of the steam turbine is certified to have entered a crack growth area, the process proceeds to the next step,
Obtained from the function consisting of the stress intensity factor range, crack length, ratio of the minimum stress intensity factor and the maximum stress intensity factor, and the crack growth limit value determined in the fifth step. The crack growth rate, the stress intensity factor range in the crack propagation load zone determined in the fifth step, the stress ratio obtained by the ratio of the minimum stress intensity factor and the maximum stress intensity factor, the crack growth lower limit value, and the crack length A sixth step for obtaining a crack growth life up to an allowable crack length obtained by integrating the inverse of the function, as a crack growth characteristic ;
A seventh step of calculating a lifetime consumption rate by converting a crack propagation life from a crack propagation characteristic in the crack propagation load zone obtained in the sixth step to a predetermined allowable crack length into a unit time ;
From the actual crack length to the predetermined allowable crack length based on the total crack growth life determined from the life consumption rate calculated in the seventh step and the operation time in the crack propagation load zone determined in the fifth step. an eighth step of calculating the time to reach,
When the time to reach the allowable crack length obtained in the eighth step cannot be maintained until the next periodic inspection, the repair and replacement of the turbine rotor or the operation avoiding the crack propagation load zone is selected, while the allowable crack length is reached. If the time to reach can be maintained until the next periodic inspection, the ninth step of selecting to continue the operation as it is ,
A crack propagation prediction method for a turbine rotor, comprising: The crack depth in the third step is a potential difference detection method for detecting the potential difference of the corresponding part, a method of detecting with a replica, a crack depth-crack length diagram created in advance in a database, an iso-stress distribution diagram created in advance in a database, 2. The method for predicting crack growth in a turbine rotor according to claim 1 , wherein any one of crack depth-crack opening amount diagrams created in a database is selected and determined . 3. The method according to claim 2 , wherein the replica is selected from a video film and a plastic material that is cured by ultraviolet rays. The hardness of the surface layer portion of the turbine rotor in the third step uses a Barkhausen noise method in which a pulse is given to the corresponding part, Barkhausen noise is calculated from the generated magnetic change, and the hardness of the surface layer portion is obtained from the calculated signal. The method for predicting crack growth in a turbine rotor according to claim 1.   2. The turbine rotor according to claim 1, wherein when the turbine rotor is repaired in the ninth step, the repair width region is deleted across the hook portion of one turbine blade and the hook portion of the adjacent turbine blade. Crack growth prediction method.   The repair of the turbine rotor in the ninth step is to determine the hardness from the operating temperature and the operating time, plot the hardness on a stress-hardness diagram prepared in advance, and the hardness is below the allowable hardness limit value. 2. The method for predicting crack growth in a turbine rotor according to claim 1, wherein the method starts.

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