JP3892629B2 - Overheat damage diagnosis method for boiler water wall pipe - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、火力発電システムの損傷診断技術に関わり、特にボイラ火炉蒸発水壁管の局部的な過熱損傷を効率的且つ高精度に診断する方法に関する。
【０００２】
【従来の技術】
発電用ボイラの火炉水壁管は、高温高圧水を１０００℃ 以上の高温燃焼ガスの輻射熱で加熱蒸発させるものであり、過酷な温度条件にあるが、水壁管材が使用限界温度以上に過熱（オーバヒート）しないような設計がなされている。しかしながらボイラを長時間運転していると水壁管の内面スケールの局所残留による流量アンバランス、メンブレン等の非圧部品の酸化減肉による熱吸収量の変化等により設計当初の流体温度や熱負荷からは予測しえない部位で水壁管材の過熱損傷が生じることがある。
【０００３】
また最近の火力発電用ボイラは、負荷変化運転が頻繁に実施されたり、低負荷運転が継続されることもあり、局所的に熱負荷が高くなる運転時間が増加する傾向にある。
【０００４】
【発明が解決しようとする課題】
従来、火炉水壁管の経時的な材料損傷は、１．５〜３年毎に実施される定期検査時の減肉量測定や非破壊探傷法で検査されている。その際、規定値以上の損傷が見出せれば、その場で新材に更新することになる。また高熱負荷部位や熱応力の高い部位では抜管による破壊検査で材料損傷度を診断しているが、検査数量が限られていることと最も損傷の激しい部位を選定するのが極めて困難という問題がある。
【０００５】
一方、過熱器や再熱器では、管内面の水蒸気酸化スケール厚さから過熱温度を予測する手法が一般的にとられている。過熱器や再熱器では管内面が過熱された水蒸気により、管内面に酸化鉄のスケールが生じる。これを水蒸気酸化と称しているが、この水蒸気酸化によるスケ−ルの厚さが過熱温度と相関関係があることから、前述のように、管内面の水蒸気酸化スケール厚さから過熱温度を予測することが行われている。
【０００６】
これは、炭素鋼や低Ｃｒ鋼の水蒸気酸化スケール厚さｙが次式（１）で表される放物線則
ｙ＝（Ｋｐ・ｔ）０．５ （１）
に従うことから過熱温度を推定する方法である。
ここで、Ｋｐは反応速度定数であり、次式（２）、（３）により求められる。
Ｋｐ＝Ａ×Ｅｘｐ（−Ｑ／ＲＴ） （２）
式（２）は水蒸気酸化の放物線則に基づく実験式であり、Ｑ（材料定数）とＡ（材料定数）は実験により求められる値であり、式（３）で
ｌｏｇ（Ｋｐ）＝ａ＋ｂ（ｌ／Ｔ） （３）
でＫｐを求めることができる。
ここで、ｔ：時間、Ｔ：温度（２７３＋℃ ）、ａ、ｂ：データ回帰式の定数である。
【０００７】
この過熱器や再熱器の管寿命を予測する方法として、特開平８−１１０００６号公報には、同一設計条件の多数の伝熱管の管内面に発生した水蒸気酸化スケールの厚さを非破壊試験により計測し、最もスケール厚さの大きい管を代表管として抽出し、該代表管から寿命を診断するボイラ伝熱管の寿命診断方法が開示されている。
【０００８】
しかし、水壁管でも生成水蒸気酸化スケール厚さｙを同定できれば過熱温度を推定可能であるが、水壁管の場合、水蒸気により酸化される管から溶出する酸化鉄と同成分、同構造の酸化鉄（Ｆｅ３Ｏ４、Ｆｅ２Ｏ３）が水中（つまり管からでなく水中から）より析出付着し、その区別ができないことと定期的（通常２〜５年間隔）に実施される水壁管の脱スケール（化学洗浄、酸洗ともいわれる）のため、単に管内面の酸化スケール厚さｙからでは過熱損傷を予測できない。事実、管内面に１ｍｍ近い酸化スケールが付着していても材料損傷のない部材もある。
【０００９】
図６に過熱器、再熱器管に付着する水蒸気酸化スケールと水中からの酸化鉄が析出して水壁管に付着するスケールが生成する場合の説明図を示す。
【００１０】
従って、現状の技術ではボイラ水壁管で突発的に発生する過熱損傷を見出す手段はないといえる。更に最近では、定期検査間隔が延長される動きがあり、その間、安定運転をするためには、水壁管過熱損傷部位の事前検出技術と数年後の損傷を高精度に予測可能な診断技術の開発が不可欠である。
【００１１】
本発明の課題は、ボイラ水壁管の過熱損傷部位を効率的且つ精度良く検出し、損傷度合い及び残余寿命を高精度に診断する技術を提供することにある。
【００１２】
【課題を解決するための手段】
本発明者らは、鋭意研究調査した結果、管外酸化スケール厚さや管内面酸化スケール密度に着目することで、ボイラ水壁管の過熱（オーバヒート）損傷度を診断できることを見いだした。
【００１３】
すなわち、本発明の上記課題は、次の（１）〜（３）の構成により解決される。
【００１４】
（１）ボイラ火炉水壁管の過熱損傷を診断する手法において、（ａ）前記ボイラ火炉水壁管にかかる熱負荷、ｂ）前記ボイラ火炉水壁管内の蒸気密度、（ｃ）前記ボイラ火炉水壁管外の燃焼ガス温度、前記ボイラ火炉水壁管内の流体温度及び該水壁管管壁の温度の（ａ）、（ｂ）及び（ｃ）のうち少なくとも一つにより過熱可能性領域を予測し、過熱部位を絞り込んだ後、該絞り込んだ部位の火炉側管外面酸化スケール厚さを測定し、該火炉側管外面酸化スケール厚さが１５０μｍ以上の部位を詳細診断部位として、該詳細診断部位のスクリーニングとランキングを行うボイラ水壁管の過熱損傷診断方法。
【００１５】
（２）ボイラ火炉水壁管の過熱損傷を診断する手法において、水壁管内面の酸化物スケールの見掛比重（密度）値より、過熱損傷の有無を評価又は判定するボイラ水壁管の過熱損傷診断方法。
【００１６】
本発明の実施の形態では。管内面酸化スケールの密度が４ｇ／ｃｍ３以上の部位を過熱損傷部位とする。そして、管内面酸化スケールの密度測定手法としては、破壊法（スケール量及びスケール厚さの測定法など）、非破壊法（Ｘ線ＣＴ法、超音波密度法など）が挙げられる。
【００１７】
（３）水壁管火炉側外面の酸化スケール厚さより、損傷部位のスクリーニング及び評価部位のランキングを行ない、水壁管火炉側外面酸化スケール厚さが所定値以上の部位について、管内面酸化スケールの密度を測定し、密度が４ｇ／ｃｍ３以上の部位を過熱損傷部位とし、管内面スケールの密度が４ｇ／ｃｍ３以上の過熱損傷部位に対して、管内面酸化スケール厚さと過熱想定時間から予測し、水壁管の寸法（径及び肉厚）及び内圧より算出した負荷応力と過熱温度、過熱時間及び当該材料の強度よりクリープ損傷率を算出し、残余寿命を診断するボイラ水壁管の過熱損傷診断方法。
【００１８】
【作用】
図２は、ボイラ水壁管断面の一部である。管外面及び内面にそれぞれ酸化スケール３、４が生成又は付着するが、その厚さは、より高温で蒸発が生じる火炉側が厚くなる。また、図３に示したように過熱損傷領域５では管外面、内面共にスケール３、４の厚さが増大する。
【００１９】
管外面酸化スケール３の生成速度も高温程大きくなるが、内面側の流体条件によって伝熱管の過熱温度は異なるため、その厚さから一概に損傷度を評価診断することはできない。図４は水壁管外面の酸化スケール３の厚さと過熱損傷度の関係をプロットしたものである。管外面酸化スケール３の厚さが２００μｍ以上の場合でも過熱損傷のないことがあり、前述したように管外面酸化スケール３の厚さだけで過熱損傷と診断することはできない。しかし、図４からは、過熱損傷の大きい部位では、管外面酸化スケール３の厚さはほとんどのケースで厚くなっており、管外面酸化スケール３の厚さから過熱損傷領域５のスクリーニングや詳細損傷評価部位のランキングをすることができる。
【００２０】
次に、過熱損傷のあった部位と健全部位の水壁管内面酸化スケール４の厚さとスケール量の関係をプロットしてみた。その結果を図５に示す。これから過熱損傷の見られた管内面スケール（ソリッドマーク）４は、健全管（オープンマーク）に比べて同じスケール厚さでも重量（ｍｇ／ｃｍ２）が多く、健全管と過熱損傷管では明確に区別できることを見出した。図中の実線は、比重４ｇ／ｃｍ３の線であり、管内面酸化スケール４に見掛比重（密度）が４ｇ／ｃｍ３以上の管で過熱損傷が生じていることになる。これは、通常の水壁管内面に水中から析出付着する酸化物スケール４は、一般に軟質でポーラスなため見掛の比重が小さいが、過熱損傷領域５では水蒸気酸化スケールが生成し、見掛比重が大きくなったためと推定できる。
【００２１】
前述したように水中からの析出付着スケールと水蒸気酸化スケールの主成分は酸化鉄（Ｆｅ３Ｏ４、Ｆｅ２Ｏ３）で、これらの酸化物の理論比重は、約５．５であり、水蒸気酸化によって生じるスケールは水中析出酸化鉄によるスケールに比べて、より緻密なため、スケールの密度は酸化鉄の密度（比重）の理論値に近づく。なお、健全部での水中からの析出付着スケールの見掛比重（密度）は、約３ｇ／ｃｍ３として、スケール量から厚さ換算されることがある。
【００２２】
スケール成分、構造及び断面光学顕微鏡観察結果から管内面の酸化スケール４が付着析出スケールか水蒸気酸化スケールかを同定することは困難であったが、見掛比重を求めることより容易に判定することができるようになる。
【００２３】
有意な厚み（通常５０μｍ以上）の水蒸気酸化スケールは時間条件にも依存するが、４５０℃ 以上で生成することから、水壁管で水蒸気酸化スケールが生じていれば過熱されていることになる。
【００２４】
管内面火炉側に生成しているスケールが水蒸気酸化スケールであれば、先に述べた放物線則を用い、過熱温度を推定することができ、更に内圧及び寸法より算出した負荷応力値と当該部の材料強度より、現状でのクリープ損傷率や残余寿命を算出できる。
【００２５】
【発明の実施の形態】
以下本発明の具体的実施例をフローシート図面をもって説明する。
図１は、本発明になるボイラ水壁管の過熱損傷診断方法のフローシートである。以下順に内容を記述する。
【００２６】
熱負荷、蒸気密度、想定温度（流体、ガス、メタル）等より過熱可能性領域を予測する。この工程は、過熱部位をある程度絞り込むために実施するものである。
【００２７】
▲２▼管外面酸化スケール３の厚さから損傷部位のスクリーニングと詳細損傷診断部位のランキングをする工程
図４に示したようにボイラ火炉水壁管の過熱損傷が生じている部位は、火炉側外面の酸化スケール３が厚くなる明確な傾向があることから、管外面酸化スケール３の厚さが１００〜１５０μｍ以上の部位を詳細評価部位に選定する。
【００２８】
詳細評価する部位の順序あるいはランキングは、外面酸化スケール厚さの厚い順にすればよい。管外面酸化スケール厚さの測定方法としては、超音波法が好適であるが、その他の方法を採用してもよい。外観上、外面酸化スケール３が剥離している場合には、より高温になっている可能性が高く、その部位は剥離分を加算して評価すべきである。
【００２９】
▲３▼管内面酸化スケール４の見掛比重（密度）を測定する工程
破壊検査法（抜管サンプルによりスケール量（ｍｇ／ｃｍ２）及びスケール厚さ（ｍｍ）を測定し、見掛比重を算出）あるいは非破壊検査法（Ｘ線ＣＴ法、超音波密度法等）で管内面側の酸化スケール４の見掛比重（密度）を測定する。
【００３０】
▲４▼過熱損傷の有無の判定をする工程
水壁管内面側酸化スケール４の見掛比重（密度）の値が、４ｇ／ｃｍ３以上である部位を過熱損傷部位と判定する（図５参照）。本発明の主旨は、水壁管内面の酸化スケール４の見掛比重（密度）から過熱損傷の有無を判定することにある。
【００３１】
▲５▼水壁管内面スケール厚さ及び過熱時間より過熱温度を算定する工程
水壁管内面の酸化物スケール４が見掛比重（密度）の高い水蒸気酸化スケールになっている場合には、水蒸気酸化スケール成長の放物線則から過熱温度を算定することができる。前述したように、水蒸気酸化スケール厚さ（ｙ：ｍｍ）は、前記（１）式で表示できる。
【００３２】
ボイラ水壁管に多用されているＳＴＢＡ２０（０．５Ｃｒ−０．５Ｍｏ鋼）を例にとり、過熱温度の試算結果（℃ ）を次の表１に示す。範囲で示したのは、データのばらつきを考慮したものである。
【００３３】
【表１】
このように、見掛比重の大きい水蒸気酸化スケール厚さと想定過熱時間から過熱温度を一義的に求めることができる。
【００３５】
▲６▼メタル温度、内圧による負荷応力及び材料強度よりクリープ損傷率及び残余寿命を予測診断する工程
【００３６】
▲５▼の計算例で３，０００ｈで３００μｍの水蒸気酸化スケールが生成している場合（メタル温度は、５９０℃ ）を例にとった試算結果を以下に示す。
【００３７】
過熱温度条件（５９０℃ ）、水壁管の寸法（外径φ２５．４×４．２ｍｍ厚さ）及び内圧（２５ＭＰａ）から算出した負荷応力（６５ＭＰａ）及び当該材（ＳＴＢＡ２０）のクリープ強度から３，０００ｈ時点でのクリープ損傷率を計算すると１８％となる。さらに同条件での残余寿命（クリープ損傷率が１００％になるまでの時間）は、９，０００ｈであると試算できる。
【００３８】
なお、クリープ損傷率は、次式（４）の当該部材の負荷応力とクリープ寿命のラルソンミラーパラメータの関係回帰式より算出できる。
Ｐ＝Ｔ＋（ｃ＋ｌｏｇ（ｔ）） （４）
ここで、Ｔは絶対温度（Ｋ：２７３＋℃ ）、ｔは時間（ｈ）、ｃは定数である。また、Ｐは温度と時間で定まるラルソンミラーパラメータ（Ｐ）と称される値であり、負荷応力とクリープ破断するＰ値との間に２次曲線で近似できる相関関係があり、その関係式を用いて損傷率を算出する。
【００３９】
例えば、ＳＴＢ４１０鋼の負荷応力とＰの関係式から、負荷応力７０ＭＰａの場合、クリープ寿命Ｐとして、Ｐ＝１５，５００が得られる。当該部の温度が、５００℃の場合、クリープ破断時間は、約２０，０００時間となる。
【００４０】
上記式（４）に、Ｐ＝１５，５００、ｃ＝１５．７５３、Ｔ＝２７３＋５００、を代入してｔを求めた値（約２０，０００ｈ）が、クリープ寿命、現時点での運転（昇温）時間が１２，０００ｈでは、残余寿命が（２０，０００−１２，０００）で８，０００ｈとなり、クリープ損傷率は、（１２，０００／２０，０００）で６０％となる。
【００４１】
【発明の効果】
本発明は、以上のような構成であることから、ボイラ水壁管の予測しえない部位で生じる過熱損傷を高精度且つ効率的に診断できることから予防保全に有効であり、火力発電プラントでの安定した電力供給が可能となる。
【図面の簡単な説明】
【図１】 本発明になるボイラ水壁管の過熱損傷診断方法のフローである。
【図２】 ボイラ水壁管の一部の断面図である。
【図３】 ボイラ水壁管の一部の断面図である。
【図４】 水壁管外面の酸化スケールの厚さと過熱損傷度の関係を示す図である。
【図５】 過熱損傷のあった部位と健全部位の水壁管内面酸化スケールの厚さとスケール量の関係を示した図である。
【図６】 過熱器、再熱器管に付着する水蒸気酸化スケールと水中からの酸化鉄が析出して水壁管に付着する場合の説明図である。
【符号の説明】
１ ボイラ火炉水壁管 ２ メンブレン
３ 管外面酸化スケール ４ 管内面酸化スケール
５ 過熱損傷領域[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a damage diagnosis technique for a thermal power generation system, and more particularly, to a method for efficiently and accurately diagnosing local overheating damage of a boiler furnace evaporative water wall pipe.
[0002]
[Prior art]
Furnace water wall pipes for power generation boilers heat and evaporate high-temperature and high-pressure water with radiant heat of high-temperature combustion gas of 1000 ° C or higher, and under severe temperature conditions, Designed to prevent overheating. However, if the boiler is operated for a long time, the fluid temperature and heat load at the initial stage of the design may be due to flow unbalance due to local residue on the inner scale of the water wall pipe and changes in heat absorption due to oxidation thinning of non-pressure parts such as membranes. May cause overheating damage to water wall pipes at unpredictable locations.
[0003]
Moreover, recent boilers for thermal power generation tend to increase the operation time during which the heat load increases locally because load change operation is frequently performed or low load operation is continued.
[0004]
[Problems to be solved by the invention]
Conventionally, the material damage of the furnace water wall pipe over time has been inspected by a thinning amount measurement or a nondestructive flaw detection method during a periodic inspection carried out every 1.5 to 3 years. At that time, if damage more than the specified value is found, it will be renewed on the spot. In addition, material damage is diagnosed by destructive inspection by extubation at high heat load parts and parts with high thermal stress, but there are problems that the number of inspections is limited and it is extremely difficult to select the most damaged parts. is there.
[0005]
On the other hand, in a superheater or a reheater, a method of predicting a superheat temperature from the steam oxidation scale thickness on the inner surface of the tube is generally taken. In the superheater and reheater, the scale of iron oxide is generated on the inner surface of the tube due to the steam heated on the inner surface of the tube. This is called steam oxidation. Since the thickness of the scale due to steam oxidation has a correlation with the superheat temperature, as described above, the superheat temperature is predicted from the steam oxidation scale thickness on the inner surface of the pipe. Things have been done.
[0006]
This is because the steam oxidation scale thickness y of carbon steel or low Cr steel is expressed by the following formula (1): parabolic law y = (Kp · t) 0.5 (1)
This is a method for estimating the overheating temperature from the following.
Here, Kp is a reaction rate constant, and is obtained by the following equations (2) and (3).
Kp = A × Exp (−Q / RT) (2)
Equation (2) is an empirical equation based on the parabolic law of steam oxidation, Q (material constant) and A (material constant) are values obtained by experiments, and log (Kp) = a + b (l / T) (3)
Kp can be obtained by
Here, t: time, T: temperature (273 + ° C.), a, b: constants of the data regression equation.
[0007]
As a method for predicting the tube life of this superheater or reheater, JP-A-8-110006 discloses a nondestructive test of the thickness of steam oxidation scale generated on the inner surface of a large number of heat transfer tubes under the same design conditions. A life diagnosis method for a boiler heat transfer tube is disclosed in which the tube having the largest scale thickness is extracted as a representative tube and the life is diagnosed from the representative tube.
[0008]
However, the superheat temperature can be estimated if the water vapor oxidation scale thickness y can be identified even in the water wall tube, but in the case of the water wall tube, the oxidation has the same composition and structure as the iron oxide eluted from the tube oxidized by the water vapor. The water wall that iron (Fe 3 O 4 , Fe 2 O 3 ) is deposited from the water (that is, not from the tube but from the water) and cannot be distinguished from the water wall that is regularly (usually every 2 to 5 years) Due to the descaling of the tube (also called chemical cleaning or pickling), overheating damage cannot be predicted simply from the oxide scale thickness y on the inner surface of the tube. In fact, there is a member that is not damaged even if an oxide scale close to 1 mm adheres to the inner surface of the tube.
[0009]
FIG. 6 shows an explanatory diagram when a steam oxidation scale adhering to the superheater / reheater tube and a scale in which iron oxide from the water is deposited and adheres to the water wall tube are generated.
[0010]
Therefore, it can be said that there is no means for detecting the overheat damage suddenly occurring in the boiler water wall pipe with the current technology. More recently, there has been a movement to extend the periodic inspection interval. During this time, in order to ensure stable operation, a technology for pre-detecting water wall overheating damage and a diagnostic technology that can predict damage after several years with high accuracy. Development is essential.
[0011]
The subject of this invention is providing the technique which detects the overheat damage site | part of a boiler water wall pipe | tube efficiently and accurately, and diagnoses a damage degree and the remaining lifetime with high precision.
[0012]
[Means for Solving the Problems]
As a result of diligent research and investigation, the present inventors have found that the degree of overheating damage of the boiler water wall tube can be diagnosed by paying attention to the thickness of the outer tube oxide scale and the tube inner surface oxide scale density.
[0013]
That is, the said subject of this invention is solved by the structure of following (1)-(3).
[0014]
(1) In a method for diagnosing overheat damage of a boiler furnace water wall pipe , (a) a thermal load applied to the boiler furnace water wall pipe, b) steam density in the boiler furnace water wall pipe, (c) the boiler furnace water Predict the overheating potential region by at least one of the combustion gas temperature outside the wall tube, the fluid temperature in the boiler furnace water wall tube, and the temperature of the water wall tube wall (a), (b) and (c). and, after narrowing down overheating site, the furnace side pipe outer surface oxide scale thickness of a portion narrowed the measured,該火furnace side pipe outer surface oxide scale thickness to a site above 150μm as the detailed diagnostic region, the detailed diagnosis site A boiler water wall pipe overheating damage diagnosis method that performs screening and ranking.
[0015]
(2) In the method of diagnosing boiler furnace water wall pipe overheating damage, the boiler water wall pipe overheating is evaluated or judged based on the apparent specific gravity (density) value of the oxide scale on the inner surface of the water wall pipe. Damage diagnosis method.
[0016]
In the embodiment of the present invention. A site where the density of the pipe inner surface oxide scale is 4 g / cm 3 or more is defined as a site of overheat damage. Examples of the density measuring method for the tube inner surface oxidized scale include a destructive method (such as a method for measuring a scale amount and a scale thickness) and a nondestructive method (such as an X-ray CT method, an ultrasonic density method).
[0017]
(3) Based on the oxide scale thickness on the outer surface of the water wall tube furnace side, the damaged portion is screened and the ranking of the evaluation portion is performed. The density is measured, and the part where the density is 4g / cm 3 or more is regarded as the overheat damage part, and the overheat damage part where the density of the pipe inner surface scale is 4g / cm 3 or more is predicted from the pipe inner surface oxide scale thickness and the estimated overheating time. Overheating of boiler water wall pipe, which calculates the creep damage rate based on the load stress calculated from the dimensions (diameter and wall thickness) of the water wall pipe and the internal pressure, overheating temperature, overheating time and strength of the material, and diagnoses the remaining life Damage diagnosis method.
[0018]
[Action]
FIG. 2 is a part of a cross section of the boiler water wall tube. Oxide scales 3 and 4 are formed or attached to the outer surface and the inner surface of the tube, respectively, but the thickness is thicker on the furnace side where evaporation occurs at a higher temperature. Further, as shown in FIG. 3, in the overheat damage region 5, the thicknesses of the scales 3 and 4 increase on both the outer surface and the inner surface of the pipe.
[0019]
The generation rate of the outer surface oxide scale 3 increases as the temperature increases. However, since the superheat temperature of the heat transfer tube differs depending on the fluid condition on the inner surface side, the degree of damage cannot be generally evaluated and diagnosed from its thickness. FIG. 4 is a plot of the relationship between the thickness of the oxide scale 3 on the outer surface of the water wall tube and the degree of overheating damage. Even when the thickness of the tube outer surface oxide scale 3 is 200 μm or more, there may be no overheating damage, and as described above, it is impossible to diagnose overheating damage only by the thickness of the tube outer surface oxidation scale 3. However, from FIG. 4, the thickness of the tube outer surface oxide scale 3 is thick in most cases at the portion where the overheat damage is large. From the thickness of the tube outer surface oxide scale 3, the overheat damage area 5 is screened and detailed damage is observed. It is possible to rank evaluation sites.
[0020]
Next, the relationship between the thickness and the amount of scale of the water wall pipe inner surface oxidation scale 4 of the site where the overheat damage was caused and the healthy site was plotted. The result is shown in FIG. The pipe inner scale (solid mark) 4 where overheat damage was seen from now on has a larger weight (mg / cm 2 ) than the healthy pipe (open mark) even at the same scale thickness. I found that I could distinguish. The solid line in the figure is a line having a specific gravity of 4 g / cm 3 , and overheating damage has occurred in a tube having an apparent specific gravity (density) of 4 g / cm 3 or more on the tube inner surface oxidation scale 4. This is because the oxide scale 4 deposited and adhered to the inner surface of a normal water wall tube is generally soft and porous, so that the apparent specific gravity is small, but in the overheat damage region 5, a steam oxide scale is generated, and the apparent specific gravity is generated. It can be estimated that has increased.
[0021]
As described above, the main component of the deposition deposit scale from water and the steam oxidation scale is iron oxide (Fe 3 O 4 , Fe 2 O 3 ), and the theoretical specific gravity of these oxides is about 5.5. Since the scale generated by oxidation is denser than the scale formed by iron oxide precipitated in water, the density of the scale approaches the theoretical value of the density (specific gravity) of iron oxide. In addition, the apparent specific gravity (density) of the deposition adhesion scale from the water in the healthy part may be about 3 g / cm 3 and converted from the scale amount to the thickness.
[0022]
Although it was difficult to identify whether the oxide scale 4 on the inner surface of the tube is an adhesion precipitation scale or a steam oxidation scale from the scale component, structure and cross-sectional optical microscope observation results, it can be easily determined by determining the apparent specific gravity. become able to.
[0023]
Although the steam oxidation scale having a significant thickness (usually 50 μm or more) depends on the time condition, it is generated at 450 ° C. or more, so if the steam oxidation scale is generated in the water wall tube, it is overheated.
[0024]
If the scale generated on the tube inner surface furnace side is the steam oxidation scale, it is possible to estimate the superheating temperature using the parabola law described above, and the load stress value calculated from the internal pressure and dimensions and the corresponding part From the material strength, the current creep damage rate and remaining life can be calculated.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of the present invention will be described with reference to flow sheet drawings.
FIG. 1 is a flow sheet of a method for diagnosing overheating damage to a boiler water wall pipe according to the present invention. The contents are described in the following order.
[0026]
Predict the overheating potential area from the heat load, vapor density, assumed temperature (fluid, gas, metal), etc. This step is intended to implement in order to narrow down the overheating site to some extent.
[0027]
(2) The process of screening damage sites and ranking the detailed damage diagnosis site based on the thickness of the oxide scale 3 on the outer surface of the pipe As shown in FIG. Since there is a clear tendency that the outer surface oxide scale 3 becomes thicker, a portion where the thickness of the tube outer surface oxide scale 3 is 100 to 150 μm or more is selected as a detailed evaluation portion.
[0028]
The order or ranking of the parts to be evaluated in detail may be in the order of increasing outer surface oxide scale thickness. An ultrasonic method is suitable as a method for measuring the outer surface oxide scale thickness, but other methods may be employed. When the outer surface oxide scale 3 is peeled in appearance, it is highly possible that the outer surface oxide scale 3 is at a higher temperature, and the portion should be evaluated by adding the peeled portion.
[0029]
(3) Process destruction inspection method for measuring the apparent specific gravity (density) of the pipe inner surface oxidized scale 4 (Measure the amount of scale (mg / cm 2 ) and scale thickness (mm) from the extracted pipe sample, and calculate the apparent specific gravity. ) Or the non-destructive inspection method (X-ray CT method, ultrasonic density method, etc.), the apparent specific gravity (density) of the oxide scale 4 on the tube inner surface side is measured.
[0030]
(4) Process for determining the presence or absence of overheating damage A portion where the apparent specific gravity (density) of the oxidation scale 4 on the water wall pipe inner surface side is 4 g / cm 3 or more is determined as an overheating damage portion (see FIG. 5). ). The gist of the present invention is to determine the presence or absence of overheating damage from the apparent specific gravity (density) of the oxide scale 4 on the inner surface of the water wall tube.
[0031]
(5) Process of calculating superheat temperature from water wall pipe inner surface scale thickness and superheat time When the oxide scale 4 on the inner surface of the water wall pipe is a steam oxidation scale with a high apparent specific gravity (density), The superheating temperature can be calculated from the parabolic law of oxide scale growth. As described above, the steam oxidation scale thickness (y: mm) can be expressed by the equation (1).
[0032]
Taking STBA20 (0.5Cr-0.5Mo steel) frequently used for boiler water wall pipes as an example, the trial calculation results (° C) of the superheating temperature are shown in Table 1 below. The range shows the data variation.
[0033]
[Table 1]
Thus, the superheat temperature can be uniquely determined from the steam oxidation scale thickness having a large apparent specific gravity and the assumed superheat time.
[0035]
(6) A process for predicting and diagnosing the creep damage rate and the remaining life from the load stress and material strength due to the metal temperature and internal pressure.
In the calculation example of (5), a trial calculation result in the case where a steam oxidation scale of 300 μm is generated at 3,000 hours (metal temperature is 590 ° C.) is shown below.
[0037]
3 from the superheat temperature condition (590 ° C.), the dimensions of the water wall tube (outer diameter φ25.4 × 4.2 mm thickness), the load stress (65 MPa) calculated from the internal pressure (25 MPa) and the creep strength of the material (STBA20). The creep damage rate at 1,000 hours is 18%. Furthermore, the remaining life (time until the creep damage rate reaches 100%) under the same conditions can be estimated to be 9,000 h.
[0038]
The creep damage rate can be calculated from the relational regression equation between the load stress of the member and the Larson mirror parameter of the creep life in the following equation (4).
P = T + (c + log (t)) (4)
Here, T is an absolute temperature (K: 273 + ° C.), t is time (h), and c is a constant. P is a value called a Larson Miller parameter (P) determined by temperature and time, and there is a correlation that can be approximated by a quadratic curve between the load stress and the P value at which creep rupture occurs. Use to calculate the damage rate.
[0039]
For example, from the relational expression between the load stress of STB410 steel and P, when the load stress is 70 MPa, the creep life P is P = 15,500. When the temperature of the part is 500 ° C., the creep rupture time is about 20,000 hours.
[0040]
The value obtained by substituting P = 15,500, c = 15.753, T = 273 + 500 into the above formula (4) (about 20,000 h) is the creep life, the current operation (temperature increase) ) When the time is 12,000 h, the remaining life is (20,000-12,000) and becomes 8,000 h, and the creep damage rate becomes (12,000 / 20,000) and 60%.
[0041]
【The invention's effect】
Since the present invention is configured as described above, it is effective for preventive maintenance because it can accurately and efficiently diagnose overheat damage that occurs in an unpredictable part of the boiler water wall pipe. Stable power supply is possible.
[Brief description of the drawings]
FIG. 1 is a flowchart of a method for diagnosing overheating damage of a boiler water wall pipe according to the present invention.
FIG. 2 is a partial cross-sectional view of a boiler water wall pipe.
FIG. 3 is a partial cross-sectional view of a boiler water wall pipe.
FIG. 4 is a diagram showing the relationship between the thickness of the oxide scale on the outer surface of the water wall tube and the degree of overheating damage.
FIG. 5 is a diagram showing the relationship between the thickness and scale amount of a water wall pipe inner surface oxidation scale of a site where overheat damage has occurred and a healthy site.
FIG. 6 is an explanatory diagram when the steam oxidation scale adhering to the superheater and the reheater tube and iron oxide from the water are deposited and adhere to the water wall tube.
[Explanation of symbols]
1 Boiler Furnace
Claims (4)
（ａ）前記ボイラ火炉水壁管にかかる熱負荷、
（ｂ）前記ボイラ火炉水壁管内の蒸気密度、
（ｃ）前記ボイラ火炉水壁管外の燃焼ガス温度、前記ボイラ火炉水壁管内の流体温度及び該水壁管管壁の温度
のうち少なくとも一つにより過熱可能性領域を予測し、過熱部位を絞り込んだ後、該絞り込んだ部位の火炉側管外面酸化スケール厚さを測定し、該火炉側管外面酸化スケール厚さが１５０μｍ以上の部位を詳細診断部位として、該詳細診断部位のスクリーニングとランキングを行うことを特徴とするボイラ水壁管の過熱損傷診断方法。In the method of diagnosing overheating damage of boiler furnace water wall pipes,
(A) heat load applied to the boiler furnace water wall pipe;
(B) the steam density in the boiler furnace water wall pipe,
(C) Combustion gas temperature outside the boiler furnace water wall tube, fluid temperature in the boiler furnace water wall tube, and temperature of the water wall tube wall
After predicting the overheatable region by at least one of the above , and narrowing down the overheated portion, the furnace side tube outer surface oxide scale thickness of the narrowed portion is measured, and the furnace side tube outer surface oxide scale thickness is 150 μm or more. A method for diagnosing overheating damage to a boiler water wall pipe, wherein the detailed diagnosis part is screened and ranked using the part as a detailed diagnosis part.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP25909699A JP3892629B2 (en) | 1999-09-13 | 1999-09-13 | Overheat damage diagnosis method for boiler water wall pipe |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP25909699A JP3892629B2 (en) | 1999-09-13 | 1999-09-13 | Overheat damage diagnosis method for boiler water wall pipe |
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| JP2001082702A JP2001082702A (en) | 2001-03-30 |
| JP3892629B2 true JP3892629B2 (en) | 2007-03-14 |
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Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN103438424B (en) * | 2013-08-28 | 2015-12-09 | 贵州电力试验研究院 | The method of supercritical once-through boiler adjustment water-cooling wall temperature and device |
| JP6510755B2 (en) * | 2013-12-27 | 2019-05-08 | 川崎重工業株式会社 | Scale adhesion amount estimation system |
| CN107490000B (en) * | 2017-08-28 | 2019-03-08 | 北京航空航天大学 | A kind of the wall temperature monitoring method and system at Dissimilar Metal Joints In Power Boilers position |
| CN111161806B (en) * | 2019-12-30 | 2023-10-17 | 国家能源集团科学技术研究院有限公司 | Method for calculating oxide film thickness of martensitic heat-resistant steel under supercritical high-temperature steam |
| JP2023078869A (en) * | 2021-11-26 | 2023-06-07 | 三菱重工業株式会社 | Maintenance method for boiler facility |
| CN116796621B (en) * | 2023-03-23 | 2023-12-12 | 国能长源荆门发电有限公司 | Oxidation detection method and system for superheater tube |
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