JP3776549B2 - Low cycle corrosion fatigue resistant steam turbine rotor - Google Patents
Low cycle corrosion fatigue resistant steam turbine rotor Download PDFInfo
- Publication number
- JP3776549B2 JP3776549B2 JP05308197A JP5308197A JP3776549B2 JP 3776549 B2 JP3776549 B2 JP 3776549B2 JP 05308197 A JP05308197 A JP 05308197A JP 5308197 A JP5308197 A JP 5308197A JP 3776549 B2 JP3776549 B2 JP 3776549B2
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- Prior art keywords
- turbine rotor
- steam turbine
- nickel plating
- corrosion fatigue
- electroless nickel
- Prior art date
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Description
【0001】
【発明の属する技術分野】
本発明は耐低サイクル腐食疲労性に優れた低合金鋼製の蒸気タービンロータに関する。
【0002】
【従来の技術】
蒸気タービンロータは通常、3.5NiCrMoV鋼などの低合金鋼で製造され、コーティング等の表面処理を施すことなく、機械加工仕上げのままで使用されている。
また、スクリュー式ポンプにおいては耐食、耐摩耗性付与を目的としてロータ表面に厚さ50μm以下の無電解ニッケルメッキの施工が行われている(特開平2−108885号公報、特開平3−290086号公報など)。
蒸気タービンの作動流体である湿り蒸気は一般的に腐食性を有している。このような腐食性環境下で低合金製タービンロータを長期間使用すると、タービンの起動、停止による遠心力変化やタービン翼の振動に起因する繰り返し荷重により翼取付け溝部や圧力バランス穴部等の高応力の繰り返しを受ける部位では、腐食疲労(低サイクル腐食疲労)が発生し、タービンロータの健全性が損なわれるという不具合が生じる。
【0003】
蒸気タービンロータに耐食、耐摩耗性付与の目的でコーティングを施す場合、蒸気タービンロータのコーティングには数十年間の長期間使用に耐えること、蒸気タービンの加工公差は1/100mmのオーダの精度なのでコーティング厚さの精度としては1/1000mmのオーダで誤差のないこと、腐食環境下での高応力の繰り返しに耐えることなどの厳しい要求を満たすことが必要で、また、コストへの影響も大きいことなどから、適当なコーティング方法は見出されていなかった。すなわち、従来の耐食、耐摩耗コーティングが施工される部品は、大きな応力が作用しない容器、軸などであり、この場合はコーティング層が密着していれば十分機能を発揮する。しかしながら、本発明が対象とする蒸気タービンロータでは大きな歪みが繰り返されるために、従来のコーティングでは破損したり、少数回の繰り返しにしか耐えられず、使用できなかった。
【0004】
【発明が解決しようとする課題】
本発明はこのような従来技術の実状に鑑み、腐食性環境下で使用される蒸気タービンロータの高応力が繰り返し作用する部位に容易に施工が可能で、腐食性環境下で高応力が繰り返し作用した場合に生じる腐食疲労(低サイクル腐食疲労)に対して優れた耐性を有するコーティング被膜が形成された蒸気タービンロータを提供しようとするものである。
【0005】
【課題を解決するための手段】
本発明者らは前記目的を達成するため、蒸気タービンロータへのコーティング被膜の形成について鋭意検討を進め、燐含有量を適切に制御した無電解ニッケルメッキが、低サイクル腐食疲労に対して優れた耐性を示すことを見出し、本発明を完成した。
【0006】
すなわち、本発明は低合金鋼製のタービンロータの高応力が腐食環境下で繰り返し作用する部位の表面に、7.5〜9.5重量%の燐を含有する無電解ニッケルメッキ層を、10〜30μmの厚さで形成させてなることを特徴とする蒸気タービンロータである。
【0007】
【発明の実施の形態】
本発明の蒸気タービンロータは3.5NiCrMoV鋼などの低合金鋼製のタービンロータの高応力が腐食環境下で繰り返し作用する部位の表面に、燐の含有量を7.5〜9.5重量%の範囲に制御した無電解ニッケルメッキ層を、10〜30μmの厚さで形成させたものである。前記無電解ニッケルメッキはタービンロータの翼取付溝など高応力が腐食環境下で繰り返し作用する部位に施工すればよいが、条件によってはタービンロータ表面全体に施工してもよいことはもちろんである。
【0008】
ニッケルメッキは燐含有量によって耐低サイクル腐食疲労特性が変化するので、高応力部位に適用するには適切な燐含有量範囲に制御する必要がある。無電解ニッケルメッキ層中の燐の含有量が前記範囲を外れると耐疲労特性が悪くなり、少数回の繰り返しでメッキ層に割れが発生し耐食効果を失うので好ましくない。
【0009】
無電解ニッケルメッキ層の厚さが10μm未満では耐低サイクル腐食疲労性の付与効果が十分でなく、また、30μmを超えるとメッキ層と基材間の密着力が弱くなり、剥離しやすくなるので好ましくない。
【0010】
次に本発明の蒸気タービンロータについて図面を用いて説明する。図1は本発明の蒸気タービンロータの1実施態様であるタンジェンシャルエントリ式と呼ばれる翼取付構造のタービンロータの翼取付溝に燐含有無電解ニッケルメッキを施した例を示す説明図であり、図1(a)は断面図、図1(b)は図1(a)のA部拡大図、図1(c)は無電解ニッケルメッキを施した翼溝の状態を示す断面図である。この例ではタービンロータ1の外周に円周方向にTルートと呼ばれる翼溝2が連続して設けられており、翼3は翼溝2に挿入され、タービンロータの円周方向に順次植え込まれている。
【0011】
翼溝2の内面に無電解ニッケルメッキ層10を形成させる施工方法としては図3の説明図にその概要を示すように、ロータ外周にシール4を介して円環状のメッキ溶液槽5を取付ける。所定濃度に調製されたメッキ溶液6はポンプ7によってメッキ溶液槽5に循環させる。メッキを安定に進行させるために、ロータ表面及びメッキ溶液槽5の外表面は温度調節器8を備えたヒータ9により一定温度に保つ構造とする。この方法により、図1(c)に示すように無電解ニッケルメッキ層10を形成させた蒸気タービンロータが得られる。
【0012】
前記無電解ニッケルメッキ層を形成させた本発明の蒸気タービンロータは、耐低サイクル腐食疲労性が改善され、高ひずみが繰り返されてもひずみ誘起による腐食溶解の程度が減少し、腐食疲労き裂発生寿命が延長されたものとなっている。
前記のとおり燐含有量5〜10重量%の無電解ニッケルメッキ自体は防食、耐摩耗用コーティング被膜として従来から使用されているが、その中でも燐含有量を7.5〜9.5重量%の範囲に調製したものは高応力が104回のオーダで繰り返される部位における低サイクル腐食疲労に耐える被膜として使用できることは知られていなかった。
【0013】
【実施例】
以下実施例により本発明の効果を実証する。
(実施例)
低合金素材で作製した試験片表面に燐含有量を変えた無電解ニッケルメッキ層を形成させ、蒸気タービン作動環境を模擬した模擬環境水中で低サイクル腐食疲労寿命測定試験を行った。
使用した試験片は図4に示す形状、寸法(図中の数値の単位はmm)の3.5NiCrMoV鋼(組成は重量%でNi:3.5%、Cr:1.8%、Mo:0.3%、V:0.1%)からなる試験片であり、これに燐含有量をメッキ層中における燐含有量がそれぞれ2、6及び8重量%となるように調製したメッキ液(主成分は硫酸ニッケル、次亜燐酸ソーダ、アルキルヒドロキシカルボン酸等)を使用して厚さ20μmの無電解ニッケルメッキ層を形成させた。これらの試験片及び比較のため無電解ニッケルメッキ層を形成させていない低合金鋼素材ままの試験片を使用して試験を行った。
【0014】
試験方法は次のとおりである。先ず、これらの試験片を疲労試験装置に取付け、試験片に環境チャンバを取付けてチャンバ内に環境水(温度130℃の純水)をポンプにより100ミリリットル/minの流量で送り試験片に接液させた。その状態で試験片に片振り繰り返し曲げ荷重を、切欠き底ひずみ速度0.014%/minの三角波状波形で連続して与え、試験片に深さ0.5mmのき裂が発生するまで継続した。
【0015】
試験片に負荷したひずみ範囲と、き裂発生繰り返し数との関係を図2に示す。図2においてき裂発生繰り返し数が大きいことは長寿命であること、すなわち、耐低サイクル腐食性に優れていることを示す。図2の結果は、燐含有量2重量%及び6重量%のものは、低合金鋼素材そのままのものに比較して僅かに長寿命となっているがその効果は小さいのに対し、燐含有量が8重量%と高燐含有無電解ニッケルメッキ層を形成させたものが著しく長寿命になることを示している。
【0016】
以上の試験結果から、低合金鋼製のタービンロータの高応力が繰り返し作用する部位の表面に高燐含有電解ニッケルメッキ層を形成させることにより、耐低サイクル腐食疲労性を著しく向上させ得ることがわかる。
【0017】
【発明の効果】
本発明の低合金鋼製のタービンロータの高応力が腐食環境下で繰り返し作用する部位の表面に、7.5〜9.5重量%の燐を含有する無電解ニッケルメッキ層を、10〜30μmの厚さで形成させた蒸気タービンロータは、腐食環境下で高応力が繰り返し作用した場合に生じる腐食疲労(低サイクル腐食疲労)に対して優れた耐性を有しており、蒸気タービンロータの長寿命化が可能となった。また、前記無電解ニッケルメッキ層は、蒸気タービンロータの高応力が腐食環境下で繰り返し作用する部位に容易に施工が可能である。
【図面の簡単な説明】
【図1】本発明の蒸気タービンロータの1実施態様を示す説明図。
【図2】実施例における試験片に負荷したひずみ範囲と、き裂発生繰り返し数との関係を示す図。
【図3】本発明の蒸気タービンロータに無電解ニッケルメッキ層を形成させる施工方法の1例を示す説明図。
【図4】実施例で使用した試験片の形状、大きさを示す説明図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steam turbine rotor made of a low alloy steel excellent in low cycle corrosion fatigue resistance.
[0002]
[Prior art]
Steam turbine rotors are typically manufactured from low alloy steels such as 3.5NiCrMoV steel and used with a machined finish without any surface treatment such as coating.
Further, in the screw type pump, electroless nickel plating with a thickness of 50 μm or less is applied to the rotor surface for the purpose of imparting corrosion resistance and wear resistance (Japanese Patent Laid-Open Nos. 2-108888 and 3-290086). Gazette).
Wet steam which is a working fluid of a steam turbine is generally corrosive. When a low-alloy turbine rotor is used for a long time in such a corrosive environment, the blade mounting groove, pressure balance hole, etc. may become high due to repeated loads resulting from changes in centrifugal force due to turbine start / stop and turbine blade vibration. In the part which receives repeated stress, corrosion fatigue (low cycle corrosion fatigue) occurs, and the malfunction that the soundness of the turbine rotor is impaired occurs.
[0003]
When coating a steam turbine rotor for the purpose of providing corrosion resistance and wear resistance, the coating of the steam turbine rotor should withstand long-term use for several decades, and the processing tolerance of the steam turbine is an accuracy of the order of 1/100 mm. The accuracy of the coating thickness must be on the order of 1/1000 mm, satisfying strict requirements such as being able to withstand repeated high stresses in a corrosive environment, and having a significant impact on cost. Thus, no suitable coating method has been found. That is, the parts to which the conventional corrosion resistance and abrasion resistance coating is applied are containers, shafts, and the like, to which no large stress acts, and in this case, the function is sufficiently exhibited if the coating layer is in close contact. However, since the steam turbine rotor targeted by the present invention is repeatedly subjected to large strains, the conventional coating is damaged or can only be used a few times and cannot be used.
[0004]
[Problems to be solved by the invention]
In view of the actual state of the prior art, the present invention can be easily applied to a portion of a steam turbine rotor used in a corrosive environment where high stress repeatedly acts, and the high stress repeatedly acts in a corrosive environment. It is an object of the present invention to provide a steam turbine rotor on which a coating film having excellent resistance against corrosion fatigue (low cycle corrosion fatigue) generated in the case is formed.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the inventors of the present invention have made extensive studies on the formation of a coating film on the steam turbine rotor, and the electroless nickel plating in which the phosphorus content is appropriately controlled is excellent for low cycle corrosion fatigue. The present invention was completed by finding that it exhibits resistance.
[0006]
That is, according to the present invention, an electroless nickel plating layer containing 7.5 to 9.5% by weight of phosphorus is formed on the surface of a site where high stress of a low-alloy steel turbine rotor repeatedly acts in a corrosive environment. It is a steam turbine rotor characterized by being formed with a thickness of ˜30 μm.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The steam turbine rotor of the present invention has a phosphorus content of 7.5 to 9.5% by weight on the surface of a portion where the high stress of a turbine rotor made of a low alloy steel such as 3.5NiCrMoV steel repeatedly acts in a corrosive environment. The electroless nickel plating layer controlled in the range of 10 to 30 μm is formed. The electroless nickel plating may be applied to a portion where high stress repeatedly acts in a corrosive environment such as a blade mounting groove of a turbine rotor, but of course, depending on conditions, the electroless nickel plating may be applied to the entire turbine rotor surface.
[0008]
Since nickel plating changes its resistance to low cycle corrosion fatigue depending on the phosphorus content, it must be controlled within an appropriate phosphorus content range for application to high stress sites. If the content of phosphorus in the electroless nickel plating layer is out of the above range, the fatigue resistance is deteriorated, and the plating layer is cracked by a few repetitions and the corrosion resistance is lost.
[0009]
If the thickness of the electroless nickel plating layer is less than 10 μm, the effect of imparting low cycle corrosion fatigue resistance is not sufficient, and if it exceeds 30 μm, the adhesion between the plating layer and the substrate becomes weak, and it becomes easy to peel off. It is not preferable.
[0010]
Next, the steam turbine rotor of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory view showing an example in which phosphorus-containing electroless nickel plating is applied to a blade mounting groove of a turbine rotor of a blade mounting structure called a tangential entry type which is one embodiment of a steam turbine rotor of the present invention. 1 (a) is a cross-sectional view, FIG. 1 (b) is an enlarged view of a portion A in FIG. 1 (a), and FIG. 1 (c) is a cross-sectional view showing a state of a blade groove subjected to electroless nickel plating. In this example,
[0011]
As a construction method for forming the electroless
[0012]
The steam turbine rotor of the present invention formed with the electroless nickel plating layer has improved low cycle corrosion fatigue resistance, and the degree of corrosion dissolution due to strain induction is reduced even when high strain is repeated. The generation life is extended.
As described above, the electroless nickel plating itself having a phosphorus content of 5 to 10% by weight has been conventionally used as a coating film for anticorrosion and abrasion resistance. Among them, the phosphorus content is 7.5 to 9.5 % by weight . It was not known that those prepared in the range could be used as a coating that withstands low cycle corrosion fatigue at sites where high stress is repeated on the order of 10 4 times.
[0013]
【Example】
The effects of the present invention will be demonstrated by the following examples.
(Example)
An electroless nickel plating layer with varying phosphorus content was formed on the surface of a test piece made of a low alloy material, and a low cycle corrosion fatigue life measurement test was conducted in simulated environment water simulating a steam turbine operating environment.
The test piece used is a 3.5NiCrMoV steel having the shape and dimensions shown in FIG. 4 (the unit of the numerical values is mm) (composition is Ni: 3.5%, Cr: 1.8%, Mo: 0% by weight). .3%, V: 0.1%), and a plating solution prepared by adjusting the phosphorus content so that the phosphorus content in the plating layer is 2, 6 and 8% by weight, respectively (mainly The component used was nickel sulfate, sodium hypophosphite, alkylhydroxycarboxylic acid, etc.) to form an electroless nickel plating layer having a thickness of 20 μm. The test was carried out using these test pieces and the test pieces made of the low alloy steel material in which the electroless nickel plating layer was not formed for comparison.
[0014]
The test method is as follows. First, these test pieces are attached to a fatigue test apparatus, an environmental chamber is attached to the test piece, and environmental water (pure water at a temperature of 130 ° C.) is sent into the chamber at a flow rate of 100 ml / min. I let you. In that state, a single-sided repeated bending load is continuously applied to the test piece in a triangular waveform with a notch bottom strain rate of 0.014% / min, and continued until a crack with a depth of 0.5 mm occurs on the test piece. did.
[0015]
FIG. 2 shows the relationship between the strain range loaded on the test piece and the number of repeated crack initiations. In FIG. 2, a large number of crack initiation repetitions indicates a long life, that is, excellent low cycle corrosion resistance. The results of FIG. 2 show that the phosphorus content of 2% by weight and 6% by weight has a slightly longer life than the low alloy steel material as it is, but the effect is small, whereas the phosphorus content The amount of 8% by weight and the formation of an electroless nickel plating layer containing high phosphorus shows that the lifetime is remarkably increased.
[0016]
From the above test results, low cycle corrosion fatigue resistance can be remarkably improved by forming a high phosphorus content electrolytic nickel plating layer on the surface of the site where the high stress of the turbine rotor made of low alloy steel repeatedly acts. Recognize.
[0017]
【The invention's effect】
An electroless nickel plating layer containing 7.5 to 9.5% by weight of phosphorus is formed on the surface of a site where high stress of the low-alloy steel turbine rotor of the present invention repeatedly acts in a corrosive environment. The steam turbine rotor formed with a thickness of 5 mm has excellent resistance to corrosion fatigue (low cycle corrosion fatigue) that occurs when high stress is repeatedly applied in a corrosive environment. The service life can be extended. The electroless nickel plating layer can be easily applied to a site where high stress of the steam turbine rotor repeatedly acts in a corrosive environment .
[Brief description of the drawings]
FIG. 1 is an explanatory view showing one embodiment of a steam turbine rotor of the present invention.
FIG. 2 is a diagram showing a relationship between a strain range loaded on a test piece and the number of repeated crack generations in Examples.
FIG. 3 is an explanatory diagram showing an example of a construction method for forming an electroless nickel plating layer on the steam turbine rotor of the present invention.
FIG. 4 is an explanatory view showing the shape and size of a test piece used in Examples.
Claims (1)
Priority Applications (1)
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JP05308197A JP3776549B2 (en) | 1997-03-07 | 1997-03-07 | Low cycle corrosion fatigue resistant steam turbine rotor |
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JP05308197A JP3776549B2 (en) | 1997-03-07 | 1997-03-07 | Low cycle corrosion fatigue resistant steam turbine rotor |
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JPH10252408A JPH10252408A (en) | 1998-09-22 |
JP3776549B2 true JP3776549B2 (en) | 2006-05-17 |
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JP05308197A Expired - Fee Related JP3776549B2 (en) | 1997-03-07 | 1997-03-07 | Low cycle corrosion fatigue resistant steam turbine rotor |
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US20040258192A1 (en) * | 2003-06-16 | 2004-12-23 | General Electric Company | Mitigation of steam turbine stress corrosion cracking |
JP4959316B2 (en) * | 2006-12-20 | 2012-06-20 | 三菱重工業株式会社 | Corrosion-resistant covering member and rotating machine |
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