JP2004019918A - Valve arrangement and method of manufacturing the valve arrangement - Google Patents

Valve arrangement and method of manufacturing the valve arrangement Download PDF

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Publication number
JP2004019918A
JP2004019918A JP2002180094A JP2002180094A JP2004019918A JP 2004019918 A JP2004019918 A JP 2004019918A JP 2002180094 A JP2002180094 A JP 2002180094A JP 2002180094 A JP2002180094 A JP 2002180094A JP 2004019918 A JP2004019918 A JP 2004019918A
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Japan
Prior art keywords
valve
hard alloy
valve device
alloy
cobalt
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JP2002180094A
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JP4220186B2 (en
Inventor
Kura Shindo
進藤 蔵
Shunichi Horii
堀井 俊一
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Toshiba Corp
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Toshiba Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly efficient and highly reliable valve arrangement capable of preventing the oxide film of the sliding parts thereof from occurring under high fluid temperature conditions and preventing sticking from occurring even when a clearance between sliding members, for example, between the valve stem and bush of a steam valve is reduced. <P>SOLUTION: In this valve arrangement installed in a flow passage for a high temperature fluid, a movable part 9 operating according to the opening and closing of the valve and a fixed member 10 allowed to abut on the movable member are heated in the fluid. The movable member 9 is made of an austenitic heat resistant alloy of 30 to 80% in Ni content, and the fixed member 10 in slidable contact with the movable member 9 is made of a corrosive and heat resistant alloy. The slidable contact surface of one member uses the hardfaced surface of a base metal, and the slidable contact surface of the other member is made of a hard alloy containing Co. <P>COPYRIGHT: (C)2004,JPO

Description

【0001】
【発明の属する技術分野】
本発明は、例えば火力発電プラントの高温蒸気流路に設けられる弁装置およびその製造方法に関するものである。
【0002】
【従来の技術】
火力発電プラントの蒸気タービンには蒸気の流入を制御するために、主蒸気止め弁,蒸気加減弁,再熱蒸気止め弁,中間阻止弁,タービンバイパス弁等の種々の弁装置が付設されている。
【0003】
このような火力発電プラントの蒸気条件の高温・高圧化は、その効率向上に寄与する非常に重要かつ基本的な要因であるが、1960年代に24.1MPa、538/566℃の一段再熱の蒸気条件がわが国の事業用火力タービンの標準的なものとして確立されてからは、最近に至るまで画期的な進展はみられなかった。しかし、オイルショック以来、省エネルギ化が強力に推進され、その後の地球温暖化問題に対する急速な関心の高まりから火力発電プラントの高効率化が押し進められ蒸気温度は、593℃、600℃、610℃というようにステップ的に上昇してきている。昨今の趨勢は、蒸気温度についてより高温化の方向にあり、さらに635℃、650℃、700℃、725℃以上の蒸気温度の採用が検討されている。
【0004】
従来では、事業用火力発電プラントにおいて、24.1MPa、538〜566℃の蒸気条件が広く採用されているが、その大きな要因となっているのは、弁装置の各部材の構成に使用される材料のコスト的制約である。
【0005】
これら弁装置の各部材を構成する材料は、弁箱がクロム−モリブデン−バナジウム鋼に代表されるフェライト系合金などの耐熱合金鋼である。また、可動部材とこれに摺接する静止部材、例えば弁棒とブッシュとの材料の組合せについては、耐摩耗性を増加させて耐用年数を長くする目的で、例えば特許第2941544号に示されているように、ブッシュ材料を12%クロム鋼、弁棒の材料をニッケル30〜50%オーステナイト系耐熱合金とし、かつそれら部材の表面処理方法として表面窒化処理を施すことが広く知られており、この技術は実際に広く使用されてきた。
【0006】
このようなブッシュ材料が12%クロム鋼、弁棒の材料がニッケル30〜50%オーステナイト系耐熱合金の場合には、高温下においては金属表面が常温に比較して活性化状態となり、雰囲気中の高温水蒸気と反応して酸化皮膜を生成し易い。昨今の趨勢から蒸気温度についても、より高温化の方向にあり、例えば650℃以上の蒸気温度の採用が検討されている。このような高温化の傾向のもとでは、生成した酸化皮膜が弁の繰返し開閉動作の度に剥離を起こし、剥離片が弁棒の摺動により表面の凹部に局部的に堆積してブッシュとの間隙を埋め、弁棒のスティックを発生させる。
【0007】
このため、蒸気タ―ビンの定検時に弁棒まわりを分解し、酸化皮膜を落とすための手入れが必要となり、また堆積物発生量を予め見込んで弁棒とブッシュとの間隙を大きくとるため、弁棒の周りから漏洩する蒸気量が多くなり、プラント全体の熱効率を低下させる等の問題が生じる。
【0008】
また、これら摺動部材の接触面に形成された窒化層は、その窒化処理温度に因り約500℃以上で分解し、軟化する性質を持ち、また窒化層の厚さが極めて薄いため窒化層がなくなると摩耗が急激に進展する欠点がある。
【0009】
【発明が解決しようとする課題】
上記のように、静止部材の材料が12%クロム鋼、可動部材の材料がニッケル30〜50%オーステナイト系耐熱合金の場合、窒化による表面硬化処理を行っているが、この窒化層は高温使用条件下においては、長期間の運転によって軟化し、耐摩耗性が低下すること、更に酸化皮膜の付着防止に対し、十分な性能が得られない等の問題がある。
【0010】
本発明はこのような事情に鑑みてなされたもので、流体温度および流体圧力が高い条件の弁装置に適用する場合、摺動部の酸化皮膜の発生を少なくすることができ、摺動部材、たとえば蒸気弁の弁棒とブッシュとの間隙を小さくしてもスティックを防止することができ、それにより漏洩蒸気量を最小にすることができ、高効率で高信頼性のある弁装置を提供することを目的とする。また、本発明は、摺動部材の耐摩耗性を増加させ、部品の耐用年数が長く、経年的な補修費或いは取替え費を軽減することができる弁装置を提供することを目的とする。
【0011】
さらに、本発明は上記の酸化皮膜の発生が抑制される弁装置の製造に有効な弁装置の製造方法を提供することを目的とする。
【0012】
【課題を解決するための手段】
酸化皮膜は時間とともに成長し、高温蒸気条件下では耐食性に優れているニッケル30〜50%オーステナイト系合金鋼は、12%クロム鋼よりも若干低いながら、共に低合金鋼に比べ1/3以上の速さで酸化皮膜が発生、成長する。一方、コバルトを主成分とするコバルト基硬質合金の酸化皮膜の発生速度は、弁と弁座の当たり面である蒸気シート部に従来から使用されてきた実績から格段に低いことが知られている。
【0013】
本発明は、このような知見に基づいてなされたものであり、ブッシュと弁棒のような弁装置における互いに摺接する可動部材と静止部材、即ちあらゆる摺動部材の接触面の酸化皮膜の生成を防止するために、摺動部材の少なくとも片方の接触面にコバルト基硬質合金肉盛層等として適用するものである。
【0014】
コバルトを主成分とするコバルト基硬質合金(例えばステライト(商品名))は、高温域での硬さの低下が小さく、クロムを多量に含有しているため耐酸化性に優れた材料である。しかし、ステライト自体は靭性に乏しいことから、溶着後の冷却速度が大きいと熱応力によって溶着金属に割れが発生することもあり、溶着施工にあたっては予熱、層間温度、後熱処理等充分に管理して行うことが重要である。
【0015】
また、肉盛を行うブッシュの材料によってはブッシュの母材自体にも割れが発生することがある。中でも、ブッシュ材料が12%クロム鋼、すなわちブッシュの母材がマルテンサイト系合金鋼は、焼き入れ硬化性が大きいこと等のため特に肉盛溶着時に割れを生じ易い。
【0016】
これに対し、ステライトの熱膨張係数は、ステライトの種類によりおおよそ13.0×10−6/℃〜15.0×10−6/℃程度であることから、ブッシュの材料(母材)と使用されるステライトの熱膨張係数に大きな差が無く、実際使用条件下における加熱冷却の熱サイクルに対して発生する熱応力が小さくなるように、ほぼ同程度の熱膨張係数にある材質、たとえばニッケルクロム鋼や3%クロム以下の低合金鋼等が選定され使用されている。
【0017】
このようなステライトの肉盛溶着方法として、コバルト基硬質合金溶接ワイヤを用いた酸素アセチレン法、TIG(Tungsten Inert Gas)法、被覆アーク法、PTA(Plasma Transferred Arc)法、レーザ法およびコバルト基硬質合金粉末を溶射あるいは塗布して硬質合金層を形成する手段等があり、被加工部品の構造や形状、寸法、材料によりそれぞれの特徴に合わせ適宜選択される。
【0018】
しかし、溶接に類するTIG法等によっては母材の溶け込み量が大きいため、母材への熱影響が大きく母材の材質劣化が懸念されるため、母材への肉盛溶着時の入熱を極小に抑えられる最適肉盛厚みを把握する必要がある。
【0019】
発明者らは、前述の各肉盛溶着方法において、母材の溶け込み(希釈)が生じても、ステライト肉盛溶着部の表面(摺動面)がステライト自体の特性(たとえば硬度を基準として)を充分に発揮する厚みとして0.1mm以上、望ましくは1mm以上、また部品の形状や材質によっては3mm程度必要であることを種々の試作試験にて見出した。なお、3mmを超えると表面形状の変化等により管理が困難となる。
【0020】
また溶射手段による場合には、母材を溶融させることなく溶射層を形成することができるので、母材の材質による影響を受けることがなく、厚みは0.5mm以下でステライト自体の十分な特性を得ることができ、溶接に比べて入熱量が非常に少量であるため母材の変形も抑えることができ、母材の組織が変化することもないことを確認している。
【0021】
ところで、今後蒸気温度が566℃以上、さらに610℃以上、特に650℃以上のように高温化し、かつ蒸気圧力も現状より高い蒸気条件が採用された場合、弁棒等の可動部材に作用する荷重は蒸気圧力に比例して増大するため、弁棒等の発生応力は大きくなる。従って、このニッケル30〜50%オーステナイト系合金鋼弁棒は高温高圧蒸気条件に耐え得るように金属組織が均質で緻密な状態の素材を鍛造にて製造する。
【0022】
しかし、将来的には、より高温強度に優れた特性を確保するため、ニッケルを50%以上含むニッケル基合金、あるいはコバルトを50%以上含むコバルト基合金に代表されるオーステナイト系合金鋼材料にかえることは有効であり実施可能である。
【0023】
一方、コバルト基硬質合金の肉盛を施したブッシュ、シーリング等の静止部材については、弁棒等の可動部材と異なり、駆動装置側から作用する荷重や蒸気圧力により作用する外力が直接作用しないため、ブッシュ等に発生する作用応力は小さい。しかし、このような高温蒸気温度が採用された場合には、単なる静止構造物でありながらも、弁棒等とブッシュ等との摺動部間隙を均等に確保するため、ブッシュ等自体は最低限剛性を保つ必要があり、そのためには耐食耐熱合金でなければならない。
【0024】
本発明においては、材料として、たとえばニッケルクロム鋼や3%クロム以下の低合金鋼等を選定して使用するが、ステライトの熱膨張係数と大きな差が無く、ほぼ同程度の熱膨張係数をもつ材質であれば、ブッシュ等の形状や寸法にこだわる必要はない。すなわち、弁装置おいて、蒸気温度が、蒸気圧力も現状より高い蒸気条件が採用された場合、ブッシュを保持している上蓋材質は、弁箱と同様なクロム−モリブデン−バナジウム鋼などのフェライト系耐熱低合金鋼であれば、ブッシュ構造(独立した部品)よりは、むしろ直接上蓋の当該部分にコバルト基硬質合金の肉盛溶着を施すことも可能である。また、上蓋のような大型鋼塊の製造性に優れ、さらに良好な耐食耐熱特性を示すコバルトを50%以上含むコバルト基合金のオーステナイト系耐熱合金を上蓋材質として採用する場合には、コバルト基硬質合金のステライトと同様な材料となり熱膨張係数の差に注意する必要なく、上蓋の当該部分に直接肉盛溶着を施すことができる。
【0025】
同様に、上蓋として大型鋼塊の製造性に優れ、さらに良好な耐食耐熱特性を示すコバルトを50%以上含むコバルト基合金のオーステナイト系耐熱合金を採用することも可能である。この場合には、弁装置の中でさらに大型である弁箱としても、自ずと耐食耐熱特性を示すコバルトを50%以上含むコバルト基合金のオーステナイト系耐熱合金が使用できることになり、上蓋及び弁箱のボルト締めによる接合部が同一材料となるため、実運転中における熱膨張差の発生も少なく、大型静止部品である弁箱は均質で良好な状態の素材を製作することができ、強度を十分に確保することができる。なお、これら上蓋や弁箱の製造手段は、鍛造と鋳造のいずれでも可能であり良好な結果が得られる。
【0026】
ステライトは、コバルトを主成分とするコバルト基硬質合金であるが、その他硬質合金の種類として機械的特性が類似したニッケルを主成分とするニッケル基硬質合金も適用することができる。
【0027】
ニッケル基硬質合金の熱膨張係数は、おおよそ12.0×10−6/程度であり、高い耐腐食性を有しているため、コバルト基硬質合金と同様に使用することが可能であることから、当該硬化層の材質を変更することは容易である。なお、上蓋および弁箱については、ニッケルを35%以上含むニッケル基合金に代表されるオーステナイト系耐熱合金によって形成することも可能である。
【0028】
一方、弁棒は硬化処理したニッケル30〜50%のオーステナイト系耐熱合金で構成するが、前述したニッケル基硬質合金もクロムを含有しているため耐酸化性に優れた材料である。したがって、当該ニッケル30〜50%のオーステナイト系耐熱合金の弁棒表面に同種材料であるニッケル基硬質合金を肉盛にて形成して作製することも可能である。
【0029】
この場合、相手方であるブッシュについては、コバルト基硬質合金を肉盛にて形成することが望ましい。両者の摺動面はニッケル基硬質合金とコバルト基硬質合金との組合せとなるが、実使用条件下では両者間に硬度差(コバルト基硬質合金>ニッケル基硬質合金)が生ずるため摺動面の焼付きは発生せず、さらに酸化皮膜の付着が最少に抑制される。なお、弁棒以外の可動部材、例えば弁体等に対しても、ニッケル基硬質合金、または材料の組合わせに応じてコバルト基硬質合金を肉盛にて形成して作製することが可能である。
【0030】
弁装置には、弁棒とブッシュの如き摺動部が多数存在し、従来ではそれらのほとんどが表面に窒化処理を施し、かつ微少間隙を有しているため、耐摩耗性が低下することや、酸化皮膜が付着する等の欠点があった。すなわち、このような弁装置ではいずれの摺動部においても同様な欠点を抱えており、今後蒸気温度が566℃以上、特に650℃以上で、蒸気圧力も現状より高い蒸気条件が採用された場合を考慮した場合には何らかの策が必要である。例えば上蓋のシールリングと弁体との摺動部も同様である。これらの部位に対しても、上述した材料の組合わせや製造方法を適用することができる。すなわち、弁棒を弁体に置き換え、またブッシュをシールリングに置き換えて本発明を適用することである。
【0031】
なお、本発明において、摺動部としては、弁棒とブッシュの如き直線運動(軸方向)に限らず、例えばバタフライ弁のように弁棒が回転運動(周方向)の場合でも、弁棒等とブッシュ等との相対関係および構造は同一であるため有効に適用することができる。
【0032】
また、本発明は、キー溝などのように、大きな形状変化部分を有する弁装置を製造する上で構造的に局部的に多量の硬質合金層を形成する必要がある場合にも適用することができる。
【0033】
キー溝のような構造では、肉盛溶着作業前の素材状態では、大きな凹加工を行い、その凹部全体に硬質合金を肉盛溶着した後でキー溝加工を行っている。この場合、既に説明したように、ステライト自体は靭性に乏しいことから、溶着後の冷却速度が大きいと、熱応力によって溶着金属に割れが発生することが知られている。このような大きな凹加工部に肉盛溶着した場合には、溶着肉盛量がその周囲円周に比べ多量となる。そこで、冷却速度が遅く、冷却速度にアンバランスが生じ、たとえ溶着施工にあたっては予熱温度、後熱処理等充分に管理しても、特に溶着肉盛量の変化する接合部分(境界部分)に割れが発生している。
【0034】
このような欠点は、コバルト基硬質合金の肉盛溶着については、たとえば均一な厚みを有する摺動面の表面層にのみ適用される技術に留まる恐れがある。すなわち、今後の弁装置の技術進歩を考えるに際し、上記のような不均一な肉厚形状に対しても硬質合金を肉盛溶着する技術が望まれる。ニッケル基のオーステナイト系鉄鋼は展延性に富む材料であることから、ニッケルを50%以上含むニッケル基合金のオーステナイト系耐熱合金を、あらかじめ凹部を囲むように全周に肉盛によって形成し、凹部の肉盛溶着部とその周囲円周の肉盛溶着部位を物理的に区分させ、その後施工するコバルト基硬質合金の肉盛溶着施工時には、コバルト基硬質合金の溶着肉盛量の変化する接合部分(境界部分)の割れを防止する緩衝材として機能させる。このような、溶着肉盛量の変化する接合部分(境界部分)に展延性に富む材料を用いて、コバルト基硬質合金肉盛層に仕切りを入れる方法は、弁棒の如く摺動面が外径に位置するものであっても、またブッシュの如く、内径に位置するものであっても、いずれの場合にも効果的に適用することができる。
【0035】
以上の知見に基づき、請求項1に係る発明では、高温流体の流路に設けられる弁装置であって、弁開閉に伴って動作する可動部材と、この可動部材に摺接する静止部材とが前記流体により高温化される構成のものにおいて、前記可動部材をNi含有率が30〜80%のオーステナイト系耐熱合金製とする一方、これに摺接する前記静止部材を耐食耐熱合金製とし、これら両部材のうち、一方の部材の摺接面は母材の硬化処理面とし、他方の部材の摺接面はCoを含有する硬質合金により構成したことを特徴とする弁装置を提供する。
【0036】
請求項2に係る発明では、前記可動部材または静止部材の摺接面を構成する硬質合金は、当該部材にその母材と同一材料により一体に構成され、または当該部材にその母材と異なる材料の肉盛により厚さが3mm以下の硬質合金層として構成され、または当該部材に固定された筒状体の表面に肉盛により厚さが3mm以下の硬質合金層として構成されている請求項1記載の弁装置を提供する。
【0037】
請求項3に係る発明では、前記硬質合金層が施される部材は、当該硬質合金の熱膨張係数と同程度の熱膨張係数を有する材質により構成されている請求項2記載の弁装置を提供する。
【0038】
請求項4に係る発明では、前記硬質合金層は、硬質合金ワイヤの溶接または硬質合金粉末の溶射もしくは塗布により形成されている請求項2または3記載の弁装置を提供する。
【0039】
請求項5に係る発明では、前記可動部材は弁体または弁棒であり、前記静止部材は弁箱または弁蓋に設けられて前記弁体または弁棒に摺接するシールリングまたはブッシュである請求項1記載の弁装置を提供する。
【0040】
請求項6に係る発明では、前記弁棒は、Ni含有率が50%以上のニッケル基合金のオーステナイト系耐熱合金またはCo含有率が50%以上のコバルト基合金のオーステナイト系耐熱合金によって形成されている請求項5記載の弁装置を提供する。
【0041】
請求項7に係る発明では、前記ブッシュは前記弁蓋に機械的な押え部材により固定され、または冷し嵌めにより固定され、または前記弁蓋の弁棒挿通部位の孔に直接硬質合金を肉盛溶着することにより硬質合金層として形成されている請求項5記載の弁装置を提供する。
【0042】
請求項8に係る発明では、前記弁蓋は、Co含有率が50%以上のコバルト基合金またはNi含有率が35%以上のニッケル基合金のオーステナイト系耐熱合金にて構成されている請求項5記載の弁装置を提供する。
【0043】
請求項9に係る発明では、前記弁箱は、Co含有率が50%以上のコバルト基合金またはNi含有率が35%以上のニッケル基合金のオーステナイト系耐熱合金にて構成されている請求項5記載の弁装置を提供する。
【0044】
請求項10に係る発明では、前記可動部材および静止部材の摺接面は、コバルト基硬質合金層とニッケル基硬質合金層との組合せとして構成されている請求項1記載の弁装置を提供する。
【0045】
請求項11に係る発明では、摺接面に作用する運動は、直線運動または回転運動である請求項1記載の弁装置を提供する。
【0046】
請求項12に係る発明では、高温流体の流路に設けられる弁装置であって、弁開閉に伴って動作する可動部材同士、または前記可動部材とこれに摺接する静止部材とが、前記流体により高温化される構成のものにおいて、前記可動部材または前記静止部材をNi含有率が30〜80%のオーステナイト系耐熱合金製とする一方、これに摺接する相手方部材を耐食耐熱合金製とし、これら両部材のうち、一方の部材の摺接面は母材の硬化処理面とし、他方の部材の摺接面はCoを含有する硬質合金により構成したことを特徴とする請求項2から11までのいずれかに記載の弁装置を提供する。
【0047】
請求項13に係る発明では、請求項1〜12のいずれかに記載の弁装置の製造に際し、前記可動部材または静止部材の摺動面にCo含有硬質合金層を形成する工程として、コバルト基硬質合金溶接ワイヤを用いた酸素アセチレン法、TIG法、被覆アーク法、PTA法、レーザ法およびコバルト基硬質合金粉末を溶射あるいは塗布して硬質合金層を形成する方法から選択される肉盛溶着を施すことを特徴とする弁装置の製造方法を提供する。
【0048】
請求項14に係る発明では、弁装置の可動部材または静止部材の摺接面に肉盛溶着により硬質合金層を形成する方法において、前記硬質合金層の肉厚が部分的に変化する場合、その肉厚が変化する境界領域に予め展延性金属を肉盛溶着し、その後に前記硬質合金層の肉盛溶着による形成を行うことを特徴とする弁装置の製造方法を提供する。
【0049】
請求項15に係る発明では、弁装置の可動部材または静止部材の摺接面のいずれかに、局部的に多量の硬質合金層を構成する場合、予めNi含有率が50%以上のニッケル基合金のオーステナイト系耐熱合金を肉盛整形し、その後にコバルト基硬質合金の肉盛溶着を施すことを特徴とする弁装置の製造方法を提供する。
【0050】
【発明の実施の形態】
以下、本発明の実施形態について、図面を参照して説明する。
【0051】
第1実施形態(図1、図2)
図1は、本発明の第1実施形態による弁装置を適用した火力発電プラントに設置される蒸気弁の一例を示す断面図である。
【0052】
この蒸気弁1は、蒸気入口2および蒸気出口3を有する弁箱1aと、この弁箱1aの蒸気出口3に設けた弁座4に一端が当接して蒸気出口3を開閉する円筒型の往復動作用の弁体5とを備えている。弁体5は、弁箱1aを塞ぐ弁蓋(上蓋)6の内面側に設けられた円筒状ガイド部7の内周面にシールリング8を介して摺接し、この弁体5の中心部に連結された弁棒9により軸心方向に沿って往復駆動する。弁棒9は、弁蓋6に設けたブッシュ10にその外周面を摺接した状態で挿通され、この弁棒9の外部突出端が駆動用のアクチュエータに連結される。
【0053】
なお、以下の実施例では可動部材としての弁棒9への適用例について説明するが、弁体5に適用する場合も同様である。また、可動部材として、その摺接面に作用する運動が直線運動である場合に限らず、回転運動を行うものである場合にも適用することができる。
【0054】
(実施例1)
上記構成において、弁棒9をニッケル基オーステナイト系耐熱合金製であるインコロイ、インコネル(商品名)等(Ni含有率32.5%、42.5%、59.8%、60%、72%等)により構成した。そして、この弁棒9の表面に硬化処理として、温度600℃のもとで窒化処理を施し、母材自体の表面を硬化させた。
【0055】
また、ブッシュ10は、ニッケルクロム鋼製の弁蓋6に、コバルト基耐食耐熱合金であるステライト(商品名(Co含有率59%、67%))を2mmの厚さで、PTA法により肉盛溶着することにより形成した。
【0056】
そして、蒸気弁1に610℃以上の高温蒸気を供給して、8000時間の稼動試験を行なった結果、いずれの構成についても、弁棒9とブッシュ10との間隙への酸化被膜の堆積は殆ど見られず、スティックも発生しないことが認められた。
【0057】
図2は、例えば650℃以上の加熱条件下における各種材料についての酸化被膜の成長特性の試験結果を示すグラフである。この図2の横軸には時間を表し、縦軸には発生した酸化被膜の厚みを表している(各々単位は無次元化処理済)。
上述したブッシュ10を構成しているコバルト基耐食耐熱合金であるステライトの場合は、図2に特性線Aとして示したように、高温下における酸化被膜の発生が極めて少なく、時間経過に伴う上昇割合が非常に少ないことが分かる。
【0058】
また、特性線Bは、上述した弁棒9の構成材料であるニッケル基オーステナイト系耐熱合金(Ni含有率30〜50%)の特性を示している。この特性線Bに示されたように、ニッケル基合金の場合は、ステライトよりも酸化皮膜の発生量は多いが、時間経過に伴う上昇割合は比較的少ない。
【0059】
これにより、実施例1で示した弁棒9とブッシュ10との材料組合せ構成によれば、流体温度が例えば650℃以上、流体圧力も30MPa以上の高い条件の弁装置に適用する場合においても、摺動部の酸化皮膜の発生を少なくすることができ、弁棒9とブッシュ10との間隙を小さくしてもスティックを防止することができ、それにより漏洩蒸気量を最小にすることができ、高効率かつ高信頼性を得られることが分かる。そして、この結果、従来技術に比して摺動部材の耐摩耗性を増加させることができ、部品の耐用年数の長期化、経年的な補修費或いは取替え費の軽減等が図れるようになる。
【0060】
また、本実施例においては、ブッシュ10を構成するステライトと、弁蓋6を構成するニッケルクロム鋼とが略同等の熱膨張係数であるため、高温使用条件下においても、発生する熱応力が小さく、ブッシュ10に割れ等が発生することがなく、したがって、この割れ防止効果によっても、耐用年数の長期化、補修費或いは取替え費の軽減等が図れる。
【0061】
なお、ブッシュ10を弁蓋6に形成する工程としては、前述した溶射のほか、コバルト基硬質合金溶接ワイヤを用いた酸素アセチレン法、TIG法、被覆アーク法、PTA法、レーザ法等を適用しても、前記同様の効果が得られる。
【0062】
(比較例1)
弁棒9については実施例1同様に、Ni含有量が30〜50のニッケル基オーステナイト系耐熱合金製とし、一方、ブッシュ10については低合金鋼および12%Cr鋼製として、比較を行なった。この結果、流体温度が例えば650℃以上、流体圧力も30MPa以上の高い条件の弁装置に適用する場合に、摺接部に酸化皮膜の発生が多く、弁棒9とブッシュ10との間隙を小さくするとスティックが生じやすく、それにより漏洩蒸気量が大きくなる傾向が見られた。
【0063】
図2の特性線Cは、12%Cr鋼の酸化被膜の発生特性を示し、特性線Dは、低合金鋼の酸化被膜の発生特性を示している。これらの特性線C,Dに示されたように、12%Cr鋼および低合金鋼については、650℃以上の高温下における酸化被膜の発生が多く、時間経過に伴う上昇割合が多いことが明かである。
【0064】
(実施例2)
弁棒9の材料とブッシュ10の材料とを、実施例1と逆とする。すなわち、弁棒9をCo含有率が50%以上のコバルト基合金のオーステナイト系耐熱合金によって形成し、ブッシュ10および弁蓋6をNi含有率が50%以上のニッケル基オーステナイト系耐熱合金製とする。
【0065】
このような構成によっても、図2の結果より、第1実施例と同様の効果が得られる。
【0066】
(実施例3)
ブッシュ10を筒状の独立構成部品として構成し、弁蓋6の孔に対し、押え板等を用いた機械的構成により固定し、または高温条件下でも抜け出ない十分な締め代(1/10mm程度)まで液体窒素を用いた超低温の冷し嵌めにより固定する。
【0067】
このような構成によっても第1実施例と同様の効果が得られる。
【0068】
(実施例4)
弁箱1および弁蓋6を、Co含有率が50%以上のコバルト基合金またはNi含有率が35%以上のニッケル基合金のオーステナイト系耐熱合金にて構成する。
【0069】
これにより、例えば650℃以上の高温蒸気の使用によっても、高信頼性の蒸気弁1を得ることができる。
【0070】
第2実施形態(図3〜図5)
本実施形態は、弁装置の製造方法、特に可動部材同士またはこれと静止部材との摺接面に肉盛溶着により硬質合金層を形成する方法についてのものである。図3は、本実施形態の対象となる可動部材について、一例として弁棒9を示す斜視図である。図4は本実施形態の製造方法を説明するための断面図(図3のX−X線断面図)であり、図5は比較例として従来方法を説明するための断面図である。なお、以下の方法は、弁棒以外の可動部材および静止部材の製造についても同様に適用することができる。
【0071】
例えば弁棒9には、図示しない弁体に対し、軸方向に相対的に摺動する連結構成のものがある。このような構成の場合、図3に示すように、弁棒9にキー溝11(あるいはスプライン溝)が設けられ、弁体側にはキー溝11に嵌合する軸方向に沿う凸部が形成され、これらが互いに摺動する。この嵌合部についても、第1実施形態と同様に、酸化皮膜の堆積を防止する要請が存在し、キー溝11の部位にステライトの肉盛を行う場合がある。
【0072】
この肉盛を行う場合、従来では図5に示すように、弁棒9に肉盛溶着作業前の素材状態において予め、溝11よりも寸法の大きな凹部12の切削加工等を行い、その後、凹部12を埋設する状態で弁棒9の周囲全体に硬質合金13を肉盛溶着し、その後にキー溝11の加工を行っている。
【0073】
この場合、例えば650℃以上の将来の蒸気高温化に備え、本発明では従来の硬質合金13に変えてステライト等のコバルト基合金を適用するが、この場合には上述したように、ステライト自体が靭性に乏しいため、溶着後の冷却速度が大きいと、熱応力によって溶着金属に割れが発生する可能性がある。特に大きな凹加工部に肉盛溶着した場合には、溶着肉盛量がその周囲円周に比べて多量となるため冷却速度が遅くなり、弁棒9の周囲の肉薄な他の部分と比較して、冷却速度にアンバランスが生じ、たとえ溶着施工にあたって予熱温度や後熱処理等を充分に管理しても、特に溶着肉盛量の変化する接合部分(境界部分)14において、ステライトに割れが発生する。
【0074】
そこで、本実施形態においては、図4に示すように、肉盛用として弁棒9に予め形成される大きな凹部12の周囲に対し、ステライト肉盛溶着の前に、コバルト基硬質合金の溶着肉盛量が変化する接合部分(境界部分)14に予めオーステナイト系鉄鋼等の展延性に富む材料、特にニッケルを50%以上含むニッケル基合金のオーステナイト系耐熱合金の肉盛溶着部15を形成し、凹部12内への肉盛溶着部位と弁棒9の周囲円周への肉盛溶着部位とを物理的に区分させる。そして、その後にコバルト基硬質合金であるステライトの全体的な肉盛溶着部13aの施工を行う。
【0075】
このような本実施形態によると、コバルト基硬質合金の溶着肉盛量が変化する接合部分(境界部分)14に予め施工した展延性に富む肉盛溶着部15が緩衝材として機能するので、その接合部分14において、コバルト基合金13aの冷却時における割れを防止することができる。
【0076】
なお、このような緩衝用の肉盛溶着部15は、前述したブッシュ10の如く、部材の内径側に凹部を有する構成の場合については、内周側における溶着肉盛量が変化する接合部分(境界部分)に施工する。
【0077】
【発明の効果】
本発明によれば、流体温度および流体圧力も高い条件の弁装置に適用する場合、摺動部の酸化皮膜の発生を少なくすることができ、摺動部材、たとえば蒸気弁の弁棒とブッシュとの間隙を小さくしてもスティックを防止することができるため、漏洩蒸気量を最小にすることができ、高効率で高信頼性の弁装置を提供することができる。また、本発明の弁装置によれば、摺動部材の耐摩耗性が増加し、部品の耐用年数が長くなるため、経年的な補修費或いは取替え費を軽減することにも繋がるなどの顕著な効果が奏される。さらに、本発明によれば、酸化皮膜の発生が抑制される弁装置の製造に際し、割れ発生等の防止に有効な弁装置を製造することができる。
【図面の簡単な説明】
【図1】本発明の第1実施形態として弁装置の構成を示す断面図。
【図2】前記実施形態による作用効果を説明する特性図。
【図3】本発明の第2実施形態として弁装置の製造方法を説明するための斜視図。
【図4】本発明の第2実施形態として弁装置の製造方法を説明するための断面図。
【図5】前記第2実施形態に対応する従来技術を説明するための断面図。
【符号の説明】
1 弁装置(蒸気弁)
1a 弁箱
2 蒸気入口
3 蒸気出口
4 弁座
5 弁体
6 弁蓋
7 円筒状ガイド部
8 シールリング
9 弁棒
10 ブッシュ
11 キー溝
12 凹部
13 硬質合金
14 接合部分(境界部分)
15 肉盛溶接部
[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to, for example, a valve device provided in a high-temperature steam flow path of a thermal power plant and a method of manufacturing the same.
[0002]
[Prior art]
A steam turbine of a thermal power plant is provided with various valve devices such as a main steam stop valve, a steam control valve, a reheat steam stop valve, an intermediate stop valve, a turbine bypass valve, and the like, in order to control the flow of steam. .
[0003]
Such high-temperature and high-pressure steam conditions of a thermal power plant are very important and fundamental factors contributing to the improvement of the efficiency. However, in the 1960s, 24.1 MPa, 538/566 ° C. single-stage reheating was carried out. Since steam conditions were established as the standard for commercial thermal turbines in Japan, no breakthroughs have been made until recently. However, since the oil crisis, energy saving has been strongly promoted, and the rapid increase in interest in global warming has led to the enhancement of the efficiency of thermal power plants, resulting in steam temperatures of 593 ° C, 600 ° C, and 610 ° C. It is rising step by step. In recent years, the steam temperature is in the direction of higher temperature, and adoption of steam temperatures of 635 ° C., 650 ° C., 700 ° C., and 725 ° C. or more is being considered.
[0004]
In the past, steam conditions of 24.1 MPa and 538 to 566 ° C. have been widely adopted in commercial thermal power plants, but the major factor is that it is used for the configuration of each member of the valve device. This is a material cost constraint.
[0005]
The material constituting each member of these valve devices is a heat-resistant alloy steel such as a ferrite alloy represented by chromium-molybdenum-vanadium steel for the valve box. Further, a combination of a movable member and a stationary member that is in sliding contact with the movable member, for example, a material of a valve stem and a bush is disclosed in, for example, Japanese Patent No. 2941544 for the purpose of increasing wear resistance and extending service life. As described above, it is widely known that the bushing material is 12% chromium steel, the valve stem material is nickel 30-50% austenitic heat-resistant alloy, and surface nitriding is performed as a surface treatment method for these members. Has actually been widely used.
[0006]
When such a bushing material is 12% chromium steel and a valve stem material is nickel 30% to 50% austenitic heat-resistant alloy, the metal surface is activated at a high temperature as compared with a normal temperature, and the atmosphere in the atmosphere has It easily reacts with high-temperature steam to form an oxide film. Due to recent trends, the steam temperature is also in the direction of higher temperature, and for example, adoption of a steam temperature of 650 ° C. or more is being studied. Under such a tendency of high temperature, the generated oxide film is peeled off every time the valve is repeatedly opened and closed, and the peeled pieces are locally deposited in the concave portion of the surface by sliding of the valve rod, and the bush is formed. Fill the gap and generate a stem stick.
[0007]
For this reason, it is necessary to disassemble around the valve stem at the time of regular inspection of the steam turbine and take care to remove the oxide film, and to increase the gap between the valve stem and the bush in anticipation of the amount of deposits generated, The amount of steam leaking from around the valve stem increases, causing problems such as lowering the thermal efficiency of the entire plant.
[0008]
Further, the nitrided layer formed on the contact surface of these sliding members has a property of decomposing and softening at about 500 ° C. or more due to the nitriding temperature, and the nitrided layer is extremely thin, so that the nitrided layer has a very small thickness. When it disappears, there is a disadvantage that abrasion progresses rapidly.
[0009]
[Problems to be solved by the invention]
As described above, when the material of the stationary member is 12% chromium steel and the material of the movable member is nickel 30-50% austenitic heat-resistant alloy, the surface hardening treatment is performed by nitridation. Under the above, there are problems such as softening due to long-term operation, lowering of abrasion resistance, and insufficient performance for preventing adhesion of an oxide film.
[0010]
The present invention has been made in view of such circumstances, and when applied to a valve device under conditions where the fluid temperature and fluid pressure are high, it is possible to reduce the occurrence of an oxide film on the sliding portion, For example, the stick can be prevented even if the gap between the valve stem and the bush of the steam valve is made small, whereby the amount of leaked steam can be minimized, and a highly efficient and highly reliable valve device is provided. The purpose is to: Another object of the present invention is to provide a valve device that increases the wear resistance of a sliding member, has a long service life of components, and can reduce the time-consuming repair or replacement cost.
[0011]
A further object of the present invention is to provide a method of manufacturing a valve device that is effective in manufacturing a valve device in which the generation of the oxide film is suppressed.
[0012]
[Means for Solving the Problems]
The oxide film grows with time, and the nickel 30-50% austenitic alloy steel, which has excellent corrosion resistance under high temperature steam conditions, is slightly lower than the 12% chromium steel, but more than one third of that of the low alloy steel. An oxide film is generated and grows at a rapid rate. On the other hand, it is known that the generation rate of the oxide film of the cobalt-based hard alloy containing cobalt as a main component is extremely low from the results of the conventional use of the steam sheet portion, which is the contact surface between the valve and the valve seat. .
[0013]
The present invention has been made on the basis of such knowledge, and it has been found that a movable member and a stationary member slidably contacting each other in a valve device such as a bush and a valve stem, that is, generation of an oxide film on the contact surfaces of all sliding members. In order to prevent this, at least one of the contact surfaces of the sliding member is applied as a cobalt-based hard alloy overlay layer or the like.
[0014]
A cobalt-based hard alloy containing cobalt as a main component (for example, stellite (trade name)) is a material having excellent oxidation resistance because of a small decrease in hardness in a high temperature range and containing a large amount of chromium. However, since the stellite itself has poor toughness, if the cooling rate after welding is high, cracks may occur in the weld metal due to thermal stress, and in welding work, carefully manage preheating, interlayer temperature, post heat treatment, etc. It is important to do.
[0015]
Also, depending on the material of the bush to be built up, the base material of the bush itself may be cracked. Above all, a 12% chromium steel bushing material, that is, a martensitic alloy steel having a base material of the bushing, has a large quenching hardenability and the like, and is particularly liable to crack during overlay welding.
[0016]
On the other hand, the coefficient of thermal expansion of stellite is approximately 13.0 × 10-6/°C-15.0×10-6/ ° C, there is no significant difference between the thermal expansion coefficient of the material (base material) of the bush and the stellite used, and the thermal stress generated in the heat cycle of heating and cooling under actual use conditions is reduced. As described above, materials having substantially the same coefficient of thermal expansion, for example, nickel-chromium steel and low-alloy steel of 3% chromium or less are selected and used.
[0017]
Such stellite build-up welding methods include an oxygen acetylene method using a cobalt-based hard alloy welding wire, a TIG (Tungsten Inert Gas) method, a coated arc method, a PTA (Plasma Transferred Arc) method, a laser method, and a cobalt-based hard metal method. There is a method of spraying or applying an alloy powder to form a hard alloy layer, and the like is appropriately selected according to the respective features depending on the structure, shape, dimensions, and material of the workpiece.
[0018]
However, depending on the TIG method or the like similar to welding, the amount of penetration of the base material is large, so that the heat influence on the base material is large and the material of the base material may be deteriorated. It is necessary to grasp the optimum overlay thickness that can be minimized.
[0019]
In each of the above-mentioned overlay welding methods, the inventors have found that the surface (sliding surface) of the stellite overlay welding portion has the characteristics of the stellite itself (for example, on the basis of hardness) even if the base material is melted (diluted). It has been found in various trial production tests that a thickness of 0.1 mm or more, desirably 1 mm or more, and a thickness of about 3 mm is required depending on the shape and material of the component. If it exceeds 3 mm, the management becomes difficult due to a change in the surface shape or the like.
[0020]
Further, in the case of using the thermal spraying means, the thermal spray layer can be formed without melting the base material, so that it is not affected by the material of the base material, and the thickness is 0.5 mm or less, and the sufficient characteristics of stellite itself are obtained. It has been confirmed that since the heat input amount is very small compared to welding, the deformation of the base material can be suppressed, and the structure of the base material does not change.
[0021]
By the way, when the steam temperature is increased to 566 ° C. or more, further 610 ° C. or more, especially 650 ° C. or more, and the steam pressure is higher than the present condition, the load acting on the movable member such as the valve rod will be increased. Since the pressure increases in proportion to the steam pressure, the stress generated in the valve stem and the like increases. Therefore, this nickel 30-50% austenitic alloy steel valve stem is manufactured by forging a material having a homogeneous and dense metal structure so as to withstand high-temperature and high-pressure steam conditions.
[0022]
However, in the future, in order to secure more excellent high-temperature strength characteristics, a nickel-based alloy containing 50% or more of nickel or an austenitic alloy steel material represented by a cobalt-based alloy containing 50% or more of cobalt will be used. That is valid and feasible.
[0023]
On the other hand, with respect to stationary members such as bushes and ceilings coated with a cobalt-based hard alloy, unlike a movable member such as a valve rod, an external force acting by a load or a steam pressure acting from a driving device side does not directly act. The acting stress generated in the bush and the like is small. However, when such a high steam temperature is employed, the bush, etc. itself is at least a minimum in order to ensure a uniform sliding portion gap between the valve stem, etc. and the bush, etc., even though it is a mere stationary structure. Rigidity must be maintained, and for that purpose, it must be a corrosion-resistant and heat-resistant alloy.
[0024]
In the present invention, for example, nickel chromium steel or low alloy steel of 3% chromium or less is selected and used as the material, but there is no large difference from the coefficient of thermal expansion of stellite, and the coefficient of thermal expansion is almost the same. If it is a material, there is no need to stick to the shape and dimensions of the bush and the like. That is, in the valve device, when a steam condition in which the steam temperature and the steam pressure are higher than the current one is adopted, the material of the top lid holding the bush is a ferrite material such as chromium-molybdenum-vanadium steel similar to the valve box. If it is a heat-resistant low-alloy steel, it is also possible to apply a build-up welding of a cobalt-based hard alloy directly to the corresponding portion of the upper lid, rather than to the bush structure (independent component). In addition, when an austenitic heat-resistant alloy of a cobalt-based alloy containing 50% or more of cobalt exhibiting good corrosion resistance and heat resistance is used as the material of the upper lid, it is excellent in productivity of a large ingot such as an upper lid. The material becomes similar to that of the alloy stellite, and the overlay welding can be directly applied to the corresponding portion of the upper lid without having to pay attention to the difference in the coefficient of thermal expansion.
[0025]
Similarly, an austenitic heat-resistant alloy of a cobalt-based alloy containing 50% or more of cobalt exhibiting excellent corrosion resistance and heat resistance can be used as the upper lid. In this case, an austenitic heat-resistant alloy of a cobalt-based alloy containing 50% or more of cobalt, which naturally exhibits corrosion and heat resistance, can be used as a valve box which is even larger in the valve device. Since the joints made by bolting are made of the same material, there is little difference in thermal expansion during actual operation, and the valve box, which is a large stationary part, can be made of a homogeneous and good material, with sufficient strength Can be secured. In addition, the means for producing the upper lid and the valve box can be either forging or casting, and good results can be obtained.
[0026]
Stellite is a cobalt-based hard alloy containing cobalt as a main component, but a nickel-based hard alloy containing nickel as a main component and having similar mechanical properties can be used as another hard alloy.
[0027]
The thermal expansion coefficient of a nickel-based hard alloy is approximately 12.0 × 10-6/ About and has high corrosion resistance, so that it can be used in the same manner as a cobalt-based hard alloy, so that it is easy to change the material of the hardened layer. Note that the upper lid and the valve box can be formed of an austenitic heat-resistant alloy typified by a nickel-based alloy containing 35% or more of nickel.
[0028]
On the other hand, the valve stem is made of a 30 to 50% nickel-hardened heat-resistant austenitic alloy, but the above-mentioned nickel-based hard alloy is also a material excellent in oxidation resistance because it contains chromium. Therefore, it is also possible to form a nickel base hard alloy, which is the same kind of material, on the valve stem surface of the austenitic heat-resistant alloy of 30 to 50% nickel by overlaying.
[0029]
In this case, it is desirable to form a cobalt-based hard alloy by overlaying on the other bush. Both sliding surfaces are a combination of a nickel-based hard alloy and a cobalt-based hard alloy, but under actual conditions of use, there is a difference in hardness between them (cobalt-based hard alloy> nickel-based hard alloy), No seizure occurs, and the adhesion of the oxide film is minimized. It should be noted that a movable member other than the valve stem, for example, a valve body, can also be manufactured by forming a nickel-based hard alloy or a cobalt-based hard alloy in accordance with a combination of materials by building up. .
[0030]
A valve device has a large number of sliding parts such as a valve stem and a bush, and most of them have conventionally been subjected to a nitriding treatment on the surface and have minute gaps. Disadvantages, such as adhesion of an oxide film. In other words, such a valve device has the same drawback in any sliding portion, and in the case where the steam temperature is 566 ° C. or more, especially 650 ° C. or more, and the steam pressure is higher than the present condition, it is adopted in the future. When taking into account the above, some measure is necessary. For example, the same applies to the sliding portion between the seal ring of the upper lid and the valve element. The above-described combinations of materials and manufacturing methods can be applied to these parts. That is, the present invention is applied by replacing the valve stem with a valve body and replacing the bush with a seal ring.
[0031]
In the present invention, the sliding portion is not limited to a linear motion (axial direction) such as a valve stem and a bush. For example, even when the valve stem is in a rotary motion (circumferential direction) such as a butterfly valve, the sliding portion is not limited. Since the relative relationship and the structure between the bush and the like are the same, it can be applied effectively.
[0032]
Further, the present invention can be applied to a case where it is necessary to form a large amount of a hard alloy layer locally locally in the manufacture of a valve device having a large shape change portion such as a keyway. it can.
[0033]
In a structure like a key groove, a large concave processing is performed in a raw material state before a build-up welding operation, and a key groove processing is performed after a hard alloy is build-up welded to the entire concave part. In this case, as described above, since stellite itself has poor toughness, it is known that if the cooling rate after welding is high, cracks occur in the deposited metal due to thermal stress. When the overlaid welding is performed on such a large recessed portion, the amount of the overlaid weld is larger than the circumference thereof. Therefore, the cooling rate is slow, and the cooling rate becomes unbalanced. Even if the preheating temperature and post heat treatment are sufficiently controlled during welding, cracks are particularly generated at the joints (boundary portions) where the amount of weld overlay changes. It has occurred.
[0034]
Such a drawback may be limited to a technique applied only to a surface layer of a sliding surface having a uniform thickness, for example, for overlay welding of a cobalt-based hard alloy. That is, in consideration of the technical progress of the valve device in the future, a technique of overlay-welding a hard alloy to the above-mentioned uneven thickness shape is desired. Since nickel-based austenitic steel is a material with high ductility, an austenitic heat-resistant alloy of a nickel-based alloy containing 50% or more of nickel is formed on the entire circumference in advance so as to surround the concave portion, and the surface of the concave portion is formed. The build-up weld and the surrounding circumferential weld area are physically separated, and when the build-up welding of the cobalt-based hard alloy is subsequently performed, the joint where the amount of build-up of the cobalt-based hard alloy changes ( It functions as a cushioning material for preventing cracks at the boundary. Such a method of forming a partition in the cobalt-based hard alloy overlay using a material having high ductility in the joint portion (boundary portion) in which the amount of weld overlay changes, such that the sliding surface is external such as a valve stem. The present invention can be effectively applied to any case regardless of whether it is located at a diameter or an inner diameter such as a bush.
[0035]
Based on the above findings, the invention according to claim 1 is a valve device provided in a flow path of a high-temperature fluid, wherein a movable member that operates with opening and closing of a valve and a stationary member that slides on the movable member are provided. In a configuration in which the temperature is raised by a fluid, the movable member is made of an austenitic heat-resistant alloy having a Ni content of 30 to 80%, and the stationary member slidingly contacting the movable member is made of a corrosion-resistant heat-resistant alloy. Among them, a valve device is provided in which the sliding contact surface of one member is a hardened surface of a base material and the sliding contact surface of the other member is formed of a hard alloy containing Co.
[0036]
In the invention according to claim 2, the hard alloy forming the sliding contact surface of the movable member or the stationary member is formed integrally with the member using the same material as the base material, or a material different from the base material is used as the member. 2. A hard alloy layer having a thickness of 3 mm or less formed by overlaying, or a hard alloy layer having a thickness of 3 mm or less formed by overlaying on the surface of a cylindrical body fixed to the member. A valve device is provided.
[0037]
The invention according to claim 3 provides the valve device according to claim 2, wherein the member to which the hard alloy layer is applied is made of a material having a thermal expansion coefficient substantially equal to a thermal expansion coefficient of the hard alloy. I do.
[0038]
According to a fourth aspect of the present invention, there is provided the valve device according to the second or third aspect, wherein the hard alloy layer is formed by welding a hard alloy wire or spraying or applying a hard alloy powder.
[0039]
In the invention according to claim 5, the movable member is a valve body or a valve stem, and the stationary member is a seal ring or a bush provided on a valve box or a valve lid and slidably in contact with the valve body or the valve stem. 1 provides a valve device.
[0040]
In the invention according to claim 6, the valve stem is formed of an austenitic heat-resistant alloy of a nickel-based alloy having a Ni content of 50% or more or an austenitic heat-resistant alloy of a cobalt-based alloy having a Co content of 50% or more. A valve device according to claim 5 is provided.
[0041]
In the invention according to claim 7, the bush is fixed to the valve lid by a mechanical pressing member, or is fixed by cold fitting, or a hard alloy is directly overlaid on a hole of the valve rod insertion portion of the valve lid. The valve device according to claim 5, wherein the valve device is formed as a hard alloy layer by welding.
[0042]
In the invention according to claim 8, the valve lid is made of an austenitic heat-resistant alloy of a cobalt-based alloy having a Co content of 50% or more or a nickel-based alloy having a Ni content of 35% or more. A valve device is provided.
[0043]
In the invention according to claim 9, the valve box is made of an austenitic heat-resistant alloy of a cobalt-based alloy having a Co content of 50% or more or a nickel-based alloy having a Ni content of 35% or more. A valve device is provided.
[0044]
According to a tenth aspect of the present invention, there is provided the valve device according to the first aspect, wherein sliding surfaces of the movable member and the stationary member are configured as a combination of a cobalt-based hard alloy layer and a nickel-based hard alloy layer.
[0045]
According to the eleventh aspect of the present invention, there is provided the valve device according to the first aspect, wherein the motion acting on the sliding contact surface is a linear motion or a rotary motion.
[0046]
According to the twelfth aspect of the present invention, there is provided a valve device provided in a flow path of a high-temperature fluid, wherein the movable members operating with the opening and closing of the valves, or the movable member and a stationary member slidingly contacting the movable member are formed by the fluid. In the configuration where the temperature is raised, the movable member or the stationary member is made of an austenitic heat-resistant alloy having a Ni content of 30 to 80%, and a mating member slidingly contacting the movable member or the stationary member is made of a corrosion-resistant heat-resistant alloy. The sliding contact surface of one of the members is a hardened surface of the base material, and the sliding contact surface of the other member is formed of a hard alloy containing Co. A valve device is provided.
[0047]
In the invention according to claim 13, when manufacturing the valve device according to any one of claims 1 to 12, the step of forming a Co-containing hard alloy layer on the sliding surface of the movable member or the stationary member includes a cobalt-based hard alloy layer. Applying overlay welding selected from an oxygen acetylene method, a TIG method, a coated arc method, a PTA method, a laser method, and a method of spraying or applying a cobalt-based hard alloy powder to form a hard alloy layer using an alloy welding wire. A method for manufacturing a valve device is provided.
[0048]
In the invention according to claim 14, in the method of forming the hard alloy layer by overlay welding on the sliding surface of the movable member or the stationary member of the valve device, when the thickness of the hard alloy layer partially changes, Provided is a method for manufacturing a valve device, which comprises depositing a spreadable metal in advance in a boundary region where the wall thickness changes, and then forming the hard alloy layer by overlay welding.
[0049]
In the invention according to claim 15, when locally forming a large amount of a hard alloy layer on either the sliding member of the movable member or the stationary member of the valve device, the nickel-based alloy having a Ni content of 50% or more in advance is used. The present invention provides a method for manufacturing a valve device, comprising: forming a build-up of an austenitic heat-resistant alloy as described above, and then performing build-up welding of a cobalt-based hard alloy.
[0050]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0051]
First embodiment (FIGS. 1 and 2)
FIG. 1 is a sectional view showing an example of a steam valve installed in a thermal power plant to which the valve device according to the first embodiment of the present invention is applied.
[0052]
The steam valve 1 has a valve box 1a having a steam inlet 2 and a steam outlet 3, and a cylindrical reciprocating valve for opening and closing the steam outlet 3 by one end abutting on a valve seat 4 provided on the steam outlet 3 of the valve box 1a. And a valve element 5 for operation. The valve element 5 is in sliding contact with the inner peripheral surface of a cylindrical guide portion 7 provided on the inner surface side of a valve lid (upper lid) 6 for closing the valve box 1a via a seal ring 8. The reciprocating drive is performed in the axial direction by the connected valve stem 9. The valve stem 9 is inserted into the bush 10 provided on the valve lid 6 with its outer peripheral surface slidably in contact with the bush 10, and the externally projecting end of the valve stem 9 is connected to a driving actuator.
[0053]
In the following embodiment, an example in which the present invention is applied to the valve rod 9 as a movable member will be described. Further, the present invention can be applied not only to a case where the movement acting on the sliding contact surface is a linear movement but also to a case where the movable member performs a rotational movement.
[0054]
(Example 1)
In the above configuration, the valve stem 9 is made of a nickel-based austenitic heat-resistant alloy such as Incoloy or Inconel (trade name) (Ni content 32.5%, 42.5%, 59.8%, 60%, 72%, etc.). ). Then, as a hardening treatment, the surface of the valve rod 9 was subjected to a nitriding treatment at a temperature of 600 ° C. to harden the surface of the base material itself.
[0055]
In addition, the bush 10 is overlaid on the valve cover 6 made of nickel-chromium steel by a PTA method with a 2 mm thick stellite (trade name (Co content: 59%, 67%)) which is a cobalt-based corrosion-resistant heat-resistant alloy. It was formed by welding.
[0056]
Then, a high-temperature steam of 610 ° C. or more was supplied to the steam valve 1 and an operation test was performed for 8000 hours. As a result, in any of the configurations, the deposition of the oxide film in the gap between the valve rod 9 and the bush 10 was almost impossible. No sticks were found, and no sticking was observed.
[0057]
FIG. 2 is a graph showing test results of growth characteristics of oxide films on various materials under heating conditions of, for example, 650 ° C. or more. In FIG. 2, the horizontal axis represents time, and the vertical axis represents the thickness of the generated oxide film (each unit has been dimensionlessly processed).
In the case of stellite, which is a cobalt-based corrosion-resistant and heat-resistant alloy constituting the bush 10 described above, as shown by the characteristic line A in FIG. Is very small.
[0058]
A characteristic line B shows the characteristics of the nickel-based austenitic heat-resistant alloy (Ni content: 30 to 50%), which is a constituent material of the valve stem 9 described above. As shown by the characteristic line B, in the case of the nickel-based alloy, the amount of oxide film generated is larger than that of stellite, but the rate of increase with time is relatively small.
[0059]
Thus, according to the material combination configuration of the valve stem 9 and the bush 10 shown in the first embodiment, even when the fluid temperature is applied to a valve device under a high condition of, for example, 650 ° C. or more and the fluid pressure is 30 MPa or more, The occurrence of an oxide film on the sliding portion can be reduced, and the stick can be prevented even if the gap between the valve stem 9 and the bush 10 is reduced, thereby minimizing the amount of leaked steam. It can be seen that high efficiency and high reliability can be obtained. As a result, the wear resistance of the sliding member can be increased as compared with the prior art, and the service life of the component can be prolonged, and annual repair costs or replacement costs can be reduced.
[0060]
Further, in the present embodiment, since the stellite constituting the bush 10 and the nickel-chromium steel constituting the valve cover 6 have substantially the same thermal expansion coefficient, the thermal stress generated even under high-temperature use conditions is small. In addition, the bush 10 does not crack or the like, so that the effect of preventing the crack can extend the useful life, reduce the repair cost or the replacement cost, and the like.
[0061]
In addition, as a process of forming the bush 10 on the valve cover 6, in addition to the above-described thermal spraying, an oxygen acetylene method using a cobalt-based hard alloy welding wire, a TIG method, a covered arc method, a PTA method, a laser method, or the like is applied. However, the same effect as described above can be obtained.
[0062]
(Comparative Example 1)
As in Example 1, the valve stem 9 was made of a nickel-based austenitic heat-resistant alloy having a Ni content of 30 to 50, while the bush 10 was made of a low alloy steel and a 12% Cr steel for comparison. As a result, when applied to a valve device having a high fluid temperature of, for example, 650 ° C. or more and a fluid pressure of 30 MPa or more, an oxide film is often generated in the sliding contact portion, and the gap between the valve rod 9 and the bush 10 is reduced. As a result, sticks were liable to be formed, which tended to increase the amount of leaked steam.
[0063]
The characteristic line C in FIG. 2 shows the generation characteristics of the oxide film of the 12% Cr steel, and the characteristic line D shows the generation characteristics of the oxide film of the low alloy steel. As shown by these characteristic lines C and D, it is clear that, for the 12% Cr steel and the low-alloy steel, oxide films are frequently generated at a high temperature of 650 ° C. or higher, and the rate of increase with time is large. It is.
[0064]
(Example 2)
The material of the valve stem 9 and the material of the bush 10 are reversed from those of the first embodiment. That is, the valve stem 9 is formed of a cobalt-based alloy heat-resistant austenitic alloy having a Co content of 50% or more, and the bush 10 and the valve cover 6 are formed of a nickel-based austenitic heat-resistant alloy having a Ni content of 50% or more. .
[0065]
With such a configuration, the same effect as in the first embodiment can be obtained from the result of FIG.
[0066]
(Example 3)
The bush 10 is formed as a cylindrical independent component, and is fixed to the hole of the valve cover 6 by a mechanical structure using a holding plate or the like, or a sufficient interference (about 1/10 mm) which does not come out even under a high temperature condition. ) And fix by ultra-low temperature cold fitting using liquid nitrogen.
[0067]
With such a configuration, the same effect as in the first embodiment can be obtained.
[0068]
(Example 4)
The valve box 1 and the valve lid 6 are made of an austenitic heat-resistant alloy of a cobalt-based alloy having a Co content of 50% or more or a nickel-based alloy having a Ni content of 35% or more.
[0069]
Thus, a highly reliable steam valve 1 can be obtained even by using high-temperature steam of, for example, 650 ° C. or higher.
[0070]
Second embodiment (FIGS. 3 to 5)
The present embodiment relates to a method of manufacturing a valve device, in particular, a method of forming a hard alloy layer by overlay welding on movable members or sliding surfaces between the movable members and the stationary member. FIG. 3 is a perspective view showing a valve stem 9 as an example of a movable member to be an object of the present embodiment. FIG. 4 is a cross-sectional view (cross-sectional view taken along line XX of FIG. 3) for explaining the manufacturing method of the present embodiment, and FIG. 5 is a cross-sectional view for explaining a conventional method as a comparative example. The following method can be similarly applied to the manufacture of a movable member and a stationary member other than the valve stem.
[0071]
For example, the valve rod 9 has a connection structure that slides relatively in the axial direction with respect to a valve element (not shown). In the case of such a configuration, as shown in FIG. 3, a keyway 11 (or a spline groove) is provided in the valve rod 9, and a convex portion is formed on the valve body side along the axial direction to be fitted in the keyway 11. , These slide on each other. As with the first embodiment, there is a demand for preventing the deposition of an oxide film on this fitting portion, and stellite may be overlaid on the keyway 11 in some cases.
[0072]
Conventionally, as shown in FIG. 5, when performing this overlaying, in the material state before the overlay welding operation on the valve stem 9, a cutting process or the like of the concave portion 12 having a size larger than the groove 11 is performed. The hard alloy 13 is build-up welded to the entire periphery of the valve stem 9 in a state where the keyway 11 is buried, and thereafter, the keyway 11 is processed.
[0073]
In this case, a cobalt-based alloy such as stellite is used in the present invention in place of the conventional hard alloy 13 in order to prepare for a future high temperature of steam of 650 ° C. or more, for example. Due to poor toughness, if the cooling rate after welding is high, cracks may occur in the deposited metal due to thermal stress. In particular, when welding is performed on a large recessed portion, the amount of the weld overlay becomes large compared to the circumference thereof, so that the cooling rate is slowed down and compared with other thin portions around the valve rod 9. As a result, the cooling rate becomes unbalanced, and even if the preheating temperature and the post heat treatment are sufficiently controlled during welding, cracks are generated in the stellite, particularly at the joint portion (boundary portion) 14 where the weld overlay changes. I do.
[0074]
Therefore, in the present embodiment, as shown in FIG. 4, before the stellite overlay welding is performed on the periphery of the large recess 12 formed in advance on the valve stem 9 for overlaying, the weld overlay of the cobalt-based hard alloy is welded. A weld overlay 15 of an austenitic heat-resistant austenitic heat-resistant alloy of a nickel-based alloy containing 50% or more of nickel is formed in advance at a joining portion (boundary portion) 14 where the build-up amount changes, such as an austenitic steel or the like, particularly a nickel-based alloy containing 50% or more of nickel. The build-up welding site in the recess 12 and the build-up welding site on the circumference of the valve stem 9 are physically separated. After that, the entire build-up welded portion 13a of stellite, which is a cobalt-based hard alloy, is formed.
[0075]
According to the present embodiment, since the weldable portion 15 with high extensibility previously applied to the joint portion (boundary portion) 14 where the amount of weld overlay of the cobalt-based hard alloy changes functions as a buffer material, In the joint portion 14, cracks during cooling of the cobalt-based alloy 13a can be prevented.
[0076]
In the case of such a configuration in which a concave portion is formed on the inner diameter side of the member, such as the bush 10 described above, such a buffer overlay portion 15 has a joint portion where the weld overlay amount on the inner peripheral side changes. At the boundary).
[0077]
【The invention's effect】
According to the present invention, when applied to a valve device under conditions where the fluid temperature and fluid pressure are also high, the generation of an oxide film on the sliding portion can be reduced, and the sliding member, for example, a valve stem and a bush of a steam valve, The stick can be prevented even if the gap between them is reduced, so that the amount of leaked steam can be minimized, and a highly efficient and highly reliable valve device can be provided. Further, according to the valve device of the present invention, the wear resistance of the sliding member is increased, and the service life of the component is prolonged, which leads to a reduction in chronological repair costs or replacement costs. The effect is achieved. Further, according to the present invention, it is possible to manufacture a valve device that is effective in preventing occurrence of cracks and the like when manufacturing a valve device in which generation of an oxide film is suppressed.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a configuration of a valve device as a first embodiment of the present invention.
FIG. 2 is a characteristic diagram illustrating the operation and effect of the embodiment.
FIG. 3 is a perspective view for explaining a method for manufacturing a valve device as a second embodiment of the present invention.
FIG. 4 is a cross-sectional view for explaining a method for manufacturing a valve device as a second embodiment of the present invention.
FIG. 5 is a sectional view for explaining a conventional technique corresponding to the second embodiment.
[Explanation of symbols]
1 Valve device (steam valve)
1a Valve box
2 Steam inlet
3 Steam outlet
4 valve seat
5 mm valve
6 valve lid
7 Cylindrical guide
8 mm seal ring
9 mm stem
10 bush
11 keyway
12mm recess
13 hard alloy
14 joining part (boundary part)
15 overlay weld

Claims (15)

高温流体の流路に設けられる弁装置であって、弁開閉に伴って動作する可動部材と、この可動部材に摺接する静止部材とが前記流体により高温化される構成のものにおいて、前記可動部材をNi含有率が30〜80%のオーステナイト系耐熱合金製とする一方、これに摺接する前記静止部材を耐食耐熱合金製とし、これら両部材のうち、一方の部材の摺接面は母材の硬化処理面とし、他方の部材の摺接面はCoを含有する硬質合金により構成したことを特徴とする弁装置。A valve device provided in a flow path of a high-temperature fluid, wherein a movable member that operates with opening and closing of a valve and a stationary member that slides on the movable member are heated to a high temperature by the fluid. Is made of an austenitic heat-resistant alloy having a Ni content of 30 to 80%, while the stationary member slidingly contacting the same is made of a corrosion-resistant heat-resistant alloy, and the sliding contact surface of one of the two members is the base metal. A valve device comprising a hardened surface and a sliding surface of the other member made of a hard alloy containing Co. 前記可動部材または静止部材の摺接面を構成する硬質合金は、当該部材にその母材と同一材料により一体に構成され、または当該部材にその母材と異なる材料の肉盛により厚さが3mm以下の硬質合金層として構成され、または当該部材に固定された筒状体の表面に肉盛により厚さが3mm以下の硬質合金層として構成されている請求項1記載の弁装置。The hard alloy which forms the sliding contact surface of the movable member or the stationary member is formed integrally with the member by the same material as the base material, or has a thickness of 3 mm by overlaying the member with a material different from the base material. The valve device according to claim 1, wherein the valve device is configured as a hard alloy layer described below, or is formed as a hard alloy layer having a thickness of 3 mm or less on a surface of a cylindrical body fixed to the member by overlaying. 前記硬質合金層が施される部材は、当該硬質合金の熱膨張係数と同程度の熱膨張係数を有する材質により構成されている請求項2記載の弁装置。The valve device according to claim 2, wherein the member to which the hard alloy layer is applied is made of a material having a thermal expansion coefficient substantially equal to a thermal expansion coefficient of the hard alloy. 前記硬質合金層は、硬質合金ワイヤの溶接または硬質合金粉末の溶射もしくは塗布により形成されている請求項2または3記載の弁装置。The valve device according to claim 2, wherein the hard alloy layer is formed by welding a hard alloy wire or spraying or applying a hard alloy powder. 前記可動部材は弁体または弁棒であり、前記静止部材は弁箱または弁蓋に設けられて前記弁体または弁棒に摺接するシールリングまたはブッシュである請求項1記載の弁装置。The valve device according to claim 1, wherein the movable member is a valve body or a valve stem, and the stationary member is a seal ring or a bush provided on a valve box or a valve lid and slidably contacting the valve body or the valve stem. 前記弁棒は、Ni含有率が50%以上のニッケル基合金のオーステナイト系耐熱合金またはCo含有率が50%以上のコバルト基合金のオーステナイト系耐熱合金によって形成されている請求項5記載の弁装置。The valve device according to claim 5, wherein the valve stem is formed of a heat-resistant austenitic alloy of a nickel-based alloy having a Ni content of 50% or more or a heat-resistant austenitic alloy of a cobalt-based alloy having a Co content of 50% or more. . 前記ブッシュは前記弁蓋に機械的な押え部材により固定され、または冷し嵌めにより固定され、または前記弁蓋の弁棒挿通部位の孔に直接硬質合金を肉盛溶着することにより硬質合金層として形成されている請求項5記載の弁装置。The bush is fixed to the valve lid by a mechanical pressing member, or fixed by cold fitting, or as a hard alloy layer by overlaying and welding a hard alloy directly to the hole of the valve rod insertion site of the valve lid. 6. The valve device according to claim 5, wherein the valve device is formed. 前記弁蓋は、Co含有率が50%以上のコバルト基合金またはNi含有率が35%以上のニッケル基合金のオーステナイト系耐熱合金にて構成されている請求項5記載の弁装置。The valve device according to claim 5, wherein the valve lid is formed of an austenitic heat-resistant alloy of a cobalt-based alloy having a Co content of 50% or more or a nickel-based alloy having a Ni content of 35% or more. 前記弁箱は、Co含有率が50%以上のコバルト基合金またはNi含有率が35%以上のニッケル基合金のオーステナイト系耐熱合金にて構成されている請求項5記載の弁装置。The valve device according to claim 5, wherein the valve box is made of an austenitic heat-resistant alloy of a cobalt-based alloy having a Co content of 50% or more or a nickel-based alloy having a Ni content of 35% or more. 前記可動部材および静止部材の摺接面は、コバルト基硬質合金層とニッケル基硬質合金層との組合せとして構成されている請求項1記載の弁装置。The valve device according to claim 1, wherein the sliding surfaces of the movable member and the stationary member are configured as a combination of a cobalt-based hard alloy layer and a nickel-based hard alloy layer. 摺接面に作用する運動は、直線運動または回転運動である請求項1記載の弁装置。The valve device according to claim 1, wherein the motion acting on the sliding contact surface is a linear motion or a rotary motion. 高温流体の流路に設けられる弁装置であって、弁開閉に伴って動作する可動部材同士、または前記可動部材とこれに摺接する静止部材とが、前記流体により高温化される構成のものにおいて、前記可動部材または前記静止部材をNi含有率が30〜80%のオーステナイト系耐熱合金製とする一方、これに摺接する相手方部材を耐食耐熱合金製とし、これら両部材のうち、一方の部材の摺接面は母材の硬化処理面とし、他方の部材の摺接面はCoを含有する硬質合金により構成したことを特徴とする請求項2から11までのいずれかに記載の弁装置。A valve device provided in a flow path of a high-temperature fluid, wherein the movable members operating with the opening and closing of the valves, or the movable member and a stationary member slidingly contacting the movable member are heated to a high temperature by the fluid. The movable member or the stationary member is made of an austenitic heat-resistant alloy having a Ni content of 30 to 80%, and the other member slidingly contacting the movable member or the stationary member is made of a corrosion-resistant heat-resistant alloy. The valve device according to any one of claims 2 to 11, wherein the sliding surface is a hardened surface of the base material, and the sliding surface of the other member is made of a hard alloy containing Co. 請求項1〜12のいずれかに記載の弁装置の製造に際し、前記可動部材または静止部材の摺動面にCo含有硬質合金層を形成する工程として、コバルト基硬質合金溶接ワイヤを用いた酸素アセチレン法、TIG法、被覆アーク法、PTA法、レーザ法およびコバルト基硬質合金粉末を溶射あるいは塗布して硬質合金層を形成する方法から選択される肉盛溶着を施すことを特徴とする弁装置の製造方法。An oxygen acetylene using a cobalt-based hard alloy welding wire as a step of forming a Co-containing hard alloy layer on the sliding surface of the movable member or the stationary member when manufacturing the valve device according to any one of claims 1 to 12. A valve method characterized by performing a build-up welding selected from a method of forming a hard alloy layer by spraying or applying a cobalt-based hard alloy powder, or a TIG method, a coated arc method, a PTA method, a laser method, and a cobalt method. Production method. 弁装置の可動部材または静止部材の摺接面に肉盛溶着により硬質合金層を形成する方法において、前記硬質合金層の肉厚が部分的に変化する場合、その肉厚が変化する境界領域に予め展延性金属を肉盛溶着し、その後に前記硬質合金層の肉盛溶着による形成を行うことを特徴とする弁装置の製造方法。In the method of forming the hard alloy layer by overlay welding on the sliding surface of the movable member or the stationary member of the valve device, when the thickness of the hard alloy layer partially changes, a boundary region where the thickness changes is used. A method for manufacturing a valve device, comprising: depositing a spreadable metal in advance, and then forming the hard alloy layer by overlay welding. 弁装置の可動部材または静止部材の摺接面のいずれかに、局部的に多量の硬質合金層を構成する場合、予めNi含有率が50%以上のニッケル基合金のオーステナイト系耐熱合金を肉盛整形し、その後にコバルト基硬質合金の肉盛溶着を施すことを特徴とする弁装置の製造方法。When a large amount of a hard alloy layer is locally formed on either the sliding surface of the movable member or the stationary member of the valve device, a nickel-base alloy austenitic heat-resistant alloy having a Ni content of 50% or more is built up in advance. A method of manufacturing a valve device, comprising shaping and then overlay welding of a cobalt-based hard alloy.
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