JP3674167B2

JP3674167B2 - Hot air pipe repair structure

Info

Publication number: JP3674167B2
Application number: JP20345396A
Authority: JP
Inventors: 義則岡島; 友一松本; 弘金谷
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 1996-08-01
Filing date: 1996-08-01
Publication date: 2005-07-20
Anticipated expiration: 2016-08-01
Also published as: JPH1046223A

Description

【０００１】
【発明の属する技術分野】
本発明は、熱風管の補修構造に関し、詳しくは、高炉用熱風炉に接続され応力腐食割れにより外周の鉄皮に亀裂が発生している熱風管の補修構造に関するものである。
【０００２】
【従来の技術】
高炉用熱風炉は通常 800℃から1400℃でかつ最高７kg/cm²程度の高温・高圧空気を高炉へ供給するための設備であり、図４に示すように、基本的には一対の竪型の燃焼室６と蓄熱室７とが互いの頂部を連結管30で連結されて単体をなし、この単体を燃焼室６に接続される熱風管１で複数並列に結合して全体が構成されている。この熱風炉で生成された高温・高圧空気は熱風管１から混冷管８に導かれ、別途図示しない送風機から冷風管10を経て供給される冷風と混合されて温度調節された後、水平管９を通って高炉に届けられる。
【０００３】
熱風炉単体についてみると、図５に示すように、燃焼室６下部に燃料ガス弁33および燃焼空気弁34が、中段に熱風管１に通じる熱風弁32が、また蓄熱室７下部に冷風弁35および煙道弁36が、夫々接続され、蓄熱室７の大部分がチェッカーレンガ31で内張りされている。
そこでは、まず燃料ガス弁33を介して燃料ガスを、また燃焼空気弁34を介して空気を燃焼室６へ導入してガスを燃焼し、熱風を発生させ、その熱風を蓄熱室７のチェッカーレンガ31の隙間へ通して熱風の顕熱をチェッカーレンガ31へ伝熱させながら煙道弁36を介して排気し（燃焼過程）、次いで、蓄熱室７のチェッカーレンガ31へ十分に熱が蓄熱完了したところで、図示のない送風機から冷風弁35を介して蓄熱室７へ冷風を圧送導入し、チェッカーレンガ31に蓄熱された熱を冷風へ伝えて高温空気とし、この高温空気を熱風弁32を介して熱風管１へ圧送する（送風過程）というサイクルで運転がなされる。
【０００４】
熱風炉は図４に示したように、かかる単体が複数並列に結合されて全体をなすので、前記燃焼・送風のサイクルを各単体間で適当にずらして運転することにより、全体として常時高温・高圧空気を熱風管１に送り込むことができる。
熱風管１には上述のように通常 800〜1400℃の高温空気が流されているが、この高温空気は燃焼室６および蓄熱室７を経由して流れるために、これら室内で燃焼中に発生し滞留していたＮＯ_xガスを含んでいる。
【０００５】
熱風管１の鉄皮内面には通常、耐火物（レンガあるいはキャスタブル）によるライニングが施されているのであるが、経時的にレンガ目地あるいはキャスタブル本体に亀裂等が生じ、かかる亀裂等を通じてＮＯ_xガスを含んだ空気が鉄皮内面に接触するようになる。鉄皮内面は鉄皮外面の大気温度の影響を受けて 100℃以下となるため不可避的に結露が生じ、これにＮＯ_xガスが溶解して結露が強酸性水と化す。一方、鉄皮には製作時の曲げ、溶接などにより残留応力が発生しており、また送風内圧もかかっているため、強酸性結露水による腐食環境下で応力腐食割れによる亀裂が発生し、高温空気の漏風などのトラブルの原因となっている。
【０００６】
通常の鉄皮亀裂の補修は、亀裂部をガウジング・溶接肉盛りする、あるいは当て板を溶接する、等により行われるが、これらの方法では溶接部に残留応力が発生するため、通常よりも腐食されやすい状況にある熱風管では、補修箇所から新たな応力腐食割れが発生するといった問題があり、補修後１年程度で再補修が必要となる。
【０００７】
このような応力腐食割れによる亀裂を生じた鉄皮の補修技術、とくにその再発生防止を企図した補修技術に関し、特開平８−3715号公報では、応力腐食割れにより発生した亀裂を溶接補修した後に当て板で補強する際の補修構造として、鉄皮と当て板との間に耐酸性塗膜層あるいは耐酸性充填層を介在させてなる構造が提案されている。
【０００８】
一方において、応力腐食割れの原因の一つである、鉄皮内面での結露を防ぐ方法として、鉄皮を外面から保温する、という方法も考えられている。
【０００９】
【発明が解決しようとする課題】
鉄皮と当て板との間に耐酸性塗膜層あるいは耐酸性充填層を介在させた前記補修構造によれば、鉄皮亀裂部に再度応力腐食割れで亀裂が発生したときに、当て板に強酸性結露水が接触することを防止できるので、当て板の応力腐食割れが阻止されて、補強部材としての寿命が延長するという長所があるが、当て板と鉄皮との溶接による内部応力の発生は防ぐことができず、当て板の周縁部での応力腐食割れによる亀裂が発生し、補強後１年から数年程度で再補修が必要になるという欠点がある。
【００１０】
また、鉄皮を外面から保温して鉄皮内面での結露を防ぐ前記方法によれば、実際の鉄皮内面での結露状態および亀裂の進展状況を確認できないため、万が一亀裂が進行していたときに、内圧による鉄皮の噴破等の重大なトラブルが発生するまで気がつかないといった危険性がある。
本発明は、このような従来技術の問題に鑑み、当て板と鉄皮との溶接残留応力起因の応力腐食割れによる再度の亀裂発生を好適に防止でき、さらには亀裂の潜在進展による鉄皮噴破等の危険性を伴わない形態で鉄皮を保温し鉄皮内部の結露を防止できる熱風管の補修構造を提供することを課題とする。
【００１１】
【課題を解決するための手段】
本発明者らの経験では、既設の高炉用熱風炉の熱風管の中で、使用開始以来10年以上経過しても鉄皮に応力腐食割れによる亀裂が発生していない例もある。この亀裂未発生の熱風管の製作条件を詳細に検討した結果、
１．鉄皮内面に耐酸キャスタブルがコーティングされている。
【００１２】
２．製作当時、鉄皮の溶接部に残留応力除去焼鈍が施されている。
という点で亀裂既発生の熱風管とは異なっていることを知見した。
鉄材に応力腐食割れが発生するには、その鉄材が、(1) 腐食環境にある、(2) 引張応力を受けている、(3) 硝酸塩中での割れ感受性が高い、という３条件が全て重なることが必要であるが、上記亀裂未発生の熱風管は、このうち(1) および(2) の条件を除去されていたといえる。
【００１３】
本発明は、かかる貴重な知見に基づき、鋭意検討を重ねて完成されたものであり、その特徴とするところは以下の通りである。
第１の発明は、外周が応力腐食割れによる亀裂発生部を含む旧鉄皮で覆われ既設のフランジで長手方向に区分された熱風管の補修構造であって、亀裂発生部を含む区間両端のフランジに両側縁を夫々全周にわたり溶接されて該区間を全周被覆する新鉄皮と、新旧両鉄皮間に設けられた間隙層とを有し、前記溶接部が残留応力除去焼鈍を施されてなることを特徴とする熱風管の補修構造である。
【００１４】
第２の発明は、外周が応力腐食割れによる亀裂発生部を含む旧鉄皮で覆われ既設のフランジで長手方向に区分された熱風管の補修構造であって、亀裂発生部を含む区間両端のフランジに両側縁を夫々全周にわたり溶接されて該区間を全周被覆する新鉄皮と、新旧両鉄皮間に設けられた間隙層とを有し、該間隙層が耐酸キャスタブルを充填されてなることを特徴とする熱風管の補修構造である。
【００１５】
第３の発明は、外周が応力腐食割れによる亀裂発生部を含む旧鉄皮で覆われ既設のフランジで長手方向に区分された熱風管の補修構造であって、亀裂発生部を含む区間両端のフランジに両側縁を夫々全周にわたり溶接されて該区間を全周被覆する新鉄皮と、新旧両鉄皮間に設けられた間隙層とを有し、該間隙層が熱風管内部の高温空気と同圧もしくはそれ以上の圧力を持つ空気を常に供給されてなることを特徴とする熱風管の補修構造である。
【００１６】
【発明の実施の形態】
図１は本発明の熱風管の補修構造を示し、（ａ）は断面図、（ｂ）は（ａ）のＡＡ矢視図である。図１において、１は熱風管、２は既設の旧鉄皮、2Aは新しく外殻とした新鉄皮、３は間隙層、４は内部レンガ、５は既設のフランジである。図１に示すように、本発明の熱風管の補修構造は、外周が応力腐食割れによる亀裂発生部を含む旧鉄皮２で覆われ既設のフランジ５で長手方向に区分された熱風管１の補修構造であって、亀裂発生部を含む区間両端のフランジ５に両側縁を夫々全周にわたり溶接されて該区間を全周被覆する新鉄皮2Aと、新旧両鉄皮2A、２間に設けられた間隙層３とを有することを基本の要件とする。
【００１７】
このように、新鉄皮2Aを旧鉄皮２に直にではなく間隙層３を介して既設のフランジ５に溶接接続することにより、旧鉄皮２に溶接残留応力を発生させないでこれを新鉄皮2Aで被覆できるから、応力腐食割れの原因の一つを回避できる。またこれにより、熱風管１の内圧保持のための構造部材としての役割を、亀裂が発生している旧鉄皮２から健全な新鉄皮2Aへと移すことができ、将来的に熱風管１の旧鉄皮２に応力腐食割れが進行して亀裂が拡大したとしても、新鉄皮2Aによってさらに外側を保護されているので、鉄皮噴破が生じる可能性を大幅に低下させることができる。
【００１８】
また、間隙層３は断熱層として働き、旧鉄皮２内面を結露温度以上に維持して旧鉄皮２内部での強酸性水の生成を防ぎ、旧鉄皮２の応力腐食割れのさらなる進行を妨げる効果がある。
新鉄皮2Aとしては、熱風炉の炉内圧に十分耐えうる強度を持つ部材を選定し、この部材が亀裂発生部を含む旧鉄皮２を間隙層３を介して全周被覆する形で、この部材の両側縁を、被覆対象の旧鉄皮２の存在区間両端に既設のフランジ５に夫々全周溶接することにより、前記補修構造を実現できる。
【００１９】
前記間隙層３の間隙は５mm以上とるのが好ましい。これを５mm未満として設計すると、新旧鉄皮2A、２に熱変形などが生じたときに間隙層３がなくなって本発明の効果を得難いためである。この間隙（層の厚み）は機能上からは上限に制約がないが、補修施工上はフランジ５の外径などで制約を受ける。
第１の発明は、上記した基本要件に加えて、フランジ５と新鉄皮2Aとの溶接部が残留応力除去焼鈍されたものであることを要旨とする。
【００２０】
新鉄皮2Aを設けただけでは旧鉄皮２の亀裂から熱風管１内部の高温空気が間隙層３に侵入し、新鉄皮2A内面に強酸性の結露を生じる可能性があるので、フランジ５と新鉄皮2Aとの溶接部を焼鈍により残留応力除去をしておく。これにより新鉄皮2Aの応力腐食割れが回避できる。
第２の発明は、上記した基本要件に加えて、間隙層３が、耐酸キャスタブルを充填されていることを要旨とする。
【００２１】
上述したように、熱風管１内部の高温空気雰囲気における耐酸キャスタブルの有用性については実績があり、この構造により、新鉄皮2A自身および新鉄皮2Aと既設のフランジ５との溶接部が腐食環境に曝されない状況をつくることができる。また、同時に旧鉄皮２の外周部も耐酸キャスタブルでライニングされることになるため、これが断熱層となって旧鉄皮２を結露温度以上に維持してそこでの強酸性水の生成が妨げられるので、応力腐食割れによる新たな亀裂の進展が抑制されることが期待される。
【００２２】
第３の発明は、上記した基本要件に加えて、間隙層３が、熱風管１の内部の高温空気と同圧もしくはそれ以上の圧力のガスを常に供給されていることを要旨とする。
これにより、新鉄皮2A内面と炉内ＮＯ_xを含んだ空気との接触が妨げられ、新鉄皮2Aの応力腐食割れが防止できると共に、間隙層３に供給されるガスが断熱層となって旧鉄皮２を結露温度以上に維持してそこでの強酸性水の生成が妨げられるので、応力腐食割れによる新たな亀裂の進展が抑制されると期待される。
【００２３】
間隙層３に供給するガスとしては空気が使用でき、その供給方法としては、例えば図４の冷風管10等の高炉への送風経路を分岐してその送風ガスの一部を供給する方法、または、別途専用の空気圧縮機を設けてそこから供給する方法のいずれでも採用可能である。後者の場合、熱風管１の内圧を検知しながら流量、圧力を制御するのが好ましい。
【００２４】
第１〜第３の発明は、相互間で鉄皮の応力腐食割れ防止効果の程度に大きな差異はなく、補修工事時の諸条件により適宜選択すればよい。
【００２５】
【実施例】
＜実施例１＞
送風量 6800Nm³/min、熱風管内部温度1400℃、圧力 5.5kg/cm²の高炉操業において、設備仕様として、外径 3.1ｍ、鉄皮厚み14mm、内部レンガ厚み 700mmの熱風管を接続した熱風炉を使用していたが、稼働後１年で熱風管に応力腐食割れによる鉄皮亀裂が発生した。
【００２６】
そこで、図１に示した形態で、炭素鋼（SM400 ）のプレート（厚さ14mm）を、旧鉄皮２の外殻用の新鉄皮2Aとして、新旧両鉄皮間に間隙50mmの間隙層３をとってフランジ５（旧鉄皮２に既設）に溶接固定した後、休風工事にて新鉄皮2Aとフランジ５との溶接部全体にわたり、電気ヒータを用いて 610±30℃×３時間の条件で焼鈍を実施した。
【００２７】
この補修後現在まで２年経過しているが、新鉄皮2Aに応力腐食割れによる鉄皮亀裂は発生していない。
＜実施例２＞
実施例１と同様の設備・操業条件の高炉用熱風炉の熱風管において、実施例１と同様に稼働後１年で熱風管に応力腐食割れによる鉄皮亀裂が発生した。
【００２８】
そこで、図１に示した形態で、炭素鋼（SM400 ）のプレート（厚さ14mm）を、旧鉄皮２の外殻用の新鉄皮2Aとして、新旧両鉄皮間に間隙50mmの間隙層３をとってフランジ５（旧鉄皮２に既設）に溶接固定した後、間隙層３に、アルミナ、シリカを骨材とした水ガラス系の耐酸キャスタブルを、予め新鉄皮2Aに開けておいた注入孔から注入して充填した。
【００２９】
この補修後現在まで２年経過しているが、新鉄皮2Aに応力腐食割れによる亀裂は発生していない。
＜実施例３＞
実施例１と同様の設備・操業条件の高炉用熱風炉の熱風管において、実施例１と同様に稼働後１年で熱風管に応力腐食割れによる鉄皮亀裂が発生した。
【００３０】
そこで、図１に示した形態で、炭素鋼（SM400 ）のプレート（厚さ14mm）を、旧鉄皮２の外殻用の新鉄皮2Aとして、新旧両鉄皮間に間隙50mmの間隙層３をとってフランジ５（旧鉄皮２に既設）に溶接固定し、間隙層３へのガス供給系として、図２に示すように、間隙層３に直通するバルブ13付き分岐管12を植設したヘッダ11を冷風管10より分岐させて設け、冷風管10内の冷風の一部を間隙層３内に供給するようにした。なお、図２において、21はエキスパンションであり、前掲の図４、図５および図１と同一または相当部分にはこれと同じ符号を付し、説明を省略する。
【００３１】
冷風管10内の冷風はチェッカーレンガ31（図５参照）を通過しないので、熱風に比べるとわずかながら圧力が高い状態にあるから、本発明を適用するのに好適である。
この補修後現在まで２年経過しているが、新鉄皮２に応力腐食割れによる亀裂は発生していない。
＜実施例４＞
実施例１と同様の設備・操業条件の高炉用熱風炉の熱風管において、実施例１と同様に稼働後１年で熱風管に応力腐食割れによる鉄皮亀裂が発生した。
【００３２】
そこで、図１に示した形態で、炭素鋼（SM400 ）のプレート（厚さ14mm）を、旧鉄皮２の外殻用の新鉄皮2Aとして、新旧両鉄皮間に間隙50mmの間隙層３をとってフランジ５（旧鉄皮２に既設）に溶接固定し、間隙層３へのガス供給系として、図３に示すように、間隙層３に直通するバルブ13付き分岐管12を植設したヘッダ11と該ヘッダ11に専用に送気する空気圧縮機14とを設け、熱風管１内の高温・高圧空気の圧力（Ｐ₁とする）とヘッダ11内の空気圧力（Ｐ₂とする）とを圧力センサ15ａ、圧力計15ｂで夫々測定し、制御装置16を用いてＰ₂がＰ₁〜Ｐ₁＋0.02kg/cm²の圧力範囲内に収まるように流量調整弁17および空気圧縮機14駆動用のモータ18を制御しながら、ヘッダ11内の空気を間隙層３内に導くようにした。なお、図３において、19はセンサケーブル、20は制御ケーブルであり、図３と同一または相当部分にはこれと同じ符号を付し、説明を省略する。
【００３３】
この補修後現在まで２年経過しているが、新鉄皮2Aに応力腐食割れによる亀裂は発生していない。
【００３４】
【発明の効果】
本発明によれば、鉄皮に応力腐食割れによる亀裂が発生している高炉用熱風炉付設の熱風管を、応力腐食割れによる再度の亀裂発生や亀裂の潜在進展による鉄皮噴破等の危険性を伴わない形態で補修できると共に、補修後の耐用期間が飛躍的に延長するという格段の効果を奏する。
【図面の簡単な説明】
【図１】本発明の熱風管の補修構造を示し、（ａ）は断面図、（ｂ）は（ａ）のＡＡ矢視図である。
【図２】実施例３における間隙層へのガス供給系の構成図である。
【図３】実施例４における間隙層へのガス供給系の構成図である。
【図４】高炉用熱風炉の全体図である。
【図５】熱風炉単体の構成図である。
【符号の説明】
１熱風管
２旧鉄皮
2A 新鉄皮
３間隙層
４内部レンガ
５フランジ
６燃焼室
７蓄熱室
８混冷管
９水平管
10 冷風管
11 ヘッダ
12 分岐管
13 バルブ
14 空気圧縮機
15 圧力センサ
16 制御装置
17 流量調整弁
18 モータ
19 センサケーブル
20 制御ケーブル
21 エキスパンション
30 連結管
31 チェッカーレンガ
32 熱風弁
33 燃料ガス弁
34 燃焼空気弁
35 冷風弁
36 煙道弁[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hot blast tube repair structure, and more particularly to a hot blast tube repair structure that is connected to a blast furnace hot blast furnace and has cracks in the outer skin due to stress corrosion cracking.
[0002]
[Prior art]
A blast furnace hot blast furnace is a facility for supplying high-temperature and high-pressure air of 800 to 1400 ° C and a maximum of 7 kg / cm ² to a blast furnace. The combustion chamber 6 and the heat storage chamber 7 are connected to each other by a connecting pipe 30 to form a single unit, and a plurality of the single units are combined in parallel by hot air tubes 1 connected to the combustion chamber 6 to constitute the whole. Yes. The high-temperature and high-pressure air generated in this hot air furnace is guided from the hot air pipe 1 to the mixed cooling pipe 8 and mixed with the cold air supplied from the blower (not shown) via the cold air pipe 10 to adjust the temperature. 9 is delivered to the blast furnace.
[0003]
As shown in FIG. 5, the hot air furnace alone has a fuel gas valve 33 and a combustion air valve 34 at the lower part of the combustion chamber 6, a hot air valve 32 leading to the hot air pipe 1 in the middle stage, and a cold air valve at the lower part of the heat storage chamber 7. 35 and flue valve 36 are connected to each other, and most of the heat storage chamber 7 is lined with a checker brick 31.
There, fuel gas is first introduced into the combustion chamber 6 through the fuel gas valve 33 and air is introduced into the combustion chamber 6 through the combustion air valve 34 to burn the gas to generate hot air, which is then used as a checker for the heat storage chamber 7. While passing through the gap between the bricks 31 and transferring the sensible heat of the hot air to the checker bricks 31, the exhaust gas is exhausted through the flue valve 36 (combustion process), and then the heat is fully stored in the checker bricks 31 in the heat storage chamber 7. Then, cold air is pumped and introduced from the blower (not shown) to the heat storage chamber 7 via the cold air valve 35, and the heat stored in the checker brick 31 is transferred to the cold air to form hot air, and this hot air is passed through the hot air valve 32. Then, the operation is performed in a cycle of pumping to the hot air tube 1 (air blowing process).
[0004]
As shown in FIG. 4, the hot stove is composed of a plurality of such single units connected in parallel, so that the combustion and blowing cycle is appropriately shifted between the single units, so that the entire temperature is constantly high. High-pressure air can be sent into the hot air tube 1.
As described above, high-temperature air of 800 to 1400 ° C. is normally flowed through the hot air pipe 1. This high-temperature air flows through the combustion chamber 6 and the heat storage chamber 7, and is generated during combustion in these chambers. it includes and NO _x gas staying.
[0005]
The inner surface of the hot air pipe 1 is usually lined with a refractory material (brick or castable), but cracks or the like occur in the brick joints or castable body over time, and NO _x gas passes through such cracks. The air containing will come into contact with the inner surface of the iron skin. The inner surface of the iron skin is affected by the atmospheric temperature of the outer surface of the iron skin and becomes 100 ° C or less, so unavoidable condensation occurs, and NO _x gas dissolves in this, and the condensation turns into strongly acidic water. On the other hand, residual stress is generated in the iron skin due to bending, welding, etc. at the time of manufacture, and internal air pressure is also applied, so cracks due to stress corrosion cracking occur in a corrosive environment with strongly acidic dew condensation water, and high temperature It causes troubles such as air leakage.
[0006]
Ordinary skin crack repair is performed by gouging and welding the cracked part, or welding a caulking plate, etc., but these methods generate residual stress in the welded part. In hot air pipes that are easily repaired, there is a problem that a new stress corrosion crack occurs from the repaired portion, and re-repairing is required about one year after the repair.
[0007]
With regard to repair technology for iron skin that has cracked due to stress corrosion cracking, particularly repair technology that is intended to prevent its reoccurrence, Japanese Patent Laid-Open No. 8-3715 discloses that after crack repairing due to stress corrosion cracking has been repaired. As a repair structure when reinforcing with a backing plate, a structure in which an acid-resistant coating layer or an acid-resistant filling layer is interposed between the iron skin and the backing plate has been proposed.
[0008]
On the other hand, as a method for preventing condensation on the inner surface of the iron skin, which is one of the causes of stress corrosion cracking, a method of keeping the iron skin warm from the outer surface is also considered.
[0009]
[Problems to be solved by the invention]
According to the repair structure in which an acid-resistant coating layer or an acid-resistant filling layer is interposed between the iron skin and the caulking plate, when a crack occurs again due to stress corrosion cracking in the iron skin crack part, Since it can prevent the contact with strong acidic dew condensation water, the stress corrosion cracking of the backing plate is prevented and the life as a reinforcing member is extended, but the internal stress due to welding between the backing plate and the iron skin is reduced. Occurrence cannot be prevented, and cracks due to stress corrosion cracking occur at the peripheral edge of the backing plate, and there is a disadvantage that re-repair is required in about one to several years after reinforcement.
[0010]
In addition, according to the above-described method for keeping the iron skin from the outer surface and preventing condensation on the inner surface of the iron skin, it is impossible to confirm the actual dew condensation state and the progress of cracks on the inner surface of the iron skin. Sometimes, there is a danger of not knowing until serious troubles such as blasting of the iron skin due to internal pressure occur.
In view of such problems of the prior art, the present invention can suitably prevent the occurrence of another crack due to stress corrosion cracking caused by the welding residual stress between the backing plate and the iron skin, and further, the iron skin jet due to the latent progress of the crack. It is an object of the present invention to provide a hot air pipe repair structure capable of keeping the iron skin in a form without risk of breakage or the like and preventing condensation inside the iron skin.
[0011]
[Means for Solving the Problems]
According to the experience of the present inventors, there is an example in which no crack due to stress corrosion cracking has occurred in the hot air tube of an existing hot blast furnace for a blast furnace even after 10 years have passed since the start of use. As a result of detailed examination of the production conditions of this cracked hot air tube,
1. The inner surface of the iron skin is coated with acid-resistant castable.
[0012]
2. At the time of production, residual stress relief annealing was applied to the welded portion of the iron skin.
It was found that this is different from the hot-air tube with cracks.
In order for stress corrosion cracking to occur in an iron material, all three conditions are: (1) in a corrosive environment, (2) subjected to tensile stress, and (3) highly susceptible to cracking in nitrate. Although it is necessary to overlap, it can be said that the above-mentioned hot-air tube without cracks has been removed from the conditions (1) and (2).
[0013]
The present invention has been completed based on such valuable knowledge and has been completed through extensive studies. The features of the present invention are as follows.
1st invention is the repair structure of the hot-air pipe which the outer periphery was covered with the old iron skin containing the crack generation part by stress corrosion cracking, and was divided in the longitudinal direction by the existing flange, Comprising: The flange has a new iron skin that is welded on both sides of the flange over the entire circumference and covers the entire circumference, and a gap layer provided between the old and new iron skin, and the weld is subjected to residual stress relief annealing. It is the repair structure of a hot-air tube characterized by being made.
[0014]
The second invention is a hot air pipe repair structure in which the outer periphery is covered with an old iron skin including a crack generation portion due to stress corrosion cracking and is divided in the longitudinal direction by an existing flange, and is provided at both ends of the section including the crack generation portion. A new iron skin that is welded to both sides of the flange over the entire circumference to cover the entire circumference, and a gap layer provided between the old and new iron coats, and the gap layer is filled with acid-resistant castable It is the repair structure of a hot-air pipe characterized by becoming.
[0015]
3rd invention is the repair structure of the hot-air pipe which the outer periphery was covered with the old iron skin containing the crack generation part by stress corrosion cracking, and was divided in the longitudinal direction by the existing flange, Comprising: A new iron skin that is welded on both sides of the flange to cover the entire circumference of the flange, and a gap layer provided between the old and new iron coats, the gap layer being hot air inside the hot air pipe The hot air pipe repair structure is characterized in that it is always supplied with air having the same pressure or higher pressure.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
1A and 1B show a repair structure of a hot air tube according to the present invention, in which FIG. 1A is a cross-sectional view and FIG. In FIG. 1, 1 is a hot-air pipe, 2 is an existing old iron skin, 2A is a new outer skin that is a new outer shell, 3 is a gap layer, 4 is an internal brick, and 5 is an existing flange. As shown in FIG. 1, the hot air pipe repair structure according to the present invention includes a hot air pipe 1 whose outer periphery is covered with an old iron skin 2 including a crack generation part due to stress corrosion cracking and is divided in a longitudinal direction by an existing flange 5. It has a repair structure, and is provided between the new and old iron skins 2A, 2A and 2A, and the new and old iron skins 2A, 2 that are welded to the flanges 5 at both ends of the section including the cracked portion and welded over the entire circumference. It is a basic requirement to have the gap layer 3 formed.
[0017]
In this way, the new iron skin 2A is welded and connected to the existing flange 5 via the gap layer 3 instead of directly to the old iron skin 2, so that the old iron skin 2 can be renewed without generating residual welding stress. One of the causes of stress corrosion cracking can be avoided because it can be covered with the iron skin 2A. In addition, this allows the role of the hot air tube 1 as a structural member for maintaining the internal pressure to be transferred from the old iron skin 2 where cracks are generated to a healthy new iron skin 2A. Even if stress corrosion cracking progresses in the old iron skin 2 and the crack expands, since the outer side is further protected by the new iron skin 2A, the possibility of iron skin blasting can be greatly reduced. .
[0018]
In addition, the gap layer 3 acts as a heat insulating layer, maintains the inner surface of the old iron skin 2 at the condensation temperature or more to prevent the formation of strong acidic water inside the old iron skin 2, and further advances the stress corrosion cracking of the old iron skin 2. There is an effect to prevent.
As the new iron skin 2A, a member having a strength that can sufficiently withstand the furnace pressure of the hot air furnace is selected, and this member covers the old iron skin 2 including the crack generation part all around the gap layer 3, The repair structure can be realized by welding both side edges of this member to the existing flanges 5 at both ends of the existing section of the old iron skin 2 to be covered.
[0019]
The gap of the gap layer 3 is preferably 5 mm or more. If this is designed to be less than 5 mm, it is difficult to obtain the effect of the present invention because the gap layer 3 disappears when the old and new iron skins 2A, 2 are thermally deformed. This gap (layer thickness) has no upper limit in terms of function, but is limited by the outer diameter of the flange 5 in repair work.
The gist of the first invention is that, in addition to the basic requirements described above, the welded portion between the flange 5 and the new iron skin 2A is subjected to annealing for removing residual stress.
[0020]
If only the new iron skin 2A is provided, high-temperature air inside the hot air tube 1 may enter the gap layer 3 from the crack in the old iron skin 2, and strong acid condensation may occur on the inner surface of the new iron skin 2A. Residual stress is removed by annealing the welded portion between 5 and the new iron skin 2A. This avoids stress corrosion cracking of the new iron skin 2A.
The gist of the second invention is that, in addition to the basic requirements described above, the gap layer 3 is filled with an acid-resistant castable.
[0021]
As described above, the usefulness of acid-resistant castable in the hot air atmosphere inside the hot air tube 1 has been proven, and this structure corrodes the new iron skin 2A itself and the weld of the new iron skin 2A and the existing flange 5. You can create a situation that is not exposed to the environment. At the same time, the outer peripheral portion of the old iron skin 2 is also lined with an acid-resistant castable, so that this becomes a heat insulating layer and maintains the old iron skin 2 at the dew condensation temperature or more, thereby preventing the production of strong acid water there. Therefore, it is expected that the development of new cracks due to stress corrosion cracking is suppressed.
[0022]
The gist of the third invention is that, in addition to the basic requirements described above, the gap layer 3 is always supplied with a gas having a pressure equal to or higher than that of the hot air inside the hot air tube 1.
Thus, impeded contact with air containing Shintetsugawa 2A interior and furnace NO _x, with the stress corrosion cracking of Shintetsugawa 2A can be prevented, the gas supplied to the gap layer 3 is a heat insulating layer Thus, since the old iron skin 2 is maintained at a temperature higher than the dew condensation temperature and the production of strongly acidic water there is hindered, it is expected that the development of new cracks due to stress corrosion cracking is suppressed.
[0023]
Air can be used as the gas to be supplied to the gap layer 3, and the supply method thereof is, for example, a method of supplying a part of the blown gas by branching a blower path to a blast furnace such as the cold air pipe 10 of FIG. Any method can be adopted in which a dedicated air compressor is separately provided and supplied from there. In the latter case, it is preferable to control the flow rate and pressure while detecting the internal pressure of the hot air tube 1.
[0024]
The first to third inventions are not significantly different from each other in the degree of the effect of preventing stress corrosion cracking of the iron skin, and may be appropriately selected according to various conditions during repair work.
[0025]
【Example】
<Example 1>
In blast furnace operation with an air flow rate of 6800Nm ³ / min, hot air tube internal temperature of 1400 ° C and pressure of 5.5kg / cm ² , hot air connected with hot air tubes with an outer diameter of 3.1m, an iron shell thickness of 14mm and an internal brick thickness of 700mm Although a furnace was used, an iron shell crack due to stress corrosion cracking occurred in the hot air pipe one year after operation.
[0026]
Therefore, in the form shown in FIG. 1, a carbon steel (SM400) plate (thickness 14 mm) is used as a new iron skin 2A for the outer shell of the old iron skin 2, and a gap layer having a gap of 50 mm between the old and new iron skins. 3 is welded and fixed to the flange 5 (existing on the old iron skin 2), and then the entire welded area between the new iron skin 2A and the flange 5 is used for the resting work. Annealing was carried out under time conditions.
[0027]
Two years have passed since the repair, but no iron cracking due to stress corrosion cracking has occurred in the new iron skin 2A.
<Example 2>
In a hot blast tube of a blast furnace hot blast furnace having the same equipment and operating conditions as in Example 1, an iron shell crack due to stress corrosion cracking occurred in the hot blast tube in one year after operation in the same manner as in Example 1.
[0028]
Therefore, in the form shown in FIG. 1, a carbon steel (SM400) plate (thickness 14 mm) is used as a new iron skin 2A for the outer shell of the old iron skin 2, and a gap layer having a gap of 50 mm between the old and new iron skins. 3 is welded and fixed to the flange 5 (existing on the old iron skin 2), and then a water glass-based acid-resistant castable made of alumina and silica as an aggregate is opened in the new iron skin 2A in advance. It was injected and filled from the injection hole.
[0029]
Two years have passed since this repair, but no cracks due to stress corrosion cracking have occurred in the new iron skin 2A.
<Example 3>
In a hot blast tube of a blast furnace hot blast furnace having the same equipment and operating conditions as in Example 1, an iron shell crack due to stress corrosion cracking occurred in the hot blast tube in one year after operation in the same manner as in Example 1.
[0030]
Therefore, in the form shown in FIG. 1, a carbon steel (SM400) plate (thickness 14 mm) is used as a new iron skin 2A for the outer shell of the old iron skin 2, and a gap layer having a gap of 50 mm between the old and new iron skins. 3 is welded and fixed to the flange 5 (existing on the old iron skin 2), and as a gas supply system to the gap layer 3, as shown in FIG. The provided header 11 is branched from the cold air pipe 10 and a part of the cold air in the cold air pipe 10 is supplied into the gap layer 3. In FIG. 2, reference numeral 21 denotes an expansion. The same or corresponding parts as those shown in FIGS. 4, 5, and 1 are denoted by the same reference numerals, and description thereof is omitted.
[0031]
Since the cold air in the cold air pipe 10 does not pass through the checker brick 31 (see FIG. 5), the pressure is slightly higher than that of the hot air, which is suitable for applying the present invention.
Although two years have passed since the repair, the new iron skin 2 has not been cracked by stress corrosion cracking.
<Example 4>
In a hot blast tube of a blast furnace hot blast furnace having the same equipment and operating conditions as in Example 1, an iron shell crack due to stress corrosion cracking occurred in the hot blast tube in one year after operation in the same manner as in Example 1.
[0032]
Therefore, in the form shown in FIG. 1, a carbon steel (SM400) plate (thickness 14 mm) is used as a new iron skin 2A for the outer shell of the old iron skin 2, and a gap layer having a gap of 50 mm between the old and new iron skins. 3 is welded and fixed to the flange 5 (existing on the old iron skin 2), and as a gas supply system to the gap layer 3, as shown in FIG. A header 11 provided and an air compressor 14 for sending air exclusively to the header 11 are provided, and the pressure of high-temperature and high-pressure air in the hot air pipe 1 (referred to as P ₁ ) and the air pressure in the header 11 (as P ₂ and ) Are measured by the pressure sensor 15a and the pressure gauge 15b, respectively, and the control device 16 is used to adjust the flow rate adjusting valve 17 and the air so that P ₂ falls within the pressure range of P _{1 to} P ₁ +0.02 kg / cm ^2. The air in the header 11 was guided into the gap layer 3 while controlling the motor 18 for driving the compressor 14. In FIG. 3, 19 is a sensor cable, and 20 is a control cable. The same or corresponding parts as those in FIG.
[0033]
Two years have passed since this repair, but no cracks due to stress corrosion cracking have occurred in the new iron skin 2A.
[0034]
【The invention's effect】
According to the present invention, a hot blast tube attached to a hot blast furnace for a blast furnace in which cracks due to stress corrosion cracking have occurred in the iron skin can be used to prevent the occurrence of re-cracking due to stress corrosion cracking or iron skin blasting due to potential crack propagation. In addition to being able to repair in a form that does not involve the nature, there is a remarkable effect that the service life after repair is dramatically extended.
[Brief description of the drawings]
1A and 1B show a repair structure of a hot air tube according to the present invention, in which FIG. 1A is a cross-sectional view and FIG.
2 is a configuration diagram of a gas supply system to a gap layer in Example 3. FIG.
3 is a configuration diagram of a gas supply system to a gap layer in Example 4. FIG.
FIG. 4 is an overall view of a blast furnace hot stove.
FIG. 5 is a configuration diagram of a single hot stove.
[Explanation of symbols]
1 Hot air pipe 2 Old iron skin
2A New iron skin 3 Gap layer 4 Internal brick 5 Flange 6 Combustion chamber 7 Thermal storage chamber 8 Mixed cooling tube 9 Horizontal tube
10 Cold air pipe
11 Header
12 branch pipe
13 Valve
14 Air compressor
15 Pressure sensor
16 Control unit
17 Flow control valve
18 Motor
19 Sensor cable
20 Control cable
21 expansion
30 Connecting pipe
31 checker bricks
32 Hot air valve
33 Fuel gas valve
34 Combustion air valve
35 Cold air valve
36 Flue valve

Claims

This is a hot air pipe repair structure whose outer periphery is covered with the old iron skin including the cracked part due to stress corrosion cracking and is divided in the longitudinal direction by the existing flange. It has a new iron skin that is welded over the entire circumference and covers the entire circumference, and a gap layer provided between the old and new iron skins, and the weld is subjected to residual stress relief annealing. The hot air pipe repair structure.

This is a hot air pipe repair structure whose outer periphery is covered with the old iron skin including the cracked part due to stress corrosion cracking and is divided in the longitudinal direction by the existing flange. A new iron skin that is welded over the entire circumference and covers the entire circumference, and a gap layer provided between the old and new iron skins, the gap layer being filled with an acid-resistant castable Hot air pipe repair structure.

This is a hot air pipe repair structure whose outer periphery is covered with the old iron skin including the cracked part due to stress corrosion cracking and is divided in the longitudinal direction by the existing flange. A new iron skin that is welded over the entire circumference and covers the entire circumference; and a gap layer provided between the old and new iron skins, and the gap layer has the same pressure or higher than the hot air inside the hot air pipe A structure for repairing a hot-air tube, characterized in that it is always supplied with air having the pressure of