JP4306002B2

JP4306002B2 - Method and apparatus for preventing red water of potable water by electrocorrosion protection and linear electrode body

Info

Publication number: JP4306002B2
Application number: JP08417199A
Authority: JP
Inventors: 実蜂谷
Original assignee: Kureha Engineering Co Ltd
Current assignee: Kureha Engineering Co Ltd
Priority date: 1999-03-26
Filing date: 1999-03-26
Publication date: 2009-07-29
Anticipated expiration: 2019-03-26
Also published as: JP2000273665A

Description

【０００１】
【技術分野】
本発明は少なくとも一部が鋼製部材からなる給水配管内面に外部電源方式の電気防食を行ない飲用水の赤水を防止する方法及び装置に関する。さらに、本発明は電気防食に用いる線状電極体に関する。
【０００２】
【従来技術】
従来、Ca²⁺及びMg²⁺を含む飲用水を給水する配管で、少なくとも一部が鋼製部材からなる給水配管の腐食による赤水が問題となっている。最近は、建造物内の給水配管にポリ塩化ビニルライニング鋼管が多用されるが、ネジ切り加工される鋼管及び継手の端面の鋼露出部で腐食が起こり、防食が必要とされている。その解決策として従来、▲１▼配管内面にエポキシ樹脂をライニングする方法、▲２▼配管内面を磁気処理する方法、▲３▼電子場処理法、▲４▼給水をセラミック充填層に通過させる方法、▲５▼給水に腐食抑制剤を注入する法、▲６▼給水を脱気する法、▲７▼カルシウム防錆法等が提案され、あるものは実施されている。しかし、▲１▼はエポキシ樹脂からのビスフェノールＡの溶出の問題があり、▲２▼、▲３▼、▲４▼はその防食効果が疑問視され、▲５▼は添加薬剤の健康への観点から次第に敬遠される傾向にあり、▲６▼は中空糸の保守を十分に行わないと防食効果が維持できず、▲７▼は長期的には優れているが、即効性に乏しいという問題がある。
【０００３】
これらに対し、電気防食法はストレージタンクの内面防食に適用される等その効果は理論的に認められており、この方法を給水管内面に適用することが検討されている。例えば特公平５−２４２３５号公報には耐蝕性線状陽極電極を配管内に挿入して通電する赤水停止方法が提案され、白金被覆チタン線にゴム、ポリ塩化ビニル、ポリエチレン、ナイロン、ポリプロピレン、ポリカーボネート等の多孔性の電気絶縁性チューブで包囲した電極線が開示されている。また特許第２８０１０３０号公報には不溶性金属線の表面に非導電性合成繊維のモノフィラメント糸を組紐状に粗く編組して被覆した管路防蝕用電極線が開示されている。さらに、実用新案登録第２５７２７８５号公報には赤水防止を目的として、チタン線に白金メッキした金属線の表面に複数本のポリエチレンやポリプロピレンモノフィラメント糸をストランド巻き角度１５〜４５°になるよう螺旋状に巻いた管路防食用電極線が開示されている。
これらの方法は給水に含まれるCa²⁺及びMg²⁺を利用して塩基性化合物の皮膜を形成させることにより赤水の発生を防止しようとするものであるが、含まれるCa²⁺及びMg²⁺の濃度によっては充分な効果を挙げられなかったり、あるいは管内に多量の塩基性化合物のスケールを生じさせるおそれがある。
【０００４】
【発明が解決しようとする課題】
本発明者は、このような現状に鑑み、飲用水の赤水を早期に停止させることを課題として研究を重ねた結果、Ca²⁺及びMg²⁺を含む飲用水を給水する配管内に線状電極体を配設し、線状電極体を陽極、配管材を陰極として、直流を断続的に通電することによりカルシウムやマグネシウム化合物の皮膜を必要にして十分な厚さに形成させ、赤水を防止する方法を見いだした。
【０００５】
【課題を解決するための手段】
本発明は、Ca²⁺及びMg²⁺を含む水を給水するにあたり、少なくとも一部が鋼製部材からなる配管内に線状電極体を配設し、線状電極体を陽極、配管材を陰極として直流を通電し配管内にカルシウム及びマグネシウムを含む塩基性化合物の皮膜を形成させることにより飲用水の赤水を防止する方法において、通電を断続的に行うことにより該皮膜を必要にして十分な厚さに維持する赤水防止方法に関する。これは通電を定期的に遮断し、遮断直後の両極間の電位差を測定し、必要な場合にはその経時的減衰を測定し、通電を再開するか否かを判定し制御することにより行うことができる。また、本発明は、少なくとも一部が鋼製部材からなる給水配管内に配設した線状電極体、該線状電極体を陽極、配管材を陰極として直流を通電する電源装置からなり、該電源装置が、定期的通電遮断・遮断直後の両極間電位差の経時的減衰測定・通電再開の可否判定を行う制御部を備えていることを特徴とする飲用水の赤水防止装置に関する。さらに、本発明は、曲がり部の多い配管に容易に配設できる特定構造の線状電極体に関する。
【０００６】
【発明の実施の形態】
本発明は、少なくとも一部が鋼製部材からなる給水配管の鉄部における腐食の発生を、給水に含まれるCa²⁺及びMg²⁺を利用して防止するものであり、Ca²⁺及びMg²⁺を総硬度として10mg/l以上含有する飲用水に適用できる。配管内には線状電極体を配設し、線状電極体を陽極、配管材を陰極として直流を通電する。通電することにより配管内面にカルシウム及びマグネシウムの塩基性化合物の皮膜が形成されるが、通電を定期的に遮断し、遮断直後の両極間の電位差を測定し、必要な場合にはその経時的減衰を測定し、通電を再開するか否かを判定する。
【０００７】
通電時の印加電圧は2.1 〜5V、好ましくは2.5 〜3.5Vとする。通電を再開するか否かの判定には遮断直後の線状電極の電位を基準として配管内面の分極状態を測定する。両極間の電位差が2.0V以上の場合は配管（鉄）の電位が、通常防食効果が得られる鉄の基準電位として知られている-0.77V(SCE) よりも分極が進んでいることを示し、良好な防食状態となる。従って、例えば印加電圧を3Vとし、通電遮断2.0 秒後の電位差（ΔＥ_2.0)が2.0V未満であれば通電を再開する。2.0V以上のときは通電を停止する。
本発明に係わる防食状態の判定の根拠は下記の事実にもとづくことを図１〜図３によって説明する。
防食電流は配管内面の鉄部、主として継手部分の露出鉄面に集中して供給される。この状態における配管表面の防食の状態を確認するために、定電流装置１、電位差計２、飽和カロメル基準電極３を備えた図１に示す装置にて試験を行った。ビーカー４に水道水を入れ、表面積4.47cm²の線状電極( 直径0.75mm、長さ19cm) ５を陽極、表面積16.2cm² の鉄片６を陰極として定電流装置より1.0mA を通電した。
【０００８】
この結果を図２に示す。線状電極５の電位は+1.58V(SCE) から150 分経過後に+1.65V(SCE) と殆ど陽分極が見られないが、鉄片６の電位は-0.44Vから150 分経過後に-0.88V(SCE) と陰分極し、更に分極が進む傾向にある。また、この間のΔE_2.0の測定結果をまとめると図３に示すように鉄片の電位と良い相関がある。
通常、防食効果が得られる鉄の基準電位として知られている-0.77V(SCE) は、図３よりΔＥ_2.0として1.95V に相当する。即ち、ΔＥ_2.0が2.0V以上に維持されていれば鉄が防食状態にあることが理論的に示すことができる。
一方、通電によって配管側の分極が進むと、陰極表面近傍がアルカリ性となるため水中に溶存しているCa²⁺、Mg²⁺より、CaCO₃、 Mg(OH)₂等の塩基性化合物が生成し、皮膜として付着する。皮膜が形成されると通電を遮断しても鋼管の自然電位に戻るのに時間がかかるようになる。この皮膜が形成されたときの等価回路は皮膜成分と分極成分と見なし得る。皮膜成分の時定数（τ_f）は約２秒であり、分極成分の時定数（τ_d）は10〜20秒と異なることが知られている。ここで時定数 (τ) は以下のように定義される。
τ_f(s) = 皮膜抵抗成分 (Ω) ×皮膜容量成分(F)
τ_d(s) = 分極抵抗成分 (Ω) ×分極容量成分(F)
このため通電遮断2.0 秒後の電位減衰が小さい方が良質な皮膜といえる。従って、ΔＥ_2.0が2.0V以上であれば、皮膜形成すなわち赤水防止効果は良好であると判定して通電を停止し、2.0V未満であれば通電を続行する。飲用水配管の場合、水の使用状況が時間的、季節的に一定しないこと、常に皮膜形成状態を監視する必要があることから、この測定は１〜３時間毎、好ましくは約２時間毎に行う。このようにして断続的に通電することにより、配管内面に形成されるカルシウム及びマグネシウムを含む塩基性化合物の皮膜を必要にして十分な厚さである10〜30μm に維持することが可能となり、配管を閉塞させるおそれなく赤水の発生が防止できる。
【０００９】
本発明では銅線にニオブと白金を圧延被覆した外径０．６〜０．８ｍｍの線状電極を用いる。この電極は銅を芯材としているため、従来の白金を被覆したチタン線より電気抵抗が小さくかつ可撓性があり、曲がり部が多くある小口径の給水配管への挿入が容易である。
この電極には配管に対して電気的接触が起こらないように絶縁被覆が必要であり、この状態において防食電流が供給できるよう、絶縁材料を用いて適当な隙間を有するように被覆する。絶縁被覆材としては、可撓性、耐酸化性、電気絶縁性に優れているとともに、飲用水中への溶出がない素材を用いる必要がある。このような素材としては、フッ素樹脂繊維、好ましくはテトラフルオロエチレン／パーフルオロアルキルビニルエーテル共重合樹脂（ＰＦＡ）を挙げることができる。
【００１０】
ＰＦＡ単繊維の劣化試験の一例を次に示す。
本発明の線状電極体の代表例として、銅線にニオブと白金を圧延被覆した直径0.75mmの線状電極に0.3mm のＰＦＡ単繊維１６本を袋編みに絶縁被覆した線状電極体を作成し、これを陽極として試験を行った。
ビーカー７内に飽和カロメル基準電極８、定電流装置９、陽極１０、陰極（リング状のステンレス板直径10cm×高さ5.0cm ）１１を備えた図４に示す装置に、硫酸ナトリウムを0.05mol/l の濃度に溶解した水道水を入れ、陰極の中心部に陽極を置き、酸素発生領域の電位＋4.0V(SCE) として、陽極電流密度 300mA/cm²で36日間通電した。なお、図中、電極体の両端部の網かけ部はテフロン製絶縁テープを線状電極体に巻き、電解電流が流れないようにしてあることを示す。それ以外のＵ字部分が供試体となる。試験終了後にＰＦＡ単繊維を取り出し、耐久性の評価をフーリエ変換赤外分光法によって行った。この結果、試験の前後で有意差は認められず、ＰＦＡ単繊維の劣化はなかった。
以下、実施例をあげて本発明を詳しく説明する。
【００１１】
【実施例１】
長さ8.0mの途中に鋼製継手のある２０Ａのポリ塩化ビニルライニング鋼管（新管）に、直径0.3mm のＰＦＡ単繊維16本を外径0.75mmのCu-Nb-Pt線状電極に袋編みにした長さ8mの線状電極体を取り付け、水道水（Ca 55mg/l 、Mg4.0mg/l 、Fe0.03mg/l、Zn0.01mg/l、SiO₂6.1mg/l ）を流しながら、80mAの直流を断続通電した。陽極電流密度は0.42mA/cm²となる。ΔＥ_2.0を2 時間毎に測定し、2.0V以上のときには通電を停止し、2.0V未満のときは通電を続行した。
このようにして８日間通電した後、鋼製継手内面を観察したところ灰白色の皮膜が認められた。この間の通電遮断時の電極電位減衰を図５に示す。なお、図中、Ａ₁は通電１日目の線状電極の電位減衰、Ｂ₁は通電１日目の鋼管の電位減衰、Ａ₈は通電８日目の線状電極の電位減衰、Ｂ₈は通電８日目の鋼管の電位減衰をそれぞれ表す。
【００１２】
通電遮断後線状電極の電位は、１日目（A₁）８日目（A₈) ともに急激に低下し、本来のPtの自然電位に漸近する。一方、鋼管の電位減衰には１日目（ B₁)と８日目（B₈）に大きな違いが認められる。すなわち B₁はA₁、A₈と同じく急激に減衰している。これは減衰の初期に溶液の電圧降下分が急に除かれるためである。一方、B₈の減衰はB₁、A₁、A₈よりも緩やかである。これは皮膜が形成されたため、皮膜成分と分極成分から構成される陰分極が大きくなったためと考えられる。
このような皮膜形成に伴う陰分極の程度を随時遅滞なく検出するためには、通電遮断直後の急激な減衰がほぼ終了した時点、即ち皮膜成分の時定数に相当する2.0 秒後の両極電位を測定すればよい。ただし、本装置においては両極間電位差 (ΔＥ_2.0)の測定がより簡便であり信頼性が高い。
本例では１日目のΔＥ_2.0は1.75V と2.0Vより小さく、８日目のΔＥ_2.0は2.23V と2.0Vより大きくなっている。
このようにしてΔＥ_2.0は配管の皮膜状態を判定する上で有効な手段となる。
【００１３】
【実施例２】
断続通電することによる効果を調べるため、２本の水道管（炭素鋼新管、 20A、長さ0.2m) を用意した。一方には実施例１で用いたのと同じ線状電極体( ただし、長さ0.2m) をとりつけて3.0Vで通電し、他方は電極体を取り付けることなく水道水を流した。水道水の水質は Ca 41mg/l、Mg 3.2mg/l、Fe 0.13mg/l 、Zn 0.01mg/l 、SiO₂ 11mg/l であった。１カ月後にこの水道管の内部表面の付着物を分析した結果を表１に示す。なお、断続通電の基準は実施例１と同様とした。
【００１４】
【表１】

この表から明らかなように、通電した管では通電しない管に比べてカルシウム、マグネシウムが多く付着した。防食電流による皮膜形成効果が現れたものである。
【００１５】
【実施例３】
建築後１５年になる家屋の２０Ａ水道配管に本発明を適用した。この配管はメーターボックスから流し台蛇口まで約８ｍの長さがある。これに実施例１で用いたのと同じ線状電極体をとりつけて3.0Vで通電した。水道水の水質は Ca 38mg/l、Mg 4.5mg/l、Fe 0.15mg/l 、Zn 0.01mg/l 、SiO₂ 6.5mg/lであった。朝一番に蛇口から採水し、溶解鉄濃度の分析によって赤水防止効果の判定を行った。結果を表２に示す。なお、断続通電の基準は実施例１と同様とした。
通電２日後には多量の溶解鉄が検出されたが、これは配管内部の既存の錆が防食電流の供給により還元されたことにより一時的に増加したものである。通電７日後には、通電前の0.2mg/l よりも低い濃度である0.04mg/lとなり、以後ほぼ一定の値で推移し、通電による赤水防止効果が認められた。
また、ΔＥ_2.0を測定した結果、通電１日目は0.9Vであったが、６日目以降３ヶ月後まで2.3 〜2.4Vと安定して推移した。この状態において防食皮膜が形成されている状態にあると推定される。この電圧2.3Vは配管の電位を推定するに -1.1V (=1.2-2.3) に相当し、赤水防止効果は十分であることが確認できた。
【００１６】
【表２】

【００１７】
【発明の効果】
本発明によれば、飲用水給水配管内に電気防食用線状電極体を装着し、線状電極体を陽極、配管を陰極として断続的に通電することにより、配管内面に必要にして十分な厚さの皮膜を形成させることができる。この結果、飲用水の赤水を効果的に防止することができる。
【図面の簡単な説明】
【図１】防食試験装置の概略図
【図２】通電時の線状電極と鉄片の電位の経時変化を示す図
【符号の説明】
Ａ：線状電極
Ｂ：鉄片
【図３】通電遮断2.0 秒後の電位差（ΔＥ_2.0)と鉄片の電位相関図
【図４】線状電極体の被覆繊維の劣化試験装置の概略図
【図５】通電遮断時の電極電位減衰を示す図
Ａ₁：通電１日目の線状電極の電位減衰
Ｂ₁：通電１日目の鋼管の電位減衰
Ａ₈：通電８日目の線状電極の電位減衰
Ｂ₈：通電８日目の鋼管の電位減衰[0001]
【Technical field】
The present invention relates to a method and an apparatus for preventing red water of potable water by performing an external power supply type anticorrosion on the inner surface of a water supply pipe at least partly made of a steel member. Furthermore, the present invention relates to a linear electrode body used for cathodic protection.
[0002]
[Prior art]
Conventionally, there is a problem of red water due to corrosion of a water supply pipe at least partly made of a steel member in a pipe for supplying drinking water containing Ca ²⁺ and Mg ²⁺ . Recently, polyvinyl chloride-lined steel pipes are frequently used for water supply pipes in buildings. However, corrosion occurs at the exposed steel pipes at the end faces of the steel pipes and joints that are threaded, and corrosion prevention is required. Conventionally, (1) a method of lining an epoxy resin on the inner surface of a pipe, (2) a method of magnetically processing the inner surface of a pipe, (3) an electron field processing method, and (4) a method of passing water supply through a ceramic packed bed. (5) A method of injecting a corrosion inhibitor into the water supply, (6) a method of degassing the water supply, (7) a calcium rust prevention method, etc. have been proposed and some have been implemented. However, (1) has a problem of elution of bisphenol A from the epoxy resin, (2), (3), and (4) are questioned about its anticorrosive effect, and (5) is a viewpoint of health of the added drug. However, (6) cannot maintain its anti-corrosion effect without sufficient maintenance of the hollow fiber, and (7) has the problem that it is excellent in the long term but lacks immediate effect. is there.
[0003]
In contrast, the anticorrosion method is theoretically recognized such as being applied to the inner surface protection of the storage tank, and the application of this method to the inner surface of the water supply pipe is being studied. For example, Japanese Patent Publication No. 5-24235 proposes a red water stop method in which a corrosion-resistant linear anode electrode is inserted into a pipe and energized. A platinum-coated titanium wire is made of rubber, polyvinyl chloride, polyethylene, nylon, polypropylene, polycarbonate. An electrode wire surrounded by a porous electrically insulating tube is disclosed. Japanese Patent No. 2801030 discloses an electrode wire for corrosion protection in which a surface of an insoluble metal wire is covered with a monofilament yarn of a non-conductive synthetic fiber which is roughly braided into a braid. Furthermore, Utility Model Registration No. 2572785 discloses a spiral shape in which a plurality of polyethylene or polypropylene monofilament yarns are wound on a surface of a metal wire platinum-plated on a titanium wire so as to have a strand winding angle of 15 to 45 ° for the purpose of preventing red water. A wound electrode wire for pipeline protection is disclosed.
These methods attempt to prevent the generation of red water by forming a basic compound film using Ca ²⁺ and Mg ²⁺ contained in the water supply, but the Ca ²⁺ and Mg ² contained Depending on the concentration of ⁺ , sufficient effects may not be obtained, or a large amount of basic compound may be generated in the tube.
[0004]
[Problems to be solved by the invention]
In view of the current situation, the present inventor has conducted research on the problem of stopping red water of drinking water at an early stage, and as a result, linearly forms piping in the drinking water containing Ca ²⁺ and Mg ^2+. An electrode body is provided, and a linear electrode body is used as an anode, and piping material is used as a cathode, and a direct current is passed through to form a film of calcium or magnesium compound to a sufficient thickness to prevent red water. I found a way to do it.
[0005]
[Means for Solving the Problems]
In the present invention, when water containing Ca ²⁺ and Mg ²⁺ is supplied, a linear electrode body is disposed in a pipe at least partially made of a steel member, the linear electrode body serves as an anode, and a piping material is provided. In a method of preventing red water of drinking water by applying a direct current as a cathode and forming a film of a basic compound containing calcium and magnesium in the pipe, the film is necessary and sufficient by intermittently conducting the current. The present invention relates to a red water prevention method for maintaining the thickness. This is done by periodically cutting off the current, measuring the potential difference between the two electrodes immediately after the interruption, measuring the decay over time if necessary, and determining whether or not to resume the current. Can do. Further, the present invention comprises a linear electrode body disposed in a water supply pipe at least partly made of a steel member, a power supply device for energizing direct current using the linear electrode body as an anode and a piping material as a cathode, The present invention relates to a drinking water red water prevention device, characterized in that the power supply device includes a control unit that periodically performs energization interruption / measurement of a time-dependent attenuation of potential difference between both electrodes immediately after interruption and whether energization can be resumed. Furthermore, this invention relates to the linear electrode body of the specific structure which can be easily arrange | positioned to piping with many bending parts.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The present invention prevents the occurrence of corrosion in the iron part of a water supply pipe at least partly made of a steel member by using Ca ²⁺ and Mg ²⁺ contained in the water supply, Ca ²⁺ and Mg Applicable to drinking water containing ²⁺ in a total hardness of 10 mg / l or more. A linear electrode body is disposed in the pipe, and direct current is applied with the linear electrode body as an anode and the piping material as a cathode. When energized, a coating of a basic compound of calcium and magnesium is formed on the inner surface of the pipe, but the energization is periodically interrupted, the potential difference between the electrodes immediately after the interruption is measured, and if necessary, the decay over time To determine whether to resume energization.
[0007]
The applied voltage during energization is 2.1 to 5V, preferably 2.5 to 3.5V. In order to determine whether or not to resume energization, the polarization state of the inner surface of the pipe is measured based on the potential of the linear electrode immediately after interruption. If the potential difference between the two poles is 2.0V or more, it indicates that the potential of the pipe (iron) is more polarized than -0.77V (SCE), which is known as the reference potential of iron, which usually provides an anticorrosion effect. It will be in a good anticorrosion state. Therefore, for example, when the applied voltage is 3 V and the potential difference (ΔE _2.0 ) 2.0 seconds after the energization interruption is less than _2.0 V, the energization is resumed. When the voltage is 2.0V or higher, turn off the power.
The grounds for determining the anticorrosion state according to the present invention will be explained based on the following facts with reference to FIGS.
The anticorrosive current is concentrated and supplied to the iron part on the inner surface of the pipe, mainly the exposed iron surface of the joint part. In order to confirm the state of corrosion prevention on the pipe surface in this state, a test was performed with the apparatus shown in FIG. 1 provided with a constant current device 1, a potentiometer 2, and a saturated calomel reference electrode 3. Filled with tap water in a beaker 4 and energizing the linear electrode (diameter 0.75 mm, length 19cm) of surface area 4.47cm ² 5 an anode, a 1.0mA from the constant current device iron pieces 6 of the surface area 16.2cm ² as a cathode.
[0008]
The result is shown in FIG. The electric potential of the linear electrode 5 is +1.65 V (SCE) after 150 minutes from +1.58 V (SCE), and almost no positive polarization is seen, but the potential of the iron piece 6 is -0.88 V after 150 minutes from -0.44 V. It tends to be negatively polarized with (SCE) and further polarized. Further, when the measurement results of ΔE _2.0 during this period are summarized, there is a good correlation with the potential of the iron piece as shown in FIG.
Usually, -0.77 V (SCE), which is known as the reference potential of iron that can provide an anticorrosion effect, corresponds to 1.95 V as ΔE _2.0 from FIG. That is, if ΔE _2.0 is maintained at _2.0 V or higher, it can be theoretically shown that iron is in an anticorrosive state.
On the other hand, when the polarization on the pipe side progresses due to energization, basic compounds such as CaCO ₃ and Mg (OH) ₂ are generated from Ca ²⁺ and Mg ²⁺ dissolved in water because the vicinity of the cathode surface becomes alkaline. And adheres as a film. When a film is formed, it takes time to return to the natural potential of the steel pipe even if the current is cut off. The equivalent circuit when this film is formed can be regarded as a film component and a polarization component. It is known that the time constant (τ _f ) of the film component is about 2 seconds, and the time constant (τ _d ) of the polarization component is different from 10 to 20 seconds. Here, the time constant (τ) is defined as follows.
τ _f (s) = film resistance component (Ω) × film capacitance component (F)
τ _d (s) = polarization resistance component (Ω) × polarization capacitance component (F)
For this reason, it can be said that the smaller the potential decay after 2.0 sec. Therefore, if ΔE _2.0 is 2.0 V or more, it is determined that the film formation, that is, the red water prevention effect is good, and the energization is stopped, and if it is less than 2.0 V, the energization is continued. In the case of potable water pipes, this measurement should be performed every 1 to 3 hours, preferably about every 2 hours, because the usage of water is not constant in time and season, and it is necessary to constantly monitor the film formation state. Do. By intermittently energizing in this way, it becomes possible to maintain a basic compound film containing calcium and magnesium formed on the inner surface of the pipe and maintain a sufficient thickness of 10 to 30 μm. The generation of red water can be prevented without the risk of blocking.
[0009]
In the present invention, a linear electrode having an outer diameter of 0.6 to 0.8 mm in which copper wire is rolled and coated with niobium and platinum is used. Since this electrode uses copper as a core material, it has a lower electrical resistance and flexibility than a conventional platinum-coated titanium wire, and can be easily inserted into a small-diameter water supply pipe having many bent portions.
This electrode needs an insulating coating so that electrical contact with the pipe does not occur. In this state, the electrode is coated with an insulating material so as to have an appropriate gap so that a corrosion-proof current can be supplied. As the insulating coating material, it is necessary to use a material that is excellent in flexibility, oxidation resistance, and electrical insulation and does not elute into drinking water. Examples of such a material include a fluororesin fiber, preferably a tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (PFA).
[0010]
An example of the deterioration test of the PFA single fiber is shown below.
As a representative example of the linear electrode body of the present invention, a linear electrode body in which niobium and platinum are rolled and coated on a copper wire and a linear electrode having a diameter of 0.75 mm and 16 0.3 mm PFA single fibers are insulated and coated on a bag. It produced and tested by making this into an anode.
In the apparatus shown in FIG. 4 equipped with a saturated calomel reference electrode 8, a constant current device 9, an anode 10, and a cathode (ring-shaped stainless steel plate diameter 10 cm × height 5.0 cm) 11 in a beaker 7, sodium sulfate was added at 0.05 mol / Tap water dissolved at a concentration of l was placed, an anode was placed in the center of the cathode, and the current was supplied for 36 days at an anode current density of 300 mA / cm ² at an oxygen generation region potential of +4.0 V (SCE). In the figure, the shaded portions at both ends of the electrode body indicate that a Teflon insulating tape is wound around the linear electrode body so that no electrolytic current flows. The other U-shaped part is the specimen. After the test, the PFA single fiber was taken out and durability was evaluated by Fourier transform infrared spectroscopy. As a result, no significant difference was observed before and after the test, and there was no deterioration of the PFA single fiber.
Hereinafter, the present invention will be described in detail with reference to examples.
[0011]
[Example 1]
Bag of 20A polyvinyl chloride lined steel pipe (new pipe) with a steel joint in the middle of 8.0m in length and 16 PFA monofilaments with a diameter of 0.3mm on a Cu-Nb-Pt linear electrode with an outer diameter of 0.75mm Install the linear electrodes of 8m long you knitting, tap water (Ca 55mg / l, Mg4.0mg / l, Fe0.03mg / l, Zn0.01mg / l, SiO 2 6.1mg / l) while flowing , 80 mA direct current was intermittently energized. The anode current density is 0.42 mA / cm ² . ΔE _2.0 was measured every 2 hours. When the voltage was 2.0V or higher, the power supply was stopped, and when it was lower than 2.0V, the power supply was continued.
After energizing for 8 days in this way, the inside surface of the steel joint was observed to find a grayish white film. FIG. 5 shows the electrode potential attenuation when the energization is cut off during this period. In the figure, A ₁ is the potential attenuation of the linear electrode on the first day of energization, B ₁ is the potential attenuation of the steel pipe on the first day of energization, A ₈ is the potential attenuation of the linear electrode on the eighth day of energization, and B ₈ Represents the potential decay of the steel pipe on the eighth day of energization.
[0012]
After the current is cut off, the potential of the linear electrode rapidly decreases on the first day (A ₁ ) and the eighth day (A ₈ ), and gradually approaches the original natural potential of Pt. On the other hand, there is a large difference in the potential decay of the steel pipe between the first day (B ₁ ) and the eighth day (B ₈ ). That is, B ₁ is abruptly attenuated, as are A ₁ and A ₈ . This is because the voltage drop of the solution is abruptly removed at the beginning of decay. On the other hand, the attenuation of B ₈ is slower than _{_{_{B 1, A 1, A 8}}} . This is considered to be because the negative polarization composed of the film component and the polarization component is increased because the film is formed.
In order to detect the degree of negative polarization accompanying such film formation without any delay, the bipolar potential after 2.0 seconds corresponding to the time constant of the film component, when the sudden decay immediately after the energization is cut off, is almost completed. Just measure. However, in this apparatus, the measurement of the potential difference between both electrodes (ΔE _2.0 ) is simpler and more reliable.
In this example, ΔE _{2.0 on the} first day is smaller than 1.75 V and 2.0 V, and ΔE _2.0 on the eighth day is larger than 2.23 V and 2.0 V.
In this way, ΔE _2.0 is an effective means for judging the coating state of the pipe.
[0013]
[Example 2]
Two water pipes (carbon steel new pipe, 20A, length 0.2m) were prepared to investigate the effect of intermittent energization. The same linear electrode body (however, 0.2 m in length) used in Example 1 was attached to one side, and electricity was supplied at 3.0 V, and tap water was allowed to flow without attaching the electrode body to the other side. The water quality of tap water was Ca 41 mg / l, Mg 3.2 mg / l, Fe 0.13 mg / l, Zn 0.01 mg / l and SiO ₂ 11 mg / l. Table 1 shows the results of analyzing the deposits on the inner surface of this water pipe after one month. The criteria for intermittent energization were the same as in Example 1.
[0014]
[Table 1]

As is clear from this table, the energized pipes had more calcium and magnesium adhered than the non-energized pipes. The film formation effect by the anticorrosion current appears.
[0015]
[Example 3]
The present invention was applied to a 20A water pipe in a house that has been built for 15 years. This pipe is about 8m long from the meter box to the sink faucet. The same linear electrode body as used in Example 1 was attached thereto, and energized at 3.0V. The water quality of tap water was Ca 38 mg / l, Mg 4.5 mg / l, Fe 0.15 mg / l, Zn 0.01 mg / l, SiO ₂ 6.5 mg / l. Water was collected from the faucet first in the morning, and the effect of preventing red water was determined by analyzing the dissolved iron concentration. The results are shown in Table 2. The criteria for intermittent energization were the same as in Example 1.
Two days after energization, a large amount of dissolved iron was detected. This is a temporary increase due to the reduction of the existing rust inside the pipe by supplying the anticorrosion current. After 7 days of energization, the concentration was 0.04 mg / l, which was lower than 0.2 mg / l before the energization, and subsequently changed to a substantially constant value, confirming the effect of preventing red water by energization.
Moreover, as a result of measuring ΔE _2.0 , it was 0.9 V on the first day of energization, but remained stable at 2.3 to 2.4 V from the sixth day to 3 months later. In this state, it is estimated that the anticorrosion film is formed. This voltage of 2.3V corresponds to -1.1V (= 1.2-2.3) to estimate the potential of the pipe, and it was confirmed that the red water prevention effect was sufficient.
[0016]
[Table 2]

[0017]
【The invention's effect】
According to the present invention, a linear electrode body for cathodic protection is installed in a potable water supply pipe, and the line electrode body is used as an anode and the pipe is used as a cathode to intermittently energize, so that it is necessary and sufficient for the inner surface of the pipe. A film having a thickness can be formed. As a result, potable red water can be effectively prevented.
[Brief description of the drawings]
[Fig. 1] Schematic diagram of anticorrosion test equipment [Fig. 2] A diagram showing the change over time in the potential of the linear electrode and iron piece during energization [Explanation of symbols]
A: Linear electrode B: Iron piece [Fig. 3] Potential difference (ΔE _2.0 ) 2.0 seconds after energization interruption and potential correlation of the iron piece [Fig. 4] Schematic diagram of the degradation test apparatus for the coated fiber of the linear electrode body [Fig. FIG. 1A shows the electrode potential decay when the current is cut off. A ₁ : Potential decay of the linear electrode on the first day of energization B ₁ : Potential decay of the steel pipe on the first day of energization A ₈ : Potential of the linear electrode on the eighth day of energization Attenuation B ₈ : Potential decay of steel pipe on the 8th day of energization

Claims

When supplying water containing Ca ²⁺ and Mg ²⁺ , a linear electrode body is disposed in a pipe made of a steel member at least partially, and direct current is generated using the linear electrode body as an anode and the piping material as a cathode. In the method of preventing red water by energizing and forming a basic compound film containing calcium and magnesium on the inner surface of the pipe, the energization is periodically interrupted, and the potential difference between the electrodes (ΔE _2.0 after 2.0 sec. ), It is determined whether or not energization is resumed, and energization is resumed or energization interruption is continued.

2. The potable water according to claim 1, wherein the energization is resumed if the potential difference (ΔE _2.0 ) between the electrodes after 2.0 seconds of energization interruption is less than 2.0 V, and the energization interruption is continued when it is 2.0 V or more. Red water prevention method.

A linear electrode body disposed in a water supply pipe at least partially made of a steel member, and a power supply device for energizing direct current using the linear electrode body as an anode and the piping material as a cathode. Measurement of the potential difference between two electrodes (ΔE _2.0 ) after 2.0 seconds of static electricity interruption / energization, whether or not energization is resumed depending on the value of potential difference between two electrodes (ΔE _2.0 ) after 2.0 seconds of electricity interruption An apparatus for preventing red water from drinking water, comprising a control unit for performing the determination.

A drinking water red water prevention apparatus comprising a linear electrode body disposed in a water supply pipe made of at least a part of a steel member, and a power supply device for energizing direct current using the linear electrode body as an anode and the piping material as a cathode. Oite linear electrode material used, the linear electrode body, the linear metal electrodes having an outer diameter 0.6~0.8mm of a three-layered structure was rolled coated niobium and platinum to copper, tetrafluoroethylene / Linear electrode body in which perfluoroalkyl vinyl ether copolymer resin single fiber is covered in a bag.