【発明の詳細な説明】[Detailed description of the invention]
本発明は、電気防食法、特に陰極防食法におけ
る流電陽極方式に関するものである。
陰極防食法には、整流器、電池、あるいは直流
発電機を使用する外部電源方式と、異種金属間の
電位差を利用して防食電流を得る流電陽極方式と
がある。
このうち外部電源方式は、電圧、電流を自由
に選ぶことができる、電極設置容積が小さい、
不溶性電極を使えば長時間メンテナンスを要し
ない等の特長を有している反面、電源、電極装
置と、それらの取付工事、配線工事等が必要で、
イニシヤルコストが高くつく、電力費が必要等
の欠点も有している。
一方、流電陽極方式は、施工が簡単でメンテ
ナンスが容易である、電源の利用できない場所
や移動する対象物に適用できる、維持電力費が
不要という特長を有するが、電圧、電流の調節
が難しい、陽極が消耗し、定期的な点検、交換
が必要である等の欠点を有している。
ところで流電陽極方式においては、被防食体に
流れる防食電流に対応するのは陽極の溶出反応で
あるから、陽極が消耗すること自体はやむを得な
いことである。しかし、陽極の消耗をできるだけ
抑えることができれば、点検、交換の期間をのば
すことができ、陽極の材料費だけでなく、点検、
交換に必要な工事費を節約でき、多大な利点が生
ずる。特に海中構造物、水中ポンプ等メンテナン
スが難しい防食対象物では、利点はより大きなも
のになる。
また、陽極の消耗を必要以上に早める原因は、
被防食体に必要以上の防食電流が流れること、す
なわち過防食である。例えば、海水中における鉄
の適性防食電位は−770〜−790ｍＶ（飽和かんこ
う電極基準、以下「vs.SCE」と称す）といわれ
ているが、陽極にアルミニウムを使用した場合、
液間抵抗が小さければ、被防食体である鉄の電位
はアルミニウムの自然電位である約−1100ｍＶ近
くまで分極する。鉄を−770ｍＶに分極させるに
要する電流より、−1100ｍＶに分極させるに要す
る電流の方が当然高くなるが、その差は不要な陽
極の消耗に費されることになる訳である。
この場合、被防食体の適性防食電位になるべく
近い自然電位を持つ金属を陽極として選べばよい
訳であるが、現実には、流電陽極方式の陽極とし
て採用できる特性を持つた実用金属の中からは任
意の電位を選ぶことは難しい。
本発明は、流電陽極方式による電気防食法にお
いて、実用金属を陽極として採用しながら防食電
流を適性に調節し、過防食を防ぎ、陽極の消耗を
最小限に抑え、陽極寿命の長期化をはかることを
目的とするものである。
本発明は、流電陽極方式による電気防食法にお
いて、陽極と被防食体を抵抗を介して導通し、被
防食体に取り付けた被防食体と同一材質のモニタ
用電極に流れる防食電流を測定しながら前記抵抗
の抵抗値を調節して過防食を防止することを特徴
とする電気防食法である。
さらに本発明の実施態様を図面を参照しながら
説明すれば、第１図示例において、腐食性溶液１
に接する被防食体２に陽極４を絶縁体６を介して
取り付け、陽極４と被防食体２とは外部に取り出
した導線１０によつて導通させるがその間に抵抗
７を介在せしめる。また、被防食体２に参照電極
３を絶縁体６を介して取り付け、電位差計８を介
して被防食体２と導通させる。また、被防食体２
と同一材質である防食電流測定のためのモニタ用
電極５を絶縁体６を介して被防食体に取り付け、
無抵抗電流計９を介して被防食体２と導通させ
る。
しかるのち、参照電極３を基準とし、該電極３
と被防食体２（又はモニタ用電極５）間の電位差
を電位差計８によつて知ることによつて、被防食
体２の電位を測定しながら、抵抗７の抵抗値を調
節して必要かつ最小限の防食電流が流れるように
して過防食を監止し、また前記電位差によつて常
に被防食体２の防食状態及び陽極４の消耗時期も
無視することができる。
ところで、このように参照電極３と被防食体２
間の電位差を監視する電位監視方式には次のよう
な問題を生ずる。つまり、金属の自然電位は環境
（電解質の種類、溶存酵素量、流速等）によつて
大きく変化するから、電位監視方式では被防食体
に流れる電流値が環境によつて大きく変わる様子
をつかむことができない。
このような環境の変化に対応させるためには、
モニタ用電極５と被防食体２間の無抵抗電流計９
によつてモニタ用電極５に流れる防食電流を測定
し、常に被防食体の所定の位置の防食電流を確実
に知り、所定の防食電流が流れているかどうか、
過防食となつているかどうかを知り、被防食体の
防食状態及び陽極４の消耗状態を監視し、抵抗７
の抵抗値を調節して適切に制御する。
なお、電位差計８及び無抵抗電流計９は常設し
ておく必要はなく、測定する時にだけ搬入、取り
付けてもよく、参照電極３と取り付けることな
く、モニタ用電極だけを取り付け、防食電流を監
視することによつて十分目的を達成することがで
きる。なお、モニタ用電極５は、被防食体２の形
状に応じて複数個設置してもよい。
また、抵抗７は、可変抵抗器であることが最も
望ましいが、防食電位、防食電流を測定しながら
所定の抵抗値をもつ抵抗を介在させるようにして
もよい。
第２図示例は、本発明の最も簡便な例を示し、
被防食体２の構造、電解質や陽極５の性状等にあ
る程度予備知識がある場合には、抵抗値をどの程
度にすれば良いかをあらかじめ予測し設定し、抵
抗７を導線を介さずに被防食体２と陽極４間に直
接抵抗を取り付けるようにしたものである。この
ようにすれば、抵抗値を途中で変えるのが難しい
が、導線を引き出したりする配線工事の手間が省
け陽極４の取り付けが容易となる。
このように本発明によれば、流電陽極方式にお
ける陽極の種類に対応して防食電流を適正に調節
し、過防食を防いで陽極の消耗を最小限にし、陽
極の寿命を長くするだけでなく、常に被防食体の
防食状態を監視することもでき、陽極の消耗時期
をも確実に知ることができるという、きわめて有
益なる効果を有するものである。
次に実験例を示す。
構成は第１図示例と同一であるが、本実験例で
は陽極４と抵抗７を結ぶ導線の途中にも無抵抗電
流計を配し、陽極４に流れる総電流も測定した。
腐食性溶液１は３％食塩水で、温度は25℃で、静
止大気開放とした。被防食体２は軟鋼製容器で50
×50×50（・cm）の寸法とした。陽極４にはアル
ムニウムを用い、その表面積は100cm2であつた。
参照電極３には飽和かんこう電極を、モニタ用電
極５には被防食体２と同じ軟鋼を用い、両者とも
陽極４の反対側の面に取り付けた。
抵抗を零にした場合（従来法）と、軟鋼の適正
防食電流密度である10μA／cm2付近になるように
抵抗を調節した場合（本発明法）の２条件につい
て測定したところ次表のような結果を得た。
なお、本発明法におけるこの時の被防食体（軟
鋼）の電位は、表中に示したように−800ｍＶ
（vs.S.C.E.）であつた。
The present invention relates to a galvanic anode method in cathodic protection, particularly cathodic protection. Cathodic protection methods include an external power source method that uses a rectifier, battery, or DC generator, and a galvanic anode method that uses a potential difference between dissimilar metals to obtain a corrosion protection current. Among these, the external power supply method allows the voltage and current to be freely selected, and the electrode installation volume is small.
Although insoluble electrodes have the advantage of not requiring long-term maintenance, they require a power source, electrode device, their installation work, wiring work, etc.
It also has drawbacks such as high initial cost and the need for electricity. On the other hand, the galvanic anode method has the advantages of being easy to install and maintain, being applicable to locations where power sources are unavailable or moving objects, and requiring no maintenance power costs, but it is difficult to adjust the voltage and current. However, it has disadvantages such as the anode wears out and requires periodic inspection and replacement. By the way, in the galvanic anode method, since it is the elution reaction of the anode that corresponds to the corrosion protection current flowing through the object to be protected, it is unavoidable that the anode is consumed. However, if anode wear can be suppressed as much as possible, the period of inspection and replacement can be extended, and not only the material cost of the anode but also the inspection and replacement period can be extended.
The construction costs required for replacement can be saved, resulting in a great advantage. The benefits are particularly significant for corrosion-protected objects that are difficult to maintain, such as underwater structures and submersible pumps. In addition, the cause of faster anode consumption than necessary is
This is over-corrosion protection, which means that more corrosion protection current than necessary flows through the object to be protected. For example, the suitable corrosion protection potential of iron in seawater is said to be -770 to -790 mV (saturated corrosion electrode standard, hereinafter referred to as "vs.SCE"), but when aluminum is used as an anode,
If the inter-liquid resistance is small, the potential of iron, which is the object to be protected, will be polarized to approximately -1100 mV, which is the natural potential of aluminum. Naturally, the current required to polarize iron to -1100 mV is higher than the current required to polarize iron to -770 mV, but the difference is wasted in unnecessary consumption of the anode. In this case, it is sufficient to select a metal with a natural potential as close as possible to the appropriate corrosion protection potential of the object to be protected as the anode, but in reality, among the practical metals that have the characteristics that can be used as the anode of the galvanic anode method, It is difficult to choose an arbitrary potential from . The present invention uses practical metals as anodes in cathodic protection methods using galvanic anodes, appropriately adjusts the anticorrosion current, prevents over-corrosion, minimizes anode wear, and extends the life of the anodes. The purpose is to measure. In the electrolytic corrosion protection method using a galvanic anode method, the present invention conducts the anode and the object to be protected through a resistor, and measures the corrosion protection current flowing through a monitoring electrode made of the same material as the object to be protected, which is attached to the object to be protected. This electrolytic protection method is characterized in that the resistance value of the resistor is adjusted to prevent excessive corrosion. Further, embodiments of the present invention will be described with reference to the drawings. In a first illustrated example, a corrosive solution 1
The anode 4 is attached to the object 2 to be corrosion protected in contact with the object 2 via an insulator 6, and the anode 4 and the object 2 to be corrosion protected are electrically connected to each other by a conductive wire 10 taken out to the outside, with a resistor 7 interposed therebetween. Further, a reference electrode 3 is attached to the object 2 to be protected from corrosion via an insulator 6, and electrically connected to the object 2 to be protected from corrosion via a potentiometer 8. In addition, the object to be protected from corrosion 2
A monitoring electrode 5 for measuring the corrosion protection current made of the same material as is attached to the object to be protected via an insulator 6,
Conductivity is established with the object 2 to be protected from corrosion via a non-resistance ammeter 9. After that, using the reference electrode 3 as a reference, the electrode 3
By knowing the potential difference between the object 2 and the monitoring electrode 5 using the potentiometer 8, the resistance value of the resistor 7 can be adjusted while measuring the potential of the object 2 to be protected as needed. Excessive corrosion protection is monitored by ensuring that the minimum corrosion protection current flows, and the corrosion protection state of the object to be protected 2 and the consumption period of the anode 4 can also be ignored at all times due to the potential difference. By the way, in this way, the reference electrode 3 and the object to be corroded 2
The following problems arise in the potential monitoring method that monitors the potential difference between the two. In other words, since the natural potential of metals changes greatly depending on the environment (type of electrolyte, amount of dissolved enzyme, flow rate, etc.), the potential monitoring method allows you to grasp how the current value flowing through the object to be protected changes greatly depending on the environment. I can't. In order to respond to such changes in the environment,
Non-resistance ammeter 9 between monitoring electrode 5 and object to be protected 2
By measuring the anticorrosion current flowing through the monitoring electrode 5, one can always know the anticorrosion current at a predetermined position of the object to be protected, and check whether the predetermined anticorrosion current is flowing.
Check whether excessive corrosion protection is achieved, monitor the corrosion protection state of the object to be protected and the wear state of the anode 4, and check the resistance 7.
Adjust the resistance value to control it appropriately. It should be noted that the potentiometer 8 and the non-resistance ammeter 9 do not need to be permanently installed, and may be brought in and installed only when measuring, and only the monitor electrode can be attached without attaching the reference electrode 3 to monitor the anticorrosion current. By doing so, you can fully achieve your purpose. Note that a plurality of monitoring electrodes 5 may be installed depending on the shape of the object 2 to be protected from corrosion. Further, it is most desirable that the resistor 7 is a variable resistor, but a resistor having a predetermined resistance value may be interposed while measuring the anti-corrosion potential and anti-corrosion current. The second illustrated example shows the simplest example of the present invention,
If you have some prior knowledge of the structure of the object to be protected 2, the properties of the electrolyte, the anode 5, etc., you can predict and set the resistance value in advance, and connect the resistor 7 without using a conductor. A resistor is directly attached between the anticorrosion body 2 and the anode 4. In this way, although it is difficult to change the resistance value midway, the trouble of wiring work such as pulling out the conductor wires is saved, and the anode 4 can be easily attached. As described above, according to the present invention, it is possible to appropriately adjust the anti-corrosion current according to the type of anode in the galvanic anode method, prevent over-corrosion, minimize anode wear, and extend the life of the anode. This has an extremely beneficial effect in that it is possible to constantly monitor the corrosion protection state of the object to be protected, and it is also possible to reliably know when the anode is worn out. Next, an experimental example will be shown. Although the configuration is the same as the first illustrated example, in this experimental example, a non-resistance ammeter was placed also in the middle of the conductor connecting the anode 4 and the resistor 7, and the total current flowing through the anode 4 was also measured.
Corrosive solution 1 was a 3% saline solution, the temperature was 25°C, and the solution was opened to static air. The object to be protected from corrosion 2 is a container made of mild steel with a diameter of 50
The dimensions were ×50 × 50 (cm). Aluminum was used for the anode 4, and its surface area was 100 cm 2 .
A saturated corrosion electrode was used as the reference electrode 3, and the same mild steel as the object to be protected 2 was used as the monitor electrode 5, and both were attached to the opposite surface of the anode 4. Measurements were made under two conditions: when the resistance was reduced to zero (conventional method) and when the resistance was adjusted to around 10 μA/cm 2 , which is the appropriate corrosion protection current density for mild steel (invention method), and the results are shown in the table below. I got good results. In addition, the potential of the object to be protected (mild steel) at this time in the method of the present invention is -800 mV as shown in the table.
(vs.SCE).
【表】
したがつて、本発明法によれば、従来の流電陽
極方式と比べて総電流を1/4.8に減少することが
できた。言い換えれば、陽極の寿命を4.8倍にの
ばすことができた。[Table] Therefore, according to the method of the present invention, the total current could be reduced to 1/4.8 compared to the conventional galvanic anode method. In other words, we were able to extend the life of the anode by 4.8 times.
【図面の簡単な説明】[Brief explanation of drawings]
第１図及び第２図はそれぞれ本発明の実施態様
を示す説明図である。
１……腐食性溶液、２……被防食体、３……参
照電極、４……陽極、５……モニタ用電極、６…
…絶縁体、７……抵抗、８……電位差計、９……
無抵抗電流計、１０……導線。
FIG. 1 and FIG. 2 are explanatory diagrams each showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Corrosive solution, 2...Object to be protected, 3...Reference electrode, 4...Anode, 5...Monitoring electrode, 6...
...Insulator, 7...Resistor, 8...Potentiometer, 9...
Non-resistance ammeter, 10... conductor.