JP6531566B2 - Method of cathodic protection of steel surface - Google Patents
Method of cathodic protection of steel surface Download PDFInfo
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Description
本発明は、海水と接触する鋼材の表面を電気防食する方法に関する。 The present invention relates to a method of galvanically protecting the surface of a steel material in contact with seawater.
高炉炉底の鉄皮は、海水を流下させて接触させることによって冷却される。また、熱交換器や冷却器、復水器において、鋼材の表面が冷却水である海水と接触する場合がある。さらに、構造物を構成する鋼材の表面が海水と接触する場合がある。 The shell of the blast furnace bottom is cooled by bringing seawater into contact with it. Moreover, in a heat exchanger, a cooler, and a condenser, the surface of steel materials may contact seawater which is a cooling water. Furthermore, the surface of the steel material which comprises a structure may contact seawater.
このように海水と接触することによって鋼材の表面が腐食するのを防止するため、陰極防食法（カソード防食法）による電気防食が用いられる。その電気防食では、格子状の電極を海水と接触する鋼材の表面に配置する。その際、電極は海水に浸漬されるとともに、電極と鋼材の表面の間には距離（隙間）が設けられる。この状態で電極を陽極とするとともに鋼材を陰極として通電すると、電極から海水を経由して鋼材にカソード電流が流れ、鋼材がカソード分極する。これにより、鋼材の表面でアノード溶解反応が抑制され、鋼材の表面を防食できる。 In order to prevent the surface of the steel material from being corroded by contact with seawater in this way, cathodic protection by cathodic protection is used. In the cathodic protection, grid-like electrodes are placed on the surface of the steel in contact with seawater. At this time, the electrode is immersed in seawater and a distance (a gap) is provided between the electrode and the surface of the steel material. In this state, when the electrode is used as an anode and the steel material is used as a cathode, a cathode current flows from the electrode to the steel material via seawater, and the steel material is cathode polarized. Thereby, the anodic dissolution reaction is suppressed on the surface of the steel material, and the surface of the steel material can be protected.
電極の基材には、例えば、チタンやチタン合金が使用され、電極（基材）の表面には貴金属（例えば白金）がめっき等によってコーティングされる場合がある。電極の基材には、チタンのほかにジルコニウム、ニオブ、タンタル等も使用され、コーティングの材料としては、白金のほかに酸化イリジウム、酸化ルテニウム等が使用される。 For example, titanium or a titanium alloy is used as a substrate of the electrode, and a surface of the electrode (substrate) may be coated with a noble metal (for example, platinum) by plating or the like. In addition to titanium, zirconium, niobium, tantalum and the like are used as a base material of the electrode, and as a material of the coating, iridium oxide, ruthenium oxide and the like are used besides platinum.
鋼材表面の電気防食に関して従来から種々の提案がなされており、例えば特許文献１がある。その特許文献１では、鋼材の表面に絶縁性ネットを介して格子状の電極を配置することが提案されている。これにより、冷却効果を損なうことなく、鋼材の表面に均一に通電できるとしている。また、格子状の電極は目開きが２０〜７０ｍｍ程度であるのが好ましいとしている。 Conventionally, various proposals have been made regarding the cathodic protection of the steel surface, and there is, for example, Patent Document 1. Patent Document 1 proposes that a grid-like electrode be disposed on the surface of a steel material via an insulating net. By this, it is supposed that current can be uniformly applied to the surface of the steel without impairing the cooling effect. Further, it is preferable that the grid-like electrode has an opening of about 20 to 70 mm.
前述の通り、格子状の電極を陽極とするとともに鋼材を陰極として通電することにより、鋼材の表面を電気防食する方法がある。その方法では、例えば、電極にチタン等が使用され、電極の表面が白金等によってコーティングされる場合がある。このような電極は高価であり、設備コストの上昇を招くので、単位面積あたりの電極の使用量（質量）を低減し、設備コストを削減することが望まれている。また、電極の目開きが小さいと、海水とともに木片や海藻といった異物が流入し、電極に付着して目詰まりを発生させる。近年増加するクラゲも異物となり、目詰まりを発生させる。 As described above, there is a method in which the surface of the steel material is subjected to cathodic protection by using a grid-like electrode as an anode and supplying electricity to the steel material as a cathode. In the method, for example, titanium or the like may be used for the electrode, and the surface of the electrode may be coated with platinum or the like. Such an electrode is expensive and causes an increase in equipment cost, so it is desired to reduce the amount (mass) of the electrode used per unit area and to reduce the equipment cost. In addition, when the openings of the electrodes are small, foreign matter such as wood chips and seaweeds flow in along with the seawater and adhere to the electrodes to cause clogging. Jellyfish, which are increasing in recent years, also become foreign matter and cause clogging.
前述の特許文献１では、格子状の電極の目開きが２０〜７０ｍｍ程度と小さい。このため、電極の使用量が増大し、設備コストが上昇する。また、海水とともに流入する異物により、電極に目詰まりが発生する。 In Patent Document 1 described above, the openings of the grid-like electrodes are as small as about 20 to 70 mm. For this reason, the usage of the electrode increases, and the equipment cost increases. In addition, foreign matter flowing in with the seawater causes clogging of the electrode.
本発明の目的は、格子状の電極の使用量（質量）を低減できるとともに、電極の目詰まりを防止できる鋼材表面の電気防食方法を提供することである。 An object of the present invention is to provide a method of preventing corrosion on the surface of a steel material which can reduce the amount of use (mass) of grid-like electrodes and prevent clogging of the electrodes.
本発明の一実施形態による鋼材表面の電気防食方法は、海水と接触する鋼材の表面を電気防食する方法であって、格子間隔が１５０〜５４０ｍｍである格子状の電極を前記鋼材の表面と距離を設けて配置し、前記電極を陽極とし、かつ、前記鋼材を陰極として通電する。 The method of cathodic protection of steel surface according to an embodiment of the present invention is a method of cathodically protecting the surface of steel in contact with seawater, wherein a grid-like electrode having a grid spacing of 150 to 540 mm is separated from the surface of the steel Are provided, the electrode is used as an anode, and the steel material is used as a cathode.
前記電極の太さを０．２５ｍｍ以上とするのが好ましい。また、前記鋼材の表面から前記電極までの距離を１ｍｍ以上とするのが好ましい。 The thickness of the electrode is preferably 0.25 mm or more. Moreover, it is preferable that the distance from the surface of the said steel materials to the said electrode shall be 1 mm or more.
本発明の鋼材表面の電気防食方法は、電極の格子間隔を従来の約２倍以上とする。このように電極の格子間隔を極めて大きく設定しても、安定して電気防食できる。加えて、格子状の電極の使用量を低減できるとともに、電極の目詰まりを防止できる。 In the method of the present invention for the surface corrosion protection of steel materials, the lattice spacing of the electrodes is about twice or more that in the prior art. Thus, even if the grid spacing of the electrodes is set to be extremely large, stable corrosion can be achieved. In addition, the amount of grid-like electrodes used can be reduced, and clogging of the electrodes can be prevented.
本発明の鋼材表面の電気防食方法における一実施形態ついて、図面を参照しながら、以下に説明する。 An embodiment of the method of the present invention for cathodic protection of steel surface will be described below with reference to the drawings.
図１Ａ〜図１Ｃは、本発明の一実施形態を示す模式図であり、図１Ａは斜視図、図１Ｂは部分断面図、図１Ｃは格子状の電極を示す上面図である。図１Ａおよび図１Ｂには、鋼材（鋼板）１１と、格子状の電極１２と、海水１３とを示す。図１Ａでは、海水１３を二点鎖線で示す。例えば、鋼材（鋼板）１１と、格子状の電極１２は、海水中１３に浸漬している状態となるので、海水１３が鋼材１１の表面と接触する。 1A to 1C are schematic views showing an embodiment of the present invention, FIG. 1A is a perspective view, FIG. 1B is a partial cross-sectional view, and FIG. 1C is a top view showing grid-like electrodes. In FIG. 1A and FIG. 1B, steel materials (steel plates) 11, grid-like electrodes 12, and seawater 13 are shown. In FIG. 1A, seawater 13 is indicated by a two-dot chain line. For example, since the steel material (steel plate) 11 and the grid-like electrode 12 are immersed in seawater 13, the seawater 13 contacts the surface of the steel material 11.
本実施形態の電気防食方法では、格子状の電極１２を海水１３と接触する鋼材１１の表面に配置する。その際、電極１２は海水１３に浸漬されるとともに、電極１２と鋼材１１の表面の間には距離が設けられる。この状態で、格子状の電極１２を陽極とするとともに、鋼材１１を陰極として通電する。これにより、鋼材１１の表面でアノード溶解反応が抑制され、鋼材１１の表面を防食できる。 In the cathodic protection method of the present embodiment, the grid-like electrodes 12 are disposed on the surface of the steel material 11 in contact with the seawater 13. At this time, the electrode 12 is immersed in the seawater 13 and a distance is provided between the electrode 12 and the surface of the steel material 11. In this state, the grid-like electrode 12 is used as an anode and the steel material 11 is used as a cathode. Thereby, the anodic dissolution reaction is suppressed on the surface of the steel material 11, and the surface of the steel material 11 can be protected.
このような電気防食方法において、本実施形態の電気防食方法は、電極１２の格子間隔（Ｗ１、Ｗ２）を１５０〜５４０ｍｍとする。本発明において、電極１２の格子間隔（Ｗ１、Ｗ２）は、互いに平行な線部１２ａの隙間の大きさＡ（目開き）でなく、図１Ｃに示すように互いに平行な線部１２ａの中心間隔とする。 In such a cathodic protection method, the cathodic protection method of the present embodiment sets the lattice spacing (W1, W2) of the electrodes 12 to 150 to 540 mm. In the present invention, the lattice spacing (W1, W2) of the electrodes 12 is not the size A (opening) of the spacing between the parallel line portions 12a, but the center spacing of the parallel line portions 12a as shown in FIG. 1C. I assume.
前述の特許文献１は、格子状の電極の目開きが２０〜７０ｍｍ程度と小さいが、本実施形態の電気防食方法は、電極１２の格子間隔（Ｗ１、Ｗ２）を１５０ｍｍ以上とする。このように、電極１２の格子間隔（Ｗ１、Ｗ２）を従来の約２倍以上と極めて大きく設定しても、後述の実施例で明らかにするように、鋼材表面の全部を電気防食できる。 Although the above-mentioned patent documents 1 have a small opening of a lattice-like electrode with about 20-70 mm, the cathodic protection method of this embodiment makes the lattice interval (W1, W2) of electrode 12 150 mm or more. As described above, even if the lattice spacing (W1, W2) of the electrode 12 is set as large as about twice or more the conventional one, the entire surface of the steel material can be subjected to cathodic protection as will be clarified in the following examples.
また、電極１２の格子間隔（Ｗ１、Ｗ２）を１５０ｍｍ以上と極めて大きくすることにより、電極の使用量（質量）を低減でき、設備コストを削減できる。加えて、電極１２の格子間隔（Ｗ１、Ｗ２）を極めて大きくすることにより、木片や海藻、クラゲといった異物が流入しても、目詰まりがほとんど発生することがなく、目詰まりを防止できる。電極の使用量（質量）をさらに低減する観点、および、目詰まりをさらに防止する観点では、電極１２の格子間隔（Ｗ１、Ｗ２）が大きいほど好ましい。 Also, by making the lattice spacing (W1, W2) of the electrodes 12 extremely large at 150 mm or more, the amount (mass) of electrodes used can be reduced, and equipment cost can be reduced. In addition, by making the lattice spacing (W1, W2) of the electrodes 12 extremely large, even if foreign matter such as wood chips, seaweeds and jellyfish flows in, clogging hardly occurs and clogging can be prevented. From the viewpoint of further reducing the amount of use (mass) of the electrode and in the viewpoint of further preventing clogging, it is preferable that the lattice spacing (W1, W2) of the electrode 12 be larger.
後述の実施例で明らかにするように、電極１２の格子間隔（Ｗ１、Ｗ２）が５４０ｍｍ以下であれば、電極の太さｄや鋼材の表面から電極までの距離Ｐに拘わらず、鋼材表面の全部を電気防食できる。このため、電極１２の格子間隔（Ｗ１、Ｗ２）は、上限を５４０ｍｍとする。後述の実施例で明らかにするように、より安定して電気防食を行う観点では、４００ｍｍ以下とするのが好ましく、３００ｍｍ以下とすることがより好ましい。 As will be clarified in the examples described later, if the lattice spacing (W1, W2) of the electrodes 12 is 540 mm or less, regardless of the electrode thickness d or the distance P from the surface of the steel to the electrodes, The whole can be protected. Therefore, the upper limit of the lattice spacing (W1, W2) of the electrodes 12 is set to 540 mm. As clarified in the following examples, from the viewpoint of performing more stable electrolytic corrosion protection, it is preferably 400 mm or less, and more preferably 300 mm or less.
電極１２の格子の形状は、正方形（Ｗ１＝Ｗ２）に限定されず、長方形（Ｗ１≠Ｗ２）であってもよい。電極１２の格子の形状が長方形である場合、電極１２の格子間隔（Ｗ１、Ｗ２）のいずれも、１５０〜５４０ｍｍとする。電極１２の格子の形状は、菱形であってもよく、この場合、２組の対辺の間隔を、いずれも、１５０〜５４０ｍｍとする。 The shape of the grid of the electrode 12 is not limited to a square (W1 = W2), and may be a rectangle (W1 ≠ W2). When the shape of the grid of the electrode 12 is rectangular, the grid spacing (W1, W2) of the electrode 12 is 150 to 540 mm. The shape of the grid of the electrode 12 may be a diamond shape, and in this case, the distance between the two sets of opposite sides is 150 to 540 mm.
後述の実施例の図６で明らかにするように、電極１２の太さｄが小さくなるのに従い、電気防食が可能な電極１２の格子間隔（Ｗ１、Ｗ２）は小さくなる傾向がある。このため、電極１２の太さｄが０．２５ｍｍ未満であれば、電極１２の格子間隔（Ｗ１、Ｗ２）が５４０ｍｍ以下であっても、鋼材の表面の一部で安定して電気防食ができないおそれがある。したがって、電極１２の太さｄは０．２５ｍｍ以上とするのが好ましい。 As clarified in FIG. 6 of the later-described embodiment, as the thickness d of the electrode 12 decreases, the lattice spacing (W1, W2) of the electrode 12 which can be protected by corrosion tends to decrease. For this reason, if the thickness d of the electrode 12 is less than 0.25 mm, even if the lattice spacing (W1, W2) of the electrode 12 is 540 mm or less, stable corrosion prevention can not be performed on part of the surface of the steel material There is a fear. Therefore, the thickness d of the electrode 12 is preferably 0.25 mm or more.
一方、電極１２の太さｄが大きいと、電極の使用量（質量）が増加するとともに、電極１２と鋼材１１の表面との隙間Ｃ（図１Ｂ参照）が小さくなって冷却水による鋼材１１の表面の冷却の妨げになるおそれがある。このため、電極１２の太さｄは、３ｍｍ以下とするのが好ましい。 On the other hand, when the thickness d of the electrode 12 is large, the usage amount (mass) of the electrode increases and the gap C (see FIG. 1B) between the electrode 12 and the surface of the steel 11 decreases and It may interfere with the cooling of the surface. Therefore, the thickness d of the electrode 12 is preferably 3 mm or less.
本実施形態において、電極の太さは、図１Ｂに示すように断面形状が正方形の場合は一辺の長さとし、断面形状が円形の場合は直径とする。 In the present embodiment, as shown in FIG. 1B, the thickness of the electrode is the length of one side when the cross-sectional shape is square, and the diameter when the cross-sectional shape is circular.
後述の実施例の図６で明らかにするように、鋼材１１の表面から電極１２までの距離Ｐが小さくなるのに従い、電気防食が可能な電極１２の格子間隔（Ｗ１、Ｗ２）は小さくなる傾向がある。このため、鋼材１１の表面から電極１２までの距離Ｐが１ｍｍ未満であれば、電極１２の格子間隔（Ｗ１、Ｗ２）が５４０ｍｍ以下であっても、鋼材の表面の一部で安定して電気防食ができないおそれがある。したがって、鋼材１１の表面から電極１２までの距離Ｐは１ｍｍ以上とするのが好ましい。 As clarified in FIG. 6 of the later-described embodiment, as the distance P from the surface of the steel material 11 to the electrode 12 decreases, the lattice spacing (W1, W2) of the electrode 12 which can be protected by corrosion tends to decrease. There is. For this reason, if the distance P from the surface of the steel material 11 to the electrode 12 is less than 1 mm, even if the lattice spacing (W1, W2) of the electrode 12 is 540 mm or less There is a risk that corrosion can not be prevented. Therefore, it is preferable that the distance P from the surface of the steel material 11 to the electrode 12 be 1 mm or more.
一方、鋼材１１の表面から電極１２までの距離Ｐが大きいと、必要な電位を確保するのに要する消費電力が増加する。このため、鋼材１１の表面から電極１２までの距離Ｐは、５００ｍｍ以下とするのが好ましく、５０ｍｍ以下とすることがより好ましい。 On the other hand, when the distance P from the surface of the steel material 11 to the electrode 12 is large, the power consumption required to secure the necessary potential increases. Therefore, the distance P from the surface of the steel material 11 to the electrode 12 is preferably 500 mm or less, and more preferably 50 mm or less.
本発明において、鋼材１１の表面から電極１２までの距離Ｐは、図１Ｂに示すように、鋼材１１の表面から電極の中心までの距離とする。 In the present invention, the distance P from the surface of the steel material 11 to the electrode 12 is the distance from the surface of the steel material 11 to the center of the electrode, as shown in FIG. 1B.
鋼材１１の材質は、例えば、炭素鋼等の低合金鋼とすることができる。電極１２の基材には、例えば、チタンやチタン合金を使用でき、電極（基材）の表面には貴金属をめっき等によってコーティングしてもよい。また、電極の基材には、ジルコニウム、ニオブ、タンタル等も使用でき、コーティングには酸化イリジウム、酸化ルテニウム等も使用できる。 The material of the steel material 11 can be, for example, low alloy steel such as carbon steel. For example, titanium or a titanium alloy can be used for the base material of the electrode 12, and the surface of the electrode (base material) may be coated with a noble metal by plating or the like. In addition, zirconium, niobium, tantalum and the like can be used as a base material of the electrode, and iridium oxide, ruthenium oxide and the like can be used as a coating.
電極１２を鋼材１１の表面と距離を設けて配置する方法については、特に制限はなく、電極１２から鋼材１１の表面までの距離を維持した状態で電極１２を支持できる限り、種々の方法を採用できる。例えば、絶縁体からなるスペーサを鋼材の表面に並べて配置し、そのスペーサによって電極を鋼材側から支持してもよい。また、特許文献１と同様に、鋼材の表面に絶縁性ネットを介して格子状の電極を配置してもよい。鋼材側の反対側から電極を適宜支持してもよい。 There is no particular limitation on the method of arranging the electrode 12 at a distance from the surface of the steel 11, and various methods may be adopted as long as the electrode 12 can be supported in a state in which the distance from the electrode 12 to the surface of the steel 11 is maintained. it can. For example, spacers made of an insulator may be arranged side by side on the surface of a steel material, and the electrodes may be supported from the steel material side by the spacers. Moreover, you may arrange | position a grid | lattice-like electrode on the surface of steel materials through an insulating net similarly to patent document 1. FIG. The electrode may be appropriately supported from the side opposite to the steel material side.
［電極の格子間隔］
本発明の効果を確認するため、鋼材表面の電位分布を求める試験を行った。本試験は、有限体積法を用いる解析によって行った。
[Grid spacing of electrodes]
In order to confirm the effect of the present invention, a test for determining the potential distribution on the surface of the steel material was performed. This test was conducted by analysis using the finite volume method.
本解析は、図１Ａ〜図１Ｃに示す実施形態を対象とし、対称性を考慮して図１Ｃでハッチングを施す領域のみをモデル化した。鋼材１１は、ＪＩＳ Ｇ ４０５１に規定される炭素鋼のＳ４５Ｃを模擬した。海水１３は、塩分濃度が３質量％の海水を模擬し、海水の厚さＴ（図１Ｂ参照）を１５ｍｍとし、海水の流速をなし（０ｍ／ｓ）とした。 This analysis targets the embodiment shown in FIGS. 1A to 1C, and models only the region to be hatched in FIG. 1C in consideration of symmetry. The steel material 11 simulated S45C of carbon steel specified in JIS G 4051. The seawater 13 simulates seawater having a salt concentration of 3% by mass, the thickness T of the seawater (see FIG. 1B) is 15 mm, and the flow velocity of the seawater is zero (0 m / s).
格子状の電極１２は、基材がチタンからなり、かつ、基材の表面に白金がめっきによって１μｍ厚さでコーティングされた電極を模擬した。電極１２の格子間隔（Ｗ１、Ｗ２）は、１０〜８００ｍｍで変化させた。電極１２の格子の形状は正方形とし、すなわち、電極１２の格子間隔をＷ１＝Ｗ２とした。電極１２の線部１２ａの断面形状は、正方形とし、電極１２の太さｄは０．５〜２ｍｍで変化させた。鋼材１１の表面から電極１２までの距離Ｐは、１〜１０ｍｍで変化させた。 The grid-like electrode 12 simulates an electrode in which the base material is made of titanium and platinum is coated on the surface of the base material to a thickness of 1 μm. The lattice spacing (W1, W2) of the electrode 12 was changed at 10 to 800 mm. The shape of the grid of the electrodes 12 is square, that is, the grid spacing of the electrodes 12 is W1 = W2. The cross-sectional shape of the wire portion 12 a of the electrode 12 was a square, and the thickness d of the electrode 12 was changed by 0.5 to 2 mm. The distance P from the surface of the steel material 11 to the electrode 12 was changed by 1 to 10 mm.
本解析では、格子状の電極１２が陽極となるとともに鋼材１１が陰極となるように電圧を印加して通電し、電位分布を求めた。印加電圧は１．７５〜５．５Ｖで変化させた。 In this analysis, a voltage was applied to conduct electricity so that the grid-like electrode 12 became an anode and the steel material 11 became a cathode, and the potential distribution was determined. The applied voltage was changed at 1.75 to 5.5V.
図２は、電位分布の代表的な一例を示す斜視図である。同図には、前記図１Ｃのハッチングで施した領域のみを示し、白色と黒色の濃淡で電位（−Ｖ.ｖｓ．ＳＣＥ）を示す。同図に示す電位分布の条件は、電極１２の格子間隔（Ｗ１、Ｗ２）が２００ｍｍ、電極１２の太さｄが０．５ｍｍ、鋼材１１の表面から電極１２までの距離Ｐが１０ｍｍ、印加電圧が２．２５Ｖであった。 FIG. 2 is a perspective view showing a representative example of the potential distribution. In the same figure, only the hatched area in FIG. 1C is shown, and the potential (-V. Vs. SCE) is shown in white and black shades. The conditions of the potential distribution shown in the figure are that the lattice spacing (W1, W2) of the electrode 12 is 200 mm, the thickness d of the electrode 12 is 0.5 mm, the distance P from the surface of the steel material 11 to the electrode 12 is 10 mm, the applied voltage Was 2.25V.
同図に示す電位分布は、電極１２のうちで角度が異なる線部１２ａ同士が交わる交差部（図１Ｃの符号１２ｂ参照）の周辺で最も卑となり、電極の交差部から遠ざかるのに従って貴となる。このため、鋼板表面の電位分布は、交差部の真下の部位（実線矢印で指し示す部位）が最も卑となり、格子（開口）の中央部（図１Ｃの符号１２ｃ参照）の真下に位置する部位（破線矢印で指し示す部位）が最も貴となる。 The potential distribution shown in the same figure is most wrinkled around the crossing portion (see reference numeral 12b in FIG. 1C) where the line portions 12a having different angles cross each other in the electrode 12, and becomes nobler as it goes away from the crossing portion of the electrodes. . For this reason, the potential distribution on the surface of the steel sheet is located most directly below the intersection (the portion indicated by the solid line arrow) at a position located directly below the central portion (see symbol 12c in FIG. 1C) The part pointed out by the broken arrow) is the most noble.
ここで、鋼板表面において、電位が−０．７７Ｖ．ｖｓ．ＳＣＥ（以下、単に「Ｖ」とも表記する）より卑であると、十分な防食が可能となる。このため、鋼板表面において最も卑な電位は、−０．７７Ｖと等しいか、あるいは、−０．７７Ｖより卑とする必要がある。また、鋼板表面において、電位が−１．０Ｖより卑であると、水素発生反応が起こり、電流量の増大や海水の減少等によって悪影響が生じるおそれがある。このため、鋼板表面において最も貴な電位は、−１．０Ｖと等しいか、あるいは、−１．０Ｖより貴とする必要がある。 Here, at the surface of the steel plate, the potential is -0.77 V. vs. When the temperature is higher than that of SCE (hereinafter, also simply referred to as "V"), sufficient corrosion prevention is possible. Therefore, the most noble potential in the steel sheet surface, or equal to -0.77V, or is required to be less noble than -0.77V. If the potential is lower than -1.0 V on the surface of the steel sheet, a hydrogen generation reaction may occur, and an adverse effect may occur due to an increase in the amount of current or a decrease in seawater. Therefore, the most noble potential at the steel sheet surface needs to be equal to -1.0 V or more noble than -1.0 V.
つまり、鋼板表面の全部において、電位を−１．０〜−０．７７Ｖとすれば、鋼板表面の全部を安定して防食できる。鋼板表面において最も卑な電位および最も貴な電位は、印加電圧や電極１２の格子間隔（Ｗ１、Ｗ２）、電極１２の太さｄ、鋼材１１の表面から電極１２までの距離Ｐによって変化する。 That is, on the entire surface of the steel plate, if the potential is set to -1.0 to -0.77 V, the entire surface of the steel plate can be stably protected against corrosion. The most subtle potential and the most noble potential on the surface of the steel sheet vary with the applied voltage, the lattice spacing (W1, W2) of the electrodes 12, the thickness d of the electrodes 12, and the distance P from the surface of the steel 11 to the electrodes 12.
図３は、印加電圧と鋼板表面の電位との関係の代表的な一例を示す模式図である。同図を得る解析では、電極の格子間隔（Ｗ１、Ｗ２）を２００ｍｍ、電極の太さｄを０．５ｍｍ、鋼材の表面から電極までの距離Ｐを１０ｍｍとし、印加電圧を変化させた。 FIG. 3 is a schematic view showing a representative example of the relationship between the applied voltage and the potential of the steel plate surface. In the analysis for obtaining the same figure, the applied voltage was changed with the electrode lattice spacing (W1, W2) 200 mm, the electrode thickness d 0.5 mm, the distance P from the surface of the steel to the electrode 10 mm.
同図より、印加電圧が増加するのに従い、鋼板表面において最も卑な電位および最も貴な電位はいずれも卑となることが確認された。同図の条件である場合、印加電圧を約２．０〜２．３７Ｖとすれば、鋼板表面の全部で電位が−１．０〜−０．７７Ｖとなり、鋼板表面の全部を安定して防食できることが確認された。 From the figure, it was confirmed that the lowest potential and the highest potential are both negative on the surface of the steel sheet as the applied voltage increases. Under the conditions shown in the figure, if the applied voltage is about 2.0 to 2.37 V, the potential on the entire surface of the steel sheet is -1.0 to -0.77 V, and the entire surface of the steel sheet is stably corroded It was confirmed that it was possible.
図４は、電極の格子間隔と印加電圧との関係の代表的な一例を示す模式図である。同図には、電極の格子間隔（Ｗ１、Ｗ２）と最も卑な電位が−１．０Ｖとなる印加電圧との関係（以下、単に「曲線Ａ」ともいう）、および、電極の格子間隔（Ｗ１、Ｗ２）と最も貴な電位が−０．７７Ｖとなる印加電圧との関係（以下、単に「曲線Ｂ」ともいう）をそれぞれ示す。同図でハッチングを施した領域は、鋼板表面の全部において電位が−１．０〜−０．７７Ｖとなり、鋼板表面の全部を安定して防食できることを示す。同図を得る解析では、電極の太さｄを０．５ｍｍ、鋼材の表面から電極までの距離Ｐを１０ｍｍとし、電極の格子間隔（Ｗ１、Ｗ２）および印加電圧をそれぞれ変化させた。 FIG. 4 is a schematic view showing a representative example of the relationship between the lattice spacing of the electrodes and the applied voltage. In the figure, the relationship between the electrode lattice spacing (W1, W2) and the applied voltage at which the lowest potential is −1.0 V (hereinafter, also simply referred to as “curve A”), and the electrode lattice spacing ( The relationship between W1 and W2) and the applied voltage at which the most noble potential is −0.77 V (hereinafter, also simply referred to as “curve B”) is shown. The hatched area in the figure indicates that the potential is -1.0 to -0.77 V on the entire surface of the steel sheet, and the entire surface of the steel sheet can be stably protected against corrosion. In the analysis for obtaining the same figure, the electrode thickness d was 0.5 mm, the distance P from the surface of the steel material to the electrode was 10 mm, and the lattice spacing (W1, W2) of the electrodes and the applied voltage were changed.
さらに、図５は、電極の格子間隔と制御可能電圧幅との関係の代表的な一例を示す模式図である。ここで、制御可能電圧幅（Ｖ）とは、曲線Ａの印加電圧（Ｖ）と曲線Ｂの印加電圧（Ｖ）の差である。 Furthermore, FIG. 5 is a schematic view showing a representative example of the relationship between the lattice spacing of the electrodes and the controllable voltage width. Here, the controllable voltage width (V) is the difference between the applied voltage (V) of the curve A and the applied voltage (V) of the curve B.
図４および図５より、従来は電極の格子間隔（Ｗ１、Ｗ２）が２０〜７０ｍｍ程度と小さかったが、それより極めて大きく電極の格子間隔（Ｗ１、Ｗ２）を設定しても、鋼板表面の全部を安定して防食できることが明らかになった。また、同図の条件である場合、電極の格子間隔（Ｗ１、Ｗ２）を６００ｍｍ程度としても、鋼板表面の全部を安定して防食できることが明らかになった。 According to FIGS. 4 and 5, conventionally, the lattice spacing (W1, W2) of the electrodes was as small as about 20 to 70 mm, but even if the lattice spacing (W1, W2) of the electrodes is set much larger than that, It became clear that the whole can be stably corroded. In the case of the condition of the same figure, it was revealed that the entire surface of the steel plate can be stably protected against corrosion even if the lattice spacing (W1, W2) of the electrodes is set to about 600 mm.
さらに、図５より、電極の格子間隔（Ｗ１、Ｗ２）が、３００ｍｍ以下であれば制御可能電圧幅はほぼ一定であり、４００ｍｍを超えると制御可能電圧幅の減少量が増大することが分かった。ここで、制御可能電圧幅の減少量とは、電極の格子間隔の単位量あたりで制御可能電圧幅が減少する量であり、図５に示すグラフの傾きである。つまり、電極の格子間隔（Ｗ１、Ｗ２）が４００ｍｍ以下であれば、制御可能電圧幅の減少量が小さく、最も貴な電位と最も卑な電位の差を確保できるため、安定して防食可能であることが分かった。また、電極の格子間隔（Ｗ１、Ｗ２）が３００ｍｍ以下であれば、従来と同レベルの制御可能電圧幅があり、最も貴な電位と最も卑な電位の差が従来と同レベルであるため、より安定して防食可能であることが分かった。 Furthermore, it was found from FIG. 5 that the controllable voltage width is substantially constant when the electrode grid spacing (W1, W2) is 300 mm or less, and the decrease amount of the controllable voltage width increases when it exceeds 400 mm. . Here, the reduction amount of the controllable voltage width is an amount by which the controllable voltage width decreases per unit amount of the lattice spacing of the electrodes, and is the slope of the graph shown in FIG. That is, if the electrode lattice spacing (W1, W2) is 400 mm or less, the amount of decrease in the controllable voltage width is small, and the difference between the most noble potential and the most slight potential can be secured. It turned out that there is. Also, if the grid spacing (W1, W2) of the electrodes is 300 mm or less, there is the same controllable voltage width as before, and the difference between the most noble potential and the least potential is the same level as before. It turned out that it is possible to prevent corrosion more stably.
そこで、電極の太さｄおよび鋼材の表面から電極までの距離Ｐをそれぞれ変化させながら、前述の曲線Ａおよび曲線Ｂを求めた。それらの曲線から、鋼板表面の全部を安定して防食可能な電極の格子間隔の最大値をそれぞれ求めた。ここで、電極の格子間隔の最大値とは、曲線Ａと曲線Ｂの交点における電極の格子間隔である（前記図４参照）。 Therefore, the above-mentioned curve A and curve B were obtained while changing the thickness d of the electrode and the distance P from the surface of the steel material to the electrode. From these curves, the maximum value of the lattice spacing of the electrodes capable of stably preventing corrosion of the entire surface of the steel sheet was determined. Here, the maximum value of the grid spacing of the electrodes is the grid spacing of the electrodes at the intersection of the curve A and the curve B (see FIG. 4).
図６は、電極の格子間隔の最大値と鋼材の表面から電極までの距離との関係を示す模式図である。同図より、電極の太さｄが小さくなるに従って電極の格子間隔の最大値が小さくなることが確認された。また、鋼材の表面から電極までの距離Ｐが小さくなるに従って電極の格子間隔の最大値が小さくなることも確認された。さらに、同図では、電極の格子間隔の最大値が、いずれも、５４０ｍｍを超えた。このため、電極の太さｄや鋼材の表面から電極までの距離Ｐに拘わることなく、電極の格子間隔（Ｗ１、Ｗ２）が５４０ｍｍ以下であれば、鋼板表面の全部を安定して防食できることが明らかになった。 FIG. 6 is a schematic view showing the relationship between the maximum value of the lattice spacing of the electrodes and the distance from the surface of the steel material to the electrodes. From the figure, it was confirmed that the maximum value of the lattice spacing of the electrodes decreases as the thickness d of the electrodes decreases. Moreover, it was also confirmed that the maximum value of the lattice spacing of the electrode decreases as the distance P from the surface of the steel material to the electrode decreases. Furthermore, in the same figure, the maximum value of the lattice spacing of the electrodes exceeded 540 mm in each case. Therefore, regardless of the thickness d of the electrode and the distance P from the surface of the steel material to the electrode, the entire surface of the steel plate can be stably protected if the grid spacing (W1, W2) of the electrode is 540 mm or less. It was revealed.
ここで、電極の格子間隔（Ｗ１、Ｗ２）を大きくすると、消費電力が増大するおそれがあるので、消費電力を調査した。 Here, if the lattice spacing (W1, W2) of the electrodes is increased, the power consumption may increase, so the power consumption was investigated.
図７は、電極の格子間隔と消費電力との関係を示す模式図である。同図には、電極の格子間隔（Ｗ１、Ｗ２）と最も卑な電位が−１．０Ｖとなる消費電力との関係、および、電極の格子間隔（Ｗ１、Ｗ２）と最も貴な電位が−０．７７Ｖとなる消費電力との関係を示す。同図に示す消費電力は、単位面積あたりの消費電力（Ｗ／ｍ２）である。同図を得る解析では、電極の太さｄを０．５ｍｍ、鋼材の表面から電極までの距離Ｐを１０ｍｍとし、電極の格子間隔（Ｗ１、Ｗ２）および印加電圧をそれぞれ変化させた。 FIG. 7 is a schematic view showing the relationship between the grid spacing of the electrodes and the power consumption. In the figure, the relationship between the electrode grid spacing (W1, W2) and the power consumption at which the lowest potential is -1.0 V, and the electrode grid spacing (W1, W2) and the most noble potential are- The relationship with the power consumption which is 0.77V is shown. The power consumption shown in the figure is the power consumption per unit area (W / m 2 ). In the analysis for obtaining the same figure, the electrode thickness d was 0.5 mm, the distance P from the surface of the steel material to the electrode was 10 mm, and the lattice spacing (W1, W2) of the electrodes and the applied voltage were changed.
消費電力を抑える場合、印加電圧は、例えば、最も貴な電位が−０．７７Ｖとなる消費電力における印加電圧を求め、その印加電圧に安全率を乗じることによって設定される。この場合、実際の消費電力は、最も貴な電位が−０．７７Ｖとなる消費電力とほとんど同じとなる。同図より、電極の格子間隔（Ｗ１、Ｗ２）が５４０ｍｍの場合の最も貴な電位が−０．７７Ｖとなる消費電力は、電極の格子間隔（Ｗ１、Ｗ２）が７０ｍｍの場合と比べ、約２倍であることが確認された。すなわち、電極の格子間隔（Ｗ１、Ｗ２）を大きくしても、消費電力の増加は約２倍以下に抑えられることが明らかになった。 When the power consumption is suppressed, the applied voltage is set, for example, by obtaining an applied voltage at the power consumption where the most noble potential is −0.77 V and multiplying the applied voltage by a safety factor. In this case, the actual power consumption is almost the same as the power consumption at which the most noble potential is -0.77V. From the figure, the power consumption at which the noblest potential is -0.77 V when the grid spacing (W1, W2) of the electrodes is 540 mm is about the power consumption when the grid spacing (W1, W2) of the electrodes is 70 mm. It was confirmed to be double. That is, it was revealed that the increase in power consumption can be suppressed to about 2 times or less even if the lattice spacing (W1, W2) of the electrodes is increased.
［電極の使用量］
続いて、本発明による電極の使用量の低減効果を確認するため、電極の格子間隔（Ｗ１、Ｗ２）と電極の使用量（質量）との関係を求めた。電極の格子間隔（Ｗ１、Ｗ２）は、１０〜８００ｍｍで変化させた。電極の格子形状は正方形とし、すなわち、電極の格子間隔をＷ１＝Ｗ２とした。電極の断面形状は、正方形とし、電極の太さｄは１ｍｍとした。電極の表面は、白金がめっきによって１μｍ厚さでコーティングされているとした。
[Amount of use of electrode]
Then, in order to confirm the reduction effect of the usage-amount of the electrode by this invention, the relationship between the lattice spacing (W1, W2) of the electrode and the usage-amount (mass) of the electrode was calculated | required. The grid spacing (W1, W2) of the electrodes was varied from 10 to 800 mm. The grid shape of the electrodes was square, that is, the grid spacing of the electrodes was W1 = W2. The cross sectional shape of the electrode was square, and the thickness d of the electrode was 1 mm. The surface of the electrode was coated with platinum to a thickness of 1 μm by plating.
図８は、電極の格子間隔と電極の使用量（質量）との関係を示す模式図である。同図に示す電極の使用量（ｇ／ｍ２）は、特に高価な白金の使用量であり、かつ、鋼材表面の単位面積あたりの使用量である。同図より、電極の格子間隔（Ｗ１、Ｗ２）を１５０ｍｍとすれば、従来の上限の７０ｍｍとする場合に比べ、電極の使用量を６５％低減できることが明らかになった。 FIG. 8 is a schematic view showing the relationship between the lattice spacing of the electrodes and the amount of use (mass) of the electrodes. The used amount (g / m 2 ) of the electrode shown in the figure is the used amount of particularly expensive platinum and the used amount per unit area of the surface of the steel material. From the figure, it is clear that if the electrode lattice spacing (W1, W2) is 150 mm, the amount of electrodes used can be reduced by 65% as compared to the conventional upper limit of 70 mm.
これらから、本発明の電気防食方法により、鋼板表面の全部を安定して防食しながら、電極の使用量を低減できることが明らかになった。 From these, it became clear that the amount of use of the electrode can be reduced while the entire surface of the steel sheet is stably corroded by the electrolytic protection method of the present invention.
本発明の電気防食方法は、格子状の電極の使用量（質量）を低減できるとともに、電極の目詰まりを防止できる。このため、高炉炉底の鉄皮の電気防食において有効に利用できる。 The electrolytic protection method of the present invention can reduce the amount of use (mass) of the grid-like electrode and can prevent clogging of the electrode. For this reason, it can utilize effectively in the electric protection of the iron skin of a blast furnace bottom.
１１：鋼材、 １２：格子状の電極、 １２ａ：線部、 １２ｂ：交差部、
１２ｃ：格子の中央部、 １３：海水
11: Steel material 12: Grid-like electrode 12a: Wire portion 12b: Crossing portion
12c: central part of the grid, 13: seawater
Claims (1)
格子間隔が１５０〜５４０ｍｍであり、かつ、太さが０．２５ｍｍ以上である格子状の電極を前記鋼材の表面と１ｍｍ以上距離を設けて配置し、前記電極を陽極とし、かつ、前記鋼材を陰極として通電し、
前記通電を行う前に、前記通電の際の前記電極と前記鋼材との印加電圧で、前記鋼材表面の全部において電位が−１．０〜−０．７７［Ｖ．ｖｓ．ＳＣＥ］となるように、前記格子の間隔、前記電極の太さ、および前記鋼材表面から前記電極までの距離をそれぞれ決定する、鋼材表面の電気防食方法。 A method of galvanically protecting the surface of a steel material in contact with seawater,
Lattice spacing Ri 150~540mm der, and the electrode is Ru lattice der than 0.25mm thickness and arranged with a surface and 1mm or more the distance of the steel, the electrode as an anode, and the Energize steel material as cathode ,
Before the energization, the applied voltage between the electrode and the steel material at the time of the energization causes a potential of -1.0 to -0.77 [V. vs. The galvanic protection method of the steel surface which respectively determines the space | interval of the said grating | lattice, the thickness of the said electrode, and the distance from the said steel surface to the said electrode so that it may become SCE] .
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