JP2951481B2 - High corrosion resistant laminated sprayed steel plate for tank bottom plate - Google Patents

Description

【発明の詳細な説明】DETAILED DESCRIPTION OF THE INVENTION

【０００１】[0001]

【産業上の利用分野】本発明は、原油、石油等の油貯蔵
タンクの底板に使用されて耐食性上、効果のあるＡｌ−
ＺｎとＺｎとの高耐食性積層溶射鋼板に関するものであ
る。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a bottom plate of an oil storage tank for crude oil, petroleum, etc., and has an effect on the corrosion resistance of Al-
The present invention relates to a high corrosion resistant laminated sprayed steel sheet of Zn and Zn.

【０００２】[0002]

【従来の技術】原油、石油等の油貯蔵タンクは、一般に
真砂土基礎やアスファルトサンド基礎上に設置され長期
間使用されるが、タンク底板（鋼板）が相当激しい腐食
を生じる。極端な場合、腐食孔からタンクの破壊につな
がることにもなるため、この腐食を防止することが極め
て重要である。タンク底板の腐食の原因は、タンク底板
が直接基礎土と接触しており、地中から滲み出す水分あ
るいはタンク周囲から侵入する雨のため底板表面に結露
を生じるためと考えられる。従来、この腐食を防ぐため
に主に採られている方法は、電気防食である。即ち、外
部電源方式や犠牲陽極方式で、タンク底板をカソードに
置くことによって防食するものであるが、これらの方法
では、均一な電流分布が得られないために完全防食には
ならないこと、および底板側で水素が発生するので鋼板
の水素脆性の問題が出ること等の大きな問題点を有して
いる。また、防食鋼板（Ａｌ被覆）を用いることも、特
開昭５７−１７１６５８号公報により公開されている
が、これはまだ実用化はされていない。2. Description of the Related Art Oil storage tanks for crude oil, petroleum, and the like are generally installed on a sand foundation or an asphalt sand foundation and used for a long period of time. However, the tank bottom plate (steel plate) causes considerable corrosion. In extreme cases, it is extremely important to prevent this corrosion, since the corrosion holes may lead to the destruction of the tank. It is considered that the cause of the corrosion of the tank bottom plate is that the tank bottom plate is in direct contact with the base soil, and that moisture is oozing out from the ground or rain invades from around the tank, causing dew condensation on the bottom plate surface. Conventionally, the method mainly employed to prevent this corrosion is cathodic protection. That is, in the external power supply method or the sacrificial anode method, corrosion is prevented by placing the tank bottom plate on the cathode.However, in these methods, uniform current distribution is not obtained, so that complete corrosion protection is not achieved. Since hydrogen is generated on the side of the steel sheet, there is a big problem such as a problem of hydrogen embrittlement of the steel sheet. The use of an anti-corrosion steel sheet (Al coating) is also disclosed in Japanese Patent Application Laid-Open No. 57-171658, but this has not been put to practical use yet.

【０００３】[0003]

【発明が解決しようとする課題】本発明者らの実験結果
によれば、前記公開公報に示された技術の場合、Ａｌに
一旦局部腐食が生じると、酸化被膜のために犠牲防食効
果が極めて弱く、加速的に進行するためと考えられる。
すなわち、従来技術はタンク底板の腐食を完全に防ぐ点
においては、極めて多くの問題点を含んでおり、タンク
底板の腐食を完全に防止する高耐食性鋼板は開発されて
いない。本発明の目的は、上述のタンク底板防食法の欠
点を解決し、タンク底板のメンテナンスフリー化を図る
ことが可能な高耐食性の積層溶射鋼板を提供することに
ある。According to the experimental results of the present inventors, according to the technique disclosed in the above-mentioned publication, once local corrosion occurs in Al, the sacrificial anticorrosion effect is extremely reduced due to the oxide film. It is considered to be weak and accelerated.
That is, the prior art has extremely many problems in completely preventing corrosion of the tank bottom plate, and a high corrosion resistant steel plate that completely prevents corrosion of the tank bottom plate has not been developed. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the tank bottom plate anticorrosion method and to provide a high corrosion-resistant laminated sprayed steel plate capable of achieving maintenance-free tank bottom plate.

【０００４】[0004]

【課題を解決するための手段】このような目的を達成す
るための本発明の要旨は、厚鋼板表面に、最下層から上
層へとＺｎ、Ａｌ−Ｚｎの順に２ないし８回繰り返し
て、最大全体膜厚が４４０μｍ以下となるように被膜を
溶射形成してなる積層溶射被膜において、それぞれのＺ
ｎ被膜の厚みを５０μｍ以上２００μｍ以下、Ａｌ−Ｚ
ｎ被膜のＡｌ濃度を５％以上５５％以下とし、厚みを５
μｍ以上２０μｍ以下とすることを特徴とするタンク底
板用高耐食性積層溶射鋼板にある。以下、本発明を更に
詳細に説明する。本発明者らは、タンク底板の腐食原因
を基礎土の水分に着目して研究した結果、腐食は５０〜
８０％の水分量を含む時に最も激しく、かつその腐食は
砂粒と鋼板が接触する場所での局部腐食であることを見
いだした。即ち、この水分によって薄い水膜が鋼板表面
に結露生成し、通気差腐食を生じ、特に海岸埋め立て地
でＣｌイオンが含まれている場合は激しく腐食すると考
えられる。したがって、常時、濡れ状態にあるので、犠
牲防食効果のある金属で被覆されていれば、犠牲防食効
果が発揮され、鋼板が防食されることになる。事実、Ｚ
ｎを溶射した鋼板では、普通鋼に比べて耐食性が良い。
しかし、周知の通り、常時、濡れ状態にある時はＺｎ被
覆鋼板は強固な亜鉛酸化被膜が形成しないためにＺｎの
腐食が相当生じる。The gist of the present invention for achieving the above object is to repeat Zn to Al-Zn from the lowermost layer to the upper layer in the order of 2 to 8 times on the surface of the thick steel plate, In the laminated sprayed coating formed by spraying the coating so that the total film thickness is 440 μm or less, each Z
The thickness of the n film is 50 μm or more and 200 μm or less, Al-Z
The Al concentration of the n film is set to 5% or more and 55% or less, and the thickness is set to 5%.
A high-corrosion-resistant laminated sprayed steel sheet for a tank bottom plate having a thickness of not less than μm and not more than 20 μm. Hereinafter, the present invention will be described in more detail. The present inventors have studied the cause of corrosion of the tank bottom plate by focusing on the moisture of the base soil, and found that the corrosion was 50 to 50%.
The most severe when containing 80% moisture, and the corrosion was found to be local corrosion where the sand grains contact the steel plate. In other words, it is considered that a thin water film is formed on the surface of the steel sheet by the moisture and causes aeration difference corrosion. In particular, when a coastal landfill contains Cl ions, the corrosion is considered to be severe. Therefore, since it is always wet, if it is covered with a metal having a sacrificial anticorrosion effect, the sacrificial anticorrosion effect is exhibited, and the steel sheet is anticorrosion. In fact, Z
The steel sheet sprayed with n has better corrosion resistance than ordinary steel.
However, as is well known, when the steel is always in a wet state, the Zn-coated steel sheet does not form a strong zinc oxide film, so that considerable corrosion of Zn occurs.

【０００５】本発明者らは、このような環境で耐食性を
発揮する溶射被膜を種々研究した結果、Ａｌ−Ｚｎ被膜
が高耐食性を示すことを発見した。さらに、極めて新規
な発見として、腐食初期はＡｌ−Ｚｎ被膜の自然電極電
位はＺｎ被膜よりも卑であるが、腐食が進行するにした
がい、この電位が逆転することを見いだした。このこと
は、Ａｌ−Ｚｎ被膜を上層に、Ｚｎ被膜を下層にして溶
射被膜を構成した場合、最初は上層のＡｌ−Ｚｎ被膜が
その高耐食性の防食効果を発揮し、腐食が進行してＡｌ
−Ｚｎ被膜の一部が腐食すると、下層のＺｎ被膜がＡｌ
−Ｚｎ被膜を防食して腐食進行を遅らせることを意味し
ている。この際、更に下層にＡｌ−Ｚｎ層が存在する積
層被膜の場合は、Ｚｎ被膜の一部が消失した部分の下に
Ａｌ−Ｚｎ被膜の新生面が露出した時、再度Ｚｎ被膜と
の電位的な逆転が生じるので、一層の耐食性向上が可能
である。Ａｌ−Ｚｎ被膜のＡｌ濃度は５％以上５５％以
下が適当である。即ち、５％未満では耐食性の効果が少
なく、５５％超ではＺｎ被膜との自然電極電位差が大き
くなりすぎるためである。[0005] The present inventors have conducted various studies on thermal sprayed coatings exhibiting corrosion resistance in such an environment, and have found that an Al-Zn coating exhibits high corrosion resistance. Further, as a very novel discovery, it has been found that the natural electrode potential of the Al—Zn coating is lower than that of the Zn coating in the early stage of corrosion, but this potential is reversed as the corrosion progresses. This means that when the thermal spray coating is formed with the Al-Zn coating as the upper layer and the Zn coating as the lower layer, the upper Al-Zn coating first exhibits its anticorrosion effect of high corrosion resistance, and the corrosion proceeds to increase the Al
-When a part of the Zn film is corroded, the underlying Zn film
-Means to prevent corrosion of the Zn coating and to delay the progress of corrosion. At this time, in the case of a laminated film in which an Al-Zn layer is further present as a lower layer, when a new surface of the Al-Zn film is exposed under a portion where a part of the Zn film has disappeared, the electric potential with the Zn film is again increased. Since the reversal occurs, the corrosion resistance can be further improved. The Al concentration of the Al—Zn coating is suitably from 5% to 55%. That is, if it is less than 5%, the effect of corrosion resistance is small, and if it exceeds 55%, the natural electrode potential difference from the Zn coating becomes too large.

【０００６】Ｚｎ被膜膜厚及びＡｌ−Ｚｎ被膜膜厚は、
タンクの最低使用年数を１０年としした時に、メンテナ
ンスフリーにするためには必要な全体膜厚（１００μ
ｍ）と、最低必要な積層化条件の２回から判断して、Ｚ
ｎ被膜厚み５０μｍ以上２００μｍ以下、Ａｌ−Ｚｎ被
膜厚み５μｍ以上２０μｍ以下とした。積層化は２層未
満では積層とならず耐食性効果が出ず、８層超となると
最低膜厚構成（５５μｍ）によっても、全体膜厚が４４
０μｍを超え、被膜の下地鋼板との密着性が極めて損な
われるため、２ないし８回の積層化とした。被膜形成は
上述の如く溶射で行うが、溶射は通常のアーク溶射（線
材、粉体）、プラズマ溶射等どのような方法によっても
よい。厚鋼板の黒皮をブラストによって除錆・表面調整
した後Ｚｎ溶射し、所定の膜厚に達した後、直ちにＡｌ
−Ｚｎ溶射を行い、更にＺｎ溶射、Ａｌ−Ｚｎ溶射を繰
り返すことによって容易に形成できる。The thickness of the Zn film and the thickness of the Al—Zn film are as follows:
When the minimum service life of the tank is 10 years, the total film thickness (100 μm
m) and the minimum required laminating conditions, J
The thickness of the n film was 50 μm or more and 200 μm or less, and the thickness of the Al—Zn film was 5 μm or more and 20 μm or less. If the number of layers is less than two, the layers will not be laminated and the corrosion resistance effect will not be obtained.
Since the thickness exceeds 0 μm, the adhesion of the coating to the underlying steel sheet is extremely impaired, so that the lamination was performed 2 to 8 times. The coating is formed by thermal spraying as described above, and the thermal spraying may be performed by any method such as ordinary arc spraying (wire material, powder) and plasma spraying. After rust removal and surface adjustment of the black scale of the thick steel plate by blasting, it is sprayed with Zn.
-It can be easily formed by performing Zn spraying and further repeating Zn spraying and Al-Zn spraying.

【０００７】[0007]

【実施例】以下、本発明を実施例に基づいて具体的に説
明する。図１は本発明（２層複層溶射鋼板）の断面構成
図であり、符号１は厚鋼板、符号２はＺｎ溶射被膜、符
号３はＡｌ−Ｚｎ溶射被膜、符号４はＺｎ溶射被膜、符
号５はＡｌ−Ｚｎ溶射被膜である。まず第一に、Ａｌ−
Ｚｎ層とＺｎ層の自然電極電位を測定した結果を表１に
示した。同表から明かなように、本発明１は、最初はＡ
ｌ−Ｚｎ被膜がＺｎ被膜より卑であるが、時間が経過す
ると逆転し、最初はＡｌ−Ｚｎ被膜で防食、Ａｌ−Ｚｎ
被膜に局部腐食が生じるとＺｎ被膜がこれを防食する能
力を有する。これに対し、比較材として用いたＡｌ濃度
が５５％を超える５８％Ａｌ−Ｚｎ被膜材は、腐食初期
は本発明と同様であるが、腐食後は電位差が大きくなり
すぎる。DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. FIG. 1 is a cross-sectional configuration view of the present invention (two-layer multi-layer thermal sprayed steel sheet), wherein reference numeral 1 denotes a thick steel plate, reference numeral 2 denotes a Zn thermal spray coating, reference numeral 3 denotes an Al—Zn thermal spray coating, reference numeral 4 denotes a Zn thermal spray coating, and reference numeral. 5 is an Al-Zn sprayed coating. First of all, Al-
Table 1 shows the results of measuring the natural electrode potentials of the Zn layer and the Zn layer. As can be seen from the table, the present invention 1 initially has A
The l-Zn coating is more base than the Zn coating, but reverses over time, initially anti-corrosion with Al-Zn coating, Al-Zn coating
If localized corrosion occurs in the coating, the Zn coating has the ability to prevent it. On the other hand, a 58% Al—Zn coating material having an Al concentration of more than 55% used as a comparative material is similar to the present invention in the initial stage of corrosion, but has a too large potential difference after corrosion.

【表１】 [Table 1]

【０００８】次に、Ａｌ−Ｚｎ被膜の組成、厚み、Ｚｎ
被膜の厚みを変化させた種々の試験材を用いて、その耐
食性と密着性を調査した結果を、表２に示した。同表か
ら明かなように、比較材１〜７の場合は、Ａｌ−Ｚｎ被
膜中のＡｌ濃度が５％未満のものおよび５５％を超える
ものは耐食性が不足しており、Ｚｎ被膜２００μｍ超の
ものおよび９層構成で４４０μｍを超えるものは、耐食
性は十分だが密着性が不良で実用に耐えない。さらに、
Ａｌ−Ｚｎ被膜の厚み５μｍ未満、２０μｍ超のものは
耐食性が悪く、Ｚｎ被膜厚み５０μｍ未満のものも耐食
性が悪く、実用に耐えない。これに対し本発明８〜１０
の場合は耐食性および密着性が優れている。表２におい
て、＊１は、実験室で、含水率６４％の真砂土中に、室
温で１年間浸漬した際に生じる最大局部腐食量を１０倍
して計算した被膜腐食量、＊２は、直角曲げ試験結果
で、○は良好、×は不良である。Next, the composition and thickness of the Al—Zn coating
Table 2 shows the results of investigating the corrosion resistance and adhesiveness of various test materials in which the thickness of the coating was changed. As is clear from the table, in the case of Comparative Materials 1 to 7, those having an Al concentration of less than 5% or more than 55% in the Al-Zn coating film lack corrosion resistance, and have a Zn coating film having a Zn coating thickness of more than 200 μm. Those having a thickness of more than 440 μm with a nine-layer structure have sufficient corrosion resistance but have poor adhesion and are not practical. further,
If the thickness of the Al—Zn coating is less than 5 μm or more than 20 μm, the corrosion resistance is poor, and if the thickness of the Zn coating is less than 50 μm, the corrosion resistance is poor and is not practical. In contrast, the present inventions 8 to 10
In the case of, corrosion resistance and adhesion are excellent. In Table 2, * 1 is the amount of film corrosion calculated by multiplying the maximum local corrosion amount which occurs when immersed in a lab at room temperature for 1 year at room temperature in a sand sand having a water content of 64% by 10 times, and * 2 is In the results of the right angle bending test, ○ is good and X is bad.

【表２】 [Table 2]

【０００９】[0009]

【発明の効果】本発明によれば、厚鋼板表面に、最下層
から上層へとＺｎ、Ａｌ−Ｚｎの順に２ないし８回繰り
返して、最大全体膜厚が４４０μｍ以下となるように被
膜を溶射形成してなる積層溶射被膜において、それぞれ
のＺｎ被膜の厚みを５０μｍ以上２００μｍ以下、Ａｌ
−Ｚｎ被膜のＡｌ濃度を５％以上５５％以下とし、厚み
を５μｍ以上２０μｍ以下とするので、得られたタンク
底板用高耐食性積層溶射鋼板は、タンク底板の耐用年数
を大幅に延長させることができ、そのため従来の電気防
食法等に比べて維持コストを大幅に低減することができ
るばかりでなく、タンクの安全性確保の面でも極めて優
れた効果を奏する。According to the present invention, the coating is sprayed on the surface of the thick steel plate by repeating Zn and Al-Zn two to eight times in order from the lowermost layer to the upper layer so that the maximum total film thickness is 440 μm or less. In the laminated sprayed coating thus formed, the thickness of each Zn coating is 50 μm or more and 200 μm or less,
-Since the Al concentration of the Zn coating is 5% or more and 55% or less and the thickness is 5 μm or more and 20 μm or less, the obtained high corrosion resistant laminated sprayed steel sheet for the tank bottom plate can greatly extend the service life of the tank bottom plate. Therefore, not only can the maintenance cost be significantly reduced as compared with the conventional cathodic protection method and the like, but also an extremely excellent effect is obtained in terms of ensuring the safety of the tank.

【図面の簡単な説明】[Brief description of the drawings]

【図１】本発明のタンク底板用高耐食性積層溶射鋼板の
断面図である。FIG. 1 is a cross-sectional view of a high corrosion resistant laminated sprayed steel sheet for a tank bottom plate according to the present invention.

【符号の説明】[Explanation of symbols]

１ 厚鋼板 ２ Ｚｎ溶射被膜 ３ Ａｌ−Ｚｎ溶射被膜 ４ Ｚｎ被膜 ５ Ａｌ−Ｚｎ被膜 DESCRIPTION OF SYMBOLS 1 Thick steel plate 2 Zn sprayed coating 3 Al-Zn sprayed coating 4 Zn coating 5 Al-Zn coating

───────────────────────────────────────────────────── フロントページの続き (72)発明者 山本 正弘 千葉県富津市新富20−１ 新日本製鐵株 式会社 技術開発本部内 (58)調査した分野(Int.Cl.⁶，ＤＢ名) C23C 4/06 C23C 28/00 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masahiro Yamamoto 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (58) Field surveyed (Int.Cl. ⁶ , DB name) C23C 4/06 C23C 28/00

Claims (1)

(57)【特許請求の範囲】(57) [Claims] 【請求項１】 厚鋼板表面に、最下層から上層へとＺ
ｎ、Ａｌ−Ｚｎの順に２ないし８回繰り返して、最大全
体膜厚が４４０μｍ以下となるように被膜を溶射形成し
てなる積層溶射被膜において、それぞれのＺｎ被膜の厚
みを５０μｍ以上２００μｍ以下、Ａｌ−Ｚｎ被膜のＡ
ｌ濃度を５％以上５５％以下とし、厚みを５μｍ以上２
０μｍ以下とすることを特徴とするタンク底板用高耐食
性積層溶射鋼板。1. A steel sheet having a surface from the bottom layer to the top layer
n and Al-Zn are repeated in order of 2 to 8 times, and the sprayed coating is formed so that the maximum total film thickness is 440 μm or less. -A of Zn coating
l The concentration is 5% or more and 55% or less, and the thickness is 5 μm or more 2
High corrosion resistant laminated sprayed steel sheet for tank bottom plate, characterized in that the thickness is 0 μm or less.