JP4417033B2 - How to prevent stress corrosion cracking in stainless steel - Google Patents

Description

【００２３】
注１）湿気硬化型芳香族ポリイソシアネートプレポリマー；「スミジュールＥ２１−１」（住友バイエルウレタン社製商品名）
注２）実施例１：ハイドロタルサイト；「ＤＨＴ−４Ａ」（協和化学工業社製商品名）
実施例２：亜硝酸型ハイドロカルマイト；「ソルカット」（日本化学工業社製商品名）
注３）「ＫＢＭ４０３」（信越シリコン社製商品名）
注４）「アディティブＴＩ」（住友バイエルウレタン社製商品名）
注５）「ＢＹＫ３５４」（ＢＹＫケミー社製商品名）
【００２４】
［性能試験結果］
ＳＣＣの有無を、ルーペで拡大し、目視観察による判定を行った試験結果、以下の通りであった。
実施例１：［温度８０℃×湿度５０％×２２０時間→温度８０℃×湿度８０％×１８０時間→温度８０℃×湿度９５％×４００時間］でＳＣＣ認められた。
実施例２：［温度８０℃×湿度５０％×２２０時間→温度８０℃×湿度８０％×１８０時間→温度８０℃×湿度９５％×８００時間］までＳＣＣ認められず。
比較例１：［温度８０℃×湿度５０％×２２０時間→温度８０℃×湿度８０％×１８０時間］でＳＣＣ認められた。
比較例２：［温度８０℃×湿度５０％×５０時間］でＳＣＣ認められた。
【００２５】
上記試験結果からも明らかな通り、本発明の実施例１及び２においては、塩素イオン濃度１ｇ／ｍ²と非常に厳しい腐食環境下においても、ＳＣＣを防止する効果が長期間優れていた。一方、腐食性イオン吸着剤を含有しない処理剤を塗布した比較例１及び無塗装テストピースの比較例２は、いずれもＳＣＣが、比較的短期間で発生した。
【００２６】
【発明の効果】
スレンレス鋼、特に、原子力発電プラントにおいて、配管等として使用されるステンレス鋼の応力腐食割れを効果的に長期間防止することができる。また、本発明で使用する処理剤は、耐熱性に優れているので、３００℃以下の高温に曝されステンレス鋼の使用条件下でも適用可能である。
【図面の簡単な説明】
【図１】ＳＣＣ試験のための４点曲げシグ装置を使用したテストピースのセッティング状態図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for effectively preventing stress corrosion cracking of stainless steel, particularly stainless steel used as piping in nuclear power plants.
[0002]
[Prior art]
Conventionally, stainless steel, which is excellent in safety and corrosion resistance, is frequently used for piping and the like used in nuclear power plants. However, stainless steel, which should be excellent in corrosion resistance, is prone to stress corrosion cracking (hereinafter abbreviated as “SCC”) under adverse conditions, and various problems caused by SCC are also caused in nuclear power plants. A case has occurred.
Therefore, conventionally, as a method for preventing SCC of stainless steel, for example, (1) a method of using stainless steel having a metal material composition that is unlikely to generate SCC (for example, Patent Document 1), or (2) a method of cathodic protection (for example, Patent Documents 2), (3) a method of applying an anticorrosion paint, and (4) a method of removing a corrosive ionic substance with ultrapure water are known as representative methods.
[0003]
However, the method (1) has a problem that it is expensive and cannot be applied to an existing nuclear power plant. The method (2) has a problem that maintenance is required regularly. The method (3) has a problem that when a scratch or the like is generated on the coating film, a corrosive ion substance accumulates at that location, and SCC is likely to occur therefrom. In addition, there are cases where the vinyl chloride resin tape is wound around the stainless steel pipe, but the tape is exposed to a high temperature of 300 ° C. or less for a long time, and chlorine ions generated from the tape cause SCC due to thermal deterioration. There are cases, and even in the method (3), the same is concerned about the paint containing chlorine.
[0004]
Therefore, a method of removing or reducing the corrosive ionic substance by the method (4) is usually employed. However, even in this method, for example, salt water has poor wettability with respect to stainless steel, and therefore, salt tends to agglomerate and concentrate at the stage of washing with ultrapure water and drying, so that stress in the elbow portion and the like is high. There is a problem that the salinity is easy to concentrate at a location where the SCC is likely to occur. In addition, when pipes are installed outdoors, sea salt particles are likely to adhere, and therefore the method (4) requires frequent removal of corrosive ionic substances, resulting in poor work efficiency, There was a problem that required wastewater treatment.
Therefore, the method (4) cannot be said to be a drastic measure for the time-consuming ratio, and a simple and drastic measure method has been desired.
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-80905 [Patent Document 2]
JP-A-11-302881 [0006]
[Problems to be solved by the invention]
The present invention has been made against the background of the problems of the prior art, and a treatment agent film in which a corrosive ion adsorbent is blended in a treatment agent having heat resistance suitable for the environment in which it is used is made of stainless steel. An object of the present invention is to provide a method for efficiently collecting and fixing a corrosive ionic substance by being formed on the surface and enabling prevention of SCC.
[0007]
[Means for Solving the Problems]
As a result of intensive studies in order to achieve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be achieved by the following method, and have reached the present invention.
That is, the present invention
On the stainless steel surface,
(A) For 100 parts by mass of the binder,
(B) 1 to 95 parts by mass of a corrosive ion adsorbent,
The present invention relates to a method for preventing stress corrosion cracking of stainless steel, characterized in that the treatment agent contained is applied in an amount of 10 to ²⁰⁰ g / m ^{2 in} terms of solid content.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
Each component of the treatment agent used in the present invention will be described.
About the component (a) The component (a) is a binder that adheres to the surface of the stainless steel and fixes various additives such as a corrosive ion adsorbent described below and other coupling agents in the treated film. .
As long as it has such a function, various resins conventionally used for paints can be used. Specifically, for example, a urethane resin system, an epoxy resin-amine curing system, a polyester resin system, etc. Typical examples include vinyl ester resin systems, chlorinated polyethylene resin systems, alkyl silicate resin systems, and alkyl alkoxysilane resin systems. Oil-based systems can also be used.
In particular, in the present invention, a moisture-curable resin that can be applied to a wet stainless steel surface or the like and has good coating workability is preferable. Specific examples include urethane resin (polyisocyanate prepolymer) systems, epoxy resin-ketimine curing systems, alkyl silicate resin systems, alkyl alkoxysilane resin systems, and the like. Among these, a moisture curable urethane resin that can easily impregnate the inside of the stainless steel surface and forms a film having excellent water resistance after curing is preferable.
[0009]
As the moisture curable urethane resin, for example, a urethane prepolymer having a free isocyanate group obtained by reacting a polyol and a polyisocyanate can be suitably used.
As the polyol, polyether polyol, polyolefin polyol, or the like can be used. The polyether polyol has 2 or more, preferably 2 to 6, hydroxyl groups such as ethylene glycol, propylene glycol, butanediol, diethylene glycol, glycerin, hexanediol, hexanetriol, glycerin, trimethylolpropane, and pentaerythritol. Obtained by subjecting a polyol having 2 to 8 carbon atoms to addition polymerization of an alkylene oxide such as ethylene oxide, propylene oxide, butylene oxide, and tetrahydrofuran, preferably 2 to 8 carbon atoms, in the presence of an alkali catalyst or the like. It is appropriate to use a polyalkylene polyol having 2 to 4 hydroxyl groups (active hydrogen groups) in the molecule.
[0010]
Examples of the polyolefin polyol include 2 to 4 molecules in a molecule obtained by addition polymerization of alkylene oxide such as ethylene oxide, propylene oxide, butylene oxide, and tetrahydrofuran to diene compounds such as butadiene and isoprene. It is appropriate to use a polydiene polyol having a hydroxyl group.
As the polyisocyanate, a compound having 2 or more, preferably 2 to 3 isocyanate groups in one molecule is suitable.
Specific examples of the polyisocyanate include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diphenyl diisocyanate, carbodiimide-modified diphenylmethane diisocyanate, hexa Isocyanate compounds such as methylene diisocyanate, xylylene diisocyanate, metaxylylene diisocyanate, 1,5-naphthalene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated toluylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate; Sumidur N (Sumitomo Bayer Urethane) Bullet polyisocyanate compounds such as company name); Death module IL, HL Bayer A.G. Corporation, trade name), Coronate E. H. Polyisocyanate compounds having an isocyanate ring such as (trade name manufactured by Nippon Polyurethane Industry Co., Ltd.); Adduct polyisocyanate compounds such as Sumijour L (trade name manufactured by Sumitomo Bayer Urethane Co., Ltd.) Can be mentioned.
[0011]
These polyisocyanates can be used singly or as a mixture of two or more.
The method for synthesizing the moisture curable urethane resin is not particularly limited, and a conventionally known method can be used. Specifically, the moisture curable urethane resin is produced, for example, by polymerizing a polyol and excess polyisocyanate. Excess polyisocyanate means that the isocyanate equivalent is more than the hydroxyl equivalent of the polyol, and the equivalent relationship can be expressed by the NCO / OH ratio.
In particular, in order to form a liquid, low-viscosity moisture-curing urethane resin, the type of polyol, the number of functional groups, the molecular weight, and the like are considered, and the NCO / OH ratio is, for example, 2 to 10, preferably 5 to It is preferable to adjust to 10. The polymerization temperature and the polymerization time are not particularly limited, but usually, in order to avoid the influence of moisture, after mixing the polyol and the polyisocyanate under a nitrogen stream, for example, the reaction is performed at 50 to 100 ° C. for 3 to 8 hours. Is appropriate. An appropriate amount of an organic metal salt urethane polymerization catalyst, a stabilizer, a dehydrating agent, a polymerization regulator or the like may be added as needed before the reaction, during the reaction, or after the reaction.
[0012]
About the component (b) The component (b) adsorbs and collects corrosive ionic substances such as Cl ^- and SO ₄ ² present on the surface of stainless steel, which causes corrosion that causes SCC, and chemically reacts. It is a corrosive ion adsorbent for forming a water-insoluble double salt, immobilizing and inactivating corrosive ions. Even if a corrosive ionic substance adheres to the surface of the stainless steel by the adsorbent and remains, it is inactivated, so that corrosion can be prevented.
Typical examples of such corrosive ion adsorbents include hydrocalumite and hydrotalcite.
Hydrocalumite has the formula
[0013]
3CaO ・ Al ₂ O ₃・ CaX _{2 / m}・ nH ₂ O
[0014]
(In the formula, X represents a monovalent or divalent anion, m represents the valence of the anion, and n represents 20 or less.)
A water-containing crystalline powder having a layered structure represented by Representative examples of the anion (X) include NO ₃ ⁻ , NO ₂ ⁻ , OH ⁻ , CH ₃ COO ⁻ , CO ₃ ^{2− and the} like. These anions, and chlorine ions when contacted with sulfuric acid ion, etc., anion exchange, NO ₃ is X ^-, NO ₂ ^- with liberating the like, adsorbing corrosive ionic material in hydrocalumite, immobilization ( Support) and inactivate. In addition, the liberated anion forms a passive film on the stainless steel surface and has the effect of further improving the corrosion resistance.
Hydrotalcite is typically a formula,
[0015]
Mg _4.5 Al ₂ (OH) ₁₃ CO ₃ · nH ₂ O
[0016]
(In the formula, n is 4 or less, preferably 3.5.)
This is a hydrous crystalline powder with a layered structure shown in Fig. 1. When it comes into contact with a corrosive ionic substance like hydrocalumite, anion exchange occurs, and the corrosive ions are adsorbed and immobilized in hydrotalcite, and desorbed from the crystal structure. It has the ability not to let it.
[0017]
(C) Coupling agent The optional component (c) improves the wettability and impregnation of stainless steel, and further improves the adhesion to the paint to be coated on it as necessary. It is a coupling agent for improving.
Examples of the coupling agent include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, vinyltriethoxysilane, Silane coupling agents such as γ-methacryloxytrimethoxysilane and γ-mercaptopropyltrimethoxysilane; isopropyl triisostearoyl titanate, tetraoctylbis (didodecyl) phosphite titanate, isopropyltrioctanoyl titanate, isopropyltridodecylbenzene Typical examples include titanium-based coupling agents such as sulfonyl titanates; aluminum-based coupling agents, zirconium-based coupling agents, and the like.
The treatment agent of the present invention contains the components (a) to (b) described above as essential components, and, if necessary, various paints such as hydrocarbon-based, ester-based, and ketone-based materials that do not contain active hydrogen. Organic solvent for use; composed of various additives such as coupling agents, antifoaming agents, wetting and dispersing agents, dehydrating agents and the like.
[0018]
In addition, the compounding ratio of each component is 1 to 95 parts by mass, preferably 5 to 40 parts by mass of the corrosive ion adsorbent as the component (b) with respect to 100 parts by mass of the binder as the component (a). More preferably, the amount of the coupling agent as component (c) is 0 to 10 parts by mass, preferably 1 to 5 parts by mass.
The amount of the organic solvent is appropriately such that the solid content of the treating agent is 20 to 80% by mass, preferably 30 to 70% by mass. Various additives are added in an amount of 0.1 to 10% by mass, preferably 1 to 5% by mass in the solid content of the treatment agent.
If the amount of the component (b) is less than the above range, the adsorption and immobilization of the corrosive ionic substance will be insufficient. Conversely, if the amount is too large, the amount of the component (a) will be relatively small and the treatment agent will be reduced. The physical and chemical strength of the film becomes insufficient, and the water resistance tends to decrease.
[0019]
In the case of a new installation, the surface of the stainless steel is pretreated such as a degreasing treatment. In the case of an existing installation, a deteriorated coating film on the stainless steel surface or a fragile portion such as rust is removed with a wire brush, scotch bright (3M Manufactured by the company), a power polishing tool, a hand polishing tool, etc., and the above-mentioned treatment agent is applied by means of a roller, a spray or the like, the coating amount (solid content conversion) 10 to 200 g / m ² , preferably 20 to 100 g / Apply m ² and let dry naturally. If the coating amount is less than the above range, the SCC prevention effect is small, and conversely if too large, the physical strength of the treatment agent film deteriorates.
In the present invention, if necessary, in order to have a long-term SCC prevention effect, it is also possible to apply a protective coating film by coating a paint having excellent weather resistance on the surface of the treatment agent film.
[0020]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. In the examples, “parts” and “%” are based on mass.
<Examples 1-2 and Comparative Examples 1-2>
The components shown in Table 1 were mixed and dispersed to prepare the treating agents of Examples 1 and 2 and Comparative Example 1, and stored in a sealed container.
[0021]
[performance test]
An aqueous magnesium chloride (MgCl ₂ ) solution is applied to the center of SUS304 stainless steel test piece 1 (100 L × 20 W × 2 T) (FIG. 1) so that the chlorine ion concentration is 1 g / m ^2, and the chloride 6 is dried. After solidifying, the treatment agents of Examples 1 and 2 and Comparative Example 1 were applied to the surface so as to have a dry film thickness of 70 g / m ² . Further, as Comparative Example 2, a non-coated test piece was also prepared in the same manner as a chlorine ion concentration with 1 g / m ² applied. After these test pieces were cured and dried at room temperature for 7 days, the test pieces were further left for 14 days in a constant temperature and high humidity bath at a temperature of 80 ° C. and a humidity of 85% in order to promote moisture penetration and curing into the treatment agent film. . The test piece 1 thus obtained was set on a four-point bending jig as shown in FIG. 1, and 250 MPa was added to the center of the test piece 1 on which the chloride 6 was applied. 50% × 220 hours → temperature 80 ° C. × humidity 80% × 180 hours → temperature 80 ° C. × humidity 95% × 800 hours]. In the four-point jig shown in FIG. 1, the stress is relieved by plastic deformation or microcracking of the test piece 1, so the operation of returning the stress to the initial value by retightening the push bolt 4 is repeated. went. The stress value was controlled by measuring the amount of strain when tightened from the strain gauge 5 attached to the test piece 1 and obtaining the stress applied to the test piece 1.
[0022]
[Table 1]
Table 1 Treatment composition
(Unit: parts)

[0023]
Note 1) Moisture-curing aromatic polyisocyanate prepolymer; “Sumijour E21-1” (trade name, manufactured by Sumitomo Bayer Urethane Co., Ltd.)
Note 2) Example 1: Hydrotalcite; “DHT-4A” (trade name, manufactured by Kyowa Chemical Industry Co., Ltd.)
Example 2: Nitrite-type hydrocalumite; “Solkat” (trade name, manufactured by Nippon Chemical Industry Co., Ltd.)
Note 3) "KBM403" (trade name, manufactured by Shin-Etsu Silicon)
Note 4) “Additive TI” (trade name, manufactured by Sumitomo Bayer Urethane Co., Ltd.)
Note 5) "BYK354" (Brand name, manufactured by BYK Chemie)
[0024]
[Performance test results]
The test result of enlarging the presence or absence of SCC with a magnifying glass and making a judgment by visual observation was as follows.
Example 1: SCC was observed at [temperature 80 ° C. × humidity 50% × 220 hours → temperature 80 ° C. × humidity 80% × 180 hours → temperature 80 ° C. × humidity 95% × 400 hours].
Example 2: SCC was not observed until [temperature 80 ° C. × humidity 50% × 220 hours → temperature 80 ° C. × humidity 80% × 180 hours → temperature 80 ° C. × humidity 95% × 800 hours].
Comparative Example 1: SCC was observed at [temperature 80 ° C. × humidity 50% × 220 hours → temperature 80 ° C. × humidity 80% × 180 hours].
Comparative Example 2: SCC was observed at [temperature 80 ° C. × humidity 50% × 50 hours].
[0025]
As is clear from the above test results, Examples 1 and 2 of the present invention were excellent in the effect of preventing SCC for a long time even in a very severe corrosive environment with a chloride ion concentration of 1 g / m ² . On the other hand, SCC occurred in a comparatively short period in both Comparative Example 1 in which a treatment agent containing no corrosive ion adsorbent was applied and in Comparative Example 2 of the uncoated test piece.
[0026]
【The invention's effect】
It is possible to effectively prevent stress corrosion cracking of stainless steel, particularly stainless steel used as piping in a nuclear power plant, for a long period of time. Moreover, since the processing agent used by this invention is excellent in heat resistance, it is exposed to the high temperature of 300 degrees C or less, and is applicable also on the use conditions of stainless steel.
[Brief description of the drawings]
FIG. 1 is a setting state diagram of a test piece using a four-point bending sig apparatus for an SCC test.

Claims (1)

On the surface of stainless steel for nuclear power plants,
(A) For 100 parts by mass of a binder comprising a moisture-curable polyurethane resin,
(B) a corrosive ion adsorbent comprising hydrocalumite or hydrotalcite, 10 to 30 parts by mass,
(C) Silane coupling agent, 1 to 5% by mass,
(D) organic solvents, antifoaming agents, wetting and dispersing agents and dehydrating agents,
A method for preventing stress corrosion cracking of stainless steel, characterized by applying a treatment agent containing only 20 to 100 g / m ^{2 in} terms of solid content.

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