JPS581189B2 - Rust inhibitor for seawater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rust preventive agent containing condensed sodium phosphate and sodium aluminate as its main components. In particular, when added to seawater that comes into contact with a metal surface, it effectively prevents the metal surface from rusting due to seawater. It can prevent corrosion and provide long-term rust prevention effects.

Conventionally known rust inhibitors for metals include chromate or dichromate, nitrite, sulfite or sulfite-based components, silicates, borates, amine-based components, phosphates, etc. The components are used alone or in combination.

However, most of these components have a good rust preventive function against fresh water, but hardly exhibit a rust preventive function against hard water or seawater.

On the other hand, phosphates are known as rust preventive agents that have a good rust preventive function against hard water.

However, even with this rust preventive agent, sufficient effects cannot be expected if it is added to hard water or seawater and left in contact with a metal surface for a long period of time.

Recently, seawater is often used for water pressure testing of large-capacity tanks, water storage, etc. due to the lack of industrial water and the need to conserve water resources.

At this time, metal corrosion on the inner surface of the tank becomes a problem due to the seawater, and the corrosion generates suspended solids such as red rust, which causes problems such as pollution and clogging of the drainage mechanism when draining water.

The present invention has a rust prevention function particularly against seawater, and contains condensed sodium phosphate and sodium aluminate as the main ingredients. This prevents and suppresses the formation of suspended solids caused by rust on steel surfaces that come into contact with seawater for long periods of time.

As mentioned above, phosphates are generally known as rust preventive agents for hard water, and sodium phosphate is particularly used because it is inexpensive.

However, even some sodium phosphates do not exhibit anti-corrosion properties against hard water.

For example, dibasic sodium phosphate and tribasic sodium phosphate react with calcium ions contained in hard water, resulting in water-insoluble Ca.
This is because it generates HPO4, Ca3(PO4)2 and does not function as a rust preventive film forming agent on metal surfaces.

In addition, when added to hard water, condensed sodium phosphates such as sodium polymetaphosphate, sodium polyphosphate, and ultrasodium phosphate have a rust-preventing function on metal surfaces that come into contact with hard water, but their long-term rust-preventing function is limited. It is not effective against

As described above, the present invention uses condensed sodium phosphate and sodium aluminate as main components, and the condensed sodium phosphates include sodium tripolyphosphate, sodium trimetaphosphate, sodium hexametaphosphate, sodium hexapolyphosphate, sodium octapolyphosphate, and ultrasodium phosphate. These components can be used singly or as a mixture.

Furthermore, among sodium phosphates, dibasic sodium phosphate and tribasic sodium phosphate produce insoluble salts when added to hard water as described above, but when added in a mixture with condensed sodium phosphate, they do not produce insoluble salts, and aluminic acid When mixed with sodium, the effects of the present invention can be exhibited.

In addition, when the above-mentioned condensed sodium phosphates are mixed together,
Or, when dibasic sodium phosphate or tribasic sodium phosphate and condensed sodium phosphate are mixed, the component weight ratio of P2O5 and Na2O contained in sodium phosphate is P2O
5/Na2O is preferably 1.3 or more.

When these rust preventive agents made of condensed sodium phosphate and sodium aluminate are added to seawater that comes into contact with metal surfaces,
In particular, it forms a passivated and stable phosphoric acid film on metal surfaces,
The film prevents and suppresses corrosion of metal surfaces.

Moreover, although sodium aluminate alone cannot be expected to have much of an anti-rust function, when added together with condensed sodium phosphate, it significantly promotes and promotes the formation of the above-mentioned phosphoric acid film.

Therefore, when a rust preventive agent containing a mixture of condensed sodium phosphate and sodium aluminate is added to seawater that comes into contact with metal surfaces, a phosphoric acid film is quickly formed on the entire surface of the metal that comes into contact with the seawater, and this film is extremely safe and prevents metal corrosion. It is possible to prevent corrosion and suppress rusting over a long period of time.

A good blending ratio of sodium condensed phosphate and sodium aluminate is 5 to 200 parts of sodium aluminate per 100 parts of condensed sodium phosphate; if the sodium aluminate is less than 5 parts, no effect can be expected, and if it is more than 200 parts, It's wasted, but there are no negative effects.

In addition, the amount of rust preventive agent made of condensed sodium phosphate and sodium aluminate added to seawater is sufficient at 30 to 80 ppm, which is a small amount compared to commonly used rust preventive agents such as phosphates and nitrites. .

As is clear from the above, since the main ingredients of the present invention are condensed sodium phosphate and sodium aluminate, it can effectively prevent rust on metal surfaces that come into contact with it simply by adding it to seawater, and it can be used for long periods of time. Even if it does, it will never rust.

The rust-preventing effect is significantly better than that of conventional rust-preventing agents, and a sufficient effect can be expected even with the addition of a small amount.

Therefore, it can be effectively carried out during hydraulic pressure tests on land-based oil tanks of several hundred thousand tons, or during hydraulic pressure tests of oil tanks of several hundred thousand tons of tankers, and water storage in ballast tanks.

Examples illustrating the effects of the present invention will be described below.

Example A rust preventive agent consisting of condensed sodium phosphate alone or a mixture of sodium aluminate was added to 500 ml each of fresh water, hard water (hardness 40°), and sea water, and a mild steel test piece (SS-41,3
0 x 50 x 1 mm) was immersed, opened, and left at room temperature for 15 days.

When the test piece was taken out after 15 days, the corrosion test was as shown in Table 1, and the amount of red rust generated was as shown in Table 2.

In Table 1, column A is the corrosion loss (mg) of the test piece;
Column B is the inhibition rate (%), column C in Table 2 is the amount of suspended solids of red rust (mg), column D is the inhibition rate of red rust (%), and each inhibition rate is expressed as a-b/a×100.

However, a: Corrosion loss of the test piece or amount of suspended solids of red rust when no rust preventive agent is added.

b: Corrosion weight loss or red rust suspended solids amount of test piece when rust preventive agent is added.

Claims (1)

[Claims] 1. A rust preventive agent containing 5 to 200 parts of sodium aluminate to 100 parts of condensed sodium phosphate having a P205/Na20 component weight ratio of 1.3 or more.