JPH0835084A - Rust preventive for metal - Google Patents

Abstract

PURPOSE:To effectively suppress the corrosion of metal such as iron and steel and zinc in fresh water. CONSTITUTION:This is a metal rust preventive added to an aq. soln. being into contact with the face of metals, and in which an aq. soln. of 10 to 20wt.% trisodium phosphate (anhydride), 5 to 15wt.% polymer phosphate and 10 to 15wt.% 1-hydroxyethylidene-1,1-diphosphonic acid is mixed with phosphoric acid to regulate its pH to 5 to 7. This rust preventive is enough in long time rust preventing properties for metals, and the transparency of the rust preventive can be maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal rust preventive agent for effectively suppressing corrosion of metals such as steel and zinc in fresh water.

[0002]

2. Description of the Prior Art Steel materials are used for storage tanks of liquefied propane gas carriers, and these tanks are subjected to a water pressure test or a water load test at the time of completion to inspect the structure, foundation, balance and the like. Many tanks for storing liquefied propane gas are huge, and when performing a water pressure test or a water load test, a water amount of several thousand tons to tens of thousands tons may be used. Therefore, the time during which water is in contact with steel, including the time for pouring and draining water into the steel tank, may be long and may take several weeks.

When tap water or industrial water is used as it is for various tests of steel tanks, the entire surface of the tank is corroded and red rust occurs, but corrosion particularly near the water line portion and the welding line becomes severe. The degree of these corrosions varies depending on the water quality, the contact time with water, the water temperature, etc., but if they are eroded due to local corrosion or the like, they have a serious influence on the structure and are important from the viewpoint of quality control. In addition, in tanks that store liquefied propane gas, iron hydroxide generated by corrosion may come off, causing serious problems such as clogging of filters for pumps that transfer liquefied gas and seizure of pumps. It has been pointed out. In a large-capacity tank, it takes a huge amount of equipment and man-hours to repair and clean the inside of the tank after discharging the water used for the water pressure or water load test.
It is said that it is almost impossible, and anticorrosion measures in this process are important problems for cleaning the inside of the tank.

Conventionally, for the rust prevention in a steel tank which comes into contact with water, a mixed aqueous solution of trisodium phosphate, 15% polyphosphoric acid and phosphoric acid, and various water-soluble rust preventive agents mainly composed of polymerized phosphate are used. However, in any case, if the rust preventive solution becomes turbid and deposits when it is in contact with water for a long period of time for 30 days or more, there is a drawback that cleaning after discharging is required.

[0005]

SUMMARY OF THE INVENTION In view of the above points, the present invention is to provide a rust preventive agent for metals such as steel and zinc which is rich in long-term rust preventive property and maintains the transparency of the rust preventive solution. Is.

[0006]

The present invention is a metal rust preventive added to an aqueous solution which comes into contact with a metal surface, wherein trisodium phosphate (anhydrous): 10 to 20 w / v%, polymerized phosphate: 5 to 5
15 w / v% and 1-hydroxyethylidene-1,1-
A metal rust preventive characterized in that pH is adjusted to 5 to 7 by adding phosphoric acid to an aqueous solution of diphosphonic acid: 10 to 15 w / v%.

The polymerized phosphates referred to in the present invention include potassium pyrophosphate, sodium tripolyphosphate, potassium tripolyphosphate, sodium tetrapolyphosphate, potassium tetrapolyphosphate, sodium hexapolyphosphate, potassium hexapolyphosphate, sodium hexametaphosphate, potassium hexametaphosphate and ultraphosphate. Sodium or the like can be used.

The compounding ratio of the anticorrosive agent is trisodium phosphate (anhydrous): 10 to 20 w / v%, polymerized phosphate: 5 to 15 w /
v% and 1-hydroxyethylidene-1,1-diphosphonic acid: Phosphoric acid is added to an aqueous solution prepared within the range of 10 to 15 w / v% to adjust the pH to 5 to 7. The rust preventive solution thus formulated and prepared is regarded as a 100% solution, and 200 to 500 mg /
It is added at a concentration of 1 liter to prevent corrosion. Addition concentration is 20
If the amount is less than 0 mg / liter, the anticorrosive solution becomes turbid during long-term rust prevention, and the effect cannot be expected. If the amount exceeds 500 mg / liter, it is wasteful but has no adverse effect.

[0009]

When the rust preventive agent of the present invention is added to an aqueous solution which comes into contact with a metal surface, a stable and passivated phosphoric acid film is formed on the metal surface, and the film prevents and suppresses corrosion of the metal surface. Although trisodium phosphate, polymerized phosphate, 1-hydroxyethylidene-1,1-diphosphonic acid, and phosphoric acid alone cannot be expected to have a rust preventive function, trisodium phosphate,
By adjusting the pH by adding phosphoric acid to an aqueous solution containing polymerized phosphate and 1-hydroxyethylidene-1,1-phosphonic acid in an appropriate amount, the optimum free phosphoric acid necessary for forming the phosphoric acid film is maintained and the formation of the phosphoric acid film is promoted. ,Facilitate. In addition, the synergistic effect of the polymerized phosphate and the organic chelate compound 1-hydroxyethylidene-1,1-diphosphonic acid chelate the eluted metal ions, prevent the precipitation during film formation, disperse the fine powder, and act on many cations. Since it is chelated, a stable and dense film having a high corrosion resistance is formed on the metal surface, and not only rusting is suppressed for a long period of time but also turbidity of the rust preventive liquid is suppressed.

[0010]

EXAMPLE To 500 ml of tap water, phosphoric acid was added to an aqueous solution of trisodium phosphate, polymerized phosphate and 1-hydroxyethylidene-1,1-diphosphonic acid shown in Table 1 below to adjust pH.
A test piece whose surface has been polished by adding a prepared rust preventive agent (material: SS41 steel plate, dimensions: 100 x 50 x 1 mm)
After immersing and opening, and leaving it at room temperature for 30 days, rust generation, surface condition and turbidity of rust preventive liquid were visually judged, and Table 1
The result is as follows. (The results of tests conducted under the same conditions with no rust inhibitor added are also shown.)

[0011]

[Table 1]

[0012]

The rust preventive agent of the present invention has a long-term rust preventive property against metals such as steel and zinc, and can maintain the transparency of the rust preventive solution, so that the rust preventive agent is deposited on the metal surface. Also, no floating matter will adhere.

Claims (1)

[Claims] 1. A metal rust preventive which is added to an aqueous solution in contact with a metal surface, and is trisodium phosphate (anhydrous): 10 to 2
0 w / v%, polymerized phosphate: 5-15 w / v% and 1-hydroxyethylidene-1,1-diphosphonic acid: 10-1
A metal rust inhibitor, which is prepared by adding phosphoric acid to a 5 w / v% aqueous solution to adjust the pH to 5 to 7.