NO129094B - - Google Patents

Description

Method of preventing corrosion of iron and steel.

The present invention relates to a

method to counteract, i.e. prevent or reduce corrosion of iron or steel, in particular corrosion of iron and steel which is in constant or periodic contact with water containing chlorine ions. Iron and steel is understood here to also include all iron alloys. The invention is particularly important in connection with corrosion of tank walls in tankers.

Prevention of corrosion in tankers

is a problem that has not yet been satisfactorily resolved. The tank walls are almost continuously exposed to corrosive influences. Mineral oils or mineral oil products transported in tankers can cause corrosion due to small amounts of water often present in such materials. Strong corrosion is also caused by the periodic cleaning of the tanks which, to save time, is often carried out at sea and consequently with seawater. For such cleaning, the seawater is often heated to 80 or 90° C, and then sprayed under pressure against the tank walls to remove as much rust as possible together with oil residues. When the tank is then empty, its walls are attacked by the atmosphere, especially at sea.

Due to the economic losses caused by contamination of the products transported in tanks, it is of greater importance to combat effective corrosion in tankers than in other cases.

When tank walls are treated with corrosion-preventing agents, known as inhibitors, one must be very careful when choosing corrosion-preventing agents. Such substances often cause turbidity or "clouding" in transported oil products, even when present in small concentrations, as they induce emulsification of water in oils. Other corrosion inhibitors are soluble in oils, which is also undesirable.

It was further found that the effect of many substances which are known as inhibitors was too small for the present purpose.

French patent no. 606 807 describes a method to prevent corrosion of iron and steel using potassium ferrocyanide, but the information given in this patent is very summary. No details are given at all with regard to the concentrations to be used.

It was now found that potassium ferrocyanide solutions have prominent corrosion-preventing properties, which are highly dependent on the concentration of the solutions. It is very important that potassium ferrocyanide does not dissolve in the oil phase and also does not cause emulsification of oils in water.

A very good anti-corrosion effect can be achieved by bringing the surfaces to be protected into contact with aqueous potassium ferrocyanide solutions with a concentration of 11-24 parts by weight. The maximum effect is achieved at concentrations of from 13 to 21% by weight, particularly at around 17% by weight. At concentrations below 11% by weight. the effect is greatly reduced. Comparative tests have shown that when surfaces are treated with 7% by weight solutions of potassium ferrocyanide, twice as much is formed

rust as when treated with a solvent

ning with a concentration of 11% by weight.

There is also a prominent reduction in the effect when the concentration of potassium ferrocyanide in the solution is increased to more than 24% by weight. When using a 30% by weight potassium ferrocyanide solution, rust formation is 1.5 times greater than when treated with a 24% solution.

The percentage values mentioned have been calculated

on potassium ferrocyanide without water of crystal.

Potassium ferrocyanide solutions can

applied to the surfaces to be protected,

using any known technique. Fairly large surfaces, such as the tank walls in tankers can be sprayed with the solution. This treatment can be carried out at normal temperature, i.e. the ambient temperature, but if so

also desired at higher temperatures, e.g.

e.g. 40—90° C. It is not necessary to

put the potassium ferrocyanide solutions on

dre substances, such as e.g. different phospha-

ter that are often present in solutions for corrosion prevention purposes. Phosphates min-

occurs most closely to the action of the potassium ferro-cyanide. The addition of surface-active compounds helps to provide an even distribution of the solution. Such compounds can be used in small concentrations, e.g. 0.001

-1 wt. The presence of chlorine ions in the potassium ferrocyanide solutions neutralize

does not affect the anti-corrosion effect.

If desired, seawater can therefore be used for the preparation of these solutions.

Example.

Strips of steel containing 0.1 percent carbon were treated in the following way:

First day: placed in synthetic seawater,

each time with 4

2 net days: intervals, each of half an hour

hour per day and night.

3rd day: sprayed with synthetic marine

water until the steel strip was just moistened.

4th day: sprayed once with a K4Fe(CN)c solution until

the bands had just been moistened.

17th day: spent an hour in light kerosene (kerosene) in which 0.1 volpst. synthetic seawater was emul-

done.

31st day: as 3rd day,

32nd day: as 4th day,

45th day: as 17th day,

59th day: trial ended.

The synthetic seawater used was

produced by mixing equal volumes of

parts of the following solutions, and by setting the mixture's pH value to 8 by adding

addition of 0.1N sodium bicarbonate solution

nothing.

Resolution 1:

In Resolution 2:

Claims (3)

1. Procedure to reduce or prevent corrosion of walls in tanks in tankers for the transport of mineral oils and mineral oil products, characterized in that these walls are treated with an aqueous solution of potassium ferrocyanide with a concentration of 11-24% by weight. 2. Method according to claim 1, characterized in that the solution of potassium ferrocyanide also contains chlorine ions. 3. Method according to claim 1 or 2, characterized in that the solution also contains a surfactant.