MD87Y - Inhibitor of steel corrosion in water - Google Patents

Abstract

The invention relates to the field of protection of metals from corrosion in water and can be used for inhibition of corrosion in closed systems of steel pipelines. Sodium thiosulfate with a concentration of 0.05…1.00 g/l is used as an inhibitor of corrosion of steel in water. The result is a reduction in corrosive losses up to 7.3 times.

Description

The invention relates to the protection of metals from corrosion in water and can be used for inhibiting corrosion in closed steel pipeline systems.

[0002] It is known that natural and technological water, containing active ions of Cl- and SO4 2-, is a rather aggressive environment, in which the corrosion of steels occurs at a high rate. Thus, the tap water from Chisinau, containing: Ca2+ - 42.5, Mg2+ - 19.5, HCO3 - - 97.6, SO4 2- - 203.7, Cl- - 56.7, g/l, has a very high corrosion rate of carbon steel, for 8 hours, reaching the value of 21.0 g/m2·day [1].

[0003] With increasing exposure time, the corrosion rate decreases (e.g., up to 4.0 g/m2 · day at 240 hours of exposure), due to the formation of an oxide-hydroxide film on the corroded surface from corrosion products, as well as from calcite CaCO3. The thickness of the pipe walls decreases, and the presence of Cl- ions on the surface can form deep cracks, which can lead to accidents.

[0004] Various corrosion inhibitors are known, which generally represent organic or inorganic substances [2-4].

[0005] For example, sodium thiosulfate is used as a component of the inhibitor mixture for the protection of low-carbon steels in NH4NO3 solutions and urea ammonia solutions. However, firstly, it is a complex multicomponent mixture, and secondly, a very high concentration of thiosulfate is used (25…30%), and importantly, this mixture is effective in acidic and alkaline solutions, but does not provide protection against corrosion in water [4].

When using thiosulfate as an inhibitor for the protection of carbon steels in water, it must be taken into account that for many anodic inhibitors there is a critical concentration, below which the corrosion intensity increases continuously with the inhibitor concentration.

[0007] The closest solution is sodium thiosulfate in the amount of 0.79…7.9 g/l for inhibiting the corrosion of copper in nitric acid. However, the use of sodium thiosulfate under the indicated conditions provides protection against corrosion only for a short period of time [4].

[0008] The problem solved by the invention is to increase the corrosion resistance of closed steel pipe systems when pumping water through them.

[0009] The problem is solved by using sodium thiosulfate with a concentration of 0.05…1.0 g/l as an inhibitor of steel corrosion in water.

[0010] The influence of inhibitor concentration and test time on corrosion rate k, g/m2 · day and braking coefficient γ are given in the table. From these data it is obvious that the greatest effect is achieved when using sodium thiosulfate with a concentration of 0.1…0.5 g/l. Thus, in a test within 24 hours, corrosion losses decrease by 7.3 times at inhibitor concentration of 0.1 g/l; by 5.8 times at concentration of 0.25 g/l and by 6.4 times at concentration of 0.5 g/l.

[0011] The amount of inhibitor introduced into the corrosive medium plays a special role. The lower limit of the concentration is 0.05 g/l, at a lower concentration the corrosive medium reduces the corrosive losses insignificantly.

[0012] Increasing the concentration of thiosulfate in the corrosive medium to 1.0 g/l has a positive effect, but at a concentration of 1.5 g/l sodium thiosulfate becomes a corrosion activator, initially separate pittings appear, which over a long testing time turn into a series of corrosive ulcers.

[0013] Table

[0014] Influence of inhibition conditions on the corrosion rate of steel СТ. 3

Inhibitor concentration, g/l

Testing time, τ, hours

Corrosion rate, g/m2 · day

Braking coefficient,γ

Inhibitor-free water

8 24 72 240

21.00 12.00 6.60 4.00

- - - -

0.025

8 24 72 24

9.10 4.80 3.10 2.10

2.3 2.5 2.1 1.9

0.05

8 24 72 240

4.50 2.30 1.60 1.30

4.7 5.3 4.2 3.1

0.1

8 24 72 240

3.00 1.65 1.30 0.90

7.0 7.3 5.2 4.7

0.25

8 24 72 240

3.30 2.10 1.20 0.90

6.5 5.8 5.4 4.3

0.5

8 24 72 240

3.80 1.90 1.50 1.10

5.6 6.4 4.5 3.8

0.75

8 24 72 240

6.20 3.20 2.40 2.20

3.4 3.7 2.7 1.8

1.0

8 24 72 240

12.40 8.00 5.50 3.60

1.7 1.5 1.2 1.1

1.5

8 24 72 240

17.50 10.90 8.25 8.00

1.2 1.1 0.8 0.5

[0016] 1. Parshutin V.V., Sholtoyan N.S., and others. Ингибирование бороглюконатом калция корозии углеродистой стали СТ.3 в воде. Corrosion in the conditions of natural aeration and forced convection. Electronic processing of materials, 1999, № 5, p.42-56

[0017] 2. Robinson J.S. Corrosion inhibitors. Moscow, 1983

[0018] 3. Rosenfeld I.L. Corrosion inhibitors. Moscow, 1977

[0019] 4. Alcybeeva A.I., Levin S.Z. Metal corrosion inhibitors. Leningrad, 1968

Claims (1)

1. Use of sodium thiosulfate as an inhibitor of steel corrosion in water at a concentration of 0.05…1.00 g/l