CS274321B1 - Method of anticorrosive steel protection - Google Patents

Abstract

The method of anticorrosion protection of steel with use of preserving solution is performed by acting of a zinc complex compound in concentration from 0.1 to 5 percent by weight in water solution at the pH value ranging from 8.5 to 10.5. The required alkalisation is achieved by addition of hydroxides of alkaline metals or alkylolamines. The solution concerns the material protection.

Description

The invention relates to a process for the corrosion protection of steel using a preservative solution.

In general engineering practice, there are many cases where steel, especially unalloyed steel, has been exposed for a long time in an aqueous environment, directly in solutions or in a humid environment. Where non-alloy steel cannot be replaced by a noble material, or where aggressive constituents are present in significant concentrations in a corrosive environment, in particular substances with aggressive properties or substances having the character of depolarizers of partial corrosion reactions, . These cases are particularly characteristic of the environment of wet materials adhering to the unprotected surface of the unalloyed steel or of metal surfaces exposed for a long time in a liquid, especially aqueous, environment. In technical practice, these conditions often occur where different fill, stop or hydraulic fluids are used, or where it is necessary to remove undesirable substances from the surface of technological components, especially when treating heat exchange or additional surfaces of power equipment,

Presently, untreated raw water is generally used for these cases, and in the case of long-term exposures of non-alloy steel in a more corrosive environment, preservative liquids are used, with an effect based on the inerting capabilities of the individual components of the solution. For the preservation of pipe materials, in gas extraction, in particular with an increased risk of immersion of aggressive gases such as carbon dioxide or sulfane into the sealing liquid, solutions containing soluble copper complements in an alkaline environment or alkaline solutions of substances with a corrosion inhibitory effect chemisorption interaction of active molecules with the protected metal surface.

Said treatments of corrosion-conserving liquids are disadvantageous in certain applications. For example, the penetration of acidic gases into a copper complex solution, especially in the case of sulfane, results in the formation of a sedimenting precipitate, which may hinder subsequent technological operations, in particular forming solid layers in the lower parts of the hydraulic spaces. The use of another type of solution based on alkaline mixtures of nitrogenous surfactants can cause technological difficulties in foam formation and possible degradation at higher temperatures and longer exposures, with the consequent loss of intrinsic functional characteristics.

These drawbacks are solved by the corrosion protection method of the steel using the preservative solution according to the invention. It is based on the fact that the steel is treated with a complex zinc compound in a concentration of 0.1 to 5 wt. in aqueous solution at pH 8.5 to 10.5. The complex zinc compounds may contain polycarboxylic acid residues and / or ammonia or derivatives thereof. Alkalization to the appropriate range is carried out with alkali metal hydroxides or alkylolamines.

The main advantage of the present method of corrosion protection according to the invention is the high corrosion efficiency in aggressive environments containing sulfane and carbon dioxide even at high temperatures and long-term exposures. The penetration of acid gases into said preservative liquid also produces a solid phase which, however, unlike the analogous analogues, does not sediment due to its voluminous character. The interaction of zinc complexes, sulfane or carbon dioxide and the zinc-containing solid phase dispersion creates a resistant passive layer on the surface of the protected metal with a long-term corrosion protection effect. There is no danger of activation of corrosive aggressiveness by the action of sulphurous bacteria on prolonged exposure with concomitant reduction of the alkalinity of the preservative solution, since in this case the zinc compounds act as an oligodynamic effect.

CS 274321 Bl

The invention is further described in several exemplary embodiments.

Example 1

Long-term corrosion protection of the steel using a preservative solution was carried out in a laboratory simulated experiment in which high-strength unalloyed steel was placed in a solution with the following composition:

0.25% zinc salt of nitrilotriacetic acid

0.05% sodium hydroxide residue water

With the simultaneous action of sulfane and carbon dioxide at a temperature of 25 ° C, the corrosion rate found in the long term was approximately 15 times lower than in a solution with the addition of complexes

-? -1 copper and was below 0.001 g.m. h .A corrosion-resistant coating was detected on the steel surface after exposure.

Example 2

A similar laboratory simulated experiment was performed in solution:

0.5 wt. tetra-zinc complex

0.1 wt. diethanolamine residue water

Similar results were reported.

Claims (1)

Process for the corrosion protection of steel using a preservative solution, characterized in that the steel is treated with a soluble complex zinc compound at a concentration of 0.1 to 5% by weight. in aqueous solution at pH 8.5 to 10.5.