CS218839B1 - Method of pickling and chemical coating of metal surfaces - Google Patents

Abstract

The purpose of the invention is to improve the technology of pickling and chemical cleaning, in particular by improving inhibition and controlled dosing of the inhibitor in the extrusion method of pickling and chemical cleaning with hydrofluoric acid. The stated purpose is achieved by preparing an acidic stock solution of a mineral and/or organic acid and an inhibitor solution with an active component comprising organic compounds with a thiazole or imidazole heterocyclic ring and a mercapto group on this heterocyclic ring dissolved in ammonia or ammonium compounds, or in ethanol, after which the inhibitor and acid solution are dosed in a controlled manner into water or an aqueous detergent solution to achieve the desired concentration in the pickling medium. The bath prepared in this way is circulated or, when using hydrofluoric acid, preferably pushed through the cleaned device once.

Description

The invention relates to a method of pickling and dry cleaning of metal surfaces, in particular the inner metal surfaces of pipes and pipe systems of power and chemical equipment.

The currently used pickling baths to remove deposits and scale from the internal metal surfaces of power and chemical equipment are inhibited by mineral or organic acid solutions. Inhibitors are used in these solutions to reduce the corrosion rate of the base material.

The inhibition of the pickling and dry-cleaning solutions is usually carried out by an inhibitor containing dibenzylsulfoxide in admixture with sodium chloride, or in combination formulations of various compositions in liquid or solid form. A disadvantage of solid-state inhibitors, such as mercaptobenzthiazole or dibenzylsuifoxide, is their poor solubility, which excludes their use in a continuous method of pickling and dry-cleaning; Inhibitors, in liquid form, require dosing at higher concentrations. their high prices bring increased costs for pickling or dry cleaning. When disposing of used baths, higher inhibitor concentrations result in higher pollution from waste liquids by organic substances and a higher risk of environmental pollution.

The above-mentioned disadvantages of the current state of pickling and dry cleaning of metal surfaces eliminate the pickling and dry cleaning method of the invention.

SUMMARY OF THE INVENTION The present invention provides an acidic solution containing mineral or organic acids, an inhibitor solution containing as an active inhibitory component at least one organic compound having a thiazole or imldazole heterocyclic ring and a mercapto group on said heterocyclic ring dissolved in an ammonium compound or compounds with a mass In a ratio of up to 1: 4 of the ammonium inhibitor compound or in ethanol at a weight ratio of up to 1: 8 of inhibitor to ethanol and of water or aqueous detergent solution, the inhibitor solution and the acid solution are dosed. can be advantageously used in particular for through-flow pickling and dry-cleaning applications.

The pickling and cleaning bath thus prepared according to the invention has a high inhibitory activity and thus a significantly reduced corrosion aggressiveness for the base metal material due to the increased solubility of the inhibitor. In addition, synergistic effects of the inhibitor with its solvent and acid are achieved, thereby further increasing the inhibitory activity and reducing the corrosion of the material during the pickling and purification process.

The possibility of using flow pickling and dry cleaning using the method according to the invention brings, in view of the current state of circulating pickling and dry cleaning, an advantage in reducing the cost of the necessary process equipment and, in particular, due to the previously mentioned and used processes in newly assembled equipment one- to two-month time savings.

Below are two examples of using the method of the invention for flow measurement or dry cleaning.

In the first example, a stock acid solution containing hydrofluoric acid and a stock inhibitor solution containing mercaptobenzthiazole dissolved in an aqueous ammonia solution in a 1:

pumped into the detergent-containing water stream such that the bath thus formed consists of 0.5 to 2 weight percent hydrofluoric acid, 0.02 to 0.03 weight percent mercaptobenzothiazole, 0.08 to 0.12 weight percent ammonia and 0.02 to 0 weight percent 0.05% by weight of the detergent, the remaining bath by weight being water. This bath is forced through the tube system of the apparatus; wherein the water jet serves as both a propellant and a diluent.

In the second example, the stock acidic hydrofluoric acid stock solution is pumped into a stream of inhibitor solution prepared by dissolving mercaptobenzthiazole in ethanol in a 1:

And diluting with water such that the resulting bath contains 0.5 to 2 weight percent hydrofluoric acid, 0.02 to 0.03 weight percent mercaptobenzothiazole, and 0.16 to 0.24 weight percent ethanol, with the remaining weight being water . The bath thus prepared is forced through a tube system of the apparatus, the inhibitor solution serving as a propellant and diluent.

Claims (1)

A method for pickling and dry-cleaning metal surfaces, comprising forming an inhibitor solution comprising at least one organic compound having a thiazole and / or imidazole heterocyclic ring and a mercapto group on said heterocyclic ring dissolved in the ammonium compound or compounds in a weight ratio of up to 1 : 4 inhibitor to the ammonium compound of the invention or in ethanol in a weight ratio of up to 1: 8 inhibitor to ethanol and the thus prepared inhibitor solution is dosed into the acid solution and / or the water stream at the point of dosing of the acid solution whereupon the bath thus prepared is extruded or circulated through the purified apparatus.