Anticorrosion treatment of metal structures: materials and technology

To ensure the durability of metal products, anti-corrosion treatment of metal structures is used. This procedure is aimed at protecting the structure from the effects of aggressive environment and atmospheric precipitation. Due to the coating, the metal surface retains its original properties, including aesthetic properties.

The essence of the process

Corrosion is the process of electrochemical or chemical interaction of metal with the environment, because of which the metal is oxidized and destroyed. Experts say that the damage from corrosion in the industrial sector reaches 4% of the gross national product of any country. Corrosion occurs due to exposure to metal of oxygen, water, so timely anti-corrosion treatment of metal structures is required. Technology involves the treatment of surfaces with a thin layer of metal, metal alloys or non-metallic compounds.

Features of processing

Due to the fact that the metal begins to break down under the influence of an aggressive environment, the strength and physicochemical properties of metal products change. And this affects the decrease in their functionality and durability. Corrosion contributes to the breakdown of equipment, vehicles. That is why anti-corrosion treatment of metal structures plays an important role, the technology of which is constantly being modernized and improved.

Outside processing

The external surfaces of metal products are most susceptible to the influence of aggressive factors. To protect them, constructive methods of protection are used. They are used in the design and manufacture of products even before the active exploitation of metal elements. Constructive methods involve the selection of a material that can withstand the effects of the environment. For these purposes, steel with a strong film, high polymeric materials, ceramics, and glass are well suited. In addition, anti-corrosion treatment of metal structures is accompanied by methods of rational operation of products:

• Elimination of cracks, cracks, gaps that can remain in the product and through which moisture can get into;
• Liquidation of zones in which moisture can stagnate;
• Protection of the surface from water;
• The introduction of inhibitors in an aggressive environment.

Passive protection

When applying passive methods of protection, the metal surface is treated with some coating, the task of which is to prevent contact of metal and oxygen or metal and moisture. To this end, anti-corrosion treatment of metal structures is carried out. Materials for this are used modern, with improved operational properties. Such coatings perform several functions:

• Barrier;
• Tread;
• Transformative;
• Passive.

Barrier protection involves mechanical isolation of the metal surface. Most often used such tools for processing ferrous metals. But if the integrity of the protective film is disrupted, under-pitting corrosion may occur.

What materials?

When an anticorrosive treatment of metal structures is carried out, the means are selected very carefully. For the passivation of surfaces paint materials are used that contain phosphate acid or chromate pigments, which slow down the corrosion processes. When applying passivation primers a sprayer is used. Depending on how many components in these formulations, they can be used for processing both ferrous and non-ferrous metals.

Passive processing can act as a protector, but in this case, paints are used, in which more than 86% of the metal dust is made from an element of high reducing ability in comparison with the treated surface. In most cases, when anti-corrosion treatment of metal structures is used, the colors are selected with the filling of fine zinc powder. This technology is called cold galvanizing, which increases the life of the metal surface and its resistance to abrasion.

Paints and enamels

Protection of metal structures is carried out on the basis of three types of means:

• Paintwork coatings that are easily and simply applied and presented in a variety of color solutions. With the help of paints, it is possible to process metal structures of large dimensions and any configurations.
• Plastic anti-corrosion coatings, which are based on fluoroplastic, nylon, PVC. These compositions are characterized by high water, acid and alkali resistance.
• Coatings with rubber in the base are used when the anticorrosive treatment of tanks and metal structures from the inside is performed.

Active protection methods

Metal requires special protection, for which active methods are used. The durability of metal products to external factors is achieved:

• Hot-dip galvanizing of parts: according to this technology the part is first degreased, then - sandblasted or etched with acid, as a result of which it is covered with a thin zinc layer. The chemical reaction leads to the formation of a protective film on the surface of the metal. It shields the metal and protects it from moisture. Most often, hot-dip galvanizing is used to handle large objects - tanks, cisterns.
• By electrochemical galvanizing: this method assumes diffusion extraction of zinc ions from a weakly acid solution during electrolysis. Galvanic processing of metal structures is used for the machining of hardware, parts of medium size.
• Thermo-diffusion deposition of zinc coating: with this technology, zinc atoms penetrate into the surface of iron under the influence of high temperature. The coating is durable and wear-resistant, and the original part is repeated completely, even if the surface is with recesses or relief.

Anticorrosion treatment of metal structures can be carried out in addition to electrochemical protection.

Modern methods

More often than not, paint coatings are used to protect the metal surface from corrosion, since they are more affordable and easy to use. But this layer needs to be updated every 5-7 years, which is laborious and costly. And to use galvanic and electrochemical methods is too expensive, although about rust can be forgotten for about 50 years.

That is why more and more often anti-corrosion treatment of metal structures is performed with the help of "liquid rubber". It is a two-component material that is able to reliably and permanently protect the surface from external influences. The use of an elastomer allows the application of a seamless membrane layer, applied by a spray gun. Rubber quickly freezes on the surface, while neither flowing nor unevenness is formed. And you can work even with a damp metal surface. Manufacturers of such products say that such a coating can last about 20 years without losing its original properties.

Surface preparation

Reliable protection of metal from rust can be achieved only if the surface has been prepared at the proper level. The equipment for anticorrosion treatment of metal structures is not difficult, so its use will not cause any problems. Surface preparation is performed mechanically or chemically. More popular are chemical methods, since mechanical methods can not provide the proper level of protective equipment. But the technology must be selected in accordance with the chosen paint and varnish coatings and the conditions for their further operation.

Phosphating and chromating

Preparation of a metal surface is performed depending on the type of metal. Surface preparation from ferrous metals is carried out by phosphating, and non-ferrous metals are processed by both methods. In general, chemical preparation of a metal surface consists of several stages:

• Surface degreasing;
• Washing with drinking water;
• Applying a conversion layer;
• Re-rinsing with drinking water;
• Washing with demineralized water;
• Passivation.

Chemical treatment of metal is carried out by spraying (blasting at low pressure), immersion, steam jet and hydrojet methods. The first two methods involve the use of special aggregates that prepare the surface. The method is chosen in accordance with the production program, configuration and dimensions of products and many other factors.

Pipeline treatment

Anticorrosion treatment of metal structures and pipelines is carried out in accordance with the requirements of state standards. Processing can be carried out both for the functioning pipeline, and during its reconstruction or repair. Pipelines can be protected by active and passive methods - it is selected in accordance with the laying method. For pipes laid on top of the earth, materials that are resistant to environmental influences are used. With the active method, the protective surface is created with substances that can provide electrochemical protection of the coating. Pipeline protection is performed in several stages:

1. First, the surface of the pipe gets rid of insulating coatings, rust, scale and all contaminants.
2. Anti-corrosive materials are applied to the cleaned surface, while the work can be carried out at a temperature of +5 degrees and at a humidity of not more than 80%.

After carrying out the treatment, you should carefully inspect the pipeline to identify defects, if any, on the surface. Special devices determine the quality of the surface and coating connection, the quality of the coating itself and the thickness of the dry coating film.

Active and passive protection

Anticorrosion treatment of metal structures, the principle of which depends on the materials used, can be performed with active and passive surface protection. Both options are aimed at protecting metal pipes from harmful environmental factors. And if the water pipe is located at great depth, there is a need to protect the metal from contact with the ground. Thanks to protective layers of paint, varnish, enamel, a continuous and very strong barrier is created, which protects the surface from the negative impact of the external environment.

Piping treatment is often performed with powder materials based on plastic materials. They are applied to a pipe, which is preheated to a certain temperature.

Thus, carrying out of anticorrosion treatment is an opportunity to prevent occurrence of a rust on any metal surfaces. A variety of options and processing methods - a guarantee that you can protect anything from pipes and car to a small metal part.