What is atmospheric corrosion

Corrosion of aluminum: how to protect against electrochemical rusting in sea water or stop its speed, how to coat the metal and its resistance

Climatic factors and the degree of atmospheric pollution act together.

For example, increased air pollution can reduce the critical value of relative air humidity at which corrosion begins to develop.

Atmospheric corrosion parameters

The resistance of aluminum and its alloys to atmospheric corrosion depends on:

on the climatic conditions in which they are located:

• humidity;
• duration and intensity of rains;
• temperature;
• number of sunny days per year;

on the degree of air pollution, that is, concentration:

• sulfur dioxide (SO2);
• nitrogen oxides (NOx);
• quantity and chemical composition of dust.

These factors can also have the opposite effect: rain increases air humidity, but also washes away dust and corrosion products, which can reduce the rate of corrosion

Relative humidity

The rate of atmospheric corrosion depends on the relative humidity of the air, and not simply on the amount or intensity of rain in a given area. Rain is one, but not the only factor on which relative air humidity depends.

Relative humidity level is the relationship between the actual water vapor pressure and the maximum water vapor pressure at a given temperature. This ratio is expressed as a percentage.

At normal room temperature, air is considered:

• dry if the relative humidity is no more than 30%;
• normal if the relative humidity is between 50 and 60%;
• humid if the relative humidity is above 80%;
• saturated with moisture if the relative humidity is about 100%.

In deserts and arid zones, relative humidity levels rarely exceed 10-20%, while in temperate climates it is generally between 40 and 60%. During a rainstorm it can reach 90-95%, and during tropical rains it can approach 100% [2].

Dew point

The dew point is the temperature at which moisture will begin to condense. For a given level of relative humidity, this is the temperature to which the air must be cooled so that it becomes saturated with moisture, and its precipitation begins on nearby surfaces.

Duration of humidification and sulfate electrolyte

Corrosion of metals in the open air depends on the so-called duration of humidification and the chemical composition of surface electrolytes.

The duration of moisture is the period during which there is enough moisture on the metal surface for corrosion to occur.

The duration of humidification is usually defined as the time during which the relative air humidity exceeds 80% and, at the same time, the temperature on the metal surface is above 0 ºС. Under these conditions, moisture condensation may occur on the metal surface.

Critical relative humidity

Atmospheric corrosion of metals, including aluminum, occurs in thin films of moisture that are located on the surface of the metal. There is a critical threshold of relative humidity below which aluminum and its alloys do not corrode.

This occurs because when there is insufficient humidity, there is not enough moisture to create a continuous electrolytic film on the surface of the metal.

No sulfates - no corrosion

In normal rural areas and in atmospheres with moderate sulfate pollution, aluminum's environmental resistance is very high. In an atmosphere with a high sulfate content and high humidity, pitting (pitting) corrosion can occur on aluminum products. In such conditions, aluminum may require corrosion protection.

Chlorides

The presence of salts (especially chlorides) in the air reduces the durability of aluminum, but to a lesser extent than for most other building materials.

The maximum depth of corrosion pits is usually only a small fraction of the thickness of the aluminum part.

Unlike carbon steel, the strength properties of aluminum parts that have been subjected to corrosion remain virtually unchanged.

Corrosion of aluminum in soil

The corrosion behavior of aluminum in soil is a very important practical issue. Electrical and telecommunications cables, water and gas distribution networks, as well as the bases of road signs, street lamps and various road structures are all very often made from aluminum and aluminum alloys.

Soil acidity-alkalinity

Assessing the corrosion resistance of metals, including aluminum, in contact with soils is very difficult.

The soil is characterized by its pH value, which is closely related to the type and content of salts dissolved in it, the amount of carbon dioxide (CO2), as well as possible pollution from industrial and domestic wastewater.

Soil electrical resistance

The corrosive aggressiveness of soil is associated with its electrical resistivity, which depends not only on the composition of the soil, but on the water content and the concentration of inorganic salts.

Forms of aluminum corrosion in soils

Unprotected aluminum in soil can exhibit the following forms of corrosion [2]:

• pitting corrosion;
• galvanic corrosion (in contact with other metals);
• corrosion from stray currents.

Protection of aluminum in soil

For aluminum that works in soil, corrosion protection in the form of a bitumen coating, as well as cathodic protection, is most often used.

Physical chemistry of water

Water is a strong solvent that can dissolve:

• many inorganic and organic compounds,
• liquids if they are polar and contain a hydroxyl group;
• gases.

Therefore, any water has a variable content:

• inorganic salts;
• dissolved gases;
• solids in the form of a suspension and
• organic substances.

However, not all of these dissolved elements affect aluminum corrosion. The main influence on aluminum corrosion is exerted by the following dissolved in water:

• chlorides;
• heavy metal ions.

Effect of chloride concentration

It is generally accepted that among all anions, chloride ions have the highest ability to penetrate the natural oxide film on the surface of aluminum. This is because these ions are very small and very mobile.

It is known that chlorides, as well as fluorides, bromides and iodides, are anions that activate corrosion of aluminum in water, while sulfates, nitrates and phosphates activate such corrosion less (Figure 5) or do not activate it at all.

The peculiarity of chlorides is that they can replace oxygen atoms in the aluminum oxide film. This leads to a weakening of the oxide film's resistance to corrosion.

Pitting corrosion

In natural fresh water and tap water, aluminum can be subject to pitting corrosion. However, with regular cleaning and drying, the risk of serious corrosion is very small.

Aluminum pots, kettles and pans, as well as soldiers' aluminum bowls, spoons and mugs, served faithfully for decades without any signs of corrosion.

The likelihood of corrosion increases if water is standing and aluminum is kept wet for long periods.

Effect of copper

The presence of copper in aluminum alloys significantly reduces their corrosion resistance. Such alloys are used only if they have reliable corrosion protection.

Chlorides in seawater

Typically seawater contains about 35 g/l of dissolved inorganic salts, of which chlorides make up about 19%. This is associated with the increased corrosiveness of sea water.

pH value of sea water

The pH value of sea water near the surface of seas and oceans is very stable and is about 8.2. This pH value is within the stability range of the natural oxide film. This explains the good corrosion resistance of aluminum in seawater.

Aluminum alloys for sea water

In seawater, aluminum-magnesium alloys (AlMg) with a magnesium content of no more than 2.5% exhibit particularly high durability. Ship hulls and other supporting structures are made from these alloys. For deck superstructures, the corrosion resistance of aluminum alloys of the 6xxx series (AlMgSi alloys) is quite sufficient.

Aluminum in contact with concrete

The use of aluminum in the construction industry forces it to come into contact with most materials used in construction: concrete, gypsum, polymers, etc.

Impact of concrete

Aluminum resists the effects of concrete and cement mortar well, despite their high alkaline properties with a pH value of about 12.

When the concrete begins to set, there is always a slight etching of the aluminum to a depth of no more than 30 microns. This effect, however, slows down after a few days of contact.

This leads to a very localized decrease in pH to 8 units and the formation of a protective film of calcium aluminate on the aluminum surface.

Concrete has a similar effect on aluminum castings. This increases adhesion between these materials. Once the concrete has hardened (dried), corrosion usually no longer occurs. However, where moisture accumulates and remains, corrosion can develop. The increased volume of corrosion products can cause cracks in the concrete.

Protecting aluminum from concrete

Therefore, splashes of wet alkaline building materials such as mortar and concrete leave superficial but clearly visible stains on aluminum surfaces. Since these stains are difficult to remove, visible aluminum surfaces must be protected, for example on construction sites.

Source: https://xn----8sbna6aihebzq3cl.xn--p1ai/sposoby-borby-s-korroziej/kak-borotsya-s-korroziej-alyuminiya.html

Protection of metal structures from atmospheric corrosion

A.P. Gulidov, engineer, NPK “Vector”, Ph.D. N.Yu.Timofeeva, MSUPP, department. "Metal technology"

Heat supply news No. 9 (September); 2003

The process of destruction of metals under the influence of the surrounding air, known to mankind for thousands of years, is usually called atmospheric corrosion. Atmospheric corrosion is the most common type of corrosion; its manifestations are so numerous and varied that improving methods of combating it does not lose its relevance.

Mechanism and main factors of atmospheric corrosion of metals

All metal structures operated in the open air (about 50% of the total available metal stock), namely: pipelines and above-ground tank equipment, metal parts of buildings, supports, bridges, transport and loading and unloading equipment, are susceptible to atmospheric corrosion. During operation, the surfaces of structures are inevitably subject to moisture and contamination, which is the root cause of the occurrence and development of corrosion processes.

According to the mechanism of occurrence, this type of corrosion in most cases is an electrochemical process, with the exception of “dry” corrosion, which occurs through a chemical mechanism.

The electrochemical process implies the presence of cathode and anodic areas on the corroding surface, as well as an electrolyte, the role of which is played by a film of moisture (from several molecular layers to one millimeter thick) that is constantly present on the metal surface.

The appearance of galvanic elements “cathode - anode” on the main structural materials - carbon steels - occurs due to the differentiation of their surface into areas with different electrode potentials (the theory of local corrosion elements).

The reasons for differentiation may be different:

•   heterogeneity of the metal structure (carbon steels contain phases - ferrite and cementite, structural components - pearlite, cementite and ferrite, which have different electrode potentials);
•   the presence of oxide films, contaminants, non-metallic inclusions, etc. on the surface of steel;
•   uneven distribution of the oxidizing agent at the metal-electrolyte interface, for example, different humidity and aeration in different areas of the metal surface;
•   uneven temperature distribution;
•   contact of dissimilar metals.

Currently, more than thirty-five factors are known that influence the rate of atmospheric corrosion, the main of which are: the degree of metal moisture, the condition of the surface of the structure (porosity, contamination), the chemical composition of the atmosphere (the presence of hygroscopic and aggressive products).

Based on the degree of moisture of the corroding surface, they are distinguished:

wet atmospheric corrosion - with a relative air humidity of about 100% and the presence of a visible film of moisture on the metal surface;

wet atmospheric corrosion - with relative air humidity below 100% and the presence of a film of moisture on the metal surface resulting from capillary, adsorption or chemical condensation;

dry atmospheric corrosion – corrosion at a relative air humidity of less than 50% and a moisture film thickness of up to 10 nm.

This distinction is quite arbitrary, because Under practical conditions, a mutual transition from one type of corrosion to another is possible. In Fig. Figure 1 shows the qualitative dependence of the rate of atmospheric corrosion of metals on the thickness of the moisture layer on the surface of the corroding metal.

Pollution of the air and, as a consequence, the surface of structures with aggressive impurities occurs as a result of the functioning of industrial facilities, due to technical imperfections of chemical and other equipment, leakage of detachable connections, accidental spills of technical fluids, depressurization of communications, the presence of microdefects in metal, etc. . Pollution is divided into two groups: organic and inorganic origin.

The former enter the surface from the outside, the latter can enter from the outside and arise as a result of the interaction of gases that pollute the atmosphere (oxides of sulfur and nitrogen, chlorine, hydrogen chloride, etc.) with the surface of the metal.

Impurities that can dissolve in water activate the electrochemical reaction due to the formation of dilute acids and an increase in the electrical conductivity of moisture films, and poorly soluble, loose, discontinuous corrosion products create conditions for the emergence and operation of macrogalvanic couples. In addition to aggressive gases, the atmosphere may contain particles of solids and aerosols of salts.

Their sources can be decaying rocks, saline soils, and coastal zones with a high content of chloride-sulfate sodium salts. Particulate matter is also released during the combustion of various fuels and the production of cement and fertilizers. Particles are transported by air masses over distances of up to one thousand kilometers and, settling on the surface of the metal, become centers of condensation of moisture from the air. It has been practically established that the rate of atmospheric corrosion in an atmosphere polluted with various gases and solid impurities is tens of times higher than in a clean atmosphere.

Methods for protecting metals from atmospheric corrosion

Extending the service life of various metal structures until they become obsolete is the main goal of solving the centuries-old problem of metal corrosion. By definition, the term corrosion means a process.

This process consists of a physical and chemical reaction between the metal and the environment, leading to changes in the properties of the material and the environment.

The result of the process is a “corrosion effect”, which reduces the service life of metal structures, worsens the functional characteristics of the technical systems that include them and leads to an increase in costs, the components of which are not only the costs of repairs and replacement of parts of equipment damaged by corrosion, but also the costs of compensation for losses from various problems resulting from corrosion (production stoppages or accidents leading to destruction or accidents). Some of these costs are unavoidable, but they can undoubtedly be significantly reduced through better use and continuous improvement in practice of the protection methods that we have today.

Corrosion protection in general represents a set of measures aimed at preventing and inhibiting corrosion processes, preserving and maintaining the functionality of components and assemblies of machines, equipment and structures during the required period of operation.

Methods for protecting metal structures from corrosion are based on targeted action leading to a complete or partial reduction in the activity of factors contributing to the development of corrosion processes, and are conventionally divided into methods of influencing the metal, the environment, and combined methods.

Among the former, the most widely used methods are the application of permanent coatings, conservation coatings, and alloying; among the latter, methods of complete or partial sealing using moisture absorbers (static air drying, purification of the surrounding atmosphere from contaminants, maintaining certain temperature conditions).

In the absence of the desired effect from the separate use of methods of influencing the metal and the environment, they resort to combined methods based on a complex effect on the metal with the help of protective coatings and the environment.

Of the methods of protection against atmospheric corrosion used in practice, the most detailed consideration, as the most common and quite effective, is the method of applying protective paint and varnish coatings (hereinafter LCP).

Paint coatings: application for protection against atmospheric corrosion and causes of failure

In the structure of global costs for anti-corrosion protection, paint and varnish coatings account for about 39% of funds, which is twice as much as the costs for the development and production of corrosion-resistant materials.

All types of paintwork coatings belong to the group of organic coatings and are a solid film of organic substances with pigments and fillers, obtained when the paintwork composition applied to the protected surface dries.

The protective properties of paintwork depend on the continuity and density of the film that isolates the metal surface from the environment, as well as the nature of the interaction of the coating with the metal surface. The thickness of coatings can vary from tens to hundreds of micrometers depending on their purpose.

The main advantages of paintwork include:

§ possibility of use for the protection of any structures, regardless of size, directly at installation and construction sites;

§ simplicity and possibility of mechanization of the technological process of coating;

§ coatings on most metal structures, pipelines and equipment can be repaired and restored directly during operation;

§ low material consumption per unit area and low cost compared to other types of protective coatings.

One of the main indicators that determines the effectiveness of using a particular type of coating is its durability, namely: the ability of the coating to maintain protective properties to the limit state with an established maintenance and repair system. The durability of a coating is determined by many factors, including its physical, mechanical and chemical properties, the degree of preparation of the metal surface before painting, and the correct choice of coating or coating system for specific operating conditions.

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Source: https://www.rosteplo.ru/Tech_stat/stat_shablon.php?id=398

Methods for protecting metal products from corrosion

Metal corrosion is the result of oxidation, which occurs due to electrochemical and chemical processes and contributes to the destruction of its structure and a decrease in physical properties and service life. Protecting metal products helps prevent premature wear, thereby reducing the cost of maintaining certain structures.

Main types of corrosion and methods of protection

The classification of corrosion of metal products includes spot, local and continuous. Spot is the first stage of damage, when traces of rust are represented by individual points. Local corrosion suggests much larger stains, while continuous corrosion indicates uniform damage to all surfaces.

As for protection methods, there are several of them. Among the main ones, one can note a change in the chemical composition of the metal due to special additives with anti-corrosion properties, insulation of metal surfaces using special materials.

The simplest but most effective ways to protect metal products from corrosion are protective coatings. They allow you to increase the electrochemical potential, increase the wear resistance and hardness of the metal. The most popular today are paint and varnish compositions that can be used both in industry and in the domestic sphere. They soften the corrosive environment, creating an oxygen-free environment or an adsorption film.

Line of anti-corrosion coatings from iPolymer

Today there is a huge variety of coatings for metal protection on the market; they differ in composition, effectiveness and price. iPolymer has been developing products for many years that provide good corrosion protection, but are easy to use and inexpensive.

After extensive research and testing, we launched 3 products on the market:

Primer-enamel. At the same time it acts as a primer, an inhibitor, and a finishing coat. It has the effect of so-called “liquid plastic”. Provides protection of metal products from corrosion, weathering, and ultraviolet radiation.

The composition is suitable for processing non-ferrous metals, as well as wooden and plastic structures. Available in several colors. Apply to a previously cleaned surface using a brush or spray gun.

Before use, it is recommended to move and, if necessary, add solvent (no more than 5 percent).

Korprotek PU 4. It is a barrier-type polyurethane coating. Contains aluminum powder and iron oxide mica. It can act both as a finishing and intermediate layer. The special composition allows the coating to be used to protect hydraulic structures, construction equipment, industrial installations, etc.

Polyzinc 03. Composition of polymers and zinc with phosphates. Its composition also includes functional additives. Characterized by high adhesion rates and chemical resistance. The coating can provide long-term protection to the metal.

Current prices, as well as detailed characteristics of all products, can be found in the Store section.

What are the advantages of ipolymer anti-corrosion coatings?

All of the above products are manufactured in a modern facility equipped with innovative equipment. Each composition has undergone a large number of tests, and also received all the permitting documentation. During production, only high-quality materials are used, which are purchased from well-known companies.

iPolymer products have a wide range of uses, and their practical applicability has already been proven by a large number of customers. By contacting the company, you can not only purchase anti-corrosion protective compounds at a competitive price, but also get advice directly from the manufacturer itself.

Source: https://ipolymer.ru/antikorroziinie-pokritiya/sposobi-zaschiti-metalicheskih-izdelii-ot-korrozii/

Services

Since 2009, the trading and production company Seid

Our company offers the “Express delivery” for rare items, non-standard sizes, or any types of fasteners simply not in stock with a delivery time from Finland of 2 – 4 calendar days .

Since 2016, Seid company Since that time, we have been producing hardware products and components according to customer drawings and sketches, as well as in accordance with GOST and OST.

We produce various samples of studs, bolts, screws, nuts from steel 25, 35, 40Х, 09Г2С, 20Х13, 14Х17Н2, 12Х18Н10Т, 20ХН3А, 30ХМА, 25Х1МФ, brass, copper, aluminum, etc.

Turning (turning) is the most common method of manufacturing parts such as rotating bodies (shafts, disks, axles, pins, trunnions, flanges, rings, bushings, nuts, couplings, etc.)

We process various materials, such as: Various grades of steel, cast iron, stainless steel, bronze, brass, aluminum, fluoroplastic, caprolon, etc.

Zinc lamel coatings are perhaps the best alternative to galvanic coatings.

Application of a protective layer, the advantages of which are:

1. No risk of hydrogenation, that is, a decrease in the ductility of alloys and resistance to cracks (primarily this applies to fasteners made of hardened steel, which automakers are forced to additionally process after coating to remove hydrogen).

Oxidation is the process of deliberate oxidation of the surface layer of metal products. The oxidation process is preceded by surface preparation by etching in alkaline solutions.

The resulting oxide films protect products from corrosion, serve as electrical insulation, and are the basis for applying protective coatings to them - varnish, paint, grease, etc.

Galvanizing of fasteners in Novosibirsk

• Colorless galvanizing
• Rainbow galvanizing
• Zinc phosphate

Cadmium is a ductile metal of silver-white color with a bluish tint. Density – 8.6. melting point – 321 °C. The protective properties of cadmium coatings are quite high when exposed to atmosphere or liquid media containing chlorides.

Cadmium plating is the process of applying cadmium coatings to the surface of steel products using the electrolytic deposition method in order to protect them from atmospheric corrosion. The thickness of the coatings is usually 15-25 microns.

Alloying galvanized coatings with nickel helps to increase their corrosion resistance while maintaining their potential with respect to the metal being protected.

Coatings containing ~2% nickel in an atmosphere with constant humidity at 20 ± 5ºС. remain light for a longer time than galvanized ones. The most corrosion-resistant coatings are those containing 25-28% Ni. Such coatings act as a cathode in relation to steel.

Anodizing fasteners in Novosibirsk

• Anodizing colorless
• Anodizing color
• Aluminum anodizing

The popularity of this method is primarily explained by the chemical properties of nickel. It is resistant to corrosion in an aqueous environment, and the nickel oxide NiO, the film of which forms on the surface of the coating, does not allow further oxidation. In addition, this metal is weakly affected by acids, alkalis and salts, with the exception of nitric acid.

Copper is a pink metal. Density 8.92 g/cm3, melting point 1083 °C. Copper in atmospheric conditions reacts with moist air containing sulfur and ammonia compounds, carbon dioxide. It dissolves intensely in nitric and chromic acids, less readily in sulfuric acid and almost does not react with hydrochloric acid.

The most labor-intensive process in electroplating is chrome plating. The preparation of electrolyte is a very responsible undertaking that requires precision and cleanliness. When chrome plating, use the purest water, preferably distilled.

Chrome plating involves working with an electrolyte and is directly dependent on its temperature.

Source: https://novosibirsk.tpkseid.ru/uslugi/

Atmospheric corrosion of iron

As you know, almost any metal is susceptible to corrosion, sooner or later. The danger of this process lies in the variety of factors that provoke it, the speed of development and spread, as well as irreversibility. True, if you use special means in a timely manner, the latter can be prevented and even prevented.

What is atmospheric metal corrosion

Atmospheric corrosion of iron is the process of destruction of metal structures located above the ground and in open spaces as a result of environmental influences.

The main factors that provoke metal rusting are:

• Increased air humidity.
• Frequent and significant precipitation (rain, snow).

Metal also corrodes due to the fact that its surface is not covered with a protective coating. This is especially true for non-alloy steels, cast irons and others.

The speed of this process depends on the nature of the metal and the conditions under which it is kept.

Types of atmospheric corrosion of metals

There are several types of this process in terms of the degree of moisture:

Dry corrosion is of chemical origin and is the process of formation of a thin film of metal oxide. Flows at a humidity of at least 60%. It is characterized by a rapid onset and slow continuation due to the fact that the resulting film performs protective functions.

Wet atmospheric corrosion of iron develops in the presence of constant high air humidity (at least 70%) and water droplets on the metal surface.

The condensate formed (a thin film of water droplets) can be capillary, absorption and chemical. Depending on the type of moisture condensation, the rate of corrosion of iron differs.

Wet corrosion occurs at absolute air humidity. For example, frequent fogs, close proximity to large bodies of water, and so on.

How to stop and prevent metal rusting

To stop the destruction of metal structures, it is necessary to use a special product, for example, a neutral rust converter. This product does not contain acids or harmful volatile impurities, but it contains active components that can quickly convert rust into a protective film. This stops the corrosion process, and if the plaque thickness is insignificant, it allows the metal surface to be restored.

Preventing rust is even easier and more realistic. There are several ways, each of which is effective in its own way:

• Application of protective paint and varnish coatings. Immediately after completing the installation of a metal structure, it must be covered with a layer of paint or varnish, which will prevent the influence of the atmosphere on the iron.
• Treatment with chemical liquids. These are progressive products with a water-repellent effect that protect surfaces from all types of precipitation, as well as gases and ultraviolet radiation. There is a wide range of different acid, alkaline and neutral based products.
• Alloying of metal, that is, the addition of chromium, nickel and other types of metal, which increases the resistance of the finished product to atmospheric conditions and corrosion.

Source: https://syntilor.ru/preobrazovatel-rzhavchiny/atmosfernaya-korroziya-zheleza/

Atmospheric corrosion

:

Types of atmospheric corrosion

Atmospheric corrosion factors

Features of atmospheric corrosion of metals

Atmospheric corrosion equation

Protection of metals and alloys (steel) from atmospheric corrosion

Atmospheric corrosion is the corrosive destruction of structures, equipment, structures operated in the surface part of the atmosphere. Atmospheric corrosion is less destructive than soil and sea corrosion.

The rate of atmospheric corrosion depends on several factors: the nature of the metal, the atmosphere surrounding it, and air humidity.

Types of atmospheric corrosion

Atmospheric corrosion, based on the degree of surface moisture, is usually divided into dry, wet and wet. Wet and wet flow through an electrochemical mechanism, and dry through a chemical mechanism.

Dry atmospheric corrosion occurs when there is no moisture film on the metal surface. If the relative air humidity is 60% or less, dry atmospheric corrosion occurs. The mechanism of corrosion destruction is chemical. Protective oxide films are formed on the surface, which inhibit the corrosion process.

At first the process proceeds quickly (formation of a thin oxide film), then it slows down greatly and a constant, very low corrosion rate is established. This phenomenon is due to the low ambient temperature.

  A thin oxide film forms on the metal almost immediately (maybe a couple of hours), which leads to tarnishing of the surface. The thickness of the oxide film on the surface of stainless steel can be 10–20 Å, on iron – 30–40 Å. The maximum thickness of the moisture layer during dry atmospheric corrosion can be 100 Å.

If there are admixtures of aggressive gases in the atmosphere (for example, sulfur dioxide), the corrosion rate increases significantly.

Wet atmospheric corrosion occurs when there is a thin film of moisture on the surface. The thickness of such a film ranges from 100 Å to 1 μm. The relative air humidity at which the formation of a wet film begins is about 60 - 70%.

The value at which condensation begins on the surface of moisture is called critical humidity. Critical humidity depends on air pollution and the condition of the metal. Moisture condensation occurs by capillary, chemical or adsorption mechanisms.

Capillary condensation of moisture. It is observed in cracks, gaps, cracks on the metal surface, pores in the film of corrosion products, under contamination, etc.

Adsorption condensation of moisture. Occurs as a result of the manifestation of adsorption forces on the metal surface.

Chemical condensation of moisture manifests itself in the interaction of corrosion products with atmospheric moisture. In this case, rust forms, which retains this moisture.

Wet atmospheric corrosion occurs at a relative air humidity of about 100%, when moisture collects on the surface in the form of clearly visible drops, or when the structure is directly exposed to rain or fog. Wet atmospheric corrosion is also observed on structures that are doused with water or completely immersed. With wet corrosion, the moisture film is more than 1 mm thick.

Air humidity during atmospheric corrosion

The presence of moisture on the surface of a metal structure increases atmospheric corrosion. Moisture most often comes in the form of precipitation (rain, fog). As the temperature increases, the relative humidity decreases.

There is a critical value of atmospheric humidity. For each alloy or metal this is a specific number. For nickel, zinc, steel, copper, the critical humidity value is about 50 - 70%.

If the relative humidity of the air falls within the limits mentioned above, then the corrosion destruction of the listed metals is insignificant. If it is higher, increased destruction begins.

In a heavily polluted atmosphere (for example, a technological environment), the concept of critical humidity is not always applied and plays an important role, because the corrosion process is significantly enhanced by harmful impurities in the atmosphere.

Impurities in the atmosphere (gases)

Atmospheric pollution with gases dramatically increases the rate of corrosion.

A very aggressive environment is the technological environment, near large industrial enterprises, which emit harmful impurities into the air every minute. The presence of SO2, SO3, HCl, H2S, Cl2, NH3 and other compounds significantly increases the rate of atmospheric corrosion.

The most interesting and strongest effect is SO2 (sulfur dioxide). Its low concentration (15 – 35 µg/m3) greatly increases the corrosion rate (tens and hundreds of times). At higher concentrations, the rate of atmospheric corrosion does not increase so much (only 5–7 times). This component is formed during the combustion of coal, gasoline, and oil.

Gases entering the moisture film on the surface of a metal structure increase the electrical conductivity of this film. SO2 and Cl2 act as cathodic depolarizers, SO3 and HCl increase the absorption capacity of corrosion products, NH3 acts as a complexing agent, SO2 and HCl are depassivators.

The content of sulfuric acid in the atmosphere greatly increases the rate of corrosion. This especially applies to metals that are unstable in it - iron, nickel, zinc, cadmium. Copper in such cases is more stable because a protective film of its main green sulfate (patina) is formed on its surface.

Particulate matter in the atmosphere

Solid active or passive particles fall from the atmosphere to the surface. They can act as depassivators, complexing agents, increase the electrical conductivity of the moisture film and the absorption capacity (hygroscopicity) of corrosion products, and facilitate capillary condensation of moisture (inert material such as sand).

The atmosphere contains such solid particles as Na2SO4, NaCl, (NH4)2SO4, coal particles, various carbon compounds, metal oxides and others. These substances in the form of solid particles or dust come into contact with the wet surface of the metal structure, form galvanic elements, intensifying the corrosion process.

Therefore, dust-free air is much less active than an atmosphere polluted with various particles.

Cathode inclusions in the atmosphere

Inclusions of copper, palladium, platinum, and some other metals somewhat increase the resistance of iron-carbon alloys to corrosion damage. Copper, which can be part of such alloys, slows down corrosion, because promotes passivation of the iron surface. During atmospheric corrosion, palladium has a similar effect even with very small additions to the alloy.

Geographical factor

In different geographical areas, humidity, air pollution, and temperature vary. Air humidity has the greatest influence on atmospheric corrosion. It has been established that in regions with constantly high humidity, corrosion processes are more intense. The main influence is not the number of rainy days, but the time the moisture film remains on the metal surface.

In deserts, where air humidity is very low, an oxide film appears on the surface of steel products after a fairly long period of time, and the products remain shiny for a long time.

Ambient temperature

As the ambient temperature increases, the process of atmospheric corrosion slows down. The moisture covering the surface of the metal product evaporates, and the absolute humidity of the air decreases. As the temperature drops, the opposite happens. The relative humidity of the environment increases, which promotes moisture condensation. The rate of atmospheric corrosion increases.

Features of atmospheric corrosion of metals

The metal surface is covered with a thin film of electrolyte. The electrolyte can be either moisture itself or corrosion products that have absorbed moisture.

A feature of atmospheric corrosion is the possibility of free access of oxygen to the corroding surface. This is due to the small thickness of the film and due to convection mixing of the electrolyte. That is why, even in acidified electrolytes, atmospheric corrosion occurs with oxygen depolarization.

Also, due to the thin layer of moisture on the surface of the corroding metal, the anodic process is difficult, while the cathodic process, on the contrary, is facilitated.

When galvanic couples operate, the small thickness of the moisture film also plays a role - the ohmic resistance of the electrolyte increases.

Atmospheric corrosion of alloys based on iron (for example, steel) occurs under anodic-taco-ohmic control. But depending on certain conditions (thickness, electrical conductivity of the moisture film, its composition, nature of the metal), anodic-taco-ohmic control can turn into predominantly anodic, predominantly cathodic or ohmic.

Atmospheric corrosion equation:

Anode: metal ions go into solution:

Мe→ Мen+ + ne

Cathode: reduction reaction takes place:

O2 + 2H2O + 4e → 4OH- (alkaline, neutral media)

O2 + 4H+ + 4e → 2H2O (acidified medium)

In many ways, the resistance of metals and alloys under conditions of atmospheric corrosion depends on the nature of the metal and the condition of its surface.

Protection of metals and alloys (steel) from atmospheric corrosion

Many different methods are used to protect against atmospheric corrosion.

Application of metallic or non-metallic coatings. Non-metallic protective coatings can be various lubricants, pastes, and paints. Often, inhibitors and pigments that passivate the surface are additionally introduced into their composition (for example, zinc chromate pigment for steel). Sometimes the surface is converted into a sparingly soluble oxide or phosphate that has protective properties. Metal coatings include zinc, nickel, and multilayer.

Decrease in relative air humidity. A very effective way to protect metal from corrosion. Moisture is removed by heating the room (heating) or dehumidifying the air. Very often it is enough to maintain atmospheric humidity to 50%. If the air contains pilus and other impurities, then 50% humidity is very high.

When the air dries or the temperature rises, it becomes more difficult for moisture to condense on the metal, which leads to a significant reduction in the corrosion rate.

The use of contact and volatile (vapor-phase) inhibitors. Contact corrosion inhibitors are applied to the surface of the product in the form of aqueous solutions. An example of a contact inhibitor of atmospheric corrosion is NaNO2.

Volatile inhibitors have high vapor pressure and are used for long-term storage of steel or other metal products and transportation.

Volatile corrosion inhibitors are used to fill a sealed space (protecting the inside of the pipe, at the ends of which there are special plugs) or to impregnate wrapping materials (paper).

Special granules can be impregnated with volatile inhibitors, which fill the packaging volume of the protected product. Examples of volatile inhibitors: carbonates, nitrites, monoethanolamine and dicyclohexylamine benzoates.

Alloying of metals. Adding a small amount of nickel, chromium, aluminum, titanium to steel (transfers the steel surface to a passive state), copper (cathode additive), and phosphorus inhibits the anodic reaction.

Source: https://www.okorrozii.com/atmosfernayakorrozia.html

Environmental problems of the fuel industry: coal, gas, oil and peat

The fuel industry is a set of industrial sectors engaged in the extraction of natural fuel resources, their transformation, transportation, distribution and consumption. The group includes coal, gas, oil and peat industries. The fuel and energy complex is one of the main sources of environmental contamination.

Main environmental problems of the fuel industry

According to official data, the bulk of the most negative environmental consequences affecting the natural environment occur in oil refineries, gas enterprises, as well as the coal and peat industries.

Coal industry

The world's coal resources occupy 15% of the earth's landmass, they are located in the coal basins of 75 countries and amount to about 14.8 trillion tons. Coal mining is carried out by open-pit (open-pit) method, using adits (inclined wells) and in mines, including underwater ones.

The open-pit method of coal mining affects the following components of the natural environment:

1. Land (it is being withdrawn).
2. Soil (pollution with sludge, flushing liquids, fuels and lubricants; reduction in soil fertility due to the accumulation of dust from quarries and dumps; disruption of physical properties during reclamation work).
3. Vegetation (destruction of trees, shrubs, death of grass, oppression of plants due to soil and atmospheric pollution).
4. Ichthyofauna (increased acidity of surface waters).
5. Groundwater (decrease in level, formation of depression funnel).
6. Surface water (pollution from drainage from mine workings, drainage from waste rock dumps).
7. Atmospheric air (emissions of dust and gases during explosions, drilling operations, transportation by vehicles, loading and unloading operations).

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Underground excavation affects the following components:

1. Surface water (pollution with fine coal and rock particles, bacteria, surfactants and dissolved chemicals as a result of mine water discharge; increased salinity and sulfate content).
2. Groundwater (impact of aquifer drainage).
3. Groundwater (pollution).
4. Geological environment (formation of underground mined-out space).
5. Alienation of land (industrial site).
6. Atmospheric air (gas and dust mine emissions - dust, carbon dioxide, methane, release of harmful gases and smoke during spontaneous combustion of waste heaps).

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Coal combustion in thermal power plants, which is the most dangerous process from an environmental point of view, affects soil, surface water and air. The main pollutants include:

• carbon dioxide;
• nitrogen and sulfur oxides;
• ash;
• uranium, arsenic, molybdenum;
• titanium, cobalt, iodine, mercury;
• strontium, zirconium, lithium and other elements.

The operation of coal-fired thermal power plants also affects thermal pollution of the environment. About 10% of the heat escapes into the atmosphere. The discharge of warm wastewater has a beneficial effect on the reproduction of heat-loving organisms, which contributes to a change in the species composition of the aquatic sphere.

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Gas industry

The world's natural gas reserves are concentrated in 16 countries, most of which (56%) are located in the depths of Qatar, Iran and Russia. Gas is extracted from wells.

Gas production technologies involve the use of up to 85 toxic substances, including:

• thickeners and thinners;
• chemical reagents to destroy aquatic bacteria;
• clay stabilizers;
• corrosion and deposit inhibitors;
• demulsifiers;
• friction reducers.

Shale gas production has a negative impact on the following:

1. Surface water (extraction requires the use of a significant amount of water resources, and pollution occurs with chemicals).
2. Groundwater (use of a large number of chemical compounds during the process of hydraulic fracturing of an underground formation that releases natural gas).
3. Groundwater (contamination with arsenic, ethylbenzene, benzene, toluene).
4. Soils (chemical spills, contamination with heavy metals - lead, cadmium, mercury).
5. Vegetation (when the aquifer drops below the shale reserve level, surrounding forests and arable lands are affected).
6. Atmospheric air (pollution with dust and gases).
7. Geological environment (increased seismicity of the territory).
8. Background radiation (increased).

When natural gas is consumed, the atmosphere becomes smoky, acid rain forms, and cloudiness changes, which increases the greenhouse effect.

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Oil industry

The distribution of oil fields, of which there are more than 50 thousand, is uneven on the planet. The largest (94% of all reserves) are concentrated in the countries of the Near and Middle East, the CIS, and Venezuela. Oil, like gas, is extracted from wells.

The stages of development and development of oil fields are accompanied by environmental problems:

• seismic surveys affect aquatic organisms and cause interference with fishing;
• During exploratory drilling, bottom landscapes are disturbed , water and air are polluted, and water areas are alienated;
• installation of drilling platforms, construction of onshore structures, and laying of pipelines are accompanied by physical disturbances and the discharge of liquid and solid waste.

The land-based method of oil production affects the following environmental components:

1. Surface water (pollution factors - grouting and drilling waste fluids, associated waters).
2. Groundwater (hydrogeological conditions change - water exchange increases, water mixes, new aquifers form, gas and chemical compositions, temperature, movement speed, water slope change).
3. Soils (loss of humus, deterioration of biological activity, ion exchange, chemical, water-physical properties, pollution with oil products and toxic salts).
4. Flora (physiological processes are disrupted, poisoning occurs with toxic components of oil, oppression, changes in the rhythm of development; in case of death of vegetation, restoration occurs after 2-3 years).
5. Fauna (reduction in the number of arthropods).
6. Atmospheric air (thermal pollution and changes in the chemical composition of air; emissions of compounds of combustion products - heavy metals, nitrogen and carbon oxides, hydrocarbons, mercury, benzopyrene, phenols, carbon monoxide, formaldehyde).
7. Land acquisition (territory is allocated for wells and other needs).
8. Geological environment (deformation of the earth's surface, increased seismicity).
9. Radiation background (increase due to the entry of substances from great depths).

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Thermal erosion and thermokarst develop along oil pipeline routes. Tanker transportation of oil causes bioinvasion (the penetration of living organisms beyond the boundaries of their natural space). As a result of drilling wastewater entering water bodies, the color, odor and transparency of the water change and the binding of oxygen dissolved in natural water by chemical reagents occurs.

Water pollution is also affected by the underwater method of resource extraction, losses during oil transportation, accidents at offshore oil refineries, and discharges of industrial wastewater. Heavy fractions of petroleum products are deposited at the bottom of the reservoir, while light fractions dissolve in water. An oil film forms on the surface of the water, which contributes to changes in physical and chemical processes, deterioration of gas exchange, and an increase in the temperature of the surface layer of water.

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When petroleum products are burned, the following pollutants are released into the atmosphere:

• dust;
• oxides of carbon and nitrogen;
• hydrocarbons;
• phenol;
• sulfur dioxide;
• hydrogen sulfide.

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For a long time, the compounds are in the form of aerosols, then they enter the ground, polluting the soil and water.

Peat industry

Peatlands occupy 3% of the earth's land and are found in 175 countries. The top five are: Russia, Indonesia, America, Canada, Finland. Peat extraction is carried out by open-pit mining.

The development of peat deposits destroys the swamp ecosystem and affects the air and water basins, soil, vegetation, and wildlife. Main consequences of influence:

• changes in natural landscapes;
• violation of the hydrological regime;
• decrease in productivity of adjacent lands;
• depletion, clogging and pollution of water bodies;
• depletion of fauna and flora;
• change in the direction of soil-forming processes.

The drainage of peat deposits has the greatest impact on the environment. When swamps are drained, vegetation is destroyed, groundwater levels drop, and the water regime and natural biosphere functions inherent in swamps are disrupted.

The combustion of peat consumes large amounts of oxygen and releases carbon dioxide, which harms the atmosphere.

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During long-term storage, peat can undergo spontaneous combustion, which leads to fires over large areas and, accordingly, deterioration of the natural environment and a negative impact on human health.

Source: https://greenologia.ru/eko-problemy/toplivnuy-promyshlennost.html

The main patterns of atmospheric corrosion - electronic catalog of products, development of mobile applications, AOS, automated training systems, seminars on oil and gas topics, development of STU, STU

Atmospheric corrosion is the most common type of metal corrosion that occurs in a humid air environment: approximately 80% of metal structures, buildings, structures, bridges, machines, etc. operated in atmospheric conditions. A distinctive feature of atmospheric corrosion is that it does not occur in the bulk of the electrolyte, but in thin films. In this case, the corrosion process proceeds according to the laws of electrochemical kinetics, but has its own specific features.

The main factors influencing the rate of atmospheric corrosion are:

• atmospheric humidity;
• chemical composition of the atmosphere;
• the duration of periods of wetting and drying of moisture films.

Rice. 1. Main corrosive hazardous impurities in the atmosphere

Let us consider in more detail the mechanism of influence of the above factors on the intensity of corrosion destruction.

Atmospheric humidity

The air always contains some amount of water vapor. Air humidity is usually described numerically by the following factors:

• absolute humidity (amount of steam), g/m3;
• water vapor pressure, atm (Pa);
• relative humidity, (φ), calculated as (P/Psat)·100%, where P is the pressure of water vapor in the air; Psac is the pressure of saturated water vapor at a given temperature.

According to air humidity indicators, atmospheric corrosion can be classified as follows:

• dry atmospheric corrosion;
• wet atmospheric corrosion;
• wet atmospheric corrosion.

Dry atmospheric corrosion occurs in very thin films (up to 10 nm) at an air humidity of 30-50% and is characterized by surface oxidation of the metal by a chemical mechanism with the formation of corresponding oxides (the phenomenon of “tarnishing” of the metal). As a rule, it does not lead to serious corrosion damage.

Wet atmospheric corrosion usually begins at relative air humidity above 70%. At this humidity, called critical, capillary condensation of moisture occurs and water begins to exhibit the properties of an electrolyte.

Capillary condensation can be stimulated by surface roughness, various irregularities, metal contamination with solid particles (dust), etc.

The thickness of the moisture films formed on the metal ranges from 0.01 to 1 microns and under these conditions a very intense supply of oxygen occurs to the metal surface, which leads to an acceleration of the corrosion process compared to the volume of the electrolyte. The mechanism of the wet atmospheric corrosion process is shown in Fig. 2.

Rice. 2. Wet atmospheric corrosion

The critical humidity may decrease due to the presence of contaminants (natural or anthropogenic) on the metal surface, which attract moisture from the air.

For example, particles of ammonium salts adsorbed on a steel surface significantly reduce the critical humidity from 70-80% to 50% (see Fig. 3).

Also, the critical humidity is reduced by corrosion products formed on the metal surface (especially steel corrosion products), which ultimately leads to the acceleration of corrosion processes.

Rice. 3. The influence of contaminants on capillary condensation of moisture on the metal surface

Wet atmospheric corrosion occurs when the thickness of the moisture film on the metal surface is from 1 to 1000 microns. The corrosion process slows down somewhat compared to wet atmospheric corrosion due to the difficulty of oxygen diffusion to the metal surface and is more similar to ordinary electrochemical corrosion.

Chemical composition of the atmosphere

The corrosive aggressiveness of the atmosphere is determined not only by humidity, but also by various chemicals: solid and gaseous. The air contains various gases of biogenic, natural and anthropogenic origin (SO2, SO3, NO2, N2O3, N2O5, H2S, Cl2, etc.), as well as particles of solids (chlorides, sulfates, silicates, dust particles, etc.) (Fig. . 1).

All these substances can dissolve in films of condensed moisture, increasing its corrosiveness. The most corrosive gases are SO2 and SO3, which form aerosols of sulfurous and sulfuric acids with water vapor in the atmosphere.

In general, the classification of corrosive aggressiveness of atmospheric media is given in the following standards:

• ISO 9223: “Corrosion of metals and alloys. Corrosive activity of the atmosphere. Classification";
• ISO 12944: “Varnishes and paints. Protection of steel structures from corrosion using protective paint systems.”

Duration of periods of wetting and drying of moisture films

Structures in an open atmosphere are exposed to precipitation, aggressive gases, aerosols and other factors.

The total duration of presence of a film of moisture on a metal surface is determined as the total duration of rain and dew, exposure to fog and thaws in winter, as well as the duration of drying of the surface.

When the moisture film thickness is more than 30 microns (wet corrosion), the rate of the corrosion process is determined by the rate of moisture evaporation, time and frequency of rewetting. The rate of evaporation depends, in turn, on relative humidity φ, temperature, and air exchange rate.

It should be noted that metal wetting processes can reduce the overall rate of atmospheric metal corrosion by washing away corrosive adsorption films and cleaning the metal surface from dust and solid salts.

Download our specialized training and reference application “Corrosion Protection”

Source: http://transenergostroy.ru/blog/osnovnye_zakonomernosti_protekaniya_atmosfernoy_korrozii.html