The development of the steel industry is inextricably linked with the search for ways and means to prevent the destruction of metal products. Protection against corrosion and the development of new techniques is a continuous process in the technological chain of production of metal and products made from it. Iron-containing products become unusable under the influence of various physical and chemical external environmental factors. We see these consequences in the form of hydrated iron residues, that is, rust.

Methods for protecting metals from corrosion are selected depending on the operating conditions of the products. Therefore it stands out:

• Corrosion associated with atmospheric phenomena. This is a destructive process of oxygen or hydrogen depolarization of a metal. Which leads to the destruction of the crystalline molecular lattice under the influence of a humid air environment and other aggressive factors and impurities (temperature, the presence of chemical impurities, etc.).
• Corrosion in water, primarily sea water. In it, the process goes faster due to the content of salts and microorganisms.
• Destruction processes that occur in the soil. Soil corrosion is a rather complex form of metal damage. Much depends on the composition of the soil, humidity, heating and other factors. In addition, products, for example, pipelines, are buried deep in the ground, which makes diagnostics difficult. And corrosion often affects individual parts pointwise or in the form of ulcerative veins.

Types of corrosion protection are selected individually, depending on the environment in which the metal product being protected will be located.

Typical types of rust damage

Methods for protecting steel and alloys depend not only on the type of corrosion, but also on the type of destruction:

• Rust covers the surface of the product in a continuous layer or in separate areas.
• It appears in the form of spots and penetrates pointwise into the depths of the part.
• Destroys the metal molecular lattice in the form of a deep crack.
• In a steel product consisting of alloys, destruction of one of the metals occurs.
• Deeper extensive rusting, when not only the surface is gradually damaged, but also penetration occurs into the deeper layers of the structure.

The types of damage can be combined. Sometimes they are difficult to determine immediately, especially when point destruction of steel occurs. Corrosion protection methods include special diagnostics to determine the extent of damage.

They produce chemical corrosion without generating electrical currents. Upon contact with petroleum products, alcohol solutions and other aggressive ingredients, a chemical reaction occurs, accompanied by gas emissions and high temperature.

Galvanic corrosion is when a metal surface comes into contact with an electrolyte, specifically water from the environment. In this case, diffusion of metals occurs. Under the influence of the electrolyte, an electric current arises, the replacement and movement of electrons of the metals that are included in the alloy occurs. The structure is destroyed and rust forms.

Steelmaking and its corrosion protection are two sides of the same coin. Corrosion causes enormous damage to industrial and commercial buildings. In cases with large-scale technical structures, for example, bridges, power poles, barrier structures, it can also provoke man-made disasters.

Metal corrosion and methods of protection against it

How to protect metal? There are many corrosion methods for metals and ways to protect against it. To protect metal from rust, industrial methods are used. In everyday life, various silicone enamels, varnishes, paints, and polymer materials are used.

Industrial

Protection of iron from corrosion can be divided into several main areas. Methods of protection against corrosion:

• Passivation. When producing steel, other metals are added (chromium, nickel, molybdenum, niobium and others). They are distinguished by increased quality characteristics, refractoriness, resistance to aggressive environments, etc. As a result, an oxide film is formed. These types of steel are called alloyed.

• Surface coating with other metals. Various methods are used to protect metals from corrosion: electroplating, immersion in a molten composition, application to the surface using special equipment. As a result, a metal protective film is formed. Chromium, nickel, cobalt, aluminum and others are most often used for these purposes. Alloys (bronze, brass) are also used.

• The use of metal anodes, protectors, often made of magnesium alloys, zinc or aluminum. As a result of contact with the electrolyte (water), an electrochemical reaction begins. The protector breaks down and forms a protective film on the surface of the steel. This technique has proven itself well for underwater parts of ships and offshore drilling rigs.

• Acid etching inhibitors. The use of substances that reduce the level of environmental impact on metal. They are used for preservation and storage of products. And also in the oil refining industry.

• Corrosion and protection of metals, bimetals (cladding). This is coating steel with a layer of another metal or a composite composition. Under the influence of pressure and high temperatures, diffusion and bonding of surfaces occurs. For example, well-known heating radiators made of bimetal.

Metal corrosion and methods of protection against it used in industrial production are quite diverse, such as chemical protection, glass enamel coating, and enameled products. Steel is hardened at high temperatures, over 1000 degrees.

On video: galvanizing metal as protection against corrosion.

Household

Protecting metals from corrosion at home is, first of all, chemicals for the production of paints and varnishes. The protective properties of the compositions are achieved by combining various components: silicone resins, polymer materials, inhibitors, metal powder and shavings.

To protect the surface from rust, it is necessary to use special primers or a rust converter before painting, especially old structures.

What types of converters are there:

• Primers - provide adhesion, adhesion to metal, level the surface before painting. Most of them contain inhibitors that significantly slow down the corrosion process. Preliminary application of a primer layer can significantly save paint.
• Chemical compounds - convert iron oxide into other compounds. They are not subject to rust. They are called stabilizers.
• Compounds that convert rust into salts.
• Resins and oils that bind and seal rust, thereby neutralizing it.

These products contain components that slow down the process of rust formation as much as possible. Converters are included in the product line of manufacturers producing metal paints. They vary in consistency.

It is better to choose primer and paint from the same company so that they match the chemical composition. You must first decide which methods you will choose to apply the composition.

Protective paints for metal

Metal paints are divided into heat-resistant, which can be used at high temperatures, and for normal temperatures up to eighty degrees. The following main types of metal paints are used: alkyd, acrylic, epoxy paints. There are special anti-corrosion paints. They are two- or three-component. They are mixed immediately before use.

Advantages of paintwork for metal surfaces:

• protect surfaces well from temperature changes and atmospheric fluctuations;
• can be applied quite easily in different ways (brush, roller, spray gun);
• most of them are quick-drying;
• wide range of colors;
• long service life.

Of the inexpensive means available, you can use ordinary silverware. It contains aluminum powder, which creates a protective film on the surface.

Two-component epoxy compounds are suitable for protecting metal surfaces that are subject to increased mechanical stress, in particular the underbody of cars.

Metal protection at home

Corrosion and methods of protecting against it at home require compliance with a certain sequence:

1. Before applying a primer or rust converter, the surface is thoroughly cleaned of dirt, oil stains, and rust. Use metal brushes or special attachments for grinders.

2. Then apply a primer layer, allow it to soak in and dry.

Protecting metals from corrosion is a complex process. It begins at the stage of steel smelting. It is difficult to list all the methods for combating rust, since they are constantly being improved, not only in industry, but also for domestic use. Manufacturers of paint and varnish products are constantly improving their compositions, increasing their corrosion properties. All this significantly extends the service life of metal structures and steel products.

Corrosion protection system: how and why?

The disadvantage of such a material as metal is that corrosion can occur on it. Today there are several methods, they need to be used in combination. The corrosion protection system will help get rid of rust and prevent the formation of layers.

Treating a metal surface with a special coating is an effective method. The metal coating increases the hardness and strength of the material and improves the mechanical properties. It should be borne in mind that in this case additional protection will be required. Non-metallic coating is applied to ceramics, rubber, plastic, wood.

Methods of protection against corrosion

Film-forming coatings are most often used; they are resistant to the external environment. A film forms on the surface, which inhibits corrosion processes.

In order to reduce corrosive activity, it is necessary to neutralize the environment exposed to its influence. Inhibitors will help you with this; they are introduced into an aggressive environment, and a film is formed that inhibits processes and changes the chemical parameters of the metal.

Alloying is widely used; it increases properties that help increase the resistance of the material to corrosion processes. Alloy steel contains a lot of chromium; it forms films that protect the metal.

It would be a good idea to use protective films. Anodic coatings are used for zinc and chromium, cathodic coatings are used for tin, nickel, and copper. They are applied using the hot method, and galvanization can also be used. The product must be placed in a container containing the protective metal in a molten state.

By using metallization, corrosion can be avoided. The surface is covered with metal, which is in a molten state, and it is sprayed with air. The advantage of this method is that it can be used to cover ready-made and fully assembled structures. The downside is that the surface will be a little rough. Such coatings are applied by diffusion into the base metal.

The coating can be protected with an oxide film, this procedure is called oxidation. The oxide film that exists on the metal is treated with a powerful oxidizing agent, as a result of which it becomes several times stronger.

Phosphating is also used in industry. Iron salts are immersed in a hot phosphate solution, eventually forming a surface film.

For temporary surface protection, it is necessary to use ethinol, technical petroleum jelly, and inhibitors. The latter slow down the reaction, resulting in corrosion developing much more slowly.

Preface

The goals, basic principles and basic procedure for carrying out work on interstate standardization are established by GOST 1.0-92 “Interstate standardization system. Basic provisions" and GOST 1.2-97 "Interstate standardization system. Interstate standards, rules and recommendations for interstate standardization. Procedure for development, adoption, application, updating and cancellation"

Standard information

1. DEVELOPED by the Technical Committee for Standardization TC 214 “Protection of Products and Materials from Corrosion” (State Unitary Enterprise of the Order of the Red Banner of Labor Academy of Public Utilities named after K.D. Pamfilov, State Unitary Enterprise VNII of Railway Transport, FSUE “VNII Standard”)

2. INTRODUCED by the Federal Agency for Technical Regulation and Metrology

3. ADOPTED by the Interstate Council for Standardization, Metrology and Certification (Minutes No. 27 of June 22, 2005)

4. This standard takes into account the main normative provisions of ISO/IEC Guide 21:1999 “Adoption of international standards as regional or national standards”.

(ISO/IEC Guide 21:1999 “Regional or national adoption of international standards deliverables”)

5. By Order of the Federal Agency for Technical Regulation and Metrology dated October 25, 2005 No. 262-st, the interstate standard GOST 9.602-2005 was put into effect directly as a national standard of the Russian Federation from January 1, 2007.

6. INSTEAD GOST 9.602-89

Information on the entry into force (termination) of this standard and amendments to it is published in the “National Standards” index.

Information about changes to this standard is published in the “National Standards” index, and the text of the changes is published in the “National Standards” information indexes. In case of revision or cancellation of this standard, the relevant information will be published in the information index “National Standards”

Introduction

Underground metal pipelines, cables and other structures are one of the most capital-intensive industries in the economy. The livelihoods of cities and towns depend on their normal, uninterrupted functioning.

The greatest influence on the operating conditions and service life of underground metal structures is exerted by the corrosive and biocorrosive aggressiveness of the environment, as well as stray direct currents, the source of which is electrified rail transport, and alternating currents of industrial frequency.

The impact of each of these factors, and especially their combination, can reduce the service life of steel underground structures several times and lead to the need for premature relaying of obsolete pipelines and cables.

The only possible way to combat this negative phenomenon is the timely application of measures for anti-corrosion protection of steel underground structures.

This standard takes into account the latest scientific and technical developments and achievements in the practice of anti-corrosion protection accumulated by operational, construction and design organizations.

This standard establishes corrosion hazard criteria and methods for their determination; requirements for protective coatings, their quality standards for different operating conditions of underground structures (adhesion of insulation to the pipe surface, adhesion between layers of coatings, resistance to cracking, resistance to impact, resistance to UV radiation, etc.) and methods for assessing the quality of coatings; requirements for electrochemical protection are regulated, as well as methods for monitoring the effectiveness of anti-corrosion protection.

The implementation of this standard will increase the service life and operational reliability of underground metal structures, reduce the costs of their operation and major repairs.

Date of introduction - 2007-01-01

Application area

This standard establishes general requirements for corrosion protection of the outer surface of underground metal structures (hereinafter referred to as structures): pipelines and tanks (including trench type) made of carbon and low-alloy steels, power cables with voltage up to 10 kV inclusive; communication and signaling cables in a metal sheath, steel structures of unattended reinforcement (NUP) and regeneration (NRP) points of communication lines, as well as requirements for objects that are sources of stray currents, including electrified rail transport, DC transmission lines using the “wire” system -earth", industrial enterprises consuming direct current for technological purposes.

The standard does not apply to the following structures: communication cables with a hose-type protective cover; reinforced concrete and cast iron structures; communications laid in tunnels, buildings and sewers; piles, sheet piles, columns and other similar metal structures; main pipelines transporting natural gas, oil, petroleum products, and branches from them; pipelines of compressor, pumping and pumping stations, oil depots and head structures of oil and gas fields; installations for complex gas and oil treatment; heating network pipelines with polyurethane foam thermal insulation and a shell pipe made of rigid polyethylene (pipe-in-pipe design), having a functioning system for operational remote monitoring of the condition of pipeline insulation; metal structures located in permafrost soils.

GOST 9.048-89 Unified system of protection against corrosion and aging. Technical products. Laboratory test methods for resistance to mold fungi

GOST 9.049-91 Unified system of protection against corrosion and aging. Polymer materials and their components. Laboratory test methods for resistance to mold fungi

GOST 12.0.004-90 System of occupational safety standards. Organization of occupational safety training. General provisions

GOST 12.1.003-83 System of occupational safety standards. Noise. General safety requirements

GOST 12.1.005-88 System of occupational safety standards. General sanitary and hygienic requirements for the air in the working area

GOST 12.2.004-75 System of occupational safety standards. Special machines and mechanisms for pipeline construction. Safety requirements

GOST 12.3.005-75 System of occupational safety standards. Painting works. General safety requirements

GOST 12.3.008-75 System of occupational safety standards. Production of metallic and non-metallic inorganic coatings. General safety requirements

GOST 12.3.016-87 System of occupational safety standards. Construction. Anti-corrosion works. Safety requirements

GOST 12.4.026-76 1) System of occupational safety standards. Signal colors and safety signs

GOST 112-78 Meteorological glass thermometers. Specifications

GOST 411-77 Rubber and glue. Methods for determining the bond strength with metal during peeling

GOST 427-75 Metal measuring rulers. Specifications

GOST 1050-88 Calibrated rolled products with special surface finishing from high-quality carbon structural steel. General technical conditions

GOST 2583-92 Batteries made of cylindrical manganese-zinc cells with salt electrolyte. Specifications

GOST 2678-94 Rolled roofing and waterproofing materials. Test methods

GOST 2768-84 Technical acetone. Specifications

GOST 4166-76 Sodium sulfate. Specifications

GOST 4650-80 Plastics. Methods for determining water absorption

GOST 5180-84 Soils. Methods for laboratory determination of physical characteristics.

GOST 5378-88 Protractors with vernier. Specifications

GOST 6055-86 2) Water. Unit of hardness

GOST 6323-79 Wires with polyvinyl chloride insulation for electrical installations. Specifications

GOST 6456-82 Sanding paper. Specifications

GOST 6709-72 Distilled water. Technical conditions.

GOST 7006-72 Protective cable covers. Design and types, technical requirements and test methods

GOST 8711-93 (IEC51-2-84) Analogue indicating electrical measuring devices of direct action and auxiliary parts for them. Part 2. Special requirements for ammeters and voltmeters

GOST 9812-74 Petroleum insulating bitumens. Specifications

GOST 11262-80 Plastics. Tensile test method.

GOST 12026-76 Laboratory filter paper. Specifications

GOST 13518-68 Plastics. Method for determining the resistance of polyethylene to stress cracking.

GOST 14236-81 Polymer films. Tensile test method.

GOST 14261-77 Hydrochloric acid of special purity. Technical conditions.

GOST 15140-78 Paint and varnish materials. Methods for determining adhesion.

GOST 16337-77 High pressure polyethylene. Specifications

GOST 16783-71 Plastics. Method for determining the brittleness temperature when squeezing a sample folded in a loop

GOST 22261-94 Instruments for measuring electrical and magnetic quantities. General technical conditions

GOST 25812-83 3) Main steel pipelines. General requirements for corrosion protection

GOST 29227-91 (ISO 835-1-81) Laboratory glassware. Graduated pipettes. Part 1. General requirements.

Note: When using this standard, it is advisable to check the validity of the reference standards using the “National Standards” index, compiled as of January 1 of the current year, and according to the corresponding information indexes published in the current year. If the reference standard is replaced (changed), then when using this standard you should be guided by the replaced (changed) standard. If the reference standard is canceled without replacement, then the provision in which a reference is made to it is applied in the part that does not affect this reference.

1) In the Russian Federation, GOST R 12.4.026-2001 “System of occupational safety standards” is in force. Signal colors, safety signs and signal markings. Purpose and rules of use. General technical requirements and characteristics. Test methods".

2) In the Russian Federation, GOST R 52029-2003 “Water. Unit of hardness."

3) In the Russian Federation, GOST R 51164-98 “Main steel pipelines” is in force. General requirements for corrosion protection."

General provisions

3.1. The requirements of this standard are taken into account when designing, constructing, reconstructing, repairing, and operating underground structures, as well as objects that are sources of stray currents. This standard is the basis for the development of regulatory documents (ND) for the protection of specific types of underground metal structures and measures to limit stray currents (leakage currents).

3.2. Means of protection against corrosion (materials and design of coatings, cathodic protection stations, instruments for monitoring the quality of insulating coatings and determining the danger of corrosion and the effectiveness of anti-corrosion protection) are used only in accordance with the requirements of this standard and having a certificate of conformity.

3.3. When developing a project for the construction of structures, a project for protecting them from corrosion is simultaneously developed.

Note: For signaling, centralization and interlocking (SCB), power and communication cables used on the railway, when it is not possible to determine the parameters of electrochemical protection at the project development stage, working drawings of electrochemical protection can be developed after laying the cables based on measurement data and trial activation of protective devices within the time limits established by the ND.

3.4. Measures to protect against corrosion of structures under construction, operating and reconstructed are provided for in protection projects in accordance with the requirements of this standard.

In construction and reconstruction projects of structures that are sources of stray currents, measures are taken to limit leakage currents.

3.5. All types of corrosion protection provided for by the construction project are accepted for use before the structures are put into operation. During the construction process for underground steel gas pipelines and liquefied gas tanks, electrochemical protection is put into effect in zones of dangerous influence of stray currents no later than one month, and in other cases - no later than six months after laying the structure in the ground; for communication structures - no later than six months after they are laid in the ground.

It is not allowed to commission objects that are sources of stray currents until all the measures provided for by the project to limit these currents have been carried out.

3.6. The protection of structures from corrosion is carried out in such a way as not to impair protection from electromagnetic influences and lightning strikes.

3.7. During the operation of structures, the effectiveness of anti-corrosion protection and the risk of corrosion is systematically monitored, as well as the causes of corrosion damage are recorded and analyzed.

3.8. Work to repair failed electrochemical protection installations is classified as an emergency.

3.9. The structures are equipped with control and measuring points (CPS).

To monitor the corrosion state of communication cables laid in cable ducts, inspection devices (wells) are used.

Corrosion Hazard Criteria

4.1. The criteria for the danger of corrosion of structures are:

Corrosive aggressiveness of the environment (soil, ground and other waters) in relation to the metal of the structure (including biocorrosive aggressiveness of soils);

Dangerous effects of stray direct and alternating currents.

4.2. To assess the corrosive aggressiveness of the soil in relation to steel, determine the electrical resistivity of the soil, measured in field and laboratory conditions, and the average cathode current density at a potential displacement of 100 mV negative than the stationary potential of the steel in the soil (Table 1). If, when determining one of the indicators, a high corrosive aggressiveness of the soil is established (and for reclamation structures - average), then the other indicator is not determined.

Methods for determining soil electrical resistivity and average cathode current density are given in Appendices A and B, respectively.

Notes

1. If the electrical resistivity of the soil, measured in laboratory conditions, is equal to or more than 130 Ohm m, the corrosive aggressiveness of the soil is considered low and is not assessed based on the average cathode current density z K.

2. The corrosive aggressiveness of the soil in relation to the steel armor of communication cables and steel structures of the NUP is assessed only by the electrical resistivity of the soil, determined in the field (see Table 1).

3. The corrosive aggressiveness of the soil in relation to the steel of pipes of ductless heating networks is assessed by the electrical resistivity of the soil, determined in field and laboratory conditions (see Table 1).

4. For heating network pipelines laid in channels, thermal chambers, inspection wells, etc., the corrosion hazard criterion is the presence of water or soil in the channels (thermal chambers, inspection wells, etc.) when the water or soil reaches thermal insulation structure or pipeline surface.

Table 1

table 2

Table 3

Table 4

Table 5

Requirements for protective coatings and quality control methods

6.1. The designs of highly reinforced and reinforced types of protective coatings used to protect steel underground pipelines, except for heat pipelines, are given in Table 6; coating requirements are in tables 7 and 8, respectively.

It is allowed to use other designs of protective coatings that ensure compliance with the requirements of this standard.

6.2. During the construction of pipelines, welded pipe joints, shaped elements (hydraulic seals, condensate collectors, elbows, etc.) and places where the protective coating is damaged are insulated under route conditions with the same materials as the pipelines, or with others whose protective properties meet the requirements given in Table 7 , not inferior to the coating of the linear part of the pipe and having adhesion to the coating of the linear part of the pipeline.

6.3. When repairing operating pipelines, it is allowed to use coatings similar to those previously applied to the pipeline, as well as those based on heat-shrinkable materials, polymer-bitumen, polymer-asmol and adhesive polymer tapes, except for polyvinyl chloride.

Note: To insulate joints and repair damaged areas of pipelines with mastic bitumen coatings, the use of polyethylene tapes is not allowed.

6.4. For steel tanks installed in the ground or embanked with soil, protective coatings of a very reinforced design type No. 5 and 7 according to Table 6 are used.

Table 6

Table 7

Requirements for highly reinforced coatings

Table 8

Requirements for reinforced coatings

6.5. The thickness of protective coatings is controlled by non-destructive testing using thickness gauges and other measuring instruments:

In basic and factory conditions for two-layer and three-layer polymer coatings based on extruded polyethylene, polypropylene; combined based on polyethylene tape and extruded polyethylene; strip polymer and mastic coatings - on every tenth pipe of one batch at least in four points around the circumference of the pipe and in places that raise doubts;

In route conditions for mastic coatings - on 10% of welded joints of pipes, insulated manually, at four points around the circumference of the pipe;

On tanks for mastic coatings - at one point on each square meter of surface, and in places where insulating coatings are kinked - every 1 m along the circumference,

6.6. The adhesion of protective coatings to steel is controlled using adhesimeters:

In basic and factory conditions - every 100m or on every tenth pipe in a batch;

In route conditions - on 10% of welded joints of pipes insulated manually;

On tanks - at least two points around the circumference,

For mastic coatings, it is allowed to determine adhesion by cutting out an equilateral triangle with a side length of at least 4.0 cm, followed by peeling the coating from the top of the cut angle. Adhesion is considered satisfactory if, when new coatings are peeled off, more than 50% of the area of ​​the peeled mastic remains on the pipe metal. The coating damaged during the adhesion test is repaired in accordance with the ND.

6.7. The continuity of pipe coatings after completion of the insulation process in basic and factory conditions is controlled over the entire surface with a spark flaw detector at a voltage of 4.0 or 5.0 kV per 1 mm of coating thickness (depending on the coating material), and for silicate-enamel - 2 kV per 1 mm of thickness, as well as on the route before lowering the pipeline into the trench and after insulating the tanks.

6.8. Defective areas, as well as through damage to the protective coating, identified during testing of its quality, are corrected before backfilling the pipeline. During repairs, ensure uniformity, solidity and continuity of the protective coating; After correction, the repaired areas are subject to secondary inspection.

6.9. After backfilling the pipeline, the protective coating is checked for the absence of external damage that would cause direct electrical contact between the pipe metal and the ground, using instruments to detect locations of insulation damage.

6.10. To protect pipelines of heating networks from external corrosion, protective coatings are used, the designs and conditions of use of which are given in Appendix P.

Requirements for electrochemical protection

7.1. Requirements for electrochemical protection in the absence of the dangerous influence of direct stray and alternating currents

7.1.1. Cathodic polarization of structures (except for pipelines transporting media heated above 20 °C) is carried out in such a way that the polarization potentials of the metal relative to the saturated copper-sulfate reference electrode are between the minimum and maximum (in absolute value) values ​​in accordance with Table 9.

Polarization potentials are measured in accordance with Appendix P.

Table 9

Requirements for electrochemical protection in the presence of the dangerous influence of direct stray currents

7.2.1. Protection of structures from the dangerous influence of direct stray currents is carried out in such a way as to ensure the absence of anode and alternating zones on the structure.

The total duration of positive potential displacements relative to the stationary potential is allowed to be no more than 4 minutes per day.

Determination of potential displacements (the difference between the measured potential of the structure and the stationary potential) is carried out in accordance with Appendix D.

Electrochemical protection of metal structures from corrosion is based on the imposition of a negative potential on the protected product. It demonstrates a high level of efficiency in cases where metal structures are subject to active electrochemical destruction.

1 The essence of anti-corrosion electrochemical protection

Any metal structure begins to deteriorate over time as a result of corrosion. For this reason, before use, metal surfaces are necessarily coated with special compounds consisting of various inorganic and organic elements. Such materials reliably protect the metal from oxidation (rusting) for a certain period. But after some time they need to be updated (new compounds applied).

Then, when the protective layer cannot be renewed, corrosion protection of pipelines, car bodies and other structures is carried out using electrochemical techniques. It is indispensable for protecting against rusting tanks and containers operating underground, the bottoms of sea ships, various underground communications, when the corrosion potential (it is called free) is in the zone of repassivation of the base metal of the product or its active dissolution.

The essence of electrochemical protection is that a direct electric current is connected from the outside to a metal structure, which forms cathode-type polarization of microgalvanic couple electrodes on the surface of the metal structure. As a result, the transformation of anodic regions into cathodic ones is observed on the metal surface. After such a transformation, the negative influence of the environment is perceived by the anode, and not the material itself from which the protected product is made.

Electrochemical protection can be either cathodic or anodic. With cathodic potential, the metal potential shifts to the negative side, and with anodic potential, it shifts to positive.

2 Cathodic electrical protection - how does it work?

The mechanism of the process, if you understand it, is quite simple. A metal immersed in an electrolytic solution is a system with a large number of electrons, which includes spatially separated cathode and anode zones, electrically closed to each other. This state of affairs is due to the heterogeneous electrochemical structure of metal products (for example, underground pipelines). Corrosion manifestations form on the anodic areas of the metal due to its ionization.

When a material with a high potential (negative) is added to the base metal located in the electrolyte, the formation of a common cathode is observed due to the process of polarization of the cathode and anodic zones. By high potential we mean a value that exceeds the potential of the anodic reaction. In the formed galvanic couple, a material with a low electrode potential dissolves, which leads to the suspension of corrosion (since the ions of the protected metal product cannot enter the solution).

The electric current required to protect the car body, underground tanks and pipelines, and the bottoms of ships can come from an external source, and not just from the functioning of a microgalvanic couple. In such a situation, the protected structure is connected to the “minus” of the electric current source. The anode, made of materials with a low degree of solubility, is connected to the “plus” of the system.

If the current is obtained only from galvanic couples, we speak of a process with sacrificial anodes. And when using current from an external source, we are talking about protecting pipelines, parts of vehicles and water vehicles with the help of superimposed current. The use of any of these schemes provides high-quality protection of the object from general corrosive decay and from a number of its special variants (selective, pitting, cracking, intergranular, contact types of corrosion).

3 How does the anodic technique work?

This electrochemical technique for protecting metals from corrosion is used for structures made of:

• carbon steels;
• passivating dissimilar materials;
• highly alloyed and;
• titanium alloys.

The anode scheme involves shifting the potential of the protected steel in a positive direction. Moreover, this process continues until the system enters a stable passive state. Such corrosion protection is possible in environments that are good conductors of electrical current. The advantage of the anodic technique is that it significantly slows down the rate of oxidation of the protected surfaces.

In addition, such protection can be carried out by saturating the corrosive environment with special oxidizing components (nitrates, dichromates and others). In this case, its mechanism is approximately identical to the traditional method of anodic polarization of metals. Oxidizers significantly increase the effect of the cathodic process on the steel surface, but they usually negatively affect the environment by releasing aggressive elements into it.

Anodic protection is used less frequently than cathodic protection, since many specific requirements are put forward for the protected object (for example, impeccable quality of welds of pipelines or a car body, constant presence of electrodes in the solution, etc.). In anode technology, cathodes are placed according to a strictly defined scheme, which takes into account all the features of the metal structure.

For the anodic technique, poorly soluble elements are used (cathodes are made from them) - platinum, nickel, stainless high-alloy alloys, lead, tantalum. The installation itself for such corrosion protection consists of the following components:

• protected structure;
• current source;
• cathode;
• special reference electrode.

It is allowed to use anodic protection for containers where mineral fertilizers, ammonia compounds, sulfuric acid are stored, for cylindrical installations and heat exchangers operated at chemical plants, for tanks in which chemical nickel plating is performed.

4 Features of tread protection for steel and metal

A fairly frequently used option for cathodic protection is the technology of using special protector materials. With this technique, an electronegative metal is connected to the structure. Over a given period of time, corrosion affects the protector, and not the protected object. After the protector is destroyed to a certain level, a new “defender” is installed in its place.

Protective electrochemical protection is recommended for treating objects located in soil, air, water (that is, in chemically neutral environments). Moreover, it will be effective only when there is some transition resistance between the medium and the protector material (its value varies, but in any case it is small).

In practice, protectors are used when it is economically infeasible or physically impossible to supply the required charge of electric current to an object made of steel or metal. It is worth separately noting the fact that protective materials are characterized by a certain radius over which their positive effect extends. For this reason, you should correctly calculate the distance to remove them from the metal structure.

Popular protectors:

• Magnesium. They are used in environments with a pH of 9.5–10.5 units (soil, fresh and slightly salted water). They are made from magnesium-based alloys with additional alloying with aluminum (no more than 6–7%) and zinc (up to 5%). For the environment, such protectors that protect objects from corrosion are potentially unsafe due to the fact that they can cause cracking and hydrogen embrittlement of metal products.
• Zinc. These “protectors” are indispensable for structures operating in water with a high salt content. There is no point in using them in other environments, since hydroxides and oxides appear on their surface in the form of a thick film. Zinc-based protectors contain minor (up to 0.5%) additives of iron, lead, cadmium, aluminum and some other chemical elements.
• Aluminum. They are used in sea running water and at objects located on the coastal shelf. Aluminum protectors contain magnesium (about 5%) and zinc (about 8%), as well as very small amounts of thallium, cadmium, silicon, and indium.

In addition, iron protectors are sometimes used, which are made from iron without any additives or from ordinary carbon steels.

5 How is the cathode circuit performed?

Temperature changes and ultraviolet rays cause serious damage to all external components and components of vehicles. Protecting the car body and some of its other elements from corrosion by electrochemical methods is recognized as a very effective way to prolong the ideal appearance of the car.

The principle of operation of such protection is no different from the scheme described above. When protecting a car body from rusting, the function of an anode can be performed by almost any surface that is capable of efficiently conducting electric current (wet road surfaces, metal plates, steel structures). The cathode in this case is the vehicle body itself.

Elementary methods of electrochemical protection of a car body:

1. We connect the body of the garage in which the car is parked through the mounting wire and an additional resistor to the battery positive. This protection against corrosion of the car body is especially effective in the summer, when the greenhouse effect is present in the garage. This effect precisely protects the external parts of the car from oxidation.
2. We install a special grounding metalized rubber “tail” in the rear of the vehicle so that drops of moisture fall on it while driving in rainy weather. At high humidity, a potential difference is formed between the highway and the car body, which protects the outer parts of the vehicle from oxidation.

The car body is also protected using protectors. They are mounted on the thresholds of the car, on the bottom, under the wings. The protectors in this case are small plates made of platinum, magnetite, carboxyl, graphite (anodes that do not deteriorate over time), as well as aluminum and “stainless steel” (they should be replaced every few years).

6 Nuances of anti-corrosion protection of pipelines

Pipe systems are currently protected using drainage and cathodic electrochemical techniques. When protecting pipelines from corrosion using the cathodic scheme, the following are used:

• External current sources. Their plus will be connected to the anode grounding, and the minus to the pipe itself.
• Protective anodes using current from galvanic pairs.

The cathodic technique involves the polarization of the protected steel surface. In this case, underground pipelines are connected to the “minus” of the cathodic protection complex (in fact, it is a current source). “Plus” is connected to the additional external electrode using a special cable, which is made of conductive rubber or graphite. This circuit allows you to obtain a closed-type electrical circuit, which includes the following components:

• electrode (external);
• electrolyte located in the soil where the pipelines are laid;
• pipes directly;
• cable (cathode);
• current source;
• cable (anode).

For tread protection of pipelines, materials based on aluminum, magnesium and zinc are used, the efficiency of which is 90% when using protectors based on aluminum and zinc and 50% for protectors made of magnesium alloys and pure magnesium.

For drainage protection of pipe systems, technology is used to drain stray currents into the ground. There are four options for drainage piping - polarized, earthen, reinforced and straight. With direct and polarized drainage, jumpers are placed between the “minus” of stray currents and the pipe. For the earth protection circuit, it is necessary to make grounding using additional electrodes. And with increased drainage of pipe systems, a converter is added to the circuit, which is necessary to increase the magnitude of the drainage current.

INTERSTATE STANDARD

Unified system of protection against corrosion and aging

METALS AND ALLOYS

Determination methods
corrosion indicators
and corrosion resistance

GOST 9.908-85

MOSCOW
IPC PUBLISHING HOUSE OF STANDARDS
1999

INTERSTATE STANDARD

Date of introduction 01.01.87

This standard establishes the main indicators of corrosion and corrosion resistance (chemical resistance) of metals and alloys for continuous, pitting, intergranular, exfoliating corrosion, spot corrosion, stress-corrosion cracking, corrosion fatigue and methods for their determination. Indicators of corrosion and corrosion resistance are used in corrosion research, testing, inspection of equipment and defect detection of products during production, operation, and storage.

1. INDICATORS OF CORROSION AND CORROSION RESISTANCE

Diagram of the dependence of the corrosion effect (integral indicator) at from time

1.6. It is allowed to use, along with the indicators given in the table, other quantitative indicators determined by operational requirements, the high sensitivity of experimental methods or the possibility of using them for remote monitoring of the corrosion process, with a preliminary establishment of the relationship between the main and applied indicators. As such indicators of corrosion, taking into account its type and mechanism, the following can be used: the amount of hydrogen released and (or) absorbed by the metal, the amount of reduced (absorbed) oxygen, an increase in the mass of the sample (while maintaining solid corrosion products on it), a change in the concentration of corrosion products in environment (with their complete or partial solubility), an increase in electrical resistance, a decrease in reflectivity, heat transfer coefficient, a change in acoustic emission, internal friction, etc. For electrochemical corrosion, the use of electrochemical indicators of corrosion and corrosion resistance is allowed. For crevice and contact corrosion, corrosion and corrosion resistance indicators are selected from the table in accordance with the type of corrosion (solid or pitting) in the crevice (gap) or contact area. 1.7. For one type of corrosion, it is possible to characterize the results of corrosion tests using several corrosion indicators. If there are two or more types of corrosion on one sample (product), each type of corrosion is characterized by its own indicators. Corrosion resistance in this case is assessed by an indicator that determines the performance of the system. 1.8. If it is impossible or impractical to determine quantitative indicators of corrosion resistance, it is allowed to use qualitative indicators, for example, changes in the appearance of the metal surface. In this case, the presence of tarnish is visually determined; corrosion damage, the presence and nature of the layer of corrosion products; the presence or absence of an undesirable change in the environment, etc. Based on the qualitative indicator of corrosion resistance, an assessment is made of the type: resistant - not resistant; pass - fail, etc. Changes in appearance can be assessed using conventional scales, for example, for electronic products according to GOST 27597. 1.9. Acceptable indicators of corrosion and corrosion resistance are established in the regulatory and technical documentation for the material, product, equipment.

2. DETERMINATION OF CORROSION INDICATORS

Where m 0 - mass of the sample before testing, kg; m 1 - mass of the sample after testing and removal of corrosion products, kg; S- surface area of ​​the sample, m2. 2.1.2. When hard-to-remove solid corrosion products are formed or their removal is impractical, a quantitative assessment of continuous corrosion is carried out by increasing mass. The increase in mass per unit surface area is calculated from the difference in mass of the sample before and after testing, per unit surface area of ​​the sample. To calculate the loss of metal mass from an increase in the mass of the sample, it is necessary to know the composition of the corrosion products. This indicator of metal corrosion in gases at high temperatures is determined according to GOST 6130. 2.1.3. Corrosion products are removed according to GOST 9.907. 2.1.4. The change in dimensions is determined by direct measurements of the difference between the dimensions of the sample before and after testing and removal of corrosion products. If necessary, change the dimensions according to mass loss taking into account the geometry of the sample, for example, change the thickness of a flat sample D L, m, is calculated using the formula

Where D m- mass loss per unit area, kg/m2; ρ - metal density, kg/m3. 2.2. Spot corrosion 2.2.1. The area of ​​each spot is determined with a planimeter. If such a measurement is not possible, the spot is outlined with a rectangle and its area is calculated. 2.2.2. The degree of damage to the metal surface by corrosion stains ( G) as a percentage is calculated using the formula

Where S i- square i-that spot, m 2; n - number of spots; S - surface area of ​​the sample, m2. In case of spot corrosion, it is allowed to determine the degree of surface damage by corrosion using a grid of squares. 2.3. Pitting corrosion 2.3.1. The maximum depth of penetration of pitting corrosion is determined by: measuring with a mechanical indicator with a movable needle probe the distance between the mouth plane and the bottom of the pit after removing corrosion products in cases where the dimensions of the pit allow free penetration of the needle probe to its bottom; microscopically, after removing corrosion products by measuring the distance between the mouth plane and the bottom of the pitting (double focusing method); microscopically on a transverse section with appropriate magnification; sequential mechanical removal of metal layers of a given thickness, for example, 0.01 mm at a time until the last pitting disappears. Pittings with an opening diameter of at least 10 µm are taken into account. The total working surface area must be at least 0.005 m2. 2.3.2. A thin section to measure the maximum depth of penetration of pitting corrosion is cut out from the area where the largest pittings are located on the working surface. The cutting line should pass through as many of these pittings as possible. 2.3.3. The maximum depth of penetration of pitting corrosion is found as the arithmetic mean of measurements of the deepest pittings depending on their number ( n) on the surface: at n < 10 измеряют 1-2 питтинга, при n < 20 - 3-4, при n> 20 - 5. 2.3.4. For penetrating pitting corrosion, the thickness of the sample is taken as the maximum penetration depth. 2.3.5. The maximum diameter of the pitting is determined using measuring instruments or optical means. 2.3.6. The degree of damage to a metal surface by pitting is expressed as the percentage of the surface area occupied by pitting. If there are a large number of pittings with a diameter of more than 1 mm, it is recommended to determine the degree of damage according to clause 2.2. 2.4. Intergranular corrosion 2.4.1. The depth of intergranular corrosion is determined by the metallographic method according to GOST 1778 on an etched section made in the transverse plane of the sample, at a distance from the edges of at least 5 mm with a magnification of 50 ´ or more. It is allowed to determine the penetration depth of corrosion of aluminum and aluminum alloys using unetched sections. Etching mode - according to GOST 6032, GOST 9.021 and NTD. (Changed edition, Amendment No. 1). 2.4.2. Changes in mechanical properties during intergranular corrosion - tensile strength, relative elongation, impact strength - are determined by comparing the properties of metal samples that were and were not subject to corrosion. The mechanical properties of metal samples that have not been subjected to corrosion are taken as 100%. 2.4.3. Samples are prepared according to GOST 1497 and GOST 11701 when determining tensile strength and relative elongation, and according to GOST 9454 when determining impact strength. 2.4.4. It is allowed to use physical methods to control the depth of corrosion penetration in accordance with GOST 6032. 2.5. Stress-corrosion cracking and corrosion fatigue 2.5.1. In case of corrosion cracking and corrosion fatigue, cracks are detected visually or using optical or other flaw detection means. It is possible to use indirect measurement methods, for example, determining the increase in the electrical resistance of the sample. 2.5.2. The change in mechanical properties is determined according to clause 2.4.2. 2.6. Exfoliation corrosion 2.6.1. The degree of surface damage during exfoliating corrosion is expressed as a percentage of the area with peeling on each surface of the sample according to GOST 9.904. 2.6.2. The total length of the ends with cracks for each sample ( L) as a percentage is calculated using the formula

Where L i- length of the end section affected by cracks, m; P- sample perimeter, m. 2.6.3. It is allowed to use a conditional scale score according to GOST 9.904 as a generalized semi-quantitative (score) indicator of exfoliation corrosion.

3. DETERMINATION OF CORROSION RESISTANCE INDICATORS

Where tm- time until the mass per unit area decreases by the permissible value D m, year; v m- rate of mass loss, kg/m 2 ∙year; t 1 - time of penetration to the permissible (specified) depth ( l), year; v 1 - linear corrosion rate, m/year. 3.1.3. When continuous corrosion occurs at an inconsistent rate, corrosion resistance indicators are determined according to clause 1.5. 3.1.4. If there are special requirements for the optical, electrical and other properties of the metal, its corrosion resistance is assessed by the time it takes for these properties to change to an acceptable (specified) level. 3.2. Spot corrosion An indicator of corrosion resistance for spot corrosion is time (t n) achieving an acceptable degree of surface damage. t value n determined graphically according to clause 1.5. 3.3. Pitting corrosion 3.3.1. The main indicator of corrosion resistance against pitting corrosion is the absence of pitting or the minimum time (t pit) for pitting to penetrate to the permissible (specified) depth. t pit is determined graphically from the dependence of the maximum pitting depth l max from time. 3.3.2. An indicator of resistance to pitting corrosion can also be the time it takes to reach the permissible degree of damage to the surface by pitting. 3.4. Intergranular corrosion 3.4.1. Indicators of corrosion resistance against intergranular corrosion are generally determined graphically or analytically from the time dependence of the penetration depth or mechanical properties in accordance with clause 1.5. 3.4.2. A qualitative assessment of resistance to intergranular corrosion of the type of struts - not struts based on accelerated tests of corrosion-resistant alloys and steel is established according to GOST 6032, aluminum alloys - according to GOST 9.021. 3.5. Corrosion cracking 3.5.1. Quantitative indicators of resistance to corrosion cracking are determined for high-strength steels and alloys according to GOST 9.903, for aluminum and magnesium alloys - according to GOST 9.019, welded joints of steel, copper and titanium alloys - according to GOST 26294-84. 3.6. Exfoliation corrosion 3.6.1. Indicators of resistance to exfoliation corrosion for aluminum and its alloys are determined according to GOST 9.904, for other materials - according to NTD.

4. PROCESSING RESULTS

ANNEX 1

Mandatory

METALLOGRAPHIC METHOD FOR ASSESSING CORROSION DAMAGES

1. Essence of the method

The method is based on determining the type of corrosion, the form of corrosion damage, the distribution of corrosion damage in metals, alloys and protective metal coatings (hereinafter referred to as materials) by comparison with the corresponding standard forms, as well as measuring the depth of corrosion damage on a metallographic section.

2. Samples

2.1. The location for taking samples from the test material is selected based on the results of a visual (with the naked eye or using a magnifying glass) inspection of the surface or non-destructive flaw detection. 2.2. Samples are cut from the following places of the material: 1) if only part of the surface of the material is affected by corrosion, samples are taken in three places: from the part affected by corrosion; from the part not affected by corrosion and in the area between them; 2) if there are areas of the surface of the material with different types of corrosion or with different depths of corrosion damage, samples are taken from all areas affected by corrosion; 3) if there is one type of corrosion damage on the surface of the material, samples are taken from at least three characteristic areas of the material under study. 2.3. If necessary, at least one sample is taken from at least five functionally necessary areas of the test material. The sample size is determined based on the size of the corrosion zone. 2.4. The samples are cut so that the plane of the section is perpendicular to the surface under study. The manufacturing method should not affect the structure of the material and destroy the surface layer and edges of the sample. For materials with protective coatings, damage to the coating and its separation from the base material is not allowed. 2.5. Sample marking - according to GOST 9.905. 2.6. When making a metallographic section, all traces of cutting, for example, burrs, are removed from the surface of the sample. 2.7. During grinding and polishing operations, it is necessary to ensure that the nature and size of the corrosion damage does not change. The edges of the polished section at the site of corrosion damage should not be rounded. Roundings are allowed that do not affect the accuracy of determining corrosion damage. To do this, it is recommended to pour the sample into the casting compound in such a way that the edge being examined is at a distance of at least 10 mm from the edge of the section. Polishing is carried out briefly using diamond pastes. 2.8. The section is assessed before and after etching. Etching makes it possible to distinguish between corrosion damage and the structure of the material. When etching, the nature and size of the corrosion lesion should not be changed.

3. Carrying out the test

3.1. Determination and assessment of the type of corrosion, the form of corrosion damage and its distribution in the material 3.1.1. When conducting the test, it is necessary to take into account the chemical composition of the material being tested, the method of its processing, as well as all corrosive factors. 3.1.2. The test is carried out on a metallographic section under a microscope at a magnification of 50, 100, 500 and 1000´. 3.1.3. When determining the type of corrosion, corrosion control is carried out along the entire length of the section. It is possible to determine several types of corrosion on one sample. 3.1.4. When testing protective coatings, the type of corrosion of the coating and the base material is determined separately. 3.1.5. If the material, in addition to the corrosive environment, is affected by other factors that influence the change in the structure of the material, for example, high temperature, mechanical stress, corrosion damage is determined by comparing the material with a specific sample exposed to similar factors, but protected from the effects of a corrosive environment. 3.1.6. Assessment of the form of corrosion damage and determination of the type of corrosion is carried out by comparison with typical schemes of corrosion damage according to Appendix 2, distribution of corrosion damage in the material - according to Appendix 3. 3.2. Measuring the depth of corrosion damage 3.2.1. The depth of corrosion damage is determined on a micrometallographic section using an ocular scale and a micrometer screw of a microscope. 3.2.2. The depth of corrosion damage is determined by the difference in the thickness of the metal of the corroded section of the surface of the polished section and the surface area without corrosion or by measuring the depth of damage from a surface that is not damaged or slightly damaged by corrosion. When testing a material with a protective coating, the results of measuring the depth of corrosion damage to the coating and the base metal are determined separately. 3.2.3. If the entire surface of the sample is affected by corrosion and the depth of corrosion damage in different areas of the surface does not differ noticeably, for example in the case of intergranular or transgranular corrosion, the depth of corrosion damage is measured in at least 10 areas of the surface. For large samples, measurements are taken in at least 10 areas for every 20 mm of the length of the controlled surface, taking into account the deepest lesions. 3.2.4. In case of local corrosion damage (for example, pitting corrosion or stain corrosion), measurements are carried out in the places of this corrosion damage, and the number of areas for measurements may differ from the requirements given in paragraph. 3.2.3. 3.2.5. To clarify the determination of the maximum depth of corrosion damage, after a metallographic assessment of the sections, they are re-polished: 1) for samples with local corrosion damage, for example, stain corrosion or pitting corrosion - to the maximum depth of corrosion damage, i.e. until the moment when the measured depth is less than the previous measurement result; 2) for samples with almost the same depth of corrosion damage in different areas of the surface, after evaluation, they are re-polished and a new metallographic section is made, on which the corrosion damage is again assessed. 3.2.6. The error in measuring the depth of corrosion damage is no more than ±10%.

4. Test report - according to GOST 9.905

APPENDIX 2

Mandatory

TYPES OF CORROSION

APPENDIX 3

Mandatory

DISTRIBUTION OF CORROSION

INFORMATION DATA