Anti-corrosion coatings for heating network pipelines and pipeline elements. Anti-corrosion coating of steel pipes

Long-term operation of steel pipelines is effectively ensured by anti-corrosion protection of gas pipelines. Its implementation has been professionally carried out by specialists from the ATEKS-M company for many years. Our clients are completely satisfied high quality works and low cost of providing services.

Types of pipeline corrosion

The main raw material for the production of gas pipelines is steel. This material is characterized by strength and durability, but without additional protective treatment it is quickly destroyed by corrosion.
There are 3 main types of corrosion:

• 1. Chemical. Occurs when steel interacts with gases and liquids in the soil. Her distinctive feature is a uniform effect on the surface of the pipes.
• 2. Electrochemical. Occurs when the pipeline comes into contact with solutions of aggressive chemical compounds. The pipe is the electrode and the solution is the electrolyte.
• 3. Electric. It influences the gas main through electric currents wandering in the soil.

Methods to combat pipeline corrosion

To combat pipe corrosion, active and passive methods are used.
Active methods of protection include:

• 1. Electrochemical drainage. It is performed by diverting electric current from the pipe. To do this, use an insulated conductor connected to the negative bus of the substation.
• 2. Cathodic protection of main gas pipelines. This is achieved by connecting the pipe to the negative pole of an external current source.
• 3. Tread protection main gas pipelines. It consists in excluding contact of the gas pipeline with stray currents. The effect is achieved by using insulating flange connections when installing the main line.

Passive methods of anti-corrosion protection of gas pipelines involve applying special insulating coatings. These include:

• paints and varnishes;
• galvanic coatings (zinc or aluminum).

The application of a protective galvanic coating is carried out during the manufacture of pipes at metallurgical plants.
Paint and varnish materials are applied directly when laying the pipeline. The choice of a specific product depends on:

• on the method of laying pipes (above-ground or underground);
• climatic conditions in a given area;
• chemical composition soils in the region.

At ATEKS-M you can always order and buy the necessary protective equipment in sufficient quantities. Our catalog contains several effective coatings.

List of works on passive anti-corrosion protection of pipelines

The complex of protective works includes 2 stages of measures:

Pipeline preparation

It is produced by abrasive blast cleaning of pipe surfaces. For this purpose, special equipment is used - a powerful compressor. Particles of sand or other abrasive material bombard the pipeline section at high speed, removing from it:

• remnants of the old protective coating;
• traces of scale and rust;
• oil and grease contamination.

After abrasive blasting, the surface of the pipe becomes rough. Remains of abrasive materials and dust are removed powerful flow air from industrial vacuum cleaners. This ensures maximum adhesion (fixation) of the paintwork.
Monitoring of the implementation of preparatory measures is carried out by visual inspection of the pipeline and using a special device (comparator or profilometer) for measuring roughness.

Application of paints and varnishes

The paints and varnishes used for processing pipelines are one- or two-component. They are applied in a thin (1-3 mm) layer using special units (installations) for airless application. These materials are sold by specialized companies.
Mandatory conditions for performing work:

• 1. The surface of the pipes must be dry.
• 2. Air temperature - more than 5° C.
• 3. Air humidity - no more than 80%.

The quality of painting work is checked by specially trained inspectors using special measuring instruments:

• adhesion meter;
• flaw detector;
• thickness gauge.

Advantages of hiring ATEKS-M specialists to combat pipeline corrosion

The service for anti-corrosion treatment of gas pipelines, provided by specialists of the ATEKS-M company, is constantly in demand among customers, since:

• 1. The cleaning products and paints we use are highly reliable.
• 2. The craftsmen performing the work have extensive practical experience and bear personal responsibility for the result.
• 3. Under the terms of the contract, you receive real long-term guarantees for all work performed.

Contact the ATEKS-M company for high-quality services for anti-corrosion treatment of gas pipelines! Our prices are low, our guarantees are long-lasting, and the quality of our work is first-class.

In industry and public utilities, water is predominantly used as a working fluid. This is due to its availability and low cost. During circulation through the pipeline and through equipment components, deposits and corrosion occur. As a result, there is a drop in efficiency technological process and the wear rate of structural elements increases. Anti-corrosion protection of pipelines is achieved by introducing special substances into the transported liquid - inhibitors that slow down oxidative processes.

Action of inhibitors

Special compounds entering a corrosive environment (or into a pipeline in in this case) in sufficient concentration, can slow down or completely stop the destruction of metal structures and pipes. The active substance can be a single component or a mixture of several compounds. To stop the reaction with the metal, 0.001-2% (the exact concentration is determined in each individual case) of the total volume of liquid is sufficient.

Pipes used to transport water, petroleum products, liquid food or chemical raw materials are constantly exposed to temperature changes and aggressive chemical environments. Until the 90s of the last century, the industry used compounds based on zinc, chlorine and amines for anti-corrosion protection of pipelines. They did a good job of slowing down oxidative processes, but were no longer used due to high toxicity. The alternative was more environmentally friendly organic matter, phosphates and silicates. The result of them long-term use are salt deposits on the internal cavity of the pipeline. Most traditional inhibitors do not cope with the problem in the case of incomplete immersion of the metal in a liquid medium.

Methods of anti-corrosion protection of pipes

On this moment The most current method of protection is the use of special corrosion inhibitors. Scientific developments and many years of testing carried out by the Spectroplast company have led to the mass production of a new generation inhibitor - "SP-V". The concentrate "SP-V" is introduced into a liquid medium or applied to a surface in a certain concentration and performs the following functions:

Anti-corrosion protection of the metal surface of pipes during storage (preservation). Application of an active liquid - inhibitor to the internal or external part of pipes during their alignment, storage or transportation open method allows you to protect the metal from the corrosive effects of negative factors external environment. During the restoration process there is no need to wash off "SP-V". In most cases, it is permissible to apply a paint layer directly onto the surface treated with the inhibitor.

When testing and repairing a pipeline, preliminary addition of a protective agent will effectively stop the corrosion process. This method is relevant during process startup, flushing, or simply after draining the circulating fluid. The metal will not be destroyed even in the presence of residual moisture without thorough preliminary drying.

Anti-corrosion protection of pipelines by slowing down corrosion processes and the formation of hardness salts and reducing the aggressiveness of water vapor. The introduction of "SP-V" helps stabilize heat transfer, prevent the formation of insoluble deposits, thereby extending the service life of the pipeline and adjacent equipment. High environmental friendliness solution makes it possible to use it not only in technical environments, but also in housing and communal services and food production.

As a result of the tests and analysis of the destructive effect of water on various types of metals, it was possible to prove the effectiveness of anti-corrosion protection of pipes using the "SP-V" concentrate. The inhibitor is active both in hot and cold cold water at temperatures from 0 to 95 o C. The substance has passed all the necessary tests and has a certificate. According to the sanitary epidemiological conclusion, it is non-toxic and safe for the environment; use in food production is permitted.

Transportation of oil, gas and petroleum products through pipelines is the most efficient and safe way to transport them over long distances. This method of delivering oil and gas from their production areas to consumers has been used for more than 100 years. The durability and trouble-free operation of pipelines directly depends on the effectiveness of their anti-corrosion protection. To minimize the risk of corrosion damage, pipelines are protected with anti-corrosion coatings and additionally with electrochemical protection (ECP). At the same time, insulating coatings provide primary (“passive”) protection of pipelines from corrosion, performing the function of a “diffusion barrier” through which access to the metal of corrosive agents (water, air oxygen) is difficult. If defects appear in the coating, a system is provided cathodic protection pipelines - “active” protection against corrosion.

In order for a protective coating to effectively perform its functions, it must satisfy a number of requirements, the main of which are: low moisture-oxygen permeability, high mechanical characteristics, high and time-stable adhesion of the coating to steel, resistance to cathodic disbonding, good dielectric characteristics, stability coatings to UV and thermal aging. Insulating coatings must perform their functions in a wide range of temperatures during construction and operation of pipelines, ensuring their protection against corrosion for the longest possible period of their operation.

The history of the use of protective coatings for pipelines goes back more than 100 years, but still not all issues in this area have been successfully resolved. On the one hand, the quality of protective coatings for pipelines is constantly improving; almost every 10 years, new insulating materials, new technologies and equipment for applying coatings to pipes in factory and highway conditions appear. On the other hand, the conditions for the construction and operation of pipelines are becoming increasingly stringent (construction of pipelines in the Far North, in Western Siberia, development of offshore oil and gas fields, deep-sea laying, construction of pipeline sections using the methods of “directional drilling”, “microtunneling”, operation of pipelines at temperatures up to 100 ° C and above, etc.).

Let's consider the main types of modern anti-corrosion coatings for pipelines, factory-applied and in-line, their advantages, disadvantages, and scope of application.

Anti-corrosion coatings for pipelines applied along the route

To insulate pipelines under route conditions, three types of protective coatings are currently most widely used:
a) bitumen-mastic coatings;
b) polymer tape coatings;
c) combined mastic-tape coatings (Plastobit type coatings).

Bitumen-mastic coatings

For many decades, bitumen-mastic coating has been the main type of external protective coating for domestic pipelines. The advantages of bitumen-mastic coatings include their low cost, extensive experience in application, sufficient simple technology application in factory and on-site conditions. Bituminous coatings are permeable to electrical protection currents and work well in conjunction with electrochemical protection. In accordance with the requirements of GOST R 51164-98 "Main steel pipelines. General requirements for corrosion protection," the design of a bitumen-mastic coating consists of a layer of bitumen or bitumen-polymer primer (a solution of bitumen in gasoline), two or three layers of bitumen mastic, between which contains reinforcing material (fiberglass or fiberglass mesh) and an outer layer of protective wrapping. Previously, bitumen-rubber-based wrapping materials such as “Brizol”, “Gidroizol”, etc. or kraft paper were used as protective wrapping. Currently, they mainly use polymer protective coatings with a thickness of at least 0.5 mm, a bitumen or bitumen-polymer primer, a layer of bitumen or bitumen-polymer mastic, a layer of reinforcing material (fiberglass or fiberglass mesh), a second layer of insulating mastic, a second layer of reinforcing material, outer layer of protective polymer wrap. The total thickness of the reinforced type bitumen-mastic coating is at least 6.0 mm, and for a normal type of route coating - at least 4.0 mm.

The following are used as insulating mastics for applying bitumen-mastic coatings: bitumen-rubber mastics, bitumen-polymer mastics (with additions of polyethylene, atactic polypropylene), bitumen mastics with additives of thermoplastic elastomers, mastics based on asphalt-resin compounds such as "Asmol". In recent years, a number of new generation bitumen mastics have appeared with improved properties.

The main disadvantages of bitumen-mastic coatings are: narrow temperature range of application (from minus 10 to plus 40 ° C), insufficiently high impact strength and resistance to punching, increased moisture saturation and low biostability of coatings. The service life of bitumen coatings is limited and, as a rule, does not exceed 10-15 years. The recommended area of ​​application of bitumen-mastic coatings is protection against corrosion of pipelines of small and medium diameters operating at normal operating temperatures. In accordance with the requirements of GOST R 51164-98, the use of bitumen coatings is limited to pipeline diameters of no more than 820 mm and operating temperatures no higher than plus 40 °C.

Polymer tape coatings

Polymer tape coatings began to be used abroad in the early 60s. last century. In our country, the peak of the use of polymer tape coatings occurred in the 70-80s, during the construction of an entire network of long gas pipelines. To date, the share of polymer tape coatings on Russian gas pipelines accounts for up to 60-65% of their total length.

The design of the polymer tape coating for route application in accordance with GOST R 51164-98 consists of a layer of adhesive primer, 1 layer of polymer insulating tape with a thickness of at least 0.6 mm and 1 layer of protective polymer wrap with a thickness of at least 0.6 mm. The total thickness of the coating is at least 1.2 mm.

When factory insulating pipes, the number of layers of insulating tape and wrapping increases. In this case, the total thickness of the coating should be: at least 1.2 mm - for pipes with a diameter up to 273 mm, at least 1.8 mm - for pipes with a diameter up to 530 mm and at least 2.4 mm - for pipes with a diameter up to 820 mm inclusive .

Starting from July 1, 1999, after the introduction of GOST R 51164-98, the use of adhesive polymer tapes for route insulation of gas pipelines is limited to pipe diameters not exceeding 820 mm and operating temperatures not exceeding plus 40 ° C. For oil and petroleum product pipelines, it is allowed to use tape coatings for route application when insulating pipes with a diameter of up to 1420 mm, but the total thickness of the coating must be at least 1.8 mm (2 layers of polymer tape and 1 layer of protective wrap are applied).

In the polymer tape coating system, the functions of the insulating tape and the protective wrap are different. The insulating tape ensures adhesion of the coating to steel (at least 2 kg/cm width), resistance to cathodic peeling, and performs the functions protective barrier, preventing the penetration of water, soil electrolyte, oxygen, i.e., to the surface of the pipes. corrosive agents. The protective wrap serves mainly to increase the mechanical and impact strength of the coating. It protects the tape covering from damage when laying the pipeline in a trench and filling it with soil, as well as during soil shrinkage and technological movements of the pipeline.

Polymer tapes and protective wrappers are supplied complete with a factory-made adhesive primer (primer).

For external insulation of pipelines, currently mainly domestic insulating materials produced by Truboizolyatsiya OJSC are used (Novokuibyshevsk, Samara region): adhesive primers such as “P-001”, “NK-50”, polymer tapes such as “NK PEL-45”, “NKPEL-63”, “Polylen”, “LDP”, protective wrapping “Polylen O”. The main foreign suppliers of insulating materials for applying polymer tape coating are the following companies: Polyken Pipeline Coating Systems (USA), Altene (Italy), Nitto Denko Corporation, Furukawa Electric (Japan).

The advantages of tape coatings include: high manufacturability of their application to pipes in factory and field conditions, good dielectric characteristics, low moisture-oxygen permeability and a fairly wide temperature range of application.

The main disadvantages of polymer tape coatings are: low resistance to shear under the influence of soil settlement, insufficiently high impact strength of coatings, ECP shielding, low biostability of the adhesive sublayer of the coating.

Experience in operating domestic gas and oil pipelines has shown that the service life of polymer tape coatings on pipelines with a diameter of 1020 mm and above ranges from 7 to 15 years, which is 2-4 times less than the standard depreciation period for main pipelines (at least 33 years). Currently, OAO Gazprom is carrying out large-scale work on the repair and re-insulation of pipelines with external polymer tape coatings after 20-30 years of operation.

Combined mastic-tape coating

The combined mastic-tape coating of the “Plastobit” type is very popular among Russian oil workers. Structurally, the coating consists of a layer of adhesive primer, a layer of insulating mastic based on bitumen or asphalt-resin compounds, a layer of insulating polymer tape with a thickness of at least 0.4 mm and a layer of polymer protective wrap with a thickness of at least 0.5 mm. The total thickness of the combined mastic-tape coating is at least 4.0 mm.

When applying insulating bitumen mastic in winter time As a rule, it is plasticized and special oils are added to prevent embrittlement of the mastic at subzero ambient temperatures. Bituminous mastic, applied over a primer, ensures adhesion of the coating to the steel and is the main insulating layer of the coating. Polymer tape and protective wrapping increase the mechanical characteristics and impact strength of the coating, ensuring uniform distribution of the insulating mastic layer along the perimeter and length of the pipeline.

Practical use combined coatings of the "Plastobit" type have confirmed their fairly high protective and performance characteristics. This type of coating is currently most often used when carrying out repairs and re-insulation of existing oil pipelines with bitumen coatings. At the same time, in the construction of the bitumen-tape coating, predominantly polyethylene heat-shrinkable tapes are used, which have increased heat resistance and high mechanical characteristics, and special modified bitumen mastics of the new generation are used as insulating mastics.

The main disadvantages of a combined mastic-tape coating are the same as those of bitumen-mastic coatings - an insufficiently wide temperature range of application (from minus 10 to plus 40 ° C) and insufficiently high physical and mechanical properties (impact strength, resistance to crushing, etc.) .).

Coating technology in highway conditions

The application of protective bitumen-mastic and polymer tape coatings under route conditions is carried out after welding the pipes and monitoring the welded joints. To apply coatings, mobile mechanized columns are used, including: pipe layers and mounted technological equipment(cleaning and insulating machines, combines, etc.), moving along a pipeline welded into a “thread” and performing operations of brush cleaning, priming the surface of pipes, and applying a protective coating to them. When performing work in winter, the equipment additionally includes a mobile oven for heating and drying pipes.

When applying bitumen coatings as part of mechanized columns, bitumen melting pots and special insulating machines are also used. Before applying coatings, the pipes are cleaned of dirt, rust, and loose scale. Scrapers, mechanical brushes and needle cutters are used to clean the surface of pipes. Priming of pipes is carried out by pouring a dosed amount of adhesive primer onto the surface of the pipes, followed by rubbing it with a tarpaulin towel. A layer of hot bitumen mastic is applied to the primed pipes using an insulating machine, after which reinforcing material (fiberglass), a second layer of bitumen mastic and a layer of outer protective wrap are applied to the pipes. Tape coatings are applied to the surface of pipelines by spirally winding a layer of insulating tape and a layer of protective wrap onto primed pipes, with a given tension force and overlap amount.

Practical experience showed that, despite a fairly high degree of mechanization of insulation work in route conditions, this insulation method does not provide high-quality application of protective coatings to pipes. This is due to the influence of weather conditions, the lack of means and methods of operational technological control, as well as insufficiently high mechanical and protective properties of bitumen and tape coatings.

Transferring the process of external pipe insulation from route conditions to factory or basic conditions not only made it possible to accelerate the pace of pipeline construction, but also significantly improved the quality and reliability of their anti-corrosion protection. When pipes are insulated at the factory, the quality of work is not affected weather, sequential operational technological control is carried out. In addition, when insulating pipes in a factory environment, it becomes possible to use modern insulating materials and technologies for their application, which cannot be implemented during route insulation of pipelines.

Factory pipe coatings

The following types of factory coatings are most often used for external insulation of pipelines:
a) factory epoxy coating;
b) factory-made polyethylene coating;
c) factory polypropylene coating;
d) factory combined tape-polyethylene coating.

These types of coatings meet modern technical requirements and provide long-term, effective protection pipelines from soil corrosion.

IN different countries preference is given various types factory coatings. In the USA, England, and Canada, epoxy pipe coatings are the most popular; in Europe, Japan and Russia, preference is given to factory-made coatings based on extruded polyethylene. To insulate offshore pipelines and “hot” (80-110 °C) sections of pipelines, polypropylene coatings are usually used. Combined tape-polyethylene coatings are used mainly for insulating pipes of small and medium diameters with operating temperatures up to plus 40 °C.

Factory polyethylene coating

For the first time, single-layer polyethylene pipe coatings based on polyethylene powder began to be used in the late 50s - early 60s. last century. The technology for applying a single-layer polyethylene coating is similar to the technology for applying coatings from epoxy powder paints. Due to low water adhesion resistance and resistance to cathodic disbondment, single-layer polyethylene coatings have not been widely used. They were replaced by two-layer coatings with a “soft” adhesive sublayer. In the design of such a coating, insulating bitumen-rubber mastics ("soft" adhesives) with a thickness of 150-300 microns, applied over a primer layer, were used as an adhesive layer, and extruded polyethylene with a thickness of at least 2.0-3.0 was used as an outer impact-resistant layer mm.

After the company "BASF" (Germany) developed a copolymer of ethylene and acrylic acid ester ("Lucalen"), which was first tested in the design of a factory polyethylene coating of pipes as a hot-melt polymer adhesive sublayer, a two-layer polyethylene coating was introduced into the practice of pipeline construction with a “hard” adhesive sublayer. Later, a whole series of hot-melt adhesive compositions based on copolymers of ethylene and vinyl acetate, ethylene and acrylate were developed. Two-layer polyethylene coatings have received very wide application and for many years became the main factory coatings for pipes.

Structurally, a two-layer polyethylene coating consists of an adhesive sublayer based on a hot-melt polymer composition with a thickness of 250-400 microns and an outer polyethylene layer with a thickness of 1.6 mm to 3.0 mm. Depending on the diameters of the pipes, the total thickness of the coating is at least 2.0 (for pipes with a diameter up to 273 mm inclusive) and at least 3.0 mm (for pipes with a diameter of 1020 mm and above).

To apply two-layer polyethylene coatings, both domestic and imported insulating materials are used (hot-melt compositions based on copolymers - for applying the adhesive layer and compositions of thermo-light-stabilized polyethylene - for applying the outer layer). In order to increase the resistance of two-layer polyethylene coatings to water and resistance to cathodic disbonding at elevated temperatures, the surface of cleaned pipes is treated (passivation) with a chromate solution. With the correct selection of insulating materials, a two-layer polyethylene coating has fairly high properties and meets the technical requirements for factory pipe coatings. It can provide protection of pipelines from corrosion for a period of up to 30 years or more.

An even more effective external anti-corrosion coating is a factory-made three-layer polyethylene coating of pipes, the design of which differs from a two-layer polyethylene coating by the presence of another layer - an epoxy primer. The epoxy layer provides increased adhesion of the coating to steel, water resistance of adhesion and resistance of the coating to cathodic disbonding. The polymer adhesion sublayer is the second, intermediate layer in the construction of a three-layer coating. Its function is to provide cohesion (adhesion) between the polyethylene outer layer and the inner epoxy layer. The outer polyethylene shell has low moisture-oxygen permeability, functions as a “diffusion barrier” and provides the coating with high mechanical and impact strength. The combination of all three layers of coating makes three-layer polyethylene coating one of the most effective external protective coatings for pipelines.

The three-layer coating was developed in Germany and introduced into pipeline construction practice in the early 80s. last century, Today this coating is the most popular and widely used type of factory pipe coating.

In Russia, the technology of factory-made three-layer polyethylene pipe insulation was first introduced in 1999 at Volzhsky Pipe Plant OJSC. In 2000, production for three-layer pipe insulation was put into operation at OJSC Chelyabinsk Pipe Rolling Plant, OJSC Vyksa metallurgical plant", State Unitary Enterprise "Moscow Experimental Pipe Procurement Plant". To date, the technology for applying a three-layer polyethylene coating has also been mastered at the enterprises of CJSC "NEGAS" (Penza), LLC "Truboplast Enterprise" (Ekaterinburg), KZIT LLC "Insulation Plant" pipes" (Kopeisk, Chelyabinsk region), Ust-Labinskgazstroy LLC.

A three-layer polyethylene coating meets the most modern technical requirements and can provide effective protection of pipelines from corrosion for a long period of operation (up to 40-50 years or more).

To apply a three-layer polyethylene coating, specially selected systems of insulating materials are used: epoxy powder paints, adhesive polymer compositions, low-, high- and medium-density thermo-light-stabilized polyethylene compositions. Currently, when applying three-layer polyethylene coatings at Russian enterprises, only imported insulating materials are used: epoxy powder paints supplied by 3M (USA), BASF Coatings (Germany), BS Coatings (France), DuPont (Canada) ); adhesive and polyethylene compositions supplied by Borealis, Basell Polyolefins (Germany), Atofina (France), etc.

JSC "ANKORT" is carrying out work on the selection, comprehensive testing and implementation of domestic insulating materials for three-layer polyethylene pipe coatings.

Factory polypropylene coating

In Europe, factory-made pipe coatings based on extruded polypropylene account for 7-10% of the production volume of pipes with factory-made polyethylene coating.

The polypropylene coating has increased heat resistance, high mechanical and impact strength, resistance to punching and abrasive wear.

The main area of ​​application of polypropylene coatings is anti-corrosion protection of “hot” (up to 110-140 ° C) sections of pipelines, protection against corrosion of offshore, offshore pipelines, underwater crossings, sections of pipelines constructed using “closed” laying methods (punctures under roads, laying pipes using the directional drilling, etc.).

The design of the factory polypropylene coating is similar to the design of the factory three-layer polyethylene pipe coating. Epoxy powder paints, hot-melt polymer compositions and thermo-light-stabilized polypropylene compositions are used for coating. Due to the high impact strength of the polypropylene coating, its thickness can be 20-25% less than the thickness of the polyethylene pipe coating (from 1.8 mm to 2.5 mm).

Polypropylene coatings are usually white in color, which is due to the use of titanium dioxide as the main light stabilizer.

The disadvantages of polypropylene coatings include their reduced frost resistance. Standard polypropylene coating is recommended for use at pipeline construction temperatures down to minus 10 °C, and the ambient temperature when storing insulated pipes should not be lower than minus 20 °C. A specially developed frost-resistant polypropylene coating can be used at pipeline construction temperatures down to minus 30 °C and storage temperatures of insulated pipes down to minus 40 °C.

To apply factory polypropylene coatings, epoxy powder paints supplied by 3M (USA), BASF Coatings (Germany), and adhesive and polypropylene compositions supplied by Borealis and Basell Polyolefins are used. The technology of factory insulation of pipes with two-layer and three-layer polypropylene coatings has been mastered at the State Unitary Enterprise "Moscow Experimental Pipe Procurement Plant" and OJSC "Vyksa Metallurgical Plant". In 2004, it is planned to introduce the technology of applying factory polypropylene coating on the equipment of Chelyabinsk Pipe Rolling Plant OJSC and Volzhsky Pipe Plant OJSC.

Factory combined tape-polyethylene coating

For anti-corrosion protection of pipelines of small and medium diameters (up to 530 mm), a combined tape-polyethylene coating has been quite widely and successfully used in recent years. A combined tape-polyethylene coating is applied to pipes in factory or basic conditions. Structurally, the coating consists of a layer of adhesive primer (primer consumption - 80-100 g/m2), a layer of duplicated polyethylene tape (thickness 0.45-0.63 mm) and an outer layer based on extruded polyethylene (thickness from 1.5 mm to 2 .5 mm). The total thickness of the combined tape-polyethylene coating is 2.2-3.0 mm.

In the design of the combined coating, polyethylene tape applied over an adhesive primer performs the main insulating functions, and the outer polyethylene layer protects the tape coating from mechanical damage during transportation, loading and unloading of insulated pipes, and during construction and installation work.

Adhesive primers and duplicated polyethylene tapes supplied by Polyken Pipeline Coating Systems (USA), Altene (Italy), Nitto Denko Corporation (Japan) or similar domestic materials can be used as insulating materials for applying a combined coating: "NK-50", "P-001", insulating tapes "NK-PEL 45", "NK-PEL 63", "Polylen" produced by JSC "Truboizolyatsiya" (Novokuibyshevsk, Samara region).

In terms of properties, the combined tape-polyethylene coating is inferior to factory-made two-layer and three-layer polyethylene pipe coatings, but at the same time it is significantly superior to bitumen-mastic and polymer tape coatings for pipelines. The coating is included in the Russian standard GOST R 51164-98. Currently, combined tape-polyethylene coating is used primarily for external insulation of oil and gas field pipes, as well as in the construction of low-pressure inter-settlement gas pipelines.

Technology for applying protective coatings in the factory

External protective coatings are applied to pipes in factory conditions using equipment from mechanized production lines. Pipe insulation production lines include: roller transport conveyors, pipe transferrs, cleaning units (shot blasting or shot blasting units), technological pipe heating furnaces (induction or gas), epoxy powder paint spraying unit, extruders for applying an adhesive sublayer and outer layer coatings, pressing devices, water cooling chambers for insulated pipes, equipment for coating quality control. The composition of the equipment for pipe insulation production lines depends on the type of factory coating and the diameters of the insulated pipes.

When applying external epoxy coatings, pipes that have undergone abrasive cleaning are heated in a continuous furnace to a temperature of 200-240 ° C, after which epoxy powder paint is sprayed on them in a special chamber in an electrostatic field. Upon contact with the hot surface of the pipes, the epoxy paint melts and hardens, forming a protective coating.

Two-layer and three-layer polyethylene coatings can be applied to pipes by two methods: the “ring” extrusion method or the lateral “flat slot” extrusion of melts of adhesive and polyethylene compositions. For pipes of small and medium diameters, the preferred coating method is the "ring" extrusion method. With this insulation method, the following are sequentially applied to pipes that are pre-cleaned and heated to a given temperature (180-220 °C), coming through the insulation line without rotation, through a double annular extruder head: a melt of a hot-melt polymer composition (adhesive sublayer) and a melt of polyethylene (outer protective layer). A reduced pressure is created between the annular head of the extruder and the insulated pipes ("vacuum"), as a result of which the two-layer coating tightly fits the surface of the insulated pipes along their entire length and perimeter. When applying a polyethylene coating using this technology, the highest productivity of the pipe insulation process is ensured, which can reach 15-20 linear meters. m/min.

When using the lateral "flat slot" extrusion method, a two-layer polyethylene coating is applied to rotating and linearly moving pipes from two extruders (an adhesive extruder and a polyethylene extruder) equipped with "flat slot" extrusion heads. In this case, melts of adhesive and polyethylene compositions in the form of extruded tapes are wound in a spiral onto pipes that have been cleaned and heated to a given temperature, overlapping in one (adhesive melt) or several (polyethylene melt) layers. After application to the pipes, the coating is rolled onto the surface of the pipes with special rollers. The insulated pipes enter the water cooling tunnel, where the coating is cooled to the required temperature, and then the pipes are accelerated along the line and, using transfer handlers, are fed to the finished product rack. At this method insulation coating can be applied to pipes with a diameter of 57 to 1420 mm, and the productivity of the insulation process, as a rule, does not exceed 5-7 linear meters. m/min.

The application of three-layer polyethylene and three-layer polypropylene coatings to pipes is carried out according to the same technological scheme as the application of a two-layer coating, with the exception of the introduction of an additional operation into the technological chain - the application of a layer of epoxy primer. An epoxy primer with a thickness of 80-200 microns is applied to pipes that have been cleaned and heated to the required temperature by spraying epoxy powder paint, after which melts of a hot-melt composition of adhesive and polyethylene are sequentially applied to the primed pipes.

When applying a combined tape-polyethylene coating to pipes, the outer surface of the pipes is first brushed. There is no technological heating of the pipes. A bitumen-polymer primer is initially applied to the cleaned pipes, and then, after drying the primer, duplicated insulating tape and an outer protective layer of extruded polyethylene are applied to the primed pipes. The polyethylene layer is rolled onto the surface of the pipes with an elastic roller, after which the insulated pipes are cooled in a water cooling chamber.

The main reason that has a significant impact on the service life of pipeline systems is corrosion. To prevent corrosive wear today there are a huge number of methods, but the most popular of them are those that have more low price. Of course, no one claims that products and only equipment made of stainless materials, in some cases it is not justified, expensive and unprofitable. And polyethylene pipes, which are highly resistant to corrosion and therefore so popular today, are not able to withstand high pressure, and therefore their use is limited.

Already for a long time In construction, steel pipes are still widely used, which, when laid in the ground without an anti-corrosion coating, quickly wear out and become unusable. Due to low efficiency and short service life, the use of bitumen and roll materials based on it is being reduced. They are being replaced by more modern materials, for example, bitumen-polymer mastics, which are ready for use straight from the package and can be used to treat any surface.

There are situations when anti-corrosion treatment of a pipeline is required in the factory using specialized equipment. Quality control carried out for each individual coating operation allows us to achieve excellent results. Currently, there are several methods for increasing corrosion resistance, for example:

— three-layer insulation based on polyethylene. The pipes are first treated with a primer coating consisting of adhesive and epoxy layers, which form a hard surface with excellent adhesion. Then polyethylene is applied to this surface to prevent the formation of corrosion.

- silicate-enamel. This coating is one of the most expensive, so it is used in the construction of critical pipeline systems in the nuclear, oil and gas industries. The advantage of this treatment is not only reliable protection against corrosion - the pipe walls become so smooth that suspended particles do not accumulate on their inner surface.

— foam-polymer-mineral (PPM) insulation is a foamed mass of polymer into which a mineral filler is introduced, for example ash or clean sand. In addition to the anti-corrosion coating, such foam effectively protects pipes from heat loss, which is why it is often used in the construction of heating networks.

All steel pipelines of heating networks and pipeline elements must be protected from external corrosion using protective anti-corrosion coatings that are applied to the outer surface of the pipes, with the exception of cases: when the pipelines of heating networks are laid using heat-insulating structures of high factory readiness (for example, pipelines with insulation made of polyurethane foam and a shell pipe made of high-density polyethylene, equipped with an operational remote monitoring system (ODC), signaling damage and the presence of moisture in the insulation, as well as for pipelines with other types of thermal insulation structures that are not inferior to the above structure in operational properties).

The protective anti-corrosion coating must have high protective properties and maintain them under operating conditions (exposure to heat, moisture, simultaneous exposure to heat and moisture, aggressive environments, stray currents), ensuring protection of pipelines during the design service life.

The choice of protective anti-corrosion coatings for newly constructed heating networks should be made depending on the method of laying heating networks, the type and temperature of the coolant.

Anti-corrosion coatings intended to protect pipelines of water heating networks from external corrosion must meet the following requirements:

– heat resistance: 1875 hours at a temperature of 145-150 °C;

– thermal and moisture resistance: 50 “wetting-drying” cycles (one cycle includes one complete moistening of the thermal insulation applied to the coated pipe, followed by drying at a temperature of 75-80 ° C for five days);

– resistance in aggressive environments: preservation of protective properties by the coating under the influence of an acidic solution pH = 2.5 for 3000 hours and an alkaline solution pH = 10.5 for 3000 hours (for metallized aluminum coatings at pH = 4.5 and pH = 9 ,5);

– resistance to the effects of applied electrical potentials: anodic plus 0.5 V and plus 1.0 V for 1500 hours at each value and cathodic minus 0.5 V and minus 1.0 V for 1500 hours at each value.

Coatings intended for use in ductless installations of heating networks must, in addition, be resistant to abrasion.

The suitability of the coating for protection against external corrosion of heating network pipelines should be assessed based on the following main indicators:

– specific volumetric electrical resistance;

– continuity;

– impact strength;

– adhesion;

– flexibility;

– water absorption.

Note. When choosing protective anti-corrosion coatings, it is necessary to take into account their application technologies in order to maintain maximum performance of the above characteristics when applying coatings in field conditions.

#G0Name of protective coating	Type of coverage	Coating structure by layers, GOST, TU for materials and products (see Appendix Yu)	Total thickness, mm	Degree of purification	Laying method. Type of coolant	Type of thermal insulation	Maximum permissible coolant temperature, °C
1. Organosilicate coating OS-51-03 (with heat treatment)*	Lacquer-colorful	Three layers of organosilicate paint OS-51-03. TU 84-725-83. Heat treatment at 200 °C	0,25-0,30	First and second
2. Organosilicate coating OS-51-03 with hardener	Lacquer-colorful	Four layers of organosilicate paint OS-51-03 (TU 84-725-83) with hardener (natural drying)	0,45	First and second	Underground in impassable channels. Water	All types of suspended thermal insulation
3. Epoxy coating EP-969	Lacquer-colorful	Three coating layers of epoxy enamel EP-969. TU 6-10-1985-84	0,1	Second	Underground in impassable channels. Water	All types of suspended thermal insulation
4. Silicon - organic coating KO*	Lacquer-colorful	Three top coats of silicone composition KO with hardener (natural drying). TU 88.USSR.0.88.001-91	0,25	Second	Underground in impassable channels. Water	All types of suspended thermal insulation
5. Complex polyurethane coating "Vector"	Lacquer-colorful	Two primer layers of mastic "Vector 1236" TU 5775-002-17045751-99. One covering layer of mastic "Vector 1214" TU 5775-003-17045751-99 (see note 3)	not less than 0.13	Second and third	Underground in impassable channels; underground channelless. Water	All types of thermal insulation
6. Silicate-enamel coating made of primer-free enamel 155T*	Silicate-enamel	Two layers of 155T enamel. TU 88-106-86 BSSR (glass enamel granulate, primer-free grade 155T BSSR), (TU 1390-001-01297858-96	0,5-0,6	First		All types of thermal insulation
7. Silicate-enamel coating made of MK-5 enamel*	Silicate-enamel	Two layers of top enamel MK-5. TU 2367-002-05282012-2000	0,5-0,6	First	Underground in impassable channels; underground channelless. Water and steam	All types of thermal insulation
8. Metallized aluminum coating*	Metallization	Two cover layers of metallized aluminum coating. #M12291 1200014731GOST 9.304#S	0,25-0,30	First	Underground in impassable channels and tunnels, underground channelless; on the walls outside of buildings, in technical undergrounds. Water	All types of thermal insulation
9. Aluminum-ceramic coating*	Metallization	One layer of plasma coating from a mixture of aluminum powders - PA-4 (or PA-3) GOST 6058 - 85% (by weight) and ilmenite concentrate TU 48-4236-91 -15%	0,2-0,3	First	Underground in impassable channels; underground channelless. Water and steam	All types of thermal insulation