Method of repair of extended steel gas lines

FIELD: protection of metals against corrosion; protection of extended underground gas lines against corrosion.

SUBSTANCE: proposed method includes restoration of defective sections of gas lines by application of insulating protective coats and connection with cathode protection system; defective section of gas line is preliminarily disconnected from gas main and is freed from natural gas; gas released from this section is compressed and is charged in reservoirs under pressure; gas line surface is cleaned from soil and defective coat by forming temperature gradient and stresses between defective coat and gas line; then finish cleaning of outer surface of gas line is performed at simultaneous suction of dust and gas line is heated to temperature of 70 to 175°C, after which layers of adhesive composition and dielectric insulating coat are applied at succession at overlapping joints between steel pipes of gas line and layer of spiral-shaped coat made from metal at potential more negative as compared with potential of gas line being protected; metal coat is applied in form of tape or foil whose ends are brought out at distance of (0.01-1)d, where d is diameter of pipe. Then, insulating plastic coat is applied on metal coat and after erection of gas line, ends of tape or foil are electrically connected at points of joints of steel pipe over entire length of gas line through switching units and parameter measuring units.

EFFECT: enhanced reliability of corrosion protection; considerable reduction of energy expenses; increased service life of metal coat.

3 cl, 10 dwg

 

The invention relates to the protection of metals from corrosion and can be used for corrosion protection of steel long underground pipeline.

A known method of manufacturing a display protect pipelines from electrochemical action, consisting in the fact that the pipe is applied two coats of insulation from kremna-nabetani and polyurethane foam in the form of "shells", cover with aluminum foil, which is fixed by the bands with their grounding through 10-50 m Between the first inner layer and outer layer of polyurethane foam glued propolymer solution tape of aluminum foil in the shape of a spiral, covering the outside of all pipe insulation. The ends of the ribbon to display in the joints of the pipe along the entire length of the pipeline and electrically connect with the bands [1].

The disadvantage of this method is the limited scope of its application only in construction and to protect pipelines from exposure to stray currents. This is due to the fact that the soil electrolyte freely falls between the "shells" of krematorien and polyurethane foam in the gaps between the spirals tape aluminum foil to the surface of the pipeline.

There is a method of integrated corrosion protection long steel buildings, carried out by isolating design and cathodic polarization from an external source of current and applying under the dielectric insulating coating layer of the metallic coating (for example, thermal method), with the potential for the environment negative potential of the protected structure (e.g., aluminum)in the system of cathodic protection anode perform in the form of a tape (or individual elements, as close as possible to the areas of the defects in the protective coatings of pipelines and the United insulated wire) and have a spiral on the structure with a step equal to its zone of protection, and cathodic polarization structures provide a current density of 5-60 mA/square meters [2].

The disadvantages of the method are that it does not protect the system from stray currents; direct contact of metals with different potentials of ionization (for example, Al - 5,V and Fe - 7,9B) creates additional contact potential difference -1,V, which is necessary to compensate for an external power source; used as a coating of aluminum can lead to an increase in the pH electrode layer and a cathodic corrosion and excessive alkalinity to the saponification of the coating and reduce the effectiveness of cathodic protection; cathodic polarization structure current density 5-60 mA/sq. m does not take into account real diverse flow conditions the corrosion process, which depends on the nature of the metal. the chemical composition, structure and condition of its surface, the composition and concentration of the electrolyte, the diffusion conditions and so is the temperature.

For example, when joining aluminum tread through the metal insulated from the ground conductor to the protected steel construction along the conductor current flows from steel structures (Earticle=be 0,55 In) tread (Farticle=-1,66). Soil is the ohmic voltage drop, so that the surface of steel structures less polarized negatively. The offset potential of these metals in the negative direction beyond the level of maximum protection potential cause an unacceptable increase in the dissolution rate of the metal cover (protector) and, in addition, additional costs of electrical energy. The formation of a dense oxide film in technical alloys of aluminum prevents the passage of current protection of steel structures.

There is a method of integrated corrosion protection long steel structures including sequential placement of layers of metal and dielectric insulation coating, and a layer of metal coating is made of a metal with potential in the installation environment is more negative than the potential of protected structures [3].

The disadvantage of this method lies in the unreliability of electrochemical protection against corrosion damage to the metal coating. Furthermore, the method does not provide mechanical protection pok is iti during transportation and installation of pipelines. In the absence of cathodic protection applied cathodic protection cannot be guaranteed to protect steel structures in various environments of their host.

There is a method of integrated corrosion protection long steel pipeline, comprising the sequential placement of layers of metal and dielectric insulation coating, and a layer of metal coating is made of a metal with potential in the installation environment is more negative than the potential of the protected structure, and cleansed, heated surface protected steel pipe is applied on the outside of the insulating dielectric plastic floor, then on the insulation coating is applied to a spiral metallic coating in the form of a tape or foil covering the outside of the pipe insulation, the ends of the tape or foil display at a distance of 0.01-1d, where d is the pipe diameter, then a metal coating is applied insulation plastic coating, after installation of pipe joints of steel pipes the ends of the tape or foil over the entire length of the pipeline is electrically connected through the switching units and measurement protection system cathodic protection [4].

The disadvantages of the method are that:

- when cleaning the pipe surface shot blasting method of a dense melodic Arsinoe cloud of dust-like particles, consisting of corrosion products, particles of the old coating and earth, inevitably deposited on the pipe surface, which dramatically affects the adhesion of the dielectric insulating coating to the surface of the pipe and, consequently, is one of the reasons intensive corrosion of the piping, resulting in abnormal destruction of pipelines (2. Borisov B. I. Insulation work during the construction of trunk pipelines. - M.: Nedra, 1990, p.56);

- all operations are successive layers of metal and dielectric insulating coating on a steel pipe is mainly carried out in the factory, that does not preclude a violation of the integrity of the coating during transport;

- to improve the adhesion to the pipe surface of the dielectric insulating coating paste the modified dielectric adhesive composition at a temperature of 180-210°s, which leads to increased energy costs;

- joints of steel pipes most susceptible to corrosion, are outside of cathodic protection, which reduces its effectiveness.

The closest technical solution is the way repairs are long steel gas pipelines, including the restoration of defective sections of the pipeline with the application of the insulating protective coatings and soy is inania with cathodic protection system [5].

The disadvantages of this method of repair of the pipeline is that the method does not provide:

- use release of natural gas and the filling of pressure vessels, which leads to the irreversible loss of its significant volumes and pollution of the environment;

- all operations are consistent insulation coating on the lengthy pipeline are carried out without finishing cleaning the defective pipeline section from the old insulation and without heat, which degrades the adhesion to the surface of the pipeline coating and leads to a reduction in service pipeline.

The task of the invention is to reduce energy costs, improve quality and efficiency of corrosion protection and reliability of steel underground pipelines.

This goal is achieved by the fact that in contrast to the known method of repair of long steel pipelines with comprehensive protection from corrosion, including the restoration of defective sections of the pipeline with applying insulating coatings and the connection to the cathodic protection system proposed provides for disabling the defective area of the gas from the main pipeline, the release of the defective area from the natural gas compression exempt nature is underwater gas and the filling of pressure vessels, surface cleaning of the pipeline from the remnants of the earth and defective coating method of exfoliation is by creating a temperature gradient and stress between the defective coating and pipeline, holding the finish Stripping the outer surface of the pipeline with the dust suction, heating the gas to a temperature of from 70 to 175°With consecutive coats of the adhesive composition, the dielectric insulating coating with overlapping joints between the steel pipe and a layer of a spiral coating of metal with a potential more negative than the potential of the protected pipeline, when the metallic coating is applied in the form of a tape or foil, the ends of which bring to the distance (0,01-1d)where d is the pipe diameter, then a metal coating is applied insulating plastic coating, and after installation of the pipeline joints of steel pipes the ends of the tape or foil over the entire length of the pipeline is electrically connected through the switching units and measurement protection system cathodic protection.

Variant provides that for peeling the defective coating from the steel pipe spend the cooling defective insulation stream of vaporized liquid nitrogen or carbon dioxide, temperature gradient and stress between the defective section of the insulation and the steel pipe to create the pulsed electric field intensity from 5 to 50 kV, heating the cleaned pipe conducting the products of combustion of natural gas, which is fed to the burner of the pressure vessels.

Option provides for cooling of the defective insulation to a temperature of from -90 to -152°C, pulsed electric field created by a coil placed around the peelable area insulation steel pipeline.

Effect: the proposed method is integrated corrosion protection long steel pipeline eliminates the disadvantages of the prototype, provides the control and reliability of electrochemical corrosion protection of steel pipelines in different environments, their placement, while significantly reducing energy costs and increasing service life of the metal coating.

The proposed method finish cleaning the pipe surface and heating the repair area of the pipeline increases the adhesion of the coating to the pipe surface, which improves the quality of the corrosion protection of steel pipeline and reduce costs for its operation.

The method allows the use of release from pipeline natural gas, which reduces environmental pollution

Analysis of the data showed that the claimed technical solution achieved is not known from the prior art, and therefore it is the line which meets the criterion of "novelty".

Such a technical solution is not obvious from the prior art and, therefore, meets the criterion of "inventive step".

A variant of implementation of the proposed method is illustrated in figure 1, 2, 3, 4, 5, 6, 7, 8, 9, 10.

In the manufacture of repairs inspect and identify insulation of pipelines 1, disable the defective section of the pipeline 1 from the main pipeline, relieve the defective area from natural gas, compressed exempt natural gas and fill their vessels under pressure (not shown).

Then perform consistently and continuously following process steps:

- digging in the soil 21 symmetrically to the longitudinal axis of the pipeline 1 trench 19 a width of four d (phase 1);

- develop in the soil symmetrically to the longitudinal axis of the pipeline trench trapezoidal shape 20 to a depth not reaching 20 mm to the top surface of the pipeline 1, separately conveying the 20 soil from the trench 19 and the soil from the trench 20 to backfill the repaired pipeline 1, develop two pit 22 in the form of a trapezoid, whose inner side is perpendicular to the base up to the level of 1.5 d deeper than the lower edge of the gas pipeline and two hollow rectangular 23 depth of 1.0 d (phase 2);

- install right 24 and left 25 working bodies, for example, is fixed on asnom the carrier's equipment (see Miglierini, Nggemuse. Construction machinery. - M.: Vysshaya SHKOLA, 1980, str-219) parallel to the pipeline 1 in both sump 22 to level to 50 mm deeper than the lower edge of the pipeline 1, include rotary working bodies 24, 25 and set them to work perpendicular to the pipeline 1, developing the soil beneath the pipeline 26, except for the portion of the soil 27, with the rotation of the rotary working bodies 23, 24 on the corner γ=90 deg. using the right 28 and left 29 rotary rod, remove the ground from under the pipeline 26 rotary working bodies 24, 25 in two pit 23 (step 3);

- clean the surface of the steel pipeline 1 from the remnants of the earth and defective coating method of exfoliation. To this cooled defective insulation stream of evaporated liquid nitrogen to a temperature -152°To place around the peelable area insulation steel pipeline 1 inductor (not shown). Create a gradient of temperatures and voltages between the defective section of the insulation 3 and the steel pipeline 1 pulsed electric field strength of 10 kV, hold the finish Stripping the outer surface of the pipeline 1 with the suction of dust prior to application of the adhesive on it mastics;

- heated purified gas pipeline 1 to a temperature of 100°With products of combustion of natural gas, which is fed to the burner of the vessels n the d pressure (not shown);

- to clean the outer surface of the pipe of the pipeline 1 is applied successive layers of adhesive composition 2, the composition of high-pressure polyethylene 3, then the insulation coating is glued with an adhesive composition 2, the metallic coating of aluminum alloy 4, covering the outside of the insulation tube 3 and the joints between the steel pipe, the outer layer of thermally stabilized composition of high-pressure polyethylene 5, the ends of the metal strip 6 to display in the areas between joints steel pipe (stage 4);

go to sleep renovated pipeline 1 soil 29 until the middle of the tube 1 (step 5) with layer-by-layer seal mechanical seals soil 30 in the pits 31 and soil beneath the pipeline 29 (step 6); after compaction 31, 29 to the initial density of the gas pipeline 1 sleep consistently ground 32 and the ground 20 (step 7);

- after installation of the pipeline to the steel pipeline weld electrodes 7, the ends of the tape 6 of aluminum alloy and electrodes 7 are electrically connected by conductors 11 through the switching unit and measuring security settings 18 with a cathodic protection system comprising a cathode-polarized steel pipeline 1, the external energy source 13. the unit of measurement and adjustment of the protective capacity of 14, in-depth cathode 9 and anode 10 ground sensor polarization potential is and 17, the sensor electrostatic fields 16 and the speed sensor corrosion 15, units of measurement and information processing, logic, telemetering and Claregalway (not shown).

After repairs in the pipeline 1 increase the pressure up to the trunk, re-examination of the pipeline 1 with the registration of its physical parameters (capacity, the intensity of the electrostatic field induced electric charges between the dielectric isolated from each other by gas and aluminum metal plating, the current density of the cathodic polarization of the pipeline) in the cathodic protection system.

When pumping through the pipeline dielectric gas pipe wall 1 is charged to a negative electric charge, and the metal coating of aluminum alloy 4 - positive electric charge. Construction of the pipeline is electrically represents a system of parallel interconnected (via the switching unit and measuring 18) capacitors. The electrical capacity of each pipe and the capacity of the pipeline depends proportionally on the dielectric permittivity of the insulation coating 3, which is located between the pipe 1 and the metal coating 4, i.e. from a state of isolation.

While maintaining the insulation of electrical energy is stored in the lining of the pipe (condenser) and is use to transmit information about the protection status of pipeline sections. When disabled, the external energy source 13 (using coaxial switch 12) protection is provided from the internal source of energy and the current density of 0.001 to 0.007 ua/sq m At the local damage of the pipeline and in non-aggressive environments, placing the current density required for the polarization of the steel to a minimum protective potential of 0.85 V), is provided from the internal source of energy due to electrical energy. accumulated in the pipeline with a current density of up to 16.5 mA/sq.m. Protection from an external source of energy is carried out only in case of insufficiency of current from the internal power source. In this case (using coaxial switch 12) connect the external power source 13 and the cathode polarization of the pipeline is performed with the current density of from 16.5 to 1614 mA/M. the Upper limit due to aggressive maximum hosting environment (polluted water mouth) when exposed steel pipelines (see Protection of metal structures from underground corrosion. - M.: Nedra, 1981).

Positive test results have proved the effectiveness and wide possibilities of practical use of the proposed method in the future.

Outlined shows that the invention conforms to the criterion "industrial applicability".

Sources of information

1. Patent RU No. 2190799 from 28.08.2001.

2 the Patent RU №96119556 from 30.09.1996; No. 98116075 from 17.08.1998.

3. Inventor's certificate SU # 1313008, 1984.

4. Patent RU No. 2237748 from 26.11.2003.

5. Patent RU No. 2053432 from 27.01.1996 (prototype).

1. The method of repair long steel pipelines with comprehensive protection from corrosion, including the restoration of defective sections of the pipeline with applying insulating coatings and the connection to the cathodic protection system, wherein the pre disable the defective section of the pipeline from the main pipeline, relieve the defective area from natural gas, compressed exempt natural gas and fill them pressure vessels, clean the surface of the pipeline from the remnants of the earth and defective coating method of exfoliation is by creating a temperature gradient and stress between the defective coating and pipeline, carry out finish cleaning the outer surface of the pipeline with the suction of dust, heat the gas to a temperature of from 70 up to 175°sequentially applied layers of adhesive compositions, dielectric insulation coating with overlapping joints between the steel pipes of the pipeline and a layer of a spiral coating of metal with a potential more negative than the potential of the protected pipeline, when the metallic coating is applied in the form of a tape or foil, the ends of which bring to the distance (0,01÷ 1)d, where d is the pipe diameter, then a metal coating is applied insulating plastic coating, and after installation of the pipeline joints of steel pipes the ends of the tape or foil over the entire length of the pipeline is electrically connected through the switching units and measurement protection system cathodic protection.

2. The method according to claim 1, characterized in that peeling the defective coating from the steel pipe spend the cooling defective insulation stream of vaporized liquid nitrogen or carbon dioxide, temperature gradient and stress between the defective section of the insulation and the steel pipe to create a pulsed electric field intensity from 5 to 50 kV, heat cleaned pipe conducting the products of combustion of natural gas, which is fed to the burner of the pressure vessels.

3. The method according to claim 2, characterized in that the cooling defective insulation carried out to a temperature of from -90 to -152°C, pulsed electric field created by a coil placed around the peelable area insulation steel pipeline.



 

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SUBSTANCE: proposed method includes restoration of defective sections of gas lines by application of insulating protective coats and connection with cathode protection system; defective section of gas line is preliminarily disconnected from gas main and is freed from natural gas; gas released from this section is compressed and is charged in reservoirs under pressure; gas line surface is cleaned from soil and defective coat by forming temperature gradient and stresses between defective coat and gas line; then finish cleaning of outer surface of gas line is performed at simultaneous suction of dust and gas line is heated to temperature of 70 to 175°C, after which layers of adhesive composition and dielectric insulating coat are applied at succession at overlapping joints between steel pipes of gas line and layer of spiral-shaped coat made from metal at potential more negative as compared with potential of gas line being protected; metal coat is applied in form of tape or foil whose ends are brought out at distance of (0.01-1)d, where d is diameter of pipe. Then, insulating plastic coat is applied on metal coat and after erection of gas line, ends of tape or foil are electrically connected at points of joints of steel pipe over entire length of gas line through switching units and parameter measuring units.

EFFECT: enhanced reliability of corrosion protection; considerable reduction of energy expenses; increased service life of metal coat.

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