RU2736599C1 - Method of combined cathodic protection against electrochemical corrosion of steel underground pipelines and cases at section of crossing with electrified railway - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to electrochemical protection against metals corrosion, in particular, to protection of underground pipelines made of carbon and low-alloy steels. Method is characterized in that at section of intersection of steel underground pipeline and case with railway, located in protection zone from cathode converter at distance of more than 500 m from point of drainage of cathode converter, installing two tread groups located to the right and to the left of the railroad bed, connected by a drain cable through a unit of adjustable resistances, installed in separate contact devices, with copper-sulphate comparison electrodes on the pipeline and case, and continuous in time cathodic polarization of steel underground pipeline and steel underground case at section of crossing with railway due to guiding value of protective total and polarization potential required for protection of pipeline and case.

EFFECT: technical result is providing efficient, continuous in time cathodic protection, prevention of technogenic accidents at railway.

1 cl, 2 dwg, 1 tbl

Description

The invention relates to the field of electrochemical protection against corrosion of the outer surface of underground steel structures, laid below ground level or in embankments, made of carbon and low-alloy steels, pipelines transporting natural gas (main and distribution pipelines), oil, oil products, and branches from them ...

The technical solutions known in this field concerning the method of protecting steel underground structures from electrochemical corrosion and methods of monitoring the effectiveness of the applied protection are embodied in the Interstate standard GOST 9.602-2016 “Unified system of protection against corrosion and aging. Underground structures "(developed by State Unitary Enterprise Academy of Public Utilities named after KD Pamfilov, State Unitary Enterprise VNII Railway Transport, FSUE VNIIstandart (hereinafter GOST 9.602-2016), which was put into effect by order of the Federal Agency for Technical Regulation and Metrology dated 07.10.16 No. 1327-st. Currently, the application of these regulatory documents is mandatory in the design, construction, reconstruction, repair, operation of underground structures in connection with the classification of protected facilities as hazardous production facilities.

During the design, construction, operation and reconstruction of underground structures, measures are taken to identify the sources of stray currents and assess their danger. Organizations operating structures and equipment that are sources of stray currents must ensure that their dangerous effects are limited. During the operation of structures, systematic monitoring of the effectiveness of anti-corrosion protection and the risk of corrosion, as well as registration and analysis of the causes of corrosion damage, should be provided.

The types of corrosive effects on the outer surface of underground steel structures are: atmospheric corrosion, corrosion in soil and groundwater and soils, biocorrosion, corrosion caused by stray currents (alternating and direct current), corrosion caused by induced alternating current.

The present invention considers protection against electrochemical corrosion caused by corrosion in soil and ground waters and soils, biocorrosion, corrosion caused by alternating stray currents, the source of which in cities is electrified transport, alternating currents of industrial frequency

The impact of each or their combination shortens the service life of an underground structure and can lead to premature re-laying of obsolete pipelines and cables. The design life of an underground gas pipeline under the conditions of anti-corrosion protection is 40 years, in practice this period is much shorter.

A known method of protecting an underground structure by using an insulating coating of an underground pipeline and by cathodic polarization.

The applied structures of the insulating coating and the requirements for them are determined in the relevant industry regulations for each type of underground structure (gas pipeline, oil pipeline, water pipeline, heat pipeline). The main materials for the formation of protective coatings are: polyethylene, polyethylene adhesive tapes, heat-shrinkable polyethylene tapes, bitumen and bitumen-polymer mastics, fused bitumen-polymer materials, roll mastic tape materials, compositions based on chlorosulfonated polyethylene, polyester resins and polyurethanes. Newly developed materials for protective coatings and their structures are introduced into the practice of construction and repair of pipelines in accordance with the requirements of normative and technical documentation agreed with the head organization for the protection of underground metal structures against corrosion by the developer of GOST 9.602-2016.

The insulating coating of the pipeline is applied regardless of the corrosiveness of the soil where the metal structure is located and the need for cathodic protection. The use of a certain type of insulating coating for the corresponding structure contributes to the performance of the functions of effective electrochemical protection, and if the requirements for the choice of the design of the insulating coating are not met, it is not effective as a method of protection against corrosion.

Similar in purpose and having similar techniques and operations with the claimed method is a method of cathodic polarization using an external DC source and using protectors.

The technical essence of the known method of electrochemical protection of steel underground structures from electrochemical corrosion is characterized by the following features similar to the essential features of the proposed method:

- the efficiency of cathodic polarization (protection zone) is determined by the magnitude of the induced negative protective potential by the magnitude of the total and polarization potential;

- the use of cathode converters (ECD) with connection through a contact device to the structure and anode grounding or protector groups, the protection zone is provided;

Detailed technical characteristics of cathodic polarization are as follows:

A cathode converter (hereinafter ECD) is used as an electrical protective device, which is an external direct current source and serves to induce an electrochemical potential. The negative pole of the ECD is connected to the protected pipeline through a contact device on the pipeline, the positive pole of the ECD is connected to the anode ground by means of a drain cable. Cathodic polarization of structures is carried out in such a way that the protective potentials of the metal relative to the saturated copper-sulfate reference electrode were between the minimum and maximum (in absolute value) values in accordance with Table 1.

As an anode grounding, grounding electrodes are usually used that have sufficient resistance to electrolytic dissolution, for example, grounding electrodes made of graphite carbon, iron-silicon, cast iron. Anode grounding is designed to provide the structure with a cathodic current. The location and configuration of the anode grounding significantly affect the distribution of the potential difference "pipe-ground" along the pipeline, and, consequently, the parameters of the electrical protection installation: voltage and current. Regulatory documents (SP 42-102-2004 "Design and construction of gas pipelines from metal pipes") are recommended to place anode grounding as far as possible from the protected structure. The reason for removing the anode grounding is the desire to obtain the greatest possible length of the protective zone. To ensure the effectiveness of cathodic protection, it is recommended to choose areas for placing anode grounding, on which there are no gaskets of other underground metal structures between the protected pipelines and the anode grounding, however, in conditions of a complex system of urban communications and dense buildings, anode grounding is located according to the possibilities of the situational plan.

Three metals are used as a tread: zinc, aluminum and magnesium. Most often, a magnesium protector is used to protect pipes made of steel or with its admixture, since the large difference in potential between steel and magnesium makes the installation quite efficient. Magnesium protectors, as a rule, are used to protect oil and gas pipelines located in soil with high resistivity, as well as on terrain where it is not easy to quickly detect and fix a problem. Protectors are installed in the ground according to standard drawings away from the protected structure, or directly under the protected structure. Connection to the protected structure is carried out with a cable through a contact device using a block of adjustable resistances.

When determining the methods of protection against corrosion of structures, the following are provided:

- assessment of the conditions of construction and operation of the structure;

- assessment of the criteria for the risk of corrosion of the structure;

- selection of protective coatings corresponding to the operating conditions of the structure;

- assessment of the need and choice of solutions for electrochemical protection (cathodic polarization) of structures;

- assessment of the need and selection of additional methods of corrosion protection.

The existing system of cathodic protection against electrochemical corrosion of steel underground pipelines and casings, including intersections with the electrified railroad, provides for a cathode converter, anode grounding, drainage and connecting cables. The use of these elements in the protection system has several disadvantages:

1. Power supply of the cathode converter (ECD) is carried out from an AC source with a voltage of 220 V, therefore, the ECD is located as close as possible to the AC source. The definition of zones of protection from a cathode converter is usually determined by the total potential, which includes the ohmic component, therefore the protection zone is quite large and the sections of intersection of the pipeline with the railway quite often do not have a sufficient protective potential, which provides protection against corrosion hazard from the stray currents of the electrified railway, t. the amount of wandering currents is not constant and depends on the state of the railway and on the load of the rolling stock (movement frequencies).

2. The point of drainage of the ECD on the pipeline is located quite far from the intersection of the underground pipeline-case and the railway, therefore, automatic adjustment does not automatically adjust the value of the protective potential. Due to emergency situations on power lines, the power supply of the ECD is quite often interrupted, and therefore, continuous cathodic polarization of the underground pipeline to be protected is not ensured.

3. Adjustment of the ECD according to the output parameters relative to the magnitude of stray currents in some cases gives an increased potential, which affects the state of the pipeline insulation coating (insulation peeling), which ultimately affects the decrease in the protection efficiency.

4. Continuous operation of the ECD is problematic, because the object is not guarded, has free access, is usually installed near a power transmission pole or near the wall of a house and is often burglarized by unauthorized persons.

5. Protection systems "pipe-sleeve" provides for the presence of an adjustable electrical jumper, and taking into account the fact that the applied control resistances have a small value of resistance and steel cases usually do not have insulation on the inner wall, which is characterized by a relatively small value of the transition resistance "pipe-ground" - this reduces the effectiveness of the cathodic protection of the steel pipeline.

6. Corrosion damage at the intersection of an underground steel pipeline and a casing with an electrified railway with ineffective cathodic protection leads to gas leaks, the formation of a gas-air and fire-explosive mixture, which is the cause of man-made accidents associated with economic losses and human casualties.

Similar accidents took place in 1988 in the Gorky region (now the Nizhny Novgorod region) near the station Arzamas 1 when a rolling stock was approaching, carrying an explosive cargo during a gas leak, an explosion occurred, which killed 91 people, injured 744 people, in 1989 in Iglinsky in the region of the Bashkir Autonomous Soviet Socialist Republic on the Asha-Ulu-Telyak stretch, a gas leak and explosion caused a man-made accident of two oncoming trains, which resulted in the death of 575 people, and more than 600 injured.

The invention is based on the task of creating a method of cathodic protection against electrochemical corrosion of steel underground pipelines and steel cases at the intersection with an electrified railway, which ensures the achievement of the technical result, which consists in providing continuous cathodic protection of pipeline sections located over 500 meters from the drainage point of the ECD. The application of the method will ensure the prevention of man-made accidents on the railroad on which dangerous and especially dangerous goods, military goods are transported.

The technical result is achieved in the following way. The method of joint cathodic protection against electrochemical corrosion of steel underground pipelines and cases at the intersection with the electrified railway is characterized by the fact that at the intersection of the steel underground pipeline and case with the railway, located in the zone of protection from the cathode converter at a distance of over 500 meters from the drainage point cathode converter, two protector groups are installed, located to the right and left of the railroad bed, connected by a drain cable through a block of adjustable resistances installed in separate contact devices, with copper-sulfate reference electrodes on the pipeline and case, and continuous in time cathodic polarization of the steel of an underground pipeline and a steel underground case at the intersection with the railway due to the induction of the value of the protective total and polarization potential required to protect the pipeline and the case.

The combined use of a cathode converter and a system of protector groups for cathodic polarization of a gas pipeline and a case at the intersection with a railway is a guarantee of the effectiveness of cathodic polarization.

The method includes the installation of protector groups (6), a joint protection unit (8), separate contact devices on the case (5) and the pipeline (4). This protection system works in conjunction with the ECD cathodic protection system. The method covers the protection zone (10) directly of the pipeline section (1) and the case (2) at the intersection with the railway (3), approximately 300 m, including 150 m to the right and left of the railway bed.

Install 2 tread bands, one on each side of the railway. The brand and the number of protectors in the group shall be determined according to a standard calculation according to the project, in the calculation take into account the specific resistance of the soil, the diameter of the pipeline, the diameter of the case, the length of the protected section of the structure and the case (i.e. the area of the protected structure). Installation of protector groups relative to the pipeline and the case is carried out in accordance with building codes. Connect the protector groups (6) with drainage cables (9) through a block of adjustable resistances (8) to separate KU (4, 5) to the pipeline (1) and a case (2) with a copper-sulfate reference electrode (7). The use of a block of resistances will ensure the adjustment of the required value of the protective potential on the pipeline and the case. The contact devices (4, 5) should be installed outside the ditch (11) of the railway in order to protect the devices from the accumulation of water and other substances in the ground from the operation of the railway that affect the aggressiveness of the soil.

The method of cathodic protection against electrochemical corrosion of steel underground pipelines and cases at the intersection with the electrified railway is illustrated and presented in figure 1 "Plan for the arrangement of elements of cathodic protection against electrochemical corrosion of steel underground pipelines and cases at the intersection with the electrified railway" and in figure 2 "Diagram of connecting elements of cathodic protection against electrochemical corrosion of steel underground pipelines and casing at the intersection with the electrified railway."

Claims (1)

A method of joint cathodic protection against electrochemical corrosion of steel underground pipelines and cases at the intersection with an electrified railway, characterized by the fact that at the intersection of the steel underground pipeline and case with the railway, located in the protection zone from the cathode converter at a distance of over 500 meters from the point drainage of the cathode converter, two protector groups are installed, located to the right and left of the railway bed, connected by a drain cable through a block of adjustable resistances installed in separate contact devices, with copper-sulfate reference electrodes on the pipeline and case, and continuous cathodic polarization is carried out in time underground steel pipeline and a steel underground case at the intersection with the railway due to the induction of the value of the protective total and polarization potential required to protect the pipeline and the case.

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