Works on the operation of electrochemical plants. Instructions for the operation of devices for electrochemical protection of engineering networks. Plants with extended or distributed anodes

RUSSIAN STATE UNIVERSITY OF OIL AND GAS I.M. GUBKINA

TRAINING AND RESEARCH CENTER OF EDUCATION OF EMPLOYEES OF THE FUEL AND ENERGY COMPLEX (TIC)

MUNC "ANTIKOR"

Final work

under the short-term professional development program:

"CORROSION PROTECTION OF GAS AND PETROLEUM EQUIPMENT, PIPELINES AND RESERVOIRS OF GAS AND OIL SECTOR"

Topic: Electrochemical protection systems, their operation

Moscow, 2012

Introduction

electrochemical corrosion protection grounding

Electrochemical protection of underground structures is a method of protection against electrochemical corrosion, the essence of which is to slow down the corrosion of a structure under the influence of cathodic polarization when the potential is shifted to a negative area under the action of a direct current passing through the “structure - environment” interface. Electrochemical protection of underground structures can be carried out using cathodic protection installations (hereinafter UKZ), drainage installations or protector installations.

In case of protection with the help of the UKZ, a metal structure (gas pipeline, cable sheath, reservoir, well casing, etc.) is connected to the negative pole of the DC source. In this case, an anode grounding is connected to the positive pole of the source, providing current input into the ground.

With protective protection, the structure to be protected is electrically connected to the metal that is in the same environment, but has a more negative potential than the potential of the structure.

In case of drainage protection, the protected structure, which is in the area of ​​action of stray direct currents, is connected to the source of stray currents; this prevents these currents from draining from the structure into the ground. Stray currents are the leakage currents from the rail tracks of DC electrified railways, tramways and other sources.

1. Installations of cathodic protection

To protect underground pipelines from corrosion, cathodic protection installations (UKZ) are being built. The UKZ includes power supply sources for the alternating current network 0.4; 6 or 10 kV, cathode stations (converters), anode grounding, instrumentation, connecting wires and cables. If necessary, the UKZ includes regulating resistors, shunts, polarized elements, control and diagnostic points (KDP), with corrosion monitoring sensors, blocks for remote control and regulation of protection parameters.

The protected structure is connected to the negative pole of the current source, a second electrode, an anode grounding electrode, is connected to its positive pole. The point of contact with the structure is called the drainage point. The schematic diagram of the method can be presented as follows:

1 - constant current source

Protected structure

Drainage point

Anode grounding

2. Overhead lines of cathodic protection installations

The operation of the overhead line consists in carrying out technical and operational maintenance, refurbishment and overhaul.

Maintenance of overhead lines consists of a set of measures aimed at protecting the elements of overhead lines from premature wear.

Overhaul of overhead lines consists in carrying out a set of measures to maintain and restore the original performance indicators and parameters of overhead lines. During overhaul, defective parts and elements are replaced either with equivalent ones or with more durable ones that improve the operational characteristics of the overhead line.

Inspections along the entire route of the overhead line are carried out in order to visually check the condition of the overhead line. During inspections, the condition of supports, wires, traverses, arrester insulators, disconnectors, attachments, bandages, clamps, numbering, posters, and the condition of routes are determined.

Extraordinary inspections are associated, as a rule, with a violation of the normal operation mode or automatic shutdown of the overhead line from relay protection, and after a successful restart, they are carried out if necessary. Inspections are purposeful in nature, they are carried out using special technical means of transportation and search for places of damage. They also identify malfunctions that threaten damage to overhead lines or human safety.

Complex of works on maintenance of overhead lines 96 V - 10 kV.

3. Transformer substations above 1 kV

KTP refers to electrical installations with voltage above 1000 V.

Complete transformer substations used in UKZ with a capacity of 25-40 kVA are designed to receive, convert and distribute electrical energy of three-phase alternating current with a frequency of 50 Hz.

A single-transformer KTP consists of an input device on the high voltage side (HVN), a power transformer, a switchgear on the low voltage side (LVSN).

During the operation of the KTP, reliable operation must be ensured. Loads, voltage level, temperature, transformer oil characteristics and insulation parameters must be within the established limits; cooling devices, voltage regulation, protection, oil facilities and other elements must be kept in good condition.

A sole inspection of a KTP can be performed by an employee who has a group of at least III, from among the operational personnel servicing this electrical installation during working hours or on duty, or an employee from among the administrative and technical personnel who has group V and the right of sole inspection on the basis of a written order the head of the organization.

4. Stations of cathodic protection

Cathodic protection stations are subdivided into stations with thyristor and inventory type converters. Thyristor stations include stations such as PASK, OPS, UKZV-R. The stations of the inventory type include stations of the OPE, Parsek, NGK-IPKZ Euro type.

Cathodic protection stations of thyristor type.

high reliability;

simplicity of design, allowing to organize the repair of the station on site by the specialists of the ECP service.

The disadvantages of thyristor stations include:

low efficiency even at rated power,

The output current has impermissibly high ripple;

Large weight of stations;

Lack of power correctors;

a large amount of copper in the power transformer.

5. Stations of cathodic protection of inverter type

The advantages of this type of station include:

high efficiency;

low level of output current ripple;

light weight (typical weight of a station with a power of 1 kW ~ 8 ... 12 kg);

compactness;

small amount of copper in the station;

high power factor (in the presence of a corrector, which is a mandatory requirement of GOST);

ease of quick replacement of the station (power converter) even by one person, especially with the modular design of the station.

The disadvantages include:

lack of the possibility of repair in the workshops of the ECP services;

lower, in comparison with thyristor, station reliability, determined by a significantly greater complexity, a large number of components and the sensitivity of a number of them to voltage surges during a thunderstorm and with an autonomous power supply system. Recently, a number of manufacturers have been supplying RMS with installed lightning protection units and voltage stabilizers, which significantly increases their reliability.

Maintenance of the converter is carried out taking into account the requirements of the technical description and according to the PPR schedule.

Routine work is a system of scheduled preventive maintenance, inspections and checks on the correct operation of ECP facilities. These works include identifying and eliminating faults and defects, checking instrumentation, accumulating and analyzing the materials obtained, characterizing wear, as well as performing periodic repairs. The essence of the system of scheduled preventive maintenance is that after the ECP means have worked out a given number of hours, a certain type of scheduled repair is carried out: current, or major.

6. Routine inspection (TO)

A complex of works on the maintenance and control of the technical condition of all structural elements of the ECP, available for external observation, carried out for preventive purposes.

During the current inspection of the VHC, the following works are performed:

checking the readings of built-in electrical measuring instruments by control devices;

setting the instrument arrows to zero of the scale;

taking readings of voltmeters, ammeters, electricity consumption meter and operating time of converters;

measuring and, if necessary, adjusting the potential of the structure at the drainage point of the RMS;

A record of the work carried out in the field logbook of the installation.

The current inspection is carried out by a by-pass method throughout the entire period of operation of the ECP facilities between scheduled repairs.

7. Current repair (TR)

Current repairs are carried out with minimal repair work. The purpose of the current repair is to ensure the normal operation of the ECP facilities before the next scheduled repair by eliminating defects and through regulation.

During the current repair of the UKZ, all works are performed, provided for technical:

Cleaning of detachable contacts and installation of connections;

removal of dust, sand, dirt and moisture from structural elements of circuit boards, coolers of power diodes, thyristors, transistors;

hauling of screw contact connections;

measurement or calculation of the resistance of the DC circuit of the UKZ;

a record of the work carried out in the field book of the installation.

8. Overhaul (KR)

The largest in terms of the scope of work is the type of scheduled preventive maintenance, in which the replacement or restoration of individual units and parts, disassembly and assembly, adjustment, testing and commissioning of the ECP system equipment is carried out. Tests must show that the technical parameters of the equipment comply with the requirements stipulated by the normative and technical documentation (NTD).

The scope of the CD of the cathodic protection station includes:

all works of medium repair;

replacement of failed supports, struts, attachments;

hauling, and, if necessary, replacing wires, insulators, traverses, hooks;

replacement of defective blocks, switching equipment;

partial or complete replacement (if necessary) of the anode and protective grounding;

inspection of the contact of the cathode cable with the protected structure.

9. Unscheduled repairs

An unscheduled repair is a repair not provided for by the PPR system, caused by a sudden failure associated with a violation of the rules of technical operation. A clear organization of the ECP service should ensure that such repairs are carried out as soon as possible. During the operation of the UKZ, measures should be taken to minimize the possibility of the need for unscheduled repairs.

Work performed in the course of all scheduled preventive and unscheduled repairs is recorded in the corresponding passports and logs for the operation and repair of electrochemical protection equipment.

10. Control and measuring points

To monitor the state of complex protection at underground structures, control and measuring points (instrumentation) must be equipped, which indicate the binding of the point of connection of the control wire to the structure.

Operation of control and measuring points (KIP) provides for maintenance and repairs (current and capital) aimed at ensuring their reliable operation. During maintenance, periodic inspections of instrumentation, preventive checks and measurements should be carried out, minor damages, malfunctions, etc. should be eliminated.

Control and measuring points (KIP) are installed on an underground structure after laying it in a trench before backfilling with earth. The installation of control and measuring points at existing structures is carried out in special pits.

Control and measuring points are installed above the structure no further than 3 m from the point of connection to the control wire structure.

If the structure is located on a site where the operation of control and measuring points is difficult, the latter can be installed in the nearest convenient places for operation, but no further than 50 m from the point of connection of the control wire to the structure.

Control and measuring points on underground metal structures must ensure reliable electrical contact of the conductor with the protected structure; reliable isolation of the conductor from the ground; mechanical strength under external influences; lack of electrical contact between the reference electrode and the structure or control conductor; availability for service personnel and the ability to measure potentials regardless of seasonal conditions.

The current inspection of instrumentation is carried out by a by-pass method throughout the entire period of operation of the ECP structures between scheduled maintenance and during seasonal measurements of protective potentials by a team of workers consisting of at least two people. Before performing work at control and measuring points, you must:

Measure the gas content.

Determine the work area and mark it with appropriate safety signs.

During the current inspection of the instrumentation, the following types of work are performed:

External examination of the instrumentation;

Checking the serviceability of the control output and outputs from the electrodes and sensors installed in the instrumentation;

Instrument alignment perpendicular to the pipeline.

Measurement production

Measure the gas content;

make an external inspection of the instrumentation;

Determine the picket and the number of the protected structure on the identification plate;

Open the shut-off device of the instrumentation and remove the cover;

get the device for measuring the protective potential;

make measurements on the terminal block of the instrumentation;

put on the instrumentation cover and close the locking device;

remove the installed safety signs;

Continue along the protected structure to the next control and measuring point (KIP).

12. Current repair (TR)

At the TR of control and measuring points, all preparatory work, current inspection work and the following types of work are performed:

Checking the serviceability of the control output and outputs from the electrodes and sensors installed in the instrumentation;

cleaning the locking devices of the column head covers;

lubrication of rubbing surfaces with CIATIM 202 grease.

coloring of control and measuring columns, racks of columns;

sodding or restoration of crushed stone blind areas;

updating and (or) restoration of identification plates;

control wire insulation check (optional);

check of contacts of test leads with a pipe (optional).

13. Overhaul (KR)

When performing a major overhaul of the instrumentation, the damaged columns, racks or posts are replaced, the control cable is replaced.

When repairing control and measuring points, work must be performed in the following sequence:

to measure the gas content;

mark the work area with appropriate safety signs;

open a pit to install the item;

open the cover of the item;

if necessary, weld the control cable leads to the pipe;

insulate the place of welding, restore the heat-insulating coating of the pipeline;

to stretch cables or wires into the cavity of the station rack, providing for their reserve of 0.4 m;

install the rack vertically into the pit;

fill the pit with soil with the compaction of the latter;

connect cables or wires to the terminals of the terminal board;

mark cables (wires) and terminals according to the connection diagram;

close the cover of the item;

apply the serial number of the point along the pipeline route with oil paint on the upper part of the rack;

to fix the soil around the point within a radius of 1 m with a mixture of sand with crushed stone with a fraction of up to 30 mm;

remove the installed safety signs.

Prior to the installation of the control and measuring point, an anti-corrosion compound must be applied to its underground part, and the above-ground part must be painted in accordance with the corporate colors of Gazprom.

Anode grounding

By location relative to the soil surface, grounding can be of two types - surface and deep.

Like all technological installations, deep anode grounding (GAS) requires proper technical operation and timely maintenance.

Inspection of the state of the GAS, maintenance (tightening the contact of the drainage cable and painting the GAS), measuring the resistance and currents of the anode in order to determine the deviation of the spreading resistance is carried out once a year after the melt water has melted and the soil has dried out. The results are recorded in the VHC journal and VHC passport.

In the case of an increase in the resistance of the GAS (this can also be noticed by the readings of the RMS ammeter or a decrease in the potential at the drainage point), the protection zone decreases.

Maintenance, periodic GAZ measurements, registration of measurements in the UKZ field log and analysis allow providing a reliable protection zone for gas pipelines and predicting further measures for the repair and restoration of GAZ.

During the operation of the cathodic protection system for underground pipelines with deep anode earthing (GAS), the problem arises of replacing them after the end of their service life. This process is complicated, and the costs are comparable to installing a new earthing switch. The desire to maximize the use of the well has led to the fact that noble, slightly soluble metals are used for the ground electrode material, as a result of which their service life increases. However, the construction cost of such GAZ is much higher than that of ferrous metal ground electrodes. In recent years, there has been an intensive search for GAZ of a replaceable design. Thus, an increase in the effectiveness of the cathodic protection of any underground pipeline can be achieved by using insulating flanges or insulating inserts. At the same time, the greatest technical and economic effect is provided by the use of insulating flanges.

At present, extended flexible anodes (PHA) for cathodic protection (SC) of oil field facilities are of great interest to ensure the possibility of reducing the cost of corrosion protection of pipelines and NPPs.

The design feature of the anode assemblies, to protect the RVS, does not allow them to be placed horizontally on the bottom due to the possible clogging of the perforations of the dielectric shell by bottom sediments. Operation with a vertical arrangement of the anodes is allowed when the water phase level is not lower than 3 m and the presence of an emergency shutdown system of the SCZ; at a lower level, protective protection is applied.

Technological efficiency of PHA application

To confirm the manufacturer's declared technical characteristics of PHA grade ELER-5V for protection against internal corrosion (VC) of capacitor equipment, specialists of NGDU "NN" together with the Institute "TatNIPIneft" developed and approved programs and methods of bench and field tests of PHA. Bench tests of samples of electrodes ELER-5V were carried out on the basis of TsAKZO NGDU "NN". Field tests were also carried out at the facilities of NGDU "NN": at the booster pump station-2 TsDNG-5 (RVS-2000) and at the UPVSN TsKPPN (horizontal settling tank GO-200).

In the course of bench tests (Fig. 1), the rates of anodic dissolution of the ELER-5V electrode in waste water were determined at values ​​of the maximum permissible linear current density and twice exceeding it and the effect of oil on the technical characteristics of the electrodes. It was found that after blocking the PHA surface with oil products, the electrodes are able to fully restore their working capacity (self-cleaning) after 6-15 days. Visual inspection of the external surface of the samples participating in the study revealed no changes.

Bench tests confirmed the technical characteristics of the PHA brand ELER-5V, declared by the manufacturer.

In preparation for field tests, the calculations of the ECP parameters of the inner surface of the vertical steel tank and the HE were performed. Taking into account the specifics of the PHA design, wiring diagrams have been developed (Fig. 2 and 3) for their placement inside the capacitive equipment.

The calculated length of the electrode for GO-200 was 40 m, the distance between the surfaces "anode-bottom" is 0.7 m. The total protection current is 6 A, the output voltage of the cathodic protection station is 6 V, the power of the cathodic protection station is 1.2 kW ...

The calculated length of the electrode for RVS-2000 was 115 m, the distance between the surfaces "anode-bottom" - 0.25 m, "anode-side surface" - 0.8 m. The total protection current - 20.5 A, the output voltage of the cathode station protection - 20 V, power of the cathodic protection station - 0.6 kW.

The estimated service life for both options is 15 years.

In the process of testing at the facilities, the parameters at the output of the SCZ were monitored and the current strength was adjusted. The potential offset, measured with a steel measuring electrode, ranged from 0.1 to 0.3 V.

According to the test report, specialists of the TatNIPIneft Institute and NGDU “NN” inspected the PHA installed in the GO (200 m 3) at the UPVSN (Fig. 4). The anode time was 280 days. The results of the examination of the PHA showed its satisfactory condition.

16. Economic efficiency of PHA application

Design features and characteristics of flexible anodes ELER-5V, according to NGDU data, made it possible to reduce the cost of equipping a HEU in comparison with protective protection by 41%. In addition, with the introduction of ELER-5V anodes, a decrease in energy consumption for VST protection was noted up to 16 times. The power consumption for the protection of the VST of NGDU "NN" was 0.03 kW (for OAO TATNEFT from 0.06 to 0.5 kW). According to the methodology for calculating the economic effect presented by NGDU "NN", when this type of anode is introduced, in comparison with protective protection, the economic effect will be 2.5 million rubles. (for the average annual volume of removal of HE for repair and cleaning at OAO TATNEFT.) The expected economic effect from the introduction of PHA in VST, annually taken out for repair at OAO TATNEFT, is 3.7 million rubles. The total annual effect will be at least RUB 6 million.

Main conclusions:

Bench and field tests of PHA at the facilities of NGDU "NN" have shown their high efficiency in the protection of tank equipment from internal corrosion (IC).

The use of PHA at OAO TATNEFT to protect the tank equipment from VC by reducing the cost of construction and operation will provide an economic effect of at least 6 million rubles.

17. Protective protection

Protection of underground structures from soil corrosion by means of protectors is effective and easy to use under certain conditions.

One of the positive features of protective protection is its autonomy.

It can be carried out in areas where there are no sources of electricity.

Protective protection systems can be used as the main ECP:

When exercising temporary protection;

As a backup protection;

for potential equalization along the pipeline;

to protect transitions;

On short pipelines.

Protectors can have various shapes and sizes and are manufactured in the form of individual castings or molds, rods, bracelet type (half rings), extended rods, wires and tapes.

The effectiveness of tread protection depends on:

Physicochemical properties of the tread;

external factors that determine the mode of its use.

The main characteristics of the protectors are:

electrode potential;

current output;

the efficiency of the tread alloy, on which the service life and the optimal conditions for their use depend.

The design of the protectors should ensure reliable electrical contact of the protectors with the structure, which should not be disturbed during their installation and operation.

To make electrical contact between the protected structure and the protector, the latter must have reinforcement in the form of a strip or rod. The reinforcement is inserted into the tread material during the manufacture of the tread.

In Russia, when protecting underground metal structures from corrosion, protectors of the PMU type, which are magnesium anodes of the PM type, packed in paper bags together with an activator, have found the greatest application.

In the center (along the longitudinal axis) of the PM protector there is a contact rod made of galvanized steel bar. A 3 m long wire is welded to the contact core. The junction of the conductor with the rod is carefully insulated. The stationary potential of magnesium protectors of the PMU type is -1.6 V relative to the MSE. The theoretical current output is 2200 A * h / kg.

In order to reduce spreading resistance and ensure stable operation, the protector is placed in a powdery activator, which is usually a mixture of bentonite (50%), gypsum (25%) and sodium sulfate (25%). The specific electrical resistance of the activator should be no more than 1 Ohm * m.

Gypsum prevents the formation of layers with poor conductivity on the tread surface, which contributes to even wear of the tread.

Bentonite (clay) is introduced to maintain moisture in the activator, in addition, clay slows down the dissolution of salts by groundwater, thereby maintaining constant conductivity, and increases the service life of the activator.

Sodium sulfate gives readily soluble compounds with corrosion products of the tread, which ensures the constancy of its potential and a sharp decrease in the specific resistance of the activator.

Under no circumstances should coke breeze be used as an activator for protectors.

After installing the protector in the ground, its current output is established within a few days.

The current output of the protectors depends significantly on the specific resistance of the soil. The lower the specific electrical resistance, the higher the current output of the protectors.

Therefore, protectors should be placed in places with a minimum resistivity and below the level of soil freezing.

18. Drainage protection

A significant danger to main pipelines is posed by stray currents of electrified railways, which, in the absence of pipeline protection, cause intense corrosive destruction in the anode zones.

Drainage protection - removal (drainage) of stray currents from the pipeline in order to reduce the rate of its electrochemical corrosion; ensures the maintenance of a stable protective potential on the pipeline (creation of a stable cathodic<#"700621.files/image019.gif">

Drainage protection schematic diagram:

Traction rail network;

Electric drainage device;

Overload protection element;

Electric drainage current control element;

Polarized element - valve manifolds assembled from several,

parallel connected avalanche silicon diodes;

Protected underground structure.

Drainage protection is not used at our factories due to the absence of stray currents and electrified railways.

Bibliography

1. Backman V, Schwenk V. Cathodic protection against corrosion: Handbook. Moscow: Metallurgy, 1984 .-- 495 p.

Volkov B.L., Tesov N.I., Shuvanov V.V. Handbook for the protection of underground metal structures from corrosion. L .: Nedra, 1975 .-- 75s.

3. Dizenko E.I., Novoselov V.F. and other Anticorrosive protection of pipelines and reservoirs. Moscow: Nedra, 1978 .-- 199 p.

Unified system of protection against corrosion and aging. Underground structures. General requirements for corrosion protection. GOST 9.602-89. M .: Publishing house of standards. 1991.

Zhuk N.P. The course of the theory of corrosion and protection of metals. M .: metallurgy, 1976.-472 p.

Krasnoyarskiy V.V. Electrochemical method of protecting metals from corrosion. M .: Mashgiz, 1961.

Krasnoyarskiy V.V., Tsikerman L.Ya. Corrosion and protection of underground metal structures. M .: Higher school, 1968. - 296 p.

Tkachenko V.N. Electrochemical protection of pipeline networks. Volgograd: VolgGASA, 1997 .-- 312 p.

Corrosion has a detrimental effect on the technical condition of underground pipelines, under its influence the integrity of the gas pipeline is disturbed, cracks appear. To protect against such a process, electrochemical protection of the gas pipeline is used.

Corrosion of underground pipelines and means of protection against it

The condition of steel pipelines is influenced by soil moisture, its structure and chemical composition. The temperature of the gas transported through the pipes, the currents wandering in the ground caused by electrified transport and the climatic conditions in general.

Types of corrosion:

• Superficial. It spreads in a continuous layer over the surface of the product. It is the least hazardous to the gas pipeline.
• Local. It manifests itself in the form of ulcers, cracks, spots. The most dangerous type of corrosion.
• Fatigue corrosion failure. The process of gradual accumulation of damage.

Methods of electrochemical corrosion protection:

• passive method;
• active method.

The essence of the passive method of electrochemical protection is to apply a special protective layer to the surface of the gas pipeline, which prevents the harmful effects of the environment. Such coverage can be:

• bitumen;
• polymer tape;
• coal tar pitch;
• epoxy resins.

In practice, it is rarely possible to apply the electrochemical coating evenly to a gas pipeline. In places of gaps, over time, the metal is still damaged.

The active method of electrochemical protection or the method of cathodic polarization is to create a negative potential on the surface of the pipeline, preventing the leakage of electricity, thereby preventing the occurrence of corrosion.

The principle of operation of electrochemical protection

To protect the gas pipeline from corrosion, it is necessary to create a cathodic reaction and exclude the anodic one. For this, a negative potential is forcibly created on the protected pipeline.

Anode electrodes are placed in the ground, the negative pole of an external current source is connected directly to the cathode - the protected object. To close the electrical circuit, the positive pole of the current source is connected to the anode - an additional electrode installed in a common environment with the protected pipeline.

The anode in this electrical circuit performs the function of grounding. Due to the fact that the anode has a more positive potential than the metal object, its anodic dissolution occurs.

The corrosion process is suppressed by the negatively charged field of the protected object. With cathodic corrosion protection, the anode electrode will be damaged directly.

To increase the service life of anodes, they are made of inert materials that are resistant to dissolution and other influences of external factors.

An electrochemical protection station is a device that serves as a source of external current in the cathodic protection system. This installation is connected to the mains, 220 W and produces electricity with set output values.

The station is installed on the ground next to the gas pipeline. It must have a degree of protection of IP34 or higher, as it works outdoors.

Cathodic protection stations can have various technical parameters and functional features.

Types of cathodic protection stations:

• transformer;
• inverter.

Transformer stations for electrochemical protection are gradually becoming a thing of the past. They are made up of a 50 Hz transformer and a thyristor rectifier. The disadvantage of such devices is the non-sinusoidal form of the generated energy. As a result, a strong current ripple occurs at the output and its power decreases.

An inverter electrochemical protection station has an advantage over a transformer one. Its principle is based on the operation of high-frequency pulse converters. A feature of inverter devices is the dependence of the size of the transformer unit on the frequency of current conversion. Higher signal frequencies require less cable and less heat loss. In inverter stations, due to smoothing filters, the ripple level of the produced current has a lower amplitude.

The electrical circuit that drives the cathodic protection station looks like this: anode grounding - soil - insulation of the protected object.

When installing a corrosion protection station, the following parameters are taken into account:

• anode ground position (anode-ground);
• soil resistance;
• electrical conductivity of object insulation.

Drainage protection installations for a gas pipeline

With the drainage method of electrochemical protection, a current source is not required, the gas pipeline is connected with the traction rails of railway transport using currents floating in the ground. Electrical interconnection is carried out due to the potential difference between the railroad rails and the gas pipeline.

The drainage current creates a displacement of the electric field of the gas pipeline located in the ground. A protective role in this design is played by fuses, as well as overload circuit breakers with reset, which adjust the operation of the drainage circuit after a high voltage drop.

The system of polarized electrical drainage is carried out using the valve manifold connections. Voltage regulation with such an installation is carried out by switching active resistors. If the method fails, more powerful electric drains are used in the form of electrochemical protection, where a railway rail serves as an anode ground electrode.

Plants for galvanic electrochemical protection

The use of protective installations for galvanic protection of the pipeline is justified if there is no voltage source near the object - power transmission lines, or the section of the gas pipeline is not impressive enough in size.

Electroplating equipment serves to protect against corrosion:

• underground metal structures not connected by an electric circuit to external power sources;
• separate unprotected parts of gas pipelines;
• parts of gas pipelines that are isolated from the current source;
• pipelines under construction temporarily not connected to corrosion protection stations;
• other underground metal structures (piles, cartridges, tanks, supports, etc.).

Galvanic protection works best in soils with electrical resistivity within 50 ohms.

Plants with extended or distributed anodes

When using a transformer station for corrosion protection, the current is distributed in a sinusoidal manner. This adversely affects the protective electric field. There is either an overvoltage at the point of protection, which entails a high power consumption, or an uncontrolled leakage of current, which makes the electrochemical protection of the gas pipeline ineffective.

The practice of using extended or distributed anodes helps to circumvent the problem of uneven distribution of electricity. The inclusion of distributed anodes in the gas pipeline electrochemical protection scheme helps to increase the corrosion protection zone and smooth the voltage line. With this arrangement, the anodes are placed in the ground along the entire gas pipeline.

The regulating resistance or special equipment provides a change in the current within the required limits, the voltage of the anode grounding is changed, with the help of this the protective potential of the object is regulated.

If several ground electrodes are used at once, the voltage of the protective object can be changed by changing the number of active anodes.

ECP of a pipeline by means of protectors is based on the potential difference between the protector and the gas pipeline located in the ground. The soil in this case is an electrolyte; the metal is restored, and the body of the protector is destroyed.

Video: Protection against stray currents

8.1 Metal structures of the MP (linear part, on-site technological pipelines, tanks, power cables, communication cables) are subject to protection against corrosion under the influence of natural and technological environments and against the action of stray currents.

8.2 The composition of means of protection of metal structures against corrosion and stray currents includes:

Protective coatings (paints and varnishes, oil bitumen coatings, polymer films and materials);

Devices for creating cathodic polarization on underground metal structures with accompanying elements (anode grounding, connecting wires and cables, connecting jumpers between parallel pipelines, control and measuring columns, reference electrodes, joint protection units);

Drainage stations (SDZ), cable lines for connecting to a source of stray currents.

8.3 To ensure the effective and reliable operation of electrochemical protection means, an ECP production service is organized as part of the OJSC main oil pipelines.

8.4 The structure, composition, equipment of the ECP service is determined by the regulations approved by the head of OJSC MN.

8.5 The ECP service organizes its work in accordance with the PPR schedule, the requirements of GOST R 51164, GOST 9.602, PEEP and the Safety Rules for the Operation of Electrical Installations of Consumers and the Regulation on the ECP Service and these Rules.

8.6 The qualification group of the service personnel must comply with the requirements of the Safety Rules for the operation of electrical installations of consumers.

8.7 Frequency of checking the operation of ECP means:

Twice a year on installations provided with remote control and on installations of protective protection;

Twice a month for installations not provided with remote control;

Four times a month at installations located in the areas of stray currents and not provided with remote control.

8.8. When checking the operation of EKhZ installations, the following indicators are measured and recorded:

Voltage and current at the output of the RMS, potential at the point of drainage;

The total operating time of the RMS under load and the consumption of active energy for the past period;

Average hourly drainage current and protective potential at the drainage point during the period of minimum and maximum load of the source of stray currents;

Potential and current at the point of drainage of tread installations.

These indicators are recorded in the ECP facilities operation log.

8.9 Measurement of protective potentials at the MP at all control and measuring points is carried out twice a year. In this case, extraordinary measurements are carried out in areas where a change has occurred:

Schemes and operating modes of ECP facilities;

Operating modes of sources of stray currents;

Schemes for laying underground metal structures (laying new ones, dismantling old ones).

8.10 Electrochemical protection must ensure, during the entire service life, continuous in time cathodic polarization of the pipeline throughout the entire length of not less than the minimum (minus 0.85 V) and not more than the maximum (minus 3.5 V) protective potentials (Appendix E).

8.11 The design of new or reconstruction of the existing ECP facilities at the MP should be carried out taking into account the conditions for laying (operating) the pipeline, data on the corrosiveness of soils, the required service life of the structure, technical and economic calculations, and the requirements of regulatory documents.

8.12 Acceptance for operation of completed construction (repair) ECP facilities must be carried out in accordance with the requirements specified in section 2 of these Rules.

8.13 The timing of the activation of electrochemical protection means from the moment of laying the sections of the underground pipeline into the ground should be minimal and not exceed one month (during repairs and routine maintenance, no more than 15 days).

Drainage protection should be put into operation simultaneously with the laying of the pipeline section in the ground, in the zone of stray currents.

8.14 Protection of metal structures of the MN from the action of aggressive components of commercial oil and produced water, protection from internal corrosion is carried out by the ECP service of JSC MN.

8.15 Control over the safety of ECP facilities on the route should be organized and conducted by the maintenance service of the linear part of the MP.

8.16 On existing oil pipelines, opening of the pipeline, welding of cathode, drainage outlets and instrumentation must be carried out by the oil pipeline operation service.

8.17 When repairing an oil pipeline with replacement of insulation, restoration of the nodes for connecting ECP facilities (instrumentation, bulkheads, SKZ, SDZ) to the pipeline should be carried out by the organization conducting the repair of insulation, in the presence of a representative of the ECP service.

8.18 A conclusion on the need to strengthen (repair) the ECP means before the complete replacement (repair) of the pipeline insulation based on electrometric measurements, visual inspection of the pipeline condition and insulation in the most dangerous places is issued by the ECP service (if necessary, representatives of research organizations are involved).

8.19 After laying and backfilling of the sections of the MP pipeline that have been completed or repaired, the ECP service must determine the continuity of the insulating coating.

If the seekers find damage to defects in the coating, the areas with defects must be opened, the insulation repaired.

8.20 To control the state of the protective coating and the operation of the ECP means, each main pipeline must be equipped with control and measuring points:

On every kilometer of the pipeline;

At least 500 m when the oil pipeline passes in the area of ​​stray currents or the presence of soils with high corrosive activity;

At a distance of 3 pipeline diameters from drainage points of ECP units and from electrical jumpers;

At water and transport crossings on both sides of the border crossing;

At gate valves;

At intersections with other metal underground structures;

In the zone of cultural and irrigated lands (ditches, canals, artificial formations).

With a multi-line piping system, instrumentation should be installed on each piping on the same cross-section.

8.21 On newly built and reconstructed MN, electrodes should be installed to control the level of polarization potential and to determine the corrosion rate without protection.

8.22 A comprehensive survey of the MN in order to determine the state of anti-corrosion protection should be carried out in areas of high corrosion hazard at least once every 5 years, and in other areas - at least once every 10 years in accordance with regulatory documents.

8.23 During a comprehensive examination of the corrosion protection of pipelines, the state of the insulating coating (insulation resistance, places of its discontinuity, changes in its physical and mechanical properties during operation), the degree of electrochemical protection (the presence of a protective potential on the entire surface of the pipeline) and the corrosion state (according to results of electrometry, pitting).

8.24 For all MN in corrosive sections of pipelines and in sections with minimum values ​​of protective potentials, additional measurements of protective potentials should be carried out using an external reference electrode, including using the shutdown method, continuously or with a step of no more than 10 m at least one once every 3 years, during the period of maximum soil moisture, as well as additionally in cases of changes in the operating modes of cathodic protection installations and in case of changes associated with the development of an electrochemical protection system, sources of stray currents and a network of underground pipelines in order to assess the degree of cathodic protection and the state of pipeline insulation ...

8.25 Anti-corrosive inspection should be carried out by ECP production laboratories at OJSC MN or by specialized organizations licensed by Gosgortekhnadzor to carry out these works.

8.26 All the damage to the protective coating detected during the inspection must be precisely tied to the route of the oil pipeline, taken into account in the operational documentation and eliminated as planned.

8.27 Electrochemical protection of pipelines' casings under roads and railways is carried out by independent protective installations (protectors). During the operation of the pipeline, it is necessary to control the presence of electrical contact between the casing and the pipeline. If there is an electrical contact, it must be removed.

8.28 The procedure for organizing and carrying out work on the maintenance and repair of ECP facilities is determined by the normative and technical documentation, which constitutes the documentary basis for the maintenance and repair of ECP units.

Work on maintenance and current repair of ECP facilities should be organized and carried out according to the operational documentation.

Work on overhaul of ECP facilities should be organized and carried out according to repair and technical documentation.

8.29 Maintenance of ECP facilities in operational conditions should include:

Periodic technical inspection of all structural elements of ECP facilities available for external observation;

In taking instrument readings and adjusting potentials;

In the timely regulation and elimination of minor faults.

8.30 Overhaul - repairs carried out during operation to ensure the operability of the ECP equipment until the next scheduled repair and consisting in the elimination of the malfunction and complete or close to full restoration of the technical resource of the ECP equipment as a whole, with the replacement or restoration of any of its component parts by adjusting them and adjustment. The scope of overhaul should include the work provided for by the current repair.

8.31 Grid cathode stations and drainage installations must be overhauled in stationary conditions, and on the track, failed installations must be replaced. For this, OJSC MN must have an exchange fund of installations.

8.32 Anode and protective grounding, protector and drainage installations, as well as power lines must be repaired by ECP teams in route conditions.

8.33 The results of all scheduled preventive repairs should be recorded in the appropriate journals and passports of ECP installations.

8.34 The norms of scheduled preventive maintenance and repair of ECP facilities are given in Appendix G.

8.35 The reserve fund of the main devices of the ECP services of OJSC MN, performing the planned technical operation (including overhaul) of the ECP devices, should be as follows:

Cathodic protection stations - 10% of the total number of SCZ in the serviced area, but not less than five;

Protectors of various types for tread installations - 10% of the total number of treads available on the track, but not less than 50;

Electric drainage installations of various types - 20% of the total number of drainage installations in the serviced area, but not less than two;

Electrodes of various types for anodic grounding of cathodic protection stations - 10% of the total number of anode grounding electrodes available on the site, but not less than 50;

Joint protection blocks - 10% of the total number of blocks available on the site, but not less than five.

8.36 The technical documentation of the ECP service should include:

ECP project for the main oil pipeline;

Insulation measurement and test reports;

ECP service work plan;

PPR and maintenance schedules;

ECP facilities operation log;

ECP failure log;

Order log;

Field logs of operation of VMS and SDZ;

Annual graphs of potential measurements through pipelines;

Defective statements for ECP equipment;

Executive drawings for anode grounding and their piping diagrams;

Factory instructions for ECP funds;

Regulation on the ECP service;

Job and production instructions;

Safety instructions.

The documentation for monitoring the state of the ECP and the protective coating must be kept throughout the entire period of operation of the oil pump.

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TECHNICAL OPERATION OF GAS DISTRIBUTION SYSTEMS - BASIC PROVISIONS - GAS DISTRIBUTION NETWORKS AND GAS EQUIPMENT ... Actual in 2018

6.8. Maintenance and repair of means of electrochemical protection of underground steel gas pipelines against corrosion

6.8.1. Maintenance and repair of means of electrochemical protection of underground gas pipelines against corrosion, monitoring the efficiency of ECP and the development of measures to prevent corrosion damage to gas pipelines are carried out by personnel of specialized structural divisions of operating organizations or specialized organizations.

6.8.2. The frequency of maintenance, repair and verification of the efficiency of the ECP is established by PB 12-529. It is allowed to combine measurements of potentials when checking the efficiency of ECP with planned measurements of electrical potentials on gas pipelines in the area of ​​operation of ECP facilities.

6.8.3. Maintenance and repair of insulating flanges and ECP units is carried out according to the schedules approved in accordance with the established procedure by the technical management of organizations - owners of electrical protection installations. During the operation of ECP facilities, a record is kept of their failures in operation and downtime.

6.8.4. Maintenance of ECP cathode installations includes:

Checking the condition of the protective ground loop (re-grounding of the neutral wire) and supply lines. An external examination checks the reliability of the visible contact of the grounding conductor with the body of the electrical protective installation, the absence of a break in the supply wires on the support of the overhead line and the reliability of the contact of the neutral wire with the body of the electrical protective installation;

Inspection of the condition of all elements of the cathodic protection equipment in order to establish the serviceability of the fuses, the reliability of contacts, the absence of traces of overheating and burns;

Cleaning equipment and contact devices from dust, dirt, snow, checking the presence and compliance of anchor signs, the condition of carpets and wells of contact devices;

Measurement of voltage, current value at the output of the converter, potential on the protected gas pipeline at the connection point when the electrochemical protection unit is turned on and off. In case of inconsistency of the parameters of the electrical protective installation with the commissioning data, it is necessary to adjust its operating mode;

Making appropriate entries in the operational log.

6.8.5. Maintenance of tread installations includes:

Measuring the potential of the protector relative to the ground with the protector turned off;

Measuring the potential "gas pipeline-ground" with the protector on and off;

The magnitude of the current in the "protector - protected structure" circuit.

6.8.6. Maintenance of insulating flange joints includes cleaning the flanges from dust and dirt, measuring the potential difference "gas pipeline-ground" before and after the flange, voltage drop across the flange. In the zone of influence of stray currents, the measurement of the potential difference "gas pipeline-ground" before and after the flange should be carried out synchronously.

6.8.7. The state of the regulated and unregulated jumpers is checked by measuring the potential difference "structure to ground" at the jumper connection points (or at the nearest measuring points on underground structures), as well as by measuring the magnitude and direction of the current (on adjustable and detachable jumpers).

6.8.8. When checking the efficiency of electrochemical protection installations, in addition to the work performed during technical inspection, the potentials are measured on the protected gas pipeline at reference points (at the boundaries of the protection zone) and at points located along the gas pipeline route, every 200 m in settlements and every 500 m on straight sections of inter-settlement gas pipelines.

6.8.9. ECP current repair includes:

All types of technical inspection work with verification of work efficiency;

Measurement of insulation resistance of live parts;

Repair of the rectifier and other circuit elements;

Elimination of breaks in drainage lines. During the current repair of ECP equipment, it is recommended to carry out its full revision in workshop conditions. At the time of the audit of the ECP equipment, it is necessary to ensure the protection of the gas pipeline by installing equipment from the replacement fund.

6.8.10. Overhaul of ECP installations includes work related to the replacement of anode ground electrodes, drainage and supply lines.

After a major overhaul, the main electrochemical protection equipment is tested in operation under load during the time specified by the manufacturer, but not less than 24 hours.

Procedure for acceptance and commissioning of electrochemical corrosion protection devices

Installations of electrochemical protection (ECP) are put into operation after completion of commissioning and stability tests for 72 hours.

Electrical protective installations are accepted into operation by a commission, which includes representatives of the following organizations: customer; design (if necessary); construction; operational, on the balance of which the constructed electrical protection installation will be transferred; offices "Podzemmetallzashita" (protection services); local authorities of Rostechnadzor; urban (rural) power grids.

The customer informs the organizations that are members of the selection committee by telephone message about the verification of the readiness of objects for delivery.

The customer submits to the selection committee: a project for an electrical protection device; certificates for the implementation of construction and installation works; as-built drawings and diagrams showing the coverage area of ​​the protective installation; a certificate on the results of setting up a protective installation; a certificate on the impact of the protective installation on adjacent underground structures; passports of electrical protective devices; certificates for acceptance of electrical protection installations into operation; permission to connect power to the electrical network; documentation on the insulation resistance of cables and spreading of protective grounding.

After reviewing the executive documentation, the selection committee checks the performance of the designed work - electrical protection means and assemblies, including insulating flange connections, control and measuring points, jumpers and other assemblies, as well as the effectiveness of electrochemical protection installations. To do this, measure the electrical parameters of the installations and the potentials of the pipeline relative to the ground on the site where, in accordance with the project, the minimum and maximum protective potential is fixed.

An electrical protective installation is put into operation only after the commission has signed an acceptance certificate.

If deviations from the project or underperformance of work affect the effectiveness of protection or contradict the requirements of operation, then they should be reflected in the act, indicating the timing of their elimination and submission for re-acceptance.

Each accepted installation is assigned a serial number and a special passport of the electrical protective installation is entered, in which all the data of the acceptance tests are entered.

When accepting the insulating flanges into operation, they present: the conclusion of the design organization for the installation of insulating flanges; a diagram of the gas pipeline route with exact bindings of the places of installation of the insulating flanges (the bindings of the insulating flanges can be given on a separate sketch); the factory passport of the insulating flange (if the latter is received from the factory).

Acceptance of insulating flanges into operation is documented by a certificate. Insulating flanges accepted for operation are recorded in a special register.

When accepting shunt electric jumpers into operation, they present the conclusion of the design organization for the installation of an electrical jumper with a justification of its type; as-built drawing of a lintel on underground structures with references to installation sites; an act for hidden works with reference to the compliance with the design of the design of the electrical jumper.

Upon acceptance into operation of control conductors and control and measuring points, an executive drawing with bindings, an act for hidden work with reference to the compliance with the design of the design of control conductors and control points is presented.

Electrical measurements on a gas pipeline

Electrical corrosion measurements on underground steel pipelines are performed to determine the degree of danger of electrochemical corrosion of underground pipelines and the effectiveness of the electrochemical protection.

Corrosion measurements are carried out in the design, construction and operation of corrosion protection for underground steel pipelines. The indicators of soil corrosivity in relation to steel are given in Table 1.

Table 1

Indicators of soil corrosivity in relation to steel

The criterion for the risk of corrosion caused by stray currents is the presence of a positive or alternating potential difference between the pipeline and the ground (anode or alternating zone). The risk of corrosion of underground pipelines by stray currents is assessed on the basis of electrical measurements. The main indicator that determines the danger of corrosion of steel underground pipelines under the influence of alternating current of electrified transport is the displacement of the potential difference between the pipeline and the ground in the negative direction by at least 10 mV in comparison with the standard potential of the pipeline.

Protection of underground steel pipelines from soil corrosion and corrosion caused by stray currents is carried out by isolating them from contact with the surrounding soil and limiting the penetration of stray currents from the environment and by cathodic polarization of the pipeline metal.

To reduce the effect of corrosion, the pipeline route is rationally chosen, and various types of insulating coatings and special methods of laying gas pipelines are used.

The purpose of corrosion measurements in the design of protection for newly constructed underground pipelines is to identify sections of routes that are dangerous in terms of underground corrosion. In this case, the corrosiveness of the soil and the values ​​of stray currents in the ground are determined.

When designing the protection of pipelines laid in the ground, corrosion measurements are carried out in order to identify areas located in areas of corrosion hazard caused by the aggressiveness of the soil or the influence of stray currents. The corrosiveness of the soil is determined by measuring the potential difference between the pipeline and the ground, as well as determining the value and direction of the current in the pipeline.

Corrosion measurements during the construction of underground pipelines are divided into two groups: carried out during the production of insulation and laying works and carried out during installation and adjustment of electrochemical protection. During installation work and adjustment of electrochemical protection, measurements are carried out to determine the parameters of electrochemical protection installations and control the effectiveness of their operation.

In the network of existing gas pipelines, the potentials are measured in the zones of action of electrical protection means of underground structures and in the zones of influence of sources of stray currents twice a year, as well as after each significant change in corrosive conditions (operating mode of electrical protection installations, power supply systems of electrified vehicles). The measurement results are recorded in the maps-schemes of underground pipelines. In other cases, measurements are taken once a year.

Soil resistivity is determined using special measuring devices M-416, F-416 and EGT-1M.

Indicating and recording devices are used to measure voltages and currents in corrosion measurements. Voltmeters are used with an internal resistance of at least 20 ohms per 1 V. When carrying out corrosion measurements, non-polarizable copper-sulfate electrodes are used.

Copper-sulfate non-polarizable electrode EN-1 consists of a porous ceramic cup and a plastic cover, into which a copper rod is screwed. A hole has been drilled in the copper rod on top for attaching the plug. A saturated solution of copper sulfate is poured into the inner plane of the electrode. The resistance of the electrode is not more than 200 ohms. The case usually contains two electrodes.

Non-polarizable copper-sulfate reference electrode NN-SZ-58 (Fig. 1) consists of a non-metallic body 3 with wooden porous diaphragm 5 fastened to the body with a ring 4 ... At the top of the vessel through a rubber stopper 1 copper rod passes 2 having a clamp (nut with washers) at the outer end for connecting the connecting wire.

Fig. 1. Non-polarizable copper-sulfate reference electrode NN-SZ-58:

1 - rubber stopper; 2 - copper rod; 3 - frame; 4 - ring; 5 - diaphragm

The portable non-polarizable copper-sulfate reference electrode MEP-AKH consists of a plastic case with a porous ceramic bottom and a screw cap with a copper electrode pressed into it. The electrode is produced with a different shape of the porous bottom - flat, conical or hemispherical. The materials from which the MEP-AKH electrodes are made, and the electrolyte poured into them, allow measurements at temperatures down to -30 ° C. The electrolyte consists of two parts ethylene glycol and three parts distilled water. In the warm season, an electrolyte from an ordinary saturated solution of copper sulfate can be used in the electrodes.

Steel electrodes are a rod 30-35 cm long and 15-20 mm in diameter. The end of the electrode, driven into the ground, is sharpened in the form of a cone. At a distance of 5-8 cm from the upper end, the electrode is drilled, and a bolt with a nut is pressed into the hole to connect the measuring instruments.

A long-term non-polarizable copper sulfate electrode with an electrochemical potential sensor is used as a reference electrode for measuring the potential difference between the pipeline and the ground, as well as the polarized potential of a steel pipeline protected by cathodic polarization.