GB/T 21448-2017Specification of cathodic protection for underground steel pipelines (English PDF)

3.1 Terms and definitions

The following terms and definitions as defined in GB/T 10123 apply to this document.

3.1.1

Anode filler anodebackfil A low-resistivity material filled around the buried anode to maintain humidity, reduce electrical resistance between the anode and the electrolyte, and prevent yang Extremely polarized.

3.1.2

Jumper bond

Use metal conductors (mostly copper conductors) to connect two points on the same metal structure or different metal structures to ensure the between two points Electrical continuity.

3.1.3

Decoupling direct device directcurrentdecouplingdevice A device that provides low impedance for AC current and high resistance channels for DC current.

For example. polarized batteries, capacitors, diodes.

3.1.4

Confluence point drainpoint the connection point between the cathode cable and the protected pipe in the cathodic protection system, through which the protection current flows back to the power source.

3.1.5

Equipotential bonding equipotential bonding the separate metal structure is directly connected to the lightning protection device by a conductor or via a surge protector to reduce the potential difference caused by the lightning current.

3.1.6

Ground bed

Buried sacrificial anode or forced current auxiliary anode system.

3.1.7

Auxiliary anode impressed-currentanode an electrode used to supply current in a forced current cathodic protection system.

3.1.8

Power-off potential instant-OFFpotential Instantaneous power-off potential to test the no-IR drop potential, the potential measured immediately after the short-term delay of the loop current interruption.

3.1.9

IR drop IRdrop

The product of all current and loop resistance (mainly electrolyte resistance and pipe resistance) in the cathodic protection circuit.

3.1.10

Polarized potential

No IR drop potential Eliminate the potential of the tube to the electrolyte after the IR drop caused by the cathodic protection current or other current.

3.1.11

Insulation device isolating/insulatingdevices it is used to isolate electrical continuity between metals, and refers to special accessories and processed parts.

3.1.12

Linear anode linearauxiliaryanode the anode body consists of a linear, continuous anode material filled with coke filler around the anode material and pre-packaged in the fabric overlay and Wear-resistant woven mesh.

For example, a conductive polymer linear anode, a mixed metal oxide (MMO-Ti) linear anode.

3.1.13

Test pile testpost

A facility located along the buried pipeline for monitoring and testing the cathodic protection parameters of the pipeline.

3.1.14

Power-on potential ONpotential the pipe-to-electrolyte potential measured during continuous operation of the cathodic protection system.

3.1.15

Pitting resistance equivalent number fittingsistanceequivalentnumber; PREN According to the chromium, molybdenum, tungsten and nitrogen components contained in the chemical composition of the stainless steel alloy, the value of the pitting resistance of the stainless steel is reflected and predicted.

3.1.16

Polarization the change in the electrolyte potential of the pipe caused by an external current.

3.1.17

Protection potential the metal corrosion rate of the pipe can be accepted in the state of the pipe to the electrolyte potential.

3.1.18

Potentiostat potentiostatunit A power supply device that automatically maintains a constant electrolyte potential to the pipe.

3.1.19

Power supply equipment rated output voltage UdN the highest output voltage specified by the power supply unit.

3.1.20

Power supply equipment rated output current IdN the maximum output current specified by the power supply unit.

3.1.21

Stray current

Current flowing in a non-designated loop.

3.2 Abbreviations

The following abbreviations apply to this document.

CCVT. Closed-cycle steam generator set.

CSE. Copper/saturated copper sulfate reference electrode.

SCC. Stress corrosion cracking.

SCE. Saturated KCl calomel electrode.

SRB. sulfate reducing bacteria.

TEG. Thermoelectric generator.

4.1 Basic requirements

4.1.1 Cathodic protection shall be adopted for buried oil and gas long-distance pipelines, oil and gas field pipelines and buried pipelines in oil and gas fields; other buried areas the pipeline should be protected by a cathode.

4.1.2 Cathodic protection shall be implemented in conjunction with the coating.

4.1.3 The cathodic protection project shall be surveyed, designed, constructed and put into operation at the same time as the main project. When the cathodic protection system is buried in the pipeline for three months Temporary cathodic protection measures should be taken to protect the pipeline when it cannot be put into operation; in a highly corrosive soil environment, temporary should be applied when the pipeline is buried Cathodic protection measures; temporary cathodic protection measures should be maintained until the permanent cathodic protection system is put into operation; for the influence of DC stray current interference Pipelines, cathodic protection systems and drainage protection measures should be commissioned within three months.

4.1.4 Cathodic protection of buried pipelines can be carried out by forced current method, sacrificial anode method or a combination of two methods, depending on the scale of the project and the soil.

The environment, the insulation performance of the pipeline anti-corrosion layer and other factors are economically and rationally selected.

4.1.5 Cathodic protection for special conditions such as high temperature, anti-corrosion layer peeling, thermal insulation layer, shielding, bacterial erosion and abnormal electrolyte pollution Protection may be ineffective or partially ineffective and should be considered during design.

4.1.6 Cathodic protection of buried pipelines in stations shall comply with the provisions of SY/T 6964.

4.2 Pipeline conditions

4.2.1 Electrical insulation

4.2.1.1 General requirements

The cathodic protection pipe shall be electrically insulated from the unprotected metal structure and the common or field grounding system.

Cathodic protection circuit piping should be electrically connected to metal structures such as pipelines in the process station, wellsite facilities, non-cathodic protected pipelines and steel casings.

insulation.

The cathodic protection pipeline can be installed with electrical insulation device in the stray current interference zone.

When electrical insulation is not possible, the cathodic protection design should provide adequate cathodic protection current and effective current distribution.

The design, materials, dimensions and construction of electrical insulation shall be in accordance with SY/T 0516 and SY/T 0086. Insulated joints should be used the overall type. For pipes conveying conductive medium, the inner surface of the insulated joint and the inner surface of the pipe connected to the insulated joint shall be coated with an inner coating.

The length of the coating should be calculated according to the resistivity of the transport medium to correct the corrosion caused by the potential difference between the two sides. The sealing material used, the anti-corrosion material and the insulating material should be adapted to the medium to be transported.

4.2.1.2 Installation position of electrical insulation device

Insulation can be placed at the following locations in the pipeline.

--- Connection with the station pipe;

--- Connection with the branch line pipe;

---Between different metal materials;

--- on the pipe segment affected by AC and DC interference;

--- Cathodic protection between the pipeline and the unprotected metal structure.

The insulating device should not be placed in a position where it is easy to form conductive condensate or free water.

4.2.1.3 Installation of electrical insulation

The installation of electrical insulation shall comply with the relevant provisions of SY/T 0086.

Insulation joints and insulation flanges shall be tested for insulation resistance before installation. The performance shall comply with the requirements of SY/T 0516.

Test facilities should be installed at the insulation joint installation.

When installing the insulation flange, it is recommended to adopt dustproof and waterproof sealing measures.

4.2.1.4 Protection of electrical insulation

Insulated joints and insulating flanges shall be provided with surge protectors.

Surge protector settings should not affect the performance of insulated joints or insulated flanges. Anti-surge protector can adopt solid state decoupler Lightning device, spark gap, electrolytic grounded battery, polarized battery, equipotential connector, etc.

4.2.2 Electrical continuity

4.2.2.1 Cathodic protection piping shall have good electrical continuity.

4.2.2.2 Electrical continuity jumpers may be placed on both sides of the electrical insulation device. For non-welded steel pipelines, electrical continuity spans shall be provided in the pipeline Joint.

4.2.2.3 Electrical continuity bridging shall be carried out in the test device.

4.2.3 Grounding

4.2.3.1 When the cathodic protection pipeline needs to be grounded, the grounding system should be compatible with the cathodic protection system, and the decoupling isolation can be installed in the grounding loop.

Device. When the pipe is partially grounded, a zinc or galvanized grounding electrode can be used to connect directly to the pipe.

4.2.3.2 All grounding facilities should not adversely affect the cathodic protection system.

4.3 Design information and site survey

4.3.1 When designing the pipeline cathodic protection system, the following technical data should be collected.

---Pipe parameters, including length, diameter, wall thickness, material type and grade, type and grade of anti-corrosion layer;

---Conveying medium, design temperature, design pressure, operating temperature and operating pressure;

--- Pipeline routing strip drawing;

--- Distribution of process stations and valve rooms;

--- Crossing the location and structure of rivers, railways, and highways;

--- Distribution of existing buried cables, metal structures and steel pipes along the line;

---Casing position and structure;

---Type of trench backfill material;

---Other electric equipment on the pipeline;

--- Topography and soil characteristics, including soil resistivity, pH, bacteria causing corrosion, frozen soil;

---Climatic conditions;

---The position, direction and rated voltage of high voltage transmission lines or buried high voltage cables;

--- Characteristic parameters of adjacent AC and DC electrified traction systems, substation locations and characteristic parameters of other interference current sources;

---Type and location of the grounding system;

--- Cathodic protection system design life;

---Environmental conditions for the installation of cathodic protection facilities;

---Insulation type and location;

---The availability of the power supply;

--- Type and location of telemetry systems that can be used for remote monitoring.

4.3.2 The site surveyed project should include the following contents.

--- The soil resistivity of different depths in the optional area of the anode bed;

--- Corrosion conditions for bacterial activity;

--- AC and DC interference source characteristic parameters and relative position relationship with the pipeline;

-- The data collected in -4.3.1 does not meet the design requirements of the project.

4.4 Cathodic protection criteria

4.4.1 No IR drop cathodic protection potential

The no-IR reduction cathodic protection potential EIRfree should meet the requirements of equation (1).

El<=EIRfree<=Ep (1)

In the formula.

El --- limit critical potential;

EIRfree---no IR drop cathodic protection potential;

Ep --- The minimum protection potential when the metal corrosion rate is less than 0.01 mm/a.

4.4.2 Cathodic protection potential

The cathodic protection potential should meet the requirements of Table 1. During the life of the pipeline, consideration should be given to the cathodic protection of the dielectric resistivity changes around the pipe.

The effect of the potential.

Table 1 Natural potential, minimum protection potential and limiting critical potential of metallic materials in soil and water

Metal or alloy environmental conditions Natural potential ECOR (Reference) Minimum protection potential Ep (no IR drop) Limiting critical potential El (no IR drop) Carbon steel, low alloy steel and cast iron General soil and water environment -0.65~-0.40 -0.85 Eal T >60°C soil and water environment c -0.80~-0.50 -0.95 Eal T1000ohm·m Oxygen-containing soil and water environment-0.40~-0.20 -0.65 Eal Sulfate-reducing bacteria (SRB) rot Oxidized soil and water environment-0.80~-0.65 -0.95 Eal Austenitic PREN40 Aussie Stainless steel Martensite or austenitic-iron Prime (double phase) stainless steel Neutral and alkaline at ambient temperature Soil and water environment-0.10~ 0.20 -0.50 Edl-0.10~ 0.20 -0.30 --0.10~ 0.20 -0.50 Edl stainless steel at ambient temperature, acidic Soil and water environment-0.10~ 0.20 Eep Edl Galvanized steel at ambient temperature, soil and water environment-0.20~0.00 -0.20 --1.10~0.00 -1.20 -Note. All potentials are relative to copper/saturated copper sulfate reference electrodes (CSE, the same below).

a For high-strength non-alloy steels and low-alloy steels with yield strengths exceeding 550 N/mm2, the critical limiting potential values should be documented or passed through experiments.

determine.

b When the temperature is 40 ° C ~ 60 ° C, the minimum protection potential value can be at 40 ° C potential value (-0.65V, -0.75V, -0.85V or -0.95V) and the potential value at 60 ° C (-0.95 V) was determined by linear interpolation.

c High pH stress corrosion cracking (SCC) risk increases with increasing temperature.

d If there is a martensite and ferrite phase, the risk of hydrogen embrittlement should be documented or experimentally determined.

e should be determined by literature or experiment.

4.4.3 Limiting the critical potential

The limiting critical potential El of the pipeline anti-corrosion layer should not be more negative than -1.20V (CSE), and should prevent the cathode from peeling off, foaming, Tube body hydrogen embrittlement phenomenon.

4.4.4 100mV cathode potential negative migration criterion

4.4.4.1 When the cathodic protection criteria of Table 1 are not met, a criterion that the cathode potential is offset by at least 100 mV can be used.

4.4.4.2 100mV cathode potential negative offset criterion is not applicable to the environment with temperature greater than 40 °C, soil containing sulfate-reducing bacteria, in the case of interference current, balancing current and earth current, there is a risk of external stress corrosion, as well as pipe connections or by various gold it is a component of the composition.

4.4.5 Cathodic protection criteria under AC interference

4.4.5.1 When the pipeline is affected by AC interference, the AC induced voltage and/or AC current density on the pipeline shall be tested to evaluate the AC dry the degree of disturbance.

4.4.5.2 For pipelines affected by AC interference, the cathodic protection potential shall meet the requirements of Table 1 and shall also meet the requirements of GB/T 50698.

Provisions.

4.4.5.3 AC interference protection measures and protective effects shall meet the requirements of GB/T 50698.

4.4.6 Cathodic protection criteria under DC interference

4.4.6.1 When the pipeline is affected by DC interference, DC interference protection measures shall be taken.

4.4.6.2 DC interference protection measures and protective effects shall meet the requirements of GB 50991.

5.1 Power equipment

5.1.1 General requirements

5.1.1.1 The power supply equipment should use the stable or reliable AC power supply of the mains or the station, and the solar energy can be used in places where there is no available power.

DC power supply for batteries, wind turbines, natural gas generators, TEG, CCVT, etc. The external power supply used by the power supply equipment should be set up independently.

Electric box.

5.1.1.2 The chassis of the power supply unit should be grounded.

5.1.1.3 The power supply equipment used in the explosion-proof area shall comply with the provisions of GB 50058.

5.1.1.4 The installation environment of the power supply device should be compatible with the environment in which the device is used. Measures should be taken to ensure that the power supply device works normally.

5.1.2 Power Equipment Selection

5.1.2.1 The power supply equipment can be selected from a potentiostat and a transformer-rectifier.

5.1.2.2 The power supply equipment shall have a constant potential, a constant current or a rectifier operating mode.

5.1.2.3 The rated output current and rated output voltage of the power supply equipment should not be less than 1.5 times of the actual requirements.

5.1.2.4 The output power of the power supply equipment can be determined by referring to Appendix A.

5.1.3 Basic requirements for power supply equipment

5.1.3.1 The power supply equipment shall be able to work normally under the following environmental conditions.

--- Ambient temperature. -25 ° C ~ 50 ° C;

---Relative humidity. 15%~90%;

--- Atmospheric pressure. 86kPa ~ 106kPa.

5.1.3.2 The power supply equipment shall be capable of operating normally under the following external power conditions.

a) AC power supply.

1) Single phase 220 (1 ± 10%) V, frequency. 50 (1 ± 5%) Hz;

2) Three-phase 380 (1 ± 10%) V, frequency. 50 (1 ± 5%) Hz.

b) DC power supply. 87.5% UdN~117.5% UdN.

5.1.3.3 The output voltage of the power supply equipment should not exceed 50V.

5.1.3.4 The insulation resistance of the input and output terminals of the power supply unit to the casing shall be not less than 10Mohm.

5.1.3.5 The electrical strength of the power supply equipment shall meet the following requirements.

a) AC power input terminal to the chassis, equipment "zero position negative" terminal to each remote interface output terminal should be able to withstand 1500V (with RMS), 50Hz test voltage, test time 1min, no arcing or breakdown phenomenon;

b) The DC power input terminal should be able to withstand 750V (effective value) and 50Hz test voltage for the casing. The test time is 1min.

Now flying arc or breakdown phenomenon.

5.1.3.6 The lightning protection of power equipment should meet the following requirements.

a) The appropriate lightning protection unit should be installed at the input and output terminals of the power supply equipment;

b) When the anode cable and piping are affected by inductive lightning, between the anode cable and the cathode cable, the anode...