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GB/T 21448-2017

Chinese Standard: 'GB/T 21448-2017'
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GB/T 21448-2017English619 Add to Cart Days<=6 Specification of cathodic protection for underground steel pipelines Valid GB/T 21448-2017
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BASIC DATA
Standard ID GB/T 21448-2017 (GB/T21448-2017)
Description (Translated English) Specification of cathodic protection for underground steel pipelines
Sector / Industry National Standard (Recommended)
Classification of Chinese Standard E98
Classification of International Standard 75.200
Word Count Estimation 34,337
Date of Issue 2017-12-29
Date of Implementation 2018-07-01
Older Standard (superseded by this standard) GB/T 21448-2008
Drafting Organization China Petroleum Pipeline Bureau Engineering Co., Ltd.
Administrative Organization National Oil and Gas Standardization Technical Committee
Regulation (derived from) National Standards Bulletin 2017 No. 32
Proposing organization National Oil and Gas Standardization Technical Committee (SAC/TC 355)
Issuing agency(ies) People's Republic of China General Administration of Quality Supervision, Inspection and Quarantine, China National Standardization Administration

GB/T 21448-2017
Specification of cathodic protection for underground steel pipelines
ICS 75.200
E98
National Standards of People's Republic of China
Replace GB/T 21448-2008
Technical specification for cathodic protection of buried steel pipelines
(ISO 15589-1.2015, Petroleum, petrochemical and naturalgasindustries-
Cathodicprotectionofpipelinesystems-Part 1. On-landpipelines, NEQ)
Released on.2017-12-29
2018-07-01 implementation
General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China
China National Standardization Administration issued
Content
Foreword I
1 range 1
2 Normative references 1
3 Terms, definitions and abbreviations 1
4 General 3
5 forced current system 7
6 sacrificial anode system 11
7 Testing and Monitoring 15
8 Additional measures 17
9 Construction and commissioning 19
10 Management and Maintenance 22
Appendix A (informative) Cathodic protection calculation formula 27
Foreword
This standard was drafted in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 21448-2008 "Technical Specifications for Cathodic Protection of Buried Steel Pipelines", compared with GB/T 21448-2008,
The main technical changes except editorial changes are as follows.
--- further clarified the requirements for temporary cathodic protection (see 4.1.3);
--- Modified the "Cathode Protection Guidelines" and added "Cathode Protection Guidelines under AC Interference" and "Cathode Protection Guidelines under DC Interference"
The provisions of "" (see 4.4);
--- Increased requirements for forced current system power supply equipment (see 5.1);
--- Increased the main performance requirements of graphite anodes, conductive polymer linear anodes and MMO-Ti linear anodes (see 5.2.5.2,
5.2.5.3 and 5.2.5.4);
--- Added "Cathodic Protection for Parallel Pipes" requirements (see 5.3);
--- Modified sacrificial anode performance specifications (see 6.2 and 6.3); increased design requirements for sacrificial anode systems (see 6.4.1);
Changed the selection requirements of the sacrificial anode type and the requirements for filling materials (see 6.4.2 and 6.5);
--- Refined the special requirements of the test device (see 7.1.2), increased the type of test piles (see 7.1.3), added "check films,
Polarized probe and resistance probe" (see 7.1.4);
--- Refined the requirements related to casing, lightning protection and surge protectors in "Additional Measures" (see 8.2, 8.3 and 8.4);
--- Added "construction and commissioning" (see Chapter 9);
---Modified the contents of "Management and Maintenance" (see Chapter 10);
--- Revised Appendix A and removed Appendix B. Appendix A was revised from a normative appendix to an informative appendix (see Appendix A).
This standard uses the redrafting method to refer to ISO 15589-1.2015 "Cathodic protection of pipeline systems for petroleum, petrochemical and natural gas industries"
Part 1. The Onshore Pipeline is compiled, and the degree of conformity with ISO 15589-1.2015 is non-equivalent.
This standard is proposed and managed by the National Oil and Gas Standardization Technical Committee (SAC/TC355).
This standard was drafted. China Petroleum Pipeline Engineering Co., Ltd., China Petroleum Planning Institute, China National Petroleum Pipeline Branch,
Southwest Branch of China National Petroleum Corporation Engineering Design Co., Ltd., Sinopec Pipeline Storage and Transportation Co., Ltd.
The main drafters of this standard. Huang Liuqun, Zhang Wenwei, Liao Wei, Luo Feng, Huang Li, Zheng Ansheng, Yan Mingzhen, Li Guohui, Teng Yanping, Zhang Ping,
Huang Chunrong, Ma Xiaocheng, Liu Jia, Ding Jie, Wang Jie, Guo Juanli, Chen Shasha, Fu Wei, Pan Huailiang, Fu Pingping, Cheng Ming, Zhang Yanfeng.
The previous versions of the standards replaced by this standard are.
---GB/T 21448-2008.
Technical specification for cathodic protection of buried steel pipelines
1 Scope
This standard specifies the design, construction, testing, management and maintenance of the external surface cathodic protection system for land-buried steel pipelines (hereinafter referred to as pipelines).
Minimum technical requirements for protection.
This standard applies to land-buried steel oil, gas, water pipelines.
2 Normative references
The following documents are indispensable for the application of this document. For dated references, only dated versions apply to this article.
Pieces. For undated references, the latest edition (including all amendments) applies to this document.
GB/T 4208 enclosure protection grade
GB/T 4950 zinc-aluminum-cadmium alloy sacrificial anode
GB/T 10123 Metal and alloy corrosion basic terms and definitions
GB/T 17731 magnesium alloy sacrificial anode
GB/T 21246 buried steel pipeline cathodic protection parameter measurement method
GB 50058 Explosion Hazardous Environment Power Equipment Design Specification
GB 50217 Power Engineering Cable Design Specification
GB/T 50698 buried steel pipeline AC interference protection technical standards
GB 50991 buried metal pipeline DC interference protection technical standards
SY/T 0029 Buried steel inspection sheet application technical specification
SY/T 0086 Cathodic Protection Pipe Electrical Insulation Standard
SY/T 0087.1 Corrosion Evaluation Criteria for Steel Pipelines and Storage Tanks Direct Evaluation of External Corrosion of Buried Steel Pipelines
SY/T 0096 forced current deep anode bed technical specification
SY/T 0516 Technical Specifications for Insulated Joints and Insulated Flanges
SY/T 6964 Technical Specification for Cathodic Protection of Oil and Gas Stations
3 Terms, definitions and abbreviations
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 polarization
The change in the electrolyte potential of the pipe caused by an external current.
3.1.17
Protection potential protectionpotential
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 ratedoutputvoltage
UdN
The highest output voltage specified by the power supply unit.
3.1.20
Power supply equipment rated output current ratedoutputcurrent
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 General
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 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
40 ° C \u003cT\u003c60℃的土壤和水环境 - Ebp Eal
T>60°C soil and water environment c -0.80~-0.50 -0.95 Eal
T<40°C, 100<ρ<1000Ω·m
Oxygen-containing soil and water environment
-0.50~-0.30 -0.75 Eal
T<40°C, ρ>1000Ω·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 PREN<40
Stainless steel
PREN>40 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 forced current system
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 10MΩ.
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 cable and the zero junction cathode cable
The limiting voltage is 100V~150V, the overvoltage current capacity is 20kA (8/20μs), the leakage current is no more than 20mA; the reference cable and
The limiting voltage between the zero-connected cables is 5V, the over-current current capacity is 50A (10/1000μs), and the leakage current is less than 0.3μA (3V).
5.1.3.7 The power supply equipment shall be equipped with an overcurrent protection device; when the output current of each phase of the cathodic protection power supply device reaches 110% of the rated value,
It should be indicated by a yellow indicator light and an alarm will be issued, which will automatically limit the current for 2 minutes.
5.1.3.8 When the potentiostat cannot operate at a constant potential, it should have the function of automatically converting into a constant current working mode, and with manual locking
The function of the potential mode of operation and the function of manually locking the constant current mode of operation.
5.1.3.9 The control accuracy of the power supply equipment shall meet the following requirements.
a) When the load changes and the grid voltage changes within the range specified in this standard, the change of the potential value of the potentiostat at the energization point should be less than
5mV.
b) When operating in constant current mode, the output current is within 2% IdN~100% IdN, and the control accuracy of constant current should be ±1%, and the offset
Not more than 50mA.
5.1.3.10 When remote monitoring and control is required, the power supply equipment shall provide a point-to-point or (and) digital communication interface.
5.1.3.11 The solder joints of the circuit boards and wires in the power supply equipment shall be treated with mildew, moisture and dust. Case protection level when installing outdoors
It should be IP55 and above specified in GB/T 4208; when installed indoors, the enclosure protection grade should be IP31 and above specified in GB/T 4208.
5.2 auxiliary anode bed
5.2.1 General requirements
5.2.1.1 The design and location of the auxiliary anode bed (hereinafter referred to as the bed) shall meet the following conditions.
--- The quality of the bed material should meet the design life of the cathodic protection system;
--- The maximum voltage drop required for the grounding resistance of the ground bed should be less than 70% of the rated output voltage;
--- Avoid unacceptable interference effects on adjacent buried metal structures.
5.2.1.2 Auxiliary anode bed is divided into deep well type and shallow buried type. The following factors should be analyzed when selecting.
--- Rock land quality characteristics and soil resistivity as a function of depth;
---Water table;
--- Extreme changes in soil conditions in different seasons;
--- Topographical features;
---Shielding effect;
--- the possibility of third party damage;
---The surrounding environment planning situation;
--- Economic.
5.2.1.3 When multiple floor beds are used, the output current of each bed should be independently adjustable.
5.2.2 Deep well anode bed
5.2.2.1 The design, installation, operation and maintenance of deep well anode beds shall comply with the provisions of SY/T 0096. Ground bed grounding resistance calculation
The soil resistivity values at the midpoint depth of the anode section length were used and the effects of soil resistivity differences at different levels were analyzed.
5.2.2.2 Deep well anode beds shall be fitted with exhaust pipes made of non-metallic chlorine-resistant materials to relieve air resistance between the anode and the conductive packing.
5.2.2.3 Permanent bed marking piles shall be provided at the deep well anode bed.
5.2.3 shallow buried anode bed
5.2.3.1 The shallow buried anode bed can be horizontal or vertical. In non-permafrost regions, the auxiliary anode should be installed below the frozen soil layer, and the buried depth is not
It should be less than 1m; in the permafrost area, the auxiliary anode should be installed in the non-permafrost layer or the frozen-thawing stratum between the island-like frozen soil.
5.2.3.2 A permanent bed marking pile shall be provided at the head end of the shallow buried anode bed.
5.2.4 auxiliary anode
5.2.4.1 Auxiliary anodes are available with high silicon cast iron anodes, graphite anodes, steel anodes, conductive polymer anodes and metal oxide anodes.
5.2.4.2 The anode material and mass selection shall be calculated as 125% of the maximum expected protection current during the design life of the cathodic protection system.
5.2.4.3 The anode should be filled with metallurgical coke, petroleum coke or graphite filler. The carbon content of the filler should be greater than 85%.
The maximum particle size should be no more than 15mm.
5.2.4.4 Auxiliary anode grounding resistance, working life and anode number calculation can be found in Appendix A.
5.2.5 Main performance of common auxiliary anode
5.2.5.1 The chemical composition of the high silicon cast iron anode shall comply with the requirements of Table 2. The allowable current density of the anode is 5A/m2~80A/m2.
The rate of consumption should be less than 0.5kg/(A · a). The contact resistance between the anode lead wire and the anode should be less than 0.01 Ω, and the pull-out force value should be greater than the anode itself.
1.5 times the mass, the joint seal is reliable. The anode lead length should be no less than 1.5m. The anode surface should be free of obvious defects.
Table 2 Chemical composition of high silicon cast iron anode
Serial number type
Mass fraction of major chemical constituents
Impurity mass fraction
Si Mn C Cr Fe PS
1 Ordinary 14.25~15.25 0.5~1.5 0.80~1.05 Balance ≤0.25 ≤0.1
2 plus chrome 14.25~15.25 0.5~1.5 0.8~1.4 4~5 balance ≤0.25 ≤0.1
5.2.5.2 The performance of graphite anodes shall comply with the requirements of Table 3. The anode should be impregnated with linseed oil or paraffin, and the anode leads to the cable and anode.
The contact resistance should be less than 0.01 Ω, the pull-off force value should be greater than 1.5 times the mass of the anode itself, and the joint should be sealed. The length of the anode cable should not be
Less than 1.5m. The anode surface should be free of obvious defects.
Table 3 Main performance of graphite anode
density
g/cm3
Porosity
Ash
Degree of graphitization
Resistivity
Ω·mm2/m
Consumption rate
Kg/(A·a)
Allow current density
A/m2
1.7~2.2 25~30 ≤0.5 ≥81 9.5~11.0 <0.6 5~10
5.2.5.3 Conductive polymer The performance of the linear anode shall comply with the requirements of Table 4.
Table 4 Main properties of conductive polymer linear anode
Maximum output line current density
mA/m
Filler without filler
Minimum construction temperature
Anode copper core cross-sectional area
Mm2
Anode outer diameter
Mm
Minimum bending radius
Mm
52 82 -18 16 13 150
5.2.5.4 MMO-Ti linear anode body shall be a linear, continuous titanium-based mixed tantalum/niobium metal oxide anode, the nature of the anode body
Can meet the requirements of Table 5.
Table 5 MMO-Ti anode body performance indicators
Project performance index test method
Substrate primary titanium ASTMB863-2010
Anti-corrosion layer thickness
g/m2
≥6 ASTMB568-2009
Service life at rated maximum line current density
≥25 NACETM108-2008
Maximum operating current density
A/m2
100 In the soil environment, use filler
5.2.5.5 The consumption rate of steel anode is 8kg/(A·a)~10kg/(A·a).
5.3 Cathodic protection of parallel pipes
5.3.1 Parallel pipelines shall be laid in the same trench, parallel pipelines with the same or similar diameters, and parallel pipelines constructed by cathodic protection stations shall be adopted.
Combined cathodic protection. The parallel pipelines to be built in the same trench and the parallel pipelines to be laid in the same trench should be respectively implemented as cathodes.
protection.
5.3.2 Parallel pipelines that are parallel to the high-voltage transmission line and parallel or multiple times with the electrified railway shall not be jointly protected.
5.3.3 When parallel pipe is used for joint cathodic protection, it is advisable to set jumper at the confluence point and other suitable positions.
5.3.4 When performing parallel cathodic protection on parallel pipelines, it is advisable to select the appropriate anode bed method or location to avoid mutual interference;
Control measures should be taken when there is interference.
5.3.5 Parallel pipelines with cathodic protection separately shall be jointly commissioned during commissioning.
6 sacrificial anode system
6.1 Basic requirements
6.1.1 Sacrificial anode systems are suitable for protecting small diameter pipes or distances laid in soils, water, marshes or wetlands with low resistivity.
A pipe that is short and has a good quality coating.
6.1.2 When selecting a sacrificial anode, the following factors should be considered.
---No suitable available power source;
---Electrical equipment is difficult to maintain;
--- Temporary protection;
--- Supplement to the forced current system protection;
---The soil melting zone around the pipeline in the permafrost;
--- Where there is a cathodic protection shield.
6.1.3 The type of material (such as trademark), anode quality (excluding anode filler) and furnace number should be marked on the sacrificial anode. The supplier should provide complete
The documentation provides information on the number, type, quality, diameter, chemical composition and performance data of the anode.
6.2 Zinc alloy sacrificial anode
6.2.1 Chemical composition
The content of zinc in the sacrificial anode component of zinc alloy should be not less than 99.314%, and the content of zinc in high-purity zinc alloy should be not less than 99.99%.
The content of his elements should meet the requirements of Table 6.
Table 6 Zinc alloy sacrificial anode chemical composition
element
The mass fraction of the main chemical components of zinc alloy
Mass fraction of main chemical components of high purity zinc alloy
Al 0.1~0.5 ≤0.005
Cd 0.025~0.07 ≤0.003
Fe ≤0.005 ≤0.0014
Pb ≤0.006 ≤0.003
Cu ≤0.005 ≤0.002
Total content of other impurities ≤ 0.1 -
6.2.2 Rod-shaped zinc alloy sacrificial anode
The electrochemical performance of the rod-shaped zinc alloy sacrificial anode shall comply with the provisions of Table 7, and the structure and dimensions shall comply with the provisions of GB/T 4950. Make
When using a zinc alloy sacrificial anode of other composition, a proof material meeting the requirements of Table 7 shall be provided.
Table 7 Electrochemical performance of a rod-shaped zinc alloy sacrificial anode in soil environment
Performance zinc alloy
Open circuit potential
-1.05~-1.10
Working potential
-1.00~-1.05
Table 7 (continued)
Performance zinc alloy
Actual capacity
A·h/kg
≥780
Current efficiency
≥95
Consumption rate
Kg/(A·a)
11.2
Note. All potentials are relative to CSE.
6.2.3 Ribbon zinc alloy sacrificial anode
The electrochemical performance of the ribbon zinc alloy sacrificial anode shall comply with the requirements of Table 8. The specifications and dimensions shall comply with the requirements of Table 9, and the sectional legend may be
See Figure 1.
Table 8 Electrochemical performance of ribbon zinc alloy sacrificial anode
model
Open circuit potential
Relative CSE vs. SCE
Theoretical capacitance
A·h/kg
Actual capacity
A·h/kg
Current efficiency
High purity zinc ≤-1.10 ≤-1.03 820 ≥740 ≥90
Note. Experimental medium - artificial seawater.
Table 9 Specification and size of strip zinc alloy sacrificial anode
Anode cross section size D1 × D2
Mm×mm
25.40×31.75 15.88×22.22 12.70×14.28 8.73×10.32
Anode strip quality
Kg/m
3.57 1.785 0.893 0.372
Steel core diameter
Mm
4.70 3.43 3.30 2.92
Standard length
30.5 61 152 305
Standard roll inner diameter
Mm
900 600 300 300
Center deviation of steel core
Mm
-2~ 2
Figure 1 is a schematic cross-sectional view of a ribbon zinc anode
6.3 magnesium alloy sacrificial anode
6.3.1 Chemical composition
The chemical composition of the magnesium alloy sacrificial anode shall comply with the requirements of Table 10.
Table 10 Chemical composition of magnesium alloy sacrificial anode
element
Standard mass fraction of major chemical components
Mass fraction of main chemical constituents of magnesium and manganese
Mn ≥0.25 0.50~1.50
Al 5.0~7.0 ≤0.05
Zn 2.0~4.0 ≤0.03
Fe ≤0.005 ≤0.03
Ni ≤0.003 ≤0.002
Cu ≤0.08 ≤0.02
Si ≤0.30 ≤0.05
Other impurities ≤0.30 ≤0.30
Mg residual margin
6.3.2 Electrochemical performance
The electrochemical performance of the magnesium alloy sacrificial anode shall comply with the requirements of Table 11. Use of other components of magnesium alloy sacrificial anodes should be provided
The certification materials specified in Table 11.
Table 11 Electrochemical performance of magnesium alloy sacrificial anode
Performance standard magnesium manganese type
Open circuit potential
-1.57~-1.60 -1.77~-1.82
Working potential
-1.52~-1.57 -1.64~-1.69
Table 11 (continued)
Performance standard magnesium manganese type
Actual capacity
A·h/kg
Actual consumption rate
Kg/(A·a)
7.5 7.5
Note. All potentials are relative to CSE.
6.3.3 Structure and dimensions
The sacrificial anode structure of magnesium alloy can be selected from rods and strips. The structure and size of magnesium alloy sacrificial anodes should conform to GB/T 17731.
Provisions.
6.4 Design of sacrificial anode system
6.4.1 Design principles
The design of the sacrificial anode system should meet the following requirements.
--- Anode material should be able to continuously provide the protection current required by the pipeline;
--- The total mass of the anode should meet the design life requirements of the cathodic protection system;
--- The total mass calculation of the anode should take into account the anode utilization factor, and the anode utilization factor is generally taken as 0.8;
--- The adverse effects of the anode and its packing on the environment should be analyzed.
6.4.2 Sacrificial anode selection
6.4.2.1 The type of sacrificial anode shall be selected in accordance with the requirements of Table 12.
Table 12 Application choices for sacrificial anode types
Anode type
Soil resistivity
Ω·m
Zinc alloy sacrificial anode <50
Magnesium alloy sacrificial anode 50~100
6.4.2.2 For zinc alloy sacrificial anodes, when the soil resistivity is greater than 50 Ω·m, the effectiveness shall be confirmed by field tests.
6.4.2.3 For magnesium alloy sacrificial anodes, when the soil resistivity is greater than 100 Ω·m, the effectiveness shall be confirmed by field tests.
6.5 Sacrificial anode filling material
The sacrificial anode packing consists of gypsum powder, bentonite and industrial sodium sulfate, and their mass percentage is 75.20.5.
6.6 Sacrificial anode to pipe connection
The sacrificial anode cable should be electrically connected to the pipe through the test device.
6.7 Sacrificial anode arrangement
6.7.1 Rod-shaped sacrificial anode
6.7.1.1 The rod-shaped sacrificial anode can be either single-buried or multi-layered. The same anode or open circuit should be used for the same anode.
A similar anode.
6.7.1.2 Rod-shaped sacrificial anode embedding method is divided into vertical and horizontal according to axial and radial directions. In general, the sacrificial anode should be suitable
The outer wall of the pipeline shall be 3m~5m, the minimum shall not be less than 0.5m, and the buried depth shall be no less than 1m from the top of the anode. When grouped,
The anode spacing should be 2m~3m.
6.7.1.3 Rod-shaped sacrificial anodes shall be buried below the frozen soil layer. Buried in a dry zone or a bed in a riverbed with a groundwater level below 3 m.
The burial should be appropriately deepened. In the permafrost zone, the anode should be installed in a non-permafrost layer between the frozen-thawing stratum or the island-like frozen soil.
6.7.1.4 When a rod-shaped sacrificial anode is arranged, there shall be no other metal structures between the anode and the pipe.
6.7.2 Ribbon sacrificial anode
The strip sacrificial anode should be laid or wound in the same trench as the pipe according to the application and needs.
6.7.3 Sacrificial anode for special purposes
When the sacrificial anode is used as a grounding electrode, AC/DC interference protection, reference electrode, etc., it should be arranged according to the application and needs.
7 Testing and monitoring
7.1 Test device
7.1.1 General requirements
The cathodic protection test device should be installed in parallel with the cathodic protection system. The test device shall be laid along the pipeline line, adjacent test
The device spacing should be no more than 3km. In urban areas or industrial areas, the interval between adjacent test devices should not exceed 1km; in stray current interference
Within the ringing area, the test set can be properly encrypted. The test device should be installed above the pipe and marked.
7.1.2 Special requirements
7.1.2.1 Test equipment should be installed at the following locations.
---Insulated joints;
---Metal casing;
--- Connection with other pipelines or facilities;
---Auxiliary test piece and grounding facility connection;
---Forcing current cathodic protection system convergence point;
---Auxiliary anode;
--- Pipeline directional drilling crossing;
--- Location where current testing is required.
7.1.2.2 Test equipment should be installed at the following locations.
--- Pipeline and intersection of AC and DC electrified railways or parallel sections;
--- Pipes and AC high voltage lines intersect or parallel segments;
--- Intersection with external pipelines;
---The intersection of the pipeline with the main road or dam;
--- Pipes crossing railways or rivers;
--- Location close to other cathodic protection structures.
7.1.2.3 For parallel pipes laid in non-slots, each pipe shall be provided with a separate test device, and the test device shall be installed in the corresponding pipe.
Above.
7.1.2.4 There shall be no less than two cables connected to the pipeline in each test device. The cables shall be distinguished by color or other marking methods and shall be fully
Line uniformity.
7.1.3 Test pile
Test pile types mainly include.
---potential test pile;
--- Current test pile;
---Insulated joint test pile;
---Pipe cross test pile;
--- Long-acting reference electrode, test piece, probe, polarization probe, DC decoupling facility and other test piles;
---Transport tube and metal casing insulation performance test pile.
7.1.4 Inspection sheet, polarized probe and resistance probe
7.1.4.1 An inspection piece, polarized probe or resistance probe can be installed under the following conditions.
--- Synchronous interrupt method can not effectively measure the ground potential of the tube;
---Evaluate the cathodic protection effect of the pipeline;
---Evaluate the risk of AC corrosion;
---Detect AC or DC current density;
--- Detect the corrosion rate of pipes in the soil.
7.1.4.2 Soil corrosion and cathodic protection can be evaluated using buried steel inspection sheets. Can be used separately or simultaneously depending on the purpose of the test
Corrosion weight loss test piece and cathodic protection potential test piece.
7.1.4.3 The inspection piece, polarized probe and resistance probe shall be installed close to the pipe. The long-acting reference electrode of the polarized probe should be close to the test piece and should be needed
To be calibrated regularly.
7.2 Monitoring device
7.2.1 Crossing with external piping
It is advisable to set up monitoring devices when crossing other external pipes. Two test cables should be connected to each pipe to connect to the monitoring device.
The cable can be connected directly or through a resistor or diode.
7.2.2 Metal casing
When the metal casing is used to pass through, the two test cables should be connected to the monitoring device on both sides of the casing and the conveying pipe;
The device detects the electrical insulation between the metal sleeve and the delivery tube.
7.2.3 Current monitoring device
Each test cable of the current test post should be identified to determine the direction of the current.
7.2.4 Insulated joints
Two test cables should be connected to the monitoring device on both sides of the insulated joint. In the monitoring device, it should be protected against surges as needed
The protection device is connected.
7.2.5 Drain point
In the area affected by stray current interference, the discharge point of direct discharge, polar discharge or forced discharge should be from the pipeline, interference source or connection.
The cable of the ground is led to monitoring.
Related standard:   GB/T 21447-2018  GB/T 21451.1-2015
Related PDF sample:   GB/T 21447-2018  GB/T 18604-2014
   
 
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