SY/T 0036-2000 Design specification for forced current cathodic protection of buried steel pipelines
Some standard content:
1 General Principles
Petroleum and Natural Gas Industry Standard of the People's Republic of China
Design Specification for Compulsory Current Cathodic Protection of Buried Steel Pipelines
Approval Department: State Administration of Petroleum and Chemical Industry Date of Approval: 2000-03-10
Effective Date: 2000-10-01
SY/T0036-2000
Replaces SYJ36--1989
1.0.1 This specification is formulated to unify the design of compulsory current cathodic protection systems for buried steel pipelines (hereinafter referred to as pipelines). 1.0.2 This specification is applicable to the design of compulsory current cathodic protection systems for the outer walls of newly built and existing pipelines. 1.0.3 In addition to implementing this specification, the design of pipeline compulsory current cathodic protection systems shall also comply with the provisions of relevant national mandatory standards and specifications in force.
2 Terminology
2.0.1 Cathodic protection A technology for controlling electrochemical corrosion through cathodic polarization. Cathodic protection has two methods: sacrificial anode method and forced current method. 2.0.2 Impressed current is also called external current. Current applied by an external power supply. 2.0.3 Auxiliary anode impressed current anode is formerly known as grounded anode. It is connected to the positive pole of the forced current power supply and is limited to electrodes for the purpose of conducting electricity. Commonly used auxiliary anodes in soil include graphite anode, high silicon cast iron anode, steel anode, magnetic iron oxide anode and flexible anode. 2.0.4 Minimum protective potential minimum protective potential is the absolute minimum negative potential value required for the metal to achieve complete protection. 2.0.5 Maximum protective potential maximum protective potential is the absolute maximum negative potential value allowed under the protection conditions. 2.0.6 Test station test station
A device drawn from the buried pipeline for measuring cathodic protection parameters. 2.0.7 IR drop IR drop
The resistance voltage drop caused by the flow of current in the medium. Note: In measuring the pipeline protection potential, IR drop is a harmful error and should be excluded. 2.0.8 Corrosion potential Electrode potential of metal in corrosion system.
2.0.9 Natural potential Natural potential Corrosion potential without external current influence.
2.0.10 Polarization potential Polarized potential The shift of electrode/electrolyte interface potential caused by the flow of current is called polarization. The potential in polarized state is called polarization potential. 2.0.11 Switch-off potential Switch-off potential The corrosion potential of pipeline measured at the moment of power failure. 698
Note: The IR drop component is eliminated in the switch-off potential. 3 Basic regulations
3.1 Design principles
SY/T 0036—2000
3.1.1 For the design of pipeline forced current cathodic protection system, a 10% margin should be reserved for its protection length according to process calculation. 3.1.2 The design life of auxiliary anode should match the protected pipeline and should not be less than 20 years. 3.1.3 When designing a forced current cathodic protection system, attention should be paid to the interference between the protection system and external metal structures, and corresponding protective measures should be taken in accordance with the requirements of the current national standard "Technical Standard for DC Drainage Protection of Buried Steel Pipelines" SY/T0017. 3.1.4 The ratio of the maximum output voltage of the power supply to the maximum output current should be greater than the total resistance of the cathodic protection circuit. 3.2 Application Technical Conditions
3.2.1 The protected pipeline must have good longitudinal conductive continuity. For non-welded pipeline joints, jumper cables should be added.
3.2.2 The newly protected pipeline should have a good quality covering layer. 3.2.3 The protected pipeline should be equipped with insulating joints or insulating flanges at the following locations, and should comply with the requirements of the current national standards "Electrical Insulation Standard for Cathodic Protection Pipelines" SY/T0086 and "Technical Regulations for Insulating Flange Design" SY/T0516. 1. The connection between the pipeline and the non-protected object within the scope of the design protection system; 2. The connection between the pipeline and the plant, station, depot, and well; 3. The connection between the trunk pipeline and the branch pipeline; the boundary between the strong interference area of stray current and the non-interference area; 5. The joint of different metals;
6. The intersection of the pipeline with the covering layer and the bare pipeline,? Other required parts.
3.2.4. In the location where the metal casing is used, the pipeline should be electrically insulated from the casing, and the two ends of the casing should be waterproof and sealed. Sacrificial anodes should be installed in the casing to protect the conveying pipe in the casing.
3.2.5. The pipeline must be electrically insulated from the supporting piers, pipe columns, pipe bridges, fixed piers, supports, pipe clamps or steel bars in concrete. However, if the two ends of the pipe bridge are equipped with insulation devices, the pipeline on the pipe bridge has been insulated from the buried pipeline, then this section of the pipeline can be laid directly on the pipe bridge without applying electrical insulation.
3.2.6. The intersection of the protected pipeline and other pipelines and cables must be electrically insulated, and the minimum spacing of 0.3m must be ensured. If necessary, an insulating plate should be placed between the two.
3.3 Cathodic protection criteria
3.3.1 Cathodic protection criteria for buried steel pipelines can be based on any one or more of the following criteria: 1 Under the condition of applying cathodic current, the measured pipe/ground potential is -850mV (relative to a saturated copper sulfate reference electrode, the same below) or more negative.
Note: To correctly interpret the pipe/ground potential measurement, the IR drop error contained in the measurement method must be considered. The following methods are usually used: 1) Measure or calculate the IR drop;
2) Check the previous performance of the cathodic protection system; 3) Evaluate the physical and electrical properties of the pipeline and its environment; 4) Determine whether there is direct evidence of corrosion. 2 The pipe/ground polarization potential relative to a saturated copper sulfate reference electrode is -850mV or more negative. 3 The minimum cathodic polarization potential between the pipeline surface and a stable reference electrode in contact with the soil is 100mV. This criterion can be used during the establishment or decay of polarization. 3.3.2 Consideration of special conditions
1 For bare steel surfaces or poorly coated pipes, at the predetermined current discharge point (anode area), determine that the net current flows from the electrolyte 699
SY/T 0036--2000
to the pipe surface.
2 When the soil or water contains sulfate-reducing bacteria and the sulfate content is greater than 0.5%, the power-on protection potential should reach -950mV or more negative.
3.3.3 The maximum protection potential limit should be determined according to the type of covering layer and the environment, so as not to damage the adhesion of the covering layer. The recommended maximum protection potential is:
Petroleum asphalt
—1.50 V
Coal tar enamel 3.0V
Epoxy powder
3.4 Others
3.4.1 The forced current cathodic protection system should be surveyed, designed and constructed at the same time as the main pipeline project. Temporary cathodic protection should be designed for pipelines in highly corrosive soil environments. 3.4.2 The design of the forced current cathodic protection system should meet the requirements of measurement, cover layer leak detection and protection effect judgment in normal management, and provide necessary technical conditions for convenient management and operation. 3.4.3 The manned cathodic protection room of the long-distance pipeline should be divided into two parts: the instrument room and the workroom. The building grade and standard should be consistent with the main project, and the usable area should not be less than 25m2. 4 Process calculation
The design parameters of the forced current cathodic protection system can be selected according to the following conventional parameters for newly built pipelines. 4.0.1
1 Natural potential: 0.55V,
2 Minimum protection potential: -0.85V;
3 Maximum protection potential: -1.25V.
Coating layer resistance:
1) Petroleum asphalt, coal tar enamel: 100000·m2; 2) Plastic covering layer: 500002·m2
3) Epoxy powder: 50000Q·m2;
4) Three-layer composite structure: 100000Q·m2, 5) Epoxy coal tar: 5000Q·m2.
5 Steel pipe resistivity:
Low carbon steel (20#) (
0.135Q mm2/m
16Mn steel
High strength steel
0.224 2 mm2/m
0.166 Q - mm2/m
6 The protection current density shall be selected according to the resistance of the covering layer: When 5 000～~10 000 Q·m2
Take 100~~50μA/m2
When ≥10000～500000·m2Take <50~~10μA/m2When >50 000Q·m2
For built pipelines, the measured value shall be taken as the basis. Take <10 μA/m2
4.0.2 The consumption rate of auxiliary anode shall be selected according to the material and working conditions, see Chapter 6 of this specification for details. 4.0.3 Soil resistivity data shall be taken from survey data or on-site measurement. 4.0.4 The protection length of forced current cathodic protection can be calculated according to formula (4.0.4). 2L =
N yuan.DJ·R
(4.0.4-1）
( 4.0.4-2 )
Wherein: 1.--single-side protection length (m)
AVt.——--difference between maximum protection potential and minimum protection potential (V), D)---pipeline outer diameter (m);
--protection current density (A/m2);
R--longitudinal electric field per unit length of pipeline (Q/m); Pr---steel pipe resistivity (α·mm2 /m); D pipeline outer diameter (mm);
---pipeline wall thickness (mm).
4.0.5 The protection current of the forced current cathodic protection system can be calculated according to formula (4.0.5). 2. = 2 yuanDJ, - L
Wherein: I-
single-side protection current (A).
4.0.6 The auxiliary anode grounding resistance shall be calculated according to the following formulas based on the burial method. 1 Calculation of single vertical anode grounding resistance: Rvi =
2 Calculation of deep buried anode grounding resistance:
3 Calculation of single horizontal anode grounding resistance: RH
Where: Rv,—--single vertical anode grounding resistance (Q); Rv2—---deep buried anode grounding resistance (Q); 2#L
RH---single horizontal anode grounding resistance (Q); anode length (including filler) (m);
d—anode diameter (including filler) (m);
t—-burial depth (the top of the filler from the ground surface) (m); soil resistivity of the anode area (α·m). 4 Calculation of anode group grounding resistance.
[43L(t 》 d)
(t》L)
(t≤L)
Wherein: R
grounding resistance of anode group (Q);
number of anodes;
F——resistance correction factor (see Figure 4.0.6); R——grounding resistance of single anode (n).
4.0.7The mass of anode shall be able to meet the requirements of minimum design life of anode and shall be calculated according to formula (4.0.7). G
Wherein: (-
total mass of anode (kg);
g—consumption rate of anode [kg/A·a)];
I---anode working current (A);
Tanode design life (a);
K~-anode utilization coefficient, take 0.7～0.85. T·gl
SY/T 0036—2000
( 4.0.6-1 )
( 4.0.6-2)
(4.0.6-3）
（4.0.6-4）
SY/T 0036—2000
Distance: (m)
Figure 4.0.6 Correction factor of anode group grounding resistance 4.0.8 The power of the power supply equipment of the forced current cathodic protection system shall be calculated according to the following formula. V
V =- I(R.+ RL +Rc)+V,
2th(aL)
I = 21,
where: V--output voltage of power supply equipment (V); R.-anode ground bed grounding resistance (Q);
Ri. wire resistance (0);
Rc. cathode (pipeline)/soil interface transition resistance (a); - pipeline attenuation factor (m-);
rt---pipeline resistance per unit length (α/m); R----covering layer transition resistance (α·m);
L.--protected pipeline length (m);
V. back electromotive force of the ground bed (V), V.-2V is taken when coke is filled; I----output current of power supply equipment (A); I. ----Protection current in one-way direction (A); P..---Power supply power (W);
--Power supply equipment efficiency, generally 0.7.
5 Power supply equipment
(4.0.8~1)
(4.0.8-2)
(4.0.8-3)
(4.0.8-4)
(4.0.8-5)
The basic requirements for AC power supply for forced current cathodic protection are: it can meet long-term uninterrupted power supply; it should give priority to using the mains or using 5.0.1
stable and reliable AC power supply for various stations; when the power supply is unreliable, a backup power supply or uninterruptible power supply special equipment should be installed. 702
5.0.2 For areas without AC power, the following power sources can be used: When solar energy resources are abundant and the load power is less than 250W, solar cells can be used; When wind energy resources are abundant and the load power is between 200W and 55kW, wind turbines can be used; For gas pipelines, when the load power is between 10 and 500W, thermoelectric generators (TEGs) can be used; SY/T0036—2000
For gas pipelines, when the load power is between 100W and 4kW, closed cycle generator sets (CCVTs) can be used; Sometimes large-capacity batteries are also economical and reasonable power supply solutions. 5.0.3 The basic requirements for power supply equipment for forced current cathodic protection are: 1 High reliability; www.bzxz.net
2 Easy maintenance;
3 Long life;
Strong adaptability to the environment;
5 Adjustable output current and voltage;
6 It should have anti-overload, lightning protection, anti-interference, and fault protection functions. 5.0.4 For the power supply equipment of forced current cathodic protection, rectifier or constant potentiostat should be used in general. When the pipe-to-ground potential or loop resistance has frequent and large changes or the grid voltage changes greatly, a constant potentiostat should be used. 5.0.5 The ripple factor of the rectifier for cathodic protection should meet the requirements of no more than 50% for single phase and no more than 5% for three phase, and the maximum temperature rise shall not exceed 70℃. Overcurrent and anti-shock protection devices should be installed at the AC input and DC output ends. 5.0.6 The outdoor rectifier device should be able to adapt to the local climate environment and can be installed on the roof, wall or pole for operation. 5.0.7 The potentiostat should usually work indoors, and its technical performance requirements are as follows: Given potential: -0.500～3.000V (continuously adjustable); 1
2 Potential control accuracy ≤ 10mV,
Input impedance: ≥1MQ,
Insulation resistance: >2MQ (power supply line to ground); 5 Anti-AC interference ability: ≥12V;
6 Withstand voltage: ≥1500V (power supply line to housing); 7 Full load ripple factor: single phase ≤10%, three phase ≤8%. 5.0.8 The printed circuit board of the potentiostat should generally take measures to prevent moisture, salt spray and bacteria. Auxiliary anode
6.1 Commonly used anode
6.1.1 High silicon cast iron anode should meet the following requirements: 1
The chemical composition of high silicon cast iron anode should comply with the provisions of Table 6.1.1-1. Table 6.1.1-1 Chemical composition of high silicon cast iron anode Type
14. 25 ~~ 15. 25
14. 25~~15. 25
Chemical composition
0. 5~0. 8
0. 5~0. 8
0.80~1.05
Impurity content
The allowable current density of high silicon cast iron anode is 5~80A/m2, and the consumption rate should be less than 0.5kg/(A·a). 2
For the specifications of commonly used high silicon cast iron anodes, see Table 6.1.1-2. 3
SY/T 0036---2000
Table 6.1.1-2
Specifications of commonly used high silicon cast iron anodes
Anode specifications
DC (mm)
Length (rm)
Specifications of anode lead wire
Cross-sectional area (mm2)
Length (mm)
≥1500
≥1500
≥1500
The contact resistance between the anode lead wire and the anode should be less than 0.01Q2, and the pull-off force value should be greater than 1/100% of the anode's own mass.5 times, the joint seal is reliable, and the anode surface should have no obvious defects. 6.1.2 The graphite anode should meet the following requirements: The graphitization degree of the graphite anode should not be less than 81%, and the ash content should be less than 0.5%. The graphite anode should be impregnated with linseed oil or paraffin. 2
The performance of the graphite anode shall comply with the provisions of Table 6.1.2-1. 3
The specifications of commonly used graphite anodes are shown in Table 6.1.2-2. Table 6.1.2-1 Main properties of graphite anodes Density
(g\cm\）
Resistivity
(Q.mm2/m)
Porosity
Table 6.1. 2-2 Specifications of commonly used graphite anodes Anode specifications
Diameter (mm)
Length (mm)
Consumption rate
[kg/(A·a)]
Allowable current density
(A/m2)
5～10
Specifications of anode lead wire
Cross-sectional area (mm)2
Length (mm)
≥1500
≥1500
≥1500
The contact resistance between the anode lead wire and the anode should be less than 0.01Q, the pull-off force value should be greater than 1.5 times the mass of the anode itself, the joint 5
seal reliably, and the anode surface should have no obvious defects. 6.1.3 Flexible anodes should meet the following requirements: Flexible anodes are composed of conductive polymers coated on copper cores, and their performance should meet the requirements of Table 6.1.3. Table 6. 1.3 Main properties of flexible anodes
Maximum output current (mA/m)
Without filler
With filler
Minimum construction temperature
The cross-sectional area of the flexible anode copper core is 16mm2, and the outer diameter of the anode is 13mm. 2
The steel anode should meet the following requirements:
The steel anode refers to the anode made of angle steel, flat steel, channel steel or steel pipe. Minimum deflection radius
2The consumption rate of the steel anode is 8~10 kg/(A·a). 6.2 Auxiliary anode design
6.2.1 The selection of the auxiliary anode location should meet the following requirements: 1 The groundwater level is high or the wet low-lying area.
2 The location with soil resistivity below 50Q·m. 3 The soil layer is thick, without stones, and it is convenient for construction. SY/T 0036—2000
4 The interference to the adjacent underground metal structures is small, and there should be no other metal structures between the anode position and the protected pipeline. 5 The vertical distance between the anode position and the pipeline should not be less than 50m. When using flexible anodes, the best position of the anode for bare pipelines is 10 times the diameter of the pipeline; for pipelines with good covering layers, they can be laid in the same trench, and the closest distance is 0.3m. 6.2.2 The selection of anode types should comply with the following principles: 1 High silicon cast iron anodes, graphite anodes, and steel anodes can be used in general soils. 2 In salt-burst soils, coastal soils, or environments with high acidity and sulfate ion content, chromium-containing high silicon cast iron anodes should be used. 3 Steel anodes should be used in places with high resistivity. 4 Flexible anodes can be used for pipelines with poor covering quality and pipelines located in complex pipe networks or areas with multiple underground metal structures, but they should not be used in oily sewage and salt water. 6.2.3 The burial method of anodes shall meet the following requirements: 1 Anodes can be buried shallowly or deeply. Shallow buried anodes should be placed below the frozen soil layer, and the burial depth should generally not be less than 1m; the burial depth of deep buried anodes should be 15 to 300m.
2 Anodes are usually buried vertically; horizontal shallow burial can be used in sandy soil, high groundwater level, and swamps; deep buried anodes can be used in complex environments or when the resistivity of the surface soil is high. 6.2.4 The use of anode bed fillers shall meet the following requirements: 1 Common fillers for anodes are coke particles and petroleum coke particles. 2 Graphite anodes should be filled with fillers; high silicon cast iron anodes should be filled with fillers, and fillers may not be added in swamps and quicksand layers; flexible anodes should be filled with fillers; steel anodes may not be filled with fillers. 3 The carbon content of the filler should be greater than 85%, the maximum particle size should be less than 15mm, and the thickness of the filler is generally 100mm. When flexible anodes are used, the maximum particle size of the filler should be less than 3.2mm and the thickness of the filler should be 45mm. Flexible anodes pre-coated with coke powder can be buried directly without the use of fillers.
6.2.5 The anode bed should also meet the following requirements: 1 The potential gradient of the auxiliary anode ground electric field should not be greater than 5V/m, and this restriction does not apply when a guardrail device is installed. 2 Gravel or coarse sand with a particle size of about 5 to 10mm should be placed on the top of the anode filler. The gravel layer should be thickened to 500mm below the ground or an exhaust pipe should be installed on the top of the gravel to above the ground. 3 The lead-out wires and parallel busbars of the anode should be copper core cables and should be suitable for underground (or underwater) laying. 4 The parallel busbars of the anode and the DC power supply output anode wire can be connected through a junction box. If the anode wire is an aluminum wire, a copper-aluminum transition joint should be used for connection.
7 Pipeline cathodic protection ancillary facilities
7.1 Test piles
7.1.1 In order to regularly detect the parameters of pipeline forced current cathodic protection, test piles should be set up as needed. The various test piles and their setting principles are generally as follows:
Potential test piles, one is set at the confluence point and every kilometer; 2 Current test piles, one is set every 5-8km; 3 Casing and pipeline potential test piles, one is set at each casing; Insulation joint test piles, one is set at each insulation connection; 4
SY/T 0036—2000
5 Crossover test piles, one is set at the intersection with other pipelines, cables and other structures, 6 In-station test piles, set up as needed. 7.1.2 Pipeline test piles are numbered according to the direction of oil and gas flow, and are generally located on the left side of the flow direction, 1.5m away from the center line of the pipeline. The piles should be marked with eye-catching signs and buried firmly and stably.
7.1.3 For test piles used to measure pipeline current, the resistance value of the measuring section shall be marked on the pile nameplate, and test piles with special functions shall be marked with special marks or instructions.
7.1.4 Test piles can be made of steel pipes, fiberglass and concrete. The test pile with potential and current test functions located at the casing has a test wiring diagram shown in Figure 7.1.4.
7.2 Buried reference electrode
7.2.1 The basic requirements for reference electrodes are small polarization, good stability and long life. The stability requirements for reference electrodes in soil are: zinc reference electrode is not greater than 30mV; copper sulfate electrode is not greater than ±10mV. The working current density is not greater than 5uA/cm2. 7.2.2 The schematic diagram of the buried zinc reference electrode is shown in Figure 7.2.2. The electrode material is high-purity zinc with a purity of not less than 99.995% and an iron impurity content of less than 0.0014.6. The electrode packing material shall comply with the provisions of the current national standard "Design Specifications for Sacrificial Anode Cathodic Protection of Buried Steel Pipelines" SY/T0019.
Unit: mm
5001000
1 and 2--Pipeline current test head, 2--Potential test head; 3-Casing test head; 1, 2, 3---Aluminum thermite welding at every two places; 4-Casing; 5-Road, 6-Signage; 7-Terminal; 8Pipeline
Figure 7.1. 4
Test pile schematic diagram
Unit: mm
1--cotton bag; 2--filling material, 3---zinc electrode, 4--joint sealing protective tube; 5-cable protective tube: 6-cable
Figure 7.2.2 Schematic diagram of buried zinc reference electrode 706
SY/T0036-2000
7.2.3 The reference electrode should be buried as close to the pipeline as possible to reduce the IR drop effect in the soil medium; for hot oil pipelines, attention should be paid to the adverse effects of thermal fields on electrode performance.
7.3 Conductor laying
7.3.1 In the forced current cathodic protection system, all connecting conductors should be laid directly underground with cables, or overhead lines can be used. Cables, overhead lines and test pile leads should adopt the following models: Cable
Overhead lines
VV-1 kV type
LGJ type
Test pile leads BVV, BVR type
7.3.2 The installation of direct buried cables and overhead lines shall comply with the provisions of the current national standards "Low Voltage Distribution Design Code" GB50054 and "Electrical Installation Engineering Low Voltage Electrical Construction and Acceptance Code" GB50254. For areas with an average annual thunderstorm day of more than 30 days, overhead lines should be equipped with lightning protection devices
7.3.3 The connection between cables and pipelines should be made of aluminum thermite welding or tin soldering. Ensure that the machinery is firm and reliable and the conductivity is good. The exposed pipe wall and wire at the welding point should be made of materials suitable for the pipeline covering layer for corrosion protection and insulation. 8 System Debugging
8.0.1 The forced current cathodic protection system should be tested once before being put into operation. The test method shall be carried out in accordance with the provisions of the current national standard "Test Method for Cathodic Protection Parameters of Buried Steel Pipelines" SY/T0023. 8.0.2. System parameter test includes the following items: 1 Soil resistivity along the line,
2 Natural potential of pipeline;
3 Soil resistivity of auxiliary anode area;
4 Auxiliary anode grounding resistance;
Covering layer resistance (can be combined with cathodic protection debugging). The insulation performance of pipeline electrical insulation devices (casing insulation support, insulation joints, brackets, etc.) should be tested. 8.0.3
Cathodic protection system debugging should include the following items: 8.0.4
Instrument output current and voltage;
Pipeline current,
Protection potential.
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