This specification is formulated to implement the relevant national policies and guidelines, unify technical standards, actively adopt new processes, new materials, new structures, and new technologies in the corrosion control engineering design of steel pipelines and steel storage tanks, so as to achieve advanced technology, economic rationality, safety and applicability, and ensure quality. This specification is applicable to the internal and external corrosion control of pipelines and storage tanks for the transportation and storage of crude oil, refined oil, natural gas and water (including sewage) with a medium temperature below 100°C that are newly built, expanded, or rebuilt in onshore corrosive environments. It is not applicable to corrosion control in marine corrosive environments. SY 0007-1999 Steel Pipeline and Storage Tank Corrosion Control Engineering Design Specification SY0007-1999 Standard Download Decompression Password: www.bzxz.net

1 General Provisions
Petroleum and Natural Gas Industry Standard of the People's Republic of China Corrosion Control of Steel Pipelines and Storage Tanks
Engineering Design Specification
Approving Department: State Administration of Petroleum and Chemical Industry Date of Approval: 1999-05-17
Effective Date: 1999-12-01
SY 0007—1999
Replaces SYI7..1984
1.0.1 This specification is formulated to implement the relevant national policies and guidelines, unify technical standards, actively adopt new processes, new materials, new structures and new technologies, and achieve advanced technology, economic rationality, safety and applicability, and ensure quality in the corrosion control engineering design of steel pipelines (hereinafter referred to as pipelines) and steel storage tanks (hereinafter referred to as tanks). 1.0.2 This specification is applicable to the internal and external corrosion control of pipelines and storage tanks for the transportation and storage of crude oil, refined oil, natural gas and water (including sewage) with a medium temperature below 100°C that are newly built, expanded and rebuilt in onshore corrosive environments. It is not applicable to corrosion control in marine corrosive environments. 1.0.3 In addition to complying with this specification, the design of pipeline and storage tank corrosion control engineering shall also comply with the provisions of the relevant mandatory standards currently in force in the country.
2 Terms
2.0. 1 Corrosive environment An environment containing one or more corrosive factors. 2.0.2 Corrosion rate
The amount of metal corrosion per unit time.
2.0.3 Coating
A protective layer covering the metal surface to isolate the metal surface from the surrounding environment in order to achieve the purpose of inhibiting corrosion. The coating can be divided into: insulating coating (also called anti-corrosion insulation layer, referred to as anti-corrosion layer) and non-insulating coating (such as plating) according to whether it is insulating or not. 2.0.4 Cathodic protection cathodic protector is an electrochemical protection achieved by reducing the corrosion potential. Cathodic protection usually has two methods: forced current protection and sacrificial anode protection.
2.0.5 Impressed current Current applied by an external power source, also known as impressed current. 2.0.6 Sacrificial anode sacrificial anode is a metal electrode connected to the protected body in an ion conductive medium and can provide cathodic protection current. Magnesium-based sacrificial anodes and zinc-based sacrificial anodes are commonly used in soil environments. 2.0.7 DC interference DC interference causes changes in the corrosion potential of buried metal structures under the action of DC stray currents in the earth. This change occurs in the anode field and is called anode interference, and occurs in the cathode field and is called cathode interference. 2.0.8 AC interference AC lines and equipment cause changes in voltage and current in nearby pipelines. According to the length of the interference time, it can be divided into three types: instantaneous interference, continuous interference and intermittent interference.
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2.0.9Insulated jointInsulated joint is a pipe connection method used to cut off the longitudinal current of the pipeline. There are two types: insulated flange connection and insulated joint connection. 2.0.10Bridge bond
A metal connection designed to control the current exchange between metal structures. There are three types: interference bridge, equalizing bridge and continuous bridge.
2.0.11 Polarization potentialpolarizationpotentialThe potential of the metal structure/electrolyte interface. It is the sum of corrosion potential and cathode polarization. 3Basic provisions
3.0.1Whether pipelines and storage tanks need to take corrosion control should consider the following factors: 1Corrosion detection, operation records and appearance inspection records; 2Examine the test results from other similar systems and similar environments; 3Engineering design specifications and safety and economy. 3.0.2The method of corrosion control should consider the environmental factors and economy of pipelines and storage tanks. 1. The corrosiveness of the medium in the environment of the pipeline and storage tank; 2. The nature of the medium being transported or stored, the working temperature, the expansion and contraction of the metal caused by the temperature difference, the soil stress generated by the backfill soil, and the working pressure of the pipeline and storage tank;
3. The location of the pipeline and storage tank and the population density and the frequency of personnel exchanges; 4. The location relationship of the pipeline and storage tank and other equipment and devices; 5. Stray current outside the system;
6. The comprehensive economic evaluation of the anti-corrosion project should be calculated in accordance with the current national standard "Economic Calculation Method of Anti-Corrosion Engineering" SYJ42. 3.0.3 The classification of the corrosiveness level of the pipeline and storage tank environment shall comply with the following provisions: The determination of soil corrosiveness is recommended to adopt the in-situ polarization method and the test piece weight loss method, and the classification shall be carried out according to the provisions of Table 3.0.3-1. ---General areas can also use the soil resistance commonly used in engineering surveys, and classify according to the provisions of Table 3.0.3-2. 2. The classification of the corrosiveness level of the medium in the pipeline and storage tank shall comply with the provisions of Table 3.0.3-3. 3 The atmospheric corrosivity classification shall comply with the provisions of Table 3.0.3-4. 3.0.4 The corrosion control of pipelines shall meet the following requirements: 1 The outer wall of the buried pipeline must have a good anti-corrosion layer. The material and structure of the anti-corrosion layer shall be determined according to the soil corrosivity and other factors specified in Table 3.0.3-1 or Table 3.0.3-2. The outer anti-corrosion layer of buried pipelines in fields, stations, and reservoirs and pipelines crossing railways, highways, rivers and lakes shall be particularly strengthened. The adoption of cathodic protection shall comply with the provisions of 5.1.2 of this specification. 2 The corrosion control of the inner wall of the pipeline shall be based on the medium corrosiveness specified in Table 3.0.3-3 or the requirements for the medium to avoid iron ion pollution, and decide whether corrosion control or isolation measures are needed. The corrosion control of the inner wall of the pipeline shall comply with the provisions of the current national standard "Standard for Internal Corrosion Control of Steel Pipelines" SY/T0078. The life of the selected internal anti-corrosion layer or isolation layer shall not be less than 5 years. For natural gas pipelines that transport acidic media containing hydrogen sulfide, the selection of pipeline materials shall be carried out in accordance with the relevant provisions of the current national standard "Requirements for Metal Materials for Natural Gas Ground Facilities to Resist Sulfide Stress Cracking" SY/T0599.
3 The outer anti-corrosion layer of overhead pipelines shall be selected according to the provisions of Table 3.0.3-4 and other factors, and appropriate anti-corrosion materials and structures shall be selected. 3.0.5 The corrosion control of storage tanks shall comply with the following provisions: 1 The inner and outer surfaces of the tank body shall be covered with appropriate anti-corrosion materials and structures according to the provisions of Table 3.0.3-3 and Table 3.0.3-4.
2 The outer wall of the bottom plate of the storage tank shall be cathodically protected. It shall be implemented in accordance with the provisions of the current national standard "Technical Standard for Cathodic Protection of the Bottom Outer Wall of Steel Storage Tanks" SY/T0088.
3 Cathodic protection measures shall generally be taken for the inner wall of the storage tank, except where it is proved that cathodic protection is not required after investigation. The corrosion control system should be equipped with inspection and monitoring facilities!
Current density (μA/cm2)
(In-situ polarization method)
Average corrosion rate
[g/(dm2a)]
(Test piece weight loss method)
Soil resistivity (α·m)
Soil corrosivity classification standard
Table 3.0.3-1
Soil corrosivity classification standard in general areas
Table 3.0.3-2
Note: The resistivity in the table adopts the minimum value of the whole yearTable 3.0.3-3
Average corrosion rate (mm/a)
Pitting corrosion rate (mm/a)
Note: The most serious result of the two indicators shall prevail. The pipes in the tanks shall comply with the corrosiveness classification standards of the medium in the tanks, etc.
0.025~0.125
0.305~~0.610
0.126~0.254
0.611~2.438
Table 3.0.3-4 Atmospheric corrosivity classification standards, etc.
Corrosion rate in the first year (um/a)
Anti-corrosion layer
SY 0007—1999
Anti-corrosion layer should have the following properties.
Effective electrical insulation: The insulation resistance of the outer anti-corrosion layer of the buried pipeline should generally not be less than 10000Q·m2. Good moisture and water resistance.
Strong mechanical strength:
1) Have a certain impact strength;
2) Good bending resistance;
3) Good wear resistance;
4) The penetration degree reaches the specified index of the material. The anti-corrosion layer has good adhesion to the steel surface. 4
The material and construction process of the anti-corrosion layer should not have an adverse effect on the performance of the parent material. 5
Good anti-cathodic peeling performance.
7 Good chemical resistance and aging resistance. Anti-corrosion layer damage is easy to repair.
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9 The impact of the anti-corrosion layer on the environment should meet the corresponding requirements. 4.0.2 The following factors should be considered when selecting the anti-corrosion layer: 1 Environmental type;
2 Operating temperature of the storage or transportation medium;
3 Geographical location and natural location;
Ambient temperature of the anti-corrosion layer during construction, transportation, loading and unloading, storage, installation, pressure testing and backfilling; 4
5 The type of the original anti-corrosion layer and the operation of cathodic protection; The treatment requirements of the anti-corrosion layer on the steel surface; 6
7 Cost.
4.0.3 The general requirements for the outer anti-corrosion layer of pipelines shall comply with the provisions of the current national standard "Technical Regulations for the Coating of Organic Coatings on the Outer Walls of Buried Steel Pipelines" SY/T 0061.
4.0.4 When the inner wall of the storage tank is coated with aluminum-zinc metal plating (coating), it shall comply with the provisions of the current national standard "Thermal Spraying of Zinc, Aluminum and Its Alloys on Metals and Other Inorganic Coatings" GB/T9793. 4.0.5 When the inner wall of the storage tank is coated with electrostatic conductive anti-corrosion coatings, it shall comply with the provisions of the current national standards "Method for Determination of Resistivity of Electrostatic Conductive Coatings for Petroleum Tanks" GB/T16906 and "Electrostatic Safety Regulations for Liquid Petroleum Products" GB13348. 4.0.6 The commonly used inner and outer wall anti-corrosion layers of pipelines shall comply with the relevant provisions of the following current national standards. 1. The petroleum asphalt anti-corrosion layer shall comply with the provisions of the Technical Standard for Petroleum Asphalt Anti-corrosion Layer of Buried Steel Pipeline SY/T0420; 2. The rigid polyurethane foam anti-corrosion and thermal insulation layer shall comply with the provisions of the Technical Standard for Rigid Polyurethane Foam Anti-corrosion and Thermal Insulation Layer of Buried Steel Pipeline SY/T0415;
3. The epoxy coal tar anti-corrosion layer shall comply with the provisions of the Technical Standard for Epoxy Coal Asphalt Anti-corrosion Layer of Buried Steel Pipeline SY/T0447; the coal tar enamel anti-corrosion layer shall comply with the provisions of the Technical Standard for Coal Tar Enamel External Anti-corrosion Layer of Buried Steel Pipeline SY/T0379; the polyethylene anti-corrosion layer shall comply with the Technical Standard for Polyethylene Anti-corrosion Layer of Buried Steel Pipeline SY/T0379; 5
6 The polyethylene adhesive tape anti-corrosion layer shall comply with the provisions of the "Technical Standard for Polyethylene Adhesive Tape Anti-corrosion Layer of Steel Pipes" SY/T0414; the fused epoxy powder outer coating shall comply with the provisions of the "Technical Standard for Fusion Epoxy Powder Outer Coating of Steel Pipes" SY/T0315; 7
8 The fused epoxy powder inner anti-corrosion layer shall comply with the provisions of the "Technical Standard for Fusion Epoxy Powder Inner Coating of Steel Pipes" SY/T0442; the liquid epoxy coating inner anti-corrosion layer shall comply with the provisions of the "Technical Conditions for Liquid Epoxy Coating Inner Anti-corrosion Coating Steel Pipes" SY/T4057. 9
4.0.7 The surface treatment of pipelines and storage tanks shall comply with the provisions of the current national standard "Specifications for Steel Surface Pretreatment before Painting" SY/T0407.
4.0.8 The coating selected for design must be a product that has passed the appraisal and shall comply with the current national industry standards or the enterprise standards of enterprises with guarantee capabilities.
4.0.9 In reed areas and areas with strong bacterial corrosion, materials such as petroleum asphalt that are easily penetrated by plant roots and are not resistant to bacterial corrosion should not be used as anti-corrosion layers. The determination of the degree of corrosion in soil containing bacteria should be carried out in accordance with the provisions of Table 4.0.9. Table 4.0.9 Evaluation indicators of soil bacterial corrosion
Corrosion level
Oxidation-reduction potential (mV)
5 Cathodic protection
100~200
200～400
5.1 General provisions
5.1.1 Cathodic protection is divided into two protection methods: impressed current and sacrificial anode. When selecting, the following main factors should be considered. 1 Project scale;
2 Whether there is an economical and convenient power supply;
3 The size of the protection current density required for the protected body; 4 The mutual influence between the protected body and the surrounding underground metal structures; 5 The size of the resistivity of the soil or medium.
SY 0007—1999
In the process design, the above factors should be considered comprehensively, analyzed and compared comprehensively, and the best ones should be selected. When the protected pipeline has a good anti-magnetic layer, low soil resistivity, and many surrounding underground metal structures, sacrificial anode protection should be adopted. 5.1.2 Long-distance pipelines and oil and gas field transmission pipelines must adopt cathodic protection; gathering and transportation trunk pipelines in oil and gas fields should adopt cathodic protection; other pipelines and storage tanks should adopt cathodic protection. The cathodic protection system should have inspection and monitoring facilities. 5.1.3 The cathodic protection project should be surveyed, designed and constructed at the same time as the main project, and should be put into operation within 6 months of the pipeline being buried. In stray current areas, after the pipeline is buried, its drainage measures should be put into operation within a limited period of time, generally not more than 3 months. 5.1.4 The design of impressed current cathodic protection pipelines and other underground pipelines should comply with the following principles: 1 Parallel pipelines with joint protection can be laid in the same trench. The spacing and specifications of the voltage-equalizing lines shall be determined based on the pipeline voltage drop, the distance between pipelines, the quality of the pipeline anti-corrosion layer and other factors. For parallel pipelines with non-joint protection, the distance between the two should not be less than 10m. When the distance is less than 10m, the pipeline constructed later shall be made of a special reinforced anti-corrosion layer on the pipe section within the distance of less than 10m and the pipe section extending more than 10m at both ends.
2 When the protected pipeline crosses other underground pipelines, the net vertical distance between the two shall not be less than 0.3m. When it is less than 0.3m, a solid insulating spacer must be provided between the two to ensure that the two crossing pipelines do not touch. At the same time, the two pipelines shall be made of a special reinforced anti-corrosion layer on the pipe sections extending more than 10m on both sides of the intersection. 5.1.5 When the impressed current cathodic protection pipeline meets the buried communication cable, the following design principles shall be met: 1 When the pipeline and the cable are laid in parallel, the distance between the two should not be less than 10m. When it is less than 10m, the pipeline or cable constructed later shall be implemented in accordance with the provisions of paragraph 1 of Article 5.1.4. 2 When the pipeline and the cable cross, the net vertical distance between them should not be less than 0.5m. At the same time, a special reinforced anti-corrosion layer should be applied on the pipe and cable sections extending more than 10m on both sides of the intersection. 5.2 Cathodic protection criteria
5.2.1 The cathodic protection effect under normal conditions should meet one or all of the following indicators. 1 After applying cathodic protection, the polarization potential measured using a copper saturated copper sulfate reference electrode (hereinafter referred to as CSE reference electrode) should be at least -850mV or more negative. When measuring the potential, the influence of "IR" drop must be considered in order to make an accurate evaluation of the measurement results. 2 When the cathodic protection polarization is formed or attenuated, the cathodic polarization potential difference between the surface of the protected pipeline or tank and the stable reference electrode in contact with the soil should not be less than 100mV. 5.2.2 The protection effect of cathodic protection under special circumstances should meet the following requirements: 1 When sulfate-reducing bacteria are present in the medium, the measured polarization potential should reach -950mV or more negative (relative to the CSE reference electrode). 2 The protected body is buried in dry or aerated high resistivity (greater than 500α·m) soil, and the measured polarization potential should be at least -750mV (relative to the CSE reference electrode). 3 When the pipeline or storage tank is in operation, stress corrosion cracking may occur due to pressure or other factors. At this time, the polarization potential of cathodic protection should be more negative than 850mV (relative to the CSE reference electrode). 5.2.3 In order to avoid cathodic stripping of the protective layer of the protected body, the polarization potential of cathodic protection should not be too negative. 5.2.4 The test of cathodic protection parameters shall comply with the provisions of the current national standard "Test Method for Cathodic Protection Parameters of Buried Steel Pipelines" SY/T0023.
5.3 Electrical insulation
5.3.1 The electrical insulation of the cathodic protection system includes insulating flanges, insulating joints, insulating fixed piers and insulating pads. 5.3.2 Insulating flanges or insulating joints should usually be installed at the following locations: 1 The connection between the pipeline and the well, station, or storage;
2 The boundary between the pipeline and the ownership of the pipeline or equipment; 3 The connection between the branch pipeline and the trunk pipeline; 683
SY 0007—1999
4 The connection between the pipeline with an anti-magic layer and the tree pipeline; 5 Both ends of the large-scale penetration and crossing sections of the pipeline;
6 The boundary between those with cathodic protection and those without cathodic protection. 5.3.3 When designing and installing insulating flanges or insulating joints, the following matters should be noted: 1. Select appropriate insulating connection facilities according to the temperature, pressure and insulation performance requirements of pipelines and storage tanks; 2. It should not be installed in places where flammable gases accumulate and in closed places; 3. It is strictly forbidden to install near pipeline thermal compensators; 4. The outer wall of the pipeline within 10m on both sides of the insulating flange and insulating joint should be made of a special reinforced anti-corrosion layer, and the inner wall of the pipeline on both sides should be coated with a certain length of internal anti-corrosion layer;
5. There should be lightning overcurrent protection facilities on the insulating connection facilities. 5.3.4. Insulating flanges and insulating joints should comply with the provisions of the following standards: Insulating flanges should comply with the provisions of the current national standard "Insulating Flange Design Technical Regulations" SY/T0516: 1
Insulating joints should comply with the provisions of the current national standard "Electrical Insulation Standard for Cathodic Protection Pipelines" SY/T0086. 1
When the pipeline is equipped with a metal casing, a reliable electrical insulating pad should be provided between the pipeline and the casing. The installed electrical insulating pads shall not slide on the pipeline 5.3.5
. Good sealing should be adopted at both ends of the casing to prevent foreign matter from entering the casing. 5.3.6 There should be reliable electrical insulation between the pipeline and the conductive support. 5.3.7 When the pipeline crosses a river, for the pipe stabilization facilities added to fix the pipeline, if the facilities have conductive metal, the metal must be insulated from the pipeline and shall not damage the anti-magic layer of the pipeline, and shall not produce electrical shielding for the pipeline. 5.4 Electrical continuity
5.4.1 On the pipeline or storage with cathodic protection, flanges and threaded elbows, tees, valves and other non-welded pipeline accessories are usually used. In order to ensure their electrical continuity, jumper cables or other effective electrical connection measures should be used. 5.5 Corrosion control detection points
5.5.1 The test points for pipeline cathodic protection should be set at the following locations: 1 The confluence point and protection end of the impressed current cathodic protection pipeline; 2 Every 1 km along the pipeline, or shorter;
3 The sacrificial anode installation point and the middle of two groups of anodes, and the pipelines on both sides of the insulating flange or insulating joint; 4
The intersection of the protected pipeline and other underground pipelines or cables; 5
Where the pipeline crosses railways, highways, rivers, and bridges, only one test point can be set at one end; 6
Pipeline casing installation point
The distance between the test points for pipelines in the AC and DC interference areas should be determined according to the specific circumstances. 8
The detection points of cathodic protection of storage tanks shall be set at the following positions: 5.5.2
The detection points of cathodic protection of the outer wall of the bottom of the storage tank shall be set at the center and appropriate positions around the outer wall of the bottom of the tank; 1
The detection points of cathodic protection of the inner wall of the storage tank shall be set at the center of the bottom of the tank and the upper, middle and lower parts of the tank wall. 2
The design of the test pile shall meet the following requirements: 5.5.3
Must be strong, durable and easy to detect, and shall be numbered in a certain direction;
The test wire shall have sufficient strength and a certain length margin to prevent breaking. The connection between the wire and the object to be tested must be firm and 3
The conductivity is good;
4The test wire must be wrapped with good anti-corrosion insulating materials, and the wrapped anti-corrosion insulating materials shall have good compatibility and affinity with the insulating materials of the wire and the anti-corrosion materials of the pipeline or storage tank. 5.5.4 The test piles for measuring pipeline current should avoid the following locations: 1. The intersection of pipelines and other underground metal structures; 2. The places with mechanically connected pipes or mechanically connected pipe fittings, such as threaded connections or flange connections; 3. The places where the pipeline diameter changes.
5.6 Cathodic protection design
5.6.1 The following items should be considered when designing the cathodic protection system: SY 0007-1999
1 Confirm the safety requirements for the installation location of the cathodic protection system, the technical requirements for the selection of materials, and the safe construction and operation and maintenance methods to ensure that the cathodic protection system can operate reliably and economically during its expected service life. 2 When determining the location of the cathodic protection station, especially the location of the anode bed, the interference effect of the cathodic protection current and the resulting ground potential gradient on nearby metal structures should be minimized. 3 A practical implementation plan should be proposed for sections with interference effects. 4 For unfavorable conditions such as sulfides, bacteria, insulation layers, high temperatures, shielding, acidic environments and the presence of foreign metals, special research should be conducted and solutions to the problems should be proposed.
5 Avoid excessively negative cathodic polarization potential, which may cause cathodic peeling of the anti-corrosion layer and over-protection that may damage high-strength steel due to hydrogen evolution.
The design of the cathodic protection system should meet the following requirements: 1. Provide sufficient protection current for the protected body and distribute it reasonably to minimize the interference to the adjacent underground metal structures; 2. Provide an anode system with a life span equivalent to that of the protected body, or provide a replacement cycle and replacement measures for the anode system; 3. The protection current of the protected body will increase with time, so the current of the cathodic protection power supply should have a certain margin; 4. Reasonably select durable anode materials and the location of the anode bed. The anode bed should be located away from other underground metal structures and not easily damaged; 5. When using sacrificial anode protection, the type, specification and size of the anode should be selected based on factors such as the resistivity of the medium. The protected body should have a complete monitoring system. The following information should be available when designing the cathodic protection system. 5.6.3
Technical data of pipeline or tank system:
1) Specification and length of pipeline or volume, diameter and height of tank, physical properties and temperature of medium; 2) Line diagram of pipeline or location diagram of storage and related topographic map; 3) Construction date;
4) Installation diagram of relevant accessories and other ancillary facilities of pipeline or tank; 5) Anti-corrosion layer and its insulation resistance;
6) Pipeline casing and its distribution;
7) Corrosion control detection device;
8) Number and location of electrical insulation devices;
9) Number and location of electrical connection points;
10) Pipeline crossing and intersection locations. Site environmental conditions of pipeline or tank system: 2
1) Existing and planned cathodic protection systems: 2) Possible interference sources,
3) Special environmental conditions,
4) Adjacent buried metal structures (including location, ownership and corrosion control measures), 5) Accessibility of pipelines or tanks;
6) Available power supply conditions,
7) Feasibility of electrical insulation from external metal structures, 3 Data obtained from site investigation, corrosion testing and operating experience: Standard Thin Network
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1) The amount of protection current required to meet the standard requirements; 2) The resistivity of the electrolyte;
3) Electrical continuity;
4) Electrical insulation;
5) The integrity of the anti-corrosion layer;
6) Leakage history;
7) Interference current;
8) Non-compliance with construction technical specifications; 9) Other related maintenance and operation information. The design of impressed current cathodic protection shall comply with the provisions of 5.6.42
SYJ36 of the current national standard "Design Specifications for Compulsory Current Cathodic Protection of Underground Steel Pipelines", and the design of sacrificial anode cathodic protection shall comply with the provisions of SY/T0019 of the current national standard "Design Specifications for Sacrificial Anode Cathodic Protection of Buried Steel Pipelines".
5.6.6 The design of cathodic protection for the outer wall of the tank bottom shall comply with the provisions of the current national standard "Technical Standard for Cathodic Protection of the Outer Wall of the Bottom of Steel Tanks" SY/T0088.
6 Control of interference corrosion
6.1 DC interference
6.1.1 Rules for judging DC interference:
1 For pipelines near DC electrified railways, cathodic protection systems and other DC interference sources, if the pipe-to-ground potential at any point is offset by 20mV from the natural potential of the point or the DC ground potential gradient in the soil adjacent to the pipeline is greater than 0.5mV/m, it can be confirmed that there is DC interference in the pipeline.
2 The soil potential gradient can be used to judge the degree of DC interference corrosion according to the indicators listed in Table 6.1.1. Table 6. 1.1. Determination of the degree of DC stray current interference. Stray current degree
Soil potential gradient (mV/m)
0.5～5.0
3. When the ground potential of any point on the pipeline is positively offset by 100mV compared with the natural potential of the point, or the DC ground potential gradient of the soil adjacent to the pipeline at the point is greater than 2.5mV, protective measures should be taken. 6.1.2 The protection of DC interference should be carried out according to the principles of drainage protection, comprehensive management, and "common protection". 1. Drainage protection is the main method of DC interference protection. DC drainage, polarity drainage, forced drainage, grounding drainage and other protection methods should be selected according to the interference degree, state, the relationship between the interference source and the pipeline, the site environment and other conditions. 2. The key points of comprehensive management are as follows:
1) Measures should be taken on the interference source side to reduce the amount of leakage current and minimize its interference to the external system. 2) In the pipeline system affected by interference, insulating flanges should be installed appropriately and reasonably to alleviate or solve the interference problem. 3) Electrical connection (including the insertion of adjustable resistors) can adjust or change the distribution of the interference current flow in the pipeline, which is helpful to improve the drainage effect.
4) Repair and strengthen the anti-corrosion layer, which can limit the interference current flowing into or out of the pipeline, which is conducive to alleviating interference and improving the drainage protection effect.
5) Change the predetermined pipeline direction or the position of the cathodic protection anode bed. 6) Adjust the output of the cathodic protection current, or use sacrificial anode protection instead of impressed current cathodic protection. 7) Setting a shielding grid or electric field shielding can help change the direction of stray current flow and the number of stray currents flowing into the interfered body. 686
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3Underground pipelines or underground power, communication and other cables with different ownership in the same interference area should be included in a common interference protection system on the basis of mutual consultation, and "common protection" should be implemented to avoid the formation of mutual regenerative interference in independent interference protection. 6.1.3 DC interference protection shall meet the following requirements: The ground potential of the pipeline affected by the interference shall be restored to the state before the interference. When implementing the drainage protection, the drainage effect shall meet the requirements of the indicators listed in Table 6.1.3. 2
Table 6.1.3 Drainage protection effect evaluation indicators Drainage type
Direct drainage to the interference source
(direct, polarity, forced drainage method) Average positive potential ratio of the pipe-to-ground potential during interference (V)
Drainage type
Indirect drainage to the interference source
(grounding drainage method)
Average positive potential ratio of the pipe-to-ground potential during interference (V)
6.1.4 The test of the influence of DC interference and the drainage protection measures taken shall comply with the provisions of the current national standard "Technical Standard for DC Drainage Protection of Buried Steel Pipelines" SY/T0017. 6.2 AC interference
6.2.1 The degree of corrosion caused by AC interference to underground pipelines can be determined by using the AC interference potential of pipelines according to the indicators listed in Table 6.2.1.
Table 6. 2. 1
Indicators for judging AC interference of buried steel pipes Severity (level)
Soil type
Alkaline soil
Neutral soil
Acidic soil
Judgment index (V)
Buried pipelines affected by AC interference should meet the indicators specified in Table 6.2.2 after drainage. Table 6. 2. 2
Soil type
Potential after drainage (V)
Evaluation index for AC drainage protection effect
The horizontal distance between various grounding devices of the AC power system and the buried pipeline should not be less than the requirements of Table 6.2.3. Table 6.2.3 Safe distance between buried pipeline and AC grounding body Power level (kv)
Grounding form
Temporary grounding
Tower or pole grounding
Substation grounding
Note: Two-wire and one-ground transmission lines are not considered. Standard zero grid
Safe distance (m)
Standardized consumer
SY0007--1999
6.2.4 The test on the influence of AC interference and the drainage protection measures taken shall comply with the provisions of the current national standard "Technical Standard for AC Drainage Protection of Buried Steel Pipelines" SY/T0032. 7 Brain corrosion control investigation and record
7.0.1 The effectiveness and reliability of corrosion control and protection shall be investigated regularly or irregularly, and the specific practices shall comply with the provisions of the current national standard "Standard for Investigation Methods of Corrosion and Protection of Steel Pipelines and Storage Tanks" SY/T0087. 7.0.2 Corrosion control records should be clear and concise, and the record content should include relevant information on corrosion control design, construction, installation, operation and maintenance.
Records of corrosion control design and construction include: selection of anti-corrosion layer materials and structures, adopted design and construction specifications, and completion data; layout design and completion data of insulation devices, anode points, detection devices, detection wires and other equipment of the cathodic protection system, and other relevant information on corrosion control.
Corrosion control maintenance records include:
Maintenance records of cathodic protection systems;
2Maintenance records of interference with corrosion control facilities; 3
Maintenance records of anti-corrosion layers;
Other relevant maintenance records. www.bzxz.net
Corrosion control records should be properly preserved and stored in a database. Standard Search Slow Network2
Soil type
Potential after discharge (V)
Evaluation index of AC discharge protection effect
The horizontal distance between various grounding devices of AC power system and buried pipelines should not be less than the provisions of Table 6.2.3. Table 6.2.3 Safe distance between buried pipeline and AC grounding body Power level (kv)
Grounding form
Temporary grounding
Grounding of tower or pole
Grounding of power station substation
Note: Two-wire and one-ground transmission line is not considered. Standard zero grid
Safe distance (m)
Standardized consumer
SY0007--1999
6.2.4 The test of the influence of AC interference and the drainage protection measures taken shall comply with the provisions of the current national standard "Technical Standard for AC Drainage Protection of Buried Steel Pipelines" SY/T0032. 7 Corrosion control investigation and records
7.0.1 The effectiveness and reliability of corrosion control and protection should be investigated regularly or irregularly, and the specific practices should comply with the provisions of the current national standard "Standard for Investigation Methods of Corrosion and Protection of Steel Pipelines and Storage Tanks" SY/T0087. 7.0.2 Corrosion control records should be clear and concise, and the record content should include relevant information on corrosion control design, construction, installation, operation and maintenance.
Records of corrosion control design and construction include: selection of anti-corrosion layer materials and structures, adopted design and construction specifications, and completion data; layout design and completion data of insulation devices, anode points, detection devices, detection wires and other equipment of the cathodic protection system, and other relevant information on corrosion control.
Corrosion control maintenance records include:
Maintenance records of cathodic protection system;
2Maintenance records of interference with corrosion control facilities; 3
Maintenance records of anti-corrosion layer;
Other relevant maintenance records.
Corrosion control records should be properly preserved and stored in the database. Standard search slow network2
Soil type
Potential after discharge (V)
Evaluation index of AC discharge protection effect
The horizontal distance between various grounding devices of AC power system and buried pipelines should not be less than the provisions of Table 6.2.3. Table 6.2.3 Safe distance between buried pipeline and AC grounding body Power level (kv)
Grounding form
Temporary grounding
Grounding of tower or pole
Grounding of power station substation
Note: Two-wire and one-ground transmission line is not considered. Standard zero grid
Safe distance (m)
Standardized consumer
SY0007--1999
6.2.4 The test of the influence of AC interference and the drainage protection measures taken shall comply with the provisions of the current national standard "Technical Standard for AC Drainage Protection of Buried Steel Pipelines" SY/T0032. 7 Corrosion control investigation and records
7.0.1 The effectiveness and reliability of corrosion control and protection should be investigated regularly or irregularly, and the specific practices should comply with the provisions of the current national standard "Standard for Investigation Methods of Corrosion and Protection of Steel Pipelines and Storage Tanks" SY/T0087. 7.0.2 Corrosion control records should be clear and concise, and the record content should include relevant information on corrosion control design, construction, installation, operation and maintenance.
Records of corrosion control design and construction include: selection of anti-corrosion layer materials and structures, adopted design and construction specifications, and completion data; layout design and completion data of insulation devices, anode points, detection devices, detection wires and other equipment of the cathodic protection system, and other relevant information on corrosion control.
Corrosion control maintenance records include:
Maintenance records of cathodic protection system;
2Maintenance records of interference with corrosion control facilities; 3
Maintenance records of anti-corrosion layer;
Other relevant maintenance records.
Corrosion control records should be properly preserved and stored in the database. Standard search slow network
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