SY/T 10008-2000 Corrosion Control of Offshore Fixed Steel Oil Production Platforms
Some standard content:
ICS75.180.10
Registration No.: 7886—2001
People's Republic of China Offshore Oil and Gas Industry Standard SY/T 10008-—2000
idt NACE RP0176:1994Www.bzxZ.net
Corrosion control of steel fixed offshore platformsassociated with petroleum production 2000-11-24 Issued
State Administration of Petroleum and Chemical Industry
2001-05-01 Implementation
SY/T 100082000
Policy Statement
NACE Preface
Chapter 1 Overview
Chapter 2
Chapter 3
Chapter 4
Chapter 5
Chapter 6
Chapter 7
Chapter 8
Chapter 9
Chapter 10
Chapter 12
Chapter 13
Chapter 14
Structural Design for Corrosion Control
Cathode Protection Criteria
Design of Cathodic Protection System:
Insulation of Cathodic Protection System
Control of Disturbance Current
Insulation Shielding
Operation and Maintenance of Cathodic Protection System
Sputtering Corrosion control measures in splash zone
Maintenance measures for corrosion control in splash zone
Surface treatment
Coating inspection
Corrosion control record
Appendix A (Appendix of standard)
Design parameters of offshore stone production model
Appendix B (Appendix of Sun Ya)
Capacity and consumption rate of sacrificial anodes for cathodic protection of offshore platforms in various industries 10
Appendix (Appendix of standard)
Consumption rate of impressed current anodes for cathodic protection of offshore platforms in seawater outlets·38 Appendix 1 (Appendix of standard) Typical calculation method of sacrificial anode output current 39
SY/T 10008—2000
In order to adapt to the development of offshore natural gas resources development and production, the original SYT10008—1996 “Corrosion Control of Steel Fixed Offshore Platforms” was revised based on the 1994 edition of the National Association of Corrosion Engineers (NACE) standard “Corrosion Control of Steel Fixed Offshore Platforms” (NACE RP 0176 Carrosion Control of Steel Fixed Offshore Platforms Associated with Petroleum Engineering Standards: 1994) as the new standard for the offshore oil and gas industry of the People's Republic of China. The new version of the standard reflects the development and progress of cathodic protection of jackets in recent years. The definition of terms and text descriptions are more precise and concise. The content and format have been greatly modified. Minor deletions and revisions are throughout the standard. The main modifications include the following aspects: - Added content related to the design of cathodic protection system for jackets: - Added three splash protection methods: - Added thermal spray anti-corrosion coating: - Made significant revisions to the design criteria for cathodic protection systems. In the design and construction of offshore natural gas development projects, if this standard encounters laws, regulations and provisions of the government or other competent authorities of the country where the original standard is located, it shall be implemented in accordance with the corresponding laws, regulations and provisions promulgated by the government of the People's Republic of China or the competent government department. The original standard is about environmental conditions data or quantitative calculation methods such as wind, waves, currents, ice, overflow, earthquakes, etc., and any data or quantitative calculation methods that meet the actual conditions of my country can be used for reference; otherwise, data or quantitative calculation methods approved by authoritative organizations and in line with the actual environmental conditions of China should be used. The units of measurement in this standard shall be based on the legal measurement list issued by the state, that is, the format of description in this standard is: the legal measurement unit is in front, and the corresponding mark of the imperial unit is in the bracket after it. In order not to change the shape characteristics, constants and parameters of the formulas and curves in the original standard, this standard still uses the imperial units of the original standard in the formulas and figures.
From the date of implementation, this standard will replace SY/10008-1996. Appendix A, Appendix B, Appendix C and Appendix D of this standard are all appendices of the standard. This standard was proposed and approved by Huaizhou Offshore Oil Corporation. The originating unit of this standard: China Offshore Oil Corporation Offshore Engineering Design Company: The main authors of this standard: Chang Wei, Li Yanxia, Zhang Shuzhen. This standard is reviewed by Zheng Yongan. The water standard was first issued in August 1996. This is the first revision. V. SYT10008—2000. Policy Statement. Offshore oil and gas industry standard. This version is aimed at general issues. When it comes to specific situations, national and local laws and regulations should be read.
Offshore oil and gas industry standards publications do not assume any responsibility for providing prior notice and training on health, safety and hazard prevention to operators, manufacturers or suppliers for their personnel and other on-site operations, nor do they assume any responsibilities under national and local regulations: The content of any offshore oil and gas industry standards publication cannot be interpreted, implicitly or otherwise, as granting any right to manufacture, sell or use any method, equipment or product involving patent rights, nor does it assume any responsibility for any person who infringes patent rights: Generally, offshore oil and gas industry standards are reviewed, revised, re-identified or revoked at least once every two years. Sometimes, this review cycle can be extended for "years", but not more than two years. Therefore, the publication is valid for no more than one year from the date of publication. Unless an extension is authorized The validity period is long. The information of the H version can be obtained from the Secretariat of the Technical Committee for Standardization of Offshore Oil and Gas Industry (Tel. 010-84522236, mailing address: Standardization Office, Development and Design Institute, CNOOC Research Center, PO Box 235, Beijing, 101149) or the Technical Committee for Standardization of Offshore Oil and Gas Industry (Tel. 010-84522673, mailing address: Science and Technology Office, 25th Floor, Jingxin Building, No. 2, Dongsanhuai North Road, Chaoyang District, Beijing, 100027). The standards for offshore oil and gas industry are published in the following ways: In order to promote proven and good process technologies and operating practices, it is not intended to exclude the need to correctly judge where these technologies and practices should be used. The formulation and publication of offshore oil and gas industry standards are not intended to in any way affect the quality of the industry. The use of any other technology and practice is restricted to any person, and this standard is available to anyone who wishes to adopt it. The Offshore Oil and Gas Industry Standardization Technical Committee and its authorized issuing units have made unremitting efforts to ensure the accuracy and reliability of the data contained therein. However, the Offshore Oil and Gas Industry Standardization Technical Committee and its authorized issuing units do not act as agents, warranties or guarantees for the standards they publish, and hereby expressly state that they will not be liable for any loss or damage caused by the use of these standards! The Offshore Oil and Gas Industry Standardization Technical Committee and its authorized issuing units do not assume any obligations or responsibilities for the consequences of using standards that may conflict with any national and local regulations, and for the infringement of any patent rights caused by the use of these standards.
SY/T10008- -2000
NACE Foreword
Building an offshore platform means a huge investment. The platform is located in the vast ocean, and its design should be able to withstand the impact of hurricanes, polar storms, tidal currents, earthquakes and large icebergs. Moreover, the water depth of the platform is getting deeper and deeper, so the platform design is getting bigger and more complex, and the investment is getting higher and higher. In order to economically generate gas, provide safety for work and life, and avoid potential harm to the environment, it is necessary to control the corrosion of the platform. This NACF standard provides the materials, practices and procedures required for corrosion control for fixed offshore steel oil production platforms. Its purpose is to provide reliable information to more effectively protect the platform. The corrosion of offshore platforms is divided into one main area: full immersion area, splash zone and gas zone. The fully immersed area also includes the part below the mudline. This standard does not include the internal corrosion control methods of the oil wells, piping and related equipment on the platform, but includes the external corrosion control methods that are not applied to the platform's active area: The recommended practices for submarine pipelines and risers are shown in NACE Standard RP0675 Corrosion Control of Marine Steel Pipelines (latest version). This aspect is not included in this standard. The first edition of this standard was issued by the North Sea Corrosion Problem T-1-2 Working Group in 1976 and revised in 1983. The revised version of NACE RP0176 in 1994 was issued by T-1-5.Prepared by Working Group: Under the auspices of Subcommittee T-1 on Corrosion Control in Petroleum Production and published by the American Association of Engineers.
Offshore Oil and Gas Industry Standard of the People's Republic of China Corrosion Control of Steel Fixed Offshore Platforms Associated with Petroleum Production Platforms Chapter 1 Overview
SY/T 10008—2000
Replaced with SY/T 10008--1996
idt NACE RP 0176: 1994
1.1 This standard provides guidance for determining the minimum requirements for corrosion control of the exterior of fixed steel offshore petroleum production platforms and associated oil and gas processing equipment. This standard divides the corrosion control of the platform into three areas: the full immersion area, the splash zone and the auxiliary area, and discusses each area separately. 1.2 Due to the complexity of environmental conditions, this standard does not provide guidance for every special situation. In many cases, the same problem may have several different solutions: some appropriate and cost-effective solutions are included. 1.3 This standard does not include internal corrosion control guidelines for oil and gas pipelines, piping and related equipment attached to the platform or built on the platform. 1.4 This standard includes external corrosion control of attached pipelines above the splash zone. When the pipeline and the platform have different owners, the shared owner’s responsibility for the pipeline usually ends at a designated point, or at the valve on the platform. 1.5 The objectives mentioned in this standard can be achieved by different methods, but the selected method can only be adopted when it is approved by qualified corrosion control experts and the objectives stated in this standard have been achieved. 1.6 This standard is divided into the following parts:
Chapter 1 Overview
Chapter 2||t Chapter 3 Chapter 4 Chapter 5 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 Chapter 12 Chapter 13 Chapter 14 Chapter 15 Structural Design of Corrosion Control Cathodic Protection Plan Design of Cathodic Protection System Cathodic Protection Installation of cathodic protection system
Control of interference current
Insulation layer
Operation and maintenance of cathodic protection system
Corrosion control measures in splash zone
Maintenance measures for corrosion control in splash zone
Surface treatment
Coating inspection
Corrosion control record
Approved by the State Administration of Petroleum and Chemical Industry on 2000-11-24 and implemented on 2001-05-01
SY/T 10008—2000
Chapter 2 Definitions
Roughness (anchor pattern) - irregular depressions on the surface of steel after high-speed sandblasting. Anode (anode) - the electrode in an electrochemical cell where oxidation reactions occur. In the circuit, the electrons flow from the anode. Corrosion usually occurs on the anode and metal ions enter the solution
Atmospheric zone (atmospheric zone) - the part of the platform above the splash zone exposed to sunlight, wind, water mist and rain. Calcareous film or deposit (calcareous coating or deposit) - the film containing calcium carbonate and other salts deposited on the protected surface due to the increase in pH near the surface protected by the cathodic expansion. Cathode (cathodc) - the electrode in an electrochemical cell where the main reduction reaction occurs. In the external circuit, neutrons flow to the cathode. Cathodic disbonding (cathodic disbond) - the product of the cathode reaction causes the coating to lose adhesion to the coated surface. Cathodic protection - A technique used to reduce the rate of corrosion on a metal surface by using the metal as an electrochemical cathode.
Chalk - A condition of a coating that results in the loss of adhesion of the coating due to exposure to ultraviolet light, causing the pigment to precipitate from the paint film. Controlling chalking ensures that the paint is cleaned up, thereby maintaining a good finish for reapplying a layer of paint.Corrosion is the deterioration of a material, usually a metal, by reaction with its surrounding environment. Corrosion specialist - a person qualified by his or her education and/or experience to evaluate and solve problems related to corrosion of materials. Corrosion specialists as defined in this standard are persons qualified to control corrosion in marine environments. Crosslink - the result of a chemical reaction that links two chains in the structure of a coating and changes the final state of the coating. Current - the rate of flow of charge carriers in the direction of positive charge flow (in a metal conductor, electrons flow in the opposite direction). Current density - the current flowing into or out of a surface per unit area of the electrode. Depolarization - - the factor that removes obstacles to the flow of current in an electrochemical cell. Dielectric shield - a non-conductive material, such as a coating, insulating sheet or tube, placed between the anode and the adjacent cathode in a cathodic protection system, usually placed on the cathode. These non-conductive materials can improve current distribution. Doublerplate - a steel plate or steel wall added to the anode/bisection connection for extra strength. Electrical isolation - the state of being electrically isolated from other metal components or the environment. Electrolyte - a chemical substance or mixture containing ions that can migrate in an electric field. Epoxy - a type of resin formed by the reaction of dioxin and epichlorohydrin. Forcign structure - any metal structure that has no role in the cathodic protection system. Sacrificial anode - a metal that, when connected to an electrolyte, provides protection for the properties of another metal at a more positive potential. This type of anode is a source of current for cathodic protection. Holiday - a break in an anticorrosive coating where the unprotected surface is exposed to the environment. Impressed current - a current supplied by a device that delivers an external current to the electrode system (e.g., a DC current for cathodic protection).
Interference current (stray current) - refers to the current that does not pass through the specified circuit: in this standard, stray current refers to the current flowing through the structure, which may not be on the specified circuit or may be on the specified circuit but not completely connected to the current source.
Inorganic zinc-rich paint - refers to a paint containing zinc powder pigment in an inorganic carrier. Well-dispersed inorganic zinc pigment is combined with the selected curing material, which can be water-based or solvent-based, and can form chemical bonds and mechanical bonds with the metal substrate: white curing zinc-rich paint can reach a fully cured state without further treatment after application. Post-curing zinc-rich paint needs to be coated with acid-based paint immediately after application to complete the curing reaction of the paint film. "J" tube - a curved pipe designed and installed on a platform to support or guide one or more pipeline risers or cables.—2
millscale
mudline
pipeline
platform
living module.
polarization
SY/T10008—2000
scale formed during the hot rolling or heat treatment of metals. seafloor surface in a specific area.
a pipe for transporting produced oil, water and gas between platforms or between platforms and onshore processing facilities. An offshore structure that may contain oil and/or gas wells and related production facilities, piping and/or the change in potential from the circuit potential caused by the passage of current through the electrode/electrolyte interface. Polymerization
Compound.
Primer
The process of many small chemical units agglomerating into larger chemical units. The resulting aggregate is called a polymer. The first coating material applied to an uncoated surface. This coating has particularly good adhesion to the coated surface and can provide a suitable surface for subsequent coatings.
Reference electrode (referenceelectrode) The relative potential of an electrode.
Resin (resin)
An electrode whose open circuit potential is constant under conditions similar to those being measured. It is used to measure other general types of plastic or polymer materials and is stable when used as a coating binder. The term "resin" is often modified by other words to indicate its type, such as alkyd, vinyl, ester, or epoxy. Riser
The section of a pipeline extending upward from the seafloor to the flat
Silver/silverchloride electrode.
The surface of the splash zone
.
Refers to a reference electrode using seawater as the electrolyte, such as A g/AgCI/Seawater due to wind and wave effects, alternating wetted parts of the platform, but excluding major storm wetted by tides,
The potential difference between the structure-electrolyte potential.
Buried or fully immersed metal structures and reference electrodes in contact with electrolytesFully immersed zone
From the splash zone down, including the part of the platform below the mud lineVolatile solvent thinner used to reduce the viscosity of the coating
Thermoplastic
Thermosetting
Material.
Tiecoat
Material with the ability to soften by repeated heating and harden by cooling
Under the action of heating, pressure, catalysis and ultraviolet rays, it undergoes chemical reactions to become a relatively refractory intermediate coating with specific functions,
overcoming the incompatibility or practical difficulties between primer and topcoat. Urethane (urethane
formed by the reaction of isocyanate
usually refers to organic coating. It is used as a transitional coating between primer and topcoat, and is a chemically cured coating
residue, among which A tough, durable, clear coating of a vinyl, vinyl acrylic or acrylic solution
valve reachrod
ballast valve.
vinyl acrylic resin (vinylacrylic) vinyl coatings (vinyl coatings)
voltage
refers to the valve extension handle, which allows the operator at the top of the platform to open or close the bottom of the platform. The vinyl resin modified with dissolved acrylic resin refers to the vinyl resin dissolved in a solvent. The vinyl solution coating can be air-dried or baked. The electromotive force or electrode potential difference expressed in volts or millivolts Voltage drop (voltagedrop) -
wash primer (washprimer)
wear plate (wearplate)
the voltage across a current-carrying resistor obtained according to Ohm's law. A dilute corrosion-inhibiting primer, usually containing chromate pigments and polyvinyl butyrate adhesive. A sacrificial component installed in the splash zone of the platform to prevent the platform from being corroded and/or eroded by ice and/or high-speed water containing mud and sand. 3
SY/T 10008—2000
Chapter 3 Structural design for corrosion control
3.1.1 This chapter recommends a simplified design method for the full corrosion control of steel structures in the semi-atmospheric zone, splash zone, and full flood zone. The structural design parameters that need to be considered to enable the platform to withstand dynamic loads and static loads should be! It is not the responsibility of the structural engineer, so it is not included in this standard:
3.2 Splash zone
3.2.1 The splash zone of the platform refers to the area of the platform that is affected by tides, wind and waves, and is alternately dry and wet, but does not include the surface that is only splashed during storms: In the Gulf of Mexico, the typical splash zone is about 2m (6ft); in the Cook Inlet of Alaska, it reaches 9m (30ft); in the North Sea, winter storms can make the splash zone reach 10m (33ft) 3.2.2 In the design of the platform structure, the surface area of steel in the splash zone should be reduced, and the use of "T" type, "K" type or "Y" type nodes should be avoided in the splash zone:
3.2.3.2.4 Use welded casing or thick-walled protective pipe to increase the wall thickness [in the Gulf of Mexico: generally increase the wall thickness by 13~19mm (0.5~0.75in)] to compensate for the corrosion in the splash zone during the service life of the platform. Steel anti-corrosion plates can be sufficient to prevent damage from operating ships or ice: 3.2.5 Pipes and other components that pass through the splash zone and are removed after the platform is installed should be clamped to the platform components instead of welded. 3.3 Atmospheric zone
3.3.1 The "atmospheric zone" refers to the area above the platform splash zone, which is exposed to light, wind, fog and rain. 3.3.2 Commonly used protective coating systems for controlling atmospheric corrosion (see Chapters 12 and 13). The following measures can reduce the area of steel surface that needs to be coated and facilitate application
3.3.2.1 Use tubular components instead of other shapes 3.3.2.2 When metal components are put together, use case welding and wrap welding. 3.3.2.3 Avoid jumping
3.3.2.4 Avoid tight fitting surfaces and overlapping surfaces. 3.3.2.5 Set up mooring eye plates to provide a way to set up the scaffolding and coating maintenance. 3.3.3 Non-ferrous metals and non-metallic materials can reduce corrosion problems. For example, aluminum and composite materials such as glass-reinforced polyester (GRP) can be used for life modules and lifeboats. Other types of corrosion-resistant materials can be made into handrails, cable guards, ladders and decks with less walking. When using different metal materials, care must be taken to prevent galvanic corrosion of active metals. Composite materials such as GRP can be used to replace metal materials where corrosion resistance and/or weight reduction are required. Safety factors should be considered when using these materials. 3. 3.4 Drilling fluids are destructive to protective coatings and nonferrous metals (such as aluminum and zinc). Therefore, in order to reduce the damage and contamination of the coating by drilling fluids, solid plates, splash walls and good exhaust systems should be used. 3.4 Wave zones - external
3.4.! The fully immersed zone refers to the area from the splash zone downward to the mud line. External corrosion control of fully immersed x can be achieved by cathodic protection or cathode protection plus coating. The following design is recommended to simplify the implementation of effective cathodic protection. 3.4.1.1 Use round pipe components as much as possible. The dead corners of the steel bars or I-beams are difficult to protect, and the seams formed by back-to-back channels or angles cannot be effectively protected. Therefore, this type of structure should not be used. 3.4.1.2 When fatigue and corrosion fatigue are important factors in the structural design, the flat installed in this case, Stress should be eliminated to reduce the corrosion that may occur in the heat affected zone (HAZ) and reduce the possibility of cracks. This is particularly important in cold water environments where the polarization process is slow. See SY/T4802\
1) SY/T4802 latest version) or Recommended Practice for Planning, Design and Construction of Sea-type Platforms. 4
SY/T10008—2000
3.4.1.3 The weld should be continuous, and skip welding or spot welding should not be used. If lap welding is used, both sides should be welded. Bolts and rivets should be avoided:
3.4.1.4 In actual applications, the ballast control valve extension rods are designed to be removed after they are in place on the platform. If left there, they may shield adjacent metal components that are protected by polarization current. Loose extension rods will wear the platform, 3.4, 1.5 Steel pipes: such as grouting pipes, cuttings pipes, discharge pipes, water supply casings and submarine pipeline risers, if clustered around the platform pile legs, will cause shielding and interfere with the flow of cathodic protection current. If economically feasible, steel pipes that are not needed for platform operation should be removed, and steel pipes that cannot be removed should be placed where they will not cause shielding. The minimum clear spacing between steel pipes should be 1.5 times the diameter of the smaller steel pipe. Steel pipe coatings can also be used to reduce shielding.
3.4.1.6 After the platform is put into operation, it is sometimes necessary to supplement or replace the anodes of the impressed current system. The designer should consider providing spare "type protective pipes" to facilitate the traction of electric current when adding anodes: and (or) provide other types of pipe racks, conductors and pipe clamps to facilitate the supplement or replacement of anodes: 3.4.1.7 The part below the mudline of the platform contains steel. The piles driven from the conductor legs are usually connected to the conductor by welding: Therefore, the steel piles are also protected by anodes: Typical skirts are driven into underwater steel pipes and fixed with cement in situ. The piles can be electrically connected to the conductor by guides, centering devices or other feasible methods: However, the corrosion rate below the mudline is low. If there is no proper electrical connection with the cathodic protection system, the corrosion rate at the mudline will increase. The rate may be high and problems may occur, especially for long-life jackets. 3.4.1.8 The riser and the riser casing should be considered as the original consideration. The riser should be electrically connected to the platform. 3.4.1.9 All protected steel structures should be electrically connected to the anode (preferably by welding) and maintained throughout the life of the structure.
3.5 Internal liquid area
3.5 Corrosion is often ignored for components or internal surfaces of sealed compartments that are not exposed to air and water after sealing: If possible, the design should take into account sealed compartments.
3.5.2 During the platform launching and tilting operations, some metal components will be filled with water and remain filled with water for half of the life of the platform. To prevent internal corrosion, the filling valve should be closed to prevent the filled compartment from being exposed to oxygen in the air. If the full water cycle of the compartment cannot be avoided, measures should be taken to prevent internal corrosion, which can be cathodic protection or the use of cathodic protection coatings. ：In a sealed water-filled cabin, bacterial growth will produce some corrosive substances, such as organic acids, carbon dioxide, and sulfide (HS). In addition to increasing corrosion, sulfate-reducing bacteria also produce highly reproducible HS gas. Bacterial corrosion can be controlled by using internal cathodic protection, chemicals that increase pH, and (or) bactericides. In areas with thicker walls (such as pile legs), bacterial corrosion may not be obvious, but there is still a risk of producing HS. 3.5.3 Gradient-bottomed pipelines are sometimes installed in traction guide sections or "J"-shaped sections. In order to limit the contact between seawater and oxygen in the atmosphere and the pipeline, after the pipeline is positioned, the water port of the annular space of the traction guide section should be sealed with a suitable non-absorbent filler. s
SY/T10008—2000
Chapter 4
Cathode Protection Criteria
4.1 Introduction
4.1.1 This chapter lists the cathodic protection criteria and corresponding detection methods. Compliance with these criteria, either individually or in combination, will indicate whether the platform is protected.
4.2 Overview
4.2.1 The purpose of applying cathodic protection is to control corrosion on metal surfaces in contact with electrolyte solutions. 4.2.2 The criteria in Section 4.3 are based on laboratory or field experience. If corrosion control is demonstrated by other means, platform protection need not be limited to these criteria.
4.2.3 Specific criteria may be selected to achieve the objectives set forth in 4.2.1. Such selection of criteria may be based in part on past experience with the successful application of the criteria on similar platforms and environmental conditions. 4.2.4 There is currently no satisfactory criterion for evaluating the effectiveness of cathodic protection under any conditions. A combination of criteria is required.
4.3 Criteria
For two single platforms, the possible
4.3.1 Potential Measurement
4.3.1.1 The negative (cathode) potential difference measured between the platform surface and a silver-silver chloride (20 cm seawater) reference electrode (Ag/AgC/ISWI) in contact with seawater shall be at least -0.80 V. The cathodic potential of the platform surface is usually measured when the protective current is applied. The specified -0.80 V includes the voltage drop of the current through the steel/water interface, but does not include the voltage drop in the water (see 4.5.1 and 4.6.1). This value can replace the criteria in 4.3.1.1. 4.3.1.2 When the protective current is applied, the minimum offset of the negative (cathode) potential of the platform surface in contact with seawater is 300 mV. The offset of the potential can be measured by the reference electrode. This quantity includes the voltage drop of the current through the steel/water interface, but does not include the voltage drop in the water (see 4.5.1.1 and 4.6.1). When in a representative environment
water in contact with air,
4.3.1.3 The potential for controlling corrosion is a function of temperature and environmental conditions. For shielded driving
temperature conditions, the criteria listed in 4.3.1.1 and 4.3.1.2 have been shown to be satisfactory. For other environmental conditions, the potential for controlling corrosion can be estimated using the Nernst equation. 4.3.2 Visual inspection
4.3.2.1 To ensure the service life of the platform, the results obtained from various visual inspection methods of the entire platform (diver observation or touch, physical measurement, photography or television scanning) should show that the corrosion progress does not exceed the limits allowed by the service life of the platform. 4.3.3 Test piece
Corrosion type and corrosion rate must be limited to the allowable range 4.3.3.1 To ensure the service life of the platform, 4.4 Alternative Reference Electrodes
The following types of standard reference electrodes can replace the -0.80V potential of the Ag/AgCI/[SW] reference electrode
Ag/AgC/ISW reference electrode. Reference electrode: -0.85V potential (can be more negative when used for protection) 4.4.1.1 Saturated copper copper sulfate (CSE)
Their potential is equivalent to
Note: This electrode is unstable when immersed in water for a long time 4.4.1.2 High purity zinc reference electrode: The potential is +0.25V (can be slightly lower than +0.25V when used for protection). The composition limits of this type of high purity zinc are aluminum: not more than 0.005%;
Cadmium: not more than 0.003%:
Iron: not more than 0.0014%:
Zinc: balance
4.4.1.3 Saturated calomel electrode (SCE [saturated KCI): -0.78 V (can be more negative when used for protection) 4.4.1.4 Zinc reference electrode: potential is +0.25 V (can be slightly lower than +0.25 V when used for protection). The composition limits of this type of zinc material are: 6
Aluminum: 0.10%~0.50%
Cadmium: 0.025%~0.15%
Iron: not more than 0.005%
Lead: not more than 0.005%
Copper: not more than 0.005%:
Silicon: not more than 0.125%
SY/T10008—2000
4.4.1.5Ag/AgCI (saturated KCl): 0.76V (can be more negative when used for protection) 4.5 Methods for measuring and evaluating cathodic protection
4.5.1 The most common method for evaluating the degree of cathodic protection is to measure the potential of the platform using an appropriate reference electrode. 4.5.1.1 When measuring the platform potential, the reference electrode immersed in water should be placed as close to the platform as possible to reduce the voltage drop factor in the measured potential. When evaluating the protection level of the platform, the data measured by the reference electrode close to the platform but away from the anode block and in the largest shielding area should be given priority.
4.5.1.2 One of the most commonly used methods for measuring potential is to hang the reference electrode freely in the water at a set position on the platform. The reference electrode is placed in a series of specified water depths to obtain data, and the process is repeated at other appropriate positions on the platform. Since the ocean current will cause the reference electrode to drift, the specific position of the reference electrode may not be known. This method is effective for determining the cathodic protection system under general conditions, but when the platform is in a critical state of being protected, this method may not determine the area with problems. 4.5.1.3 The reference electrode can be carried by a diver or a remotely controlled vehicle (RCV). These two methods can accurately know the position of the reference electrode and meet various accuracy requirements for potential measurement. When evaluating platforms protected by impressed currents, the safety of the divers must be considered. To this end, the output current may be reduced or at least part of the system may be switched off during the measurement. If the system power supply is switched off, the corresponding reduction in the degree of protection should be taken into account when evaluating the potential. 4.5.1.4 The reference electrode may be lowered by means of a guide rope so that its position can be better controlled. The directional guide rope may be permanently mounted on the platform or temporarily anchored to the bottom of the platform with the aid of weights. If it is temporarily installed, the guide rope (if it is made of metal) should be electrically insulated from the platform. This guided reference electrode can provide a more accurate measurement of the potential than a free-hanging reference electrode because the guide rope is close to the platform structure.
4.5.1.5 A certain number of permanent reference electrodes may be installed on the platform. Although the position of these reference electrodes is known accurately, the information obtained from them is limited to the potential of the platform surface in the vicinity. Although any potential measurement is limited to a local area, it can provide a reproducible basis for comparing potentials at different times. The accuracy of the permanent reference electrode should be checked periodically with other electrodes. Combining zinc and silver/silver chloride into a dual electrode, mounted on a permanent device, can help detect/reduce the occurrence of faults.
4.5.2 In addition to potential measurements, valuable information can be obtained by measuring current density. Using a specially designed reference electrode system, current density can be measured by determining the potential gradient in the seawater surrounding the structure. Although these measurements cannot determine the degree of protection of the current structure, they can be used to determine the current distribution and predict the remaining life of the anode. 4.5.3 Visual inspection is sometimes used to obtain detailed information that cannot be obtained by other methods. 4.5.3.1 Visual inspection can be performed by a diver, and in turbid or dimly lit areas, it can be checked by touch. 4.5.3.2 If equipped with appropriate instruments, visual inspection can also make physical measurements such as crack length and depth, wall thickness or pitting depth, and anode size and condition.
4.5.3.3 A permanent record of platform conditions can be obtained by underwater photography. 4.5.3.4 During underwater operations, if decisions must be made, underwater television can be used to provide surveillance on the platform. Videotapes can provide a permanent record of underwater conditions.
4.5.4 Steel coupons made of the same material as the platform components should be installed on the platform to allow for later sampling to determine the effectiveness of corrosion control measurements. Such coupons may be particularly useful in areas where it is suspected that cathodic protection currents are difficult to reach. 4.6 Notes
4.6.1 In addition to considering the steel/seawater interface voltage drop (R) when evaluating platform potential data, other voltage drops (IR) should also be considered.5 A certain number of permanent reference electrodes may be installed on the platform. Although the location of these reference electrodes is known accurately, the information obtained from these reference electrodes is limited to the potential of the adjacent platform surface. Although any potential measurement is limited to a local area, it can provide a reproducible basis for potential comparison at different times. The accuracy of the permanent reference electrodes should be regularly checked with other electrodes. Combining zinc and silver/silver chloride into a double electrode and installing it on a permanent device can help to find/reduce the occurrence of faults.
4.5.2 In addition to potential measurements, measuring current density can also provide valuable information. Using a specially designed reference electrode system, the current density can be measured by determining the potential gradient in the seawater around the structure. Although these measurements cannot determine the current protection level of the structure, they can be used to determine the current distribution and predict the remaining life of the anode. 4.5.3 Sometimes visual inspection is used to obtain detailed information that cannot be obtained by other methods. 4.5.3.1 Visual inspection can be carried out by divers, and in turbid or dimly lit areas, it can be checked by touch. 4.5.3.2 If properly instrumented, the visual inspection may also include physical measurements such as crack length and depth, wall thickness or pitting depth, and anode size and condition.
4.5.3.3 A permanent record of the platform condition may be obtained by underwater photography. 4.5.3.4 During underwater operations, underwater television may be used to provide surveillance of the platform if decisions must be made. Videotapes may provide a permanent record of underwater conditions.
4.5.4 Steel coupons of the same material as the platform components may be mounted on the platform to allow for later sampling to determine the effectiveness of corrosion control measurements. Such coupons may be particularly useful in areas where it is suspected that the cathodic protection current is difficult to reach. 4.6 Notes
4.6.1 In addition to the steel/seawater interface voltage drop (R) considered when evaluating platform potential data, other voltage drops (IR) should also be considered.5 A certain number of permanent reference electrodes may be installed on the platform. Although the location of these reference electrodes is known accurately, the information obtained from these reference electrodes is limited to the potential of the adjacent platform surface. Although any potential measurement is limited to a local area, it can provide a reproducible basis for potential comparison at different times. The accuracy of the permanent reference electrodes should be regularly checked with other electrodes. Combining zinc and silver/silver chloride into a double electrode and installing it on a permanent device can help to find/reduce the occurrence of faults.
4.5.2 In addition to potential measurements, measuring current density can also provide valuable information. Using a specially designed reference electrode system, the current density can be measured by determining the potential gradient in the seawater around the structure. Although these measurements cannot determine the current protection level of the structure, they can be used to determine the current distribution and predict the remaining life of the anode. 4.5.3 Sometimes visual inspection is used to obtain detailed information that cannot be obtained by other methods. 4.5.3.1 Visual inspection can be carried out by divers, and in turbid or dimly lit areas, it can be checked by touch. 4.5.3.2 If properly instrumented, the visual inspection may also include physical measurements such as crack length and depth, wall thickness or pitting depth, and anode size and condition.
4.5.3.3 A permanent record of the platform condition may be obtained by underwater photography. 4.5.3.4 During underwater operations, underwater television may be used to provide surveillance of the platform if decisions must be made. Videotapes may provide a permanent record of underwater conditions.
4.5.4 Steel coupons of the same material as the platform components may be mounted on the platform to allow for later sampling to determine the effectiveness of corrosion control measurements. Such coupons may be particularly useful in areas where it is suspected that the cathodic protection current is difficult to reach. 4.6 Notes
4.6.1 In addition to the steel/seawater interface voltage drop (R) considered when evaluating platform potential data, other voltage drops (IR) should also be considered.
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