NACE SP0408-2014 Cathodic Protection of Reinforcing Steel in Buried or Submerged Concrete Structures (Item No 21133).pdf

1、 Standard Practice Cathodic Protection of Reinforcing Steel in Buried or Submerged Concrete Structures This NACE International (NACE) standard represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any respect preclud

2、e anyone, whether he or she has adopted the standard or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not in conformance with this standard. Nothing contained in this NACE standard is to be construed as granting any right, by implication or otherwise, to

3、 manufacture, sell, or use in connection with any method, apparatus, or product covered by letters patent, or as indemnifying or protecting anyone against liability for infringement of letters patent. This standard represents minimum requirements and should in no way be interpreted as a restriction

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11、ational NACE SP0408-2014 Item No. 21133 SP0408-2014 _ Foreword The purpose of this NACE standard practice is to present guidelines for cathodic protection (CP) of reinforcing steel in buried or submerged concrete structures. These guidelines provide corrosion control personnel with information to co

12、ntrol corrosion of conventional reinforcing steel in portland cement concrete structures through the application of CP. For more information on design, evaluation, maintenance, and rehabilitation of reinforcing steel in concrete, refer to NACE SP0187,1SP0390,2 and SP0308.3CP of reinforcing steel in

13、atmospherically exposed concrete is described in NACE SP0290.4For a state-of-the-art overview on criteria for CP of prestressed concrete structures, refer to NACE Publication 01102.5For more information on CP of prestressed concrete cylinder pipelines, refer to NACE SP0100.6This NACE standard was or

14、iginally prepared in 2008 and revised in 2014 by Task Group (TG) 048, “Reinforced Concrete: Review and Revise as Necessary SP0408-2008.” To provide the necessary information on all aspects of the subject and to provide input from all interested parties, TG 048 included corrosion consultants, consult

15、ing engineers, architect-engineers, CP engineers, researchers, structure owners, and representatives from industry and government. TG 048 is a component of Specific Technology Group (STG) 01, “Reinforced Concrete,” and is sponsored by STG 05, “Cathodic/Anodic Protection.” It is published by NACE und

16、er the auspices of STG 01. In NACE standards, the terms shall, must, should, and may are used in accordance with the definitions of these terms in the NACE Publications Style Manual. The terms shall and must are used to state a requirement, and are considered mandatory. The term should is used to st

17、ate something good and is recommended, but is not considered mandatory. The term may is used to state something considered optional. _ NACE International i SP0408-2014 _ NACE International Standard Practice Cathodic Protection of Reinforcing Steel in Buried or Submerged Concrete Structures Contents

18、1. General 1 2. Definitions 1 3. Criteria . 3 4. Design of Cathodic Protection Systems 4 5. Installation Practices . 8 6. Energizing and System Adjustment . 8 7. Post-Energization Operation and Maintenance of Cathodic Protection Systems 9 8. Records . 11 References 12 Bibliography 12 Appendix A: Add

19、itional Information Useful for Design (Nonmandatory) . 13 Appendix B: Test Equipment (Nonmandatory) 15 Figure 1: Typical Polarization Decay and Development Curves. 4 _ ii NACE International SP0408-2014 _ Section 1: General 1.1 Background 1.1.1 Reinforcing steel is compatible with concrete because of

20、 similar coefficients of thermal expansion and because concrete usually provides the steel with excellent corrosion protection. The corrosion protection is the result of the formation of a passive oxide film on the surface of the reinforcing steel by highly alkaline portland cement contained in the

21、concrete. This passive oxide film can be compromised by (1) excessive amounts of chloride or other corrosive ions and gases, or (2) the steel not being sufficiently encased by the concrete. 1.1.2 Corrosion occurs as a result of the formation of an electrochemical cell. An electrochemical cell consis

22、ts of four components: an anode, where oxidation occurs; a cathode, where reduction occurs; a metallic path electrically connecting the anode and cathode, where electrons flow; and an electrolyte (concrete), where ions flow. The anodic and cathodic areas can occur as a result of coupling dissimilar

23、metals, exposure to different environmental conditions, or both. If any one of the four elements of the electrochemical cell is eliminated, corrosion is prevented. 1.2 Cathodic Protection 1.2.1 The basic principles of corrosion can be used to understand the theory of CP. CP reduces the corrosion of

24、a metal surface by making the corroding surface the cathode of an electrochemical cell. 1.2.2 CP is a proven technique for controlling corrosion of steel in chloride-contaminated concrete structures. However, CP neither replaces lost steel nor returns corroded reinforcing steel to its original cross

25、 section. 1.2.3 CP of reinforcing steel in atmospherically exposed concrete is described in NACE SP0290. Many of the practices described in that standard are relevant to buried and submerged elements. Other anode types are also applicable to buried and submerged elements, as the soil or water provid

26、es a somewhat homogenous medium for the anode system, which need not be attached directly to the concrete. The application of CP to prestressed concrete cylinder pipelines is described in NACE SP0100. 1.3 Scope and Limitations 1.3.1 The provisions of this standard should be applied under the directi

27、on of a registered Professional Engineer or a person certified by NACE as a Corrosion Specialist or a CP Specialist. The persons professional experience shall include suitable experience in CP of conventionally reinforced and prestressed concrete structures. Under certain circumstances, a CP system

28、may either become a structural component or significantly affect the serviceability and structural performance of a reinforced concrete structure; therefore, such impact by the CP system should be reviewed by a qualified registered structural engineer or the equivalent. 1.3.2 The guidelines presente

29、d in this standard are limited to CP systems for new or existing buried or submerged reinforced concrete elements. 1.3.3 When the reinforcing steel is bonded to the facilitys grounding, as is commonly required by the National Fire Protection Associations(1)(NFPA) NFPA 70, National Electrical Code,7

30、the resulting galvanic corrosion cell and the possible adverse effects on the quantity and distribution of CP current to the reinforcing steel shall be considered. _ Section 2: Definitions Attenuation: Electrical losses in a conductor caused by current flow in the conductor. Cathodic Protection: A t

31、echnique to reduce the corrosion rate of a metal surface by making that surface the cathode of an electrochemical cell. (1)National Fire Protection Association (NFPA), 1 Batterymarch Park, Quincy, MA 02169-7471. NACE International 1 SP0408-2014 Corrosion Potential (Ecorr): The potential of a corrodi

32、ng surface in an electrolyte measured under open-circuit conditions relative to a reference electrode (also known as electrochemical corrosion potential, open-circuit potential, or free corrosion potential). Design Specifications: A set of documents that, in aggregate, form the nucleus for well-foun

33、ded, understandable, and equitable contract documents. These documents include written specifications and drawings. Dielectric Shield: An electrically nonconductive material, such as a coating, sheet, or pipe that is placed between an anode and an adjacent cathode, usually on the cathode, to improve

34、 current distribution in a cathodic protection system. Electrical Continuity: A closed circuit (unbroken electrical path) between metal components under consideration. Electrical Isolation: The condition of being electrically separated from other metallic structures or the environment. Electrode Pot

35、ential: The potential of an electrode in an electrolyte as measured against a reference electrode. Energizing: The process of initially applying power to turn on an impressed current cathodic protection system. Hydrogen Embrittlement: Embrittlement caused by the presence of hydrogen within a metal o

36、r alloy. Impressed Current: An electric current supplied by a device employing a power source that is external to the electrode system. (An example is direct current for cathodic protection.) Instant-Off Potential: The polarized half-cell potential of an electrode taken immediately after the cathodi

37、c protection current is stopped, which closely approximates the potential without IR drop (i.e., the polarized potential) when the current was on. IR Drop: The voltage across a resistance when current is applied in accordance with Ohms Law. Near Short: A situation where the proximity of the anode to

38、 any embedded steel adversely impacts distribution of CP current. Overlay: A layer of concrete or mortar placed over and usually bonded onto the worn or cracked surface of a concrete slab to restore or improve the function of the previous surface. Photo-Electric Effect: The change in potential of a

39、reference electrode caused by sunlight striking the electrode. Polarization: The change from the corrosion potential as a result of current flow across the electrode/electrolyte interface. Polarization Decay: The change in electrode potential with time resulting from the interruption of applied curr

40、ent. Potential Survey: The process of obtaining potentials with respect to a reference electrode at multiple, approximately equal intervals along the concrete structure. Prestressed Concrete: Concrete in which internal stresses of such magnitude and distribution are introduced that the tensile stres

41、ses resulting from the service loads are counteracted to a desired degree; in reinforced concrete, the prestress is commonly introduced by tensioning the tendons. Rectifier: An electrical device for converting alternating current to direct current. Reference Electrode: An electrode having a stable a

42、nd reproducible potential, which is used in the measurement of other electrode potentials. Step Potential: The potential difference between two points on the earths surface separated by a distance of one human step, which is defined as 1.0 m (3.3 ft), determined in the direction of maximum potential

43、 gradient. Stray Current: Current flowing through paths other than the intended circuit. Touch Potential: The potential difference between a metallic structure and a point on the earths surface separated by a distance equal to the normal maximum horizontal reach of a human (approximately 1.0 m 3.3 f

44、t). 2 NACE International SP0408-2014 _ Section 3: Criteria 3.1 The criteria in this section serve as a guide for achieving CP and providing corrosion control for reinforcing steel embedded in concrete in buried or submerged structures. Compliance with these criteria is dependent on analysis of repre

45、sentative potential data in each situation. The number and locations of potential measurements made during data collection should be commensurate with the complexity of the structure being protected. Sign conventions for potential and current density as well as conventions for graphical presentation

46、 of data should be in accordance with ASTM(2)G3.83.2 If high-strength steels ( 690 MPa 100 ksi), which are susceptible to hydrogen embrittlement, are present within the concrete structure, care should be taken to ensure that the instant-off potential is not more negative than 1.000 V measured agains

47、t a copper-copper sulfate electrode (VCSE) at 25 C, or 0.934 V AgCl (KCl 0.5M/seawater); 0.883 V AgCl (KCl sat), to avoid hydrogen embrittlement. 3.3 These criteria were developed through empirical evaluation of data obtained from successfully operated CP systems and from results in numerous researc

48、h papers and articles. NOTE: People using this standard should review data made available after this standards publication to determine whether more effective criteria have been established. It is not intended that people responsible for corrosion control be limited to these criteria if it can be demonstrated by other means that corrosion control has been achie