1、 Standard Practice Impressed Current Cathodic Protection of Reinforcing Steel in Atmospherically Exposed Concrete Structures This NACE International standard represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any
2、respect preclude 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 International standard is to be construed as granting any right, by
3、 implication or otherwise, to 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
4、interpreted as a restriction on the use of better procedures or materials. Neither is this standard intended to apply in all cases relating to the subject. Unpredictable circumstances may negate the usefulness of this standard in specific instances. NACE International assumes no responsibility for t
5、he interpretation or use of this standard by other parties and accepts responsibility for only those official NACE International interpretations issued by NACE International in accordance with its governing procedures and policies which preclude the issuance of interpretations by individual voluntee
6、rs. Users of this NACE International standard are responsible for reviewing appropriate health, safety, environmental, and regulatory documents and for determining their applicability in relation to this standard prior to its use. This NACE International standard may not necessarily address all pote
7、ntial health and safety problems or environmental hazards associated with the use of materials, equipment, and/or operations detailed or referred to within this standard.Users of this NACE International standard are also responsible for establishing appropriate health, safety, and environmental prot
8、ection practices, in consultation with appropriate regulatory authorities if necessary, to achieve compliance with any existing applicable regulatory requirements prior to the use of this standard. CAUTIONARY NOTICE: NACE International standards are subject to periodic review, and may be revised or
9、withdrawn at any time in accordance with NACE technical committee procedures. NACE International requires that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of initial publication. The user is cautioned to obtain the latest edition. Purchasers
10、of NACE International standards may receive current information on all standards and other NACE International publications by contacting the NACE International FirstService Department, 1440 South Creek Drive, Houston, Texas 77084-4906 (telephone +1 281 228-6200). Reaffirmed 2007-03-12 Revised 2000-0
11、6-16 Approved April 1990 NACE International 1440 South Creek Drive Houston, Texas 77084-4906 +1 281/228-6200 ISBN 1-57590-103-X 2007, NACE International NACE SP0290-2007 (formerly RP0290-2000) Item No. 21043 SP0290-2007 NACE International i _ Foreword The purpose of this NACE standard practice is to
12、 present guidelines for impressed current cathodic protection of reinforcing steel in atmospherically exposed concrete structures. This standard is aimed at owners, engineers, architects, contractors, and all those concerned with rehabilitation of corrosion-damaged reinforced concrete structures. Fo
13、r more information on design, maintenance, and rehabilitation of reinforcing steel in concrete, refer to NACE Standard RP01871 and NACE Standard RP0390.2For a state-of-the-art overview regarding the use of reference electrodes for atmospherically exposed reinforced concrete structures, refer to NACE
14、 International Publication 11100.3For a state-of-the art overview on criteria for cathodic protection of prestressed concrete structures, refer to NACE International Publication 01102.4This standard was originally prepared in 1990 by NACE Task Group T-3K-2, a component of Unit Committee T-3K on Corr
15、osion and Other Deterioration Phenomena Associated with Concrete. It was revised by Work Group T-11-1a in 2000, and reaffirmed by Specific Technology Group (STG) 01 in 2007. It is issued by NACE International under the auspices of STG 01 on Reinforced Concrete. In NACE standards, the terms shall, mu
16、st, should, and may are used in accordance with the definitions of these terms in the NACE Publications Style Manual, 4th ed., Paragraph 7.4.1.9. Shall and must are used to state mandatory requirements. The term should is used to state something good and is recommended but is not mandatory. The term
17、 may is used to state something considered optional. _ SP0290-2007 ii NACE International _ NACE International Standard Practice Impressed Current Cathodic Protection of Reinforcing Steel in Atmospherically Exposed Concrete Structures Contents 1.General 1 2.Definitions 1 3.Criteria . 2 4.Design of Im
18、pressed Current Cathodic Protection Systems . 5 5.Installation Practices7 6.Energizing and System Adjustment. 7 7.Operation and Maintenance of Impressed Current Cathodic Protection Systems 8 8.Records 9 References 10 Bibliography 10 Appendix AAdditional Information Useful for Design (Nonmandatory 11
19、 Appendix BTest Equipment (Nonmandtory) . 12 Figure 1Typical Polarization Decay Curve 4 Figure 2Typical Polarization Development Curve Showing “Instant-Off” Potentials Only 4 _ SP0290-2007 NACE International 1 _ Section 1: General 1.1 Background 1.1.1 Reinforcing steel is compatible with concrete be
20、cause of similar coefficients of thermal expansion and because concrete normally provides the steel with excellent corrosion protection. The corrosion protection is the result of the highly alkaline Portland cement that allows a stable, corrosion-mitigating passive oxide film to form and be maintain
21、ed on the surface of the encased steel. If the film does not form, or is weakened or destroyed so that it does not protect the steel, corrosion can occur. The protective oxide film does not form or is destroyed if (1) excessive amounts of chloride or other aggressive ions are present, (2) alkalinity
22、 is lost by reaction with aggressive gases, or (3) the concrete does not fully encase the steel. 1.1.2 Corrosion occurs as a result of the formation of an electrochemical cell. An electrochemical cell consists of four components: an anode, where oxidation occurs; a cathode, where reduction occurs; a
23、 metallic path, where the electric current is electron flow; and an electrolyte (concrete), where the electric current is ion flow in an aqueous medium. The anodic and cathodic areas occur as a result of coupling dissimilar metals or exposure to differential environmental conditions. If any one of t
24、he four elements of the electrochemical cell is eliminated, corrosion can be prevented. 1.2 Cathodic Protection 1.2.1 The basic principles of corrosion can be used to understand the theory of cathodic protection. Cathodic protection is defined as a technique to reduce the corrosion of a metal surfac
25、e by making that surface the cathode of an electrochemical cell. 1.2.2 Cathodic protection is a proven technique for controlling corrosion of steel in existing chloride-contaminated concrete structures. However, cathodic protection will neither replace lost steel nor return corroded reinforcement to
26、 its original cross-sectional area and strength. There may be areas of the reinforced concrete structure that appear sound by traditional inspection techniques that are, in fact, corroding and experiencing corrosion-related tensile stress near the rupture levels. Such distressed areas may crack, spa
27、ll, or delaminate subsequent to the application of cathodic protection. 1.3 Scope and Limitations 1.3.1 The provisions of this standard should be applied under the direction of a registered Professional Engineer or a person certified by NACE International as a Corrosion Specialist or certified as a
28、Cathodic Protection Specialist. The persons professional experience should include suitable experience in cathodic protection of reinforced concrete structures. Under certain circumstances, a cathodic protection system may either become a structural component or significantly affect the serviceabili
29、ty and structural performance of a reinforced concrete structure; therefore, review of such impact by the cathodic protection system should be made by a qualified registered Structural Engineer or the equivalent. 1.3.2 The guidelines presented here are limited to impressed current cathodic protectio
30、n systems for new or existing atmospherically exposed reinforced concrete and are not applicable to prestressed concrete. _ Section 2: Definitions Attenuation: Electrical losses in a conductor caused by current flow in the conductor. Cathodic Protection: A technique to reduce the corrosion of a meta
31、l surface by making that surface the cathode of an electrochemical cell. Corrosion Potential (E corr): The potential of a corroding surface in an electrolyte relative to a reference electrode under open-circuit conditions (also known as rest potential, open-circuit potential, or freely corroding pot
32、ential). Depolarization: The removal of factors resisting the current in an electrochemical cell. Design Specifications: A set of documents that, in aggregate, form the nucleus for well-founded, understandable, and equitable contract documents. These documents include written specifications and draw
33、ings. Drying Effect: Migration of water molecules away from the anode as a result of current flow. Electrical Continuity: A closed circuit (unbroken electrical path) between metal components under consideration. Electrical Isolation: The condition of being electrically separated from other metallic
34、structures or the environment. SP0290-2007 2 NACE International Electrode Potential: The potential of an electrode in an electrolyte as measured against a reference electrode. (The electrode potential does not include any resistance losses in potential in either the electrolyte or the external circu
35、it. It represents the reversible work to move a unit of charge from the electrode surface through the electrolyte to the reference electrode.) Energizing: The process of initially applying power to turn on an impressed current cathodic protection system. Foreign Structure: Any metallic structure tha
36、t is not intended as a part of a system under cathodic protection. Immediate Voltage Shift: The difference between the potential value when the power source is on and the instant-off value. (This is also referred to as IR Drop.) Instant-Off Potential: The polarized half-cell potential of an electrod
37、e taken immediately after the cathodic protection current is stopped, which closely approximates the potential IR drop (i.e., the polarized potential) when the current was on. IR Drop: The voltage across a resistance in accordance with Ohms Law. Overlay: A layer of concrete, mortar, or asphalt place
38、d over and usually bonded onto the worn or cracked surface of a concrete slab to restore or improve the function of the previous surface. Open-Circuit Potential: The potential of an electrode measured with respect to a reference electrode or another electrode in the absence of current. Polarization:
39、 The change from the open-circuit potential as a result of current across the electrode/electrolyte interface. Polarization Decay: The decrease in electrode potential with time resulting from the interruption of applied current. Potential Survey: Obtaining potentials with respect to a reference elec
40、trode at multiple locations on the surface of the concrete structure. Prestressed Concrete: Concrete in which internal stresses of such magnitude and distribution are introduced that the tensile stresses resulting from the service loads are counteracted to a desired degree; in reinforced concrete, t
41、he prestress is commonly introduced by tensioning the tendons. Rectifier: An electrical device for converting alternating current (AC) to direct current (DC). Reference Electrode: An electrode whose open-circuit potential is constant under similar conditions of measurement, which is used for measuri
42、ng the relative potentials of other electrodes. Rest Potential: See Corrosion Potential. Step-and-Touch Potentials: The electrical potential gradients that may exist between two points on the electrolyte surface equal to one pace (one meter) or between a grounded metallic object and a point on the e
43、lectrolyte surface separated by the distance equal to a humans normal reach (one meter). Stray Current: Current through paths other than the intended circuit. _ Section 3: Criteria 3.1 The criteria in this section serve as a guide for achieving cathodic protection and providing corrosion control for
44、 reinforcing steel embedded in atmospherically exposed concrete. Compliance with these criteria is dependent on analysis of representative data in each situation. These criteria are applicable only with impressed current systems. The number and locations of measurements made during data collection s
45、hould be commensurate with the complexity of the structure being protected. Sampling plans should be in accordance with ASTM(1)E 105.5Sample size should be determined in accordance with ANSI(2)/ASQC(3)Z1.4,6with the unit of product typically being 0.836 m2(1.00 yd2) of protected metal surface area.
46、For structures in which cathodic protection systems are divided into discrete zones, testing inspection lots should be defined. Acceptable quality and confidence levels should also be defined. Potentials of reinforcing steel or other embedments measured against portable reference electrodes shall be
47、 obtained in accordance with the techniques described in ASTM C 876.7Sign conventions for potential and current density as well as conventions for graphical presentation of data should be in accordance with ASTM G 3.8_ (1)ASTM International (ASTM), 100 Barr Harbor Dr., West Conshohocken, PA 19428-29
48、59. (2)American Natinal Standards Institute (ANSI), 11 W. 42ndSt., New York, NY 10036. (3)American Society for Quality (ASQ), 611 East Wisconsin Ave., Milwaukee, WI 53201-3005. SP0290-2007 NACE International 3 3.2 Situations in which physical conditions effectively preclude full implementation of sampling programs derived fro
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