NACE SP0177-2014 Mitigation of Alternating Current and Lightning Effects on Metallic Structures and Corrosion Control Systems (Item No 21021).pdf

1、 Mitigation of Alternating Current and Lightning Effects on Metallic Structures and Corrosion Control Systems 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 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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7、ipment, and/or operations detailed or referred to within this standard. Users of this NACE standard are also responsible for establishing appropriate health, safety, and environmental protection practices, in consultation with appropriate regulatory authorities if necessary, to achieve compliance wi

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10、r NACE publications by contacting the NACE FirstService Department, 1440 South Creek Dr., Houston, TX 77084-4906 (telephone +1 281-228-6200). Revised 2014-03-08 Revised 2007-06-22 Reaffirmed 2000-09-19 Revised March 1995 Revised July 1983 Approved July 1977 NACE International 1440 South Creek Drive

11、Houston, Texas 77084-4906 + 1 281-228-6200 ISBN 1-57590-116-1 2014, NACE International SP0177-2014 (formerly RP0177) Item No. 21021 SP0177-2014 NACE International i _ Foreword This standard practice presents guidelines and procedures for use during design, construction, operation, and maintenance of

12、 metallic structures and corrosion control systems used to mitigate the effects of lightning and alternating current (AC) power transmission systems. This standard is not intended to supersede or replace existing electrical safety standards. As shared right-of-way and utility corridor practices beco

13、me more common, AC influence on adjacent metallic structures has greater significance, and personnel safety becomes of greater concern. This standard addresses problems primarily caused by proximity of metallic structures to AC-powered transmission systems. The hazards of lightning and AC effects on

14、 aboveground pipelines, while strung along the right-of-way prior to installation in the ground, are of particular importance to pipeline construction crews. The effects of AC power lines on buried pipelines are of particular concern to operators of aboveground appurtenances and cathodic protection

15、(CP) testers, CP designers, safety engineers, as well as maintenance personnel working on the pipeline. Some controversy arose in the 1995 issue of this standard regarding the shock hazard stated in Section 5, Paragraph 5.2.1.1 and elsewhere in this standard. The reason for a more conservative value

16、 is that early work by George Bodier1at Columbia University and by other investigators has shown that the average hand-to-hand or hand-to-foot resistance for an adult male human body can range between 600 ohms and 10,000 ohms. A reasonable safe value for the purpose of estimating body currents is 1,

17、500 ohms hand-to-hand or hand-to-foot. In other work by C.F. Dalziel2on muscular contraction, the inability to release contact occurs in the range of 6 to 20 mA for adult males. Ten mA hand-to-hand or hand-to-foot is generally established as the absolute maximum safe let-go current. Conservative des

18、ign uses an even lower value. Fifteen volts of AC impressed across a 1,500 ohm load would yield a current flow of 10 mA; thus, the criterion within this standard is set at 15 volts. Prudent design would suggest an even lower value under certain circumstances. Many are now concerned with AC corrosion

19、 on buried pipelines adjacent to or near overhead electric transmission towers. This subject is not quite fully understood, nor is there an industry consensus on this subject. There are reported incidents of AC corrosion on buried pipelines under specific conditions, and there are also many case his

20、tories of pipelines operating under the influence of induced AC for many years without any reports of AC corrosion. The members of NACE Task Group (TG) 025 agreed that criteria for AC corrosion control should not be included in this standard. However, the mitigation measures implemented for safety a

21、nd system protection, as outlined in this standard, may also be used for AC corrosion control. This standard was originally published in July 1977 by Unit Committee T-10B on Interference Problems and was technically revised in 1983 and 1995, and reaffirmed in 2000 by T-10B. NACE continues to recogni

22、ze the need for a standard on this subject. Future development and field experience should provide additional information, procedures, and devices for Specific Technology Group (STG) 05, “Cathodic/Anodic Protection,” to consider in future revisions of this standard. This standard was revised in 2007

23、 and 2014 by TG 025, “Alternating Current (AC) Power Systems, Adjacent: Corrosion Control and Related Safety Procedures to Mitigate the Effects.” It is sponsored by STG 03, “Coatings and Linings, ProtectiveImmersion and Buried Service,” and STG 35, “Pipelines, Tanks, and Well Casings.” This standard

24、 is issued by NACE under the auspices of STG 05. 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 ter

25、m should is used to state something good and is recommended, but is not considered mandatory. The term may is used to state something considered optional. _ SP0177-2014 ii NACE International _ Mitigation of Alternating Current and Lightning Effects on Metallic Structures and Corrosion Control System

26、s Contents 1. General 1 2. Definitions 1 3. Exposures and Effects of Alternating Current and Lightning 3 4. Design Considerations for Protective Measures . 5 5. Personnel Safety . 15 6. AC and Corrosion Control Considerations 19 7. Special Considerations in Operation and Maintenance of Cathodic Prot

27、ection and Safety Systems . 21 References 22 Bibliography 23 Appendix A: Wire Gauge Conversions . 24 FIGURES Figure 1: Approximate Current Required to Raise the Temperature of Stranded Annealed Soft-Drawn Copper Cable . 9 Figure 2: Allowable Short-Circuit Currents for Insulated Copper Conductors 11

28、Figure 3: Allowable Short-Circuit Currents for Insulated Copper Conductors 12 Figure 4: Zinc Ribbon Ampacity 13 TABLES Table 1: Maximum 60 Hz Fault CurrentsGrounding Cables . 8 Table 2: Average Impedance for Various Conductor Sizes 10 Table 3: Human Resistance to Electrical Current . 16 Table 4: App

29、roximate 60-Hz Alternating Current Values Affecting Human Beings 16 Table A1: Wire Gauge Conversions . 24 _ SP0177-2014 NACE International 1 _ Section 1: General 1.1 This standard presents acknowledged practices for the mitigation of AC and lightning effects on metallic structures and corrosion cont

30、rol systems. 1.2 This standard covers some of the basic procedures for determining the level of AC influence and lightning effects to which an existing metallic structure may be subjected and outlines design, installation, maintenance, and testing procedures for CP systems on structures subject to A

31、C influence, primarily caused by proximity of metallic structures to AC power transmission systems. However, this standard is not intended to be a design guide or a “how-to” engineering manual to perform AC interference studies or mitigation designs. 1.3 This standard does not designate procedures f

32、or any specific situation. The provisions of this standard should be applied under the direction of competent persons, who, by reason of knowledge of the physical sciences and the principles of engineering and mathematics, acquired by professional education and related practical experience, are qual

33、ified to engage in the practice of corrosion control on metallic structures. Such persons may be registered professional engineers or persons recognized as being qualified and certified as corrosion specialists by NACE, if their professional activities include suitable experience in corrosion contro

34、l on metallic structures and AC interference and mitigation. 1.4 This standard should be used in conjunction with the references contained herein. _ Section 2: Definitions 2.1 Definitions presented in this standard pertain to the application of this standard only. Reference should be made to other i

35、ndustry standards when appropriate. AC Exposure: Alternating voltages and currents induced on a structure because of the AC power system. AC Power Structures: The structures associated with AC power systems. AC Power System: The components associated with the generation, transmission, and distributi

36、on of AC. Affected Structure: Pipes, cables, conduits, or other metallic structures exposed to the effects of AC or lightning. Bond: A low-impedance connection (usually metallic) provided for electrical continuity. Breakdown Voltage: A voltage in excess of the rated voltage that causes the destructi

37、on of a barrier film, coating, or other electrically isolating material. Capacitive Coupling: The influence of two or more circuits upon one another, through a dielectric medium such as air, by means of the electric field acting between them. Circular Mil: A unit of area of round wire or cable equal

38、 to the square of the diameter in mils (1 mil = 0.0254 mm = 25.4 m). Coating Stress Voltage: Potential difference between the metallic surface of a coated structure and the earth in contact with the outer surface of the coating. Coupling: The association of two or more circuits or systems in such a

39、way that energy may be transferred from one to another. Dead-Front Construction: A type of construction in which the energized components are recessed or covered to preclude the possibility of accidental contact with elements having electrical potential. Electric Field: One of the elementary energy

40、fields in nature. It occurs in the vicinity of an electrically charged body. Electric Potential: The voltage between a given point and a remote reference point. SP0177-2014 2 NACE International Electrolytic Grounding Cell: A device consisting of two or more buried electrodes installed at a fixed spa

41、cing, commonly made of zinc, and resistively coupled through a prepared backfill mixture. The electrical characteristics of a grounding cell include a small degree of resistance and a subsequent reduced voltage drop across the cell during a fault condition. Fault Shield: Shallow grounding conductors

42、 connected to the affected structure adjacent to overhead electrical transmission towers, poles, substations, etc., to provide localized protection to the structure and coating during a fault event from nearby electric transmission power systems. Gradient Control Mat: A system of bare conductors con

43、nected to the affected structure and placed on or below the surface of the earth, usually at above grade or exposed appurtenances, arranged and interconnected to provide localized touch-and-step voltage protection. Metallic plates and grating of suitable area are common forms of ground mats, as well

44、 as conventional bare conductors closely spaced. Gradient Control Wire: A continuous and long grounding conductor or conductors installed horizontally and parallel to the affected structure at strategic lengths and connected at regular intervals to provide protection to the structure and coating dur

45、ing steady-state and fault AC conditions from nearby electric transmission power systems. Ground: An electrical connection to earth. Ground Current: Current flowing to or from earth in a grounding circuit. Grounded: Connected to earth or to some extensive conducting body that serves instead of the e

46、arth, whether the connection is intentional or accidental. Grounding Grid: A system of grounding electrodes consisting of interconnected bare conductors buried in the earth to provide a common electrical ground. Ground Potential Rise: Ground Potential Rise or Earth Potential Rise (as defined in IEEE

47、(1)Standard 367)3is the product of a ground electrode impedance, referenced to remote earth, and the current that flows through that electrode impedance. This occurs when large amounts of electricity enter the earth. This is typically caused when substations or high-voltage towers fault, or when lig

48、htning strikes occur (fault current). When currents of large magnitude enter the earth from a grounding system, not only does the grounding system rise in electrical potential, but so does the surrounding soil. The resulting potential differences cause currents to flow into any and all nearby grounded conductive bodies, including concrete, pipes, copper wires, and people. Inductive Coupling: The influence of two or more circuits on one another by means of ch