Mitigation of Alternating Current and Lightning Effects on Metallic Structures and Corrosion Control Systems
- NACE International (NACE International)
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- NACE International
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- NACE International
- , lightning arresters, electric shields, alternating current power systems, electric shock, cathodic protection, corrosion control, electrical grounding, TG 025
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Presents guidelines and procedures for use during design, construction, operation, and maintenance of metallic structures and corrosion control systems used to mitigate the effect of lightning and overhead alternating current (AC) power transmission systems. It addresses problems primarily caused by proximity of metallic structures to AC-powered transmission systems.
This standard practice presents guidelines and procedures for use during design, construction, operation, and maintenance of 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 become 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 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 (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 184.108.40.206 and elsewhere in this standard. The reason for a more conservative value is that early work by George Bodier1 at 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 1,500 ohms hand-to-hand or hand-to-foot. In other work by C.F. Dalziel2 on 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 design 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.
NACE SP21424, “Alternating Current Corrosion on Cathodically Protected Pipelines: Risk Assessment, Mitigation and Monitoring,” should be referenced to address AC corrosion.3 There are reported incidents of AC corrosion on buried pipelines under specific conditions, and there are also many case histories 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 and 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. It was revised in 2007, 2014, and 2019 by TG 025, “Alternating Current (AC) Power Systems, Adjacent: Corrosion Control and Related Safety Procedures to Mitigate the Effects,” which is administered by STG 05, “Cathodic/Anodic Protection,” and sponsored by STG 03, “Coatings and Linings, Protective—Immersion and Buried Service,” and STG 35, “Pipelines, Tanks, and Well Casings.” This standard is issued by NACE under the auspices of STG 05.
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