Magazines Hydrocarbon Engineering LNG Industry
World Coal World Pipelines World Cement
Sign in | Subscribe |
Contact us | Newsletter
There are three basic methods by which alternating currents (AC) and voltages can be induced on metallic structures near power lines. The first one is electrostatic coupling where the structure acts as one side of a capacitor with respect to ground. This is only of concern when the structure is above grade. Secondly, electromagnetic induction may occur when the structure is either above or below ground. In this case, the structure acts as the single-turn secondary of an air-core transformer in which the overhead power line is the primary. Finally, resistive coupling is caused by fault currents from AC power towers that flow on and off the underground structure.
Stray currents due to these induced voltages can cause corrosion of metallic structures although the amount of metal loss is less than what an equivalent amount of DC current discharge would produce. The magnitude of AC stray current is often large – hundreds of amperes under electromagnetic induction and thousands of amperes during power line faults. These high current and voltage levels can produce a shock hazard for personnel and can damage the structure and related equipment, such as cathodic protection facilities. According to NACE International Recommended Practice RP0177, ‘Mitigation of Alternating Current and Lightning Effects on Metallic Structures and Corrosion Control Systems’, potentials in excess of 15 volts should be considered hazardous and steps should be taken to reduce the hazardous potential level.
Mitigation of alternating current interference is performed through the use of isolating or coupling/decoupling devices. A tailored design of the remediation solution can be a tedious task taking into account the growing complexity of corridors. Since the last decade, Cathodic protection engineers can take advantage of 3-D software that replaces empirical approaches.
View more of the latest upstream news
View more of the latest downstream news
View more of the latest pipelines news
South America's LNG market developments
Many experts predict that South America will become a net exporter of LNG in the future, however many challenges remain to the industry's development.
LNG 16 in Algeria
Algeria will be a fitting venue for next year's LNG 16 Conference, having staked its place as the EU's third largest supplier of foreign gas.
Australia and India: LNG partnership
Exxon Mobil's Australian division and India's Petronet have signed a 20 year LNG supply contract, signaling a step towards approval for the Western Australian Gorgon project on Barrow Island.
A pipeline demonstration centre
Siemens' Pipeline Demo Center simulates technologies on a model pipeline system.
Palladian Publications publishes five international B2B magazines targeted specifically
at the global energy sector. Each title provides its subscribers with a unique industry
insight via a combination of news, reviews, comments, analysis, regional reports,
case studies, technical articles and more. Magazines include Oilfield Technology,
World Coal, Hydrocarbon Engineering, World Pipelines and LNG Industry.
Would you like to receive Oilfield Technology magazine for FREE?
Every issue includes technical articles, news reports, regional features and much more...
YES, send me my free magazine now »
No, I don't want to keep up-to-date with the latest upstream news