PROTECTING PETROLEUM IN HIGH LIGHTNING-RISK AREAS.
In the heart of Africa, the Chad/Cameroon Development Project opened a revenue stream a few years ago with the completion of an estimated 1-billion barrel oil field in Chad and a 663-mile pipeline through Cameroon to an offshore marine export terminal.
To meet market demand and protect production, one oil production operation in Chad had to proactively consider how to protect its facilities from lightning risk. Where an isokeraunic number of 30 indicates average lighting activity of about 13.7 strikes per square mile annually, the region developed by the oil production operation has an isokeraunic number of 120, indicating about 41 annual lightning strikes per square mile.
"Chad has some of the most intense, most frequent lighting strikes in the world, with about two lightning storms a week from mid May to early October," said an electrical engineer for the oil production operation in Chad. "Still to meet demand and production goals, we have to stay up and running without unscheduled downtime."
To sufficiently protect its facilities, including a central processing site and three outlying gathering sites, the oil production operation decided against using traditional lighting rods, which are designed to attract lightning.
"The problem with lightning rods is they attract lightning," explains the engineer. "The question is, after you get hit by lightning, can you put the energy in the ground before it damages instrumentation and shuts down your facility? I don't think an operating facility could survive in Chad using lightning rods that attract our kind of intense, frequent lightning."
Instead, the oil production operation opted to proactively protect its central processing site and three outlying gathering sites. To maximize production uptime by avoiding lightning-related equipment damage, they turned to Lightning Eliminators and Consultants, Inc. (LEC), a Boulder, Colorado-based leader in lightning prevention technology, to engineer "zones of protection" for each facility.
From simple lightning protection to lightning prevention with a 100% no-strike warranty, companies such as LEC are at the forefront of maintaining oil and gas equipment and process uptime in the face of lightning threat. For the oil production operation, LEC custom engineered, designed, and deployed interconnected systems for strike prevention and low impedance grounding, utilizing its Dissipation Array System (DAS).
DAS, a charge transfer technology that's being lauded as a comprehensive, preventive solution for modern lightning protection, essentially prevents strikes by continually lowering the voltage differential between the ground and charged storm clouds to well below lightning potential. In the US and abroad, DAS has proven to be the preventative solution for lightning protection, substantially cutting storm-induced voltages as compared to the unprotected surroundings, thus eliminating the lightning strike risk.
Since it prevents, DAS is often the best long-term solution to lightning strike problems.
In order to protect about 1.25 sq. miles of facility space -- including the central site encompassing about 0.5 sq. miles, and three separate gathering sites encompassing about 0.25 sq. miles each -- LEC took into account factors such as each facility's location, size, shape, equipment, geography, and exposure to lightning activity.
To discharge structures of the voltage differential between the ground and charged storm clouds, DAS was deployed in various configurations across the protected sites. Stack arrays were used to protect turbine generators, which have protruding exhaust stacks. U-bracket arrays were used to protect buildings or structures with architectural or weight restrictions. Hemisphere arrays were used to protect a telecom tower and high-mass lights used for nighttime illumination.
While rim arrays were used to prevent lightning strikes to floating roof storage tanks, multiple Retractable Grounding AssembliesTM were deployed to prevent arcing at the gap between the seal of the floating roof and the tank wall, caused by lighting storm and ground current activity. The RGA, a device that provides a direct connection to the tank roof from the tank wall, uses a wide, thick-braided wire cable wound on a heavy stainless steel reel, with tension held by spring loading. The path of impedance is kept to a practical minimum by the combination of the shortest path, wide braid, and constant tension.
In addition, an ultra-low impedance grounding system was also necessary to transfer induced ground charges efficiently, since transient voltages such as lightning are affected by impedance while resistance pertains to DC voltage. An appropriate number, sizing and spacing of Chem-Rods, which use natural mineral chemicals to improve conductivity up to ten fold over traditional grounding rods, helped achieve a significantly reduced ground resistance with a target of less than one ohm. Reducing grounding impedance was important, as the natural soil resistivity at various sites ranged from less than 30 ohms near a riverbank to over 500 ohms up a sandy hill.
The result of such proactive protection of upstream facilities has been significant.
"With the engineered 'zones of protection' in place, not a single lightning strike has hit us in our protected zones, and it's been over three years now," relates the engineer. "Only once, when CCTV installers mistakenly put a camera above a protected zone, did it get struck by lightning. The CCTV camera was shattered. To me, it was quite a demonstration of the effectiveness of DAS."
While initially skeptical of the "zone of protection" concept, the engineer admits that he's a believer now. He considers the odds of the facilities not getting hit in their protected zones, in over three years, in one of the most active lightning spots in the world highly unlikely without the addition of the integrated lightning protection system.
In a region with an isokeraunic number of 120, indicating about 41 annual lightning strikes per square mile, the oil production operation's approximately 1.25 sq. miles of upstream facilities would be expected to have about 51 lightning strikes per year and over 150 in a typical three year period. Instead, the facilities have had zero strikes in their protected zones.
The net effect of this kind of lightning protection has been significant to the bottom line.
"If we didn't have DAS and the 'zones of protection,' we'd have at least 10 to 15 percent more downtime during our long lightning season," said the engineer. "I'd be working 24 hours a day fixing remote instrument enclosures, doing incident investigations on lightning strike shutdowns and the like. Instead, we're in production. That translates into tens of millions of dollars a year in avoided downtime and additional revenue."
"If you're in a lightning prone area, properly protecting yourself from electrical shutdowns, equipment failure, and downtime is the wise thing to do whether you're in upstream production or downstream refining," concludes the engineer. "If you don't, you'll pay for it, especially in remote areas where getting the right part can take weeks or months."
LEC has used Dissipation Array Systems to provide engineered "zones of protection" in a variety of oil and gas facilities including upstream production, downstream refining, and offshore oil platforms. DAS provides complete lightning protection to an extensive list of customers and facility types, including many Fortune 500 firms such as ExxonMobil, ChevronTexaco, PPG Chemical, Union Camp, and Federal Express.
Over 35 years, DAS has accumulated over 40,000 system-years of history with 99.85% no-strike performance. It has been installed at thousands of locations in 55 countries worldwide, including facilities as large as three square kilometers and structures as high as 1,700 ft.
For more information, visit http://www.LECglobal.com or call 303/447-2828.
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|Date:||Jul 1, 2007|
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