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Laclede Gas Discovers Alternative Method For Cathodic Protection
Process Helps Speed Anode Installation Process
Dean Pieper, Ron Adler and Dave Biggs collectively have been involved in the natural gas utility business for 63 years and have seen a number of changes in the industry. They are part of the construction and maintenance department responsible for the installation and maintenance of more than 1,800 miles of steel gas lines for Laclede Gas in the North District of St. Louis.
Laclede Gas Company, based in St. Louis, MO, is the largest natural gas distribution utility in Missouri, serving 630,000 residential, commercial and industrial customers in the city of St. Louis and 10 other counties in eastern Missouri. The company operates more than 16,000 miles of gas lines, an underground natural gas storage field, a propane storage cavern and propane vaporization facilities.
Part of the ongoing maintenance of the system is the installation of sacrificial galvanic anodes for cathodic protection of the steel gas distribution lines to control corrosion. This is achieved by burying a more active, easily corroded metal (typically a magnesium anode) and electrically connecting it to the steel gas line to be protected. The anode provides a negative charge to the steel line, which enables the line to resist electrochemical corrosion.
“We’ve been installing anodes along our lines for decades as a routine maintenance program,” says Dave Biggs, a Laclede Gas construction and maintenance department employee. “The anode will cathodically protect the gas lines in case there’s a problem with the coating. The anode is designed to corrode to protect the gas line. Therefore the anode must be replaced periodically.”
Checking the lines requires a crew of inspectors who take potential readings of the gas lines at designated test point locations. Should the potential reading for a section of pipe drop below a negative 850mV and it is determined that additional cathodic protection is required, an inspector will issue a ticket for the installation of an anode in that designated area.
In the past, installing an anode required excavation by hand or equipment over the steel lines. A majority of the lines are located under streets layered with eight inches of concrete, which would require the crews to use a jack hammer or concrete saw to open the street. A dry vacuum would then be used to extract the soil and replace the anode. The process took hours and in some cases required the replacement of an entire concrete pad costing almost $5,000.
That all changed when Greg Borgschulte with Vermeer Midwest contacted Laclede Gas in the fall of 2008.