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Tough Crossing To A New Record: Successful HDD River Crossing Of Nearly 2 Miles
What a difference six years makes.
In 2004, Michels Directional Crossings set a horizontal directional drilling (HDD) industry record for its completion of two parallel 7,080-foot-long, 8-inch diameter steel high voltage transmission lines beneath the Cooper River in Charleston, SC.
At the time, drilling and installing pipe at such a distance was considered almost inconceivable and a near-marvel of engineering.
Fast forward to 2010.
Fifteen miles upriver of the previous crossing, Mother Nature was winning a battle against a natural gas pipeline that crossed beneath the Cooper River. The pipeline, owned by Carolina Gas Transmission (CGT), a SCANA company, was installed in 1970 and served as the sole natural gas supply line for a number of coastal towns and direct industrial customers. The crossing was in a bend in the river that was eroding along the western bank, and this erosion continually removed cover over a section of the pipeline. Despite CGT’s considerable effort to stabilize the bank, something needed to be done.
“Nothing we do as a company is more important than providing safe and reliable transportation service,” CGT President Paul Fant said. “We take this responsibility very seriously. Our customers have consistently rated the reliability of our firm transportation service as being among the leaders in the industry. ”
Since continued erosion of the riverbank was inevitable and public safety and system reliability was of the utmost concern, CGT decided that the best course of action was to replace the pipeline across the entire riverbed. The new pipeline was to be located 40 feet beneath the river bottom and new mainline valves were to be installed on either side of the river to facilitate in-line inspections.
After performing engineering feasibility studies, obtaining necessary permits, and developing engineering specifications for the project, CGT issued a Request for Proposal (RFP) for the project. The RFP set forth two possible approaches.