Gel-plug technology used to clean FLAGS gas line

After testing and evaluating several methods, Shell chose a gelled-water and scraper (pig) system to remove about 350 tons of mill scale and other debris from the 36-in.-diam, 280 mile FLAGS gas line in the North Sea. The cleaning operation proved safe, environmentally acceptable, and inexpensive. Inhibited fresh water injected into the line at 70 bbl/min drove the 22,000-ft gel cleaning train through the line in 17 days at about 1 ft/s. The total project cost was only about one-half that of a high-velocity flush.