A digester system cannot be shut down for more than a few hours without serious consequences. “If you end up turning the system off for too long, you destroy the biological process, [and] the plant will not function,” says Seth Hall, manufacturer’s representative for Victaulic Co. “If you test the effluent coming out of the plant, you will be in violation of the EPA rules and regulations.” Permissible downtime is limited to four hours, maximum, but “no one on the planet” is comfortable working within that limit, Hall says.

To keep plant downtime to a minimum, Victaulic is supplying more than 400 flexible couplings for the Back River plant’s stainless-steel aeration pipe system. Temperature swings from 125°F to 300°F will thermally stress the pipes, causing expansions and contractions that could wreck the pipe couplings. For every 100°F change, the stainlesssteel pipe expands and contracts up to 1.28 in. per 100 linear ft, Hall says. Victaulic’s stainless-steel bellows coupling expands and contracts on multiple planes. Depending on the outside diameter of the pipe, the flexible coupling can handle axial expansion and contraction ranging between 1.5 in. and 4 in., he estimates.

KCI Technologies Inc. designed the system, and “they were very specific,” Hall says. “They did not want a steel weld or rubber bellows system. The field weld typically will not give you a quality product at the end, and the rubber bellows are actually designed to fail.” Ultraviolet light and heat would dry-rot rubber couplings, and replacement would require periodic plant shutdowns. The Victaulic coupling’s body is all stainless steel; the gaskets are enclosed within the inside diameter of the coupling. “This is as close as you can get to a system that will never fail, that an owner will not have to get into,” Hall says.