The SEI Group consists of three corporations, which share common majority ownership. Southern Erectors, which is the group's namesake, is a mechanical contractor that has specialized in industrial metal fabrication and erection since 1973. Thermal Systems Group and Southern Environmental have provided engineering and design of integrated systems, which have been fabricated and erected by Southern Erectors. Thermal Systems Group, formed in 1985, custom designs paper mill, paper machine air systems and nonprocess HVAC, utility piping, air handling equipment and miscellaneous steel and sheet metal fabrication. Since 1988, Southern Environmental has supplied air pollution control equipment and specialized in fast-track services for short project lengths with minimal outage time for electrostatic precipitators and other equipment.