Large-diameter exhaust duct sections that mated on the first attempt

Client Requirements

A regional power generation facility needed replacement exhaust ductwork with large-diameter sections that had to mate perfectly to existing in-plant flanges during a scheduled outage. Field alignment was the expensive risk: large-diameter sections had to mate to fixed existing flanges within a fixed outage window, so every section had to fit on the first attempt.

Northern’s Approach

Sheet stock was CNC laser cut to programmed flat patterns, rolled to diameter on our Roundo PS 310 plate roll, then seam-welded using a mix of robotic GTAW for the long longitudinal passes and manual GTAW for tie-ins and branch fittings, under procedures qualified to ASME BPVC Section IX. Before release, every assembly was fit up dry on the shop floor against its mating section to verify alignment to our inspection drawings. No “we’ll adjust in the field” allowances.

Outcome

Field crews installed the duct run without rework, with sections dropping into position on the first attempt. The facility’s project manager credited the factory dry-fit: every section dropped onto its mating flange without forced alignment or field rework.

From the floor

Heavy-gauge stainless duct section with stiffening bands Full-envelope module staged under the overhead cranes Panel welding on the fixture table Large stainless weldment under the shop cranes