Client Requirements
A regional wastewater authority needed a 100-foot 304L stainless trough to replace a failed unit during a scheduled plant outage. The specification was simple but unforgiving: straightness held within 1/8 inch end-to-end over the full 100-foot run. An earlier vendor had attempted the job and couldn’t hold tolerance across the span, which is what brought the work to Northern.
Northern’s Approach
Distortion on a 100-foot stainless weldment comes from heat input accumulating across the length. We treated straightness as the controlling fabrication constraint and built the entire weld sequence around holding it.
Sections were fit and laser-aligned before each weld pass. Welding followed our qualified 304L austenitic WPS (procedures qualified per ASME BPVC Section IX, P8 austenitic stainless), with controlled interpass temperatures and a deliberately moderated heat input to limit cumulative distortion. The work was jigged specifically for the 100-foot span, with alignment verified between passes rather than only after completion. Forming and fit-up were staged to let the assembly settle between critical operations.
Because the trough runs in continuous wastewater service, weld zones were cleaned of heat tint and free iron and the passive layer restored with in-house pickling and passivation per ASTM A380 and A967, with no outside processor in the chain.
Outcome
The trough delivered straight within 1/8 inch over 100 feet, tighter than the specified tolerance. Installation went in without field rework or shimming. The trough has been in continuous service since.
