Welded grease duct straight run
Horizontal kitchen exhaust
The approved design, adopted code, qualified procedure, and exact manufacturer instructions control this installation.
Before you start
- Grease duct is a fire/life-safety system. Verify the approved design, adopted code, hood and fan requirements, listed enclosure or shaft details, and inspection hold points before fabrication or installation.
- Confirm whether the system is field-welded, shop-welded, or part of a listed assembly. Do not mix those approaches.
- Verify material, gauge, weld procedure, welder qualification, route, clearances, slope or drainage intent, access locations, and support detail.
- Inspect every section for damaged seams, contaminated weld edges, warped ends, or field cuts that were not approved.
- Coordinate hot-work permits, fire watch, ventilation, shielding, and protection of nearby combustible or finished work.
Tools and materials
Approved grease-duct sections, welding equipment and filler for the specified material, fit-up clamps, alignment tools, grinder and stainless-compatible preparation tools where required, fire blankets, fire extinguisher, PPE, lighting, inspection mirror, level or laser, and dedicated noncombustible supports.
Lay it out
- Lay out the duct centerline, elevation, required drainage direction, access-door positions, and support locations before sections are lifted.
- Keep enough clearance around every joint for complete welding, inspection, enclosure, and cleaning access.
- Position seams and joints so the welder can reach the full perimeter without an unapproved blind weld.
Set and support it
- Install the dedicated noncombustible supports before closing joints.
- Support both sections independently so the weld is not carrying the weight or being pulled while it cools.
- Hold the pieces aligned without using the weld bead to bridge a large gap or force a racked section into shape.
Make the connection
- 1
Clean and prepare the mating edges using the approved welding procedure.
- 2
Bring the sections together on their supports and verify alignment, drainage direction, and fit-up around the entire perimeter.
- 3
Clamp or tack the joint in the approved sequence while checking that the duct remains square and the route does not move.
- 4
Complete the continuous liquid-tight weld using the qualified procedure.
- 5
Allow the joint to cool without moving or loading it.
- 6
Clean the weld area as required for the specified material and finish.
- 7
Inspect the complete perimeter for missed areas, pinholes, cracks, undercut, distortion, or incomplete fusion.
- 8
Complete required testing or inspection before the joint is wrapped, enclosed, or concealed.
Check the install
- The weld is continuous and liquid-tight around the full perimeter.
- The duct remains aligned, supported, and free of weld-induced distortion.
- Required clearances, slope, access, and enclosure space are maintained.
- No joint is hidden before the required inspection or test.
- Hot-work debris, slag, sharp edges, and combustible exposure have been cleared.
Common mistakes
- Welding while one section is hanging from the joint. Movement during fit-up and cooling can open or crack the connection.
- Leaving an inaccessible back side because the route was installed too close to structure.
- Using sealant, patch material, or a short weld to cover an incomplete liquid-tight joint.
- Allowing unqualified field modification of a fire/life-safety system.
Stop and ask
Stop for an unapproved field cut, unknown weld procedure, unqualified welder, clearance conflict, inaccessible joint perimeter, wrong material, missing hot-work controls, or any condition that prevents inspection of the completed weld.