Ducting Pipe

Function

The duct system controls gas temperature, velocity, and distribution between the drum and the pollution-control unit. Correct velocity — typically 12–20 m/s in the main duct — prevents dust from settling in horizontal runs, which creates partial blockages and uneven gas distribution across the baghouse cell rows. Excessive velocity causes erosive wear of duct walls at elbows and transitions. Adequate external insulation prevents the gas from cooling below the acid dew point (approximately 110–130 °C for typical bituminous fuel fume), which would cause condensate corrosion of duct walls and filter-bag blinding, substantially increasing maintenance frequency.

Construction & quality

Straight sections fabricated from 4–6 mm mild steel (IS 2062 / ASTM A36) rolled plate with full longitudinal seam welds and circumferential girth welds. Elbows are fabricated with a minimum bend radius of 1.5 × duct diameter and lined at the outer wall with 6–8 mm HARDOX 400 bolt-in wear sections at all direction changes of 45° or greater. Flanged connections at all joints: 10 mm flat-face flanges jointed with high-temperature compressed-fibre (aramid) gaskets rated to 400 °C. External insulation: 75–100 mm mineral wool (96 kg/m³) clad in 0.7 mm aluminised steel banding. Bolted access ports (200 mm round covers) at every third section for internal inspection and tube cleaning. Sections are supplied in standard 1,500–2,000 mm lengths for transport and field assembly.

When to replace

• Localised thinning or perforation at elbow outer walls from abrasive dust-laden gas flow
• Cold spots or condensation on the duct exterior indicating insulation or cladding failure
• Dust settlement audible as redistribution thumping on duct walls during fan startup and shutdown
• Flange gasket failure indicated by visible dust leakage or streak staining at joint faces
• Corrosion pitting at the internal duct base in long horizontal runs from settled dust and moisture retention