How to select laboratory anti-corrosion exhaust ducts: usage diameters of flame-retardant PP and PPs ducts
The laboratory exhaust duct often carries moist corrosive gases with acid-base mist and organic solvent vapors. The duct material must address two key questions: corrosion resistance and flammability. PP (polypropylene) is corrosion-resistant, lightweight, and easy to weld, making PP ducts a common solution for corrosion-resistant exhaust ventilation. In fire-requiring areas, flame-retardant grade PP sheet material must be used to fabricate flame-retardant PP ducts. The choice between sheet or welded pipe, and the specific material, should be determined based on the medium, layout space, and fire safety requirements.
What are the differences between PP and PPs
PP sheet material exhibits excellent chemical corrosion resistance and does not rust in ambient acid-base environments over long periods, making it suitable for general corrosion-resistant exhaust ventilation and indoor duct sections. PPs is a sheet material with flame-retardant properties based on PP, used in ceilings, pipe shafts, fire compartment penetrations, and high-fire-requiring laboratory exhaust systems. The material's combustion performance grade must comply with design and fire safety requirements and provide corresponding material specifications.
The same system can be segmented in material selection: critical duct sections with both corrosion and fire requirements use flame-retardant PP sheet material, while general indoor branch ducts are selected based on the medium. Specific selections are determined by ventilation and fire safety design, and standard sheet material should not replace flame-retardant sheet material in high-fire-requiring areas.
How to choose between formed ducts and processed ducts
Formed ducts are extruded or injection-molded with standard diameters, uniform wall thickness, and fast delivery, making them suitable for conventional branch ducts within standard series. Processed ducts are formed by rolling or folding welded sheet material, offering flexible diameters, cross-sections, and wall thicknesses. They are suitable for large-diameter main ducts, rectangular square ducts, and non-standard interfaces, as well as high-airflow main ducts, compact ceiling-mounted sections, and equipment interfaces. In engineering, formed ducts are often used in conventional sections, while plate-welded processed ducts are used in main and non-standard sections.
What to pay attention to in layout and installation
Plastic ducts have lower rigidity than metal, so support and hanger spacing should be increased based on duct diameter and wall thickness. Heavy components like valves and silencers require separate supports to avoid transferring weight to adjacent duct sections. Straight duct sections must account for thermal expansion and contraction, and flexible connectors or expansion compensators may be used when necessary. When penetrating walls and floors, sleeves must be added with fireproof sealing, and fire dampers must be installed as per fire safety design at fire compartment penetrations. Materials, connections, and supports must meet corrosion-resistant exhaust requirements to ensure long-term air tightness and prevent deformation.
