PP Fire-Retardant Process Ductwork

Product Model	PPs Plate Welded Round Duct Series
Category	PP Machined Products
Reference Price	Price on request

Hot Customizable for Working Conditions 11 Technical Parameters

Product Overview

Flame-retardant PP welded ductwork is circular ventilation pipes processed from flame-retardant PP sheets through cutting, bending, welding, and flange reinforcement. Compared to extruded ducts, welded ducts are not limited by standard diameters and can be manufactured in large diameters, thick walls, and special lengths, making them suitable for high-capacity exhaust gas transportation main pipes and non-standard corrosion-resistant ventilation projects.

The duct body is formed from PP flame-retardant sheets, with longitudinal seams welded using PP flame-retardant electrodes for hot fusion welding. The seams are dense and have the same service life as the base material. Flanges or sockets are welded at both ends of the pipe segments for connection. PP material has good toughness, acid/alkali/salt corrosion resistance, lightweight properties, and smooth inner walls that prevent dust accumulation. It does not rust or scale when transporting corrosive exhaust gases, and also possesses flame-retardant self-extinguishing properties, making it ideal for indoor and fire-rated applications.

Xicheng Environmental can design and produce flame-retardant PP welded ductwork based on drawings and on-site conditions, along with complete sets of fittings such as elbows, tees, reducers, dampers, and supports. Eco-friendly, non-toxic PP, and recyclable, it has been widely used in corrosion-resistant engineering in chemical, environmental wastewater treatment, and surface finishing industries as a steel alternative.

Working Principle

Welded ducts serve as gas transportation channels in ventilation systems. Exhaust gas flows along the pipes under the pressure differential provided by the fan. The circular cross-section ensures uniform stress distribution and low air resistance, while the smooth inner walls reduce flow resistance compared to metal rusted pipes. The welded pipe segments are connected via flanges or spigots to form a continuous network, collecting exhaust gas from collection points and conveying it to purification equipment, which then treats and discharges the gas through a stack.

The corrosion and flame-retardant properties of the ducts are provided by the PP sheet material itself. Polypropylene does not react with acidic or alkaline exhaust gases, preventing rust and thinning of the pipe wall due to corrosive gas flow. The flame-retardant components ensure the sheet self-extinguishes upon contact with fire, preventing the pipe from becoming a fire spread path when installed indoors or in suspended ceilings. The welds use PP flame-retardant electrodes, ensuring the joints maintain the same corrosion and flame-retardant properties as the entire pipe, avoiding weak points at connection points.

Structural Composition

A single welded duct consists of the body, longitudinal seams, circumferential reinforcement, and end connection components. The body is formed by rolling PP sheets, with longitudinal seams created at the joints. For large-diameter or high-negative-pressure segments, circumferential reinforcement rings are welded to the outer wall to enhance external pressure resistance and prevent collapse due to fan suction. PP flanges are welded at the ends for bolted connection, or sockets are formed for slip-fit welding.

Pipe segments are connected via flanges with gaskets and bolts, or sealed with electrodes after slip-fitting. Elbows, tees, reducers, and other fittings are processed using the same materials and techniques as straight pipes. External supports and hangers are installed based on load requirements, with independent brackets near flanges for large-diameter pipes. The entire duct system, from sheets to electrodes and flanges, uses the same plastic series, ensuring consistent thermal expansion and contraction, and minimizing stress at connections.

Specification Model Table

The table below compares the characteristics of welded ducts and extruded ducts. Specific diameters and wall thicknesses are determined based on airflow design.

Item	Welded Duct	Extruded Duct
Diameter	Non-standard large diameter	Standard series
Wall Thickness	Can be thickened as needed	Standard wall thickness
Connection	Flange / Spigot	Spigot For the main
Application	High-capacity main pipes	Standard branch pipes

Product Features

Flame-retardant PP welded ducts offer flexible diameters and corrosion/flame-retardant properties, making them the preferred choice for high-capacity non-standard corrosion-resistant ventilation projects. Key features include:

PPs flame-retardant sheet welding, self-extinguishing in case of fire, safe for indoor use
Corrosion resistance to acids, alkalis, and salts; does not rust when transporting corrosive exhaust gases
Unrestricted by standard diameters; can be processed in large diameters and thick walls
Welds and base material share the same material, ensuring equal corrosion service life at joints
Round cross-section reduces air resistance, smooth inner walls prevent dust accumulation
Weight is about one-fifth of steel pipes, easing installation and handling
Complete set of accessories available; supports non-standard customization based on drawings

Material	PPs Flame Retardant Boards
Processing Technology	Hot Welding of Rolled Plates
Section Shape	Round
Flame Retardancy	Self-extinguishing
Corrosion Resistance Performance	Acid and Alkali Salt Resistant
Connection Method	Flange / Butt-welding
Inner Wall Features	Smooth and dust-free
Specifications and Features	Large Diameter Non-Standard Customization
Accessories	Bend Tee Convergent Divergent Air Valve
Sheet Thickness	Select by caliber
Strengthening Method	Outer wall reinforcement ring

Application Industries

Main air conveying pipes for large airflow acid-alkali exhaust in chemical enterprises
Corrosion-resistant exhaust main pipes in electroplating and surface treatment workshops
Large-diameter flame-retardant exhaust pipes in semiconductor and photovoltaic factories
Main air conveying pipes for acid pickling line exhaust collection in metallurgical plants
Large-diameter connecting pipes for fans in environmental treatment projects
Corrosion-resistant pipes for odor collection and exhaust in wastewater treatment plants
Fireproof exhaust main pipes in indoor and suspended ceilings

Typical Process Locations

Flame-retardant ducts are primarily used for main pipes and large-diameter sections in exhaust systems. They collect air from various hoods and branch pipes at the front end, run along supports to purification equipment, and are discharged after treatment via fans and exhaust stacks. Large-diameter sections are concentrated at fan inlets/outlets and main passages between equipment, while standard-formed ducts are used for smaller branch pipes, connected via diameter changes and flanges.

In indoor and crowded areas, flame-retardant ducts are installed openly along columns, beams, or dedicated supports, or laid in ceilings and pipe galleries. When pipes pass through fire compartments, fireproof sealing is used. During installation, pipe segments are aligned at flanges with gaskets for sealing, and supports are set based on pipe weight and thermal expansion. Extra bending moments must not be applied near flanges, and thermal expansion compensation must be considered for long straight pipe sections. Before installation, pipe diameters, wall thicknesses, and flame-retardant ratings are verified. Pipe segments are aligned and grouped on supports, with flange gaskets sealed and bolts tightened evenly. Long straight sections are provided with expansion allowances for thermal expansion. When passing through fire compartments or floors, fire dampers and incombustible sealing are used. Outdoor pipe sections require corrosion and rain protection for supports. Regular inspections are conducted during operation to check welds, flanges, and supports. If wind leakage, collapse, or abnormal vibration is detected, the system is shut down for repair to maintain pipe sealing and support stability.

Formed ducts are extruded or injection-molded with standard diameters and uniform wall thickness, offering low cost and fast delivery, suitable for branch ducts and conventional sections within the standard series; fabricated ducts are roll-welded from sheet metal with flexible diameters and wall thickness, capable of large diameters, thick walls, and special lengths, suitable for high-airflow main ducts, non-standard equipment interfaces, and specifications not covered by formed ducts; in projects, formed ducts are typically used for branch ducts and conventional sections, while fabricated ducts are used for main ducts and non-standard sections to balance cost and adaptability.

The longitudinal seams of PPs ducts and circumferential seams of fittings in standardized welding are continuous and full. The welding electrodes melt seamlessly with the base material, ensuring no air leakage under normal use. Air leakage primarily occurs at weld defects such as incomplete fusion, porosity, or lack of penetration, or at worn-out or failed flange gaskets. During machining, bevels should be opened according to plate thickness and pressure, welding temperature and gun travel speed should be controlled, and thick plates should be welded in multiple passes. After welding, visual inspections of the ducts are required, and for high-purity systems, section-wise air leakage tests can be conducted. During installation, flange bolts should be tightened diagonally and evenly, with gaskets centered and intact. Butt welds should be fully welded along the circumference to keep the system's air leakage rate within the design range. If leaks are detected, mark their locations, perform patch welding or replace gaskets after pressure relief. Negative pressure duct sections, in particular, must ensure longitudinal seam and flange sealing.

The ability of circular ducts to withstand negative pressure is directly related to wall thickness, diameter, and the spacing of reinforcement rings. The larger the diameter and the higher the negative pressure, the more wall thickness needs to be increased, and the reinforcement rings on the outer wall need to be densified. Otherwise, the tube wall may be sucked and deformed under negative pressure. During design, the wall thickness and reinforcement ring spacing should be verified based on the total pressure of the fan and the negative pressure at various points in the pipeline. The negative pressure is the highest at the fan inlet section, which should be given special attention. For large-diameter pipe sections, the spacing of supports and hangers should also be controlled to prevent deformation of the pipeline under its own weight and negative pressure. Selecting an experienced manufacturer to configure wall thickness and reinforcement structure according to the negative pressure level can fundamentally avoid collapse issues. If concave deformation, abnormal sounds, or airflow anomalies are detected in the tube wall after operation, the machine should be shut down to inspect the reinforcement rings and wall thickness. If necessary, the weak sections should be reinforced or replaced.

Okay, but focus on UV and temperature effects. PP material will age and become brittle when exposed to direct sunlight for a long time. Outdoor-mounted PP ducts are recommended to use weather-resistant sheet material with UV-resistant additives, or to have a UV-protective coating applied to the outer wall, or to install sunshades. Pipe supports must consider wind load, snow load, and thermal expansion and contraction. Fixed supports and sliding supports should be set up reasonably, and thermal expansion compensation should be reserved for long straight pipe sections. In cold regions, the material's low-temperature toughness must be noted to avoid impacts and concentrated loads. Outdoor flanges and bolts should be made of corrosion-resistant materials or have corrosion protection to prevent rust from rain. Installation indoors or in pipe galleries away from direct sunlight ages slower, with more favorable usage conditions. Regardless of indoor or outdoor installation, flammability and corrosion resistance requirements should be configured according to the medium and fire protection regulations.

Wall thickness is determined comprehensively by duct diameter, internal/external pressure difference, installation span, and whether reinforcement is required. Larger diameter, higher negative pressure, and wider support spacing require greater wall thickness, with reinforcement rings used if necessary. While industry typically uses empirical tables to select wall thickness based on diameter and pressure, critical projects must rely on design calculations. Avoid using excessively thin plates on large-diameter, high-negative-pressure sections to prevent collapse, vibration, and noise; however, full-thickness reinforcement is unnecessary and wasteful, with segmented configuration being the most rational.

There are requirements. The elastic modulus of plastic is lower than that of metal, resulting in smaller pipe stiffness and closer spacing of supports compared to steel pipes. The spacing should be smaller for larger diameters and thinner wall plates, and horizontal and vertical pipes have different spacing requirements. Supports should be individually installed at flanges, valves, silencers, and heavier components to bear the weight, without allowing adjacent pipe sections and welds to carry it. Soft padding or dedicated pipe clamps should be added between supports and pipes to prevent wall wear while allowing axial thermal expansion of the pipes. Specific spacing should be determined according to pipe diameter, wall thickness, water filling, and dust accumulation loads by referring to plastic pipe installation regulations, with appropriate densification for large-diameter and high-negative-pressure pipe sections. Support installation should precede pipe connection to avoid welding on suspended pipes, and after operation, regular inspections should be conducted to check for support looseness, pipe deflection, and flange misalignment.

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