PP Flame Retardant Processed Square Tube

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

Hot Customizable for Working Conditions 11 Technical Parameters

Product Overview

PP Flame-Retardant Process Rectangular Duct, also known as rectangular air duct, is a square or rectangular cross-section ventilation duct made by folding, splicing, and flange reinforcement of PP flame-retardant plates. The rectangular duct can be laid closely to building beam bottoms, walls, and ceilings, effectively utilizing space. In workshops and laboratories with limited ceiling height and dense pipelines, it is more convenient to arrange than round ducts, making it a common type of pipe in corrosion-resistant exhaust systems.

The rectangular duct is formed by folding or splicing four PP plates into a rectangle. The four corner seams are continuously welded along the length of the pipe. Reinforcing ribs are welded on the outer wall according to the cross-sectional size and negative pressure. Square flanges are welded at both ends. The PP material is acid and alkali-resistant, flame-retardant, and self-extinguishing with a lightweight design. The inner wall of the rectangular duct is smooth and flat, preventing rust, dust accumulation, and corrosion when conveying corrosive exhaust gases. The rectangular cross-section also facilitates direct connection with square dampers and square equipment interfaces.

Xicheng Environmental can design the cross-sectional dimensions of the rectangular duct based on on-site space and airflow. The length and width specifications are flexible and are not limited by standard round duct diameters. It is also accompanied by processed components such as square elbows, square tees, square transitions to round, and square dampers. The rectangular duct is particularly suitable for compact corrosion-resistant ventilation applications in electroplating workshops, laboratory fume hoods, equipment attics, and ceiling spaces.

Working Principle

Like round ducts, the rectangular duct is used for exhaust gas transportation. Under the pressure difference generated by the fan, the gas flows along the rectangular cross-section. Rectangular ducts can be designed with a flat and wide shape under the same cross-sectional area, allowing them to be arranged close to beam bottoms and ceilings, reducing the occupied ceiling height. When laid parallel to walls, the rectangular duct is installed close to the wall for stability and aesthetics. The rectangular duct forms a pipeline network through flange connections, transporting exhaust gas from collection points to purification equipment and exhaust stacks.

The corrosion and flame-retardant mechanism of the rectangular duct is the same as that of the round duct, relying on the chemical stability and flame-retardant components of the PP plates. It should be noted that the rectangular cross-section has weaker resistance to internal and external pressure differences compared to a circular cross-section. The flat side walls are prone to inward deformation under negative pressure, so the outer wall of the rectangular duct must be equipped with reinforcing ribs or frames to divide the large plates into smaller spans, increasing the stiffness of the wall panels. Properly reinforced rectangular ducts can maintain cross-sectional stability under design negative pressure without significant deformation or vibration.

Structural Composition

The rectangular duct is formed by four plates: an upper plate, a lower plate, and two side plates. The four corners are folded and welded or spliced by four plates. The longitudinal corner seams are continuously sealed along the full length. Vertical or horizontal reinforcing ribs are welded on the outer wall of the pipe at certain intervals. Large cross-sectional rectangular ducts use a combination of inner and outer reinforcement. Square PP flanges are welded at both ends, with holes drilled on the flange surfaces for connection using bolts and gaskets.

Rectangular duct components include square elbows, square tees, square reducers, square transitions to round, and square dampers, all processed and welded from PP plates. When connecting to round equipment or round ducts, a square-to-round transition is used. Pipe supports and hangers hold the bottom of the rectangular duct and fix the sides. Long pipe sections are equipped with expansion compensators. Flange-connected rectangular ducts can be disassembled in sections, while spigot-welded rectangular ducts are fixed connections.

Specification Model Table

The following table compares the layout characteristics of rectangular ducts and round ducts. The cross-sectional dimensions are designed based on airflow and space.

Item	Rectangular Duct	Round Duct
Space Utilization	Top and wall mounting, space-saving	Larger ceiling height occupation
Pressure Resistance	Requires reinforcing ribs	Uniform stress distribution
Cross-Sectional Dimensions	Flexible length and width	By diameter series
Applicability	Attics, ceilings, laboratories	Outdoor main pipelines

Product Features

PP Flame-Retardant Process Rectangular Duct offers flexible layout and space-saving benefits, making it a common choice for corrosion-resistant exhaust systems in compact workshops and laboratories. Key features include:

Rectangular cross-section allows for ceiling and wall mounting, effectively saving space
PP plates are acid and alkali-resistant and self-extinguishing, providing corrosion and fire protection
Flexible length and width dimensions, customizable for on-site space
Easy to connect with square dampers and equipment interfaces
Outer reinforcing ribs ensure cross-sectional stability under negative pressure
Smooth inner wall prevents corrosion, dust accumulation, and rust
Complete system with matching components such as square elbows and square transitions to round

Material	PPs Flame Retardant Panels
Processing Technology	Panel splicing
Section Shape	Square / Rectangular
Flame Retardancy	Self-extinguishing
Corrosion resistance performance	Acid and Alkali Salt Resistant
Strengthening Method	Outer wall reinforcement rib
Connection Method	Square Flange
Specifications and Features	Non-standard custom section size
Accessories Fittings	Square Bend Square Transition Square Air Valve
Sheet Thickness	Select according to section size
Inner Wall Features	Smooth, low friction

Application Industries

Rectangular ducts for laboratory fume hood exhaust in suspended ceiling
Corrosion-resistant exhaust pipes for wall and beam installation in plating workshops
Flat-wide main exhaust ducts for low-ceiling workshops
Square exhaust ducts in equipment mezzanines of semiconductor factories
Connecting pipe sections between fume hoods, exhaust hoods, and square dampers
Corrosion-resistant rectangular ventilation pipes for underground and semi-underground spaces
Parallel-installed square ducts in dense pipe galleries

Typical Process Locations

Square ducts are primarily used for indoor, suspended ceiling, equipment mezzanine, and wall-mounted exhaust pipelines. They connect to fume hoods, collection hoods, and square dampers at the front, horizontally arranged along beam bottoms or walls, and transition to outdoor circular main pipes or fans at appropriate locations via square-to-round adapters. In laboratory exhaust systems, horizontal pipe sections from fume hood outlets to vertical shafts extensively employ rectangular square ducts to accommodate limited suspended ceiling space.

During installation, square duct flanges must maintain parallel alignment and centered positioning, with complete sealing gaskets. Support brackets should stabilize the bottom of the duct and secure it on both sides to avoid unbalanced loading. Due to the large span of rectangular wall panels, bracket spacing should be reduced based on cross-sectional dimensions, with reinforcement direction and bracket positioning properly coordinated. Square ducts transition to round pipes or equipment interfaces using square-to-round or flexible connectors. When passing through walls or floors, sleeves should be pre-installed with proper sealing. Before installation, verify cross-sectional dimensions, plate thickness, and flange hole positions. Pipe sections are assembled and leveled on the ground before being hoisted and installed in segments, ensuring parallel flange alignment and continuous gasket sealing. For large-span rectangular wall panels, brackets are spaced according to cross-sectional dimensions, supporting the bottom surface, with reinforcement direction aligned with brackets. Sleeves are added when passing through walls or floors, sealed with non-flammable materials. During operation, inspect flanges and welds for air leaks and wall panel vibrations, promptly tightening and rewelding as needed.

The main advantages of square tubes are space-saving and flexible layout. When the workshop ceiling height is limited, pipes need to be attached to beams or ceilings, laid within suspended ceilings or equipment mezzanines, or need to connect with square air dampers or rectangular outlets of ventilation cabinets, choosing square tubes is more suitable, effectively utilizing flat and wide spaces and reducing bending. Round pipes have uniform stress distribution, low air resistance, less material consumption, and strong pressure-bearing capacity. They are preferred for outdoor main pipes and high-negative-pressure pipe sections. In practical projects, square tubes are often used in indoor compact sections, round pipes in outdoor main sections, and square-to-round transition fittings are used for smooth transitions at roof outlets or fan connections. Selection should be determined comprehensively based on building space, cross-sectional stress, and equipment interfaces. Rectangular tubes are commonly used in suspended ceilings, while circular tubes are preferred for long-distance transportation and high-negative-pressure sections. The combination of both maximizes space utilization and operational energy efficiency.

Buckling or concaving of the panel surface indicates insufficient panel reinforcement. Rectangular large panels will warp under differential internal and external pressure. Reinforcing bars or frames must be installed based on the magnitude of negative pressure and the panel span to divide the large panels into multiple smaller cells, reducing unsupported spans. Square tubes showing obvious deformation should be taken out of service. Additional reinforcement and denser support brackets must be added externally, and thicker materials or smaller cross-sections may need to be replaced if necessary. During the design phase, panel thickness and reinforcing bar spacing must be verified against the full pressure of the fan. It is crucial to address buckling or suction collapse during installation rather than waiting for post-installation remediation, especially for high-negative-pressure systems. The specifications, spacing, and welding methods of reinforcing bars must match the panel thickness and cross-section. For pipe sections with high negative pressure, reinforcement should also be added near the flanges. After commissioning, focus on observing the panel for breathing fluctuations and abnormal noises. Stop the machine and address deformation promptly upon detection.

The weld seams and flange lengths of square tubes are typically longer than those of round tubes with the same cross-sectional area. If the processing and installation quality are the same, there may be slightly more potential air leakage points. However, as long as the four-corner longitudinal seams are continuously welded through, the flanges are flat, the gaskets are intact, and the bolts are tightened diagonally evenly, the air leakage rate can still be controlled within the design requirements. The key to controlling air leakage lies in the processing and welding quality, as well as flange sealing, rather than the cross-sectional shape itself. For negative pressure systems with high air leakage requirements, the weld seam appearance inspection and flange tightening acceptance should be strengthened, and air leakage testing should be conducted in sections if necessary. The rigidity of rectangular flanges is relatively weaker, so care should be taken during tightening to prevent flange warping, which could cause local gaps. After installation, combine system commissioning to inspect the flanges, weld seams, and openings, and promptly repair leaks by welding or replacing gaskets. The overall sealing performance of square tubes can meet the requirements for corrosion-resistant ventilation.

Under the same cross-sectional area and airflow rate, circular pipes have a smaller wet perimeter and more uniform airflow distribution, typically exhibiting lower frictional resistance compared to rectangular pipes. Rectangular pipes, especially those with a wide flat shape, have low-velocity zones at their four corners, resulting in slightly higher resistance, which becomes more pronounced with a larger length-to-width ratio. However, as long as the internal flow velocity is properly controlled, the inner wall welds remain smooth, and the number of elbows and abrupt cross-sectional changes is minimized, the frictional resistance of square pipes remains fully within acceptable limits. The value of square pipes lies in their strong adaptability to space, allowing them to fit along beam bottoms and ceiling layouts. When selecting, it is essential to comprehensively compare layout requirements, frictional resistance, and fan energy consumption, rather than focusing solely on the coefficient of friction. For long-distance, high-negative-pressure main pipes, circular pipes should be prioritized, while square pipes are suitable for indoor wide flat sections and beam-mounted segments. When necessary, the resistance can be compensated by appropriately enlarging the rectangular cross-section and reducing the flow velocity, ensuring both circular and square pipe energy consumption remains at reasonable levels.

First, calculate the required cross-sectional area based on the exhaust airflow and the recommended internal pipe velocity. Then, determine the length and width of the rectangle by considering the ceiling height, clear space under the beam, and equipment interface. The aspect ratio of the rectangle should not be too high. A excessively flat square pipe has more dead zones at the corners, higher resistance, and is prone to vibration on the plate surface. Generally, the aspect ratio is kept within a reasonable range to avoid being overly flat and narrow. After determining the cross-section, verify the plate thickness and stiffener spacing based on the fan negative pressure to ensure the strength and stiffness of the wall plate. Laboratory fume hoods also require compliance with face velocity control and variable air volume systems' demands for pipeline tightness and response speed. When necessary, the ventilation department should uniformly calculate the cross-sectional areas of each section. Once the cross-section is determined, minimize the number of specifications to facilitate processing, standardize support and suspension brackets, and streamline spare parts for later use.

Hollow section steel can be modified on-site using a plastic welding gun and spare plates for minor adjustments, such as opening branch holes, adding short tubes, or adjusting local layouts. However, the overall cross-sectional dimensions and reinforcement structures are more reliably determined in the factory according to the drawings. After on-site modifications, new welds must be continuously sealed, and flanges or reinforcement frames must be added at new openings. Weakened wall plates require additional welding of reinforcement bars to maintain original strength. For significant dimensional changes, it is recommended to return to the factory or have professional machining personnel re-manufacture according to the drawings to avoid on-site modifications affecting strength, sealing, and flame retardancy compatibility. Welding electrodes used for on-site repairs must match the base material in terms of material and flame retardancy grade; ordinary electrodes cannot be used. After modifications, visual and air leakage inspections must be conducted to confirm the qualification of welds, reinforcements, and flanges before putting into use. On-site modified areas must be marked in the completion documents.

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