Description

Product Overview

A PP air duct coupling is an injection-moulded polypropylene fitting that joins two duct sections end to end, making a long run one continuous line. It is the fitting used where a PP duct is extended, repaired or connected section to section, and it matches the round PP duct range from φ110mm to φ600mm.

The coupling is injection moulded in PP or flame retardant PPs, in beige or grey, and joins the duct run by hot air welding, with socket connection reinforcement at the joint. Being a moulded fitting, each size has consistent dimensions and wall thickness across batches. For the straight duct the coupling connects to, see Polypropylene Round Ducts.

A duct coupling is one part of a ventilation system: it connects straight duct sections together rather than replacing them, and matching fittings are available from the same supplier so a complete PP duct line can be specified from one source.

Product Selection Summary

Good Fit

• Extending a PP duct run with additional straight sections
• Repairing or re-joining a cut duct section in place
• Building long main lines from standard duct sections
• Projects needing flame retardant fittings for part or all of a run

Conditions To Confirm

• Duct diameter (φ110mm to φ600mm, 11 standard sizes) and quantity
• Material grade: PP or flame retardant PPs
• Gas composition, concentration, temperature and moisture at the operating point
• Where the run needs removable access (use flanges there instead)

Not a Replacement For

• Fans, airflow balancing devices, flexible connectors or gas treatment equipment

Technical Specifications

Confirmed Product Parameters

Parameter	Value
Product Type	PP Air Duct Coupling (polypropylene duct coupling)
Material	PP (polypropylene) or PPs flame retardant grade
Size Range	φ110-600mm – 11 standard sizes
Connection	Hot air weld; socket connection reinforcement
Fabrication	Injection molding
Color	Beige / Grey
Working Temperature	-15℃ to 80℃
Chemical Resistance	pH 1-14 (acid and alkali)
Certification	ISO9001, ISO14001, RoHS

Available Sizes (φ)

Diameter	Diameter
φ110mm	φ355mm
φ160mm	φ400mm
φ200mm	φ450mm
φ250mm	φ500mm
φ315mm	φ550mm
	φ600mm

Material & Performance

Because round fittings are injection moulded rather than welded from sheet, the coupling keeps the same corrosion resistance as the welded duct while offering consistent moulded dimensions, smooth surfaces and a shorter production time for standard sizes.

PP air duct couplings are injection moulded from polypropylene, chosen for corrosive fume handling in ductwork:

• Acid and alkali resistance: PP withstands corrosion by high-concentration acids and alkalis across a wide pH range (pH 1-14).
• Sound insulation: PP reduces vibration and noise transmitted through the joint.
• Light weight: moulded PP fittings are light and easy to handle and weld on site.
• Consistent moulded dimensions: each size is produced to a standard mould, giving uniform dimensions and wall thickness across batches.
• Long service life: PP duct systems offer a service life of up to 50 years under specified operating conditions.
• Anti-condensation: PP conducts heat poorly, reducing condensation and heat loss at the fitting.
• Wear resistance: the smooth moulded surface resists scaling and deposit buildup, keeping the joint area clean through service.

Flame retardant PPs is available where fire-rated ductwork is required; specify the required flame retardant grade when inquiring. The material grade applies to the whole fitting, so a single grade can be specified across the duct, fittings and accessories in the run.

Applications

Extending and Repairing Duct Runs

Couplings connect straight duct sections end to end, which is how a long main line is built from standard sections and how a damaged section is replaced:

• Run extension – adding straight sections to reach new equipment or extend the line
• Section replacement – cutting out a damaged section and coupling a new one into the run
• Standard-section building – assembling long mains from factory duct lengths
• Joint reinforcement – the socket connection reinforces each end-to-end joint

Each coupling adds one welded joint to the run. Along a straight line, the joint is sealed by the same hot air welding used for the rest of the duct, so the extended run keeps one continuous corrosion-resistant interior.

For a run extension, the new straight section is aligned with the existing line, the coupling is welded over the joint, and the socket connection reinforces the join before the next section continues. This keeps later adjustments simple: a section can be cut out and a new one coupled in without replacing the whole run.

Selection Notes & Quotation Information

Coupling or Flange?

A coupling makes a permanent welded joint that extends the run as one continuous line. A duct flange makes a bolted joint that can be opened later. Use couplings along the run for permanent connection; use flanges at maintenance points and equipment access.

To Quote PP Air Duct Coupling

Provide: duct diameter (φ110-600mm), quantity, material grade (PP or flame retardant PPs), color (beige or grey), application, destination port, and your duct schedule or drawings.

MOQ and lead time are confirmed per project. Request a quote via WhatsApp or email using the contact block below.

Installation & System Integration

PP air duct couplings are joined to the duct run by hot air welding, and each joint is reinforced with a socket connection. The same joining method applies to straight duct and other fittings, so the extended run is welded and sealed as one continuous system.

The socket connection is formed as part of the moulded coupling, so the joint is reinforced by a sleeve of the same material rather than relying on the weld seam alone. This gives the end-to-end connection additional stiffness at the joint while keeping the interior smooth for airflow.

Complete systems combine couplings with straight duct, elbows, tees and reducers. See the full range of PP duct systems.

Related Products

• Polypropylene Round Ducts
• PP Air Duct Flange
• PP 90° Elbow
• PP Air Duct Tee
• PP Concentric Reducer
• Full PP Duct Range
• PP Air Duct Guide – a complete guide to PP duct types, sizes and materials.

FAQ

What is a PP air duct coupling?

It is an injection-moulded polypropylene fitting that joins two duct sections end to end, making a long run one continuous line – used to extend, repair or connect PP duct runs.

What sizes are available?

11 standard sizes from φ110mm to φ600mm: φ110, φ160, φ200, φ250, φ315, φ355, φ400, φ450, φ500, φ550 and φ600mm.

Coupling or flange – which should I choose?

A coupling makes a permanent welded joint that extends the run as one continuous line. A flange makes a bolted joint that can be opened later, used at maintenance points.

How is it connected?

By hot air welding to the duct sections, with socket connection reinforcement at the joint – the same method used for straight duct and other round fittings.

Is flame retardant PP available?

Yes. The coupling is available in standard PP or flame retardant PPs; specify the required flame retardant grade when inquiring.

What do I need to provide for a quote?

Duct diameter, quantity, material grade, color, application, destination port, and your duct schedule or drawings.