Fabrication And Installation Of TDF Air Duct (Project Construction Scheme)

1. Project overview

The terminal project is about 180000 square meters. It is a two-and-a-half-story terminal with partial mezzanine and three floors.

The aboveground building area is 170000 square meters, the highest point is about 39 meters, and the underground pipe gallery is 7100 square meters.

It is divided into hydropower and HVAC pipe galleries.

The length of the two pipe galleries is about 900 meters and the pipeline is about 10000 meters.

The plane layout of the terminal is divided into main building (area a), corridor (area B) and satellite Hall (area C).

The main functions are:

The first floor is the domestic and international baggage sorting, picking up, welcome hall, office area, equipment rooms and air conditioning room;

The second floor is the departure hall, aircraft handling, security inspection, waiting hall and business district; The mezzanine is the access.

Due to the large amount of air duct, about 90000 square meters, and the tight construction period, it is necessary to adopt fully mechanized centralized processing of air duct.

Therefore, a special construction scheme on air duct processing is prepared.

The preparation basis is as follows:

(1) This work is based on professional construction drawings and other relevant documents;

(2) Code for acceptance of construction quality of ventilation and air conditioning engineering (GB50243-2002) (GB50242-2002);

(3) Unified standard code for construction quality acceptance of building engineering GB50300-2001;

(4) Standard for safety inspection of building construction (JGJ59-99);

(5) Technical code for safety of temporary electricity on construction site (JGJ46-2005);

(6) Technical code for safety of high altitude operation in building construction (JGJ80-91);

2. Selection of construction process

Due to the tight construction period of the project and the large volume of air duct, about 90000 square meters, an advanced process needs to be selected to complete the air duct processing in a short time.

In addition, considering that the TDF flange air duct has the advantages of angle steel flange air duct, stronger structural strength, no welding, good corrosion resistance, tight connection and low air leakage rate.

Therefore, the project selects the TDF flange air duct to process the air duct.

The air duct adopts the full-automatic production line, and combined with the world’s advanced numerical control and optical fiber information technology.

It can produce not only the galvanized straight rectangular air duct, but also various special-shaped air duct components such as elbow, tee and cross.

The process features are as follows:

1. The production line has a high degree of mechanization and automation, which greatly improves the manufacturing efficiency and the manufacturing accuracy of the air duct.

2. The air duct forms its own flange to reduce the weight of the air duct, so as to reduce the self-weight of the building.

3. The air duct has good sealing performance, significantly reduces air leakage, saves energy and reduces the operation cost of the main engine.

4. The air duct is automatically reinforced, with high strength, beautiful and tidy appearance, and no damage to the zinc layer.

5. Fast production and installation, reduce labor intensity, improve labor efficiency and meet the needs of modern projects.

3. Process principle

1. According to the diameter and shape of the on-site air duct, it is input into the computer, and the blanking of the equipment is controlled by the program software.

2. The machine-made TFD flange forming machine is used to turn the flange on the air duct to form the flange. Use the equipment to make the corresponding connection angle.

3. During field installation, use flange angle and flange fixing clamp to connect the air duct to achieve the purpose of installation.

4. Construction technology

1. Air duct fabrication

(1) Duct thickness selection

(2) Sketch duct machining

Thickness of air duct (mm); 

Large side size of air duct (mm)

Rectangular duct

Medium and low voltage system

Smoke exhaust system


















By design

According to the construction drawings and the actual situation of the site (air duct elevation, direction and coordination with other disciplines), draw the processing sketch according to the system served by the air duct, and number it according to the system.

(3) Production process of straight pipe

Input the size of the air duct to the computer according to the sketch → enter the galvanized plate and straighten it in the production line → beading (large side size > 630mm) → corner cut by notching machine → cut the plate by the plate shear → lock (snap and insert) → machine-made TFD flange forming machine → bend by the folding machine (fold it into a straight line, L-shape, U-shape and 口 shape according to the size of the caliber) → quality inspection.

(4) Production process of special-shaped pipe (elbow, tee and other accessories)

Make cutting drawing by computer according to the drawing → cut semi-finished products by plasma cutting machine → single machine lockformer → TFD flange forming machine → bending by folding machine → quality inspection.

The schematic diagram of TDF air duct is as follows:

Schematic diagram of TDF flange air duct

Schematic diagram of TDF air duct

2. Air duct installation

(1) Air duct reinforcement

① When the large side size of the air duct is 630 ~ 1000mm, the reinforcement shall be directly pressed on the production line, the arrangement shall be regular, the spacing shall be uniform, and the plate surface shall not have obvious deformation.

② When the size of the large side of the air duct is more than 1000mm, angle steel, flat steel, steel pipe, z-groove, reinforcing bar, through wire screw, etc. can be used for internal and external reinforcement of the duct.

As shown in the figure below:

Air duct reinforcement

③ For the reinforcement of angle steel or reinforcing bar, its height shall be less than or equal to the height of air duct flange, the arrangement shall be neat, the spacing shall be uniform and symmetrical, and shall not be greater than 220mm, and the riveting with air duct shall be firm.

④ The inner part of the pipe is supported and reinforced with through wire screw.

Its special gasket is placed on the inner wall of the external insulation air pipe.

For the non insulation air pipe or internal insulation air pipe, it is placed on the outer wall of the air pipe.

The through wire screw should be set at the center of the air pipe.

When the section of the air pipe is large, a through wire screw should be added on both sides close to the flange for support and reinforcement.

⑤ When the section of the air duct is more than 1250 * 630mm, in order to keep the adjacent walls perpendicular to each other, 90 ℃ inclined support should be adopted at the four corners of the air duct for reinforcement.

⑥ When the length of the air duct of medium pressure and high pressure system is greater than 1250mm, reinforcement frame shall be used for reinforcement.

(2) Duct connection

① Since the air duct production line and the construction site cannot be in the same place, the air duct shall be processed into semi-finished products according to the sketch drawn in the workshop, and the air duct shall be assembled according to the number on the construction site according to the system number.

② The machine-made air duct adopts joint-angle lock connection to strengthen the tightness of the air duct.

③ The branch pipe is connected with the main pipe by joint biting or reverse side riveting with the main pipe with pull nails, and the connection is sealed with glass glue to prevent air leakage.

④ The connection between the air duct flange and the flange adopts a special TFD flange angle, which is tapped into the flange with a hammer and then connected with bolts.

The process dimensions of the flange angle are shown in the following table:

Long side of air duct

Minimum flange size (mm)

Thickness of corner connecting plate (mm)

Flange clamp thickness (mm)



Below 400









Above 1200


⑤ When the size of the large side of the air duct exceeds 450mm, in order to strengthen the strength of the flange and the air duct, the flange fixing clamp shall be used.

⑥ The spacing of flange fixing clips shall be in accordance with the following table:

Side length of air duct (mm)

Installation diagram of flange clamp

Flange clamp installation requirements

Standard flange clamp length dimension


spacing of flange fixing clips

no need to add

spacing of flange fixing clips



Add one in the center


Add two under equal distance


Add one if the spacing is less than 250mm

(3) The spacing between supports and hangers of machine-made air ducts, if not required by the design, shall comply with the following provisions:

① The air duct shall be installed horizontally, the long side size shall be ≤ 400mm, and the spacing shall not be greater than 4m;

Greater than or equal to 400mm, not greater than 3m. If the length of the straight pipe exceeds 25m, fixed points to prevent swing shall be added.

② The air duct shall be installed vertically, and the spacing shall not be greater than 4m, but the fixed parts of each riser shall not be less than 2.

Dimension of long side of air duct (mm)

Maximum spacing (mm)

Boom size (mm)

Bracket size (mm)

















above 2500

According to design regulations

③ The minimum size of rectangular horizontal air duct supports and hangers is shown in the table below.

3. Sealing of air duct

(1) The TDF air duct shall be sealed at the flange corner and inside and outside the connection between the branch pipe and the main pipe.

The low-pressure air duct shall be sealed from the folding part of the air duct joint to 40 ~ 50mm inside the duct;

The high-pressure air duct shall also be sealed at the longitudinal bite of the air duct and the composite part of the air duct.

The flange sealing strip should be installed near the outside of the flange or in the middle of the flange.

When the flange sealing strip overlaps at the flange end face, the overlap is about 30 ~ 40mm.

(2) The four flange corner connections of the TDF air duct flange must be sealed with glass glue to prevent leakage.

The joint bite 80mm downward from the flange corner must be sealed with glass glue to prevent leakage.

The sealant should be set on the positive pressure side of the air duct.

(3) See the attached figure for the specific method of TDF air duct sealing.

method of TDF air duct sealing

4. Installation steps of TDF air duct

  • Air duct assembly
  • Mounting flange angle
  • Flange sealant leakage prevention and flange sealant gasket installation
  • Four corner screw connection of air duct flange
  • Air duct flange edge mounting flange clamp
Installation steps of common flange air duct

5. Light leakage detection of air duct

Light leakage detection is a method to detect the tightness of the air duct of the system by using the strong penetration of light to the small hole.

1. Standard for light leakage detection

When the light leakage method is used to detect the tightness of the system, the air duct of the low-pressure system is qualified with no more than 2 light leakage points per 10m joint and no more than 16 joints per 100m;

For the medium pressure air duct, it is qualified if the light leakage point is no more than 1 for every 10m joint and no more than 8 for every 100m joint.

2. Specific operation method of light leakage detection

The safety light source with certain intensity, not less than 100W low-voltage lighting lamp with protective cover, shall be used as the light source for light leakage detection.

When detecting the light leakage of the air duct of the system, the light source can be placed inside or outside the air duct, but the opposite side should be in a dark environment.

The detection light source moves slowly along the detected part and joint, and observes on the other side.

When light is found to be emitted, it means that obvious air leakage is found and recorded.

The air duct of the system adopts the method of segmented detection and summary analysis.

On the basis of strict installation quality management, the detection of system air duct is mainly based on main pipe and main pipe.

If slit shaped light leakage is found in light leakage detection, it shall be treated according to different light leakage parts.

If it is at the flange, tighten the bolts and replace the sealing gasket;

In case of undercut, seal with sealant.

If the light leakage of undercut joint is serious, the air duct of this section shall be fabricated and installed again, and the light leakage test shall be conducted again.

If the light leakage test is unqualified, the air leakage test shall be conducted according to the specified sampling rate.

6. Installation of air duct components

1. Installation of fire damper

Before installing the fire damper, check whether its spring and transmission mechanism are intact.

After the installation of fire damper and regulating valve, action test shall be conducted to ensure sensitive and reliable operation.

When installing the fire damper, the distance from the wall must be greater than or equal to 200mm, and the thickness of the wall powder and the keel for decoration shall be fully considered, otherwise it cannot be operated.

The installation of fire damper must pay attention to the direction, and the fusible sheet must be placed on the windward side.

The fire damper and silencer must be separately provided with supports and hangers.

2. Air outlet installation

(1) After the tuyere arrives, check the specification and size of the tuyere according to the drawing, stack it separately according to the system, and make marks to avoid mistakes during installation.

(2) Before installing the air outlet, carefully check the air outlet to see if it is damaged and if there are scratches on the surface.

For all tuyeres with adjustment and rotation parts, check whether the moving parts are flexible, whether the blades are straight and whether there is friction with the frame.

For the openable air outlet with filter screen, check whether the filter screen is damaged and whether the shutter can be opened and closed freely.

After the air outlet is installed, the movable parts of the air outlet shall be checked again.

(3) When installing the air outlet, pay attention that the lines of the air outlet are consistent with other facilities in the room, such as lamps, smoke detectors, nozzles and so on.

Especially when the air duct is concealed, the air outlet shall obey the room line.

The diffuser installed on the ceiling shall be flush with the ceiling.

The air outlet shall be installed firmly and reliably.

(4) In order to enhance the overall decorative effect, the installation of air outlet and diffuser adopts the internal fixation method:

Fix the air outlet on the keel frame or wooden frame with self tapping screws from the side of the air outlet, and add angle steel support frame if necessary.

(5) The levelness and position of the exhaust outlet shall be ensured with a level ruler and tape during the installation of the exhaust outlet, and the straightness of the same exhaust outlet / diffuser shall be ensured with the pull wire method.

7. Quality requirements

1. The fabrication and installation of air duct shall be in accordance with the code for acceptance of construction quality of ventilation and air conditioning engineering GB50243-2002.

2. The air duct joint shall be tight, the width shall be uniform, and there shall be no defects such as holes, half bites and expansion cracks.

3. The flange connection of air duct shall be firm, with straight angle and uniform arc.

4. The reinforcement of air duct shall be reliable, neat, with appropriate spacing, uniform and symmetrical.

5. When the size of the large side of the air duct is ≤ 300mm, the allowable error is 0 ~ 1mm. When the size of the large side of the air duct is more than 300mm, the error is 0 ~ 2mm.

6. The allowable error of flange inner side length is 1.0 ~ 3.0mm.

7. The allowable error of air duct flatness is ± 2mm.

8. The error of the difference between the two diagonals of the rectangular flange is < 3mm.

9. The allowable error of flange flatness is ± 2mm.

8. Safety precautions

1. When working in the manufacturing workshop, all kinds of equipment shall be managed by special personnel.

All operating parts of the equipment shall be provided with protective measures such as protective covers, and the operating procedures of the equipment shall be strictly observed.

2. Be careful not to scratch hands and feet during the handling of galvanized steel plate.

3. The emergency stop protection switch of various equipment shall be flexible and reliable.

4. During the on-site hoisting of air duct, special personnel shall be assigned to command, and the selection of hoisting points shall be firm and reliable.

When hoisting, the air duct shall be lowered

No one is allowed to stand.

5. The leakage protection switch of various small electric tools used on-site shall be flexible and reliable.

9. Workforce mix

No.Type of workNumber of peopleOperation days
3Electric welder5120
4General worker20120
5Total151 /

10. Construction machines and tools

No.Machine nameSpecificationsCompanyquantity
1CNC shearing machine Set1
2Plasma cutting machineFPC3600Set1
3Flange forming machineTFD2000Set1
4Corner cutting machine Set1
5Lockformer machineYZL-12-380Set2
6Folding machine Set1
7Electric welding machineBXI-315AISet5
8Impact electric drill pcs4
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