Duct production

1. General Provisions.This chapter applies to the inspection and acceptance of the processing and manufacturing quality of metal ducts, non-metal ducts and composite ducts or ducts used in ventilation and air conditioning projects of construction projects.

Note: The processing and manufacturing quality of metal ducts and non-metal ducts used in ventilation and air conditioning projects of industrial and civil buildings shall comply with the provisions of this chapter, and the quality inspection and acceptance shall be carried out in accordance with the corresponding provisions.

2. The acceptance of the manufacturing quality of ducts shall be carried out according to the different materials, system categories and places of use, mainly including the material, specifications, strength, tightness and appearance quality of the finished products.

(Figure 1: Construction Engineering Pipeline Production)

Note: The ducts shall be accepted according to the materials and the processing quality specified in the different divisions. First, the ducts shall be accepted according to the types of ducts, whether they are high-pressure systems, medium-pressure systems or low-pressure systems; second, they shall be accepted according to which sub-division the ducts belong to.

3. The acceptance of the manufacturing quality of ducts shall be carried out according to the design drawings and the provisions of this specification. The purchased ducts used in the project must also provide corresponding product qualification certificates or conduct strength and tightness verification, and can only be used if they meet the requirements.

Note: The basis for duct acceptance is the provisions and design requirements of this specification. In general, the quality of ducts can directly refer to this specification. However, when the design believes that the quality standard of duct construction needs to be higher than the provisions of this specification based on the needs of the project, more stringent requirements can be put forward. 

At this time, the construction unit should carry out construction according to higher standards, and the supervisor should accept according to high standards. 

At present, the processing of ducts has a trend towards productization, which is worth promoting. 

As a product (finished product), the corresponding product certificate must be provided or the strength and tightness must be verified to prove the processing technology level and quality of the ducts provided. The purchased ducts used in the project should be checked according to the requirements, and only those that meet the requirements can be agreed to use.

(Figure 2: Ventilation duct specifications)

4. For the acceptance of the specifications of ventilation ducts, the ducts shall be based on the outer diameter or outer side length, and the ducts shall be based on the inner diameter or inner side length. The basic series should be used first for round ducts. Irregular oval ducts refer to rectangular ducts, and the length of the long diameter plane and the short diameter size are used as the standard.

Note: This article stipulates that the specifications and sizes of ducts are based on the outer diameter or outer edge length; the building duct is based on the inner diameter or inner edge length. The thickness of the duct sheet is relatively thin, and the outer diameter or outer edge length has little effect on the cross-sectional area of the duct, and it can match the duct flange based on the inner diameter or inner edge length. The wall thickness of the building duct is relatively thick, and the inner diameter or inner edge length can correctly control the inner cross-sectional area of the duct.

The article stipulates two series for circular ducts: basic and auxiliary. The basic series should be used for general supply, exhaust and Air conditioning systems. The ducts of dust removal and pneumatic conveying systems have high flow rates in the pipes, and the pipe diameter has a greater impact on the resistance loss of the system. Under the premise of giving priority to the basic series, the auxiliary series can be used. This specification emphasizes that the purpose of adopting the basic series is to implement standardized construction of the project on the premise of meeting the needs of engineering use. For the diameter size of rectangular ducts, from the perspective of engineering construction, there are many specifications and it is not easy to clearly stipulate.

5. The air duct system is divided into three categories according to the working pressure of the system, and the classification should comply with the provisions in the table.

Note: This article stipulates that the air ducts in ventilation and air-conditioning engineering should be divided into three levels according to the nature of the system and the working pressure, namely low-pressure system, medium-pressure system and high-pressure system. 

Air ducts of different pressure levels can be applied to different types of air duct systems, such as general ventilation, air conditioning and purification air conditioning systems. This is proposed based on the needs of the current development of ventilation and air-conditioning engineering technology and the technical level of air duct manufacturing. The table also lists the sealing requirements of three levels for selection in actual projects.

6. Galvanized steel plates and various types of steel plates with composite protective layers should be connected by bite joints or riveting, and welding connections that affect the anti-corrosion performance of the protective layer shall not be used.

Note: The excellent anti-corrosion performance of galvanized steel plates and steel plates with various types of composite protective layers mainly depends on this protective film. If electric welding or gas welding is used, the high temperature will not only cause the galvanized layer at the weld to be burned, but also cause the protective layer of the plate surface that is several times larger than the weld range to be damaged. The composite steel plate after the protection is damaged may increase the corrosion rate at the weld range exponentially due to the electrochemical effect. 

(Figure 3: Galvanized steel sheet)

Therefore, it is stipulated that galvanized steel plates and steel plates containing such composite protective layers shall not be connected by welding methods that damage the protective layer under normal circumstances.

7. The sealing of the air duct should be mainly based on the sealing of the plate connection, and can be sealed by sealant caulking and other methods. The performance of the sealant should meet the requirements of the use environment, and the sealing surface should be set on the positive pressure side of the air duct.

Note: This article stipulates the key points of air duct sealing in terms of materials and construction methods.