What are the installation specifications of stainless steel welded air duct in ventilation and dust removal engineering of sheet metal processing workshop?

Specification for installation of stainless steel welded air duct in ventilation and dust removal engineering of sheet metal processing workshop

In the ventilation and dust removal project of sheet metal processing workshop, the installation of stainless steel welded air duct should be combined with the dust characteristics (such as metal dust and welding smoke), equipment layout and safety and environmental protection requirements, and follow the six core specifications of preliminary preparation, welding construction, installation positioning, sealing inspection, anti-corrosion and acceptance to ensure the stable operation of the system, no air leakage and compliance with safety standards.

First, the preparation specification: adapt to the workshop working conditions and design requirements.

Verification of materials and specifications

Stainless steel materials that meet the design requirements should be selected (304 or 316L is commonly used, and 316L is more suitable for workshops containing acid welding smoke), and the wall thickness of the air duct should be checked (the dust removal system usually needs ≥1.2mm, and the negative pressure section is ≥1.5mm) to avoid the deformation of the air duct due to insufficient wall thickness;

Check the flatness of the semi-finished products of the air duct. The inner wall should be free of scratches, depressions and rust, and the roughness of the polished surface should meet the requirements (Ra≤0.8μm) to prevent dust from adhering and accumulating.

Field measurement and planning

Combining with the layout of equipment (such as punch, bender and welding station) in sheet metal workshop, accurately measure the direction of air duct, diameter changing point and tuyere position, avoiding equipment operation area and maintenance channel;

Plan the installation points of supports and hangers to ensure that the spacing conforms to the specifications: the spacing of supports and hangers for horizontal air ducts is ≤3m, and that of vertical air ducts is ≤2.4m, and the supports and hangers shall not directly contact the air ducts (rubber pads shall be added for isolation to prevent sparks caused by metal friction and meet the requirements of dust explosion prevention).

Second, the welding construction specification: guarantee the sealing and structural strength.

Welding process selection

Argon arc welding (TIG welding) is preferred to avoid gas welding (which may easily lead to deformation of the air duct), and welding wires matching the material of the air duct (such as 304 air duct with ER308 welding wire) should be used to ensure that the weld strength is not lower than the base metal;

Butt weld shall be fully welded, and there shall be no missing welding, virtual welding and undercut (undercut depth ≤0.5mm, length ≤ 10% of the total length of the weld). The surface of the weld shall be smooth, free of flash and air holes, so as to prevent dust from accumulating in the weld depression.

Welding environment control

Windproof measures (such as setting temporary enclosure) should be taken during workshop welding to avoid the influence of wind speed > 2m/s on welding quality;

After welding, the welding slag shall be cleaned in time, and the weld shall be treated with special passivation paste for stainless steel (passivation time ≥ 15min) to prevent the weld from rusting (especially in humid areas such as Suzhou, where corrosion protection needs to be strengthened).

3. Installation and positioning specifications: ensure stability and smooth airflow.

Duct splicing and fixing

When splicing air ducts, the axes should be aligned (deviation ≤2mm/m), the flange connection surface should be flat (flatness deviation ≤1mm), the flange bolts should be made of stainless steel (to avoid dissimilar metal corrosion), and the bolt tightening torque should be uniform (set according to the pipe diameter, such as DN200 air duct bolt torque ≥ 15 nm);

When installing special-shaped parts (such as tees and elbows), it is necessary to set a deflector (curvature radius ≥1.5 times the pipe diameter) at the corner to reduce airflow resistance and avoid dust accumulation at the corner.

Support and hanger installation

The supports and hangers shall be made of angle steel or channel steel (the material shall be matched with the air duct to avoid electrochemical corrosion), and anti-corrosion treatment (galvanized or painted with anti-corrosion paint) shall be done before installation;

3-5mm thick oil-resistant rubber pad should be added between the air duct and the support and hanger, which can not only prevent the vibration transmission of the air duct, but also avoid the direct contact of metal to generate static electricity (to meet the requirements of dust explosion prevention).

Fourth, seal inspection specification: prevent air leakage from affecting dust removal efficiency.

stress testing

After the installation is completed, the negative pressure air leakage detection is carried out on the air duct system (the negative pressure of-500~-1500Pa is usually required for the sheet metal dust removal system), and the "light leakage method" is adopted for preliminary detection: a light source is placed in the air duct, and no light leakage is observed from the outside; If the pressure drop method is used for accurate detection, the air leakage rate should be ≤2% (according to the requirements of Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Engineering (GB 50243)).

Local seal reinforcement

If air leakage is found during inspection (such as flange joints and welds), it is necessary to repair welding with stainless steel welding wire (air leakage in welds) or use silicone sealants (high temperature glue with temperature resistance of 200℃ or higher is required for flange sealing surface, which is suitable for the high temperature environment of welding station), and it is necessary to conduct inspection again after repairing glue to ensure no air leakage.

V. Anti-corrosion and protection specifications: adapt to the complex environment of the workshop.

External wall anticorrosion treatment

For the air duct section with high humidity near the cooling liquid volatilization area, the outer wall needs to be painted with special stainless steel anticorrosive paint (2-3 times) to prevent external corrosion;

When the air duct passes through the wall or floor, it is necessary to set fire-proof sleeves (made of incombustible materials, with the length ≥ wall thickness or floor thickness+100mm), which meet the requirements of Code for Fire Protection in Building Design (GB 50016).

Inner wall protection

Avoid scratching the inner wall with tools during installation. If there are scratches, use fine sandpaper to polish and repair them (the roughness should be restored to Ra ≤ 0.8μ m). After installation, use compressed air (pressure ≤0.6MPa) to purge the inner wall, remove dust, welding slag and other sundries, and prevent the tuyere from being blocked after startup.

VI. Acceptance specifications: in line with safety and environmental protection standards.

Appearance and structural acceptance

Check the verticality (deviation ≤3mm/m) and levelness (deviation ≤2mm/m) of air duct installation, and make sure that the supports and hangers are arranged neatly without looseness; The weld surface is smooth, and the anti-corrosion layer does not fall off.

Functional acceptance

Commissioning of linked dust removal equipment (such as pulse dust collector) to detect the wind speed of each tuyere (which should meet the design requirements, usually the wind speed of the tuyere at welding station is ≥1.5m/s and that at cutting station is ≥2m/s) to ensure the dust collection effect;

Acceptance data should be complete, including material certificate, welding test report, air leakage test record and anti-corrosion construction record, which should be filed for future reference.

Following the above specifications can ensure that the stainless steel welded air duct can meet the dust characteristics and safety requirements of the sheet metal processing workshop, reduce the problems of air leakage, blockage and corrosion in the later period, ensure the long-term stable operation of the ventilation and dust removal system, and meet the environmental protection and occupational health standards (such as occupational exposure limits on Hazardous Factors in Industrial Places, GBZ 2.1).