How to choose stainless steel welded air duct suitable for your own needs?

Guide for accurate selection of stainless steel welded air duct

The core of selecting stainless steel welded air duct is to determine the core requirements of the use scenario first, then match the material, specification and process, and screen around the four key dimensions of "anticorrosion grade, temperature/pressure, cleanliness and installation environment", taking into account the cost performance and post-installation maintenance. The following selection method can be directly implemented step by step, covering all application scenarios such as industry, HVAC and environmental protection, and quickly matching the adaptation scheme.

Step 1: Select the core material first-according to "anticorrosion/temperature/cleanliness requirements", and the cost performance is preferred.

Stainless steel material is the foundation of air duct, and the mainstream is 304, 316L, 301/201 (321/310S for minority special scenes). The properties of corrosion resistance, high temperature resistance and food grade of different materials are quite different, so it is not necessary to blindly select high-end materials, but to match them according to the scene requirements. Refer to the core selection:

Material core characteristics to adapt to the scene (core) cost-effective remarks

304 General-purpose models for conventional anti-corrosion, temperature resistance ≤600℃, food-grade, easy-to-process food/medicine clean workshop, conventional acid and alkali waste gas, high-end heating and ventilation in buildings, hot air from boilers and environmental protection dust removal (no strong corrosion) account for more than 90% of the market.

316L has strong corrosion resistance (high-concentration acid and alkali/salt fog resistance), temperature resistance ≤800℃, ultra-clean chemical/electroplating high-concentration acid and alkali waste gas, coastal areas with high salt fog, marine engineering, food-grade aseptic transportation, desulfurization and deaeration. The corrosion resistance is 2-3 times that of 304.

201/301 High-temperature ventilation with weak corrosion resistance, temperature resistance ≤300℃, low price, dryness and no corrosion (such as dry hot air in forging workshop), and low ventilation of temporary works are easy to rust, so it is strictly prohibited to be used in wet/anti-corrosion scenes.

321/310S ultra-high temperature resistant (321≤800℃/310S≤1200℃), thermal deformation resistant metallurgical/glass furnace high-temperature flue gas (≥800℃) and boiler high-temperature steam (≥ 600℃) are special for low special high-temperature scenes, and the processing is difficult.

Core principles:

Food/medicine/drinking water transportation: food grade 304/316L must be selected (material test report is required to ensure that no heavy metals are precipitated);

Coastal/high salt fog environment: 316L is preferred to avoid short-term rust of 304;

Conventional scenes (such as office building heating and ventilation, general dust removal): 304 is enough, with the highest cost performance;

No corrosion, only dry at high temperature: 201 can be selected (to reduce costs), but long-term use is not recommended.

Step 2: Determine the specifications of the air duct-according to the "air volume/installation space/medium characteristics", so as to match accurately and not waste.

Specifications include pipe diameter/side length (circular/rectangular), wall thickness and welding method, which are calculated according to "actual use parameters+installation environment" to avoid waste of "large pipe with small air volume" or excessive wind resistance of "small pipe with large air volume". Key points of core selection are as follows:

1. Shape selection: circular VS rectangular, according to installation space+air volume.

Circular air duct: it has small wind resistance, better sealing performance and high compressive strength, and is suitable for large-volume transportation, high-pressure ventilation and explosion-proof/anti-corrosion scenes (such as industrial waste gas and boiler hot air), but it takes up a large installation space and needs to be equipped with elbows when turning;

Rectangular air duct: it is easy to fit the wall/ceiling, and the installation space is small, which is suitable for building heating and ventilation, ceiling ventilation of clean workshop and small space installation (such as office buildings and hotels), but the wind resistance is slightly large, so the large-diameter rectangle needs to be strengthened.

2. Diameter/side length: Calculate according to "actual air volume" and find the professional accounting of the manufacturer.

Without self-calculation, inform the manufacturer of the core parameters: actual air volume (m/h), wind speed requirements (conventional 8-15m/s, corrosion prevention/high temperature can be appropriately reduced) and installation length, and the manufacturer will accurately calculate the pipe diameter/side length according to the formula to avoid air volume loss; Conventional reference: 300-500mm pipe diameter is selected for office HVAC air volume ≤ 5000m/h, and 800-1500mm pipe diameter is selected for industrial waste air volume ≥ 10000m/h..

3. Selection of wall thickness: according to "pipe diameter/pressure/installation method", the thicker/the greater the pressure, the thicker the wall thickness.

The wall thickness directly affects the compressive strength and deformation resistance of the air duct, and the thicker the duct, the better. Too thick will increase the cost and processing difficulty. Refer to the wall thickness of conventional 304 material (unit: mm):

Small pipe diameter (≤500mm): 0.8-1.0mm for low pressure ventilation (≤3kPa) and 1.0-1.2mm； for medium and high pressure ventilation (3-10kPa);

Medium pipe diameter (500-1000mm): 1.0-1.2mm for low pressure and 1.2-1.5mm； for medium and high pressure;

Large pipe diameter (≥1000mm): 1.2-1.5mm for low pressure and 1.5-2.0mm； for medium and high pressure;

Special scenes: coastal/high-altitude installation (wind resistance) and high-temperature flue gas (thermal deformation resistance), and the wall thickness is increased by 0.2-0.5mm on the basis.

4. Welding method: according to "sealing/cleaning/anti-corrosion requirements", the mature technology of the manufacturer is given priority.

The core welding methods of stainless steel welded air duct are argon arc welding (TIG) and plasma welding, all of which are seamless welding, and the sealing performance is far superior to splicing. Please refer to the selection:

Argon arc welding: universal, with smooth welding, good sealing and moderate processing cost, suitable for 99% scenes (HVAC, waste gas, clean workshop);

Plasma welding: the welding is denser, with no welding scar, smooth inner wall and no dead angle. It is suitable for ultra-clean scenes (GMP workshop, food aseptic transportation) and high-pressure explosion-proof scenes, and the processing cost is slightly higher.

Step 3: Match the additional process-customize according to the "special requirements of the scene" to avoid rework in the later stage.

According to the requirements of anticorrosion, cleanliness, heat preservation and installation of the scene, the targeted technology is added, which is the key detail of the type selection and directly affects the service life and use effect of the air duct. The core additional technology and adaptation to the scene:

Polishing/passivation of inner wall: mirror polishing of inner wall (Ra≤0.8μm) is required for food/medicine cleaning workshop and drinking water transportation, so there is no dust accumulation and it is easy to clean and disinfect; Conventional anticorrosion/HVAC scenes can be passivated to improve the corrosion resistance of stainless steel and prevent the welding joint from rusting;

Anti-corrosion spraying on the outer wall: in strong corrosive environments such as coastal high salt fog and chemical workshop, anti-corrosion paint/fluorocarbon paint is sprayed on the outer wall, which is double anti-corrosion and prolongs the service life;

Thermal insulation treatment: high-temperature medium transportation (boiler hot air, flue gas) needs external thermal insulation (rock wool/aluminum silicate)+galvanized sheet shell to reduce heat loss; Cold preservation treatment (polyurethane) is required for low-temperature refrigerant transportation (cold air in cold storage) to prevent condensation;

Reinforcement/flange customization: For air ducts with large diameter (≥1000mm) and installed at high altitude, internal reinforcing ribs/external reinforcing rings are required to resist wind and deformation; Install custom-made stainless steel flanges (304/316L) at the butt joint to avoid the influence of flange rust on sealing, and choose temperature-resistant/anti-corrosive models (such as silicone pads and fluororubber pads) for flange gaskets;

Customization of special-shaped parts: when there are columns/corners in the installation space, inform the manufacturer of the site size in advance, and customize the special-shaped parts such as elbows, tees, and reducers to ensure seamless installation on site and avoid damage to the stainless steel anticorrosion layer by cutting and processing on site;

Air leakage detection: For high pressure, explosion-proof and clean scenes, manufacturers are required to conduct overall air leakage detection (air leakage rate ≤3%) to ensure sealing performance and avoid medium leakage.

Step 4: Confirm the manufacturer's supporting services-select according to the "installation/after-sales" requirements to avoid landing risks.

Stainless steel welded air duct is a customized product, and the processing accuracy, installation service and after-sales guarantee of the manufacturer directly affect the use effect. The following points should be made clear when selecting the type to avoid later disputes:

Machining accuracy: the manufacturer is required to provide material inspection report (spectral inspection) and wall thickness inspection report to ensure that the material/wall thickness is consistent with the contract and avoid cutting corners; After welding, there is no welding scar and deformation, and the pipe diameter error is ≤ 1 mm;

Installation service: priority should be given to manufacturers who can be installed at home, especially in industrial waste gas and high-altitude HVAC scenes. Professional installation team can ensure that the welding joint is sealed and the bracket is firmly fixed to avoid air leakage/falling off in the later period;

Support/Accessories Matching: The manufacturer is required to match stainless steel support/elevator (to avoid rusting and polluting the air duct with carbon steel support), and the materials of accessories are consistent with the air duct, so as to purchase them in one stop, so as to reduce the problem of on-site adaptation;

After-sales guarantee: specify the warranty period (1-2 years for conventional warranty, and 1 year or more for joint corrosion protection), and the manufacturer shall provide post-maintenance service. If the joint is rusted or leaked, it can be treated at home.

Step 5: Cost-effective control-three principles, don't waste money.

Do not blindly choose high-end materials: 304 can meet the scene, never choose 316L, such as ordinary office building HVAC, drying and dust removal, 304 cost-effective is much higher than 316 L;

Specification according to actual parameters: air volume and pressure are calculated according to actual use value, not the maximum value, so as to avoid the waste of "large pipe and small air volume" and "thick wall and low pressure";

Priority is given to local/nearby manufacturers: stainless steel air ducts are bulky and have high transportation costs. Local manufacturers can reduce transportation losses, and door-to-door installation and after-sales response are more timely.

General Process of Core Selection (Quick Landing Edition)

Sort out their own core requirements: scene (such as food workshop/chemical waste gas)+medium (such as hot air/acid and alkali waste gas)+parameters (air volume/temperature/pressure)+installation environment (coastal/high altitude/small space);

Preliminary matching material: 304 (universal) /316L (strong anticorrosion/high salt spray) /310S (ultra-high temperature);

Inform the manufacturer of the parameters, and let them check the specifications (shape/pipe diameter/wall thickness)+welding method;

Confirm additional processes: polishing/passivation/heat preservation/reinforcement (according to scene requirements);

Clear the manufacturer's supporting facilities: test report+door-to-door installation+stainless steel fittings+after-sales guarantee;

Sign the contract, mark all details such as material, specification, technology and quality assurance, and attach drawings as attachments.

Examples of common scene selection (direct reference)

Sterile transportation in food processing plant: food grade 304+circular air duct+argon arc welding+mirror polishing of inner wall+stainless steel flange+silicone gasket;

Acid-base waste gas from chemical electroplating: 316L+circular air duct+argon arc welding+internal and external passivation+external wall anticorrosion spraying+reinforcing ring+fluororubber gasket;

High-end HVAC for office buildings (coastal): 304+rectangular air duct+argon arc welding+passivation treatment+stainless steel bracket+ceiling installation with special-shaped parts;

Boiler high-temperature hot air (800℃): 321 stainless steel+circular air duct+argon arc welding+external rock wool insulation+galvanized sheet shell+internal reinforcement;

Pharmaceutical GMP clean workshop: 304/316L+circular air duct+plasma welding+mirror polishing of inner wall+air leakage detection+sterile flange.