Why choose stainless steel welded ventilation pipe for environmental protection treatment of waste gas and smoke?

Stainless steel welded ventilation pipe is selected in the environmental protection treatment project of waste gas and smoke, mainly because it has irreplaceable advantages in corrosion resistance, safety, stability and environmental protection, and can meet the strict requirements of industrial waste gas treatment. The following analysis is carried out from three dimensions: technical characteristics, engineering requirements and economic benefits:

First, the core technical characteristics adapt to the waste gas treatment environment

1. Super corrosion resistance, dealing with complex waste gas components.

Typical components of industrial waste gas:

Acid gases (such as SO, HCl, NOx, from chemical, metallurgical, incineration and other scenes);

Alkaline gas (such as NH, from pharmaceutical and fertilizer industries);

Oil mist, water vapor, dust and corrosive particles (such as sulfide and chloride).

Corrosion resistance mechanism of stainless steel;

A compact Cr₂O₃ oxide film is formed on the surface of stainless steel (such as 304/316L/310S), which can resist the corrosion of corrosive media such as acid, alkali and salt spray. For example:

316L stainless steel contains molybdenum (Mo), and its pitting resistance in chloride ion (Cl) environment (such as waste gas from garbage incineration) is 2-3 times that of 304 stainless steel.

310S stainless steel (high temperature resistant) can maintain chemical stability in high temperature waste gas at 800-1200℃, and is suitable for high temperature waste gas incineration pipeline.

Compare the disadvantages of traditional materials:

Carbon steel pipe: it needs to be coated with anticorrosive coating (such as epoxy resin), but it is easy to fall off after long-term contact with acidic waste gas, resulting in pipeline perforation and leakage;

PVC/PP pipeline: not resistant to high temperature (usually ≤80℃), easy to soften and deform in case of burning waste gas or high temperature gas in drying process, and poor mechanical impact resistance.

2. High temperature resistance and fire resistance, ensuring system safety.

High temperature exhaust gas scene:

The temperature of waste gas discharged by industrial boilers, smelting furnaces, incinerators and other equipment can reach 200-1000℃. Ordinary pipes (such as galvanized iron sheets and plastics) will be deformed due to high temperature and release toxic gases (such as dioxin generated by PVC combustion). Stainless steel pipes can withstand such high temperatures for a long time to avoid fire or waste gas leakage accidents caused by pipeline rupture.

Fire safety advantages:

Stainless steel is a non-combustible material, which meets the fire protection requirements of industrial pipelines in Code for Fire Protection Design of Buildings (GB 50016), and is especially suitable for flammable and explosive waste gas environment (such as VOCs waste gas in spraying workshop) to reduce the risk of open flame ignition.

3. The surface is smooth, which reduces the adhesion and blockage of pollutants.

The roughness of the inner wall of stainless steel pipe is only 0.02-0.05mm (about 0.1-0.2mm for carbon steel pipe), and impurities such as dust and oil mist in waste gas are not easy to stay, which can reduce the incidence of the following problems:

Pipeline blockage: reduce the decrease of ventilation efficiency caused by particle accumulation (such as paint mist deposition in spraying workshop);

Microbial breeding: avoid the organic matter in the waste gas from forming an adhesive layer on the inner wall of the pipeline and breeding bacteria or molds (such as oil in the waste gas from food processing);

Accelerated corrosion: impurity accumulation is easy to form "corrosion battery", and the smooth surface of stainless steel can delay the electrochemical corrosion process.

Second, the irreplaceability of engineering demand angle

1. The high-strength structure adapts to the complex installation environment.

Advantages of welding process:

By argon arc welding, plasma welding or laser welding, the pipeline and pipe fittings (elbows, tees and flanges) can be fully sealed, and the weld strength is close to that of the base metal, thus avoiding the air leakage problem caused by vibration and temperature difference in traditional flange connection (relying on rubber sealing rings).

Case: In the production line with large vibration (such as waste gas pipeline in mine crushing workshop), the air leakage rate of stainless steel welded pipeline can be controlled within 1%, while the air leakage rate of flanged carbon steel pipe can reach 5%-10%.

Mechanical impact resistance:

Stainless steel has strong rigidity (tensile strength is 520-795MPa), which can withstand collision or external load (such as vibration of pipeline hanger) during installation, and reduce the risk of waste gas leakage caused by pipeline deformation.

2. Long-term sealing ensures the environmental protection effect.

In the waste gas treatment system (such as the pipeline at the front end of desulfurization, denitrification and dust removal equipment), the pipeline sealing directly affects the treatment efficiency:

Air leakage will lead to the fluctuation of waste gas quantity and affect the parameter matching of purification equipment (such as the imbalance of liquid-gas ratio in spray tower);

Leakage of acid waste gas may corrode surrounding equipment or cause environmental pollution in the workshop.

The permanent sealability of stainless steel welded pipes (without fragile seals) can ensure the long-term stable operation of the system, especially suitable for industrial scenes that need continuous operation (such as power plants and steel plants).

3. It is convenient for cleaning and maintenance, and meets the requirements of environmental protection and compliance.

Environmental laws and regulations (such as Integrated Emission Standard for Air Pollutants (GB 16297)) require the waste gas treatment system to be maintained regularly to prevent secondary pollution:

Stainless steel surface is corrosion-resistant, which can be directly washed by high-pressure water gun and chemical cleaning agent (such as sodium hydroxide solution) to remove oil dirt, dust and other pollutants on the inner wall;

The welding interface has no dead angle, which avoids the stubborn dirt accumulated in the gap of traditional threaded connection and reduces the maintenance difficulty and time cost.

Third, the analysis of economic benefits and sustainability

1. Lower life cycle cost

Index Stainless steel welded pipes Ordinary carbon steel pipes (with anticorrosion)

The initial investment cost is 30%-50% higher and lower.

Service life is 20-30 years and 5-10 years (in corrosive environment)

Annual maintenance cost is low (no anti-corrosion treatment is required) and high (anti-corrosion painting is required every year).

Low loss due to shutdown (low replacement frequency) and high loss due to shutdown every 5-8 years.

Long-term economy: Although the initial investment of stainless steel is high, its comprehensive cost (procurement+maintenance+shutdown loss) is only 50%-70% of that of carbon steel pipe in corrosive environment. For example, a chemical company used 316L stainless steel in its acid waste gas pipeline, which saved more than 800,000 yuan in maintenance cost within 10 years.

2. Recyclable, in line with circular economy.

Stainless steel pipes can be recycled and smelted 100% after being scrapped, and the recycling rate is over 95%, which is much higher than that of plastic pipes (which are difficult to degrade and have high recycling cost) or carbon steel pipes coated with anti-corrosion layers (which need to be peeled off to produce hazardous waste). This is in line with the requirements of sustainable utilization of industrial materials in the Circular Economy Development Strategy and Recent Action Plan.

3. Adapt to the upgrading trend of environmental protection equipment

With the improvement of environmental protection standards (such as stricter emission limits of VOCs), waste gas treatment processes are upgraded to high-efficiency technologies such as high-temperature incineration (RTO), catalytic oxidation (CO) and wet desulfurization, which put forward higher requirements for high-temperature resistance and corrosion resistance of pipelines. Stainless steel pipes can seamlessly adapt to the equipment upgrading requirements in the next 10-15 years, and avoid the cost of system transformation caused by backward pipeline materials.

IV. Typical Application Scenarios and Selection Suggestions

1. Typical industry applications

Chemical industry: 316L stainless steel is used to treat waste gas containing HCl and H₂SO₄, and an acid mist purification tower is provided;

Iron and steel/metallurgical industry: 310S stainless steel is selected to treat high-temperature dusty waste gas (such as blast furnace gas) with bag filter;

Waste incineration industry: to treat waste gas containing Cl and dioxin, duplex stainless steel (such as 2205) is selected to improve pitting corrosion resistance;

Spraying/printing industry: 304 stainless steel is used to treat VOCs-containing waste gas, and it is equipped with activated carbon adsorption device or RTO incinerator.

2. Selection of key parameters

Material model: according to the composition of waste gas (such as 304 for dry environment, 316L for wet/chlorine-containing environment and 310S for high temperature environment);

Wall thickness design: the wall thickness of high-pressure waste gas (such as fan outlet pipeline) needs to be increased (≥3mm), and the low-pressure waste gas (such as gas collecting hood branch pipe) can be 2-2.5 mm;

Welding standard: Code for Construction of Industrial Metal Piping Engineering (GB 50235) shall be implemented, and the weld shall be subjected to colored flaw detection or pressure test (such as air pressure test of 0.6MPa).