What is the performance of 304 stainless steel welded ventilation pipe in different temperature environments?

The performance of 304 stainless steel welded ventilation pipe is closely related to temperature, and its corrosion resistance, mechanical properties and sealing performance will show different performances with the change of environmental temperature. The following is a detailed analysis from four sections: low temperature, normal temperature, moderate high temperature and extreme high temperature:

1. Low temperature environment (-196℃~0℃): Excellent toughness and no embrittlement risk.

304 stainless steel belongs to austenitic stainless steel, which has excellent toughness and stability at low temperature, as shown in the following:

Mechanical properties are stable: its tensile strength and yield strength are slightly improved at low temperature, and there is no low-temperature embrittlement (ductile-brittle transition temperature is much lower than-196℃). Even in the liquid nitrogen environment at-196℃, it can still maintain good plasticity and impact toughness (impact energy ≥27J), and the toughness of the welding part (treated by argon arc welding and other processes) is basically the same as that of the base metal, and the weld will not crack due to low temperature.

Corrosion resistance is not affected: at low temperature, the passive film (Cr₂O₃) on the surface of stainless steel is more stable, and it is not easy to be damaged due to temperature drop. It still has good corrosion resistance to wet low-temperature dust with a small amount of salt (such as ventilation and dust removal in cold storage).

Application scenario: It is suitable for low-temperature workshops (such as cold chain food processing workshops and low-temperature laboratory ventilation), and the pipeline will not be deformed or leaked due to temperature fluctuation.

Second, normal temperature environment (0℃~100℃): the performance is comprehensive and optimal.

This is the best working range of 304 stainless steel welded pipeline, and all the properties are in an ideal state:

The best corrosion resistance: at room temperature, the passive film is fast and stable, which can effectively resist the corrosion of air, water vapor and industrial dust (such as machining iron filings and wood dust). The passive film in the heat affected zone (HAZ) formed by argon arc welding can be quickly repaired without obvious corrosion weakness.

Mechanical properties are balanced: tensile strength (520-720MPa), yield strength (205-310MPa) and elongation (≥40%) all keep the standard values, and the overall rigidity after welding is sufficient to cope with the wind pressure (positive pressure ≤ 3,000 Pa, negative pressure ≥-2,000 Pa) and airflow impact of the ventilation system, and the pipeline has no hidden dangers of deformation and vibration.

Reliable sealing performance: at room temperature, the expansion and contraction of the pipeline are very small (the linear expansion coefficient is about 17.3× 10/℃), the welded joint will not produce cracks due to temperature changes, and the air leakage rate can be stably controlled within 1%.

3. Medium and high temperature environment (100℃~600℃): The performance changes gradually, and targeted design is needed.

When the temperature exceeds 100℃, the properties of 304 stainless steel will change gradually with the increase of temperature, and the following points should be paid attention to:

The mechanical properties are decreased, but it can still meet the requirements:

100-300℃: the tensile strength and yield strength decrease slowly (for example, the yield strength decreases to about 140MPa at 300℃), but the rigidity of welded structure can still adapt to medium and high wind speed (10-20m/s) and conventional wind pressure, and the pipeline has no obvious deformation.

300-600℃: the strength decreases rapidly (the yield strength is only about 80MPa at 600℃). It is necessary to increase the pipe wall thickness (for example, from 1.2mm to 2.0mm) or add stiffeners to avoid bending caused by self-weight or airflow pressure at high temperature.

Corrosion resistance fluctuates slightly, but it is still reliable as a whole:

100-400℃: The passivation film has good stability and still has corrosion resistance to dry dust (such as high-temperature sand dust in foundry) and weakly oxidizing gas (such as CO in welding smoke).

400-600℃: If there is water vapor or high-temperature gas containing sulfur and chlorine (such as sulfur-containing dust in chemical workshop) in the environment, it may accelerate the intergranular corrosion in the welding heat affected zone (due to the combination of carbon and chromium to form CRC, resulting in insufficient chromium content in some areas). Solution treatment (heating to 1050-1100℃ and rapid cooling after welding) is needed to restore the passive film, or low-carbon 304L stainless steel (carbon content ≤0.03%) is selected to reduce the risk of intergranular corrosion.

Thermal expansion needs to be controlled: for every 100℃ increase in temperature, the length of the pipeline will be extended by about 1.7mm per meter. If there are fixed brackets or rigid connections in the system, expansion joints (such as bellows) should be reserved to avoid stress caused by thermal expansion and contraction, which will lead to weld cracking or pipeline displacement.

IV. Extreme high temperature environment (> 600℃): The performance is obviously attenuated, so it is not recommended to use it for a long time.

When the temperature exceeds 600℃, the properties of 304 stainless steel will obviously deteriorate:

The mechanical properties drop sharply: at 650℃, the tensile strength drops to about 200MPa, and the yield strength is close to 1/3 of normal temperature. The pipeline is prone to plastic deformation (such as bending and bulging) due to its own weight or air impact, and the welded parts may crack due to insufficient strength.

Failure of oxidation resistance: at high temperature (especially > 800℃), the surface passivation film will be destroyed by oxidation, forming loose oxide scale (FeCr₂O₄), which leads to the rapid thinning of pipeline wall thickness and shortened service life to 1-3 years.

Application limitation: It can only be used in intermittent high-temperature scenes for a short time (such as the occasional emergency ventilation in a metal smelting workshop at 800℃), and the wall thickness and weld integrity of the pipeline should be tested regularly.

summary

The temperature adaptability of 304 stainless steel welded ventilation pipe shows the characteristics of "excellent in the middle and limited at both ends";

Normal temperature (0-100℃): It has the best comprehensive performance and is the first choice for ventilation and dust removal in most factories.

Low temperature (-196-0℃): the toughness and corrosion resistance are stable, suitable for low temperature environment.

Medium-high temperature (100-600℃): The performance needs to be maintained through material optimization (such as 304L), structural design (such as expansion joints) and process treatment (such as solution treatment), which can meet most industrial high-temperature scenes (such as drying workshops and heat treatment workshops).

Extreme high temperature (> 600℃): the performance is obviously degraded, so it is not recommended to use it for a long time, and it needs to be replaced by high temperature resistant stainless steel (such as 310S) or ceramic composite pipes.

In practical application, it is necessary to select the pipe thickness, welding technology and auxiliary design according to the continuous temperature, temperature fluctuation range and medium corrosiveness of the factory building to maximize its service life and safety.