304 square tube, a widely used stainless steel pipe, relies primarily on the chromium oxide film formed on its surface for corrosion resistance. However, the stability of this protective film varies significantly in different corrosive environments, which in turn affects the pipe's service life. In normal humid environments, such as outdoors or indoors in high-humidity areas, 304 square tube performs relatively stably. The chromium oxide film effectively isolates moisture from the pipe substrate, typically preventing noticeable corrosion. However, if impurities such as dust and pollutants are present, these impurities will adhere to the pipe surface and combine with moisture to form a localized electrolyte. Over time, this can damage the integrity of the oxide film, resulting in pitted rust on the pipe surface. This affects the appearance but does not pose a threat to the pipe's structural safety.
In acidic environments, the corrosion resistance of 304 square tube decreases significantly, especially in strong acidic media such as hydrochloric acid and sulfuric acid. The acid reacts rapidly with the chromium oxide film, destroying the film's tightness. When the acid concentration is high or the temperature rises, the corrosion rate accelerates further, resulting in uniform corrosion on the pipe surface, manifested as increased surface roughness, gradual thickness reduction, and even the formation of holes in severe cases, directly affecting the pipe's structural strength. In weakly acidic environments, such as the acetic acid environment used in food processing, 304 square tube exhibits relatively good corrosion resistance. However, long-term exposure still requires careful concentration control. If the acid concentration exceeds a certain range, slow corrosion will also occur.
Alkaline environments have different effects on 304 square tube than acidic environments. In low-concentration alkaline environments, such as soapy water and detergent solutions in daily life, 304 square tube exhibits relatively stable corrosion resistance, and the chromium oxide film is not easily damaged. However, when the alkaline concentration and temperature rise, such as the concentrated sodium hydroxide solution used in industrial production, the alkaline substances react with the iron in the pipe, causing intergranular corrosion on the pipe surface. This corrosion begins at the grain boundaries within the pipe and is difficult to detect in the early stages. However, once discovered, it often has already seriously affected the pipe's mechanical properties, reducing its impact resistance and load-bearing capacity.
The marine environment is one of the harshest corrosive environments for 304 square tubes. Seawater contains large amounts of chloride ions, which are highly penetrating and can easily penetrate the protective chromium oxide film and react with the tube substrate. In marine atmospheres, salty moisture forms a salt film on the tube surface, inducing pitting and crevice corrosion, manifesting as dense, small rust spots. Furthermore, in seawater immersion, in addition to chloride ion corrosion, microorganisms in the seawater adhere to the tube surface, forming a biofilm, further accelerating the corrosion process and causing localized perforations or fractures. Therefore, when using 304 square tube in marine-related projects, special attention must be paid to corrosion resistance.
It is crucial to adopt targeted protective measures for 304 square tubes based on the characteristics of different corrosive environments. In normal humid environments, the primary protective measure is regular cleaning. Wipe the tube surface with clean water or a neutral detergent to remove attached dust and impurities and prevent the formation of localized electrolytes. Maintain a well-ventilated, dry environment to reduce humidity, minimize the residence time of moisture on the tube surface, and slow the breakdown of the oxide film. For pipes with minor pitting rust, gently polish with a specialized stainless steel cleaner. After removing the rust, wipe dry immediately to restore surface cleanliness.
In acidic or alkaline environments, the key to protection is to isolate the pipe from direct contact with corrosive media. Depending on the type and concentration of the media in the environment, appropriate coatings can be selected for protection. For example, spraying a corrosion-resistant epoxy resin coating or polytetrafluoroethylene coating on the pipe surface can form a dense protective film, preventing acidic and alkaline substances from contacting the pipe surface. Furthermore, the concentration and temperature of the media must be strictly controlled during use to avoid exceeding the corrosion resistance range of 304 square pipe. If high-concentration corrosive media cannot be avoided, consider installing a corrosion-resistant lining in areas of contact with the media to further enhance protection.
For environments with high chloride ion concentrations, such as those in the ocean, in addition to conventional cleaning and coating, cathodic protection can be used. This involves attaching sacrificial anodes, such as zinc blocks, to the surface of the 304 square pipe. Using electrochemical principles, the sacrificial anodes corrode preferentially, thereby protecting the pipe substrate from damage. Furthermore, during pipe processing and installation, surface defects such as scratches and cracks should be avoided, as these defects can easily become starting points for corrosion. Surface damage caused during processing can be repaired through grinding and polishing to ensure the integrity of the chromium oxide film. Furthermore, regular corrosion testing of pipes, such as ultrasonic testing or penetrant testing, can be performed to promptly identify potential corrosion issues and implement appropriate repair measures to ensure the safe and stable use of 304 square tube in complex corrosive environments.
