When processing stainless steel fittings, it is important to avoid particle contamination and moisture; otherwise, the stainless steel will suffer severe corrosion
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The heating coil used in a certain factory is covered with 304-type stainless steel (with a coating thickness of 0.2–0.3 mm). It is stored at the construction site for 3 to 5 years before being used. During installation, it was found that nearly 20% of the heating coils were broken, and the heating coils received just now had cracks in many places. There are numerous brownish-red rust spots on the surface of the coil, with cracks starting from these rust spots. The cause of corrosion is the contamination of the stainless steel coil surface with iron particles during processing, which rust under humid conditions. Corrosion products are hygroscopic, thereby causing corrosion beneath the deposits. In the marine atmosphere at the construction site, the adsorption and concentration of chloride ions are accelerated, leading to stress corrosion cracking. Therefore, in the processing and manufacturing of stainless steel equipment, it is necessary to prevent surface damage and contamination, especially iron particle contamination. This is because the corrosion resistance of stainless steel comes from its ability to form a passive surface layer that creates a protective film on its surface. Many factors can cause the breakdown of the passivation film; for example, active ions in the environment (with chloride ions being the most common) can lead to localized damage of the passivation film, thereby triggering local corrosion such as pitting, crevice corrosion, and stress corrosion cracking.
When processing and storing stainless steel fittings, it is indeed necessary to pay special attention to the following points to prevent corrosion: 1. **Avoid particle contamination**: During the processing stage, it is important to keep the working environment clean to prevent foreign substances such as iron particles from adhering to the surface of the stainless steel. Iron particles tend to rust in humid environments. This rust not only directly damages the surface of stainless steel but can also cause electrochemical corrosion, accelerating the degradation of the stainless steel. 2. **Prevent moisture absorption**: Stainless steel materials should be stored in a dry environment to avoid prolonged exposure to humidity. Humid environments promote the rusting of iron particles, and the hygroscopicity of the corrosion products exacerbates local corrosion issues. 3. **Protection of the surface passivation film**: The corrosion resistance of stainless steel stems primarily from its surface passivation film. During processing and use, materials and tools that may damage the passivation film, such as ordinary steel tools, should be avoided. At the same time, contact with harmful chemicals should be avoided, especially those containing chlorine, as chloride ions are a common factor that damages the passivation film. 4. **Regular inspection and maintenance**: Stainless steel equipment that is stored or used for extended periods should be inspected regularly to identify and address issues such as rust and cracks in a timely manner. This includes physical inspections and, if necessary, chemical tests to assess the integrity of the passivation film and the overall condition of the equipment. By adopting these preventive measures, the service life and safety of stainless steel equipment can be significantly improved, thereby avoiding economic losses and safety incidents caused by corrosion. .