Which factors will affect the hygiene and safety performance of stainless steel pipes

Core conclusion: The key factors influencing the hygiene and safety performance of stainless steel pipes are concentrated in five dimensions: material itself, processing technology, surface treatment, installation and use, and compliance certification. Any deficiency in any of these aspects will lead to medium contamination, microbial growth, or the release of harmful substances, especially affecting the safety of use in sensitive industries such as food and medicine. 

1. Material foundation: The "inherent conditions" determining hygiene and safety

Material grade: Food-grade / pharmaceutical-grade stainless steel (such as 304, 316L, 2205) must be selected. Industrial-grade stainless steel (containing many impurities and poor corrosion resistance) is prohibited.

Contamination control: The content of heavy metals (lead, cadmium, mercury) and harmful non-metallic impurities must comply with FDA, GB 4806.9 standards. To avoid leaching into the medium.

Carbon content: Low-carbon materials (such as 316L, 2205) are better as they reduce the risk of intergranular corrosion and lower the probability of material leaching, especially suitable for welding scenarios.

Material purity: Use raw materials only, prohibit recycled materials (which are prone to contain unknown impurities and have a high risk of leaching), and provide material certificates (MTC). 

2. Processing techniques: Key steps to avoid "post-harvest contamination"

Forming process: Prioritize cold processing (cold bending, cold drawing), and prohibit hot processing (hot processing is prone to generating oxide scales that can fall off and contaminate the medium); the bending radius should be ≥ 3D, and avoid internal wall wrinkles (which can accumulate dirt and contaminants).

Welding process: Must use argon arc welding (TIG welding) + internal inert gas protection, and prohibit using ordinary welding rods for welding (which is prone to generating slag and pores); the welding wire must be of the same material as the base material (e.g., 316L uses ER316L, 2205 uses ER2209), and avoid material mismatch that leads to leaching.

Cutting and port treatment: Use laser / plasma cutting (without burrs), and after cutting, the sharp edges and burrs of the ports need to be removed (to avoid scratching the seals or leaving residues), and prohibit using ordinary grinding wheels for cutting (which generates iron filings and causes contamination).

Processing environment: Processing must be carried out in a clean workshop (free of dust and oil stains), and it is prohibited to mix with carbon steel tools (to prevent rust contamination), and during processing, avoid using non-food-grade lubricants (food-grade silicone oil can be used). 

3. Surface Treatment: Directly Affects Cleanliness and Microbial Control

Surface Roughness: The inner wall must be polished to Ra ≤ 0.8 μm (≤ 0.4 μm in highly clean scenarios), excessive roughness will lead to residue of the medium and microbial adhesion, making thorough cleaning difficult.

Polishing Process: Prefer electrolytic polishing (smooth surface, no polishing powder residue), use mechanical polishing with caution (easily causes scratches, residual polishing powder, difficult to clean); the inner wall polishing must be uniform, without local roughness or depressions.

Passivation Treatment: Must perform food-grade acid washing passivation (prohibited use of chromium-containing and heavy metal industrial passivators), form a dense passivation film to enhance corrosion resistance, avoid material oxidation and rusting; after passivation, rinse with deionized water until pH = 6-8, no residual chemicals.

Appearance Quality: No scratches on the surface (depth ≤ 0.1 mm), no oxide spots, no welding slag residue, the weld seam needs to be ground to be flush with the base material to avoid forming cleaning dead corners. 

4. Installation and Usage: Key Steps to Avoid "Secondary Pollution"

Connection Method: Preferentially choose sanitary compression type, quick-connect flanges or butt welding connections. Avoid threaded connections (threaded gaps are prone to retaining media and cannot be thoroughly cleaned); the sealing components used for connection must be FDA-certified materials (EPDM, PTFE), and ordinary rubber rings are prohibited (they are prone to aging and falling off).

Pipeline Layout: Slope ≥ 3‰ (for easy drainage and residue removal), no blind pipes (length ≤ 3 times pipe diameter), use large radius for elbows (≥ 3D), avoid right-angle hard bends (forming stagnant liquid dead zones).

Material Matching for Contact: Auxiliary components such as supports and bolts must be made of stainless steel or have stainless steel isolation pads. Direct contact of carbon steel with stainless steel pipes is prohibited (to prevent electrochemical corrosion and rust contamination).

Cleaning and Maintenance: Before installation, the inner wall must be rinsed with pure water (flow rate ≥ 1.5m/s) to remove transportation residues; during use, regular cleaning and sterilization (such as SIP sterilization) are required to avoid residual media breeding microorganisms. 

5. Compliance and Testing: The "Final Guarantee" for Hygiene and Safety

Comprehensive Certification: Must have food-contact stainless steel certification (GB 4806.9), FDA 21 CFR Part 175 certification. For pharmaceutical grade, a biocompatibility test report is also required.

Testing Compliance: Must pass dissolution tests (heavy metals, organic residue ≤ standard limit), microbial tests (bacterial count <10CFU/mL), and salt spray tests (no rust spots after 72 hours).

Traceability: Must retain material certificates, welding records, surface treatment reports, and test reports to facilitate GMP audits or quality traceability. Products without traceable information are prohibited. 

Key points for avoiding pitfalls:

Don't overlook "hidden risks": For instance, using industrial-grade 304 instead of food-grade, using mechanical polishing instead of electrolytic polishing, or using threaded connections in a sterile environment all pose hygiene safety hazards.

Matching process and material: For example, 316L welding requires ER316L welding wire, while 2205 requires ER2209 welding wire. Mixing different welding wires will cause the weld seam to corrode and dissolve.

Avoid excessive processing: For instance, excessive internal wall polishing (Ra <0.2μm) will reduce the adhesion of the passivation film and instead affect the corrosion resistance. The roughness should be controlled according to industry standards.