What are the specific requirements for the material of sanitary-grade stainless steel pipes

The pharmaceutical industry has extremely strict requirements for the material of sanitary-grade stainless steel pipes, which must meet core demands such as no pollution, corrosion resistance, easy cleaning, and compliance with Good Manufacturing Practice (GMP) for pharmaceutical production. The following provides a detailed explanation from aspects such as material characteristics, standard compliance, and performance requirements: 

I. Chemical Composition Requirements: Strict Control of Impurities and Alloy Elements

1. Main Stainless Steel Grades and Composition Restrictions

The commonly used grades in the pharmaceutical industry are 304 (06Cr19Ni10) and 316L (022Cr17Ni12Mo2). The chemical composition of these grades must meet the following key indicators (based on the ASTM A270 standard):

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2. Impurity Control

Recycled waste materials are prohibited. The raw materials must be pure to avoid the residue of heavy metals such as lead (Pb) and cadmium (Cd), to prevent contamination of the drugs.

The silicon (Si) content is usually ≤ 1.0%, to avoid affecting the surface polishing effect. 

II. Mechanical Properties and Machinability

1. Strength and Ductility

Tensile strength: ≥ 515 MPa (304/316L), yield strength: ≥ 205 MPa. This ensures that the pipeline is less likely to deform or crack during installation (such as bending, welding).

Elongation: ≥ 30%. This guarantees the machinability of the pipe material (such as cold bending, expansion), avoiding the formation of micro-cracks (cracks are prone to accumulate dirt and contaminants).

2. Welding Performance

It is necessary to use inert gas protection welding (such as TIG welding). The material must meet that there are no gas pores, slag inclusions, or incomplete fusion after welding. After welding, a passivation treatment (such as nitric acid passivation) should be carried out to restore the passivation film on the welding area, preventing corrosion.

Due to its lower carbon content, 316L has a much lower intergranular corrosion risk after welding than 304, making it more suitable for scenarios with frequent welding (such as pipeline system renovation). 

III. Corrosion Resistance: Adapting to the Multiple Challenges of Pharmaceutical Environments

1. Resistance to Chemical Corrosion

It can withstand acid/alkali solutions (such as hydrochloric acid, sodium hydroxide), organic solvents (ethanol, acetone), and disinfectants (hydrogen peroxide, ozone) during the pharmaceutical process.

Due to the presence of molybdenum in 316L, its corrosion resistance to chloride-containing media (such as physiological saline, purified water) is significantly superior to that of 304, and it is often used in water for injection (WFI) systems.

2. Resistance to Intergranular Corrosion

It must pass the ASTM A262 E test (bicarbonate immersion test) or the ASTM A262 C test (sulfuric acid - copper sulfate test) to ensure that no intergranular chromium carbide precipitates at the sensitization temperature (450-850°C), avoiding intergranular corrosion that leads to pipeline leakage or contamination.

3. Resistance to High Temperature and Steam Corrosion

It can withstand 121°C high-pressure steam sterilization (SIP), and the material does not undergo oxidation peeling or release metal ions (such as iron ion contamination of the medicine) at high temperatures. 

IV. Surface Treatment and Hygiene Characteristics

1. Surface Roughness (Ra Value)

The inner surface roughness should be ≤ 0.8 μm (the ideal value should be ≤ 0.4 μm), and the outer surface roughness should be ≤ 1.6 μm. A smooth surface can reduce the attachment of bacterial biofilms (as required by the FDA for drug contact surfaces "no cracks, no depressions").

Usually, electrolytic polishing (EP) is used to enhance the surface smoothness. After EP, a more uniform passivation film is formed on the surface, and the corrosion resistance is improved by more than 30% compared to mechanical polishing (MP).

2. No Pores and Adsorption Properties

The material should be dense and free of pores to avoid the residue of drugs or cleaning agents; the surface should not adsorb organic substances and must pass the "water contact angle test" (the contact angle should be ≥ 60° to ensure the surface is hydrophilic and easy to clean). 

V. Compliance and Certification Standards

1. International and Industry Standards

FDA (U.S. Food and Drug Administration): Compliant with 21 CFR Part 177.2400, ensuring no migration substances when the material comes into contact with the drug.

GMP (Good Manufacturing Practice for Pharmaceutical Products): The material must be traceable, and each batch of pipe material must provide a material certificate of analysis (COA), including chemical composition, mechanical properties, and surface treatment report. ISO 14644 (Cleanroom Standard):

For pipes directly in contact with drugs in Class A clean areas (sterile production environment), they must pass surface particle testing (≤ 0.5μm particle count ≤ 3520 per m³).

2. Biocompatibility Certification

Pipes that come into direct contact with drugs must comply with USP Class VI (U.S. Pharmacopeia Class VI) or ISO 10993 (Biological Evaluation of Medical Devices), passing tests such as cytotoxicity, sensitization, and irritation to ensure no biological toxicity. 

VI. Additional Requirements for Special Scenarios

1. Pure Steam System

The material must be 316L and must be certified by ASME BPE (Biological Processing Equipment Standard) to prevent the contamination of drugs by metal ions in the steam.

2. Aseptic Drug Production

The tubing must be able to withstand online sterilization (SIP) and chemical sterilization (such as formaldehyde fumigation), and the material should not undergo performance degradation (such as the detachment of the passivation film) after repeated sterilization.

3. High-Purity Medium Transportation

When transporting injection water (WFI) and purified water (PW), the total organic carbon (TOC) in the material must be ≤ 500 ppb, and the dissolved substances must be ≤ 0.5 ppm to avoid water quality contamination. 

VII. Material Selection and Application Scenario Comparison

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Summary

The pharmaceutical industry's requirements for the material of sanitary-grade stainless steel pipes are centered around "safety, no pollution, and traceability". From chemical composition, mechanical properties to surface treatment, all must meet strict standards to ensure that no impurities are introduced during the drug production process and no corrosion occurs. 316L, due to its excellent corrosion resistance, has become the preferred choice for sterile preparations and the transportation of high-purity media, while 304 is suitable for general scenarios with less corrosive conditions.