When selecting stainless steel seamless pipes suitable for high-purity gas pipelines, it is necessary to focus on four core dimensions: gas purity requirements, working conditions, industry standards, and processing and installation needs. Based on these, a precise match should be made in accordance with specific application scenarios. Here are the structured selection steps and key points:

I. Prioritize the determination of the stainless steel grade (selecting the core material) 

The stainless steel grade directly determines the corrosion resistance, cleanliness and chemical stability of the pipeline. It needs to be selected based on the type of gas, purity level and environmental humidity. 

304/304L stainless steel 

Application scenarios: Suitable for inert gases (such as nitrogen and argon) with moderate purity requirements, dry compressed air, ordinary industrial high-purity gas transportation, and scenarios without strict limits on carbon content. 

Core advantages: Moderate cost, high versatility, easy surface passivation treatment, meeting the requirements of conventional cleanliness levels. 

Key difference: 304L is a low-carbon type (with carbon content ≤ 0.03%), preventing the formation of chromium carbide during high-temperature welding, which can cause intergranular corrosion. It is more suitable for long-distance pipeline systems that require welding. 

316/316L stainless steel 

Application scenarios: Applicable to high-purity, highly corrosive gases or those containing trace amounts of halogens, such as electronic special gases (fluorine gas, chlorine gas), moist hydrogen, medical high-purity gases, and high-purity gases for use in marine environments. 

Core advantage: Adding molybdenum element (2% - 3%), the resistance to pitting and crevice corrosion is enhanced by 5 to 10 times compared to the 304 series. The low-carbon 316L is more suitable for applications where no solution treatment is required after welding. 

Industry preference: For high-purity gas pipelines in high-end fields such as semiconductors, photovoltaics, and biomedicine, 316L stainless steel is the preferred material. 

Special stainless steel (such as 316Ti, 317L, and Hastelloy alloy) 

Application scenarios: Suitable for extremely harsh conditions involving ultra-high purity (above 99.999%) and highly corrosive gases (such as hydrogen chloride, hydrogen fluoride), as well as high temperatures and high pressures (above 300℃, above 20MPa). 

Features: High cost, difficult to process. It is only used when conventional stainless steel cannot meet the requirements. 

II. Matching pipeline specification parameters 

The pipe diameter, wall thickness and accuracy grade should be determined based on the gas flow rate, pressure and installation space. 

Pipe diameter (nominal diameter DN) 

Based on the gas flow rate formula: The recommended flow rate for high-purity gases is 5 to 15 m/s (for flammable and explosive gases, the lower limit is taken, and for inert gases, the upper limit is taken). Avoiding too fast a flow rate to prevent the generation of static electricity or turbulence. 

Common specifications: DN6, DN8, DN10, DN15, DN20 (mainly small diameters, suitable for small flow rate transportation of high-purity gases). 

Wall thickness (SCH grade) 

According to the ASME B36.10M wall thickness standard, select based on the working pressure: 

Low-pressure condition (≤ 1 MPa): Select SCH10S thin-walled pipe to reduce costs and installation weight; 

Medium and high pressure conditions (1 - 10 MPa): Use SCH40S standard thickness tubes; 

Ultra-high pressure conditions (＞10 MPa): Select SCH80S and above thick-walled pipes to ensure structural strength. 

Note: The wall thickness should be reserved with an allowance for corrosion. In humid or corrosive gas environments, it can be appropriately increased. 

Accuracy level

For high-purity gas pipelines, cold-drawn (cold-rolled) pipes should be selected. These pipes have high precision grades and the inner wall surface finish Ra is less than or equal to 0.8 μm (for electronic grade, Ra should be less than or equal to 0.2 μm); hot-rolled pipes have lower precision and rougher inner walls, and are not suitable for high-purity applications. 

III. Pay attention to surface treatment processes (the key to ensuring cleanliness) 

The inner wall cleanliness of high-purity gas pipelines is extremely demanding. Therefore, a suitable surface treatment method needs to be selected: 

Pickling and Passivation 

Basic processing technology: removes surface oxide scale and oil stains, forms a dense Cr₂O₃ passivation film, preventing the release of metal ions and pollution of gases. Suitable for medium-purity gas pipelines. 

Electrolytic Polishing (EP) 

High-end processing technology dissolves the protruding parts on the surface through electrochemical action, reducing the roughness of the inner wall to 0.1-0.2 μm. The surface becomes smooth without any dead corners, preventing particle accumulation and bacterial growth. 

Required scenarios: Semiconductor, biomedicine, and ultra-high purity gas (such as electronic specialty gases) transportation pipelines. 

Vacuum cleaning + Packaging 

The processed pipelines need to undergo vacuum cleaning in a clean workshop to remove residual impurities. Then, they should be sealed and packaged with high-purity nitrogen gas to prevent secondary contamination during transportation and installation. 

IV. Adhering to Industry Standards and Certifications 

Ensure that the pipeline complies with the specifications for transporting high-purity gases, and avoid potential quality risks: 

Domestic standards: GB/T 14976 (Stainless steel seamless tubes for fluid transportation), GB/T 30063 (Technical Specifications for Stainless Steel Pipelines for High-Purity Gases). 

International standards: ASTM A269 (medical / food-grade stainless steel tubes), ASTM A312 (austenitic stainless steel seamless tubes), ISO 9001 quality certification. 

Industry-specific certification: In the semiconductor field, it must comply with the SEMI standards; in the biopharmaceutical field, it must meet the FDA certification requirements. 

V. Considering both processing and installation requirements 

Welding compatibility: Select pipe materials that can be welded using high-purity argon arc welding (TIG welding). During the welding process, high-purity argon gas protection (purity ≥ 99.999%) must be adopted to prevent weld oxidation or contamination. 

Connection method adaptation: For small-diameter pipelines, the socket-type connection (such as VCR joints) is preferred as it offers good sealing performance and is convenient for disassembly and assembly; for large-diameter pipelines, flange connections are used, and metal gaskets (such as stainless steel spiral wound gaskets) need to be used in combination. 

Adaptability to low temperature/high temperature: For low-temperature conditions (such as the transportation of liquid oxygen and liquid nitrogen), the low-temperature toughness of the pipe material must be confirmed to avoid low-temperature cracking; for high-temperature conditions, a grade with good heat resistance (such as 316Ti) should be selected.