Stainless steel pipes: the “tubular core” for corrosion-resistant fluid transportation and structural support

In high-end industrial manufacturing and public projects, stainless steel pipe, with its combined advantages of "stainless steel's corrosion resistance and hollow tubular structure," has become the material of choice for demanding applications where carbon steel pipe cannot. Made from stainless steel billets or coils, and processed into tubular form through seamless rolling or welding, it inherits stainless steel's core properties of "passivation film corrosion protection, hygienic and eluting-free, and extreme environmental resistance," while also offering the functional characteristics of "low-resistance fluid transport and lightweight structural support." It is widely used in the food and pharmaceutical, marine engineering, new energy, high-end construction, and other fields, serving as a key carrier for "safe transportation and long-term support" in high-end industrial chains. I. Basic Concepts and Core Characteristics of Stainless Steel Pipes
The core composition of stainless steel pipes is the same as that of stainless steel plates/coils: iron (Fe) as the base, containing ≥10.5% chromium (Cr) (forming a dense passive film, Cr₂O₃, that blocks corrosive media from contacting the substrate), supplemented with alloying elements such as nickel (Ni) to enhance toughness and acid resistance and molybdenum (Mo) to enhance chloride ion corrosion resistance, and a carbon content of ≤0.12% to mitigate the risk of intergranular corrosion. The key difference lies in its "hollow tubular form and functional positioning": through processing, it forms a structure with open ends and a round, square, or special-shaped cross-section. Diameters range from 6mm (precision pipe fittings) to 3000mm (large-diameter welded pipe). Lengths are customizable (typically 6-12m, with large-diameter welded pipes up to 18m). Some thin-walled pipes can be supplied in coils (suitable for long-distance, seamless transportation). The combination of tubular structure and stainless steel provides three core benefits: first, long-lasting corrosion-resistant transport, eliminating the need for frequent replacement in environments such as acidic and alkaline environments, seawater, and high temperatures (its lifespan is 5-8 times that of carbon steel pipes); second, hygienic and safe compliance, with a smooth, non-porous surface and no coating peeling, meeting food-grade (GB 4806) and pharmaceutical-grade (GMP) standards; and third, lightweight support, weighing only 90% of carbon steel pipe under the same load (due to the higher strength of stainless steel), making it suitable for weight reduction needs in construction, marine applications, and other sectors.
II. Core Classification of Stainless Steel Pipes (Based on Manufacturing Process and Microstructure)
The classification logic for stainless steel pipes must take into account both the "pipe manufacturing process" and "stainless steel microstructure characteristics," which together determine its performance and application scenarios. The main classifications are as follows:
(I) Classification by Manufacturing Process (Core Dimension)
Seamless Stainless Steel Pipe: No welds, the preferred choice for high-pressure applications
Process: Made from stainless steel billets, the pipes undergo a process of heating and piercing (1100-1250°C), hot/cold rolling to size, and annealing and finishing. They have no welds and exhibit uniform mechanical properties throughout.​
Sub-Types and Features:

Hot-rolled seamless pipe: Thickness range 3-50mm, diameter 25-630mm, good toughness (elongation ≥35%), pressure rating 10-40MPa, surface scale (pickling required);

Cold-drawn/cold-rolled seamless pipe: Thickness 0.5-20mm, diameter 6-200mm, thickness tolerance ±0.05mm (far superior to hot-rolled), smooth surface (Ra ≤ 1.6μm), pressure rating up to 50MPa.

Core Advantages: No weld seams, strong impact and corrosion resistance, suitable for conveying high-pressure, high-temperature, and highly corrosive media.

Welded stainless steel pipe: Welded, cost-effective, and a major choice for large diameter pipes.

Process: Stainless steel coils are used as raw material, through slitting into steel strips, continuous forming (round/square), welding (high-frequency welding/submerged arc welding), and sizing. The cost is only 60%-70% of seamless pipe of the same specification.​
Sub-Types and Features:

Elongated Seam Welded Pipe (ERW): The weld seam is distributed along the length. Diameters range from 15-630mm, lengths range from 6-12m, pressure resistance ranges from 2-10MPa, and production efficiency is high (10-20 meters per minute).

Spiral Welded Pipe (SSAW): The weld seam is spiral. Diameters range from 219-3000mm. Single pipe lengths range from 12-18m. The weld seam distributes stress (better crack resistance than ERW), and pressure resistance ranges from 3-15MPa.

Laser Welded Pipe: High-precision welding with a narrow weld seam (≤1mm). Diameters range from 6-200mm, and thicknesses range from 0.3-3mm. Suitable for precision fluid transportation (such as pharmaceutical pipelines).

Core Advantages: Strong large-diameter manufacturing capabilities at low cost, suitable for low-pressure, high-flow applications. (II) Classification by Stainless Steel Structure (Performance Dimension)

Austenitic Stainless Steel Pipe (Approximately 75%)

Compositional Characteristics: Contains 18% Cr + 8% Ni (304), 16% Cr + 10% Ni + 2% Mo (316L). Non-magnetic and cannot be hardened by heat treatment.

Performance Advantages: Strong corrosion resistance (304 is resistant to room temperature acids and alkalis, 316L is resistant to seawater/chlorine corrosion), low-temperature brittleness (stable at -196°C), and excellent weldability. Representative Models and Applications:
304 Seamless Pipe: Food pipes (e.g., yogurt production lines, Φ25-50mm), household water pipes (e.g., water purifiers, Φ15-20mm), and architectural decorative pipes (e.g., guardrails, Φ50-100mm);
316L Seamless Pipe: Marine engineering pipes (e.g., desalination plants, Φ100-200mm), pharmaceutical reactor connection pipes (Φ32-65mm), and chemical hydrochloric acid pipes (Φ50-150mm);
304 Spiral Welded Pipe: Municipal drinking water pipes (Φ300-800mm, no secondary pollution), and food storage tank connection pipes (Φ200-400mm).
Ferritic Stainless Steel Pipe (approximately 20%)
Composition Characteristics: Contains 16%-20% Cr, contains no nickel (lower cost), is magnetic, and cannot be heat-hardened. Performance Advantages: Excellent oxidation resistance (stable from room temperature to 800°C), excellent thermal conductivity (1.5 times that of austenitic steel), and a price tag of only 60%-70% of 304 pipe.

Representative Models and Applications:

430 Longitudinal Welded Pipe: Building guardrails (Φ48-76mm, outdoor rain-resistant), appliance exhaust pipes (Φ32-50mm, high-temperature resistance to 400°C);

409L Longitudinal Welded Pipe: Automobile exhaust system pipes (Φ50-80mm, low-temperature corrosion resistance), water heater liner connection pipes (Φ20-32mm, low-cost, corrosion-resistant). Duplex/Martensitic Stainless Steel Pipe (approximately 5%)
Duplex stainless steel pipe (2205, 2507): Contains 21%-25% Cr, 3%-5% Ni, and 2%-4% Mo, with a 50% austenite/50% ferrite ratio. Its strength is twice that of 304 and its chloride corrosion resistance is superior to 316L. It is used for offshore platform oil pipelines (Ø150-300mm) and desulfurization tower flue pipes (Ø200-400mm).
Martensitic stainless steel pipe (410, 420J2): Contains 12%-17% Cr and high carbon (0.1%-1.2%). It is quench-hardenable (hardness HRC50+). It is used for tool blanks (Ø10-30mm) and valve core pipes (Ø20-50mm). Polishing is required to improve corrosion resistance. (III) Classification by Surface Treatment and Cross-Section (Functional Derivation)
Surface Treatment: Pickled tubes (to remove oxide scale for subsequent welding), Polished tubes (Ra ≤ 0.8μm, for food and pharmaceutical applications), Nickel-plated tubes (to improve salt spray resistance, for outdoor decoration), Anti-corrosion Coated tubes (3PE coating, for buried chemical pipes);
Cross-Sectional Shapes: Circular tubes (mainstream, accounting for over 85%, for fluid transportation), Square tubes (for building guardrails, furniture frames, Φ20×20-100×100mm), Rectangular tubes (for curtain wall support, Φ30×50-80×120mm), Special-Shaped tubes (such as oval tubes and grooved tubes, for decorative purposes).

III. Key Performance Advantages of Stainless Steel Pipes (Comparison of Carbon Steel Pipes and Stainless Steel Sheets/Coils)

The performance advantages of stainless steel pipes are the combination of stainless steel's corrosion resistance and tubular structure functionality, precisely addressing the core pain points of high-end applications:

Corrosion Resistance: From "Frequent Maintenance" to "Maintenance-Free"

The corrosion rate of 304 stainless steel pipe in tap water is only 0.001mm/year (compared to approximately 0.1mm/year for carbon steel pipes), eliminating the need for painting. The corrosion rate of 316L stainless steel pipe in seawater is 1/20 that of carbon steel pipe, enabling its use on offshore platforms (carbon steel pipes rust and perforate within 1-2 years). Duplex 2205 pipes are resistant to 20% hydrochloric acid corrosion (which instantly dissolves carbon steel pipes), making them a perfect replacement for expensive Hastelloy pipes.

Hygiene and Safety: "Zero Substitution" in the Food and Pharmaceutical Industry

Smooth, non-porous surface (polished tube Ra ≤ 0.4μm), no risk of coating peeling, and autoclavable (121°C steam). Compliant with GB 4806.9-2016 food contact standards. Carbon steel pipe paint can easily peel and contaminate food. Stainless steel sheets/coils must be processed into tubing for transportation and cannot be directly adapted for piping applications.

Adaptable to Extreme Environments: Covers high and low temperatures and harsh media.

Low-temperature applications: 304 seamless pipe exhibits no brittleness when transporting liquid nitrogen at -196°C (carbon steel pipe cracks at -40°C), making it suitable for cryogenic storage tank connections.

High-temperature applications: 310S stainless steel pipe exhibits stability in 1100°C flue gas (carbon steel pipe oxidizes and scales at 600°C), making it suitable for high-temperature furnace flues.

High-corrosion applications: 316L seamless pipe withstands 98% sulfuric acid (concentration ≤ 50%) and is suitable for chemical acid transportation. Full-Lifecycle Cost-Effectiveness: "High Initial Cost + Low Lifecycle Cost"
The initial price of 304 stainless steel pipe is 3-4 times that of carbon steel pipe, but it has a service life of 20-50 years (compared to 5-10 years for carbon steel pipe) and requires no painting or maintenance (the average annual maintenance cost for carbon steel pipe is 15 yuan/m2). For example, the total cost of 304 welded pipe over 50 years is approximately 220 yuan/m2, while the cost of carbon steel pipe (including maintenance) is approximately 380 yuan/m2, making it more economical in the long run.

IV. Key Application Areas of Stainless Steel Pipes

Stainless steel pipes' corrosion resistance and tubular properties make them a dominant force in high-end applications not covered by carbon steel pipes. Key applications are as follows:

(I) Food and Pharmaceuticals (approximately 25%)

Food Processing: 304 polished seamless pipes (Ø15-50mm) for juice/dairy product delivery pipes (weld-free, contamination-resistant); 304 straight seam welded pipes (Ø80-150mm) for food storage tank connection pipes (easy to clean);

Pharmaceutical Manufacturing: 316L cold-rolled seamless pipes (Ø10-32mm) for pharmaceutical reactor feed pipes (GMP-compliant); 316L laser-welded pipes (Ø6-20mm) for vaccine delivery pipes (high precision, seamless sterilization). (II) Marine Engineering and Water Treatment (approximately 20%)
Offshore Platforms: 2205 duplex steel seamless pipes (Ø100-300mm) for platform oil pipelines (seawater corrosion resistant), 316L spiral welded pipes (Ø500-1200mm) for seawater cooling pipes (high flow);
Water Treatment: 304 straight seam welded pipes (Ø200-800mm) for municipal drinking water pipes (no secondary pollution), 316L seamless pipes (Ø50-100mm) for seawater desalination reverse osmosis membrane connection pipes (resistant to high-salinity wastewater). (III) New Energy and Chemical Industry (approximately 25%)
New Energy: 316L seamless pipes (Φ20-50mm) for hydrogen transport pipes (resistant to hydrogen permeation); 304 ultra-thin seamless pipes (Φ8-15mm) for lithium battery slurry transport pipes (resistant to electrolyte corrosion);
Chemical Industry: 316L seamless pipes (Φ32-100mm) for hydrochloric acid/sulfuric acid transport pipes (resistant to severe corrosion); 2205 duplex steel welded pipes (Φ200-500mm) for desulfurization tower flue pipes (resistant to chlorine-containing flue gases). (IV) Architectural Decoration and High-end Equipment (approximately 20%)
Architectural Decoration: 304 square tubes (Φ30×30-80×80mm) for stair railings/guardrails (aesthetically pleasing and corrosion-resistant); 304 mirror-finished seamless tubes (Φ50-100mm) for hotel curtain wall supports (bright finish);
Automotive Industry: 409L straight seam welded tubes (Φ32-50mm) for automobile exhaust pipes (resistant to high-temperature oxidation up to 400°C); 316L seamless tubes (Φ10-20mm) for new energy vehicle battery cooling tubes (electrolyte-resistant);
Precision Machinery: 304 cold-rolled seamless tubes (Φ6-20mm) for medical devices (such as surgical catheters); 316L seamless tubes (Φ8-15mm) for aerospace hydraulic hoses (high-pressure and corrosion-resistant).
V. Future Development Trends of Stainless Steel Pipes

With the upgrade of high-end manufacturing and the advancement of the "dual carbon" goal, stainless steel pipes are developing towards "nickel conservation, high performance, greenness, and customization":

Nickel conservation: reducing costs and alleviating resource dependence

Developing "nickel-free/low-nickel stainless steel pipes": Ferritic 443 welded pipe (21% Cr, no Ni), with corrosion resistance approaching that of 304 pipe, is 30% cheaper and is used for building guardrails; Duplex 2101 pipe (1.5% Ni, only one-fifth the strength of 304), with a strength of 550 MPa, is used in chemical pipelines, replacing high-nickel austenitic pipes. High Performance: Breaking Through Extreme Scenarios

Developing "super-corrosion-resistant stainless steel pipes": Hastelloy C276 composite pipes (stainless steel base + Hastelloy surface layer), resistant to 98% sulfuric acid, for use in high-end chemical applications; and "ultra-high-temperature pipes" (HR3C steel), capable of withstanding temperatures up to 1250°C, for use in supercritical power plant boilers, replacing nickel-based alloy pipes.

Green Manufacturing: Carbon Reduction and Emission Reduction, Recycling

Promoting the "short-process steelmaking - seamless pipe" process: Using scrap stainless steel as raw material (instead of iron ore), electric arc furnace steelmaking reduces carbon emissions by 70% compared to the traditional long process; developing "chromium-free passivation technology" (replacing hexavalent chromium) to reduce heavy metal pollution; establishing a stainless steel pipe recycling system, achieving a recycling rate of over 95% for scrap pipes, which are then re-smelted into new pipes. Customization: Adapting to Specific Scenarios

We offer special specification pipes: ultra-thin-wall seamless pipes (0.1mm thick, 2-6mm Φ) for microsensors; ultra-large-diameter spiral welded pipes (over 3000mm Φ) for ultra-large chemical storage tanks; and special-shaped pipes (such as internally threaded pipes and corrugated pipes) for enhanced heat exchange (in automotive cooling systems).

Conclusion
Stainless steel pipes, combining the corrosion resistance of stainless steel with the transportation and support functions of pipes, address the pain points of carbon steel pipes (easily corroded and difficult to meet hygiene requirements) while also addressing the need for secondary processing of stainless steel sheets/coils into tubular form. They have become an irreplaceable material for safe transportation and long-term support in the high-end industrial chain. From sterile piping in food processing plants to corrosion-resistant oil well pipes in deepwater, from battery cooling pipes for new energy vehicles to decorative railings in high-end hotels, stainless steel pipes are used across the entire spectrum of "people's livelihoods, precision manufacturing, and extreme environments." In the future, with breakthroughs in nickel-saving technologies, high-performance alloy research and development, and green processes, stainless steel pipes will further reduce costs and expand their boundaries, becoming a "key foundational component" supporting global high-end manufacturing and infrastructure upgrades.