Stainless steel pipes are classified by material into ordinary carbon steel pipes, high-quality carbon structural steel pipes, alloy structural pipes, alloy steel pipes, bearing steel pipes, stainless steel pipes, as well as bimetallic composite pipes (to save precious metals or meet special requirements), and coated pipes. Stainless steel pipes come in a wide variety, with different uses, varying technical requirements, and diverse production methods. Currently produced pipes range in outer diameter from 0.1 mm to 4500 mm and in wall thickness from 0.01 mm to 250 mm. To distinguish their characteristics, pipes are usually classified according to the following methods. Production Method Stainless steel pipes are divided into two main categories based on production method: seamless pipes and welded pipes. Seamless pipes can be further categorized into hot-rolled pipes, cold-rolled pipes, cold-drawn pipes, and extruded pipes (cold drawing and cold rolling are secondary processing). Welded pipes include straight seam welded pipes and spiral welded pipes, among others. Cross-Sectional Shape Stainless steel pipes can be classified by cross-sectional shape into round pipes and shaped pipes. Shaped pipes include rectangular pipes, diamond pipes, oval pipes, hexagonal pipes, octagonal pipes, and various asymmetrical cross-section pipes. Shaped pipes are widely used in structural components, tools, and mechanical parts. Compared to round pipes, shaped pipes generally have larger moments of inertia and section moduli, offering greater resistance to bending and torsion, which can significantly reduce structural weight and save steel. Stainless steel pipes can also be classified by longitudinal section shape into constant cross-section pipes and variable cross-section pipes. Variable cross-section pipes include conical pipes, stepped pipes, and periodic cross-section pipes. Pipe End Shape Based on pipe end condition, stainless steel pipes can be classified as plain-end pipes and threaded pipes. Threaded pipes can be further divided into ordinary threaded pipes (for low-pressure applications like water and gas conveyance, using ordinary cylindrical or tapered pipe threads) and special threaded pipes (for oil and geological drilling; important threaded pipes use special thread connections). For some special-purpose pipes, to compensate for the weakening effect of threading on the pipe end strength, upsetting (internal upsetting, external upsetting, or internal-external upsetting) is usually performed before threading. Classification by Application By application, pipes can be categorized into: oil well pipes (casing, tubing, and drill pipe, etc.), line pipe, boiler tube, mechanical structural tube, hydraulic prop tube, gas cylinder tube, geological drill pipe, chemical industry pipes (high-pressure fertilizer pipe, petroleum cracking pipe), and shipbuilding pipe, etc. Stainless Steel Welded Pipe Production Process Decorative Welded Pipe: Raw Material -> Slitting -> Tube Welding -> End Finishing -> Polishing -> Inspection (Marking) -> Packaging -> Shipping (Warehousing) Industrial Welded Pipe (for Piping): Raw Material -> Slitting -> Tube Welding -> Heat Treatment -> Correction -> Straightening -> End Finishing -> Pickling -> Hydrostatic Testing -> Inspection (Marking) -> Packaging -> Shipping (Warehousing) Chloride Ions & Corrosion Chloride ions are widely present, for example in salt, sweat, seawater, sea breeze, soil, etc. Stainless steel corrodes rapidly in environments containing chloride ions, even exceeding the corrosion rate of ordinary mild steel. Chloride ions form complexes with iron (Fe) in the alloy, lowering the positive potential of Fe, which is then oxidized as oxidizing agents take away its electrons. Therefore, the operating environment for stainless steel must be carefully considered, and it needs to be wiped frequently to remove dust and kept clean and dry. 316 and 317 Stainless Steel Types 316 and 317 stainless steel are molybdenum-bearing grades. The molybdenum content in 317 stainless steel is slightly higher than in 316. Due to its molybdenum content, the overall performance of 316 stainless steel is superior to that of 310 and 304 stainless steels. At high temperatures, 316 stainless steel has a wide range of applications when sulfuric acid concentration is below 15% or above 85%. Type 316 stainless steel also offers good resistance to chloride ion corrosion, making it commonly used in marine environments.    

S321 Stainless Steel Equivalent Standard Grades: Corresponds to Chinese grade 1Cr18Ni9Ti, U.S. grades 321, S32100, TP321, and Japanese grade SUS321. Material Properties 2.1 Chemical Composition: Carbon (C) ≤ 0.08%, Silicon (Si) ≤ 1.00%, Manganese (Mn) ≤ 2.00%, Sulfur (S) ≤ 0.030%, Phosphorus (P) ≤ 0.035%, Chromium (Cr): 17.00–19.00%, Nickel (Ni): 9.00–12.00%, Titanium (Ti) ≥ 5×C%. The addition of Ti enhances resistance to intergranular corrosion but makes it unsuitable for decorative components. 2.2 Corrosion Resistance: Exhibits good corrosion resistance in organic and inorganic acids of varying concentrations and temperatures, particularly in oxidizing media. Prolonged heating in temperature ranges prone to chromium carbide formation may degrade corrosion resistance in harsh environments. Generally comparable to S347 in most environments but slightly inferior to annealed S347 in strongly oxidizing conditions. Mechanical Properties: Tensile strength (σb) ≥ 520 MPa, Yield strength (σ0.2) ≥ 205 MPa, Elongation (δ5) ≥ 40%, Reduction of area (ψ) ≥ 50%, Hardness ≤ 187 HB, ≤ 90 HRB, ≤ 200 HV. Offers better ductility and stress rupture resistance than 304 stainless steel at elevated temperatures. Weldability: Good weldability. Ti addition suppresses chromium carbide formation during welding, reducing intergranular corrosion risks. Requires controlled welding parameters (current, voltage, speed). Common methods include TIG and manual arc welding. Fabrication: Suitable for cold/hot working. Cold working may require intermediate annealing due to significant work-hardening. Hot working temperature: 1000–1150°C. Applications: Structural engineering (beams, bridges, transmission towers), industrial equipment (furnaces, reactors, pipelines), and high-temperature components (427–816°C), such as aircraft engine parts. Post-Weld Heat Treatment: Solution treatment (920–1150°C rapid cooling) is recommended for high-temperature or high-stress applications. Stabilization treatment (850–930°C) may be specified. Non-Destructive Testing (NDT): Ultrasonic and radiographic testing for internal defects. Fluorescent magnetic particle testing (enhanced sensitivity for magnetic zones) and penetrant testing for surface defects. S347 Stainless Steel Equivalent Standard Grades: 347, S34700, 0Cr18Ni11Nb. Material Properties 2.1 Chemical Composition: Carbon (C) ≤ 0.08%, Manganese (Mn) ≤ 2.00%, Nickel (Ni): 9.00–13.00%, Silicon (Si) ≤ 1.00%, Phosphorus (P) ≤ 0.045%, Sulfur (S) ≤ 0.030%, Niobium (Nb) ≥ 10×C%, Chromium (Cr): 17.00–19.00%. Nb addition improves resistance to intergranular corrosion. 2.2 Corrosion Resistance: Excellent resistance in acids, alkalis, and salts, with oxidation resistance up to 800°C. Similar to S321 in most environments but slightly superior in aqueous and low-temperature conditions. Designed for high-temperature applications requiring strong anti-sensitization to prevent intergranular corrosion. Mechanical Properties: Solution-treated: Yield strength ≥ 206 MPa, Tensile strength ≥ 520 MPa, Elongation ≥ 40%, Hardness ≤ 187 HB. Superior high-temperature stress rupture and creep resistance compared to 304 stainless steel. Weldability: Good weldability (TIG, submerged arc welding). Nb minimizes intergranular corrosion, but excessive heat input must be avoided. Fabrication: Similar to S321. Cold working requires attention to work-hardening; hot working temperature: 1050–1200°C. Applications: Aerospace, power generation, chemical/petrochemical industries. Common in high-temperature equipment (boilers, heat exchangers). Post-Weld Heat Treatment: Solution treatment is standard. Stabilization may be added for specific requirements. NDT: Similar to S321. Fluorescent magnetic particle and penetrant testing for surface defects. Key Differences & Selection Guidelines Sensitization Resistance: S347 (with Nb) outperforms S321 (with Ti) in post-weld and high-temperature anti-corrosion. Fabrication: S321’s Ti increases cold-working difficulty; S347’s Nb has less impact on workability. Cost: S347 is more expensive due to Nb scarcity. Summary: S347: Preferred for long-term high-temperature stability and weld reliability (e.g., boilers, aerospace). S321: Cost-effective for moderate/low-temperature applications (e.g., structural components, pipelines).

Product Overview 304 stainless steel, an austenitic stainless steel alloy, is renowned for its exceptional corrosion resistance, durability, and versatility. Composed of 18% chromium and 8% nickel (18/8 stainless steel), it is one of the most widely used stainless steel grades globally. Its balanced composition ensures superior performance across diverse environments, making it a cornerstone material in industries ranging from construction to food processing. Key Properties Corrosion Resistance: Resists oxidation and corrosion in mild environments, including exposure to water, acids, and atmospheric conditions. High Temperature Resistance: Maintains strength and stability at temperatures up to 870°C (intermittent) and 925°C (continuous). Formability and Weldability: Easily fabricated into complex shapes and welded without compromising structural integrity. Hygienic Surface: Non-porous and easy to clean, ideal for applications requiring strict hygiene standards. Aesthetic Appeal: Polished or brushed finishes provide a sleek, modern appearance for architectural and decorative uses. Advantages Over Competing Alloys Cost-Effectiveness: Offers a favorable balance between performance and cost compared to higher-grade alloys like 316 stainless steel. Wide Availability: Readily available in various forms (sheets, coils, tubes, bars) to meet diverse manufacturing needs. Sustainability: Fully recyclable, aligning with global efforts toward eco-friendly material practices. Applications Across Industries Food & Beverage: Used in kitchen equipment, storage tanks, and processing machinery due to its non-reactive nature. Architecture & Construction: Ideal for façades, railings, and structural components in both indoor and outdoor settings. Medical Equipment: Employed in surgical tools, sterilization trays, and hospital fixtures for its sterilizable surface. Chemical & Pharmaceutical: Utilized in tanks, piping, and reactors where resistance to corrosive substances is critical. Automotive: Components like exhaust systems and trim benefit from its heat resistance and aesthetic qualities.

The microsand ballasted high-efficiency sedimentation process is a solid-liquid separation clarification technology (similar to traditional sedimentation methods) that physically removes suspended solid particles from water. It also employs physico-chemical removal of dissolved phosphates through the addition of coagulants (aluminum/iron salts). By introducing microsand into the water, flocculation reactions form sand-core flocs, which are ultimately separated from the water. The high density of sand-containing flocs enables rapid settling, resulting in a surface loading rate far exceeding that of conventional high-efficiency sedimentation tanks. Microsand Properties: Material: Natural quartz sand with SiO₂ content > 98%. Particle size (d₁₀): 80–150 μm (adjusted based on application requirements). Density: 2650 kg/m³. Key Advantages: Enhanced Coagulation: Microsand increases collision frequency among particles, improving coagulation efficiency. Rapid Settling: The increased density of flocs accelerates sedimentation, significantly boosting the surface loading capacity of the tank. Sludge Compatibility: Microsand does not cause abrasion to existing sludge treatment systems. Sand-containing sludge can be conventionally disposed of or incinerated without adverse effects.