Water Used Pipe

Water-related industrial carbon steel pipes serve as the backbone of industrial systems for water conveyance, circulation, cooling, wastewater treatment, and reclaimed water reuse. With cost-effectiveness, mechanical compatibility, and easy installation, these pipes are widely used in power generation, chemical processing, metallurgy, municipal water supply, and textile dyeing industries. Their core requirements include adapting to water environment corrosion, meeting varying water pressure and temperature demands, while ensuring airtightness and operational stability during transportation.

I. Core Features and Water Environment Compatibility Requirements

Industrial carbon steel pipes exposed to water must prioritize resistance to water corrosion, scale formation, and temperature-pressure fluctuations. Their core features include water corrosion resistance, pressure adaptability, scale prevention, and easy processing.

1. Basic Mechanics and Pressure Resistance

Industrial water conveyance systems operate under extensive pressure ranges (municipal water supply 0.2-1.0MPa, industrial circulating water 1.0-4.0MPa, and high-pressure cooling water at 4.0-10MPa), requiring carbon steel pipes to meet specific yield and tensile strength requirements. Standard materials typically exhibit yield strengths of 235-345MPa and tensile strengths of 410-550MPa, with wall thicknesses (3-20mm) adjustable to accommodate varying pressure demands. Seamless or welded structures (depending on diameter) must be defect-free to prevent high-pressure water leakage. Seamless pipes are better suited for high-pressure applications, while welded pipes are more suitable for medium and low-pressure scenarios.

2. Water Resistance and Corrosion Resistance Properties

Water media containing oxygen, carbon dioxide, chloride ions, hardness ions, and microorganisms can readily cause carbon steel pipes to suffer from oxygen corrosion, electrochemical corrosion, scaling corrosion, and microbial corrosion. Therefore, the pipes must possess fundamental corrosion resistance capabilities: First, they should be manufactured from low-sulfur and low-phosphorus carbon steel to reduce corrosion-sensitive impurities. Second, targeted anti-corrosion treatments are required, such as internal wall coatings with epoxy coal tar pitch, cement mortar linings, or galvanization, while external walls may employ anti-corrosion paints or 3PE simple coatings. Third, water quality adjustments should be implemented, such as adding corrosion inhibitors to circulating water to reduce corrosion rates (the conventional requirement is an annual corrosion rate ≤0.1mm/a).

3. Temperature Resistance and Scale Resistance

Industrial water systems operate across a wide temperature range (typically from ambient to 150°C, including boiler feedwater and high-temperature cooling water). High temperatures accelerate corrosion and scaling. Carbon steel pipes must meet specific temperature resistance requirements, with conventional applications suitable for temperatures ≤120°C. For high-temperature water environments (120-150°C), heat-resistant carbon steel (e.g., 20G grade) is required. Additionally, the inner pipe surfaces must maintain a high level of smoothness (roughness ≤12.5μm) to minimize scale formation. This prevents pipe diameter reduction, reduced heat transfer efficiency, and intensified localized corrosion caused by scaling.

4. Processing and Installation Compatibility

Industrial water pipeline installation involves complex routing requiring frequent cutting, welding, and bending operations. Carbon steel pipes demonstrate excellent weldability and plasticity, with stable mechanical properties after welding. They support various connection methods including flanges and grooves, ensuring on-site installation flexibility. Dimensional accuracy must meet specifications: ±1.0% for outer diameter tolerance and ±1.5% for wall thickness tolerance, guaranteeing airtight joints to prevent water leakage.

II. Common Materials, Types, and Implementation Standards

Water-related industrial carbon steel pipes are categorized into seamless and welded types based on production processes. Material selection must consider water quality, temperature, and pressure, while strictly adhering to national standards. The specific classifications are as follows:

III. Core Production Process

Water-related industrial carbon steel pipe manufacturing processes are categorized into seamless and welded pipe techniques, with core procedures designed to ensure material uniformity, minimize defects, and enhance water resistance.

1. Seamless Carbon Steel Pipe Manufacturing Process (High-Pressure Water Environment Compatible)

Core process: Round tube blank (carbon steel grades 20#, Q345A, etc.) →Heating (1100-1250°C)→Piercing (obtaining hollow tubes via inclined rolling piercing) →Continuous rolling/diameter adjustment (controlling outer diameter and wall thickness for dimensional accuracy) →Cooling (air/water cooling to prevent grain coarsening) →Straightening→Non-destructive testing →Anti-corrosion treatment (internal wall painting, galvanizing, etc.) →Hydrostatic test →Finished product inspection →Warehousing.

Features: Weld-free construction, high pressure resistance, smooth inner surface, resistant to scaling and corrosion, suitable for industrial water conveyance under high pressure, high temperature, and complex water conditions.

2. Welding Process for Carbon Steel Pipe (Designed for Medium/Low Pressure Water Environments)

(1) Straight seam welded pipe: Carbon steel coil →Uncoiling and leveling →Forming (rolling into round pipe) →High-frequency welding (continuous seam formation) →Deburring→Diameter setting →Cooling→Anti-corrosion treatment →Hydrostatic test →Storage;

(2) Spiral seam welded pipe: Carbon steel coil →Forming (spiral rolling) →Submerged arc welding (seam is secure) →Straightening→Pipe cutting →Anti-corrosion treatment →Hydrostatic test →Storage.

Key features: High production efficiency, low cost, and a wide diameter range (DN100-DN2000), making it ideal for municipal water supply and sewage treatment applications requiring high flow rates and low pressure. Rigorous weld inspection is essential to prevent leaks.

3. Zinc-coated carbon steel pipe manufacturing process (compatible with clean low-pressure water)

Core process: Carbon steel pipe (seamless/welded) →Pickling (removing surface oxide scale) →Cleaning→Hot-dip galvanizing (immersion in molten zinc at 450°C to form a galvanized layer) →Cooling→Passivation (enhancing corrosion resistance of the galvanized layer) →Inspection→Storage.

Key features: The galvanized coating with a minimum thickness of 85μm effectively prevents water contact with carbon steel, significantly reducing corrosion rates. This makes it ideal for both domestic water supply and clean industrial water applications.

IV. Key Quality Inspection Points

Given the unique characteristics of water environments, water-related industrial carbon steel pipes require rigorous testing of sealing performance, corrosion resistance, and dimensional accuracy. The key inspection items are as follows:

1. Sealing test (core testing item)

Hydraulic Testing: All finished pipes must undergo hydraulic testing, pressurized to 1.5 times the rated pressure (≥0.6MPa for low-pressure pipes), maintained for over 30 minutes, with no leakage or permanent deformation to be deemed qualified. High-pressure steel pipes must additionally undergo a gas tightness test to ensure stable operation under high-pressure water conditions.

2. Non-destructive testing (defect detection)

Seamless steel pipes: Ultrasonic testing (UT) detects 100% internal defects (porosity, cracks), while eddy current testing (ET) identifies surface defects.

-Welded steel pipes: The welds shall undergo radiographic testing (RT) or ultrasonic testing, with a sampling rate of no less than 30%, to ensure the absence of defects such as incomplete fusion, porosity, or cracks, thereby preventing water-mediated penetration corrosion.

3. Corrosion Resistance Testing

-Galvanized pipes: Measure the thickness of the galvanized coating (using a coating thickness gauge), adhesion (grid test, ensuring no peeling of the galvanized layer), and salt spray resistance (neutral salt spray test for ≥48 hours without corrosion).

-Anti-corrosion coated pipes: Test coating adhesion, thickness, and water immersion resistance (no wrinkling or peeling after 72-hour immersion);

-Raw materials: Analyze sulfur and phosphorus content in carbon steel to ensure low levels, thereby enhancing corrosion resistance.

4. Dimension and Appearance Inspection

-Dimensional inspection: Laser diameter gauge and wall thickness gauge are used to measure outer diameter, wall thickness, and ovality to ensure compliance with tolerance requirements;

-Visual inspection: Examine the surface visually or under magnification for cracks, dents, rebarbing, or residual oxide scale. Ensure the galvanized pipe surface is free from exposed base or peeling.

V. Application and Maintenance Considerations

1. Precise scenario selection

-High-pressure and high-temperature water (e.g., boiler feedwater, high-temperature cooling water): Use 20G, Q345A seamless carbon steel pipes, with epoxy coating applied to the inner walls when necessary.

-For medium and low-pressure high-flow water systems (e.g., municipal water supply or circulating water): Use Q235B straight/spiral-welded steel pipes to reduce costs.

-Clean low-pressure water (e.g., domestic or electronic industry water supply): Use galvanized carbon steel pipes or internally polished seamless steel pipes.

-For highly corrosive water (e.g., wastewater or chlorinated cooling water), use 20# seamless steel pipes with either cement mortar lining or epoxy coal tar coating.

2. Installation and Construction Requirements

-Welding control: Seamless steel pipes shall be constructed with argon arc welding for base metal and electric arc welding for filler metal. Post-weld slag removal shall be performed promptly, and post-weld heat treatment shall be conducted when necessary to prevent stress corrosion of welds. Welded pipe seams shall be polished smooth to prevent scaling.

-Sealing protection: Flange connections utilize rubber or metal-wrapped gaskets to meet water environment sealing requirements; groove connections require secure clamping to prevent leakage.

-Anti-corrosion connection: During installation, avoid damaging the galvanized layer or anti-corrosion coating, and promptly repaint any damaged areas; use gentle bends at pipeline turns and diameter changes to reduce localized corrosion caused by water impact.

3. Operation and Maintenance Points

-Water Quality Management: Regularly monitor water quality parameters (pH value, chloride ion concentration, hardness), maintaining pH within the range of 7.5-9.0 to prevent excessive acidity or alkalinity that may accelerate corrosion; add corrosion inhibitors and scale inhibitors to the circulating water to prevent scaling and corrosion.

-Regular inspection: Conduct annual thickness measurement of pipeline walls using ultrasonic thickness gauges, with particular attention to elbows, valve proximity areas, and regions with water quality fluctuations. Pipes showing a wall thickness reduction exceeding 10% require immediate replacement.

-Anti-corrosion maintenance: Inspect the external wall anti-corrosion coating every 2-3 years, and inspect the internal wall coating or galvanized layer every 5 years. Repairs should be promptly made for any damaged areas. For pipelines in long-term disuse, drain internal water to prevent internal wall corrosion.