ISO 2531 Explained: Complete Technical Guide for Ductile Iron Pipes in Water Supply Systems

 1. Standard Positioning and Technical Evolution

ISO 2531 is the core international standard for ductile iron pipes for water conveyance developed by the International Organization for Standardization (ISO), under the jurisdiction of ISO/TC 5 (Black Metal Pipes Committee). The latest version has replaced the 1998 fifth edition, with key technical features including:

• Pressure classification is based on the Permitted Working Pressure (PFA), defining C25/C30/C40 grades, replacing the traditional wall thickness coefficient method and transforming design from empirical values to mechanical modeling.

• China's national standard GB/T 13295 adopts this standard equivalently with modified adaptations (MOD) based on local engineering requirements.

• Covers the full range of DN40-DN2600 pipes and fittings, applicable to the conveyance of drinking water, gas, and other fluids, with pressure uniformly measured in bars (1 bar = 100 kPa).

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2. Core Technical Parameter Requirements

1. Material and Mechanical Properties

• Metallographic structure: Graphite spheroidization rate ≥ 80%; pearlite content ≤ 20% for small-diameter pipes (DN ≤ 300) and ≤ 25% for large-diameter pipes (DN ≥ 600).

• Mechanical performance: Tensile strength (Rm) ≥ 420 MPa; Brinell hardness must comply with ISO 6506 testing standards.

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2. Dimensions and Tolerances

3. Pressure Ratings and Test Standards

3. Technical Specifications for Fittings and Joints

1. Fitting Classification

• Elbow fittings: 90°/45°/22.5° double-socket bends, covering DN40-DN2600 diameters.

• Branch fittings: Full-socket T-joints classified into three ranges by diameter: DN40-250, DN300-700, and DN800-2600.

• Special provisions: The PFA value of tee fittings may be lower than that of straight pipes of the same diameter and must be marked separately.

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2. Joint Sealing Requirements

• Flexible joints: Push-on (Type T) for underground pipe networks; mechanical joints (Types N1/X/S) for high-constraint areas.

• Flange connections: Dimensions comply with ISO 7005-2; pipe pressure-bearing capacity ≥ flange PN rating (e.g., PN25 flanges require C25 or higher grade pipes).

• Sealing materials: Rubber gaskets must meet ISO 4633 drinking water hygiene standards.

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4. Coating and Anti-Corrosion Systems

1. External Protective Coatings

2. Internal Lining Requirements

• Cement mortar lining: Complies with ISO 4179, with thickness 3-6mm for DN80-DN600; no sand particle detachment on the surface.

• Special coatings: Epoxy resin coatings (0.3-0.5mm) for high-sulfate or soft water environments.

• Repair specifications: For damage areas ≤ 5cm²/m², zinc repair paste may be used for patching.

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5. Quality Control and Engineering Application

1. Testing Requirements

• Sealing tests: C30 grade pipes must maintain 41 bar pressure for 2 hours in internal pressure tests (pressure fluctuation ±0.5 bar); pressure drop ≤ 0.09 bar at -0.9 bar in negative pressure tests.

• Type tests: ISO 10804-1 deflection tightness testing is required for design changes.

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2. Engineering Application Specifications

• Selection principles: C40/C30 for main pipelines, C25 for branch pipes; additional radial toughness design required for seismic zones.

• Installation requirements: Backfill with fine-grained soil compacted in layers to avoid damaging the zinc coating; flexible joint deflection ≤ design limits (e.g., 2° maximum for DN500).

• Maintenance requirements: Regular monitoring of pipe-to-soil potential; damaged linings repaired with 2:3:1 cement/sand/108 adhesive mixture.

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6. Industry Trends and Standard Value

• Technical evolution: Application of C100 grade fittings, intelligent fittings integrated with stress-sensing modules, and solvent-free epoxy coatings replacing traditional asphalt paints.

• Lifecycle value: Material optimization through wall thickness formulas; 30% strength improvement via centrifugal casting compared to sand casting; 50-year maintenance-free service life reducing municipal costs by 20%.

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ISO 2531 establishes a water pipeline safety system through material standardization (graphite spheroidization rate ≥ 80%) and mechanical modeling (wall thickness formula). Combined with intelligent monitoring and eco-friendly material applications, it continues to lead technological development in water supply infrastructure.

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DAWN | Pig Iron & Castings Procurement Advisor
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