In ductile iron pressure piping systems, fasteners (such as bolts, nuts, and gaskets), though small, are critical components for ensuring the tightness, structural integrity, and safe operation of pipe connections. EN4016, “Ductile iron pipes, fittings, and accessories – Drinking water supply – Requirements and test methods,” sets clear technical requirements for fasteners used in such pipes. This article provides basic information about fasteners based on this standard.
The EN4016 standard not only covers ductile iron pipes and fittings themselves, but also specifically specifies the performance, materials, and corrosion protection of the fastener systems used to connect them (including bolts, nuts, and washers). Selecting and using fasteners that comply with this standard is fundamental to ensuring the compliance and safety of the entire piping system.
Basic Requirements for Fasteners
According to EN4016, fasteners used in ductile iron pipes (particularly those used for drinking water supply) must meet the following basic requirements:
1. Material and Mechanical Properties
- Bolts: should generally be made of materials with sufficient strength and toughness, such as carbon steel or alloy steel. Their mechanical property grade should be at least 8.8 (denoting a nominal tensile strength of 800 MPa and a yield strength ratio of 0.8). For higher pressure applications, bolts with a strength of 10.9 or higher may be required.
- Nuts: should match the bolt’s property grade, typically using grade 8 or 10 nuts, to ensure a consistent connection and prevent thread stripping.
- Forgeability: should have good forgeability and machinability to ensure the absence of internal defects.
2. Threads should conform to ISO metric thread standards (e.g.,ISO68-1, ISO261)，be clean, complete, and free of burrs, cracks, and other defects to ensure smooth engagement between the bolt and nut.
3. Dimensions and Tolerances must comply with the tolerance requirements specified in the design drawings and relevant standards (such as EN ISO 4014 and EN ISO 4032) to ensure interchangeability and consistency in assembly.
Because ductile iron pipes are often used underground or in humid environments, and because they transport drinking water, the corrosion resistance of fasteners is extremely high. EN4016 has strict regulations on this:
1. Corrosion Risk
Carbon steel fasteners are highly susceptible to electrochemical corrosion in humid environments. Severe corrosion can lead to bolt breakage, joint leakage, and even pipe system failure.
For contact with drinking water, the anti-corrosion coating must be non-toxic, odorless, and non-affective to water quality.
2. Recommended Anti-Corrosion Coatings, EN 4016 recommends the following anti-corrosion treatments for drinking water environments:
Hot-dip galvanizing (HDG): This is a very common and effective protection method. After pickling and fluxing, the fasteners are immersed in molten zinc to form a dense zinc-iron alloy layer and a pure zinc layer.
Requirement: The thickness of the galvanized layer must meet relevant standards (such as ISO 10684), typically requiring an average thickness of at least 50μm to ensure long-term corrosion protection. Dacromet/Zinc-Chromium Coating: A hydrogen-embrittlement-free corrosion-resistant coating technology, formed by applying a slurry composed of zinc powder, aluminum powder, and chromic acid and then baking it at high temperature.
Advantages: Excellent corrosion resistance (typically superior to hot-dip galvanizing of equivalent thickness), no risk of hydrogen embrittlement, and a uniform coating.
Fully complies with the hygienic requirements for materials in contact with drinking water.
Epoxy Coating: A tough epoxy resin protective film is applied to the fastener surface using methods such as electrostatic spraying.
Advantages: Excellent chemical resistance and aesthetically pleasing appearance. However, the coating must be intact and free of damage, as this can cause corrosion.
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Post time: Sep-19-2025
