Zinc coatings - Guidelines and recommendations for the protection against corrosion of iron and steel in structures - Part 3: Sherardizing
1Key Takeaways
This document provides guidance and recommendations on general design principles applicable to articles subjected to zinc diffusion for corrosion protection. The protection provided by a zinc-dipped coating depends on the coating application method, the design of the article, and the specific environment in which it is…
2Expert Interpretation
This in-depth analysis of the ISO 14713-3:2017 international standard for thermal diffusion galvanizing covers key technical points such as design specifications, surface treatment requirements, coating thickness control, and threaded component clearance adjustment, providing standardized solutions for steel structure corrosion protection.
Analysis of the core content of the standard
Scope of application and process principles
This standard applies to the technical specifications for anti-corrosion protection of steel structures through the thermal diffusion galvanizing process (Sherardizing).
- Processing temperature: 300-500℃ (usually lower than the melting point of zinc 419℃)
- Coating thickness: 10-75μm (can be customized to be thicker)
- Typical applications: scaffolding connectors, fasteners, chains and other wear-resistant parts
Comparison of key technical requirements
| Elements | Conventional galvanizing | Thermal diffusion galvanizing |
|---|---|---|
| Process temperature | ≥419℃ (molten zinc) | 300-500℃ (solid state diffusion) |
| Coating characteristics | Pure zinc layer + zinc-iron alloy layer | All zinc-iron alloy structure (hardness 350HV) |
| Threaded parts clearance | According to ISO 10684 specification | An additional 120-900μm is required (see Table 1) |
Critical process control points
Surface preparation requirements
Sand blasting must be used to remove oxide scale and oil stains to avoid the risk of hydrogen embrittlement caused by pickling. 10
Special Material Handling Recommendations
High Strength Steel and Spring Steel
For materials with tempering temperature within the process range:
- Requires a low-temperature process of 320-380℃
- Processing time extended by 1-2 hours
- Spring parts should be processed in a free state
Limitations for large components
The standard processing container size is 2000×480×400mm. Oversized components require:
- Separate processing and then assembly
- Use special equipment (such as large processing systems for the oil and gas industry)
Implementation Notes
Post-treatment process selection
Post-treatment scheme recommended by the standard:
- Phosphating treatment: Improve paint adhesion
- Chromate passivation: Prevent white rust during storage
- Lubrication treatment: Adjust the friction coefficient of threaded parts
Storage and transportation specifications
To prevent coating damage:
- Pipes should be stored vertically
- Threaded parts need to be protected separately
- Use sealed containers for transportation in humid environments