1. Introduction
For heavy-duty engineering, wind power, bridge, municipal and offshore supporting projects, ordinary electro-galvanized fasteners can no longer meet long-term anti-corrosion requirements. Dacromet and Hot Dip Galvanized (HDG) are currently the two mainstream heavy-duty anti-corrosion surface treatment processes for high-end industrial fasteners.
Most overseas buyers only know that “both are heavy anti-rust treatments” but cannot distinguish their core differences in temperature resistance, hydrogen embrittlement risk, salt spray life, assembly performance and project cost. This leads to wrong material selection, hidden safety hazards in high-temperature and vibration working conditions, or unnecessary cost waste.
Different from conventional galvanizing processes, Dacromet solves the pain points of hydrogen embrittlement and high-temperature peeling of hot-dip galvanizing, while HDG has absolute advantages in ultra-long outdoor weather resistance. We provide customized Dacromet and hot-dip galvanized high-strength fastener solutions for global heavy engineering projects to help customers accurately select processes and balance safety and cost performance.
2. Process Principle & Core Characteristic Differences
2.1 Dacromet Coating Process
Dacromet, also known as zinc-chromium coating, is a non-electrolytic inorganic coating process. It forms a uniform silver-gray protective film on the fastener surface through dipping and low-temperature baking (below 300°C). The coating is thin, smooth, non-polluting, and features no hydrogen embrittlement, high temperature resistance and excellent friction matching. It is a new environmental protection heavy anti-corrosion process widely used in high-end equipment and wind power industries.
2.2 Hot Dip Galvanized (HDG) Process
Hot-dip galvanizing is a traditional high-temperature immersion anti-corrosion process. Fasteners are soaked in 450°C molten zinc liquid to form a thick zinc-iron alloy layer. The coating has strong weather resistance and ultra-long outdoor service life. However, the high-temperature process is prone to hydrogen embrittlement on high-strength bolts, and the thick coating will affect thread assembly accuracy, with poor high-temperature resistance.
3.1 Hydrogen Embrittlement Risk (High-Strength Bolt Hard Rule)
Dacromet: Zero hydrogen embrittlement risk. The whole process is low-temperature baking without pickling and electrolysis, which will not cause hydrogen penetration. It is the standard safe process for 10.9 and 12.9 high-strength bolts, completely avoiding sudden brittle fracture hazards.
Hot Dip Galvanized: High hidden danger of hydrogen embrittlement. High-temperature immersion and acid washing processes easily lead to hydrogen residue inside high-strength steel. Long-term vibration and load operation may cause sudden bolt fracture, which is prohibited in many high-end wind power and precision heavy industries.
Dacromet: Excellent high-temperature resistance, stable working at 300℃–500℃ for a long time, no coating peeling, discoloration or failure. It is suitable for high-temperature equipment, thermal power and heat-dissipating structural fasteners.
Hot Dip Galvanized: Poor temperature resistance. The zinc layer will soften, oxidize and turn white at temperatures above 200°C, resulting in rapid coating peeling and loss of anti-corrosion ability. It cannot be used in high-temperature working conditions.
3.3 Salt Spray Life & Weather Resistance
Dacromet: Thin and dense coating, stable neutral salt spray life of 500–800 hours. It has excellent corrosion resistance in chemical, humid and coastal mild salt spray environments, with uniform and beautiful appearance.
Hot Dip Galvanized: Super thick alloy coating, salt spray life up to 1000–2000 hours. In open-air, windy, sandy and strong ultraviolet outdoor environments, the weather resistance is far better than Dacromet, with an outdoor service life of more than 10 years.
Dacromet: Coating thickness is only 5–10μm, smooth surface, no thread occlusion, no need for secondary thread trimming, original thread precision is completely retained, and the locking torque is stable.
Hot Dip Galvanized: Coating thickness 60–120μm, easy to cause thread jamming. Secondary tooth cleaning and matching are required, with large friction deviation and unstable locking torque.
4.1 Unit Price Difference
Dacromet process costs are higher than conventional hot-dip galvanizing. The raw material formula and low-temperature baking process determine its high-end process positioning, suitable for high-value-added high-end equipment supporting.
Hot-dip galvanizing has mature technology and low unit price for mass production, which is more cost-effective for large-scale civil engineering and municipal projects.
4.2 Long-Term Project Comprehensive Cost
For high-end precision, high-temperature and high-strength bolt projects, Dacromet avoids hydrogen embrittlement failure and later maintenance risks, with lower comprehensive failure cost. For long-term outdoor open-air bridge and municipal facilities, hot-dip galvanizing has longer weather resistance life and stronger long-term cost performance.
5. Exclusive Applicable Scenarios (Zero Mistake Selection Standard)
5.1 Must-Choose Dacromet Working Conditions
Wind power equipment, new energy precision structural fasteners
10.9/12.9 high-strength bolt supporting projects (avoid hydrogen embrittlement)
High-temperature thermal power, industrial furnace and heat-resistant equipment
Chemical workshop, mild acid-base corrosive environment
High-precision thread assembly scenarios requiring no tooth trimming
5.2 Must-Choose Hot Dip Galvanized Working Conditions
Long-term open-air bridges, guardrails, municipal infrastructure
Coastal ports, wharf facilities, strong salt spray and ultraviolet environment
Large-scale steel structure engineering, outdoor power tower facilities
Civil engineering projects with large volume and cost-sensitive budget
6. Overseas Procurement High-Frequency Pitfalls
Pitfall 1: Confuse heavy anti-corrosion standards. Think all heavy-duty anti-rust processes are universal, and use HDG for high-strength bolts, causing hydrogen embrittlement hidden dangers.
Pitfall 2: Ignore high-temperature failure. Use hot-dip galvanized fasteners for high-temperature equipment, resulting in rapid peeling and rusting.
Pitfall 3: Over-pursue low cost. Use ordinary galvanizing instead of Dacromet for wind power and new energy projects, failing project acceptance.
Pitfall 4: Neglect assembly precision. Use HDG fasteners for precision thread matching, causing thread jamming and assembly failure.
7. FAQ
Q1: Is Dacromet better than hot dip galvanized? A: No absolute superiority. Dacromet is good for high temperature, high strength and precision scenarios; HDG dominates outdoor long-term weather resistance.
Q2: Can hot-dip galvanized bolts be used for 12.9 grade high-strength bolts? A: Not recommended. It is easy to cause hydrogen embrittlement fracture, and Dacromet is the standard matching process.
Q3: How long is the service life of Dacromet fasteners? A: It can maintain stable anti-corrosion performance for 3–5 years in humid and chemical environments, suitable for high-end equipment long-term operation.
Q4: Do you support customized heavy anti-corrosion fasteners for wind power projects? A: Yes. We provide Dacromet and HDG customized fastener solutions for global wind power, bridge and heavy industry projects with complete test reports.
