Detailed Explanation of Salt Spray Test Standards for Fasteners

Salt spray (or salt fog) testing is a corrosion test method used to evaluate the corrosion resistance of metal fasteners, such as bolts, nuts, and screws. By simulating a saline environment that accelerates corrosion, the test assesses the protective performance of coatings and platings. Test durations typically range from 24 to 1000 hours, depending on factors such as material type (e.g., carbon steel, stainless steel), surface treatment (e.g., electroplated zinc, Dacromet coating), and industry requirements (e.g., automotive, construction).

• Electroplated zinc fasteners: Neutral Salt Spray (NSS) test for 24–72 hours, white rust may appear.
• Hot-dip galvanized bolts (approx. 45μm coating): NSS test for 240–500 hours, no red rust.
• Dacromet-coated screws: NSS test for 100–1000 hours.
• Stainless steel nuts (316): NSS test for 480+ hours with no visible corrosion.

The primary national standard for salt spray testing of screws is:

GB/T 10125-2021: Artificial Atmospheres — Corrosion Tests — Salt Spray Tests

This standard outlines methods to expose fasteners to a simulated marine environment to evaluate their corrosion resistance. The purpose is to predict real-world corrosion performance, supporting design decisions, material selection, and manufacturing processes.

• Most common method
• Uses a 5% ± 0.5% NaCl solution
• Temperature: 35°C ± 2°C
• pH: 6.5–7.2
• Relative humidity: 85%–95%
• Salt fog fall-out rate: 1–2 mL/hour
• Test duration: 2–240 hours
• Applicable to: General metals and basic coatings (e.g., zinc-plated screws)

• Based on NSS but with added acetic acid
• pH: 3.1–3.3
• Test duration: 2–24 hours
• Faster corrosion rate
• Applicable to: Decorative electroplated coatings

• Based on AASS with added copper sulfate
• Temperature: 50°C ± 2°C
• Highly aggressive
• Test duration: 24–72 hours
• Applicable to: High-performance requirements (e.g., automotive components)