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Corrosion can turn a seemingly minor fastener issue into a costly problem. Rusted or deteriorating bolts, screws, nuts, and washers can weaken connections, increase maintenance requirements, damage surrounding components, and shorten the life of an entire assembly.
But what actually causes fasteners to corrode? The answer isn't always simply exposure to water. Fastener corrosion can result from moisture, chemicals, incompatible metals, environmental conditions, or even choosing the wrong coating for an application.
Understanding the most common causes of corrosion can help manufacturers, contractors, engineers, and purchasing teams select fasteners that provide better long-term performance.
What Is Fastener Corrosion?
Corrosion is the deterioration of metal caused by chemical or electrochemical reactions with its surrounding environment. For steel fasteners, the most familiar form is rust — when iron in the steel reacts with oxygen and moisture, iron oxide forms and gradually deteriorates the material.
The speed and severity of corrosion depend on several factors:
- Fastener material and protective coating
- Moisture and humidity exposure
- Temperature
- Chemicals and contaminants
- Contact with dissimilar metals
- Installation environment
What Causes Fasteners to Corrode?
Moisture and humidity
Water is one of the most common contributors to fastener corrosion. Rain, condensation, high humidity, and frequent washdowns all accelerate deterioration. Especially critical for:
- Outdoor construction
- HVAC equipment
- Agricultural equipment
- Food processing facilities
- Marine and coastal applications
Salt exposure
Salt dramatically accelerates corrosion. Chlorides reach fasteners through saltwater, coastal air, road salt, deicing chemicals, and certain industrial processes. For marine and coastal environments, 316 stainless steel is commonly specified for its superior chloride resistance.
Chemicals and industrial environments
Fasteners in manufacturing and industrial settings may encounter cleaning agents, acids, solvents, process chemicals, fertilizers, and industrial fumes. A coating that performs well outdoors may not provide adequate protection in a chemical processing environment.
Galvanic corrosion
Occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte such as water. The less noble metal corrodes preferentially. The further apart two metals sit on the galvanic series, the greater the corrosion risk — so material compatibility across the entire assembly matters.
How Fastener Coatings Help Prevent Corrosion
Protective coatings create a barrier — or provide sacrificial protection — to help prevent the underlying steel from corroding. The two most common options are zinc plating and hot-dip galvanizing.
Zinc plating
Thin coating (~0.2–0.3 mils) via electroplatingGood corrosion resistance for indoor and general-purpose applications where moisture exposure is limited. The zinc layer corrodes sacrificially before the underlying steel.
Hot-dip galvanizing
Thick coating (~1.4–3.9 mils) via molten zinc bathSignificantly greater corrosion protection with a metallurgical bond to the base steel. The right choice for outdoor construction and applications with sustained moisture or weather exposure.
What About Stainless Steel?
Unlike coated carbon steel, stainless steel derives its corrosion resistance from the alloy itself. Chromium creates a thin passive oxide layer that protects the underlying metal — and if the surface is scratched, this layer reforms naturally when oxygen is present.
18-8 / 304 Stainless Steel
Excellent general corrosion resistance for outdoor, manufacturing, and food equipment applications. The most widely used stainless grade for industrial fasteners.
316 Stainless Steel
Contains molybdenum for superior chloride resistance. The preferred choice for marine, coastal, and chemically aggressive environments.
Can Installation Damage Cause Corrosion?
Yes. Even the right fastener can experience premature corrosion if its protective coating is damaged during installation. Scratches, chips, and abrasion can expose the underlying steel directly to the environment. Installation practices should minimize unnecessary coating damage, particularly when working with coated fasteners in corrosive environments.
Why Corrosion Matters Beyond Appearance
A rusty fastener may be unattractive, but corrosion isn't merely cosmetic. As it progresses, it affects:
How to Choose Fasteners for Corrosive Environments
Before selecting a fastener, consider the conditions it will face throughout its service life.
Frequently Asked Questions
Prevent Corrosion Before It Becomes a Problem
The best time to address fastener corrosion is before installation. Selecting the appropriate material, finish, and grade for the operating environment can help extend component life, reduce maintenance, and improve the reliability of the entire assembly.
Blue Ribbon Fastener supplies stainless steel, zinc-plated, hot-dip galvanized, and specialty-coated fasteners for manufacturing, construction, OEM, and industrial applications.