Why Corrosion Protection Matters for Shims
Pipe support shims are permanently installed in outdoor environments where they are exposed to rain, humidity, salt spray, and temperature extremes. Without proper corrosion protection, bare carbon steel shims will rust and deteriorate, reducing their load-bearing capacity and compromising pipe support integrity over time.
Selecting the right shim material and coating for your environment is essential for long-term reliability and to avoid costly replacement during maintenance shutdowns.
Hot-Dip Galvanized Shims
Hot-dip galvanizing is the most common corrosion protection method for steel shims used in pipeline construction. The process involves immersing the steel shim in molten zinc, which bonds to the surface and provides both a physical barrier and sacrificial cathodic protection.
Advantages of Hot-Dip Galvanized Shims
- Long service life: 25 to 50 years or more in most outdoor environments
- Self-healing: Minor scratches and damage are protected by the surrounding zinc
- Cost-effective: Less expensive than stainless steel while providing excellent corrosion resistance
- Compatible with galvanized steel: No galvanic corrosion when used with galvanized structural steel
- Industry standard: Widely accepted and specified on pipeline and industrial projects
Thickness Considerations
The zinc coating added during hot-dip galvanizing typically adds 0.003 to 0.005 inches (75 to 125 microns) per side. For precision shimming applications, this additional thickness must be accounted for when specifying shim dimensions. Some specifications require shims to be galvanized before final thickness verification.
Other Corrosion Protection Options
Shim Material Comparison
- Stainless steel (304/316): Best corrosion resistance, required for marine and chemical environments. Higher cost but no coating needed.
- Hot-dip galvanized carbon steel: Good corrosion resistance for most outdoor environments. Cost-effective and widely available.
- Zinc-plated carbon steel: Thinner zinc layer than hot-dip, suitable for indoor or sheltered applications. Lower cost but shorter outdoor life.
- Bare carbon steel: No corrosion protection. Only suitable for indoor, climate-controlled environments.
- Brass/bronze shims: Used in specialized marine and naval applications where galvanic compatibility is critical.
Galvanic Corrosion Concerns
When dissimilar metals are in contact in the presence of moisture, galvanic corrosion can accelerate the deterioration of the less noble metal. This is a common concern at pipe supports where shims, structural steel, and pipe shoes may be made of different materials.
- Carbon steel shim on stainless steel: The carbon steel will corrode faster. Use stainless shims or isolate with non-metallic pads.
- Galvanized shim on galvanized steel: No galvanic issue. This is the preferred combination.
- Stainless shim on carbon steel: The carbon steel support will corrode faster. Apply protective coating to the support or use galvanized shims instead.
Environment-Based Selection Guide
- Inland, dry climate: Galvanized or bare carbon steel shims are sufficient
- Coastal or marine: Stainless steel 316 or heavily galvanized shims are recommended
- Chemical plant: Stainless steel shims matched to the process environment
- Arctic or extreme cold: Impact-rated steel with galvanized or stainless coating
- Buried or underground: Heavy galvanized or epoxy-coated shims with cathodic protection
Tracking Shim Materials Digitally
When a project uses multiple shim materials across different areas or systems, tracking which material is installed at each support becomes critical for maintenance and future inspections. ShimSheet lets you record not just shim dimensions but also material type at each support point, ensuring your as-built records capture the complete picture.
Track Shim Materials and Dimensions Together
Use ShimSheet to record shim thickness, material type, and coating at every pipe support. Generate reports that include complete material documentation.
Try ShimSheet FreeFrequently Asked Questions
Should I use galvanized or stainless steel shims?
Galvanized shims are suitable for most outdoor pipeline applications and are more cost-effective. Stainless steel is recommended for marine, coastal, or chemical environments where higher corrosion resistance is needed.
Does galvanizing affect shim thickness?
Yes. Hot-dip galvanizing adds approximately 0.003 to 0.005 inches per side. For precision applications, verify final dimensions after galvanizing.
What causes galvanic corrosion at pipe supports?
Galvanic corrosion occurs when dissimilar metals are in contact with moisture present. Use matching materials (galvanized on galvanized, stainless on stainless) or isolating pads to prevent it.