Coating failures on exhaust systems, silencers, and other heat-exposed steel components are more than a cosmetic issue. They can shorten service life, accelerate corrosion, and increase maintenance costs. High temperature coatings are designed to protect these parts from extreme heat, oxidation, and environmental wear, but even the best formulation can fail if the preparation and application are not done correctly.
This article explains why failures occur and how to prevent them, while introducing examples from Forrest Technical Coatings’ INFERNEX® line of high temperature coatings that are engineered for long-term performance in demanding thermal environments.
Steel used in exhaust systems, manifolds, silencers, and burner assemblies expands, contracts, and oxidizes through repeated heat cycles. These conditions require coatings that can handle sustained temperatures from 600 °F up to, and sometimes beyond, 1000 °F while maintaining adhesion and appearance.
High temperature coatings such as INFERNEX® powder and liquid formulations are created to meet these needs. They provide corrosion resistance and color stability when applied to properly prepared substrates. However, long-term success depends on how the surface is cleaned, blasted, and cured, not only on the chemistry of the coating itself.
Step 1: Clean the Surface Thoroughly
Most coating failures begin with poor surface cleaning. Oil, grease, cutting fluids, and fingerprints can all interfere with adhesion. Cleaning should follow SSPC-SP1 Solvent Cleaning standards, using xylene, toluene, or acetone with clean rags that are changed often. Avoid mineral spirits or treated wipes because they leave residues that block proper bonding.
A coating can only adhere to clean steel, not to contaminants or residues left behind during fabrication or handling.
Step 2: Create the Right Surface Profile
Abrasive blasting provides the mechanical anchor needed for a coating to grip the substrate.
The target surface profile is between 0.75 and 1.5 mils. Smooth or polished metal often leads to flaking and peeling once the part heats and expands.
Step 3: Control Environmental Conditions
Temperature and humidity directly affect how coatings cure. Ideal conditions are around 50 percent relative humidity with substrate and air between 50 °F and 80 °F. The metal should be at least 5 °F above the dew point to prevent condensation that can cause blistering or corrosion beneath the coating film.
Step 4: Apply the Correct Film Build
Applying too heavy a coating can trap solvents and cause early failure. Too thin a film may leave the surface unprotected. Typical INFERNEX® powder coatings perform best at 1.5 to 2.5 mils dry film thickness. Follow the recoat windows carefully so that each layer bonds properly and cures as a single, uniform film.
Step 5: Verify Proper Cure
Under-cured coatings may look acceptable at first but will degrade quickly when exposed to heat. For powders, verify cure based on the substrate temperature rather than the air temperature. For example, many formulations require 20 minutes at 400 to 450 °F. For liquid coatings, allow for solvent flash-off before heating and ensure in-service bake cycles are controlled. Rushing the cure can trap solvent and lead to bubbles, peeling, or early corrosion.
Step 6: Match the Coating to the Actual Heat Cycle
There is an important difference between peak temperature (short bursts) and continuous service temperature (sustained exposure). If the component runs continuously at 900 °F, a product rated for only 800 °F continuous service will eventually fail even if its peak rating is higher.
INFERNEX® coatings are formulated to maintain adhesion and corrosion resistance across a range of heat cycles, from moderate exhaust applications to extreme industrial service.
Preventing coating failure on exhaust systems and other high-heat steel components depends on controlling the variables that affect adhesion, cure, and long-term performance:
When these practices are followed, INFERNEX® high temperature coatings provide durable protection, helping engineers and job shops achieve consistent results while extending the life of metal components exposed to heat and corrosion.
Explore the INFERNEX® coating line —and check out our powder vs. liquid INFERNEX® comparison blog.