In the world of infrastructure and manufacturing, corrosion is the “silent killer.” For metals submerged in harsh environments, like the salty, turbulent depths of the ocean, protection isn’t just a preference; it’s a necessity.
But how do we know which coatings actually work? That’s where ASTM G31 comes in.
What is ASTM G31?
ASTM G31 is the gold standard guide for Laboratory Immersion Corrosion Testing of Metals. Rather than a rigid, “one-size-fits-all” procedure, ASTM G31 serves as a comprehensive guide for designing tests that simulate real-world immersion conditions.
The guide covers every critical variable that can influence how a metal reacts to its environment, including:
- Test Conditions: Solution composition, temperature, and fluid motion.
- Apparatus & Sampling: How specimens are supported and the volume of solution used.
- Interpretation: Calculating corrosion rates and identifying pitfalls that could lead to misleading results.
Why is This Test Important?
The primary goal of ASTM G31 is to promote better correlation of results and reduce conflicting reports. Because different metals and alloys respond uniquely to environmental factors, a standardized approach to recording data ensures that when a coating claims to protect a metal, that claim is backed by rigorous, scientific observation.
Real-World Results: CoilSafe® vs. The Gulf of Mexico
To put these standards to the ultimate test, Coat Zone conducted a massive field exposure evaluation on Galveston Island, Texas. Using the principles of ASTM G31, we submerged metal samples to a depth of 3 meters in the sea for a staggering 26,200 hours.
The environment was brutal: continuous exposure to chloride ions, tidal flows, and seasonal temperature cycling.
The Methodology
Three common industrial metals, Aluminum, Galvanized Steel, and Stainless Steel, were tested. Each sample was “half-and-half”: one side was left bare, while the other was protected by CoilSafe®, an 8-micron covalent film.
The Results
The contrast between the coated and uncoated sections was night and day. After nearly three years of submersion, the results verified by CZI labs showed:
| Parameter | CoilSafe® Coating | Uncoated Metal |
| Corrosion | None | Severe |
| Pitting | None | Heavy |
| Microbial Growth | Slight | Severely Degraded |
| Adhesion | Covalent Bond | N/A |
While the uncoated sections suffered from extensive deterioration driven by chloride-driven corrosion, the CoilSafe® sections exhibited complete corrosion resistance.
The Verdict
The Galveston Island test proves that when it comes to extreme submersion, the right science makes all the difference. By following the rigorous guidelines of ASTM G31, Coat Zone has demonstrated that their 8-micron covalent film provides a nearly impenetrable barrier against the ocean’s most corrosive elements. Learn more here.