Webinar recap: Corrosion Accelerated Test with Controlled Humidity (CATCH)

Corrosion is a multi-billion dollar enemy of the automotive industry. As manufacturers shift toward lighter materials like aluminum to increase vehicle efficiency, testing of corrosion protection strategies must evolve. Our team recently hosted a webinar on the development of CATCH (Corrosion Accelerated Test with Controlled Humidity), a modern testing method designed by SAE China to bridge the gap between laboratory speed and real-world accuracy.

Traditional Salt Spray Tests

For decades, standards like ASTM B117 have been widely used for quality control. However, these older tests often fail to replicate real-world conditions because they don't control Relative Humidity (RH). Outdoor environments aren't just "wet" or "dry"; they spend a significant amount of time at intermediate values of RH (50-76% RH). Test that don't control RH at these values can miss completx chemistry and corrosion morphology, including effects from Galvanic Corrosion.

What is the CATCH Test?

Developed by SAE China, CATCH was created to harmonize testing protocols for domestic manufacturers while incorporating known best practices from existing international test cycles.

The CATCH cycle utilizes modern corrosion testers, such as the Q-FOG CRH chamber, to simulate a corrosive environment by including multiple step types:

1. Shower Phase: Short periods of application of a dilute, acidified salt solution.
2. RH Cycling: Linear transitions between high humidity (90%) and intermediate levels (70%) to mimic natural drying cycles.
3. Deep Dry: A final "extreme dry" phase (down to 20% RH) inspired by high-performance European standards.

Understanding the Test Method: Steel & Aluminum

To validate CATCH, Q-Lab and 30 other organizations (including Chinese domestic automakers and major OEMs like Ford and Volkswagen) conducted a massive study involving 5,000 specimens.

The Steel Phase

Researchers compared CATCH against four different outdoor environments, including marine seaside locations. The results showed that CATCH had a much higher correlation to outdoor results than older, less sophisticated tests.

The Aluminum Focus

As aluminum replaces steel for weight reduction, testing for filiform corrosion (thread-like decay under the paint) becomes critical. CATCH successfully reproduced the morphology (shape and type) of corrosion seen on vehicles driven in real-world "proving grounds" and outperformed traditional harsh tests like CASS (copper-accelerated acetic acid salt spray), which often over-corrode materials and provide "false failures."

The Future: CATCH 3.0

While the original test (pH 4.0) was shown to provides reliable results, test intervals were relatively long. A follow-on study found that by slightly increasing the acidity from ph=4.0 to pH=3.0, researchers could achieve the same results three times faster without losing accuracy. This faster, more acidified version is now an official national standard (TCSAE 130-2020).

Is the CATCH Test Right for You?

The CATCH test is designed primarily for evaluating automotive coatings on aluminum and steel substrates. Its primary advantage is providing a reliable correlation to real-world outdoor environments by accurately simulating the intermediate relative humidity zones where natural corrosion typically occurs.

Interested in performing CATCH testing? Contact our team today!

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Frequently Asked Questions

Q: What does "CATCH" stand for?

A: CATCH stands for Corrosion Accelerated Test with Controlled Humidity. It is a specialized test cycle designed to evaluate how well coatings protect automotive materials, specifically aluminum and steel, from corrosion.

Q: Why was the CATCH test developed if we already have standards like ASTM B117?

A: Traditional "salt spray" tests like ASTM B117 do not control relative humidity (RH). Since real-world environments spend a lot of time at intermediate humidity levels (50–76% RH), CATCH was developed to replicate these transitions, which are critical for accurate corrosion chemistry and morphology.

Q: What is the difference between CATCH 4.0 and CATCH 3.0?

A: CATCH 4.0: The original version with a pH of 4.0. It offers excellent correlation but takes a significant amount of time (up to 2,980 hours). CATCH 3.0: A more acidified version with a pH of 3.0. It provides the same accuracy as the original but is roughly three times faster, making it ideal for rapid quality control.