A few years back, customers started asking Legacy if there was better corrosion protection than hot-dipped galvanising (HDG). HDG presented some problems in highly corrosive environments, not least of which is the fact that it doesn’t really stop corrosion but merely slows it down. It is also a frame finish that is difficult to repair once damaged.
There were enough drawbacks to HDG that the company started looking into epoxy coatings for its steel frames. Legacy constructs its tension fabric buildings with tapered solid steel I-beams and many of its customers are in industries where corrosion is very significant:
The company recently completed a storage structure for Northern Coop in northern Minnesota, US. Brent Benike, General Manager for Northern Coop, says it best: “Everything that fertilizer dust touches wants to corrode.”
After Legacy started getting requests for alternatives to HDG, the company began to investigate epoxy coatings for steel. There was already evidence it was very effective to coat steel rebar and large girder beams with epoxy when constructing bridges.
So the company embarked on an R&D project into epoxy coatings that resulted in constructing its own epoxy coating facility on the campus of its headquarters. Legacy’s paint shop is itself a tension fabric structure (what else?) dominated by the blasting booth and a paint booth. Three beams supported from the roof structure transport its steel from the front of the shop, through the booths, and finally to the drying area.
Then the company decided to test it.
Legacy contracted with PPG Protective and Marine Coatings and contracted with an independent testing lab to conduct corrosion testing on U-shaped pieces of steel that included HDG and all the options in its EpoxxiShield™ suite:
- EpoxxiShield™ COR Plus, which is a two-coat epoxy frame finish.
- EpoxxiShield™ COR Pro, which combines a single coat of zinc-rich epoxy and a single coat epoxy frame finish.
- EpoxxiShield™ COR Elite, which combines a single coat of zinc rich epoxy with a two coats of epoxy frame finish. The zinc rich epoxy layer provides a galvanic protection similar in thickness to hot dip galvanising with Legacy’s zinc rich epoxy. Another two layers of additional epoxy are added on top of the zinc rich layer which provides the ultimate in barrier protection (13 ml). This is the same finish utilised in many bridge construction projects.
Once complete, the company’s partners sent a report showing the results after 2000 hours of testing in a salt-fog chamber.
The pieces were placed in a closed environment and then exposed to salt fog. The 2000-hour test is on the aggressive side. Tests that go for that long are for products and surfaces that want to distinguish themselves. Anything longer is usually reserved for steel in extreme conditions, such as offshore oil rigs or bridges in coastal areas.
Once the test started, the independent testing lab followed a process of taking out the samples and visually inspecting them. Each surface was then given a rating from 0 - 10, with 0 meaning the sample was more than 50% rusted and 10 meaning there was .01% or less rusted. They were also given a letter (P, S and G) to indicate whether the rust was pinpoint rust, spot rust or general overall rust. There were two other observations recorded for each sample. One was blistering and the other measured the rust, in ml, for a line scribed in the surface.
The salt fog test was not just a measure of the surface of the epoxy coatings. It also measured the corrosion protection if the surface was significantly chipped or scratched. Therefore, each sample had a line scraped into it using a carbide tool before they were tested in the salt fog. This was a way to let rust happen to one part of the sample to see if the coatings slowed the spread of corrosion further into the rest of the piece. The reality is that most steel gets accidentally scraped or dented or chipped during its life span, and if that introduces corrosion to the surface, you want to slow it down as much as possible until it can be repaired.
The HDG member was vastly and significantly impacted by the chambered conditions while the EpoxxiShield™ COR coated products produced little-to-no affects with the exception to the purposefully damaged area. Even in that area, the corrosion did not penetrate and bleed under the epoxy coating to any significant degree. Because epoxy dings are easy to fix, making sure that corrosion didn’t spread under the coatings was an important finding.
All of this was great news for Legacy and its customers and future customers who need protection against corrosion. The epoxy coatings seem to provide the kind of protection that could last for decades.
DISCLAIMER: the intent of this test is not to suggest the performed spray fog is equivalent to any real-life condition or life expectancy but to demonstrate the performance of coatings when subjected to a caustic condition. Performance of coatings will vary per actual exposed condition. Only EpoxxiShield™ COR or HDG coated products are intended to be used in caustic/corrosive environments.
Read the article online at: https://www.drybulkmagazine.com/special-reports/06042021/legacy-building-solutions-is-corrosion-protection-the-next-frontier-in-dry-bulk-storage/
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