Corrosion of new steel pilings at Colman Dock caused by unknown bacteria

Maritime transportation is heavily relied upon by businesses and commuters in coastal regions, as it provides a cost-effective means of moving people and products from port to port. Well-maintained ferry terminals and waterway-shipping infrastructure provide passengers and commodities with easy watercraft access, making them a crucial transportation hub for these locales. But how vulnerable are they to damage and corrosion?

In early January, the Kitsap Sun reported that an unidentified organism caused aggressive corrosion to the support structure of a new ferry terminal in Seattle, Washington. The organization in charge of the project, Washington State Ferries, announced that several of the steel pilings supporting the terminal at Colman Dock showed signs of "accelerated" corrosion – easily distinguished by its bright orange hue.

Workers first discovered the problem back in June 2018, while monitoring the pier's infrastructure along the waterline of Elliott Bay. In total, around 500 steel piles were installed to support the new terminal, each measuring 150 feet long. By utilizing a vibratory hammer, construction crews were able to drive the hollow piles 138 feet into the ground to ensure maximum stability, but few predicted corrosion would be a factor so early in the process.

"Corrosion happens, we know that we're in a natural environment," said WSF spokesperson Broch Bender. "We made them thicker so that even if they did corrode they'd have the 75-year lifespan."

But the rate of corrosion was more fast-paced than engineers considered possible (under normal circumstances), which lead the WSF to launch a 20-month study into the incident. The first round of testing indicated that an unknown bacteria had caused the piling to rapidly decay, though the organism in question has still not been identified. This uncertainty has been a source of great frustration for engineers working on the project and has demonstrated the importance of diligent environmental testing for construction materials, especially for offshore projects.

The WSF has begun applying a marine coating system to piles that have already been installed at Colman Dock and will similarly treat all future pilings over the next two years of construction. These supporting features are a crucial part of the overall reconstruction project, as they were designed to make the ferry terminal safer and more resistant to earthquakes. The original infrastructure used over 24,000 tons of creosote piles and timbers to support the weight of the terminal, most of which will be replaced by the new steel pilings.

Marine coating boosts corrosion resistance
Building on or around bodies of water like Elliot Bay poses a significant challenge for engineers, as the salinity of brackish water has a natural corrosive effect on metal. Even industrial-grade metals corrode when exposed to high degrees of moisture, which explains why the marine coating industry plays such a major role in offshore construction projects. Some experts have suggested switching to manufactured plastics to avoid the risks of structural rusting, but at present there are no commercially viable options that can support the extensive weight of a modern watercraft terminal.

"The global corrosion resistant resin market is predicted to grow at a CAGR of 4.9 percent between 2018 and 2025."

Until a long-term solution is found, engineers will continue to rely on marine coating resins to ensure their building materials are protected from rapid degradation. A 2018 survey from QY Research predicts that the global corrosion resistant resin market will grow at a CAGR of 4.9 percent between 2018 and 2025. The resin products benefiting the most from this market surge will include epoxy, polyester, polyurethane and vinyl ester. While composites do make up a healthy portion of the market, anti-corrosion resin coatings are expected to be the largest application source over the forecasted period. Not only do these coatings provide protection against corrosion, but they can also extend the lifespan of metal components that are regularly exposed to extreme conditions.

Most engineering and construction companies spend a lot of time and money testing their materials, but some environmental factors cannot be reasonably predicted. As is the case with the Colman Dock ferry terminal, nature has a way of introducing minor complexities that grow into major issues for construction projects. The effects of high moisture and salinity can be tested, but understanding the potential impact of unknown bacteria requires experience and expertise. This accounts for why A2LA environmental testing laboratories are so important early in the planning phase. While such laboratories may not be able to account for the effects of undiscovered organisms, they can ensure the strictest quality standards are upheld during the evaluation process.