WEST BETHESDA, Md. —
The Corrosion and Coatings Engineering Branch at Naval Surface Warfare Center, Carderock Division faces a challenge that has cost the U.S. Navy billions of dollars in research and repairs. Engineer Dr. Charles White and Chemist Dr. Kylee Fazende test and evaluate paint and coating products that aim to mitigate corrosion on Navy ships.
Paint fulfills more than an aesthetic purpose in America’s fleet. The need to stay camouflaged and undetected out at sea calls for efficient ship coating, which requires a series of tests to determine the paint’s survivability in different sea-state environments. Factors such as exposure to sunlight, temperature and biofouling, to name a few, are taken into consideration before deciding which coat of paint is best to apply onto a hull. All decisions must meet the requirements and qualifications of Naval Sea Systems Command’s (NAVSEA) standard item numerical index and be approved by their corresponding technical warrant holders.
Each part of a hull is coated differently to accommodate the potential environment and influencing variables. For example, the coating used on the outside of a ship, which is exposed to warmer temperatures, will be different from the coating used on the inside of a ship, which will be cooler and air-conditioned.
“Anti-condensation coatings are used outside air-conditioned habitable spaces, but a lot of other parts of the ship do not have that commodity. In those air-conditioned spaces, the surrounding bulkheads will start condensing water because of the difference in the temperature inside and outside,” Fazende said. “So you have to factor in that there’s going to be standing water on this wall permanently when selecting a proper coating.”
At the Philadelphia Navy Yard, pierside ships have been uncontrollably bleached into a bright pink color. The discoloration of the hulls was caused by intense sunlight exposure that chemically broke down the polymer, affecting the pigment of the vessels in the process.
“The biggest enemies to any exterior coating that you have are sunlight, water and salt. The sunlight itself will cause the breakdown of the polymer, and the water will soak into the polymers and can cause delamination and corrosion,” White said, adding that the danger of water seeping into any cracks within the coating is that it can either evaporate and freeze or otherwise erode the coating and cause performance failure.
According to White, paints are not one size fits all; therefore, some coatings are made for special purposes to accommodate demanding environments. Specialty coatings have precise formulations and are made in a specific way using certain ingredients, Fazende said. For example, the specialty coating for nonskid flight-deck material must be able to withstand mechanical wear and a challengingly hot surface. While the coating material is important, it is imperative to select an appropriate color, too.
“A black coating can work really well for some applications and deck camouflage until you start factoring how much sun it is going to absorb. You can get elevated deck temperatures very quickly,” warned White.
Polysiloxane paint, which recently replaced silicone alkyd, has demonstrated its superiority in color retention, UV resistance and adhesion over its predecessors. Latex paint, which is used to paint homes, would struggle to survive in the intense environment.
At Carderock’s West Bethesda, Maryland, headquarters White and Fazende use special chambers to test coated panels in an accelerated environment.
“What we do here is shorter term, so it’s our way of being able to test the paints and be able to get an idea of how their performance is going to be. We have accelerated light exposure, salt spray and salt fog, which simulates what the ships would actually experience with humidity, water coming off of the waves and salt content in the air,” Fazende said.
According to White, this is a way to test quickly and give manufacturers some criteria before they invest their time and money on multi-year long projects.
After initial testing, White and Fazende travel to one of Carderock’s Florida detachments to run and monitor real-world exposure tests.
“We do a lot of laboratory testing here (West Bethesda site) to troubleshoot problems and conduct failure analysis. Kylee and I specifically paint panels that go down to our South Florida Ocean Measurement Facility (Dania), where we do a lot of corrosion studies for the Marine Corps and for the Navy,” White said. “We can also take a specific piece of equipment like a window latch or truck bed down there and do atmospheric exposure and biofouling studies in an aggressive environment like south Florida.”
Marine life has contributed to the corroding effects of paint coating, as well. Although White and Fazende do not work closely with this focus, they are aware of the paints available to discourage biological growth.
“There is another team within our code (at Carderock) that focuses on that, but they use other coatings such as ablative coatings. It’s a thick coating that erodes when the hull begins to move, dropping the critters along with it,” White said.
Another way to discourage biological growth on a ship is the application of antifouling paint. The slippery paint does not allow any marine life to latch on and slides the little critters off.
“Biological growth on hulls causes additional friction in the water, requiring more energy for the propeller to get the same speed and potentially damaging the rudder,” White said.
The joint effort to combat corrosion for the Navy and Marine Corps is essential to keeping equipment healthy and performance ready.
“Corrosion is one of those complicated multivariate processes that is difficult to control by addressing only one variable. Many pathways for corrosion propagation and control exist, and the Corrosion and Coatings Engineering Branch is structured to address them as a team to make sure the Navy platforms and equipment stay in the best condition,” White said.