Coping with Corrosion

Corrosion can turn millions of dollars' of safe, proven airframes into deadly accidents just waiting to happen. "In the United States alone, aircraft corrosion is a multi-billion dollar problem," says www.corrosion-doctors.org. "On some military aircraft types, corrosion maintenance hours are known to outstrip flight hours."

"Prevention of corrosion is best done by design; avoiding pockets where moisture, acids, and salts can accumulate," says Peter Burgher. He owns and operates GSH Corporation, developer of the corrosion control product NO COR. "But this is not always possible in the real world, so corrosion treatment substances are necessary."

Without treatment and prevention, corrosion can lead to deadly consequences. For instance, "crevice corrosion" led to 18' of B737 skin ripping off Aloha Airlines Flight 243 on April 28, 1988. Although Flight 243 managed to land, stewardess Clarabelle Lansing died after being expelled from the 737-200 during explosive decompression, and eight passengers were seriously injured. According to the subsequent NTSB investigation, metal fatigue and stress fractures made worse by corrosion led to "significant disbonding and fatigue damage" to the 737-200's exterior covering, which led to "lap joint failure and separation."

Of the various forms of corrosion that aircraft operators have to combat, "Intergranular corrosion would be considered the most difficult to treat by far," says Jim Van Gilder; chairman of Corrosion Technologies (www.corrosionx.com). "The potential for this type of corrosion is the result of metallurgical flaws caused by, for example, improper quenching. In this case, grain boundaries are created that invite the intrusion of corrosion-causing electrolytes. The result is laminar expansion as corrosion products are formed causing exfoliation. The part must then be replaced."

Adding to the challenge of combating today's corrosive enemies are trends such as using "composites in [aircraft] structure rather than just trim," Burgher says. Other trends which make corrosion control more important than ever include "lighter structures, longer cycles between C- and D-checks, and sensationally greater life expectancies for airframes and components."

Granitize Blocks Corrosion with Xzilon 3AECI Aircraft Exterior Corrosion Inhibitor

Life is tough on an aircraft's outer skin; the rain, the sun, and the constant expanding and contracting due to temperature changes. To help keep an aircraft exterior's looking better, longer, Granitize Aviation has developed Xzilon 3AECI Aircraft Exterior Corrosion Inhibitor. It is designed to "prevent oxidation on paint and exposed exterior metals (Bright-Work)," says Dale Forton, national sales manager for Granitize Aviation."This extends the time between polishing bright work as well as extends overall paint life on an aircraft." One note: The aircraft surface must be properly cleaned before applying Xzilon; typically by using an XC-12 2,000 grit polymer clay bar and Granitize's XC-11 Spray and Shine. Once the surface is ready, it takes three coats of Xzilon applied in 20 minute intervals to do the job.

So how tough is Xzilon? "It has passed Boeing Materials Technology testing in Renton, Washington and withstood 1,400 hours of salt spray exposure," replies Forton. In the air, this product has "a UV30 block to prevent high altitude paint fade built in and gives operators up to 90 days of bright work protection and 400 flight hours of protection on painted surfaces." (This said, it is not recommended to apply Xzilon to yourself before heading to the South Seas.) He adds that Xzilon "aids in protection behind PT-6 exhaust trails. Although this only lasts for about forty hours the ease of cleaning during that time makes it very worthwhile."

To date, Xzilon 3AECI has been used "for the last four years on the Boeing BBJ program to protect the Polished Aluminum Engine Inlet Lips from pitting corrosion due to aircraft storage, ocean salt spray and harmful environmental industry fallout," Forton tells Aviation Maintenance. "It is referenced specifically in Boeing Service Letter SL-737-71-053A. As well as Boeing and others, Gulfstream recently recommended the product for all of its models in their Breakfast Minutes from January 2006 ... [and] Bombardier is in evaluation for the Global Express Airframe."

Find out more at www.granitizeaviation.com.

Lear Chemical Research's Tried-and-True ACF-50

Developed in the 1980's, Lear Chemical Research's ACF-50 "pioneered the use of Thin Film corrosion preventatives," says Mark Pearson, the company's managing director of operations and R&D. As well, Lear Chemical Research "developed the concept and fogging process that set the standard for `complete airframe protection'." Since that time, ACF-50 has been updated to incorporate new anti-corrosion advances in dealing with harsh sulphurous acid/salt spray environments, while retaining the core of its original formulation,

One thing is certain: ACF-50 has used its pioneering lead to build a loyal base of users globally. Among these are "many of the world's major airlines like Hawaiian, who has arguably the toughest corrosion environment," Pearson says. ACF-50 is also used by the DEA, U.S. Customs, FBI, and the U.S. Border Patrol find ACF-50; and is recommended by more than 25 OEMS such as Cessna and Sikorsky.

"Recently, a U.S. Navy field evaluation showed that one application of ACF-50 reduced corrosion-related costs on the aircraft treated by more than 37.5 percent," he says. "Similar evaluations by the US Army found ACF-50 to be the over[all] best material tested." Find out more at www.learchem.com.

GSH's NO COR Fights Galvanic Corrosion

Galvanic corrosion is one of the most subtle, yet most potentially devastating forms of corrosion there is. As ions flow between chemically dissimilar materials--not just metals, but composites adjacent to metals--the atomic structures of the affected components are fundamentally altered, and not for the better.

This is where GSH's NO COR comes in. It is an ion transfer inhibitor that eliminates the negative pole in a galvanic reaction. With no ion transfer occurring, corrosion doesn't happen. It's as simple as that. Better yet, NO COR "is transparent and does not have to be removed for inspection," says GSH owner Peter Burgher.

"NO COR meets Mil spec C-16173 and Mil spec C-15074 for corrosion prevention and fingerprint removal, respectively," he tells Aviation Maintenance. "It penetrates, eliminates moisture and isolates dissimilar metals (and carbon fiber composites). Rigorous testing has shown NO COR does no harm and is effective in the very worst of circumstances." In contrast, traditional aircraft corrosion solutions such as wax, oil and paint "only mask underlying problems," Burgher says. "Waxy thick film substances just cover up the problems and can inhibit proper drainage ... Oils run away and lose their effectiveness and paint is, well, just paint. None of these can inhibit the transfer of ions from one part of a structure to another."

Meanwhile, if you think that the next generation of airframes will be more corrosion-resistant, think again: Composite airframes are just as vulnerable to galvanic corrosion as their all-metal cousins. "Carbon fiber containing structures are conductive and galvanic corrosion has been known to be occurring where composites contact aluminum or alloy substructures," Burgher says. "Some composites are hygroscopic, that is they attract and hold moisture, sure causes of corrosion."

CorrisionX

Packaged in pressurized spray cans by Corrosion Technologies (www.corrisionx.com), CorrosionX Aviation is a treatment that can be used throughout the entire airframe to stop and prevent corrosion. Besides preventing corrosion, this Fluid Thin Film Technology oil product lubricates rod ends, hinges, locks, and closure mechanisms; it can also penetrate rusted and corroded components such as exhaust studs, and inspection plate screws.

"CorrosionX can be placed directly over existing corrosion where it penetrates and polar bonds at the molecular level to the underlying base metal," says Corrosion Technologies' chairman Jim Van Gilder. "During this action, it separates electrolytes from the surface and leaves an interfering dielectric barrier to prevent the transfer of electrons. The result is to deactivate the corrosion process, the same as removing the fluid from your car's battery."