[Gerhardus H. Koch] AFCPCO experts expect that the application of research knowledge in design and manufacturing phase of the aircraft production would reduce corrosion related maintenance expenditure by around 40% ($320 million). [Daniel E. Bullock]
Corrosion Control by Coating
Using appropriate coating methods, galvanic corrosion of metal surfaces can be avoided. For example titanium surfaces are plated with cadmium and primed before they are attached to aluminum surfaces. The aluminum alloy surface is typically coated with corrosion inhibiting primers such as Skydrol-resistant epoxies. Before applying the coating the surface is anodized using phosphoric acid anodizer. [Gerhardus H. Koch] the most poplar method of corrosion prevention however is the use of chromate surface treatments of the aluminum structures. Using hexavalent-chromium compounds for surface coating is however an environmentally unsound practice as chromium is well-known as a highly toxic and carcinogenic agent. The U.S. air force has done extensive research to find an environmentally safer alternative to chromium as a surface coating agent. This research has shown promising results and already self-assembled, nano-phase particles (SNAP) is suggested as an environmentally safer and long lasting (30 years) alternative to the toxic chromium coating method. Electrochemical impedance spectroscopy (EIS) studies have confirmed that SNAP system offers better corrosion protection compared to chromate coating. [Donley]
Though tackling corrosion at the designing and manufacturing phase is key to successful control of the corrosion menace, proper maintenance also occupies a significant role in remedying the damage and in prolonging the life of the aircrafts. Detecting corrosion earlier would help avoid costly repair operations. There are numerous non-destructive forms of tests that are available to assess the level of damage without inducing any real damage to the aircraft. Ultrasonic testing, optical testing, eddy current testing, electrochemical impedance spectroscopy and radiography are some of the commonly used non-destructive testing procedures. By means of selective 'blend out', affected regions are removed and in case the damage exceeds the acceptable limit of 10% of the surface thickness the whole part is replaced. Typically, maintenance programs include daily inspection by the pilots, regular structural checks and periodic total inspection. [Gerhardus H. Koch]
Corrosion is a big problem for domestic and military aircrafts. Both government as well as private airlines are forced to spend a huge amount of money on maintenance operations. Corrosion preventive strategies are more cost efficient and performance boosting than remedial measures and the return on investment for corrosion control programs is very attractive. It would be forthright to implement the best possible corrosion control methods for our domestic and military aircrafts as it would not only improve the performance and life of these fleets but also be a huge cost saver on the maintenance budget. A common standard for corrosion control programs has to be evolved and all concerned industries should adhere to these standards. To address the problem more effectively it would be necessary for the government as well as the private sector which are involved avionics production to work in a cooperative manner.
Maj Daniel E. Bullock and Mr. Timothy Anderl, " Air Force Experts Fight the Good Fight Against Corrosion to Maintain Mission Readiness," Accessed on 24th Oct 2004, http://www.afrlhorizons.com/Briefs/Feb04/ML0302.html
Gerhardus H. Koch, PH.D., "Corrosion control and Prevention," Accessed on 24th Oct 2004, http://www.corrosioncost.com/pdf/aircraft.pdf
Donley, M.S, a.J. Vreugdenhil and V.N. Balbyshev, "Nanostructured Silicon Sol-Gel Surface Treatments for Al 2024-T3 Protection," the Journal of Coatings Technology; 4/1/2001
Kennedy, Harold, "U.S. Navy Struggles to Keep its aging Aircraft Fleet Flying,"
National Defense; 12/1/2001
Wynne, Michael W, Corrosion Prevention and Control: Status and Update. (Policy Update),