The US government will increasingly look into ways to preserve high value assets critical to national defense such as the F-22 and F-35 fifth generation fighter aircraft from the pervading effects of corrosion. The House of Representatives bill 1540 passed May 28th 2011 when becoming National Defense Authorization Act for Fiscal Year 2012 will mandate the Under Secretary of Defense for Acquisition, Technology and Logistics with implementing a 4-point program for preventing and controlling corrosion affecting military equipment. The new measures have been previously articulated in General Accounting Office audit report 11-171R released to the public December 16th 2010. The audit provides follow up analysis of a Department of Defense corrosion study report #111-166 that accompanied HR bill 2647 prior to it becoming the National Defense Authorization Act for Fiscal Year 2010.
The degradation of military equipment through the effects of corrosion, while detrimental to overall military readiness also adds a $21 billion yearly cost to the taxpayers according to a July 2010 DOD study. Also influencing Congress decision to confront the issue is the unique case of both of America’s fifth generation fighters aircraft, the F-22 Raptor and F-35 Lightning II. Although the scope of Corrosion Protection and Control (CPC) programs to appear in the near future will not be limited to these operationally critical weapons systems, the F-22 and the F-35 are receiving attention commensurate with their cost and function within US defense strategy. The F-22 Raptor already somewhat operationally constrained due to the limited number of aircraft that will be acquired (187) is America’s Air Superiority fifth generation stealth combat aircraft. The F-35 Lightning II/JSF, a stealth multirole fifth generation combat aircraft will form the basis of US Air Force, US Navy aircraft carrier and US Marines Expeditionary forces for the foreseeable future as well as that of at least 8 allied nations. With both program having suffered near prohibitive cost growth, the unchecked effects of corrosion can potentially inhibit operational capabilities while also being very costly. These considerations have already resulted in Corrosion Prevention and Control programs oversight and planning being assigned to a newly established Office of Corrosion Policy and Oversight whose Director answers directly to the Under secretary of Defense for Acquisition, Technology and Logistics.
With 137 aircraft produced at the time of the GAO audit report publishing, the F-22 is nearing the end of its production target run of 187 aircraft. Having entered service in 2007, it has provided uniquely valuable insight into corrosion prevention particularly with regard to the treatment of the advanced ‘stealth’ attributes applied throughout its airframe. The F-35 JSF/Lightning II program having already suffered widely published cost overruns and schedule delays is now only emerging into the Low Rate Initial Production phase.
Corrosion: the experience of the F-22 Raptor
The Government Accounting Office 11-171R report titled “Defense Management: DOD Needs to Monitor and Assess Corrective Actions resulting from Its Corrosion Study of the F-35 Joint Strike Fighter” has provided factual basis for incorporating corrosion prevention and control solutions already tested with the F-22 into the F-35 JSF program. The report has provided critical information regarding corrosion being encountered on the F-22. It is reported that “severe environment corrosion of the F-22 aluminum skin panels” had already been observed less than 6 months after the aircraft service entry in the Spring of 2007. The report describes how by October 2007, corrosion of the airframe substructure seemed systemic with at least 534 documented occurrences. The resulting cost to the government repair work and retrofit will reach $228 million once completed in the year 2016.
Practical lessons were drawn from observing the program.
1. The F-22 program had failed to guard against galvanic corrosion in at least two areas; the paint used on the aircraft skin panel and the gap filler used to maintain contact between different surfaces. In each one of these instances, the aluminum skin panels appear to have been in contact with metals or materials with differing electrochemical properties. As a result a conductive path for electricity to flow between both materials led to oxidization and corrosion.
2. Another case of corrosion was encountered as a nonchromated primer was initially used for the F-22 prior to painting the aircraft. The selection of a nonchromated primer was made out of concerns for workers health. It transpired that this new primer resistance to corrosion had never significantly been tested prior to its debut on the F-22. Experience had proven that coating aluminum surfaces with hexavalent Chromium VI (Cr+6) generally provide materials such as aluminum with additional resistance to abrasion and corrosion by anodizing it into a pure oxide.
Additionally the F-22 design which requires the presence of small drainage holes on its fuselage seams has led to water accumulating and eventually contributing to corrosion.
In response to the observations realized on the F-22 program, the GAO describes some of the F-35 program’s approach regarding corrosion, systematically responding to each point of concern highlighted in the F-22 Raptor:
-the F-35 program is neither using a conductive gap filler nor paint in an effort to limit corrosion. Materials that have near similar galvanic properties to aluminum are employed instead.
-Another design approach for the F-35 has been to employ fewer seams lowering the requirements in gap filler.
-The water drainage problem, one of the corrosion-sensitive area on the F-22 has been circumvented on the F-35 thanks to adequately sized drain holes.
The report however finds that the F-35 has also selected a non chromated primer that has never been tested on an aircraft in a corrosive operating environment, apparently compromising the additional protection offered by chromated paint applied to aluminum panels.
The measures mandated by Congress
HR1540 section 327 directly orders the Under Secretary of Defense for Acquisition, Technology and Logistics to take 4 recommended (corrective) actions described in GAO-11-171R and report to Congress on progress made consequently no later than January 31st 2012.
These actions comprise documenting the anti-corrosion measures specified in the corrosion study as applicable not only to the F-22 and F-35 programs, but also to the CH-53K Helicopter, the joint High Speed Vessel, the Broad Area Maritime Surveillance Unmanned Aircraft System and the Joint Light Tactical Vehicle weapons programs. The full scope of work involves establishing processes for monitoring and evaluating the effectiveness of such corrective actions.
The Under secretary has also been tasked with documenting both Air Force and US Navy specific recommendations with respect to their applicability as formulated in the corrosion study. Finally DOD would articulate specific actions as part of fully documented policies and processes in order to ensure that effective corrosion prevention practices become fully integrated throughout DOD weapons systems program.
Shortcomings Observed in Program Management
The report did recognize the inherently stronger F-35 airframe in comparison to the F-22 due to its longer service life requirement of 30 years (the F-22 service life is limited to 20 years). Because it will field a naval variant, the F-35 program factored-in stronger corrosion protection and increased strength in anticipation of aircraft carrier’s more rigorous environmental and operational demands. In fact the US Navy requires more stringent corrosion qualification tests along with appropriate technical performance metrics.
These strong points however have been negatively counter-balanced by the fact that adequate testing has not been fully conducted at an earlier stage of the program. This leaves open the possibility that shortcomings will not be discovered in a timely manner further contributing to costly re engineering at a later stage. The F-22 program is now suffering from the some of those effects: no operational level tests for corrosion were conducted on the F-22 prior to initial operating capability while the length of full scale climatic tests was cut in half. The F-35 program appears headed in the same direction as its program office is currently considering reducing full scale tests as well.
Overall Project Planning
The report suggests that for a program to implement a fully satisfactory Corrosion Prevention and Control outcome, requirements must become an integral part of the program plans at a higher level in order for corrosion risks to be fully managed throughout the system life cycle. A thorough documentation of CPC must become part of the systems requirements. In the F-35 case, the report insists that program requirements emphasized corrosion resistance whereas it should have been introduced as a complete corrosion prevention user requirement. The report has also suggested that corrosion prevention advisory teams should be established, in support of integrating newly engineered processes. Another proposal is for developing cost accounting models for corrosion throughout an entire system life cycle in order to help program executives make cost-based cognizant decisions on corrosion prevention and control.