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An overview of the advances in understanding the impact of corrosion on structural integrity and the associated tools available for inspection, assessment and repair is presented. A comprehensive set of these tools would allow for a significant shift in aircraft maintenance concepts.

In the “in‐service” maintenance and inspection of aircraft structures, an uneasy alliance exists between corrosion detection and Non‐Destructive Testing. NDT is a widely used and generally successful way of inspecting for structural defects and as the service life of aircraft is extended and corrosion therefore tends to become a not uncommon structural defect, why should not NDT be as useful in this situation as it often is in detecting cracks occasioned by extended flying hours and increased flight cycles? This paper tries to answer that question by pointing out some of the advantages and disadvantages of NDT applied to corrosion detection in the aviation industry.

The aerospace industry relies heavily on protective treatments and processes to ensure that the structural integrity of an aircraft is not degraded in service as a result of operating under harsh corrosive conditions. Many of the chemicals and processes currently employed in metal finishing have been found to cause pollution and long‐term damage to the environment. Legislation and international agreements are now in place which ultimately will lead to a ban or major reduction in the use of many of these processes and coatings. The aircraft constructors and operators are seeking to adopt new protective schemes and treatments which will satisfy future environmental requirements.

The second day of the Aerospace Corrosion Control Symposium, held at the Rai, Amsterdam, commenced with a paper presented by Aydin Akdeniz of the Boeing Commercial Airplane Group, USA. Entitled “Integrated Structural Maintenance Programme”, it outlined surveys conducted by Boeing of selected ageing aircraft to review the condition of the structure along with the airlines' maintenance practices. The results suggest that there is a great variation in the actual levels or degree of structural corrosion in the aircraft fleets. The paper gave a background to corrosion prevention and control programmes (CPCPs) and outlined a procedure for consolidating the CPCP with other structural maintenance tasks. It concluded that properly scheduled structural inspection and correctly applied ageing aircraft programmes establish minimum standards to ensure continued airworthiness (see Figure 1).

Held recently in Amsterdam, the 3rd Aerospace Corrosion Control Symposium attracted speakers and delegates from a wide spectrum of the Aerospace industry, as well as from universities and research bodies. Discussion, debate and the exchange of information were facilitated by the presence of over 50 nationalities.

The current corrosion maintenance philosophy reflected in aviation regulations and recommended practices does not stimulate progress in corrosion related technology. A US Air Force (USAF)‐sponsored survey has recommended re‐examination of corrosion maintenance policies and practices to identify lower cost alternatives, and has encouraged research into tools and techniques that reduce maintenance costs while preserving safety. In particular, these include models to predict the impact of existing corrosion damage on structural integrity, methods of predicting corrosion growth rates and nondestructive inspection systems capable of providing corrosion metrics. The Institute for Aerospace Research of the National Research Council Canada (IAR/NRC) has pioneered work on the application of enhanced visual methods for corrosion detection in lap joints and the assessment of the impact of corrosion on lap‐joint structural integrity. The role of these enhanced visual methods in the new corrosion management is described.

The purpose of this investigation was to develop a digital instrument for the quantitative evaluation of pitting corrosion in metals.

This investigation comprised two central parts: research, testing and monitoring of the formation of pitting by conventional methods and applying American Society for Testing and Materials (ASTM) Standards, and the development of a virtual instrument based on the LabVIEW 2010 platform.

The methodology used was suitable for the analysis of pitting on carbon steel and aluminum alloy UNS A96061, used in the aerospace industry.

This technique allows pits to be to localized, measured and quantified on metallic surfaces, for corrosion evaluation in atmospheric and industrial environments.

This combination of conventional and digital methods can assist in corrosion control of pitting in industrial equipment.

In the past, the RAF’s approach to corrosion was reactive: corrosion occurred, was identified and then rectified. Such a strategy is no longer acceptable, as corrosion rectification is costly both in terms of material and aircraft availability. More importantly, as escalating replacement costs force us to retain aircraft in service for ever‐longer periods, the threat posed to structural integrity by corrosion and repeated corrosion repairs can no longer be tolerated. Consequently, the RAF has had no option but to develop a policy of corrosion prevention. Aerospace Maintenance, Development and Support, part of Headquarters Royal Air Force Logistics Command, has therefore been actively involved with the evaluation and trialling of a range of important corrosion prevention techniques that are compatible with the RAF’s current stance. Aircraft washing and rinsing practices have been reviewed to confirm their effectiveness, and trials have shown that dehumidified air permeates readily through a full‐size airframe, reducing relative humidity and arresting the rate of corrosion. From our work we have concluded that effective washing should be supported, where possible, by freshwater rinsing, and, if a cost effective system can be developed, structural dehumidification should also be practised. Notwithstanding a policy of corrosion prevention, we know that we operate aircraft that have already accumulated corrosion damage which has to be located and recorded. Non‐destructive testing is employed widely, and the use of information derived from the process to populate structural databases is being explored. Additionally, we are involved with refining the methodologies associated with structural inspections to ensure the ongoing integrity of our ageing aircraft fleets.