01 Mar 2007
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The F35 Lightning II Joint Strike Fighter
Corrosion costs the US armed forces an estimated $40 billion a year to fix. It’s a threat that is literally eating away defence assets and is a major headache for those who have to maintain the ‘through-life’ capability of military platforms. A new sensor system invented at the ATC called Sentinel is now at the vanguard of corrosion monitoring and control for both US and UK defence programmes. It provides early warning signs so that corrosion can be anticipated and prevented before it becomes an expensive problem.
‘Through Life Capability Management’ has emerged as a major theme in the MoD’s Defence Industrial Strategy. Behind the jargon is the simple message that defence capability must be fit for function for as long as possible and ready for action at any time. When it comes to maintaining military hardware in tip top condition, technology has its part to play in meeting that need. A mantra increasingly heard in life-cycle management circles is ‘predict and prevent’ rather than ‘find and fix’.
That’s exactly what the ATC Sentinel corrosion sensor is designed for. The devices work by sensing that paintwork on a structure is beginning to break down: a sure prelude to the start of corrosion. Through a team effort led by BAE Systems Australia, Sentinel has recently been selected for the System Development and Demonstration (SDD) phase of the F35 Lightning II joint strike fighter programme. The partnership with the company’s ‘Through life support’ business in Australia has ensured a route to market for this technology. Sentinel has also been installed on military ground vehicles on active service with UK armed forces.
All military vehicles including aircraft, ships and land vehicles are protected from corrosion when they are built by using a combination of chemical treatments and paint. Wear and tear from normal usage will eventually damage this protection and expose the structure to the ravages of the environment. Depending on their use and location, platforms can be exposed to a barrage of salt water, sand and grit blasting and even chemical attack. Often, by the time the effects of corrosion are spotted during routine inspection, the damage is already done and costly repairs are necessary. Sentinel works by monitoring the breakdown of that protection using custom electrical sensors and giving advance warning that corrosion could start soon. Preventative action can then be taken at the soonest, convenient opportunity.
“Sentinel is essentially a paint sensor.” says Mike Hebbron, corrosion specialist at the ATC, “The sensor is designed to simulate the part of the structure you’re monitoring. We mimic the structure itself using thin layers of alloy and also include the protective coating applied in the same way. The sensor then has all the same ingredients as the part of the structure it is monitoring and will see all the same conditions.” he says.
The principle is similar to the ‘witness’ crack gauges sometimes seen on the side of buildings to monitor subsidence cracks. Every now and then, the condition of the gauge is monitored to see if any significant changes have happened. In the case of Sentinel, the sensors are either periodically hooked up to a small hand held instrument to check their status or they form part of a continuous, on-line monitoring system.
“Even if readings are missed, the history of how the corrosion protection is degrading is stored in the materials of the sensor itself, simply by being there.” says Mike.
Work on Sentinel has generated several patents that are now in the process of being filed by BAE Systems. The sheer simplicity and effectiveness of this sensor was one reason why it was selected for the F-35 SDD aircraft. If successful it could be a candidate for the production aircraft due to enter service in 2012 where it would become an integral component in the aircraft’s health monitoring system for decades to come.
