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Failure of aluminium tubes in automobile AC evaporators

July 7, 2009

Part description: Aluminium tubes are used in car evaporators to cool the air blowing into the passenger cabin. Atmospheric air is blown onto the aluminium tubes containing refrigerant. The cooled air then blows into the passenger cabin.

Part failure: Currently we are receiving some failures on leakage of refrigerant from aluminium tubes after some 30,000 kms. We found the aluminium tubes rusted and leaking from the rusted spots. Further analysis showed that there was dust accumulation and the dust contained low quantities of sulfur, calcium,copper and iron.

Does this elements and dust play a major part in aluminium rusting? if so how?

Rakesh Mahendiran
engineer trainee - Nashik, Maharashtra, India

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First, only metals containing iron can rust--by definition of rust as an iron oxide.
Your pits / leaks quite probably are in a welded area which need to be of very high quality to not pit if they are in and area of moisture and yours are probably dripping water. By the dust holding water, it will speed up any corrosion that could be caused by the ions that you have identified. Different alloys are affected differently by different ions.

James Watts
- Navarre, Florida
July 7, 2009