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In our refinery the tubes of aero-condenser (air-cooled heat exchanger) suffers a remarkable thickness reduction. In January, 2009 we have replaced all the tubes with 2.77 mm thickness. During routine shutdown in October, 2011 we had found that thickness reduced dramatically. We had recorded the lowest thickness of 1.4 mm. At that time we had replaced the bottom layer of one bank which contains that tube.
After that one tube of adjacent bank was plugged due to pinhole type leak. A few months later expansion groove of one tube of this bank found corroded. We had taken few sample thickness in June, 2012 and got minimum thickness of 0.9 mm.
We found that only rear end tubes are facing significant thickness reduction. Again there is no vent or drain nozzle/plug in the rear header so it is not possible to clean the header properly during shutdown. After investigating we also found that the dosing of corrosion inhibitor and caustic soda suspended for several times due to unavoidable circumstances.
My question is what are the main reasons (including dosing interruption) behind the thickness reduction and what is the expected service life of tubes and header of aero-condenser?
 
Answers
23/07/2012 A: Mike Watson, Tube Tech International Ltd, mike.watson@tubetech.com
Air-cooled heat exchangers often suffer from under scale corrosion which could be one main reason. We find it a lot after cleaning and inspection. Your figures are not unusual but certainly not the norm either.
Even without vent or drain nozzle/plugs in the rear header it IS POSSIBLE to clean and inspect the header 100% during shutdown. We find also by using our Rflex polishing method it minimises this corrosion pattern too.

23/07/2012 A: RAUL FLORES, PDVSA INTEVEP, fraulf@hotmail.com
1. What is the stream cooled (typical composition) and from where does it come?
2. What are the materials involved in the aero-condenser