Inspectioneering Journal

99 Diseases of Pressure Equipment: Catastrophic Oxidation (Fuel Ash Corrosion)

This article appears in the July/August 2004 issue of Inspectioneering Journal.

Catastrophic oxidation can occur when certain contaminants are present in a high temperature environment, i.e. inside furnace fireboxes, in our industry. Those contaminants are typically vanadium pentoxide with sulfur oxide or sodium sulfate. When these contaminants are present in the combustion atmosphere, liquid slags can form on components operating above 1000oF (538oC) which can cause exceedingly high rates of corrosion (sometimes up to 1000 mpy).

If you have this problem, you probably already know it because of the high rate of corrosion and the glassy, hard slag on the surface of the components being inspected. Furnace tubes may not be affected if they operate below the molten slag temperature, but support structures and tube hangers are often exposed to fuel ash corrosion. There are a variety of methods to reduce the risk of catastrophic oxidation; several of which are covered in API RP 571.

Would your management of change (MOC) process catch any changes in fuel oil firing that might introduce vanadium contamination into your fireboxes? Does your RBI assessment take into consideration the potential for fuel ash corrosion?

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