Study on high-temperature naphthenic acid corrosion and erosion-corrosion of aluminized carbon steel

High-temperature naphthenic acid corrosion (NAC) and erosion-corrosion (NAEC) behaviors of pack-aluminized carbon steel have been investigated in laboratory to evaluate the resistance of aluminized layer to the NAC and NAEC. A field erosion-corrosion test of 700 days was also performed in an oil refinery. Parallel tests were carried out for carbon steel. It was found that the aluminized steel exhibited a better NAC resistance only at early testing stage than the carbon steel in high total-acid-number (TAN) environment. The NAC resistance degraded rapidly with increasing testing time, and became even worse than that of the carbon steel at final testing stage, accompanying a step-like or lamellar spallation in the aluminized layer. In low TAN environment, the aluminized steel exhibited a much better resistance to both the NAC and NAEC in comparison with the carbon steel. Similarly a good erosion-corrosion resistance was found for the aluminized steel in actual oil-refining environment although relatively serious erosion-corrosion attack simultaneously took place in the aluminized layer. Based on the above results, possible NAC and NAEC mechanisms for the aluminized steel are discussed.