Case studies in high temperature naphthenic acid corrosion

4 Case studies in high temperature naphthenic acid corrosion 

1 Crude oils with low sulfur and high total acid number (TAN) 

Heavy crude oils with low sulfur and high TAN were processed within the atmospheric and vacuum units in Refinery B. The average TAN was about 3.0 mg KOH/g and the sulfur content was lower than 0.5%. It was found that severe corrosion occurred in the vacuum distillation systems during the inspection carried out in May 2006. The materials used to fabricate the wall of the third and fourth floors of the tower were carbon steel and 316L stainless steel. The inspection revealed that a lot of pits were formed on the inner wall as shown in Fig. 17.3. 

The packing materials (316LSS) of the third and fourth floors suffered severe corrosion attack. After one and a half years, a big hole (400 mm in diameter and 500 mm in depth) was observed on the fourth floor of the tower due to the collapse of the packing materials (Figs 17.4 and 17.5). At the same time, corrosion of the oil collection tank on the third floor was severe as well (Fig. 17.6). 

3 Corrosion pits on the inner wall of the tower wall on the third floor. 

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