Study on High-Temperature Naphthenic Acid Corrosion of Type 304 and Type 316L Stainless Steel and Their Welded Joints

Abstract

High-temperature naphthenic acid corrosion (HNAC) behaviors of type 304 and type 316L stainless steel have been investigated in the laboratory with the experimental devices, that were designed and built by ourselves and had applied a patent, to evaluate the resistance of the base metal and their welded joints to the HNAC. Corrosion dependencies on the test temperature (ranging 220–320°C), total acid number (TAN) (ranging 1.86–32.0 mg KOH/g) and media physical states (liquid or vapor) were assessed. Specimens after HNAC tests were characterized by field emission scanning electron microscopy (FESEM) and energy dispersive X-ray (EDX) spectroscopy. A database of corrosion rates of type 304 and type 316L steel in high-temperature naphthenic acid solution was established. It was found that the HNAC resistance of both type 304 and type 316L degraded rapidly with increasing temperature and TAN. The tests which were conducted simultaneity in liquid media and gas media revealed that both the type 304 and type 316L stainless steel with weld showed worse HNAC compared to the type 304 and type 316L base metal at all temperatures in liquid media, but the difference between them was not obvious. In gas media, the HNAC rates of the type 304 and type 316L stainless steels with welds were greater than those without welds.