Abstract
High chromium austeno-ferritic duplex stainless steel NTK R-4 has been widely used as the heat exchanger tube in main steam condensers of ships and seawater heat exchangers of chemical plants for eight years. In this paper, relations between the corrosion failure rate FR on the heat exchangers using NTK R-4 tube and their designs, structures, maintenances and service conditions (seawater velocity, and temperature and pressure in a shell side) were investigated respectively.
Forms of the corrosion failures encountered in some heat exchangers were related to their service conditions. They have been caused through a hot spot corrosion and a crevice corrosion under the corrosion product. The adequate service conditions for NTK R-4 heat exchanger, a cooler and a condenser, were defined according to the value t(°C)×p(kg/cm2) in their shell side conditions. It was concluded that keeping the seawater velocity at least 1.5m/sec, a sterilization of sea-organisms by chlorine and excluding the trash entering into the heat exchanger were required for this tube.
