A field test in a multi-stage flash (MSF) once-through plant has been evaluated. Six metallic construction materials, five stainless steels and one nickel base alloy, were exposed for a period of 28 months in the hot chlorinated and air saturated seawater stream of the first flash chamber at a temperature of 100 degrees C. The lowest alloyed grades, i.e., type 316, S31726 ("317LMN"), and S31803 suffered pitting and crevice corrosion while the highly alloyed grade S31254 suffered superficial crevice corrosion. The most highly alloyed stainless steel S32654 and the nickel base alloy N06625 were fully resistant. No material suffered stress corrosion cracking. A 6Mo grade such as S31254 is a good choice for the first stage of evaporator vessels. The first six stages of the plant where the test was performed are made of solid S31254.