Improving passivation of carbon steel in steam cycles of power plants with a film forming amine

Different types of corrosion phenomena present a threat for economical, uninterrupted and safe operation of both conventional and nuclear power plants. Many types of corrosion damage are induced by impurities that tend to accumulate in crevices or beneath corrosion product deposits. Especially important phase for corrosion protection is during different transitions, shut-downs and at two-phase regions. Several efforts for decreasing general corrosion rate and thereby also corrosion product accumulation on power plant surfaces have been done by changing the plant water chemistry. One very promising protecting method is treating systems with film-forming amines (FFA), such as octadecylamine (ODA). FFAs form a thin, some nanometers in thickness, film on metallic surfaces. Application of ODA decreases the rate of flow assisted corrosion (FAC) in the feed water line and thus reduces the amount of iron oxide that is available for deposition. ODA has also been observed to decrease the amount of crevice corrosion and stress corrosion cracking by hindering the enrichment of chloride ions and changing electrochemical properties of the surface. Recent studies at VTT show that at high temperatures (T=228-300°C) under ammonia water chemistry, ODA reduces carbon steel corrosion rate by a factor of three and that the once-formed film also remains stable at surfaces at high temperatures.