CORROSION AND INHIBITION OF AGED 347 GRADE STAINLESS-STEEL BOILER TUBES

General and pitting corrosion of both service and laboratory aged 347 grade stainless steel superheater tubes have been investigated. SEM an alysis showed the precipitate phases to have a double structure consis ting of sigma phase and carbide. EDA analysis of the precipitates indi cated the [Cr]/[Fe] ratio to increase with exposure time. For both set of specimens, the general corrosion rate in 1 m H2SO4 increased with aging whilst the pitting studies (in 3.5% NaCl) also indicated increas ed pitting susceptibility with aging. These trends are consistent with corrosion from the chromium depleted areas adjacent to the precipitat es. Methoxypropylamine is effective as an inhibitor for pitting corros ion and the concentration required to prevent this form of attack incr eases with exposure time for both types of specimens.