The aim of this paper is to study the corrosion behavior at elevated temperatures of four commercial heat resistant alloys exposed to a slag containing sodium sulfates and vanadates. Laboratory corrosion tests were conducted to obtain information on the performance of the alloys. The UNS specifications of the tested alloys were S44600, N06601, N08330, and ODS MA956. The slag used as corrosive agent was collected from the high temperature zone of an utility oil-fired boiler.
Corrosion weight-loss measurements as well as microscopic observations were performed to evaluate resistance of alloys to internal corrosion and sulfidation. The interrelationship between the corrosion behavior of materials and alloy chemistry and temperature are examined. The corrosion mechanisms involved in the degradation of the alloys in the range of 600°C-900°C are discussed. The influence of temperature on alloy degradation is found to be described by a curve with a maximum in the range of 750°C to 805°C. It is illustrated through the characteristics of the corrosion product scales, which have been studied by SEM and x-ray microanalysis. All the alloys exhibited sulfidation at least at the temperature of maximum corrosion rate.
Keywords: high temperature, oil-ash corrosion, hot corrosion, vanadium attack, stainless steel, 601 Ni-based alloy, MA956, Fe-25Cr steel, 35Cr1 9Ni superalloy, sulfidation.