Abstract
Fuel oil ash corrosion has been studied using laboratory crucible testing methods on four stainless steels with nominal specifications of 12%Cr, 9% Ni, Type 347 and 25 Cr 20Ni. These have been corroded for periods of 1, 5, 24, 48, 72 and 100 hours in a synthetic slag of 70 wt.% V[2]C[5] and 30 wt.% Na[2]SO[4], under atmospheres of either pure oxygen, air or pure argon. A kinetic study has been carried out by measuring the reduction in specimen thickness with time. The specimens have been examined by Electron Probe Microanalysis and Scanning Electron Microscopy techniques and the results presented in the form of scanning electron micrographs with the position of the analysis for the elements Fe, Cr, Ni, V and S indicated. Samples of eight corroded steels from the Marchwood Power Station 10,000 hour trials have also been studied and the results presented as with the laboratory prepared specimens. The results from the study indicate that the main mechanism of corrosion is one of sulphidation, but that the rate controlling step is probably determined by the composition and physical nature of the vanadate layers which are produced. Chromium vanadate appears to give a greater measure of protection to the steels than other corrosion products. A mechanism for fuel oil ash corrosion has been given which indicates that the sulphur content of the slag will have the greatest influence in corroding superheater materials, especially if nickel is present as an alloying element.