Air preheater corrosion in oil firing boilers has been the subject of many research works, but almost all workers have not made any mentions on the relations between corrosion and deposits. We have examined the corrosion phenomena by deposit analysis with chemical and physical method, i.e. X-ray difraction or infrared spectroanalysis. Results are summarized as follows.
1) With the decrease in the surface temperature, corrosion and acid deposition on metal surface are highly increased, and this seems to be different from D. H. Kear's result, who observed a peak in the corrosion rate.
2) A correlation exists between the free acid contents (or Fe
2+/Fe
3+) and combustible residue contents in the deposits.
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