Sulfur Dewpoint Corrosion

Abstract

This paper describes sulfur dewpoint corrosion of steels in the low-temperature parts of oil-burning boilers such as economizer, air-preheater and chimney.
The contents of this paper are summarized as follows.
1. The outline of sulfur dewpoint corrosion: The phenomena of sulfur dewpoint corrosion is explained as regards the effects of several influential factors on the corrosion.
2. The development of laboratory test method for sulfur dewpoint corrosion which is correlated well with field test in boilers: This laboratory test method has been used to study the effects of alloying elements on the corrosion resistance of steels.
3. The mechanism of sulfur dewpoint corrosion: It has been cleared that sulfur dewpoint corrosion proceeds by three-step mechanism, i, e., first, second and third steps. The third step is the most important, because corrosion resistant low alloys are passivated at this stage whereas other steels still continue active dissolution.
4. Corrosion preventive measures:
i) Use of low-sulfur content heavy oil.
ii) Boiler operation at low excess oxygen ratio.
iii) Use of additive such as dolomite to neutralize flue gas.
iv) Use of corrosion resistant low alloys.
There have been developed corrosion resistant low alloys, i. e., CRIA, S-Ten 1, NAC-1, RIVERTEN-41S, TAICOR-S. It is recommended for them to be used to low-temperature parts of boilers from the viewpoints of economy and utility safety.