High Temperature Corrosion Test Method in Simulated Oil Fired Boiler Environment for Survice Life Evaluation of Boiler S/H Tubes

Abstract

In order to evaluate the survice life of supper heater tubes of oil fired boiler, a new high temperature corrosion test technique was developed where specimens were surrounded by double layer corrosives. Inner layer is 85% V₂O₅+10%Na₂SO₄+5%Fe₂O₃ (melted once at 900°C to form compounds with low melting point such as Na₂O·V₂O₄·5V₂O₅ and NaO·V₂O₄ and clushed to powder) corrosive and outer 10%V₂O₅+85%Na₂SO₄+5%Fe₂O₃ corrosive, simulating the situation commonly observed on the S/H tubes extracted from the actual boiler. This test environment reproduced local concentration of Ni and S at the interface between scale and metal as commonly observed on damaged tubes during survice operation. Corrosion resistance of some S/H tube materials are examined using this newly developed test technique. Furthermore, the effects of rare earth metal addition to 316HTB stainless steel named as 316-X on high temperature corrosion rate was examined by this technique. Results obtained showed that the 347 s. s. has higher resistance than 316 and 321 s. s. and also the addition of rare earth metal to 316 s. s. markedly improved the corrosion resistance. Some future problems which have to be solved for life prediction of boiler S/H tubes are discussed.