基于“环境破坏说”的氧化皮剥落理论

A Discussion on Exfoliation Behavior of Duplex Scales Based on Ecocide Hypothesis

在"环境破坏说"的基础上阐释了锅炉高温受热面氧化皮剥落的理论.双层氧化皮内、外层界面存在的空穴是氧化皮剥落的内因,氧化皮承受的应力是氧化皮剥落的外因.氧化皮空穴的成因又可分为内因和外因,内因主要是金属含铬量,外因主要包括蒸汽参数和蒸汽含氧量等.主蒸汽含氧量与铬酸根含量之间具有显著的正相关性,而主蒸汽氢电导率是反映氧化皮铬蒸发的特征指标.外层氧化皮剥落以后,内层氧化皮会继续增厚,但难以剥落.对于已经发生了氧化皮大面积剥落的超(超)临界锅炉,如果检查确认高温受热面氧化皮剥落比较完全,剥落之氧化皮清理比较彻底,则在相当长时期内氧化皮剥落问题都将不再是运行忧患.

Based on Ecocide Hypothesis, theories about the exfoliation of duplex scales on high-temperature heating surfaces of boiler are elaborated. The exfoliation is found to be caused by both internal and external factors, which are mainly the voids existing at the interface between inner and outer layer of scale, and the stresses lying in the scale. Furthermore, the internal and external causes that affect the formation of the voids are respectively chromium content in steel and steam conditions. In superheated steam, oxygen content bears pronounced correlation with chromate content. The cation conductivity of superheated steam could serve as the characteristic index of the chromia evaporation from scale. The inner layer would contin- ue to increase in thickness after exfoliation of outer layer, but it is hard to flake off then. In this case, supercritical units that have suffered thorough exfoliation would be relatively safe, without a worry about peeling off of oxide scales for a long period of time.