深度调峰长期服役TP347H钢管内壁氧化皮结构与形成机理

目的 掌握和应对深度调峰带来的新的安全隐患，对某深度调峰超临界机组的高温过热器和屏式过热器TP347H钢管内壁氧化皮开展研究。方法 采用物相成分测试和显微组织分析相结合的方法，探讨氧化皮的结构及其形成机理。结果 中间气孔层将氧化皮分为内外2层，外层为Fe2O3，结构疏松；内层较致密，主要为(Fe, Ni)Cr2O4，其中部分晶界富Cr相与含氧水蒸气反应、气化，形成气孔。含氧水蒸气通过气孔向钢基体扩散，并与其中的Cr反应，形成不连续的Cr2O3薄层。钢中的Fe原子通过Cr2O3薄层的缝隙扩散至内外层氧化皮界面，氧化形成Fe2O3，促进外层氧化皮的生长。结论 深度调峰促进了管道内壁氧化及氧化皮中气孔的形成，同时在外层氧化皮表层诱发微裂纹，促使氧化皮剥落。

Microstructure and Formation Mechanism of Inner-wall Oxide Layers of TP347H Steel Tube in Long-term Service Involving Deep Peak-load Shaving

The work aims to study the inner-wall oxide layers of the TP347H high-temperature superheater and pendant superheater tubes of a super critical unit involving deep peak-load shaving to master and handle the new safety issues brought with deep peak-load shaving. Phase composition and microstructure tests were conducted to clarify microstructure and its formation mechanism of the oxide layers. The results showed that the oxide layer was divided into the inner and outer sub-layers by the medium layer of pores. The outer-sublayer had a loose structure, and consisted of Fe2O3; meanwhile, the inner-sublayer was dense, and mainly consisted of (Fe, Ni)Cr2O4, in which the Cr-rich grain-boundary phase partly reacted with the vapor containing oxygen, and then gasified to form the in-situ pores. The vapor diffused through the pores, and reacted with Cr in the steel, resulting in formation of the thin discontinuous Cr2O3 layer. On the other hand, the Fe atoms in the steel diffused into the inner/outer sublayer interface though the voids in the thin Cr2O3 layer, and reacted with the vapor to form Fe2O3, promoting the growth of the outer sublayer. Deep peak-load shaving accelerates oxidation of the inner-wall of the TP347H steel tubes and formation of the pores in the oxide layers, and also induces microcracks in the outer sublayer. As a result, exfoliation of the inner-wall oxide layer is promoted.