某电厂锅炉水冷壁管发生了爆管。通过失效管道宏观形貌和显微组织观察、管材化学成分和力学性能检测、腐蚀产物成分分析等对该水冷壁管爆管的原因进行了分析。结果表明:爆管位置有明显腐蚀沟槽,局部位置发生了Na元素浓缩,腐蚀产物主要为铁的氧化物(Fe₃O₄和Fe₂O₃)、水垢和一定量的NaFeO₂;断口无明显塑性变形,宏观形貌表现为脆断特征,微观形貌表现为沿晶断裂特征;爆管位置组织为铁素体+珠光体,组织中有大量沿晶裂纹;锅炉运行期间,锅炉水pH出现过一段时间较高(10.0～10.2)的情况。综合以上分析,确定水冷壁管失效原因为碱腐蚀引起的应力腐蚀开裂。

A water wall tube of a boiler in a power plant burst. The burst reasons of the water wall tube were analyzed by observing the macroscopic morphology and microstructure of the failed tube, testing the chemical composition and mechanical properties of the tube material, and analyzing the composition of the corrosion products. The results showed that there were obvious corrosion grooves in the burst location, and Na element concentration occurred in local location. The corrosion products were mainly composed of iron oxides (Fe₃O₄ and Fe₂O₃) and scale, and a certain amount of NaFeO₂. There was no obvious plastic deformation in the fracture showing brittle failure characteristic on macro morphology and intergranular cracking characteristic on micro morphology. The microstructure of the burst tube was ferrite and pearlite, and there were a large number of intergranular cracks in the microstructure. During the operation of the boiler, the pH of the boiler water was high (10.0-10.2) for a period of time. Based on the above analysis, it was determined that stress corrosion cracking caused by alkali corrosion was the failure reason of the water wall tube.