通过裂纹宏观形貌、显微组织、力学性能等分析,研究了1021 t/h锅炉用TP304H 屏式过热器夹持管弯头高温运行62000 h泄漏原因.结果表明,在高温运行敏化温度下,冷加工成型TP304H弯管腐蚀敏感性增强,弯管内外部存在腐蚀介质,长期运行过程中,在运行管内蒸汽应力、热应力以及管排振动、锅炉启停等产生的交变应力作用下,产生应力腐蚀. 蒸汽侧应力腐蚀是造成泄漏的主要原因.
Fracture analysis of bend TP304H tube on pendant-heater operated on super-heater for 62000 hours in a 1021 t/h boiler was carried out by means of examinations such as macro-morphology of crack, mechanical property and metallographic of tube steel. The results showed that the corrosion cracking resistance of the TP304H steel tube was degraded due to the existing residual stress brought by original cold-forming process and also due to the operation temperatures of tubes which were just around the sensitivation temperature of the steel. Besides the ash deposits on the surface of tubes and inner corrosive environment all accelerated the corrosion of the tubes. It is expected that large tensile stress such as operating thermal stress and alternating stress of start-up and lay-up of boiler may existe at the bend tube. All the above factors may induce intergranular corrosion cracking of the tube for long operation time. It follows that the steam side stress corrosion cracking may be mainly responsible for the failure of tubes for the pendant-heater.
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