合成氨废热锅炉换热管的应力腐蚀研究

Study on Stress Corrosion Cracking of Exhaust-heat Recovery Boiler for Synthesis Ammonia

研究了合成氨废热锅炉换热管失效后的微观组织结构,提出了换热管除了遭受高温氧化外,主要还遭受了磷酸盐引起的应力腐蚀破裂。用4XCZ型金相显微镜鉴定和分析金属内部结构组织,对材料组织测定分析;用X射线衍射(XRD)并结合惠普3510型原子吸收分光光度计对腐蚀产物进行了分析;结合腐蚀产物及裂纹特点,提出了腐蚀坑的形成因素及锅炉用水处理中过量的磷酸盐引起的应力腐蚀破裂的机理。

The microstructures of failure heat exchanger tube in exhaust-heat recovery boiler from a ammonia plant are analyzed in this paper . It is shown that phosphates cause stress corrosion cracking (SCC) besides high temperature oxidation in heat exchanger tube .The metal microstructures were identified and analyzed by the 4XCZ metalloscope; The deposits scraped from the inside surface of the heat exchanger tubes were subjected to chemical analysis and X-ray diffraction and HP 3510 atomic absorptive spectrometer. The etch pits factors are presented according characteristic of cracking and corrosion products. The mechanism of stress corrosion cracking induced by excess phosphates in boiler water treatment is concluded.