1000MW超超临界机组双相不锈钢循环水泵异常断裂的失效分析及解决对策

发布时间：2018-10-30 19:57

【摘要】：作为超超临界火力发电机组的重要辅机,循环水泵运行的正常与否直接影响到整个火力发电机组的发电效率和安全运行。由于循环水泵所处的环境一般为强腐蚀性的海水,且在运行过程中不可避免会产生频繁的振动,用于循环水泵的材质需要具备极好的耐腐蚀性能和优异的力学性能。当前,双相不锈钢以其优异的力学性能和良好的耐腐蚀性能,广泛地应用在石油、化工、造纸、食品、军事以及海洋工业等领域,并成为火力发电机组用材料的最佳选择之一。作为华东最大的火力发电厂之一,浙江某火力发电厂三期拥有两台一百万千瓦超超临界火力发电机组,该机组的循环水泵在国内首次选用2205双相不锈钢作为母材材质,设计服役寿命为三十年,但是运行不到一年便发生了大面积异常断裂的重大失效事故,严重影响到火力发电机组的正常运行,造成了巨大损失。本文综合运用了失效分析的理论基础和基本方法,采用了一系列宏微观表征分析手段,从材料材质、制造工艺、运行工况、断口形貌等多方面对这一重大失效事故进行了系统的研究与分析,最终找出引发这一重大失效事故的根本原因,并提出行之有效的解决对策,具体从以下三个方面进行展开。首先利用化学成分分析、金相组织观察、电子背散射衍射技术等对该超超临界机组循环水泵用双相不锈钢材质及焊接接头进行了检验,并利用摆锤式冲击试验机对母体材料冲击韧性进行评定,结果表明,循环水泵选用的母体材料成分、显微组织以及冲击韧性完全符合美国ASTM318O3标准的要求,质量评定合格,但焊接接头中碳元素含量明显超标,并且存在铁素体相和奥氏体相比例不匹配的严重缺陷。这是引发焊接接头脆化、强度下降的重要原因之一其次对发生严重失效的循环水泵进行了全面的现场调查和合理的取样,确定了率先发生断裂失效的位置,利用三维体式显微镜(3D-OM)、扫描电子显微镜(SEM)、能谱分析仪(EDS)等一系列宏微观分析手段分别对失效循环水泵的法兰、筒体以及吊耳等部件进行了系统分析,结果表明,不同段法兰间拼接焊缝内严重的未焊透缺陷,是引发法兰率先发生断裂、进而引起整个循环水泵普遍发生异常断裂的根本原因,而筒体的焊接处存在的未焊透和凝固裂纹等缺陷,是引起焊接接头强度显著下降、进而引发筒体发生过早断裂的另一重要原因。最后,本文根据这一分析结果,提出了对应的切实可行的解决措施,最终经采纳并实施,有效地解决了这一重大失效事故,保证了这两台百万级超超临界火力发电机组安全可靠地运行。
[Abstract]:As an important auxiliary unit of ultra supercritical thermal power generating unit, the operation of circulating water pump directly affects the generating efficiency and safe operation of the whole thermal power generating unit. Because the environment of circulating water pump is generally strong corrosive sea water and frequent vibration will inevitably occur in the process of operation, the material used for circulating pump must have excellent corrosion resistance and excellent mechanical properties. At present, duplex stainless steel is widely used in petroleum, chemical, papermaking, food, military and marine industries for its excellent mechanical properties and good corrosion resistance. As one of the largest thermal power plants in East China, a thermal power plant in Zhejiang Province has two 1 million kilowatts ultra supercritical thermal power generating units in the third phase. The circulating water pump of this unit is the first time in China to select 2205 duplex stainless steel as the base material. The design service life is 30 years, but within a year of operation, a large area of abnormal fracture occurred, which seriously affected the normal operation of thermal power generating units, resulting in huge losses. In this paper, the theoretical basis and basic method of failure analysis are synthetically used, and a series of macro and micro analysis methods are adopted, from material, manufacturing technology, operation condition. The fracture morphology and other aspects have systematically studied and analyzed the major failure accident, finally found out the root cause of the major failure accident, and put forward effective countermeasures, which are carried out from the following three aspects. At first, the material of duplex stainless steel and welded joint for circulating water pump of this ultra-supercritical unit were tested by chemical composition analysis, metallographic observation and electron backscatter diffraction technique. The impact toughness of the parent material was evaluated by using a pendulum impact testing machine. The results show that the composition, microstructure and impact toughness of the matrix material selected by the circulating water pump fully meet the requirements of the ASTM318O3 standard of the United States, and the quality evaluation is qualified. However, the content of carbon in welded joints is obviously over the standard, and there is a serious defect that the proportion of ferrite phase and austenite phase does not match. This is one of the important reasons for the brittleness of welded joints and the decrease of strength. Secondly, a comprehensive field investigation and reasonable sampling of circulating water pumps with serious failure have been carried out, and the position where the fracture failure occurred first has been determined. A series of macro and micro analysis methods, such as three dimensional solid microscope (3D-OM), scanning electron microscope (SEM),) energy spectrum analyzer (EDS) and so on, were used to analyze the flange, cylinder and hoist of the failed circulating water pump. The results show that the serious failure of weld penetration in the weld joint between flanges in different sections is the fundamental reason that leads to the fracture of the flange, and then causes the abnormal fracture of the whole circulating water pump. However, the defects such as weld penetration and solidification cracks in the welded part of the cylinder are another important reason for the decrease of the strength of the welded joint and the premature fracture of the cylinder. Finally, according to the results of this analysis, this paper puts forward the corresponding practical solutions, which are finally adopted and implemented to effectively solve this major failure accident. These two million-class ultra-supercritical thermal power generating units are safely and reliably operated.
【学位授予单位】：复旦大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM621

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