【摘要】：作為超超臨界火力發電機組的重要輔機,循環水泵運行的正常與否直接影響到整個火力發電機組的發電效率和安全運行。由于循環水泵所處的環境一般為強腐蝕性的海水,且在運行過程中不可避免會產生頻繁的振動,用于循環水泵的材質需要具備極好的耐腐蝕性能和優異的力學性能。當前,雙相不銹鋼以其優異的力學性能和良好的耐腐蝕性能,廣泛地應用在石油、化工、造紙、食品、軍事以及海洋工業等領域,并成為火力發電機組用材料的最佳選擇之一。作為華東最大的火力發電廠之一,浙江某火力發電廠三期擁有兩臺一百萬千瓦超超臨界火力發電機組,該機組的循環水泵在國內首次選用2205雙相不銹鋼作為母材材質,設計服役壽命為三十年,但是運行不到一年便發生了大面積異常斷裂的重大失效事故,嚴重影響到火力發電機組的正常運行,造成了巨大損失。本文綜合運用了失效分析的理論基礎和基本方法,采用了一系列宏微觀表征分析手段,從材料材質、制造工藝、運行工況、斷口形貌等多方面對這一重大失效事故進行了系統的研究與分析,最終找出引發這一重大失效事故的根本原因,并提出行之有效的解決對策,具體從以下三個方面進行展開。首先利用化學成分分析、金相組織觀察、電子背散射衍射技術等對該超超臨界機組循環水泵用雙相不銹鋼材質及焊接接頭進行了檢驗,并利用擺錘式沖擊試驗機對母體材料沖擊韌性進行評定,結果表明,循環水泵選用的母體材料成分、顯微組織以及沖擊韌性完全符合美國ASTM318O3標準的要求,質量評定合格,但焊接接頭中碳元素含量明顯超標,并且存在鐵素體相和奧氏體相比例不匹配的嚴重缺陷。這是引發焊接接頭脆化、強度下降的重要原因之一其次對發生嚴重失效的循環水泵進行了全面的現場調查和合理的取樣,確定了率先發生斷裂失效的位置,利用三維體式顯微鏡(3D-OM)、掃描電子顯微鏡(SEM)、能譜分析儀(EDS)等一系列宏微觀分析手段分別對失效循環水泵的法蘭、筒體以及吊耳等部件進行了系統分析,結果表明,不同段法蘭間拼接焊縫內嚴重的未焊透缺陷,是引發法蘭率先發生斷裂、進而引起整個循環水泵普遍發生異常斷裂的根本原因,而筒體的焊接處存在的未焊透和凝固裂紋等缺陷,是引起焊接接頭強度顯著下降、進而引發筒體發生過早斷裂的另一重要原因。最后,本文根據這一分析結果,提出了對應的切實可行的解決措施,最終經采納并實施,有效地解決了這一重大失效事故,保證了這兩臺百萬級超超臨界火力發電機組安全可靠地運行。
[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.
【學位授予單位】：復旦大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TM621

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