【作者】 缪存坚；

【导师】 郑津洋；

【作者基本信息】 浙江大学 ， 化工过程机械， 2012， 博士

【摘要】 能源的储运是全球能源发展战略的重要环节,随着低温技术的发展和能源需求的不断增长,低温液化储运已成为能源高效率储运的重要手段。以天然气为例,液化天然气(LNG)的储运已然成为天然气的主要储运方式。深冷容器作为LNG等低温液化气体的常用储运装备,在医疗、化工机械、航空航天等领域已得到了广泛应用,在我国“十二五”期间能源结构转型和节能减排等战略目标的实现过程中发挥着重要作用。奥氏体不锈钢应变强化深冷容器具有重量轻(其内容器在同等压力参数下比常规内容器轻30～50%)、容重比高、制造运行能耗少等优点,符合国家倡导的“低碳”、“绿色”、“轻量化”等发展理念。开展奥氏体不锈钢深冷容器的应变强化适应性研究,揭示应变强化对深冷容器材料与构件的强度、韧性、抗疲劳性的影响规律,对促进应变强化深冷储运设备的发展、实现安全与经济并重、安全与资源节约并重具有重要意义。疲劳特性是应变强化深冷容器尤其是移动式容器的重要特性,是评估分析深冷容器全寿命周期安全性的重要依据。应变强化深冷容器目前已被纳入欧盟、澳大利亚、美国、ISO等多部标准以及中国的多部企业标准中,然而这些标准并没有给出应变强化深冷容器疲劳方面的具体设计。另一方面,深冷工况是应变强化深冷容器的主要工作环境,而当前的疲劳设计并没有考虑深冷温度对疲劳性能的影响。此外,研究发现,国内外缺乏在深冷环境下检测材料疲劳特性的手段,且国内目前还没有能够实现此功能的试验装置。本文在国家高技术研究发展计划(863计划)重点项目“极端条件下重大承压设备风险评价与寿命预测关键技术研究”(项目编号为2009AA044801)的支持下,针对目前最为缺乏的应变强化深冷容器疲劳设计问题,从研制搭建深冷疲劳试验装置、研究应变强化奥氏体不锈钢室温和深冷下的疲劳特性等方面开展研究,主要完成的工作如下：(1)基于奥氏体不锈钢深冷环境下拉伸和疲劳过程的力学响应,确定了深冷疲劳试验装置的吨位、深冷温度、应变检测等方面的关键参数。综合考虑试验装置加载系统、恒温系统、控制系统、数据检测系统和安全系统的结构与运行原理,提出了恒温功能和试验功能的集成方法。在此基础上搭建了能实现室温至-196℃温度下材料拉伸和疲劳功能的深冷疲劳试验装置,并通过试验验证了其功能。对比分析横梁位移控制和引伸计控制两种试验速率控制方式的特性和差异,提出适用于深冷环境试验的数据检测方法。(2)通过应变强化奥氏体不锈钢EN1.4301材料与容器的室温疲劳试验研究,得到了应变强化前后材料疲劳应力响应、循环本构关系以及应变-寿命关系的变化规律,分析了强化对材料和容器疲劳寿命的增益作用。基于材料力学特性、组织相变行为以及位错运动等宏微观角度,讨论了应变强化对材料疲劳性能的增益机制。基于试验数据获得了应变强化影响下的S-N曲线并分析了曲线的特征,将曲线与标准中疲劳设计曲线对比,分析了现有S-N曲线对应变强化容器的适用性。(3)基于室温和液氮温度下奥氏体不锈钢试验数据,得到了奥氏体不锈钢拉伸和疲劳性能在应变强化和液氮环境作用下的力学性能响应规律。在本文试验背景下,从宏观力学行为和组织相变角度分析了深冷和应变强化对材料拉伸和疲劳性能的强化作用,以及两者对奥氏体不锈钢疲劳寿命的增益作用。更多还原

【Abstract】 With the development of cryogenic technology and the growing energy demand, the storage and transport of cryogenic liquid gases have become an important and effective way for transporting energy. The storage of LNG and other liquefied gases have been an important step in the development strategy of global energy. To transport LNG, for example, cryogenic pressure vessels are commonly used in the field of medical treatment, chemical engineering, and aerospace, playing an important role in the development of energy plan about our country’s "Twelve Five-Year Planning Program".Cold stretched cryogenic pressure vessels from austenitic stainless steels have the advantages of thinner thickness, lighter weight (the inner vessel is about30-50%lower in comparison with the conventional ones), bigger volume, lower cost, and lower energy consumption, which are consistant with the development concept of "low carbon","green", and "light". It is great and meaningful to impell the development of cold stretched cryogenic pressure vessels, and to fulfill the concept of safe and economy by researching on behaviors of cold stretched cryogenic pressure vessels and responses of cold stretching on strength, ductility and fatigue properties of materials or structures.Fatigue response is important for the design of cold stretched cryogenic pressure vessels and risk accessments in vessels’entire lives. Nowadays, these products have been included in the standard of Europe, Australia, America, ISO, and China, though there are no design details about the fatigue for cold stretched pressure vessels, and no relative design about the effect of cryogenic temperature on material properties. Furthermore, it is found that there are few methods to test the material’s fatigue properties at cryogenic temperature, and there are no equipments for such functions in China.Based on the research of fatigue design of cold stretched cryogenic pressure vessels, this paper aims to design and manufacture the fatigue testing machine for cryogenic environment, so the fatigue properties at room and cryogenic temperature environment could be obtained. The main contents and work of this paper are described here: (1) Based on the mechanical response of austenitic stainless steel’s tensile and fatigue tests, the parameters of the fatigue testing machine for cryogenic environment are determined such as the load, the temperature, and data detecting methods. Considering the loading structures, temperature control system, machine control system, data collecting system, and safe security, some integrated methods to mix the temperature control system and the testing function are proposed. The fatigue testing machine for cryogenic environment is manufactured, and is justified to be workable in tensile and fatigue tests from room temperature to-196℃. Strain detecting method is found by comparing crosshead control method and strain gauge control method for cryogenic environment.(2) Fatigue tests of cold stretched austenitic stainless steel and vessels are conducted, and the mechanical behavior is gained such as material fatigue response, cyclic stress-strain curve and strain-life curve. The mechanism of improving the fatigue resistance by cold stretching is analyzed from material’s mechanical properties, strain-induced martensite transformation, and dislocation’s movement. The S-N curves about cold stretching are gained to analysis the effect of cold stretching, and the curves are compared with the ones in standards. Further, the use of ASME VIII-2design curves for cold stretched vessels are justified.(3) Based on the tests’data at room and cryogenic temperature, the response of tensile and fatigue under the influence of cryogenic temperature and cold stretching are obtained. Under the test parameters of this paper, the strengthening effect in tensile and fatigue behavior by cryogenic temperature and cold stretching have been discussed from the points of view with micro and macro behavior in phase structure and mechanical properties respectively. The improving effect of cryogenic temperature and cold stretching on material’s fatigue life has also been discussed.We would like to acknowledge the financial support from the key projects in the National High Technology Research and Development Program (863Program)(Project No.:2009AA044801).更多还原