【作者】 朱加雷；

【导师】 焦向东；

【作者基本信息】 北京化工大学 ， 化工过程机械， 2010， 博士

【摘要】 核电是未来世界电力发展的趋势,也是低碳经济发展的需要。为了减少核辐射的影响,核电站内部设备的检查和维修往往要在水中进行。目前的核电站内部水下维修以手工焊为主,考虑到操作人员的健康、修复质量和修复效率等因素,核电水下环境焊接作业的发展趋势是远程控制自动化。局部干法水下焊接综合了干法水下焊接的高焊缝质量和湿法水下焊接技术简便易行的优点,是核电站水下焊接修复的首选方式,但目前尚未解决持续有效排水密封、局部干式焊接环境营造和焊接操作自动化问题,导致焊接过程欠稳定,接头质量不能完全满足核电相关标准要求,且罕见针对核电结构材料进行水下焊接工艺和焊缝性能研究的报导。本研究首先对核电结构材料的焊接性进行研究,通过核电用不锈钢材料的陆上焊接试验,掌握了不同焊接方式、焊接保护气体、送丝速度及电源设置弧长等参数对焊接过程和焊缝成型的影响,为随后的水下焊接试验提供基础数据。其次,建立了基于微型排水罩的局部干法自动水下焊接试验系统,主要由水下焊接试验舱、试验环境系统、焊接监视系统、自动焊接平台、电控系统和焊接电源等部分组成。各部分之间协调动作,能够模拟15m水深的焊接试验环境,并可以对焊接区域进行全过程的实时远程视频监控。在自动水下焊接试验系统当中集成了焊接质量分析系统,对焊接工艺参数及过程稳定性进行监控,以预测焊接质量。排水装置的有效排水密封是局部干法自动水下焊接顺利进行的前提条件,本研究通过理论计算及数值分析,获得了排水装置内部稳定的气体流动状态。采用组合材料密封垫设计,可以大大降低焊接电弧及熔池对密封部位的损伤,延长有效排水时间。在上述基础之上,进行了321不锈钢和304不锈钢材料的远程控制自动水下焊接试验,掌握了影响排水装置密封效果的因素及影响规律,确立了送丝速度、保护气体、运动参数、坡口形式和水深环境等对水下焊接质量的影响规律：随着送丝速度的提高,焊接过程的稳定性提高；保护气体中添加活性气体可以改善焊缝成型和优化熔滴过渡状态。获得了321不锈钢坡口对接焊和304不锈钢平板堆焊、坡口堆焊和坡口对接焊的水下焊接工艺参数；对不同结构下密封垫的持续密封性能进行了试验研究,通过使用组合材料密封垫获得了良好密封性能。最后进行了水下焊接焊缝的综合测试,结果表明：本研究获得的水下焊接工艺参数可以得到良好的水下焊接质量,而局部干法水下焊接过程的不连续是水下焊接缺陷产生的主要原因；与母材性能相比,焊缝的强度满足要求,韧性有所降低、硬度稍有增加,5m和15m水深的不同对焊缝力学性能没有明显影响。对坡口堆焊的焊缝化学成分分析表明,不锈钢水下焊接焊缝的耐腐蚀性能优于母材。根据理论分析和试验验证,由于水下环境对焊缝的强制冷却作用,焊缝在高温区停留的时间较短,奥氏体不锈钢水下焊接时不会产生晶间腐蚀,因此可以采用提高焊接效率的焊接工艺参数,这对于核辐射环境下的远程控制水下焊接而言非常重要。焊缝截面的宏观检测表明水下焊接焊缝与母材能够良好熔合,无可见缺陷。焊缝的微观金相组织分析表明,水下环境的焊缝在铁素体-奥氏体相变时扩散受到限制,铁素体的分布形态与干式环境不同。而对于不同环境水深下的焊缝而言,在排水效果良好的前提下,水的冷却作用与水深基本没有关系,水深对焊缝中铁素体含量及分布形式基本没有影响。能谱分析结果说明水下环境焊缝的Fe、Ci、Ni含量较干式焊缝中均有不同程度的提高,但Cr/Ni的比值比干式焊缝的略高。以上研究结果为局部干法自动水下焊接技术及奥氏体不锈钢材料的水下焊接工艺研究提供了良好基础。更多还原

【Abstract】 Nuclear power is not only the trends of power development, but also the needs of a low-carbon economic development. In order to reduce the effects of exposure to nuclear radiation, inspection and maintenance of internal equipments in nuclear power plant are often carried out in the water. The current underwater maintenance in nuclear reactors is mainly fulfilled by the manual welding. Considering such factors as the health of operators, repair quality and repair efficiency, the trend of nuclear power station underwater welding is remote control automation. Local dry underwater welding is the first choice of nuclear power station during underwater welding repair because it combines the advantages of high-weld-quality in dry underwater welding and easy-to-do in wet welding. But local dry underwater welding method has not solved the problems such as continuous and effective drainage seal, creating sealed environment for local dry welding and welding automation, which lead to less stability of the welding process and which mean joint quality can not fully meet the relevant standards of nuclear power. Besides the study report is rarely in view on underwater welding technology and welding joints properties of nuclear power structural materials.Firstly, this research studies the nuclear power structural material’s weldability through the-in-air welding test of nuclear power station with stainless steel material, and while getting to know the regular pattern of different welding methods, welding shielding gas, wire feed speed and arc length to weld processes and the welded joint formation, the basic data is gained for the following tests.Secondly, this study has established the local dry automatic underwater welding test system based on miniature draining water cover, which is mainly composed of underwater welding test cabin, test environmental system, welding monitoring system, automatic welding platform, electronic control system and welding power supplies. Coordinating action of different parts of system can simulate the welding test environment under 15-meter-depth water, and can realize the real-time remote surveillance of whole process on the welding regions. Integrated the welding quality analysis system in the automatic underwater welding test system can monitor the welding process parameters and the stability to forecasts the welding quality.Effective seal of draining water device is a prerequisite for the local dry automatic underwater welding to carry on smoothly. The research has obtained the gas flow stability in drainage system through theoretical calculation and numerical analysis. Using the combination material gasket design can significantly reduce the damage to the sealed parts from welding arc and weld pool, and extend the effective drainage timeBased on the above, remote control automatic underwater welding experiments of 321 and 304 stainless steel have been conducted. With the experiments the key factors and rules influencing the sealing effect have been recorded, and the law of effect has been established of wire feed speed, shielding gas, moving parameters, groove form and depth of water environment to the welding quality, which says along with the increase of wire feed speed the welding stability of process has been enhanced and adding the active gas to shielding gas can improve the welded joint formation and the optimize melt drop state of transition. The test has also obtained underwater welding technological parameters of 321 stainless steel groove butt welding and 304 stainless steel surfacing welding, built-up welding and groove butt welding.Conducting the experimental study on continually sealing performance of different gasket structure, obtained good sealing property by using combination material gasket.Finally, the comprehensive test has been carried out on underwater weld. The results show:the underwater welding technological parameter obtained in the study can achieve a good underwater welding quality, and not-continuous local dry underwater welding process is the main reason which leads to the underwater welding flaw; compared with the parent metal performance, weld strength meets the requirements while toughness is decreased and hardness is increased slightly; 5m and 15m water depth does not have the obvious different effects on the weld mechanical properties. Chemical composition analysis on the built-up welding weld shows that the anti-corrosive performance of underwater stainless steel weld is superior to the parent metal.According to theoretical analysis and experimental confirmation, the time that weld stay at high temperatures is shorter than in the air due to the forced cooling effect on the weld in underwater environment, and thus the underwater welding of austenitic stainless steel will not have the intercrystalline corrosion. Therefore the welding process parameters can be used to improve welding efficiency, which is very important for the remote control of underwater welding in nuclear radiation environment.The weld macro-analysis of cross-section has showed that underwater welding weld with the parent material can be a good fusion with no visible defects. Microstructure analysis showed that the ferrite-austenite phase transformation has been restricted in underwater welding weld. The distribution of ferrite morphology is different to that in dry environment weld.As for the weld under different environments in terms of water depth, under the premise of good draining water effect, the water cooling effect basically has nothing to do with the water depth, and the water depth has no effect on ferrite content and distribution morphology. Energy-dispersive spectrometry(EDS) analysis shows that the Fe, Cr, Ni contents in underwater environment weld increase to some degree and the Cr/Ni is slightly higher than that in dry environment weld.The above results have laid a good foundation for the local dry automatic underwater welding technology research and austenitic stainless steel materials underwater welding technology research.更多还原