核电异种钢焊缝性能及超声检测技术

发布时间：2018-03-22 22:16

本文选题：压力容器　切入点：异种钢焊缝　出处：《东南大学》2015年硕士论文　论文类型：学位论文

【摘要】：核能是世界公认的安全、经济、清洁能源,许多国家都将发展核能作为本国能源计划的重点。核能的堆型和容量有很多种,且在不断地发展和完善,目前世界上装机容量最多的是轻水压水反应堆(PWR)。轻水压水堆核电站一回路包括反应堆压力容器、稳压器、蒸汽发生器、主泵、主管道等,压力容器的异种钢之间焊接所产生的焊缝性能如何,将直接影响到核电的安全性。本文研究了核电压力容器异种钢焊缝的性能及其薄弱环节,通过超声仿真检测技术模拟了缺陷的形状、分布、位置和超声检测参数,采用核电现场多通道双晶纵波聚焦超声检查技术对仿真结果进行了验证。针对异种钢焊缝,开展了焊缝成分、组织和性能研究,分析了断口微观形貌,并研究了焊缝融合线处的合金元素迁移率等,从而为探寻压力容器异种钢焊缝可能存在的薄弱环节提供实验依据。研究结果表明,压力容器异种钢焊缝低合金钢侧热影响区存在明显的粗晶区和细晶区,细晶区显微硬度相对于母材增加了17%左右；热影响区冲击值波动较大,冲击性能不稳定,脆化和裂纹倾向较高,拉伸试样全部断于该部位；同时由于低合金钢强度级别明显低于奥氏体不锈钢,判断低合金钢侧热影响区是整个异种钢接头性能的薄弱环节。根据异种钢焊缝性能研究结果,利用CIVA超声仿真软件在压力容器异种钢焊缝低合金钢侧熔合线粗晶区域构建超声仿真模拟裂纹,模拟裂纹基本特征为：30mm×10mm矩形,方向与焊缝熔合线相平行,距工件内表面的深度为9mm。超声仿真研究结果表明,针对构建的模拟裂纹,采用1.5MHz、70°TRL FS20超声探头检测时缺陷响应幅值最大,检测效果最好。在超声仿真试验结果基础上,本文选择了4个1.5MHz、70°TRL FS20双晶纵波聚焦斜探头,辅以4个1.5MHz、45°TRL FS20双晶纵波聚焦斜探头和1个2MHz单晶纵波直探头,从不同方向对超声试块进行了验证性扫查。1.5MHz、70°TRL FS20探头扫查深度范围为距RPV试块内表面0～13mm,1.5MHz、45°TRL FS20探头扫查深度范围为距试块内表面3-23mm,覆盖了超声仿真裂纹模拟区域。超声检查结果：选取带缺陷的试块进行验证性超声扫查,发现试块内表面存在三处缺陷,缺陷长、高分别为20.5mm、7.4mm,27.5mm、13.1mm,38.4mm、15.4mm;本课题RPV超声试块焊缝及两侧热影响区无可记录缺陷,表明该试块既无仿真预估的裂纹,也无气孔、夹杂等其它缺陷存在。根据试验研究结果,本论文探讨了压力容器异种钢焊缝服役环境和性能劣变机理,晶粒尺寸对超声波检查的影响,仿真技术与超声波检测的关系,以及压力容器异种钢焊缝超声波检测参数的优化等。
[Abstract]:Nuclear energy is recognized as a safe, economic and clean energy source in the world. Many countries have made the development of nuclear energy the focus of their energy plans. There are many types and capacities of nuclear energy, and they are constantly developing and improving. At present, the largest installed capacity in the world is the light water pressure water reactor (LWPRR). The primary circuit of the LPWR nuclear power station includes reactor pressure vessels, regulators, steam generators, main pumps, main pipes, etc. The safety of nuclear power is directly affected by the weldability of dissimilar steel welded between different kinds of steel in pressure vessel. This paper studies the performance and weak link of the welding seam of dissimilar steel in nuclear pressure vessel. The shape, distribution, location and ultrasonic parameters of defects were simulated by ultrasonic simulation technique. The simulation results were verified by using multi-channel dual-crystal longitudinal wave focused ultrasonic inspection technique in nuclear power field. The composition, microstructure and properties of the weld were studied, the micromorphology of the fracture surface was analyzed, and the mobility of alloying elements at the fusion line of the weld was studied. The results show that there are obvious coarse-grained and fine-grained areas in the heat-affected zone of the low alloy steel weld of the dissimilar steel weld of pressure vessel. The microhardness of fine-grained zone increases by about 17% compared with the base metal, the impact value of the heat-affected zone fluctuates greatly, the impact property is unstable, the tendency of embrittlement and crack is higher, and the tensile specimens are all broken in this part. At the same time, because the strength grade of low alloy steel is obviously lower than that of austenitic stainless steel, judging the side heat affected zone of low alloy steel is the weak link of the whole dissimilar steel joint performance. The ultrasonic simulation crack was constructed by using CIVA software in the coarse grain region of the low alloy steel side fusion line of the dissimilar steel weld of pressure vessel. The basic characteristic of the simulated crack was: 1: 30mm 脳 10mm rectangle, and the direction was parallel to the weld seam fusion line. The depth from the inner surface of the workpiece is 9 mm. The results of ultrasonic simulation show that the defect response amplitude is the largest and the detection effect is the best when using 1.5 MHz TRL FS20 ultrasonic probe to detect the simulated crack. Based on the results of ultrasonic simulation test, In this paper, four 1.5 MHz FS20 70 掳TRL FS20 double crystal longitudinal wave focusing oblique probes, four 1.5 MHz TRL 45 掳TRL FS20 double crystal longitudinal wave focusing oblique probes and one 2MHz single crystal longitudinal wave straight probe are selected. The scanning depth range of 70 掳TRL FS20 probe is 0.13mm from the inner surface of the RPV specimen and 1.5 MHz 45 掳TRL FS20 probe is 3-23mm from the inner surface of the sample, covering the simulated ultrasonic crack area. Test results: the samples with defects were selected for verification ultrasonic scanning. It was found that there were three defects on the inner surface of the specimen, the length and height of which were 20.5mm / 7.4mm / 27.5mm / 13.1mm / 38.4mm / 15.4 mm respectively. There were no recorded defects in the weld seam and the heat-affected zone of both sides of the RPV ultrasonic test piece, which indicated that there were neither simulated cracks nor pores in the specimen. On the basis of the experimental results, this paper discusses the service environment and the mechanism of poor performance of the welding seam of pressure vessel dissimilar steel, the effect of grain size on ultrasonic inspection, and the relationship between simulation technology and ultrasonic testing. And the optimization of ultrasonic detection parameters of dissimilar steel weld in pressure vessel.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG441.7

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