基于线阵探测器的X和γ射线角焊缝检测试验分析

为了检测管子-管板角焊缝内部缺陷,提出了基于线阵探测器的管子-管板角焊缝射线数字检测方法。介绍了线阵列探测器成像原理,通过对管子-管板角焊缝试件的射线数字透射成像试验,分析了线阵列探测器在X和γ射线照射下的图像特点。试验表明,相比X射线,利用γ射线采集的图像质量稍差,并且整体灰度偏暗,采集时间较长。得出了影响线阵列探测器γ射线数字图像质量的一些关键因素,为线阵列探测器应用于γ射线提供了试验及应用依据。     

Root cause analysis of stress corrosion at tube-to-tubesheet joints of a waste heat boiler

Leakage at the tube-to-tubesheet joints occurred in a waste heat boiler. The mode and the root cause of the failure were investigated by chemical composition analysis of the tube material, metallographic structure and crack observation, and corrosion product analysis of the damaged tubes, as well as the operation condition examination of the waste heat boiler. Results revealed that failure of the tubes occurred due to the stress corrosion cracking (SCC), which was caused by tensile stress and chloride-buildup in the narrow and long gap between the tube and tubesheet hole. The gap formation was further analyzed by comparison of the minimum expansion pressure from the common formula provided by the manufacturer, with that from finite element method computations. It is found that the minimum expansion pressure used in manufacture is small and cannot eliminate the initial gap. Meanwhile, the enrichment of chloride in the gap was briefly discussed.     

动态效应对管子与管板液压胀接接头接触压力的影响

常见的低碳钢换热管与低合金钢管板胀接为例,采用有限元法进行了管子与管板液压胀接的动态和静态分析,研究了材料应变率等动态效应对胀接接头接触压力的影响。计算结果表明将液压胀管过程简化为静态过程处理,能够节省大量计算时间,而且对结果影响甚微,因此,在换热器管子与管板液压胀接过程中,材料加工的动态效应不显著,将其简化为静态过程是合理的。计算结果为换热器管子与管板液压胀接的理论分析和数值模拟提供了参考。     

蒸汽发生器管子—管板接头设计的计算方法

本文主要介绍液压胀接管子-管板接头设计的一种理论计算方法。该方法是:将接头的整个胀接过程分为四个阶段,以此为数学模形,用弹性理论和塑性理论分阶段对管子或管子和管板的应力、应变和位移进行分析,从而估算胀管压力、变形、残余应力和拔脱力等。该方法可用于设计蒸汽发生器和钢制管壳式换热器。文中指出,对核蒸汽发生器的管子-管板接头来说,采取液压胀后再局部滚胀比只进行液压胀更好。     

Investigation of welded structures on mechanical properties of 304L welded tube-to-tubesheet joints

This paper presents an investigation on effects of welded structures on pullout force and fatigue life of welded joints of 304L heat exchanger tube-to-tubesheet. Welded structures including inner-hole with a groove of 45°, extension, inner-hole with a groove of U-shape and plain-end were discussed. Full-size test blocks covering four types of welded structures were used to conduct pullout test and low cycle fatigue test. Furthermore, optical microscopy (OM) and scanning electron microscopy (SEM) were utilized to analyze the failure mechanism. The results show that the joints of the extension welded structure have the largest pullout force and fatigue life because of its largest fracture length, and the undeformed welded zone revealed favorable quality of weld. The cracks originate at the outer surface of tube and striations propagate at an average rate of 50 μm for a loading cycle, finally, the separation commences at the inner surface of the tube, exhibiting equiaxed or hemispheroidal dimples.     

管子—管板角焊缝自动超声波检测系统的研制

针对化工生产设备和核电站中列管式热交换器中的管子—管板角焊缝 ,研制了自动超声波检测系统。介绍了该系统的控制原理、总体结构、扫描图像获取、扫描机械手设计和系统软件开发等方面的关键技术。该系统采用计算机控制扫描机械手扫描管子—管板角焊缝 ,并采集相应的超声回波信号 ,经过一定的处理后 ,显示和打印图形化结果。扫描结果中显示了焊缝所存在的焊接缺陷及缺陷的准确位置。系统可以检测到直径为 0 .5 m m的缺陷 ,检测一个点的时间小于 0 .0 2秒。经实际应用表明该系统完全可以满足工业现场要求。