发动机燃油总管分油管断裂分析

采用外观检查、金相检验、断口宏观和微观分析,对发动机燃油总管分油管断裂的原因进行了分析。结果表明:分油管的断裂均为疲劳断裂,疲劳断裂位置一般位于管子接头的焊接区域,主要原因是该区域存在露出表面的焊接缺陷和装配应力过大。     

板片表面缺陷尺度对印刷板式换热器扩散焊接的影响研究

针对印刷板式换热器换热板片表面缺陷的尺度问题,开展试验分析研究,重点研究了板片表面缺陷宽度对换热器芯体扩散焊性能的影响规律,从拉伸强度和微观界面组织两个方面阐述了缺陷宽度对扩散焊接的影响情况.结果 表明,当缺陷深度小于0.1 mm,宽度小于0.82 mm时,表面缺陷不影响印刷板式换热器的焊接性能.     

锈蚀焊接空心球节点随机抗压承载力研究

焊接空心球节点(WHSJs)自1966年被提出以来,已经广泛地应用于空间网格结构中,至今已有55年的应用历史。由于环境的侵蚀、后期维护不到位等,焊接球节点锈蚀的现象屡见不鲜。该文针对随机锈蚀后焊接空心球节点的抗压承载力的变化规律进行了研究,基于随机有限元分析方法进行了大量的随机数值分析,研究了锈蚀深度概率分布模型对抗压承载力折减系数的影响;利用曲线拟合技术提出了折减系数下限和上限曲线的理论计算公式;通过随机有限元的大量分析结果揭示了抗压折减系数随锈蚀深度概率分布模型的变化规律;提出了用于预测抗压折减系数概率分布模型的拟合公式;通过对具有不同几何参数的焊接空心球节点的分析,得到了该文结论对不同几何尺寸下焊接球节点的适用性。研究结果表明,所提出的方法可以准确确定随机锈蚀焊接空心球节点抗压承载力折减系数的随机概率分布模型,可为随机锈蚀焊接球节点承载力的评估提供理论分析基础。     

中性盐雾环境下钢板表面锈蚀深度随机场模型

为了得到中性盐雾环境下钢板表面锈蚀深度随机场模型,采用中性盐雾循环试验对10组试件进行加速锈蚀,获得了锈蚀钢板表面轮廓图及锈蚀深度三维坐标数据.研究了锈蚀深度概率分布特性,分析了锈蚀深度均值、标准差与锈蚀率的关系.对锈蚀深度进行了平稳性与各态历经性检验,提出了锈蚀深度随机场自相关函数模型.结果表明:钢板表面锈蚀深度符合正态分布;随锈蚀率的增大,锈蚀深度均值、标准差也增大;钢板表面锈蚀深度具有平稳性与各态历经性;余弦三角函数随机场模型能较精确地表征锈蚀深度分布特征.     

焊接对金属材料腐蚀性能的影响

金属材料在焊接加工过程中,焊接接头区各部分性能、组织和化学成分会发生较大变化,同时焊接还会对材料的腐蚀性能产生较大影响.焊接接头区是受力状况最恶劣、腐蚀行为最复杂并集中体现的区域.首先,焊接造成的表面缺陷如焊瘤、咬边、未焊透等,均使熔敷金属与母材间形成缝隙.喷溅也使母材和金属粒之间相接触的部位形成缝隙.在电解质溶液(如NaCl水溶液)中,这些缝隙处往往会发生缝隙腐蚀.当然,发生缝隙腐蚀的条件包括缝隙大小、介质的滞流状态和腐蚀特性等诸方面的因素.但焊接表面缺陷无疑给发生缝隙腐蚀提供了场所.     

304不锈钢冷却管束加工缺陷产生原因分析

通过化学成分分析、金相检验和断口分析等方法检测分析了在某一批次加工304不锈钢冷却管束过程中产生缺陷的原因。结果表明:缺陷主要有清理焊缝后出现的凹坑和焊后出现的裂纹两种;由于材料中存在微量氧和锡等有害元素以及分布不均的铜和铈元素,导致在管子焊接过程中,钨极氩弧焊接过程中熔池中产生氧化物熔渣,有的残留在焊缝金属表面被去除后产生凹坑;焊管在弯曲过程中,由于Cu-Sn合金产生铜脆而在钢管的受拉应力的一侧产生局部裂纹。因此,这些缺陷是由此批次不锈钢的纯净度较差引起的。     

汽轮机叶片锈蚀原因分析

H356汽轮机叶片在装机时发现有大量锈蚀情况.通过宏观和微观检验、化学成分分析以及能谱分析等手段对锈蚀叶片进行了全面分析,并对该叶片进行了不同环境及条件下的锈蚀试验,从而对叶片锈蚀的原因进行了分析.结果表明:叶片锈蚀为点腐蚀,叶片材料中铬含量偏低,叶片表面大面积地接触到氧化剂和活性离子(Cl-),并长期储存于湿度高于6...     

旋转速度与焊接速度对铝铜异种材料搅拌摩擦焊接头成形的影响

目的为了获得较好的铝铜异种材料搅拌摩擦焊焊缝,研究旋转速度与焊接速度对焊缝成形的影响规律。方法采用对接的方式对4mm厚的纯铝和紫铜进行搅拌摩擦焊,对比了不同旋转速度和焊接速度对铝铜异种金属焊缝表面的影响,并对焊缝内部成形变化进行了分析。结果旋转速度和焊接速度对焊缝的成形影响较大,当旋转速度为1200 r/min,焊接速度为10 mm/min时,焊缝表面成形美观,焊缝表面相对较为光滑,焊缝内部存在相互交叠的片层结构和漩涡状结构,焊缝内部未见明显缺陷;与旋转速度1200 r/min,焊接速度10mm/min相比,在焊接旋转速度减小或者焊接速度变大时,由于焊接热输入减小,造成焊缝表面出现沟槽、孔洞等焊接缺陷,同时搅拌针的旋转搅拌作用影响焊缝成形和焊缝内部缺陷的产生。结论选择合适的旋转速度和焊接速度能够获得宏观成形较好和内部缺陷较少的焊缝。     

钢桥面板纵肋与横隔板焊接细节表面缺陷及疲劳效应研究

初始焊接缺陷是影响结构件疲劳性能的关键因素之一。在断裂力学评估框架下引入特征化初始焊接缺陷,结合相互作用积分法与复合断裂准则解决由表面缺陷所导致的复合型疲劳裂纹扩展问题,在此基础上编写裂纹扩展模拟程序,建立表面焊接缺陷效应评价方法,通过分析揭示了不同形态和尺度的初始焊接缺陷对于钢桥面板纵肋与横隔板构造细节裂纹扩展关键性度量指标和疲劳寿命预测的影响。结果表明:所建立的方法可有效用于评估焊趾部位表面焊接缺陷对于疲劳性能的效应;面状缺陷对于裂纹扩展度量指标和疲劳寿命预测结果的影响更为显著,其初始缺陷深度和形态均是影响疲劳性能的关键因素,体积型缺陷对于疲劳寿命的影响主要由深度方向的缺陷尺寸决定;焊接缺陷的形态和几何参数取值应根据工程实际和规范建议值共同确定,直接简化为面状缺陷会低估结构件的疲劳寿命;考虑焊接缺陷不确定性的可靠度评估方法尚需进一步研究。     

单晶高温合金表面缺陷焊接修复的研究进展

单晶高温合金的性能优异,但是制造成本昂贵,因此其表面缺陷的焊接修复一直是单晶高温合金领域的重要研究课题。本文全面阐述了各类焊接修复(包括熔焊、钎焊和瞬时液相扩散焊)方法对修复区的组织和修复后力学性能的影响,分析了各类焊接修复方法的局限性和存在的问题,并指出了单晶高温合金表面缺陷焊接修复的发展方向。     

A study on fitness-for-service assessment for crack-like defects and corrosion in nuclear reactor pressure tubes

This paper looks forward to thoroughly assess zirconium alloy (Zr-2) pressure tubes used in nuclear power reactors for crack like and corrosion type defects. It emphasizes on the use of reliability concept for determining the probability of failure of zirconium alloy pressure tubes based on deuterium ingress. The in depth analysis carried out to calculate the reliability index for the above two problems is based on FORM approach. A steady state corrosion rate is assumed to estimate the growth in the dimensions of corrosion defects. The methodology suggested in this paper is useful for designers and plant engineers in timely detection of the cracks and leaks in the pressure tubes used in nuclear reactors and initiate suitable corrective actions based on their criticality.     

火力发电厂凝汽器铜管的腐蚀与防护

介绍了火力发电厂凝汽器铜管在使用寿命期间的腐蚀状况,指出黄铜管的腐蚀主要表现为脱锌腐蚀、应力腐蚀开裂和冲蚀等,分析讨论了其各自的腐蚀机理及相应的控制措施,介绍了铜管主要保护方法--硫酸亚铁成膜技术,对控制电厂铜管腐蚀提供一定的参考.     

Sulfuric acid dew point corrosion in waste heat boiler tube for copper smelting furnace

This paper presents the sulfuric acid dew point corrosion found on waste heat boiler tube for a copper smelting furnace. Macroscopic and microscopic observation results for the failed boiler tubes are shown. Then the analyzed results by X-ray fluorescence, X-ray diffraction and EPMA on failed boiler tubes are demonstrated. Finally effective alloying elements for waste heat boiler tube material against sulfuric acid dew point corrosion are briefly described on the basis of the exposure test results for three kinds of steels in the radiation section of the waste heat boiler.     

Failure Analysis of T12 Boiler Re-Heater Tubes During Short-Term Service

The failure of T12 re-heater tubes that had been in service only for 3000 h was investigated. The wall thickness of the tubes was visibly reduced by heavy oxidation corrosion on the outer and inner walls. The original pearlite substrate completely decomposed. Uniform oxide scale appearance on the inner wall shows obvious vapor oxidation corrosion characteristics. Corrosion originated in the grain boundary, and selective oxidation occurred due to ion diffusion in the substrate. The layered oxide scale formed on the inner wall is related to the different diffusion rates for different cations. Exposure to high temperature corrosive flux accelerated the corrosion on the outer wall. The microstructure degradation and corrosion characteristics of the tubes indicate that the tubes failed primarily because of overheating, as evidenced by calculations.     

累积退火参数对SZA-4合金管材耐腐蚀性能的影响

目前有关累积退火参数对大型先进压水堆用锆合金SZA-4耐腐蚀性能影响的研究还不系统。通过改变管材加工过程中管坯的热处理温度和成品退火制度(再结晶退火、去应力退火),制备了4组累积退火参数不同的SZA-4合金包壳管,在Li OH水溶液和400℃蒸汽中进行了高压釜腐蚀试验,研究了累积退火参数对管材耐腐蚀性能的影响规律。结果表明:累积退火参数对SZA-4合金包壳管的耐腐蚀性能影响不显著;成品退火温度是影响SZA-4合金耐腐蚀性能的主要因素;再结晶态包壳管的耐腐蚀性能比去应力态的好。     

蒸汽管线三通管的泄漏原因分析

催化装置的蒸汽管线上有多个三通管均在焊缝处发生蒸汽泄漏。采用化学成分分析、硬度测试、宏观和微观分析等方法对泄漏的三通管进行了分析。结果表明,由于在焊接时,接口处未焊透留下了缝隙,在工作介质和焊接应力的长期作用下产生了缝隙腐蚀和应力腐蚀,最终导致泄漏。     

改性PTFE软管的材质鉴定及性能比较与评价

采用XRD、FT-IR、XPS、DSC等方法对两种颗粒改性PTFE软管的组成、结构、热性能等进行了表征分析;通过腐蚀介质浸泡试验,对软管的耐腐蚀性能进行了评价;并使用三维体视电镜对其表面形态进行了观察。两种软管的性能比较表明国产软管的主要性能已达到国外同类产品的水平。     

Pitting corrosion of steel tubes in an air preheater

Severe pitting corrosion of a carbon steel tube was observed in the air preheater of a power plant, which runs on rice straw firing. Approximately 1450 tubes were removed from Stage 3 of the preheater (air inlet and flue gas outlet) due to corrosion and local bursting. Samples from Stage 2 (where corrosion was low) and Stage 3 (severe corrosion) were taken and subjected to visual inspection, scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness measurement, and chemical and microstructural analysis. It was determined that extended non-operation of the plant resulted in the settlement of corrosive species on the tubes in Stage 3. The complete failure of the tube occurred due to diffusion of these elements into the base metal and precipitation of potassium and chlorine compounds along the grain boundaries, with subsequent dislodging of grains. The nonmetallic inclusions acted as nucleating sites for local pitting bursting. Nonuniform heat transfer in Stage 3 operation accelerated the selective corrosion of front-end tubes. The relatively high heat transfer in this stage resulted in condensation of some corrosive gases and consequent corrosion. Continuous operation of the plant with some precautions during assembly of the tubes reduced the corrosion problem.     

Failure analysis of carbon steel components in a water bath heater and the influence of ethylene glycol concentration

Water bath heaters are designed to heat the gas prior to pressure reduction. In this paper, corrosion failure of coil tubes, fire tubes and inner surface of the shell from a large water bath heater is described and the effect of ethylene glycol concentration has been investigated. In order to study the main cause of failure, non-destructive and destructive tests, including evaluation of mechanical properties, X-ray diffraction, scanning electron microscopy, EDS (energy dispersive spectroscopy), microanalysis of corrosion products and chemical analysis of water used in the heater were carried out on specimens prepared from coil tubes. The results indicated that insufficient control of water level in the tank resulted in oxygen concentration corrosion. After evaporation of water content, a residue remained on the surface leading to under deposit corrosion and, through that, a blister-like damage took place on the shell roof. After detachment, corrosion products and scales, fell down and remained on the upper surface of the components, leading to scale corrosion of carbon steel coil and fire tubes. Results of laboratory corrosion tests revealed that water containing 10–40% ethylene glycol had the lowest corrosion rate, whereas with concentrations < 10%, the corrosion rate was high.     

In-service defects in the heat-exchange tubes of steam generators at nuclear power plants

We consider specific features of the in-service defects in the heat-exchange tubes of steam generators at nuclear power plants with VVéR (water-moderated water-cooled power reactor) power-generating units. The existence of correlation between the character of defects and the mechanism of their formation under the operating conditions is established. It is shown that the process of formation of defects is connected both with the intercrystalline and intracrystalline mechanisms of cracking detected in different sections of the tubes. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 4, pp. 109–113, July–August, 2008.