紫铜管与低碳钢管焊接件开裂分析

某紫铜管与低碳钢管焊接件焊接后在焊接接头靠近紫铜管侧出现了大量开裂现象,通过对开裂部位紫铜管部分进行宏观分析、化学成分分析、扫描电镜断口观察及金相检验,对焊接件的开裂原因进行了分析。结果表明:紫铜管原材料中氧含量超标以及焊接温度过高共同引起晶界弱化,致使在焊接接头处叠加了较大的组织应力和热应力,当叠加应力大于材料的承受能力时就会引起晶界破裂,导致焊接件开裂。最后在分析的基础上提出了改进措施。     

发电机组再热主汽阀阀碟断裂分析

采用宏观和微观检验、化学成分分析、力学性能测试及断口分析等方法对断裂的发电机组再热主汽阀的两个阀碟进行了分析。结果表明：阀碟材料的显微组织中有较严重的带状组织偏析,同时δ铁素体在晶界上呈链状分布,这类组织缺陷大）。增加了阀碟材料的脆性,在冲击载荷作用下导致了脆性断裂。     

304奥氏体不锈钢护栏断裂失效分析

某教学楼阳台304奥氏体不锈钢护栏发生断裂失效。采用宏观检查、化学成分分析、金相检验、扫描电镜及能谱分析等对护栏断裂原因进行了分析。结果表明:304奥氏体不锈钢护栏母材显微组织中存在大量非金属夹杂物,焊接接头存在的未焊透现象降低了接头强度;母材碳含量较高,在焊接热循环作用下,活动能力强的碳原子与铬化合形成碳化物析出,使热影响区晶界贫铬,形成"敏化",增加了材料的晶间腐蚀倾向,降低了焊接接头的强度,最终导致护栏断裂失效。     

储气球罐连接阀螺栓断裂分析

储气球罐连接阀螺栓在使用过程中发生异常断裂。通过宏观观察、扫描电镜及能谱分析、金相检验等方法对螺栓断裂的原因进行了分析。结果表明:螺栓在低应力及环境腐蚀性介质作用下发生了应力腐蚀开裂,产生的原因是晶界析出较多高铬碳化物,局部呈网络状,使晶界贫铬,导致了晶界的耐腐蚀性能下降。可以从改善环境条件及对材料进行稳定化处理等途径解决该问题。     

316L不锈钢焊管横向裂纹产生原因

某316L不锈钢管发生开裂现象，裂纹方向垂直于焊缝，采用宏观观察、化学成分分析、金相检验、扫描电镜及能谱分析等方法对裂纹产生原因进行分析。结果表明：铜元素在断口表面富集，并呈沿晶分布特征；不锈钢焊管在焊接时发生了铜污染，在随后的热处理过程中，低熔点的铜液化并沿晶界渗入，使晶界脆化，在冷却拉应力的作用下产生铜污染裂纹，导致钢管开裂。     

波纹管开裂原因分析

采用扫描电镜、能谱分析等手段分析了某机电产品用不锈钢波纹管开裂的原因。结果表明:在焊接过程中波纹管的焊接接头区域发生敏化,随后酸洗造成该区域形成沿晶界腐蚀裂纹,波纹管在经过振动试验时承受径向交变载荷,在交变应力下裂纹由最初的晶界腐蚀裂纹根部开始扩展直至穿透管壁;断口表面能够发现明显的贝纹线,证明波纹管开裂是一种疲劳失效。     

液化石油气钢瓶焊缝裂纹分析

采用金相检验和化学成分分析等测试手段对液化石油气钢瓶瓶嘴焊缝裂纹进行了分析。结果表明，瓶嘴材质硫含量极高，在焊接过程中导致晶界严重弱化，增大了焊接裂纹的倾向性，降低了材料的可焊性，最终导致焊接热裂纹的产生。     

环氧乙烷精制塔开裂原因分析

通过金相检验、断口分析以及腐蚀产物能谱分析等方法,对某石化公司环氧乙烷精制塔开裂的原因进行了分析。结果表明:材料在焊接过程中,焊接热影响区的组织受到敏化影响,铬的碳化物沿晶界析出,造成该区域贫铬,从而在应力和腐蚀介质的共同作用下,发生了晶间腐蚀开裂。最后提出了相应的预防措施。     

全低压空分设备空气损失率和氧提取率的计算

全低压空分设备的空压机排量并不能全部用来分离氧、氮产品,有一部分空气正切换式换热器切换时损失掉了,这部分损失叫切换损失。它随切换周期缩短而加大。此外,如果强制阀、自动阀,均压阀、膨胀空气旁通阀等漏,或者设备有漏气、漏液时,都要损失一部分空气,使产量减少。这个损失叫漏损。这两部分损失的总和称空气总损失。空气总损失本来     

加氢裂化装置出口线短管开裂分析

加氢裂化装置新氢压缩机出口排凝K101B阀侧短管在使用中出现开裂,通过宏观和微观检验、化学成分分析、硬度测试和能谱分析等方法对开裂原因进行了分析。结果表明:由于短管焊接结构上存在几何不连续性,结构的截面变化幅度较大,产生了严重的应力集中,在短管焊接热影响区魏氏组织最薄弱的地方形成了裂纹源,在交变载荷的共同作用下裂纹逐渐扩展,最终导致瞬时断裂。最后提出了相应的预防措施。     

2024铝合金水下搅拌摩擦焊热力耦合仿真分析

目的 优化搅拌摩擦焊接工艺参数，以提高接头的力学性能。方法 基于ABAQUS软件建立了热力耦合有限元模型，使用耦合欧拉-拉格朗日方法对典型的航空航天用板材2024铝合金的水下搅拌摩擦焊接过程进行了仿真研究。分析了搅拌摩擦焊接过程中板材的温度场分布和材料变形情况，同时研究了前进侧和后退侧相应位置材料的流动特征，进一步讨论了搅拌头冷却速度和摩擦因数对焊接温度和材料流变场的影响。结果 当摩擦因数较小时，针对焊接过程的有限元模拟将会失败;前进侧和后退侧材料变形和流动差异显著;焊接温度和等效应变随摩擦因数的增大而升高，随冷却速度的增大而降低。结论 当摩擦因数为0.8时，能较好地完成焊接。相对于空冷，水冷能明显缩短高温持续时间。     

Failure Analysis of Welded Radiant Tubes Made of Cast Heat-Resisting Steel

Radiant tubes made of cast heat-resisting steels were cracked after 4 years of operation at 1020 °C temperature in hydrocarbon cracking furnace. Optical microscopy of the tubes showed that there was extensive precipitation and intermetallic compound formation especially as brittle networks with progressive reduction in toughness and resistance to thermal and mechanical stresses. SEM and EDS analysis proved both decarburization and oxidation on interior and exterior surfaces. Apart from cracking due to long-term heating, the tubes experienced high temperature creep. HAZ cracking after welding of cracked and/or creeped tubes due to formation of brittle carbide networks was overcome by localized solution heat treatment followed by fast dry air cooling. Localized dissolution of carbide networks and intermetallic compounds resulted in lower strain microstructures and enhanced resistance of parts to thermal and mechanical stresses during repair welding. It is evident that localized solution heat treating other than lowering strains can cause the precipitates to be more uniformly and finely distributed. Fast dry air cooling rate after solution heat treating and similar cooling after welding can help to control precipitation of carbides. Detailed non-destructive testing after welding along with tensile testing proved that post-weld cracking was controlled.     

Welding sheet F-2M fluorinated plastic

Summary Measurements have been made on the mechanical strength, microhardness, and morphology of welded joints in F-2M sheet plastic as affected by the temperature conditions during liquid welding. Liquid welding has advantages over hot air welding. Differential thermal analysis shows that destructive processes occur in the thermal welding of F-2M fluorinated plastic.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 26, No. 4, pp. 99–103, July–August, 1990.     

Improvement of weld temperature distribution and mechanical properties of 7050 aluminum alloy butt joints by submerged friction stir welding

Submerged friction stir welding (FSW) in cold and hot water, as well as in air, was carried out for 7050 aluminum alloys. The weld thermal cycles and transverse distributions of the microhardness of the weld joints were measured, and their tensile properties were tested. The fracture surfaces of the tensile specimens were observed, and the microstructures at the fracture region were investigated. The results show that the peak temperature during welding in air was up to 380 °C, while the peak temperatures during welding in cold and hot water were about 220 and 300 °C, respectively. The temperature at the retreated side of the joint was higher than that at the advanced side for all weld joints. The distributions of microhardness exhibited a typical “W” shape. The width of the low hardness zone varied with the weld ambient conditions. The minimum hardness zone was located at the heat affected zone (HAZ) of the weld joints. Better tensile properties were achieved for joint welded in hot water, and the strength ratio of the weld joint to the base metal was up to 92%. The tensile fracture position was located at the low hardness zone of the weld joints. The fracture surfaces exhibited a mixture of dimples and quasi-cleavage planes for the joints welded in cold and hot water, and only dimples for the joint welded in air.     

Study on seam performance of polymer-modified bituminous roofing membranes using T-peel test and microscopy

The aim of the study was to understand how the T-peel strength of heat-welded seams in polymer-modified bituminous roofing membranes depends on the welding method and on the material properties. Seam samples of ten different commercial products, three of Atactic Polypropylene (APP)-modified bitumen and seven of Styrene-Butadiene-Styrene copolymer (SBS)-modified bitumen, were prepared by different welding methods with different heating media, i.e. hot air or gas torch, welding speed and weight of pressure roller joining seams. The welding conditions were precisely controlled during the preparation, and the temperature in the seam sample was measured. T-peel tests were carried out at 23°C and at ?10°C on specimens cut out from each heat-welded sample to measure the T-peel strengths. The fracture propagation during T-peel testing was studied visually. Some seam specimens were also studied using microscopy. In order to identify the material properties and differences in the material compositions influencing the seam strengths, each product was characterised by different chemical and thermal methods, which were described in recently published reports [1,2]. It was concluded that the choice of welding speed and pressure weight for the optimum design of welding machine should make reference to the thermal properties, such as specific heat, and to the rheological properties, such as viscosity.     

复杂环境下氧化铝储槽定向爆破拆除

在较为复杂的环境下,爆破拆除钢筋混凝土氧化铝储槽。该储槽自重大、呈圆形,内有4根立柱支撑下料漏斗。为使储槽顺利定向倒塌,通过爆破方案选择、参数确定,采取梯形切口和预处理以及安全防护和减振措施,使储槽爆破拆除获圆满成功。     

汽车制造厂焊接车间空调通风系统模拟研究

对焊接车间的污染源进行了测试与模拟,对通风与空调系统进行了模型试验,同时进行了数值模拟,在保证消除有害物、保证室内温湿度要求的情况下,得到最佳的、节能的通风空调形式,从而指导工程设计与施工.     

爆炸焊接界面温升组成理论分析

爆炸焊接过程中,焊接件界面温度的高低对焊接质量产生直接影响,因此爆炸焊接界面温度场是爆炸焊接理论研究的一个重要内容。通过对引起爆炸焊接界面温升的因素进行理论分析后,认为引起焊接界面温升的因素除了前人指出的基板和复板的冲击温升、畸形变形能温升之外,还应包括基板和复板之间的气体绝热压缩温升这三部分组成。其中基板和复板的冲击温升可由Hugoniot方程和自由电子气模型得出,畸形变形能引起的温升采用Johnson-Cook热黏塑性本构方程进行计算,气体绝热压缩引起的温升则通过气体的状态方程推导得出。     

Effects of intense cooling on microstructure and properties of friction-stir-welded Ti–6Al–4V alloy

Friction stir welding (FSW) was used to join Ti–6Al–4V alloy in air and under intense cooling conditions. The results show that the application of liquid nitrogen is beneficial in decreasing the peak temperature and in reducing the extent of the high-temperature region during welding, leading to a smaller stir zone (SZ). Intense cooling can lead to refined and homogeneous grains in the SZ, resulting in increased microhardness. The FSW joint produced with intense cooling had a tensile strength of 1020?MPa, which is nearly equivalent to that of the base material and is up to 2.6% higher than for the air-cooled joint. The fractographs for both types of joint were characterised by dimples, indicating that the fractures were ductile.     

Friction stir welding of dissimilar metal joints

Friction stir welding is a solid‐state welding technology, which is suitable for joining dissimilar metals such as aluminium and copper. Because the solidus temperature is typically not exceeded, the formation of intermetallic phases can be reduced when compared to fusion welding processes. In friction stir welding, the intermetallic layer thickness, which determines the seam properties, is influenced by the welding temperature and is formed in correspondence with the Arrhenius law. It is typically in the range of a few hundred nanometers thick. In turn, the process temperature is determined by the process parameters, primarily the rotational speed and the feed rate of the machine tool. In this study, a temperature‐controlled friction stir welding process has been applied to lap joints of aluminium and copper. Welding experiments with various welding speeds and probe lengths were performed in order to assess the effect of the temperature‐time profile near the welding interface. The joints were investigated by tensile shear tests as well as optical microscopy and scanning electron microscopy.