烟囱焊接开裂分析

经焊接后的SUS430不锈钢烟囱在制造弯曲过程中出现开裂。对开裂件进行了化学成分分析、宏微观检验和力学性能测定。结果表明,材料在焊接过程中由于热影响区晶粒异常长大,并伴随α脆性相出现,导致材料的塑性降低,在后续工艺中冷变形作用下发生开裂。探讨了SUS430焊接过程中的热处理工艺。     

船舶用带铜衬套通舱管件焊接开裂原因

船舶用带铜衬套通舱管件焊接后造成表面开裂.采用化学成分分析、金相检验、断口分析和拉伸试验等方法,分析了管件开裂的原因.结果表明:带铜衬套通舱管件端面开裂类型为液态金属致脆开裂;在焊接过程中,S221锡黄铜中的低熔点金属从管件端面沿晶界进入材料内部,导致管件脆化形成裂纹,在拉应力作用下,裂纹扩展造成管件端面发生开裂.     

Q345钢输油管道开裂原因分析

某电厂Q345钢输油管道在运行过程中发生开裂泄漏。通过宏观分析、化学成分分析、硬度测试和金相检验等方法,对管道开裂原因进行了分析。结果表明:由于弯头的选材不当,后续对直管段和弯头进行焊接前未能正确识别材料,造成制订的焊接工艺不恰当。不恰当的焊接工艺使得焊接热影响区产生了冷裂纹,最终导致该Q345钢输油管道开裂。     

乙烯裂解炉管运行失效研究及焊接修复

乙烯裂解炉管由于服役环境恶劣,长时间运行后容易产生破损需要进行修复,但在焊接修复时极易开裂,为了找出其易开裂的原因,本文用扫描电镜和金相显微镜观察分析了HP40Nb乙烯裂解炉管服役前后的组织性能变化,并通过热力学计算对试验结果进行分析,找出了焊接性能恶化的原因,并制定热处理工艺改善其焊接性.结果表明:长时间服役后,炉管析出相为M23C6、M7C3和MC相,析出相严重长大粗化,沿晶界呈链状分布,使材料塑性几乎为0,这是导致焊接易开裂的主要原因;通过热处理改善碳化物的分布形态,可以有效提高旧管的塑性和焊接性;通过热力学计算得出,当基体中固溶的Cr质量分数大于10%时,为M23C6的析出过程,基体固溶的Cr质量分数小于10%时,为M7C3的析出过程.     

军用H62黄铜罐开裂原因

某工厂生产的军用H62黄铜罐在水压试验后入库存放,一段时间后出现开裂现象.通过化学成分分析、金相检验、硬度测试、扫描电镜分析和能谱分析等方法,结合生产工艺和现场工况,对该黄铜罐的开裂原因进行了分析.结果表明:黄铜罐在机械打孔及焊接后未进行退火处理,导致焊缝部位产生应力集中,之后的水压试验提供了潮湿环境,引起显微组织中的...     

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。     

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。     

行波管用阴极钼支撑筒开裂和变形原因分析

针对阴极组件在组装过程中出现脱落现象,利用扫描电子显微镜(SEM)对呈现出不同程度开裂和变形的钼支撑筒进行了微观对比分析,找出了钼支撑筒开裂和变形问题的原因.结果表明:对比焊接处采用电子束焊接方式,经激光焊接的钼筒易开裂;相比焊接处采用环形结构的阴极,搭接结构的钼筒在焊接过程易变形;焊接处采用搭接结构且经激光焊接后的钼筒开裂现象较为严重.     

乙二醇不锈钢蒸发器开裂原因分析

采用金相分析、断口微观分析以及腐蚀产物能谱分析等方法，对某石化公司乙二醇不锈钢蒸发器开裂原因进行了分析和研究。结果表明，由于材料在焊接过程中，焊接热影响区的组织受到敏化，铬的碳化物沿晶界呈网状析出，造成该区域贫铬，从而在应力与腐蚀介质的共同作用下，导致设备发生了晶问应力腐蚀开裂。     

环戊烷进料线三通裂纹原因分析

通过宏观检验、壁厚及硬度测试、化学成分分析和金相检验等方法,对环戊烷进料线三通产生裂纹及补焊后再次开裂的原因进行了分析。结果表明:三通中的裂纹是制造加工时产生的,在安装应力及管系应力的作用下开裂并造成泄漏;补焊后的焊接应力作用于未消除裂纹部位造成了再次开裂。最后对补焊修复和同类型三通检验提出了建议。     

Failure investigation of a convection line elbow

Failure investigation was carried out on a cracked 5″ 304L stainless steel elbow tube for the convection line of an ethylene furnace. The crack was observed in the heat-affected zone (HAZ) at the end leading to the elbow parent material. The crack was along the circumference and was about 12″ in length. The crack started from the toe of the weld to the parent metal on the elbow side. The failure investigation revealed that the HAZ of the elbow tube suffered from stress corrosion cracking and mild grain boundary carbide precipitation during welding. The carbide precipitation was possibly due to improper welding practices such as high heat input and/or extended welding time. The tube thickness, which is relatively thick, was a contributing factor in making proper welding more difficult.     

安全阀配对法兰焊口裂纹产生原因分析

某集气装置原料气放空安全阀配对法兰焊口处出现裂纹,通过宏观以及微观检验、化学成分分析、力学性能测试等方法对裂纹产生的原因进行了分析。结果表明：该裂纹为硫化物应力腐蚀开裂所致,焊接工艺不当或焊后冷却速度过快导致焊接接头区域出现硫化物应力腐蚀开裂敏感性组织是该焊口产生裂纹的主要原因。     

磷脱氧铜无缝管断裂原因分析

用ＳＥＭ等方法对电冰箱压缩机用磷脱氧无缝铜管异常断裂进行了分析。结果表明，夹杂物局部偏聚是铜管断裂的内在原因，焊接时产生的热应力及弯曲变形是铜管断裂的外部诱发因素。有效的改进措施是严格控制杂质含量、将高温焊接工艺改为低温焊接工艺。     

Failure of a furnace outlet pipe in a benzene plant by internal oxidation due to improper welding practice

A furnace outlet pipe made of INCOLOY^® alloy 800H to handle gaseous hydrocarbon in a benzene plant developed cracks in the weld heat-affected zone during operation at 595 °C. Microstructural characterization revealed that the cracks were of the ductile intergranular mode, which could be related to localized plastic deformation alongside the grain boundaries. The microstructure of the heat-affected zone was distinguished from the base metal by a coarser grain structure and intergranular oxidation in addition to higher hardness indicating the presence of residual stresses from the welding process. Intergranular oxidation was found to result in a mixture of Cr and Fe oxides enveloping a Ni-rich solid-solution adjacent to the grain boundary. Therefore, the observed ductile intergranular cracking could be related to localized plastic deformation in the relatively “soft” zone of Ni-rich solid-solution. Most evidence indicated that the failure occurred because of improper welding atmosphere leading to internal oxidation under relatively low oxygen potential, which is oxidizing to Cr and to a lesser extent Fe, and reducing to Ni.     

Single pass laser joining of Inconel 718 superalloy with filler

Abstract

Microstructure and mechanical property of CO₂ laser beam welded IN 718 superalloy were studied by electron microscopy and hardness testing. The use of a welding filler wire produced a sound fusion zone with no cracking but grain boundary microfissuring occurred in the heat affected zone (HAZ) and was observed to be significantly influenced by pre-weld heat treatment and laser welding speed. Crack-free weld was produced by a pre-weld heat treatment that minimised non-equilibirum grain boundary boron segregation and inhibited grain growth. While post-weld heat treatment (PWHT) reduced the difference between the hardness values of the base alloy, HAZ and the fusion zone, it resulted in increased HAZ cracking, which was likely aided by pre-existing cracks. The PWHT cracking was, however, avoided by subjecting pre-weld material to the heat treatment condition that produces crack-free weld during welding process.     

Welding solidification cracking susceptibility and behavior of a Ni-28W-6Cr alloy

Welding solidification cracking of alloys is associated with the range of solidification temperature that can be greatly affected by the amount of refractory metals and other additives. In this work, solidification cracking of Ni-28W-6Cr alloy with high W content was studied by gas tungsten arc welding, showing that the welding current, alloying elements and precipitates all affect the cracking susceptibility. The lengths of cracks increase linearly with the welding current in the range from 150 to 250 A. The relatively high cracking susceptibility is mainly attributed to the high content of Si, which tends to segregate with other elements including W, Cr, Mn as films or components with low melting point in the last solidification stage and weaken the binding force of grain boundaries. Moreover, the existence of precipitated continuous eutectic M_6C carbides in the grain boundaries also acts as nucleation sites of crack initiation, and the cracks often propagate along solidification grain boundary.     

紫铜焊接脆化原因分析

通过对材料的金相组织和断口的SEM观察,对压缩机贮液罐用铜导管的脆断进行了分析,认为铜管氧含量过高,钎焊时被C2H2还原是造成脆化的重要原因。