大厚度奥氏体不锈钢筒体填丝激光焊接变形和应力分析

目的 研究大厚度奥氏体不锈钢筒体填丝激光焊接,优化结构设计和工艺设计。方法 建立大厚度奥氏体不锈钢筒体填丝激光焊接数值分析模型,通过数值模拟的方法,定量分析大厚度奥氏体不锈钢筒体焊接变形和应力。结果 零件下部38 mm厚焊缝位置处的最大径向收缩量为1.2 mm;零件下部60 mm厚焊缝位置处的最大径向收缩量为2.0 mm;零件中部60 mm厚焊缝位置处的最大径向收缩量为1.9 mm;零件上部60 mm厚焊缝位置处的最大径向收缩量为1.8 mm。填丝激光焊接轴向收缩量为0.55 mm。焊接残余应力最大值在450 MPa左右,应力主要分布在焊缝附近。热处理后,焊接残余应力都有明显降低,最大残余应力从450 MPa左右降低到200 MPa左右,焊接残余应力范围存在一定程度减小;焊接残余变形变化较小,热处理后某些位置的变形略微有所增大。结论 模拟结果表明,大厚度奥氏体不锈钢筒体填丝激光焊接变形和应力在可接受范围内,焊后热处理对释放残余应力有重要作用。     

304不锈钢焊接接头的耐应力腐蚀性能

碳钢/304不锈钢复合管如果不锈钢钢管的焊接工艺参数不当,焊接接头便容易发生应力腐蚀。采用钨极氩弧焊方法焊接了304不锈钢钢管,通过慢应变速率拉伸和双环动电位再活化试验研究了不同焊接工艺参数焊接接头的耐应力腐蚀性能。结果表明,可有效提高耐应力腐蚀性能的最优焊接工艺:氩气流量为12~15 L/min,焊丝为ER308,焊接电压为50 V,电流为50 A,焊接速度为8~10 cm/min;选择合适的焊丝和降低焊接电流可有效增加304不锈钢焊接接头处的耐应力腐蚀性能。     

波纹管内高压成形焊接区变形特征研究

准确建立焊接管材母材、热影响区和焊缝的材料力学模型,是焊接波纹管内高压胀形工艺分析的前提条件。基于焊接区单向拉伸试验和硬度测试等条件建立焊接区混合材料准则,确定了热影响区和焊缝的材料力学模型。通过波纹管液压胀形工艺仿真与试验,研究胀形液体压力和凹模初始高度等工艺参数对波纹管变形特征的影响,并结合变形前后的组织分析发现,焊接区的枝状晶组织使成形后波纹管焊接区与母材壁厚存在差异,并且变形后马氏体相的存在促进裂纹的形核,引起后期使用中的应力腐蚀破裂。     

7A52铝合金焊缝应力腐蚀性能研究

本文用20mm厚的7A52铝合金板材,采用钨极氩孤焊接工艺焊接,用慢应变速率实验方法,应变速率为1．58×10^-6s^-1,在3．5％氯化钠溶液和惰性气体中,研究了7A52铝合金焊接接头的应力腐蚀性能。试验结果表明：7A52铝舍金焊缝对应力腐蚀较为敏感,在3．5％氯化钠溶液中应力腐蚀断裂均发生在焊缝熔合线附近区,而在惰性气体中试样断裂发生在焊缝中间部位。     

反复焊接对超低碳奥氏体不锈钢耐腐蚀性能的影响

通过对反复焊接1～5次的超低碳奥氏体不锈钢的晶间腐蚀试验及应力腐蚀试验，研究了反复焊接对超低碳奥氏体不锈钢的耐腐蚀性能的影响。试验结果显示，在同一部位反复焊接5次后，超低碳奥氏体不锈钢的晶间腐蚀倾向和应力腐蚀敏感性没有发生明显变化，表明超低碳奥氏体不锈钢在选择合适的焊接材料、焊接工艺和焊接方法的前提下，同一部位可反复焊接5次，而其耐腐蚀性能不会受到影响。     

不锈钢A-TIG的抗腐蚀性能探讨

本文以该不锈钢输水管道的焊接为研究背景,用A—TIG焊接提高焊缝质量和生产效率,深入了解焊接后接头处残余应力应变的分布规律,对304不锈钢的抗应力腐蚀开裂开裂能力进行评估,并研究残余应力与应力腐蚀之间的关系。本研究完成后,必将对现有的生产过程起到很好的指导作用,具有较好的实用价值和经济效益。     

高压临氢管道焊接技术

在南京扬子石化2 00万t/a高压加氢裂化装置TP321奥氏体不锈钢管道焊接施工中,通过合理的焊接工艺和焊后稳定化热处理等质量控制措施,有效防止了焊缝及热影响区出现晶间腐蚀及热裂纹倾向,保证了施工质量.其焊接工艺及质量控制措施,可供同类工程的管道焊接施工参考借鉴.     

核电站控制棒驱动机构Canopy焊缝焊接温度场和应力-应变场模拟

目的 研究机加工和拉拔2种成形方式下得到的填充环对Canopy焊缝的影响,获取焊接焊缝成形、焊接残余应力和变形的相关数据,以指导Canopy焊缝焊接工艺。方法 采用数值模拟的方法,建立Canopy焊缝焊接数值分析模型,模拟焊接温度场、焊接残余应力和焊接残余变形。结果 拉拔成形环焊接熔池高度为9 mm,机加工成形环焊接熔池高度为8.3 mm;机加工成形环焊接最大残余应力为255.6 MPa,而拉拔成形环焊接最大残余应力为277.8 MPa,均出现在管座紧贴焊缝的位置;机加工成形环焊接残余变形为0.19 mm,拉拔成形环焊接残余变形为0.186 mm,最大残余变形均出现在焊接起始位置附近,在焊缝与管座交接的位置。结论 熔池形貌直接影响了热影响区域的大小,拉拔Y型环焊接熔池高度更大,焊接的热影响区域更大;拉拔Y型环焊接残余应力略大于机加工Y型环焊接残余应力;机加工成形环和拉拔成形环焊接残余变形相近。     

金属波纹管补偿器的应力腐蚀开裂分析

采用宏观及微观断口分析、金相检验与化学成分检测等方法,对某铬一镍奥氏体不锈钢波纹管补偿器的腐蚀开裂失效原因进行了分析。结果表明：由于该铬一镍奥氏体不锈钢波纹管在氯离子含量超标的环境中服役,并承受来自于波纹管自身加工变形过程中形成的残余应力、工作应力以及装配应力,最终导致波纹管补偿器发生了由表及里的应力腐蚀开裂。     

矩形脉动真空灭菌器内腔开裂原因

某医院矩形脉动真空灭菌器内腔发生开裂事故,通过宏观分析、金相检验和光谱分析等方法,结合工作介质,对内腔开裂的原因进行了分析。结果表明:灭菌器内腔与加强筋不连续焊接处存在焊接残余应力,且靠近内腔弯折处存在局部应力集中现象;灭菌器内腔的工作介质中含有氯离子,而氯离子水溶液是300系列不锈钢发生应力腐蚀开裂的敏感介质。灭菌器内腔在焊接残余应力、含氯离子介质等因素的综合作用下发生起始于靠近内腔弯折的焊接起始处的应力腐蚀开裂。     

Failure analysis of girth weld cracking of mechanically lined pipe used in gasfield gathering system

Girth weld cracking of mechanically lined pipe was occurred after 75 days operation in a gasfield gathering system in China. Failure causes were analyzed based on operation histories, field documents, and laboratory tests. Results showed that the girth weld failure was mainly due to two aspects, girth weld martensite microstructure and external stress. The crack was initiated from sealing pass zone and filling pass zone, which is a hard and brittle martensite structure with hardness of HV 350–450. The failed pipe area had undergone the heavy rain for 2 days, pulling stress, bending stress, and shear stress generated by soil movement resulted in high stress concentration at girth weld. The girth weld cracking failure was initiated from outer carbon steel, and propagated along the weld-fusion line in intergranular mode, which is a typical stress corrosion cracking failure.     

不锈钢管道焊缝区域的海水腐蚀性能

通过化学成分分析、金相试验和腐蚀试验,分析了不锈钢管道焊缝及附近区域耐海水腐蚀的特点,揭示了该焊缝及附近区域的海水腐蚀规律,并总结出该焊缝及附近区域金相组织变化对耐海水腐蚀性能的影响。     

管道连接头腐蚀失效分析

对石化厂管道连接头腐蚀泄漏失效进行了检查和分析，冷凝气体的液体介质含有Cl^-1和S^-2是产生点和晶间腐蚀的根源。错用钢材及运行后未及时清洗管道是导致点蚀和晶间腐蚀最终引起泄漏失效的主要原因。     

Stress corrosion cracking of stainless steel pipes for Methyl-Methacrylate process plants

In a Methyl Methacrylate (MMA) plant, tree-like transgranular cracks were found near the weld of a pipe that had been used for transferring MMA material at 110 °C and 0.77 kg/cm². The pipe was made of ASTM A312 TP304 stainless steel.In this study, it was shown that the failure was due to the stress corrosion cracking (SCC) caused by the chloride that remained in the pipe. Corrosion pitting occurred on the inside surface of the pipe. The stress corrosion cracking started from the pits and grew out through the thickness. Concentrated chloride was found in the deposit stuck to the pipe in addition to the pre-process MMA materials. Many work-hardened grains were observed in the area of SCC, providing the evidence of high residual stress due to welding, which could serve as the driving force for the SCC. Recommendations are made for preventing further failure due to SCC in such cases.     

Stress corrosion failure of high-pressure gas pipeline

Incidents of failure due to corrosion/stress corrosion cracking of high-pressure gas pipelines in Pakistan have been observed to occur after about 15–20 years of service. The present paper constitutes the failure analysis of an 18-inch diameter electric resistance-welded gas pipeline. The failure was characterized, on the basis of all the available evidence and the metallurgical examination carried out on the ruptured pipe, as a stress corrosion failure that had initiated at a longitudinal ‘stress raiser’. This stress raiser, which was essentially a manufacturing defect, constituted a longitudinal ‘step’ on the pipe surface that had resulted from the faulty trimming/shaving of the weld flash. The findings of this study, thus, emphasize the need for the care that must be taken during the shaving-off of the weld flash.     

304不锈钢管TIG焊接头凝固行为及热力耦合研究

目的 对2mm厚不锈钢管的焊接工艺参数进行优化,并基于模拟仿真软件对接头的热应力场进行模拟,以解决薄壁管件接头应力测试不方便的问题。方法 以TIG焊对2 mm不锈钢管进行焊接,通过对接头宏观形貌、微观组织、显微硬度等结果进行优化进而得到最佳焊接工艺参数,采用双椭球热源和温度-位移耦合方法结合最优工艺参数进行数值模拟。结果 当焊接电流为150 A、焊接速度为66 cm/min时,焊接接头全部熔透,且正面及背面焊道均匀致密,成形良好。焊缝中心上部区域和下部区域均呈现等轴晶形貌,下部区域尺寸较上部区域尺寸略大,熔合线附近为柱状晶组织。焊接接头显微硬度整体分布呈现U形,其中热影响区显微硬度（197HV）大于焊缝区域硬度（162HV）,熔合线附近显微硬度达到最低值（145HV）。模拟结果显示,在焊接过程中,当纵向残余应力从母材向焊缝中心过渡时,由压应力逐步转化为拉应力;焊缝中心横向应力呈现为压应力,向两侧母材过渡时应力值逐渐趋近于0,径向应力值变化幅度较小,模拟数据变化趋势与实测数据变化趋势接近。     

Failure analysis on weld joints between the elbow and straight pipes of a vacuum evaporator outlet

This study presents an analysis on a weld joint leakage accident between elbow and straight pipes that connect the inlet of a catalyst plant vacuum pump and the outlet of a vacuum evaporator tank. Moreover, the causes and mechanisms of material degradation are investigated by analyzing the chemical compositions and observing the microstructures with the use of a metallographic microscope and a scanning electron microscope. Energy dispersive spectroscopy was used on the test materials and corrosion products to examine the changes in the elements during material degradation. The results show that stress corrosion cracking caused the cracks and the leakage on the joints. The fracture morphologies were dominated by river cleavage and fan-shaped cleavage patterns. The existence of Cl⁻ and residual stress from the installation of the elbow pipe and the heat effect of the welding process contributed to the stress corrosion cracking.     

热输入对Q1100钢焊接接头低温韧性及耐蚀性能的影响

采用10 kJ/cm和15 kJ/cm两种焊接热输入对Q1100超高强钢进行熔化极气体保护焊,研究焊接接头的组织性能及局部腐蚀行为。结果表明：两种热输入焊接接头的焊缝组织主要为针状铁素体和少量的粒状贝氏体,粗晶区组织均为板条贝氏体,细晶区组织均为板条贝氏体和粒状贝氏体,临界相变区组织为多边形铁素体、马奥岛和碳化物的混合组织。两种热输入焊接接头中电荷转移电阻均为母材>热影响区>焊缝区,母材耐蚀性最好,热影响区次之,焊缝区耐蚀性最差。在腐蚀过程中,焊缝区作为阳极最先被腐蚀,当腐蚀一定时间后,腐蚀位置发生改变,阳极腐蚀区域转移到母材区,而焊缝区作为阴极得到保护。热输入为10 kJ/cm时,焊接接头具有更好的低温韧性和耐蚀性,其焊缝和热影响区-40℃冲击功分别为46.5 J和30.2 J。     

冷凝器换热管失效分析

采用宏观检查,化学分析和金相检验等方法对冷凝器换热管报废原因进行了分析,结果表明,由于不锈钢焊接管在含有氯离子的冷却水中形成钝化－活化微电池,致使不锈钢焊接管腐蚀而报废,采取改换材料为18－8型无缝奥氏体不锈钢管和改良冷却水等措施,取得良好效果。     

Failure investigation of 321 stainless steel pipe to flange weld joint

Failure investigation was conducted on a refinery pipe-to-flange weld joint that suffered cracking. Both the pipe and flange are made of AISI 321 stainless steel. The flange was circumferentially welded to the pipe which is seam welded. The investigation revealed that both the circumferential and seam welds were in sound conditions, namely no evidences of sensitization, lack of weld penetration, and voids or porosities. Thus, welding practices were not suspected to be the cause of failure. The failure of the weld joint was found to have started at the δ-ferrite phase in the flange material and propagated through the circumferential and seam welds. The failure mode was concluded to be chloride stress corrosion cracking synergized by the presence of H₂S. The presence of corrosive compounds in the refinery stream and the residual stresses at the weld joint triggered active anodic dissolution of the δ-ferrite precipitates, resulting in cracking of the material.