共查询到19条相似文献,搜索用时 203 毫秒
1.
某纺织公司染缸热交换器在检修过程中发现焊缝及筒体附近母材出现裂纹。通过宏观分析、化学成分分析、硬度测试、金相检验和氯离子检测等方法对热交换器焊缝开裂的原因进行了分析。结果表明:该热交换器焊缝及筒体附近母材的开裂模式为应力腐蚀开裂。由于蒸汽冷凝水中氯离子质量浓度过高,在焊接残余应力和工作应力的共同作用下,焊缝发生应力腐蚀开裂。 相似文献
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《理化检验(物理分册)》2017,(7)
某660 MW高压加热器的筒体接管角焊缝在焊接过程中发生开裂并扩展至筒体母材。对其进行了宏观检验、硬度测试、金相检验、扫描电镜及能谱分析,以分析开裂原因。结果表明:接管与筒体角焊缝根部成形不良,存在夹渣、气孔等焊接缺陷;在焊接应力、结构拘束应力的作用下,焊接缺陷处产生应力集中,裂纹从此处萌生并扩展开裂。采用了与筒体返修开口尺寸匹配的整体锻件返修方案,强度计算满足设计要求,并一次返修合格。 相似文献
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王荣 《理化检验(物理分册)》2006,42(11):580-582
在检修雏护换热器汽包时发现汽包封头泄漏,在汽包封头的阀盖角焊缝处出现裂纹,裂纹平行于焊缝。采用宏观形貌分析、化学成分分析、金相检验、显微硬度测定、能谱分析以及应力分析等方法对泄漏处进行了分析。结果表明,汽包中水质含有较高浓度的碱性元素和氧、硫、氧等强腐蚀性元素,又在焊接残余应力的作用下发生应力腐蚀开裂,最后导致汽包封头产生泄漏。 相似文献
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《中国新技术新产品》2017,(22)
本文主要分析了一台医用灭菌器内筒筒体产生应力腐蚀裂纹的原因及影响因素。通过对新旧医用灭菌器使用情况的分析,作者发现该台医用灭菌器产生裂纹的主要原因与其所使用的内筒材料、使用环境和应力集中有关。本文再次论证了不锈钢材料在有Cl存在的环境条件下,在结构突变有应力集中的部位极易产生应力腐蚀裂纹。本文从几个方面阐述了避免此类医用灭菌器产生应力腐蚀裂纹的方法,比如改变盛装介质器具、内筒材料的选取、改变内筒结构以及容器投用后的使用环节。 相似文献
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通过宏观检查、化学成分分析、硬度测试、金相检验等方法,对某电厂超超临界锅炉高温再热器进口集箱T23钢管焊接接头的泄漏原因进行了分析。结果表明:由于T23钢管硬度偏高,加之焊接装配拘束应力较大,使得集箱T23钢管接头在管座角焊缝处萌生裂纹,裂纹不断扩展最终引起蒸汽泄漏。 相似文献
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316L不锈钢板式换热器使用约半年后频繁出现泄漏事故,通过扫描电镜分析、能谱分析、金相检验、显微硬度检测和有限元模拟分析等方法对泄漏原因进行了分析.结果表明:316L不锈钢板片发生了应力腐蚀开裂,造成泄漏.板片冷加工后产生了较大的残余拉应力且环境中存在Cl-腐蚀介质,导致残余应力较大的波峰和波谷处产生裂纹和腐蚀坑,是造... 相似文献
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《中国新技术新产品》2016,(12)
本文主要通过国内电站Canopy密封焊缝硼酸泄漏事件,分析出泄漏原因为应力腐蚀导致的裂纹,并根据核电设备制造过程容易引入的应力腐蚀影响因素提出制造、运输及安装等各阶段的预防措施。 相似文献
11.
赵雪芸 《理化检验(物理分册)》2003,39(5):271-274
应用光学显微镜、扫描电镜和能谱仪等手段对321不锈钢焊接波纹管表面腐蚀物的化学成分、焊缝区域的显微组织、腐蚀裂纹的形态特征等方面进行检验和分析。结果表明,波纹管局部电镀端内壁腐蚀导致漏气失效,即加工应力、焊接残余应力与含Cl^-或含Cl^-和溶解氧的腐蚀性介质的联合作用使波纹管局部电镀端产生了点蚀和应力腐蚀开裂;退火工艺设计的不合理和钎焊工艺控制不恰当使焊缝热影响区敏化而出现了晶间腐蚀。据此提出了降低和避免321不锈钢焊接波纹管因腐蚀而漏气的措施。 相似文献
12.
Nozzle zone before valve of negative pressure chamber from main pipe coolant system in the secondary circuit of reactor is made of F316 stainless as usual. The butt weld between nozzle and socket in main pipe is the weakest part. If the rupture occurs, it will directly lead to the leakage of main system. One nuclear power plant finds a local penetration crack in the weld of nozzle zone, and it leads to leakage in the inspection. The length of crack is 23.6 mm, nearly 41.7% of the perimeter. In this work, crack morphology observation, composition analysis, metallographic structure observation and hardness measurement are done for the leak part. Analysing with the service environment and force condition, the inner wall of nozzle has a greater stress concentration. It easily leads to fatigue cracking near the fusion line area with poor welding, and the crack extends from inner wall to outer wall. The fatigue crack evolves to corrosion fatigue crack during the crack propagation, and the further advices for use are provided. 相似文献
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M. Bergman B. Brickstad 《Fatigue & Fracture of Engineering Materials & Structures》1995,18(10):1173-1188
Abstract A procedure is described which predicts the growth of an initial circumferential surface crack through a pipe wall and further on to final failure of the pipe. The crack growth mechanism can either be fatigue or stress corrosion. Consideration is taken to complex crack shapes, since especially the last growth mechanism often results in a substantially longer crack length on the inside of the pipe than on the outside for the initial leaking crack due to the distribution of weld residual stresses. The procedure has been implemented in a computer program that in an integrated fashion calculates crack sizes and mass leak rates as a function of time and also predicts when leakage and final failure occur. The information obtained makes it possible to judge if the concept of leak before break is fulfilled. 相似文献
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The weld magnification factor method has been widely used in the determination of the stress intensity factor (SIF) for weld-toe
cracks in welded structural components. Weld magnification factors M
kare normally derived from two-dimensional crack models with fillet weld profiles to take account of the effect of weld-notch
stress concentration at the deepest point of the crack front. This paper presents a detailed three-dimensional analysis of
weld-toe surface cracks in fillet welded T-butt joint models using the finite element method. Effects of the weld notch and
the welded attachment stiffness on the SIFs of the weld-toe surface cracks have been studied quantitatively. Weld magnification
factors applying to the whole surface crack fronts have been estimated. Numerical results show two contradictory effects;
that the effect of weld notch increases SIF values throughout the shallow surface crack fronts which are in the region of
notch stress concentration, while the effect of local structural constraint reduces the SIF values. The increase in the SIF
values mainly depends upon the relative crack front depth and the decrease in the SIF values mainly depends upon the crack
shape aspect ratio for a specific weld profile. Both effects on the weld magnification factors can be estimated separately.
A simple approach for deriving the weld magnification factors for various weld-toe surface crack problems is proposed for
engineering applications. 相似文献
15.
E. Smith 《International Journal of Fracture》1985,27(1):75-79
The paper presents a theoretical analysis which gives the stress intensity factor for a crack that is perpendicular to a weld, the residual stress being tensile in the immediate vicinity of the weld and compressive away from the weld. Whether or not the stress intensity factor becomes zero when the crack tip is at a finite distance within the compressive region, is shown to be dependent on the fine details of the residual stress pattern. The conclusions are relevant to the arrest of a crack in a material with a low stress corrosion crack growth resistance. 相似文献
16.
A study of fatigue crack growth from artificial corrosion pits at welded joints under complex stress fields 下载免费PDF全文
Z. Y. Jie Y. D. Li X. Wei 《Fatigue & Fracture of Engineering Materials & Structures》2017,40(9):1364-1377
The paper studies the effects of artificial corrosion pits and complex stress fields on the fatigue crack growth of full penetration load‐carrying fillet cruciform welded joints with 45° inclined angle. Parameters of fatigue crack growth rate of welded joints are obtained from S‐N curves under different levels of corrosion. A numerical method is used to simulate fatigue crack growth using different mixed mode fatigue crack growth criteria. Using polynomial regression, the crack shape correction factor of welded joints is fitted as a function of crack depth ratios. Because the maximum circumferential stress criterion is simple and easy to use in practice, fatigue crack growth rate is modified using this criterion. The relationship of effective stress intensity factor, crack growth angle and crack depth is studied under different corrosion levels. The simulated crack growth path obtained from the numerical method is compared with the actual crack growth path observed by fatigue tests. The results show that fatigue cracks do not initiate at the edge or bottom of pits but at the weld toes where the maximum stress occurs. The artificial corrosion pits have little effect on the effective stress intensity factor ranges and crack growth angle. The fatigue crack growth rates of welded joints with pits 1 and 2 are 1.15 times and 1.40 times larger than that of the welded joint with no pit, respectively. The simulated crack growth path agrees well with the actual one. The fatigue life prediction accuracy using the modified formulation is improved by about 18%. The crack shape correction factor obtained using the maximum circumferential stress criterion is recommended being used to calculate fatigue life. 相似文献
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This study presents the root cause analysis of a weldment failure in a thermowell assembly operating in a natural gas processing plant. Laboratory investigations indicated inferior quality for the fillet weld joining the thermowell flange to the pipe supporting the thermowell to the main pipe. The fillet weld exhibited excessive concavity, lack of penetration and lack of fusion. This led to minute weldment cracking, which was exacerbated by flow-induced vibrations exceeding safe operational limits. This promoted small magnitude, high frequency stress cycling coupled with high mean stress at the poorly welded joint, which led to accumulation of high cycle fatigue damage and final fracture causing gas leakage. Mitigation plans included use of a shorter support pipe and revised safe operational envelope of the pipeline under consideration. 相似文献
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A study has been made of the fatigue behavior of fillet welded ASTM A515 steel. As-welded and stress-relieved skip fillet weld specimens were tested under pulsed tension and altering cyclic load to determine stress-life and crack propagation behavior. Crack initiation and propagation features were determined from sectioned surfaces. All fatigue cracks were semi-elliptic and initiated from weld end toes. The length/depth ratio was approximately constant during propagation. There was no consistent effect of tensile residual stress on fatigue life under pulsed tension but there was a detrimental effect under alternating loads. An equivalent crack model has been proposed to quantify the stress concentration effect at the crack initiation site based on the application of the Paris equation. The test results show that the equivalent crack can give a reasonable prediction of the fatigue life of a welded structure and is a potentially convenient tool in fatigue design. 相似文献