共查询到20条相似文献,搜索用时 15 毫秒
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针对空调器用翅片管式蒸发器铜管点蚀泄漏故障,结合铜管点蚀失效机制,从使用环境及蒸发器结构方面进行分析。研究发现,空气中含有的氯气或氯化物、氨气等溶解于冷凝水中形成腐蚀性离子,蒸发器相邻翅片叠加位置存在明显的孔洞状间隙,使冷凝水长期积存引起腐蚀性离子对铜管表面的腐蚀破坏作用,是导致蒸发器铜管点蚀泄漏的根本原因,鉴于此,提出避开腐蚀源、采用高耐腐蚀铜管、在铜管表面涂覆缓蚀剂、优化蒸发器翅片与铜管接触结构等预防措施。 相似文献
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Microscopical and structural analyses as well as visual inspection of copper tubes were used to investigate the cause of pitting corrosion failure of copper tubes in the wet pipe sprinkler system. Chemical analysis of the water in the copper tubing and XRF/XRD analysis of its sediments were also used to obtain hints on what was happening in the copper tubing during the progress of the pitting corrosion. It was found from the failed copper tube that a significant amount of pressurized air was present over the water in the copper tubing during operation and a series of corrosion pits were aligned adjacent to the water/air line. The waterline localized corrosion, a type of differential oxygen concentration cell corrosion, induced by pressurized air over the water in the copper tubing was identified as the cause of the pitting corrosion failure. A state of a very low oxygen concentration was maintained under the envelope of a dense layer of malachite, the corrosion byproduct, which was evidenced by the formation of Cu2O crystalline particles inside the corrosion pit. CuO particles observed on the inside surface of the copper tube do not seem to help prevent local as well as general corrosion. Accelerated pitting corrosion of the copper tube in the wet fire sprinkler system was simulated using a differential aeration cell. Finally, measures for stopping or delaying the pitting corrosion of the copper tube in the wet sprinkler system are suggested. 相似文献
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This paper reports on the failure analysis of a finned heat exchanger which leaked in the pressure test during commissioning. The heat exchanger was composed of panels made of thin-walled copper tubes and aluminum fins, and the structure was typical of equipment used in the heating, ventilation and air-conditioning industry. The tube material was phosphorus deoxidized copper Cu–DHP. In the pressure test, one of the tubes was found to have three leakage points. The investigation showed that the failure was a consequence of ant-nest corrosion, as all the experimental findings, together with the copper grade and the tube dimensions, were typical of this corrosion mechanism. Corrosion had initiated from the outer surface of the tube. The paper presents the morphology of the failure using optical and scanning electron microscope (SEM) micrographs. The presence of a contaminating organic substance on the outer tube surface and inside the corrosion crack was verified by SEM/EDS analyses. The corrosion mechanism and the relevant chemical reactions given in the literature are summarized, and the conditions in which the failure may occur are presented. Ant-nest corrosion is a special form of local corrosion, and associated most often with deoxidized copper tubes used in heat transfer applications as in this study. 相似文献
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Pankaj Sharma 《Journal of Failure Analysis and Prevention》2014,14(3):314-317
The investigation was performed to examine the probable cause of failure of a heat exchanger tube at a fertilizer plant. Detailed metallographic analysis, chemical analysis, and microbiological culture tests were carried out to ascertain the cause/causes of failure. A detailed scanning electron microscopic analysis was a necessary supplement to this investigation. The results obtained indicate that pitting and fouling in a heat exchanger tube occurred due to microbiological-influenced corrosion. 相似文献
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A sulfuric acid plant was equipped with heat exchangers with Nicrofer 3620 tubing. The cooling medium was sea water. Within 5 weeks after start-up some of the tubes failed by pitting, showing that it is impossible to use stainless steel as a heat transfer material in sea water unless the molybdenum content is very high. 相似文献
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《Engineering Failure Analysis》2003,10(4):405-421
Long-term overheating is a major cause of failures in boiler tubes of different designs and operation conditions. These failures are usually related to the formation and growth of internal oxide scales or deposits at areas of high heat flux. Deposits might have different sources; poor water treatment and general corrosion in the system are two common types of these sources. Thickening of the deposit layer hinders heat transfer and local spots of high metal temperature are created in the tube wall. With increasing metal temperature, creep becomes much faster leading to tube failure under internal pressure. In this paper, a case history involving this type of failure is presented. Using finite element modeling the failure are analyzed and some methods to prevent this type of failure are recommended. 相似文献
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Amrita Kumari S. K. Das P. K. Srivastava 《Journal of Failure Analysis and Prevention》2016,16(5):703-711
This paper emphasis on the study of typical premature failure of water wall tubes of two thermal power plant boiler of same capacity (250 MW) and same operational parameter but with different boiler water chemistry. The investigation concludes on the water-side corrosion in both of the cases. One boiler is running with coordinated phosphate treatment (CPT) and another with all volatile treatment (AVT). The causes of corrosion were discovered and proposed measures for their elimination were given. Visual examination, chemical analysis of deposits, oxide scale thickness measurement, and microstructural examination were carried to ascertain the probable cause/causes of failure. From the investigation, it was finally concluded that the combination of localized high tube metal temperature and wall thinning due to under deposit corrosion led to the premature tube failure in boiler running with CPT and localized pitting corrosion in boiler running with AVT. Based on the results and discussions, a possible way to combat the corrosion was proposed. 相似文献
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椭圆管换热器由于良好的流动和换热特性,在换热设备中有广泛的应用。本文利用计算流体力学方法,对椭圆管翅片换热器应用于空调室内机的流场和声场进行数值模拟,并与圆管作对比。计算结果表明,换热管形状对贯流风机内部偏心涡的形成位置和大小没有影响;与采用相同截面积的圆管翅片换热器的室内机相比,相同条件下,采用椭圆管换热器对于室内机增加风量,改善制冷性能,降低噪声尤其是低频噪声方面有良好的效果。其中,长短轴之比为2的椭圆管可以降低室内机噪声4 d B。 相似文献
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Corrosion fatigue behaviour of a medium strength structural material was studied in air and in 3.5% NaCl solution. Emphasis was placed on the study of corrosion pit formation and the development of cracks from pits. Pitting and crack propagation were quantified throughout the fatigue loading thereby allowing a model to be developed that included the stages of pitting and the pit-to-crack transition in order to predict the fatigue life. The results showed that a large number of corrosion pits with small size form at a very early stage in the fatigue lifetime. The number of pits and subsequent cracks was found to be higher at higher stress levels leading to multiple crack development and coalescence. When compared to air, fatigue life in a corrosive environment was significantly reduced at low stress levels due to pitting damage, indicating a dominant role of corrosion over that of mechanical effects. The corrosion fatigue model proposed shows good agreement with the experimental test data at lower stress levels but predicts more conservative lifetimes as the stress increases. Kitagawa–Takahashi diagram was produced for both test environments where it is indicated that the fatigue limit can be eliminated in a corrosive environment. 相似文献
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火电厂循环冷却水对铜合金的点蚀 总被引:1,自引:0,他引:1
以北方某电厂循环冷却水为例,用电化学方法研究了Cl-、SO2-4、S2-和pH值等因素对HSn701-B铜合金管材点蚀的影响.极化曲线表明:在该电厂冷却水水质条件下,该管材的点蚀电位随水样中Cl-浓度的增大而下降,腐蚀电位也随之下降,但钝化电流变化不大,点蚀电位与Cl-浓度关系的表达式为:Eb=61.19-14.83lg[Cl-];少量SO2-4的加入对铜管的腐蚀有阻碍作用,当溶液中[HCO-3]/[SO2-4]<0.47时,又有促进作用;S2-的加入使铜管的点蚀电位负移、钝化电流增大;pH值的降低会使管材的点蚀电位负移. 相似文献
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通过模拟计算讨论降膜式蒸发器在运行过程中,换热管束内外流体不均匀分布对换热器整体性能的影响。管外性能的模拟计算采用根据管束中换热管位置、沿换热管束长度方向上网格离散的三维网格格式,管内性能的计算采用三维CFD计算方式。计算和分析表明,换热流体在换热器中的分布均匀性对换热器内管外局部干斑出现的比例,以及整体性能有明显的影响。 相似文献
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Leakage at the tube-to-tubesheet joints occurred in a waste heat boiler. The mode and the root cause of the failure were investigated by chemical composition analysis of the tube material, metallographic structure and crack observation, and corrosion product analysis of the damaged tubes, as well as the operation condition examination of the waste heat boiler. Results revealed that failure of the tubes occurred due to the stress corrosion cracking (SCC), which was caused by tensile stress and chloride-buildup in the narrow and long gap between the tube and tubesheet hole. The gap formation was further analyzed by comparison of the minimum expansion pressure from the common formula provided by the manufacturer, with that from finite element method computations. It is found that the minimum expansion pressure used in manufacture is small and cannot eliminate the initial gap. Meanwhile, the enrichment of chloride in the gap was briefly discussed. 相似文献
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A study has been presented on pitting corrosion on internal walls of automotive exhaust muffler due to exhaust gas condensation. The problem mainly exists in the rear section of the exhaust system close to the tail end pipe such as the muffler, especially when the temperature of the muffler does not go up during short distance run or winter. The water vapour condenses on the muffler's inner wall in the form of water droplets. The dissolution of corrosive gases coming from the internal combustion of engine as well as condensation of low-pH acidic vapours in the water droplet can cause severe pitting corrosion on standard exhaust steel. In this work, an experiment is reported for internal corrosion, by using mufflers as test bed subjected to different environmental conditions. Based on observations, a mechanistic model has been developed which involves three main techniques: (i) the dropwise condensation technique predicts the condensation rate and is based on heat and mass transfer theory, (ii) the species breakdown in the droplet is established through the main thermodynamic and chemical equilibrium, and (iii) the pitting corrosion involving pit depth is predicted using electrochemical kinetic reactions, species transport and chemical reactions occurring inside the droplet. Lastly, the accuracy of the model has been validated by comparison between experimental and predicted results showing good agreement. 相似文献
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空气源热水机使用一段时间后其换热器换热管出现开裂泄漏,经金相、电镜分析确认为应力腐蚀。本文以降低残余应力为目的,构建换热管加工的简化理论模型和有限元模型,模拟计算模具参数的定量影响,并通过回归方程的构建取得最优参数。在参数优化后,经有限元模拟,残余应力减小25.7%,调整后制品经腐蚀性压力脉冲试验验证,耐应力腐蚀试验寿命显著提高。 相似文献
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M.A. Virk M.A. Butt A. Chughtai M. Ahmad I.H. Khan K.M. Deen 《Engineering Failure Analysis》2010,17(2):447-454
A Polyester plant is using Proprietary heat exchange fluids (26.5% biphenyl, 73.5% diphenyloxide). The plant hot condensate tank, condensate feed tank, and heat exchanger vapor phase dead end and ventable lines (ASTM 106 Grade B) with isolation valves were suffering frequent leakages with severe gouging and pitting corrosion. Lustrous (shiny) coke deposit was prominent inside the cut sections due to coke formation by low boiler products. Some adhered brown iron oxide (rust) deposits were also visible. A sludge sample was analyzed by XRD which revealed that carbon was the major constituent with γ-Maghemite-C (an iron oxide) as second mineral in order of abundance. The failure was diagnosed as severe localized corrosion and gouging at temperatures of about 200 °C and 53 psi by non-condensable low boilers decomposed corrosive products. The remedy was suggested which has been validated over the 2 years trouble free performance. 相似文献