Failure analysis of heat exchanger tubes

Primary waste heat exchanger tubes of material ASTM A213 grade T11 failed after operation of only three and a half months. The heat exchanger was of the bayonet type with boiler water inside the tubes and secondary reformer outlet process gas at the shell side. The heat exchanger environment was rich in hydrogen, carbon monoxide and nitrogen. The temperature of the process gases was 960 °C and the heat exchanger was producing steam at a temperature of 306 °C and a pressure of 1500 psig. The failed, used and new heat exchanger tubes were subjected to stereo/optical microscopy, chemical analysis and hardness testing. The cause of the failure was thoroughly investigated using optical/scanning electron microscope equipped with energy dispersive spectrometer. The study revealed that the material was exposed to thermal cycling and excessive local heating. The same was also confirmed by simulated experimentation. These conditions lead to thermal fatigue of the material with consequent failure.     

水冷套管式CO_2气冷器的设计及实验研究

本文设计了一台CO_2套管式气冷器并对其进行了换热特性的实验研究。该气冷器采用逆流三重套管,CO_2在内管流动,冷却水在内外管间流动。实验研究了不同CO_2质量流量、入口压力和冷却水温度对传热系数、换热量和换热器效能系数的影响。实验结果表明,随着CO_2质量流量的增加,传热系数和换热量均呈先增后减的趋势,换热器效能系数逐渐减小;CO_2质量流量不变时,传热系数、换热量和换热器效能系数均随气冷器CO_2入口压力的升高而逐渐增大;随着冷却水温度的升高,传热系数、换热量和换热器效能系数均逐渐减小。     

Multichannel low temperature heat exchanger

A new type of multichannel low temperature heat exchanger is described which is mainly designed for liquefiers and refrigerators with small and average capacity.The heat exchanger consists of one or more pairs of tubes soldered along their length, which are tightly coiled around a cylindrical casing so that one of them always remains in the periphery. The tubes are wrapped tightly by a second cylindrical casing in such a way that a corresponding number of channels is formed among the different coils of the soldered tube couples and the two casings.The experimentally obtained criterium equations are given and the formulas derived from them for calculation of the heat exchanger.     

Failure Analysis of Stainless Steel Heat Exchanger Tubes in a Petrochemical Plant

Journal of Failure Analysis and Prevention - A shell and tube heat exchanger had failed its four tubes after just over a year in service. One of these tubes was analyzed in this examination. This...     

5mm管径铜管换热器应用的冷凝性能研究

近年来,随着小管径换热器研究的深入和推广,目前各空调厂家已逐步应用推广。小管径换热器特点在于提高换热性能和节约产品材料成本。同时国内销售的空调器已由R22定频转向R410A变频空调器,小管径换热器随R410A冷媒的替代其强化传热影响更加显著,具备良好的应用前景。综合5mm管径换热器在空调系统中应用的性能数据比较,其冷凝性能优于大管径换热器,满足制冷量和能效的条件下,尤其空调制热量的提高非常显著。     

换热器管板孔内不开槽的强度胀接

工业冷冻机组和中央空调水冷冷水机组用换热器的换热管通常有钢管、铜管、铜镍管和钛管等,其与管板的连接方式采用强度胀接的方式。传统的管板与换热管的强度胀接是通过在管板孔内开若干条胀管槽实现的。本文根据管板孔内不开槽的强度胀接工艺试验和实际生产中的应用情况,说明换热管与管板的强度胀接也可通过管板孔内不开槽和加胀管胶水实现。     

圆形翅片管换热器计算模型与算法收敛性研究

本文以单排换热管为换热单元,建立了圆筒形翅片管换热器的分排参数数学模型,并提出采用二分法迭代求解换热方程组的数值求解方法,重点讨论了在对单排换热管进行迭代求解时出现的收敛性问题。本文提出两个迭代判据条件,并给出通过求解条件方程零点的方法确定迭代变量(各排换热管的进水温度)的下限值。对模型进行验证,结果表明各排换热管的进水温度迭代下限值是总进水温度的线性递增函数。在总进水温度较低的情况下,该方法可以避免迭代计算进入不合理区间,保证算法稳定收敛。     

某锅炉换热器换热管断裂原因分析

某锅炉换热器仅运行2 h即发生换热管断裂事故,采用光学显微镜、扫描电子显微镜、能谱仪、拉伸试验机和直读光谱仪等设备对换热管的断裂原因进行了分析。结果表明:该换热管外壁表面在运行前就已存在原始横向裂纹和机械损伤,在服役过程中这些裂纹和机械损伤处容易形成应力集中,加之换热管的使用温度较低,从而导致其在运行仅2 h后就发生早期脆性断裂。最后对该换热管的生产提出了建议。     

Air-side performance evaluation of three types of heat exchangers in dry,wet and periodic frosting conditions

The performances of three types of heat exchangers that use the louver fin geometry: (1) parallel flow parallel fin with extruded flat tubes heat exchanger (PF²), (2) parallel flow serpentine fin with extruded flat tubes heat exchanger (PFSF) and (3) round tube wave plate fin heat exchanger (RTPF) have been experimentally studied under dry, wet and frost conditions and results are presented. The parameters quantified include air-side pressure drop, water retention on the surface of the heat exchanger, capacity and overall heat transfer coefficient for air face velocity 0.9, 2 and 3 m/s, air humidity 70% and 80% and different orientations. The performances of three types of heat exchanger are compared and the results obtained are presented. The condensate drainage behavior of the air-side surface of these three heat exchanger types was studied using both the dip testing method and wind tunnel experiment.     

Failure analysis of a copper tube in a finned heat exchanger

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.     

降膜式蒸发器管束间流量分配均匀性对其性能的影响

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。     

Estimation of Fretting Wear-Limited Life of a Shell and Tube Heat Exchanger Tubes: Analytical Formulation,Computer Implementation and Qualification Against Actual Reported Failure

In a typical shell and tube-type heat exchanger, the tubes are clamped at the ends by tube sheets and supported by intermittent baffles with gaps. Vibration of tubes makes them susceptible to impacting and rubbing with the baffle support or adjacent tubes. Damage caused by these impacts and rubbing motions is termed fretting. An analytical tool is developed to carry out fretting wear-limited life of heat exchanger tubes. The developed tool is evaluated with reported cases of failure. The authors had earlier conducted this evaluation (Patil et al. in J Fail Anal Preven 17:126–135, 2017) in cases where the vibration was excited by vortex shedding. This paper extends the study to include the other flow-induced mechanism of turbulent buffeting, thus making the tool more comprehensive.

     

Failure assessment of crude oil preheating tubes in mono ethylene glycol–water mixture solution

Aqueous solutions of glycol are commonly used in many applications as heat transfer media. In this study, failure analysis and the leakage of oil tubes in a crude oil pre-heater of a desalting plant were assessed. Crude oil pre-heater (furnace) is a type of heat exchanger in which heat is transferred to oil tubes via ethylene glycol solution in order to increase its temperature for further processing. With the increase of temperature, the viscosity of the oil plus water mixture inside the tubes is reduced and desalting is facilitated. Reports show that, these tubes facing external corrosion in the form of smooth cavities finally lead to leakage. These tubes are made from ASTM A106 Gr B steel. The failure assessment of tubes was carried out by performing various chemical and metallurgical tests. Corrosion coupons were also immersed in ethylene glycol fluid at different places inside the furnace. The investigation revealed that degradation of ethylene glycol forming organic acids (acetic acid, carbonic acid, and formic acid), as the consequent reduction of the pH, take place progressively, being responsible for carbon steel acidic corrosion and eventually to the failure of pre-heating tubes. An action was taken to examine different pH stabilizers for mono ethylene glycol solution. The results obtained by polarization curves showed that, by using stabilizer EN231 at pH = 10.5, corrosion rate reduces to a minimum.     

Identification of microbiologically influenced corrosion (MIC) in industrial equipment failures

The present study demonstrates different approaches towards MIC identification in three real cases of technological equipment failures.

In the first case the failure of carbon steel heat exchanger as a result of tubes, lids, tube sheets, and connection pipes clogging was investigated. Chemical analysis of cooling water and precipitates, as well laboratory screening of deposits for bacteria, revealed that activity of iron-oxidizing bacteria present in cooling water led to heat exchanger blockage.

The second case is related to MIC detection on floating roofs made of magnesium–aluminum alloy following a 3-weeks hydro-test. Corrosion tests carried out on the original and sterilized water used in hydro-test confirmed MIC process.

In the third case the potential of MIC occurrence in engine cooling system made of cast aluminum alloy and filled with 20% ethylene glycol coolant solution was evaluated. The simulation tests allowed determining the real causes of the severe corrosion attack of examined system, including MIC high probability.     

Corrosion analysis of a heat‐exchanger in epichlorophydrin production process

The failure of E230 heat‐exchanger in the production of epichlorophydrin (ECH) form dichloropropanol (DCP) was analyzed and material solutions are recommended. The analysis indicates that the combined effect of stress corrosion cracking (SCC) and dissolution of HCl and HClO in the DCP mixture solution in the E230 heat‐exchanger chamber to the tube surface and chamber wall contributes to the failure of heat‐exchanger tubes and the perforation of E230 heat‐exchanger chamber. It is recommended to reduce the content of Cl^– in the DCP mixture solution and to increase its pH. Titanium, Type 316L stainless steel (SS), and electroless Ni‐P coating can be considered as the candidate materials. Also, the process can be divided into two series step with one step heating the temperature from 30°C to 60°C, and the other step heating the temperature from 60°C to 90°C. For the lower temperature step, the Type 316L SS or electroless Ni‐P coating can be used. For the higher temperature step, Titanium can be applied. Periodic cleaning of the tube surface and chamber inner surface deposit is necessary. Intensifying the in‐service inspection and monitoring is also required.     

Erosion–corrosion of heat exchanger tubes

The shell and tube heat exchanger failed before 5 years of operation. The failure was caused by pits on the tube outside surface developing until its perforation. Inside the Cu-DHP tubes in soft temper a cooling agent circulated to cool down industrial water at the shell side from 16 to 4 °C. The cooled water was hard, rich in chloride ions with relatively low sulphate ions concentration and pH ranging from 4 to 7. The leaking tubes were subject to standard metallographic examination, hardness measurement, scanning electron microscopy and X-ray energy dispersion analysis. It was found that the tube damage was caused by erosion–corrosion induced by two factors: disturbed flow of water containing suspended solid particles and chemical composition of water rich in chlorides that resulted in loss of stability of protective cuprous oxide layer.     

Analytical Reconstruction of Failure of a Shell and Tube Heat Exchanger

Heat exchanger tubes are supported at intermediate points by support plates. Flow-induced vibration of tube can cause it to impact or rub against a support plate or against adjacent tubes and can result in tube fretting wear. Fretting wear damage assessment procedure has been presented. This procedure is implemented by studying classical heat exchanger cases of premature failures. The authors expect this study to be useful for estimating the fretting wear damage of heat exchanger tubes. The study shows that based on fretting wear volume rate the life of heat exchanger tube can be predicted.

     

Failure analysis of AISI 321 tubes of heat exchanger

The present study is about the failures of tubes from a tube shell heat exchange in one of the compression stages used to cool and purify the gas produced in an off-shore platform. Conventional hydrostatic tests did not detect leaking in the heat exchanger, but these tests were conducted at room temperature, i.e., very distant to the service temperature (163 °C). However, tightness tests with helium gas have detected leaking. Some tubes were taken off for analysis and the liquid penetrating test detected cracks in crevices formed between the tube and the tube sheet. The cracks were found to be typical stress corrosion cracks with branched pattern. A non-destructive test with Eddy current probes was developed to give high percentage of detection. The work was conclusive about the main cause of failures. Due to the increase of chloride content of the water processed to concentrations higher than 1000 mg/L over the years, the substitution of AISI 321 tubes by superduplex steel is recommended.     

椭圆管换热器对空调室内机声场影响的数值模拟

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。     

单一金属高螺纹翅片管换热器的探索与实践

通过对管壳式换热器几种常见翅片管的结构特点、换热性能和制造经济性进行分析比较和研究,研制出传热效率更高、结构更紧凑、制造成本更低廉的新型换热元件——单一金属轧制的高螺纹翅片管;提出了传热学意义上最佳翅片截面轮廓线的通用解析式。通过生产实践与不断改进,形成了一组高螺纹翅片管系列产品,并成功地应用于为透平压缩机配套的大中型管壳式换热器。