Failure of ethylene furnace outlet transfer line due to overheating

An outlet transfer line tube of an ethylene-cracking furnace failed after five years of service. The tube, made from Incoloy alloy 800H, developed cracks that penetrated the entire thickness. Optical and scanning electron microscopy, X-ray diffraction, and microhardness tests were used to evaluate the failed tube. It was found that the tube was considerably embrittled by high-temperature carburization, leading to intergranular fracture at the inner surface. Carburization appeared to have been caused by high-temperature exposure to the carbonrich atmosphere associated with the coke adhered to the inner surface. Additionally, the decrease in heat transfer due to the coke deposits caused the wall temperature to increase during service. However, at the outer surface, the tube fractured by a fatigue process that could result from the use of a counterweight to prevent sagging of the tube as a result of the coke deposition. Based on the results obtained, a short-term solution was to modify various process parameters to reduce the extent of coke deposition and/or increase the frequency of decoking and to discontinue the use of a counterweight. However, the long-term solution is to replace alloy 800H.     

高温碳化环境对镍－铬－铁基耐蚀耐热合金的组织和性能的作用

研究了镍－铬－铁基耐蚀耐热合金ＩＮＣＯＬＯＹ８００Ｈ的高温抗碳化性能。该合金经７００℃、８００℃和９００℃城市煤气环境中长期保持后，其外观明显变化，８００℃及９００℃样品外表层严重剥落，剥落层主要由石墨、碳及氧化铬组成。而次表层则为碳化铬、氧化铬、氧化铁等混合物组成。经碳化后合金的高温机械性能有明显变化，屈服强度因表层化合物的强化作用而升高，抗拉强度及伸长率则下降，碳化温度越高则降低越显著。     

高温碳化环境对镍－铬－铁基耐蚀耐热合金的组织和性能的作用

研究了镍－铬－铁基耐蚀耐热合金ＩＮＣＯＬＯＹ８００Ｈ的高温抗碳化性能。该合金经７００℃、８００℃和９００℃城市煤气环境中长期保持后，其外观明显变化，８００℃及９００℃样品外表层严重剥落，剥落层主要由石墨、碳及氧化铬组成。而次表层则为碳化铬、氧化铬、氧化铁等混合物组成。经碳化后合金的高温机械性能有明显变化，屈服强度因表层化合物的强化作用而升高，抗拉强度及伸长率则下降，碳化温度越高则降低越显著。     

Failure in a high pressure feeding line of an oil refinery due to hydrogen effect

This work describes failure analysis of a feeding pipeline of an oil refinery. For this analysis visual inspection, dye penetration, optical and electron microscopy, XRD, tensile tests, fracture toughness tests and stress calculations were used. Result of the investigations show that hydrogen embrittlement has played an important role in the failure of the pipeline. For completing the case, hydrogen embrittlement damage of the piping material made from commercial ASTM A105M low alloy manganese steel was studied by using baking and hydrogenation treatments. Baking treatment was carried out at 520 °C for 20 min followed by slow cooling while hydrogenation treatment was carried out in a solution of H₂SO₄ which contained As₂O₃ for 0–6 h under cathodic situation. Then change in the mechanical properties and fracture toughness of the steel after the treatments were measured by tensile and fracture toughness tests. In addition, fractography was carried out using a scanning electron microscope (SEM) and image analyzer. Results show that the baking treatment increased elongation to failure and fracture toughness significantly and reduced yield strength slightly compared to the failed condition of the pipe. Hydrogenation treatment decreased elongation to failure and fracture toughness of the material considerably and increased strength barely. Increase in the hydrogenation time reduced ductility of the steel further more. These results indicate that hydrogen through hydrogen embrittlement mechanism, made the pipe material brittle and susceptible to cracking. Embrittlement with the assistance of an emergency shutdown and stress concentration provides damage nucleation and finally developed brittle fracture.     

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.     

Effects of phase lags on wave propagation in an infinite solid due to a continuous line heat source

The present work is concerned with the wave propagation in a homogeneous, isotropic and unbounded solid due to a continuous line heat source under the theory of thermoelasticity with three phase-lags (Roychoudhari in J Therm Stress 30:231?C238, 2007). For the solution of the problem, we employ a potential function approach together with Laplace and Hankel transform method. Analytical expressions for the distributions of different fields like temperature, displacement and stresses inside the medium are derived by inverting Laplace transforms in an approximate manner for small values of time. The problem is illustrated by computing numerical values of the field variables for a particular material. The theoretical as well as numerical results are compared with the corresponding results for other theories of thermoelasticity reported earlier.     

Effects of additive hydrogen gas on the instability due to air exposure in ZnO-based thin film transistors

The effect of adding hydrogen gas (H₂) when depositing a zinc oxide (ZnO) thin film in a thin film transistor (TFT) using the ZnO as the channel layer on the electrical characteristics of the ZnO-TFTs, particularly the change in the characteristics according to long-term exposure to air, was investigated. As the amount of added H₂ gas was increased, the resistivity of ZnO films was monotonously decreased and their crystallinity was weakened. Compared with the TFT using a ZnO without H₂ addition, the threshold voltage (V_th) decreased and the on/off current ratio (I_on/I_off) greatly increased, if the amount of H₂ entry was small (≤ 0.3 sccm). However, when an excessive (≥ 0.5 sccm) amount of H₂ was added, the TFT's properties deteriorated. In addition, the ZnO TFTs showed a positive V_th-shift with increased air exposure time. The analysis using the X-ray photoelectron spectroscopy (XPS) confirmed that this was attributed to the reduction of oxygen vacancies due to air exposure. It was noticed that the TFTs that were manufactured using ZnO films with H₂ addition showed significant suppression of the V_th-shift according to air exposure.     

Effect of stochasticity on targeted energy transfer from a linear medium to a strongly nonlinear attachment

In this work the problem of targeted energy transfer (TET) from a linear medium to a nonlinear attachment is studied in the presence of stochasticity. Using a Green’s function formulation, complexification-averaging technique and diffusion approximation we derive a complex, nonlinear, Ito stochastic differential equation that governs the slow dynamics of the system. Through the numerical solution of the corresponding Fokker-Planck-Kolmogorov (FPK) equation we study the optimal regime of TET and its robustness to stochasticity for the case of nonlinear interactions of the nonlinear attachment with a single mode of the linear system. The probabilistic analysis reveals that in the presence of stochasticity the optimal TET regime, predicted in the deterministic theory, is not only preserved but also is enhanced due to the interaction of nonlinearity and stochasticity.     

Influence and its mechanism of temperature variation in a muffle furnace during calcination on the adsorption performance of rod-like MgO to Congo red

Calcination temperature plays a crucial role in determining the surface properties of generated MgO, but the influence of temperature variation in a muffle furnace during calcination on its performance is rarely reported. Herein we observed that the temperature in a muffle furnace during calcination demonstrated a gradually increasing trend as the location changed from the furnace doorway to the most inner position. The variation in temperature had a great impact on the adsorption performance of generated rod-like MgO without and/or with involvement of Na₂SiO₃ to Congo red in aqueous solution. To get a better understanding on the detailed reasons, various techniques including actual temperature measurement via multimeter, N₂ physical adsorption, CO₂ chemical adsorption and FT-IR spectrometry have been employed to probe the correlation between the adsorption performance of generated MgO from various locations and the inner actual temperature of used muffle furnace as well as their physicochemical properties. In addition, two mechanisms were proposed to elucidate the adsorption process of Congo red over the surface of generated MgO without and/or with presence of Na₂SiO₃, respectively.     

基于开裂能密度及裂纹扩展特性的橡胶隔振器疲劳特性预测

基于开裂能密度的连续介质力学参数及橡胶材料裂纹扩展特性(裂纹扩展速率与撕裂能之关系),获得橡胶部件多轴疲劳特性计算公式,并计算某汽车动力总成橡胶隔振器的疲劳特性。计算与试验对比表明,橡胶隔振器疲劳特性预测(寿命、开裂位置及开裂方向)与实测较一致。预测疲劳寿命分布在实测疲劳寿命的1/2倍分散因子内,满足工程疲劳寿命预测要求。提出的橡胶隔振器多轴疲劳特性预测方法,可用试验效率较高、投入较少的材料裂纹扩展试验代替耗时较多的材料疲劳破坏试验,不仅能为橡胶部件前期疲劳设计提供参考,亦能大幅缩短产品疲劳设计周期。     

Freezing of a water droplet due to evaporation—heat transfer dominating the evaporation–freezing phenomena and the effect of boiling on freezing characteristics

One of the authors has proposed a novel transport/storage system for the waste cold from the gasification process of liquefied natural gas (LNG), which consists of an evaporator, a cold trap, and a pipeline. In order to estimate the performance of this system, one should know the pressure in the evaporator, in which evaporation–freezing of a PCM occurs, and in the cold trap, as well as the pressure drop of the pipeline due to the flow of low pressure vapor of the PCM. In this paper, the cooling/freezing phenomena of a water droplet due to evaporation in an evacuated chamber was experimentally examined, and the heat transfer dominating the evaporation-freezing phenomena was investigated in order to estimate the pressure in the evaporator. From the results, it was shown that the water droplet in the evacuated cell is effectively cooled by the evaporation of water itself, and is frozen within a few seconds through a remarkable supercooling state, and that the cooling rate of the water droplets were dominated by heat transfer within the droplet under the abrupt evacuation condition. The later result means that, in order to obtain an ice particle by evaporation–freezing, the surroundings of the water droplet should be evacuated at the pressure as low as the saturate pressure of water at the maximum supercooling temperature of the droplet.