Carburization of Ethylene Pyrolysis Furnace Tube in a Petrochemical Plant

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Tao Chen ◽  
Xuedong Chen ◽  
Chunjiao Liu ◽  
Juan Ye ◽  
Defu Nie
Keyword(s):  
Grain Boundaries ◽  
Mixed Oxides ◽  
Microscopic Analysis ◽  
Oxidation Zone ◽  
Petrochemical Plant ◽  
Pyrolysis Furnace ◽  
Inner Surface ◽  
Aging Product ◽  
Furnace Tube ◽  
Product Zone

Carburization phenomena of the ethylene pyrolysis furnace tube made of 25Cr35NiNb alloy were investigated after service for approximate 30,000 h in a petrochemical plant. Three different zones, namely, oxidation zone, carburization zone, and aging product zone, were observed in the cross section of furnace tube by microscopic analysis. The oxidation zone near the inner surface has a thickness of about 700 μm and possesses the characterization of many loose pores and voids. The inner surface has a continuous thin Cr2O3 layer and the grain boundaries near the inner wall are mainly composed of mixed oxides of Cr2O3 and SiO2. In addition, segregation of impurities S and P was detected at grain boundaries. The dark gray SiO2 distributes in the front of the oxidation zone. Carbides distribute at grain boundaries in the carburization zone with lots of voids and micro cracks. The width of grain boundary is broadened. According to the experimental results, the initiation of cracks may be promoted by carbides at grain boundaries. The uneven distribution of the Cr element was found in the carburization zone, and direct experimental evidence of Cr element diffusion was detected. In the aging product zone, the carbides evolution was observed. The chromium carbides are composed of Cr7C3 and Cr23C6. The microstructure and composition evolutions of the furnace tube and their effects on service life of ethylene pyrolysis furnace tube were also discussed.

Carburization of Ethylene Pyrolysis Furnace Tube in a Petrochemical Plant

2014 ◽  
Author(s):  
Tao Chen ◽  
Xuedong Chen ◽  
Chunjiao Liu ◽  
Juan Ye ◽  
Defu Nie
Keyword(s):  
Grain Boundaries ◽  
Mixed Oxides ◽  
Microscopic Analysis ◽  
Oxidation Zone ◽  
Petrochemical Plant ◽  
Pyrolysis Furnace ◽  
Inner Surface ◽  
Aging Product ◽  
Furnace Tube ◽  
Product Zone

Carburization phenomena of the ethylene pyrolysis furnace tube made of 25Cr35NiNb alloy was investigated after service for approximate 30,000h in a petrochemical plant. Three different zones, namely oxidation zone, carburization zone and aging product zone, were observed in the cross section of furnace tube by microscopic analysis. The oxidation zone near the inner surface has a thickness of about 700μm and possesses the characterization of many loose pores and voids. The inner surface has a continuous thin Cr2O3 layer and the grain boundaries near the inner wall are mainly composed of mixed oxides of Cr2O3 and SiO2. In addition, segregation of impurities S and P were detected at grain boundaries. The dark grey SiO2 distributes in front of the oxidation zone. Carbides distribute at grain boundaries in the carburization zone with lots of voids and micro cracks. The width of grain boundary is broadened. According to the experimental results, the initiation of cracks may be promoted by carbides at grain boundaries. The uneven distribution of the Cr element was found in the carburization zone, and direct experimental evidence of Cr element diffusion was detected. In the aging product zone, the carbides evolution was observed. The chromium carbides are composed of Cr7C3 and Cr23C6. The microstructure and composition evolutions of the furnace tube and their effects on service life of ethylene pyrolysis furnace tube were also discussed in this paper.

The Relationship Between Magnetism and Microstructure of Ethylene Pyrolysis Furnace Tubes after a Long-term Service

2018 ◽  
Vol 24 (5) ◽  
pp. 478-487 ◽  
Author(s):  
Jingfeng Guo ◽  
Tieshan Cao ◽  
Congqian Cheng ◽  
Xianming Meng ◽  
Jie Zhao
Keyword(s):  
Saturation Magnetization ◽  
Outer Region ◽  
Cr Content ◽  
Pyrolysis Furnace ◽  
The Matrix ◽  
Furnace Tube ◽  
Primary Carbides ◽  
The Relationship ◽  
Very High

AbstractThe magnetism and microstructure of Cr25Ni35Nb and Cr35Ni45Nb alloy tubes after 5 years of service were investigated in this paper. The saturation magnetization of the Cr25Ni35Nb alloy tube in the thickness direction is more than 20 emu/g, and the tube becomes ferromagnetic. The inner and outer walls of Cr35Ni45Nb alloy tubes also become ferromagnetic. But the saturation magnetization of the Cr35Ni45Nb alloy tubes approaches to zero in the center zone. The primary carbides M7C3 and NbC are changed into M23C6 and G phase at the outer region of the furnace tube. However, the M23C6-type carbides were replaced by carbon-rich carbides M7C3 at the carburization zone. Cr-depleted zones are formed at the inner and outer walls of the furnace tubes owing to oxidation. Carburization and oxidation reduce the Cr content of the matrix. Accordingly, the saturation magnetization is very high at the carburization zone and Cr-depleted zone. The magnetism of Cr25Ni35Nb and Cr35Ni45Nb alloy tubes has a high correlation with the Cr content of the matrix. Carburization and oxidation are the main reasons that make the paramagnetic ethylene pyrolysis furnace tube change to ferromagnetic.

scholarly journals Nanocompositional Electron Microscopic Analysis and Role of Grain Boundary Phase of Isotropically Oriented Nd-Fe-B Magnets

2017 ◽  
Vol 2017 ◽  
pp. 1-17 ◽  
Author(s):  
Gregor A. Zickler ◽  
Josef Fidler
Keyword(s):  
Domain Wall ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Magnetization Reversal ◽  
Coercive Field ◽  
Microscopic Analysis ◽  
Realistic Model ◽  
Boundary Phase ◽  
Electron Microscopic ◽  
The Impact

Nanoanalytical TEM characterization in combination with finite element micromagnetic modelling clarifies the impact of the grain misalignment and grain boundary nanocomposition on the coercive field and gives guidelines how to improve coercivity in Nd-Fe-B based magnets. The nanoprobe electron energy loss spectroscopy measurements obtained an asymmetric composition profile of the Fe-content across the grain boundary phase in isotropically oriented melt-spun magnets and showed an enrichment of iron up to 60 at% in the Nd-containing grain boundaries close to Nd2Fe14B grain surfaces parallel to the c-axis and a reduced iron content up to 35% close to grain surfaces perpendicular to the c-axis. The numerical micromagnetic simulations on isotropically oriented magnets using realistic model structures from the TEM results reveal a complex magnetization reversal starting at the grain boundary phase and show that the coercive field increases compared to directly coupled grains with no grain boundary phase independently of the grain boundary thickness. This behaviour is contrary to the one in aligned anisotropic magnets, where the coercive field decreases compared to directly coupled grains with an increasing grain boundary thickness, if Js value is > 0.2 T, and the magnetization reversal and expansion of reversed magnetic domains primarily start as Bloch domain wall at grain boundaries at the prismatic planes parallel to the c-axis and secondly as Néel domain wall at the basal planes perpendicular to the c-axis. In summary our study shows an increase of coercive field in isotropically oriented Nd-Fe-B magnets for GB layer thickness > 5 nm and an average Js value of the GB layer < 0.8 T compared to the magnet with perfectly aligned grains.

Microscopic Analysis of Residuals on Polycrystalline CdTe Following Wet CdCl2 Treatment

2001 ◽  
Vol 668 ◽  
Author(s):  
Timothy A. Gessert ◽  
Manuel J. Romero ◽  
Craig L. Perkins ◽  
Sally E. Asher ◽  
Rick Matson ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Grain Boundaries ◽  
Ion Beam ◽  
Microscopic Analysis ◽  
Coated Surface ◽  
Cdcl2 Treatment ◽  
Cdte Surface

ABSTRACTIn this study we report on the spatial distribution and composition of residuals on the CdTe surface following a typical wet CdCl2 treatment, and the effect that our ion-beam milling has on this residual-coated surface. Results show that residuals are spatially discrete, located primarily along grain boundaries, and are likely a cadmium oxychloride. Results also show that the residuals may penetrate deep into the CdTe surface such that typical ion-beam milling procedures do not produce complete residual removal.

Effect of RE on Microstructure and Properties of AM60 Magnesium Alloy

2014 ◽  
Vol 1004-1005 ◽  
pp. 172-176
Author(s):  
Yao Li ◽  
Jun Jie Yang ◽  
Ping Xue ◽  
Zhi Jiang Zuo
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Rare Earth ◽  
Magnesium Alloy ◽  
Grain Boundaries ◽  
Grain Refinement ◽  
Network Structure ◽  
Microscopic Analysis ◽  
Elongation Rate ◽  
Mg17al12 Phase

Industrial AM60 magnesium alloy, to which mixed rare earth containing Y, Gd and Nd elements is added, was used to study the effects of rare earth (RE) on their casting microstructures and properties. The experimental results showed that RE could effectively improve grain refinement and the internal organization, which transferred the Mg17Al12 phase from the network structure into grainy one. The microscopic analysis indicated that by adding the mixed RE, the amount of Mg17Al12 compounds was less than that without mixed RE on the grain boundaries, and it was replaced by Al-RE compounds. In addition, the mechanical properties of the alloy with mixed RE had been significantly improved and the maximum tensile strength was up to about 260MPa and the elongation rate could reach more than 10%. When the mixed RE content was more than 2%, coarse Al-RE compounds were formed in the alloy, which degraded the mechanical properties.

Effect of Temperature on Damage Evolution of Cr25Ni35Nb Alloy Subjected to Combined Mechanical and Environmental Degradation

2015 ◽  
Vol 34 (4) ◽  
Author(s):  
Limin Shen ◽  
Huansheng Liu ◽  
Jianming Gong ◽  
Luyang Geng
Keyword(s):  
Environmental Degradation ◽  
Damage Evolution ◽  
Damage Mechanics ◽  
Continuum Damage Mechanics ◽  
Effect Of Temperature ◽  
Damage Prediction ◽  
Actual Observation ◽  
Inner Surface ◽  
Furnace Tube ◽  
Abaqus Code

AbstractDue to combined mechanical and environmental degradation, i.e. coupled creep and carburization, Cr25Ni35Nb alloy often fails prior to the expected design life. In the present paper, based on the continuum damage mechanics, the constitutive model of coupled multi-damage factors for computing the damage evolution of Cr25Ni35Nb alloy was proposed. The damage prediction was carried out by using finite element method based on ABAQUS code. And then damage evolution processes at different operating temperatures (950 °C and 1050 °C) were simulated and the effect of service temperature on the damage evolution was discussed. The results showed that the rate of damage increased obviously with operating temperature increasing. The location with maximum damage is along the inner surface of tube, which implies that fracture begins along the inner surface of tube under the action of coupled creep and carburization damage and this is coincident with the actual observation of the failure of furnace tube.

Microstructure and Hardness Property of Internally Oxided AgCdO Alloy

2012 ◽  
Vol 152-154 ◽  
pp. 440-443 ◽  
Author(s):  
Hyo Soo Lee ◽  
Hyung Won Shin ◽  
Taek Kyun Jung ◽  
Tae Bum Kim ◽  
Min Ha Lee
Keyword(s):  
Grain Boundaries ◽  
Internal Oxidation ◽  
Oxidation Zone ◽  
Holding Time ◽  
Dispersion Strengthening ◽  
Free Zone ◽  
Hardness Property

Microstructure and hardness property of AgCd alloy internally oxided at 973K for 1 h - 24 h with O2 atmosphere of 3 atm was investigated. Band typed CdO phase was formed at grain boundaries, and particle typed CdO phase was formed at grain interior. In this alloy, it was found that oxygen adsorpted at surface diffuses to interior through grain boundaries, and it subsequently diffuses into grain interior during internal oxidation. No Ag exduation was found in this alloy. The thickness of oxidized layer increased with increasing holding time at given temperature. Hardness of the oxidation zone was 125 ± 5 Hv, which value is higher two times than that of the oxidation free zone. The higher hardness of oxided region than the oxidation free zone was attributed to the dispersion strengthening by CdO particles.

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