A metallurgical forensic investigation was conducted to determine the cause of a failed superheater tube. Analysis techniques by Visual Examination, Energy Dispersive X-ray Analysis, Mechanical Testing and Metallograp...A metallurgical forensic investigation was conducted to determine the cause of a failed superheater tube. Analysis techniques by Visual Examination, Energy Dispersive X-ray Analysis, Mechanical Testing and Metallographic Investigation were conducted, together with a comparative study from an inlet elbow section that did not fail. The superheater tube suffered premature failure after being in service for about two years. It was concluded that the failed tube underwent overheating, corrosion-erosion, embrittlement, and eventual failure under its internal pressure by stress rupture. The analysis revealed intergranular cracks, window fracture features and spheroidization of pearlite with grain growth. A possible contribution to embrittlement was from copper. Follow-ups and recommendations were provided, as well as covering materials, inspection, and operational considerations.展开更多
Corrosion behavior of TP316L was investigated with simulated atmosphere and ash deposition for the superheater in biomass boiler.Corrosion dynamic curves were plotted by mass gain.The results showed that the corrosion...Corrosion behavior of TP316L was investigated with simulated atmosphere and ash deposition for the superheater in biomass boiler.Corrosion dynamic curves were plotted by mass gain.The results showed that the corrosion was dependent on temperature and was greatly accelerated by ash deposition.The mass gain was distinctly reduced in the presence of SO2 with and without ash deposition on the specimens.Corrosion rates with ash deposit at different temperatures were calculated.Two feasible methods were provided to avoid serious high-temperature corrosion in the biomass boiler.展开更多
After research on a 2000t/h subcritical forced-circulation balanced ventilation were applied boiler and the structure and operation of its auxiliary system builds up this heat transfer model of a superheater's pip...After research on a 2000t/h subcritical forced-circulation balanced ventilation were applied boiler and the structure and operation of its auxiliary system builds up this heat transfer model of a superheater's pipe wall and analyze the effect of primary factors on the overtemperature of the pipe wall. Fault tree structure was used to uncover the multiplayer logic between the overtemperature of the superheater's pipe wall and the faults.展开更多
The mechanical stress distribution and the stress concentrations of the superheater outlet header of a 600MW supercritical boiler were analyzed by the finite element method. The results showed that the stress concentr...The mechanical stress distribution and the stress concentrations of the superheater outlet header of a 600MW supercritical boiler were analyzed by the finite element method. The results showed that the stress concentrated at the inside conjunction area between the pipe and the header cylinder , and the value of the maximum mechanical stress concentration factor is 2.51.展开更多
Superheater tubes temperature control is a necessity for long lifetime, high efficiency and high load following capability in boiler. This study reports a new approach for the control strategy design of boilers with s...Superheater tubes temperature control is a necessity for long lifetime, high efficiency and high load following capability in boiler. This study reports a new approach for the control strategy design of boilers with special shields. The presented control strategy is developed based on radiation thermal shields with low emissivity coefficient and high reflectivity or scattering coefficient. In order to simulate the combustion event in boiler and heat transfer to superheater tubes, an effective set of computational fluid dynamic (CFD) codes is used. Results indicate a successful identification of over- heated zones on platen superheater tubes and effect of radiation shields for solving this problem.展开更多
Although the solid-state lighting market is growing rapidly, it is still difficult to obtain ultra-high brightness white light emitting diodes(LEDs). V-pits are inevitably introduced during the metalorganic chemical v...Although the solid-state lighting market is growing rapidly, it is still difficult to obtain ultra-high brightness white light emitting diodes(LEDs). V-pits are inevitably introduced during the metalorganic chemical vapor deposition(MOCVD)growth of multiple quantum wells(MQWs) in Ⅲ–nitride LEDs, and thus affecting the carrier dynamics of the LEDs.Specifically designed structures are fabricated to study the influence of the V-pits on the hole transportation and efficiency droop, and double quantum wells(QWs) are used to monitor the transportation and distribution of holes based on their emission intensity. It is found that when compared with the planar QWs, the injection of holes into the QWs through the side walls of the V-pits changes the distribution of holes among the MQWs. This results in a higher probability of hole injection into the middle QWs and enhanced emission therein, and, consequently, a lower efficiency droop.展开更多
Structural uniformity is an important parameter influencing physical and mechanical properties of lotus-type porous metals prepared by directional solidification of metal-gas eutectic (Gasar). The effect of superheat ...Structural uniformity is an important parameter influencing physical and mechanical properties of lotus-type porous metals prepared by directional solidification of metal-gas eutectic (Gasar). The effect of superheat on structural uniformity as well as average porosity, pore morphology of porous metals was studied. The experimental results show that, when the superheat is higher than a critical value (ΔTc), the bubbling or boiling phenomenon will occur and the gas bubbles will form in the melt and float out of the melt. As a result, the final porosity will decrease. In addition, a higher superheat will simultaneously cause a non-uniform porous structure due to the pores coalescence and bubbling phenomenon. Finally, a theoretical model was developed to predict the critical superheat for the hydrogen to escape from the melt and the corresponding escapement ratio of hydrogen content. Considering the escapement of hydrogen, the predicted porosities are in good agreement with the experimental results.展开更多
文摘A metallurgical forensic investigation was conducted to determine the cause of a failed superheater tube. Analysis techniques by Visual Examination, Energy Dispersive X-ray Analysis, Mechanical Testing and Metallographic Investigation were conducted, together with a comparative study from an inlet elbow section that did not fail. The superheater tube suffered premature failure after being in service for about two years. It was concluded that the failed tube underwent overheating, corrosion-erosion, embrittlement, and eventual failure under its internal pressure by stress rupture. The analysis revealed intergranular cracks, window fracture features and spheroidization of pearlite with grain growth. A possible contribution to embrittlement was from copper. Follow-ups and recommendations were provided, as well as covering materials, inspection, and operational considerations.
文摘Corrosion behavior of TP316L was investigated with simulated atmosphere and ash deposition for the superheater in biomass boiler.Corrosion dynamic curves were plotted by mass gain.The results showed that the corrosion was dependent on temperature and was greatly accelerated by ash deposition.The mass gain was distinctly reduced in the presence of SO2 with and without ash deposition on the specimens.Corrosion rates with ash deposit at different temperatures were calculated.Two feasible methods were provided to avoid serious high-temperature corrosion in the biomass boiler.
文摘After research on a 2000t/h subcritical forced-circulation balanced ventilation were applied boiler and the structure and operation of its auxiliary system builds up this heat transfer model of a superheater's pipe wall and analyze the effect of primary factors on the overtemperature of the pipe wall. Fault tree structure was used to uncover the multiplayer logic between the overtemperature of the superheater's pipe wall and the faults.
文摘The mechanical stress distribution and the stress concentrations of the superheater outlet header of a 600MW supercritical boiler were analyzed by the finite element method. The results showed that the stress concentrated at the inside conjunction area between the pipe and the header cylinder , and the value of the maximum mechanical stress concentration factor is 2.51.
文摘Superheater tubes temperature control is a necessity for long lifetime, high efficiency and high load following capability in boiler. This study reports a new approach for the control strategy design of boilers with special shields. The presented control strategy is developed based on radiation thermal shields with low emissivity coefficient and high reflectivity or scattering coefficient. In order to simulate the combustion event in boiler and heat transfer to superheater tubes, an effective set of computational fluid dynamic (CFD) codes is used. Results indicate a successful identification of over- heated zones on platen superheater tubes and effect of radiation shields for solving this problem.
基金Project supported by the National Key Research and Development Project of China(Grant No.2017YFB0403303)the Key Technologies Research and Development Program of Tianjin,China(Grant Nos.18YFZCGX00760 and 18YFZCGX00400)
文摘Although the solid-state lighting market is growing rapidly, it is still difficult to obtain ultra-high brightness white light emitting diodes(LEDs). V-pits are inevitably introduced during the metalorganic chemical vapor deposition(MOCVD)growth of multiple quantum wells(MQWs) in Ⅲ–nitride LEDs, and thus affecting the carrier dynamics of the LEDs.Specifically designed structures are fabricated to study the influence of the V-pits on the hole transportation and efficiency droop, and double quantum wells(QWs) are used to monitor the transportation and distribution of holes based on their emission intensity. It is found that when compared with the planar QWs, the injection of holes into the QWs through the side walls of the V-pits changes the distribution of holes among the MQWs. This results in a higher probability of hole injection into the middle QWs and enhanced emission therein, and, consequently, a lower efficiency droop.
基金Project(51271096)supported by the National Natural Science Foundation of ChinaProject(NCET-12-0310)supported by the Program for New Century Excellent Talents in University,Ministry of Education,China
文摘Structural uniformity is an important parameter influencing physical and mechanical properties of lotus-type porous metals prepared by directional solidification of metal-gas eutectic (Gasar). The effect of superheat on structural uniformity as well as average porosity, pore morphology of porous metals was studied. The experimental results show that, when the superheat is higher than a critical value (ΔTc), the bubbling or boiling phenomenon will occur and the gas bubbles will form in the melt and float out of the melt. As a result, the final porosity will decrease. In addition, a higher superheat will simultaneously cause a non-uniform porous structure due to the pores coalescence and bubbling phenomenon. Finally, a theoretical model was developed to predict the critical superheat for the hydrogen to escape from the melt and the corresponding escapement ratio of hydrogen content. Considering the escapement of hydrogen, the predicted porosities are in good agreement with the experimental results.
