Optimization for Materials Selection and its Importance in a Management Performance

The complexity and importance of the management activities, and implicitly decision-making activities requires in the current period, the use of modern techniques and methods, very well scientifically founded. A power plant management activity involves making decisions based wealth of information and often involve the most varied criteria: technical, economic, environmental and others. Using methods of multi-criteria decision becomes an indispensable decision factor. In this paper, we apply such a method for prioritizing namely Onicescu method in solving the problems as the optimal choose of materials for the realization of thermal to a superheater. Are analyzed three materiale10CrMo9-10, 13CrMo4-5, 16Mo3 taking into account criteria such as technical resistance duration, creep limit, cost and others.

Current Status and Future Development of LWAC

Light weight aggregate concrete (LWAC) has gained popularity as an alternative to ordinary concrete for structural purposes, but its using still needs to get promoted in China. With the intention of shading some lights on LWAC development and broadening its application in China, this paper analyses the development of LWAC. It presents the current status and trend of LWAC application. On the basis of introduction of concept, advantages and disadvantages of LWAC are analyzed. It can be summarized that characteristics such as lightweight, high strength, excellent seismic performance, better fire resistance, good crack resistance, good durability and economic benefits improve its popularity. However, properties like easiness to delaminate and difficulty to pump, as well as problem of shrinkage and creep, limit its application. Owing to its properties, the main application range of LWAC includes high-rise buildings, bridge engineering, sound-absorbing products, and decorating nowadays. It is concluded the use of LWAC will be lead to higher strength and more energy saving in the future. Moreover, the recycling and energy efficiency of LWAC will be further improved.

Material Damage Analysis and Life Prediction of Cr5Mo Used as Furnace Tubing

Cr5Mo furnace tubes have served in a coking furnace nearly 15 years. For the purpose of risk reduction and to assure a safe long term stable operation of the furnace, these tubes have been investigated by measns of macrographic observation, chemical composition analysis, mechanical property analysis, hardness and metallurgical structure analysis, etc. The experiment results shows that after a long period serve at high temperature, the hardness of the tube has decreased in 15 years. However, the hardness of inner wall is higher than the others, from which we can infer that the inner wall of the tubes is carburized. Taking GB9948-2006 as a reference standard, the yield stress of the furnace tube in normal temperature has decreased by 16%, and the yield stress in high temperature is also failed to fit the standard. Metallographic analysis shows that the grain fineness is 6 grade and the nodulizing grade is 3.5 grade, pearlite spheroidization is getting severer and it will reduce the creep limit and creep rupture strength. Based on the result of high temperature endurance test, isotherm method and L-M extrapolation are adopted to predict the remaining life of furnace tubes, assessment shows that these furnace tubes are able to serve for another cycle under the operating temperature of 650°C and the stress of 18MPa.

Comparative Study of Flange-to-Seal Contact Couplings With Bolt Relaxation Under Creep Condition

Future coal-fired steam turbines promise increased efficiency and low emissions. However, this comes at the expense of increased thermal load from higher inlet steam temperatures and pressures leading to severe creep that significantly influences the sealing behavior and high temperature strength of bolted flange-seal couplings. Flanges with different thicknesses were employed for a comparative study. The important stress/creep values in the flanges and U-type seals had been obtained for variations in flange thickness and bolt relaxation while maintaining other leading parameters constant. The variation of contact stresses due to creep deformation plays an important role in achieving a leak proof sealing. In this paper, a two-dimensional finite element analysis of bolted flange-seal couplings has been carried out by taking the relaxation of bolt stress under full-loading turbine service. The creep strength of flanges and U-type seals are investigated by Cocks–Ashby (C–A) equivalent strain method. The multiaxial state of stresses is considered in this method by using C–A multiaxial coefficient. According to ASME allowable creep limit, the C–A equivalent strains of three flange-seal couplings are evaluated and compared. Furthermore, based on the results of contact stresses, the creep behavior of U-type seals is analyzed varying flange thickness. Finally, analysis shows that the thinner flange-seal coupling has larger long-term contact stress, while the U-type seal with the thicker flange has the least creep strength.

Comparative Study of Flange-to-Seal Contact Couplings With Bolt Relaxation Under Creep Condition

Future coal-fired steam turbines promise increased efficiency and low emissions. However, this comes at the expense of increased thermal load from higher inlet steam temperatures and pressures leading to severe creep that significantly influences the sealing behavior and high temperature strength of bolted flange-seal couplings. Flanges with different thicknesses were employed for a comparative study. The important stress/creep values in the flanges and U-type seals had been obtained for variations in flange thickness and bolt relaxation whilst maintaining other leading parameters constant. The variation of contact stresses due to creep deformation plays an important role in achieving a leak proof sealing. In this paper, a two-dimensional finite element analysis (FEA) of bolted flange-seal couplings has been carried out by taking the relaxation of bolt stress under full-loading turbine service. The creep strength of flanges and U-type seals are investigated by Cocks-Ashby (C-A) equivalent strain method. The multiaxial state of stresses is considered in this method by using C-A multiaxial coefficient. According to ASME allowable creep limit, the C-A equivalent strains of three flange-seal couplings are evaluated and compared. Furthermore, based on the results of contact stresses, the creep behavior of U-type seals is analyzed varying flange thickness. Finally, analysis shows that the thinner flange-seal coupling has larger long-term contact stress, while the U-type seal with the thicker flange has the least creep strength.

A Study on Microstructures and Creep Behaviors in the Mg-3Sr-xY Alloys

In this paper, the author successfully fabricated Mg-3Sr-xY alloys by melting-leaching reduction method using SF6 and N2 as protected gas. The microstructures of the Mg-3Sr-xY alloys were investigated in details，and the results showed that Mg-3Sr-xY alloys are composed of dendrite α-Mg and eutectic α-Mg and Mg17Sr2 and Mg24Y5 particulates, the second phases distribute in the α-Mg dendrites and interdendrites. The fiber microstructures form after thermal extrusion and the dynamic recrystallization occurs. In Mg-3Sr-xY alloy, the tensile strengths, the yield strengths and elongation rates increase firstly, reach the peak values, decrease with the increasing in Y content. Mg-3Sr-xY alloy have the best mechanics properties, including yield strengths and ultimate strengths and elongation rates and creep properties by the addition of 0.6%Y content. The tensile behaviors at elevated temperatures are accord to general laws for the metals at room temperature. The Mg-3Sr-xY alloys with 0.4-1.0% Y are of best creep limit. The dislocation sliding and climbing is the main creep mechanism for Mg-3Sr-0.6Y alloys.