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Water wall tube temperature is a major parameter in the steam generator design which has a significant role in keeping the steam generator available. Thus, knowing the tube average temperature in different operating conditions is very important to avoid the causes of tube failures. High temperatures are a major cause of various types of failures, such as overheating, hydrogen damage, thermal stress, etc. Furthermore, deposits on the inner tube wall contribute to such failure by changing the thermal resistance of the tube wall, which causes a significant increase in the tube wall's average temperature, consequently lowering the allowable stress. Therefore, the model was created by using ANSYS FLUENT (Canonsburg, PA, USA) to determine the wall average water tube wall temperature considering the deposit layer thickness (magnetite). Furthermore, this model was verified. It was found that increasing tube thickness can increase the average tube temperature but combining it with increasing deposit thickness leads to higher temperatures. In other words, the effect of the deposit on the tube with higher thickness is higher than on the tube with lower thickness. By discussing the minimum thickness of the water wall tube, the suitable selection of the tube thickness and courses of action concerning the operating conditions that minimize the potential overheating of water tubes in the furnace section of the boiler can be determined. [ABSTRACT FROM AUTHOR]

Water wall tube temperature is a major parameter in the steam generator design which has a significant role in keeping the steam generator available. Thus, knowing the tube average temperature in different operating conditions is very important to avoid the causes of tube failures. High temperatures are a major cause of various types of failures, such as overheating, hydrogen damage, thermal stress, etc. Furthermore, deposits on the inner tube wall contribute to such failure by changing the thermal resistance of the tube wall, which causes a significant increase in the tube wall’s average temperature, consequently lowering the allowable stress. Therefore, the model was created by using ANSYS FLUENT (Canonsburg, PA, USA) to determine the wall average water tube wall temperature considering the deposit layer thickness (magnetite). Furthermore, this model was verified. It was found that increasing tube thickness can increase the average tube temperature but combining it with increasing deposit thickness leads to higher temperatures. In other words, the effect of the deposit on the tube with higher thickness is higher than on the tube with lower thickness. By discussing the minimum thickness of the water wall tube, the suitable selection of the tube thickness and courses of action concerning the operating conditions that minimize the potential overheating of water tubes in the furnace section of the boiler can be determined.

Heat recovery steam generator (HRSG) is a critically important subsystem of a combined cycle. The global objective of a HRSG is to heat the stream of water. The HRSG is com-posed of three major sections, including an economizer, an evaporator, and a super-heater. In this study, a water tube HRSG is considered and its main design features are deduced from the minimization of the entropy generation by using the constructal theory. Entropy generation is obtained by considering all irreversibilities associated with the processes. Considering the minimum total entropy generation as the objective function, the optimum parameters in the HRSG unit are derived by using the genetic algorithm method under the fixed total volume condition. In the present work, the number and arrangement of the tubes, the optimal diameters of tubes and spacing between adjacent tubes for three main sections, total length, width, and height of the HRSG unit and the water flow rate are significant features of the flow configuration inducted by the constructal design. Furthermore, the effect of changing in the size of the flow system on the flow archi-tecture is determined. [ABSTRACT FROM AUTHOR]

Abstract: Unalloyed high purity copper, deoxidized with phosphorus is widely used in tubing and fittings for sanitary installations due to its ease of use and corrosion resistance properties. Certain factors related to installation operating conditions on the one hand, and improper design/installation features on the other hand, often lead to unexpected failures. The case examines a Cu-tube that failed in a pump station after 2–3years in-service. The investigation findings suggest strongly that the failure was the result of a complex mechanism involving corrosion–erosion process, facilitated by stress–corrosion cracking mechanism. Stress–corrosion cracking referred as a delayed failure mechanism resulted from the synergistic effect of corrosive environment, susceptible material and externally applied or residual – due to the manufacturing process-stress. In case of hard-drawn tubes, the development of tensile (circumferential or hoop) stress field at the outer surface area after cold drawing, enhances the propensity for stress–corrosion cracking (SCC), especially under the presence of corrosive environment. [Copyright &y& Elsevier]