Analysis of Tube-to-Tubesheet Welding in Carbon Steel Heat Exchangers of a Double Plate Header Box

The rear wall of the header box serves as a tubesheet in heat exchangers of double plate header box. Tube-to-tubesheet welding must be performed using orbital Gas Tungsten Arc Welding (GTAW) with a head extension, which is passed through the corresponding hole in the front wall (plugsheet) of the header box, where the welding machine is supported. In this project, the effect of parallelism deviations between the plugsheet and the tubesheet of carbon steel header box is analyzed to evaluate its influence on the quality of the tube-to-tubesheet welding. Welded tube (SA-210 Gr. A1) to tubesheet (SA-516 Gr. 70) coupons are manufactured simulating the parallelism deviations previously analyzed in two double plate header boxes of air-cooled heat exchangers using two different preheating temperatures. Macrographic analysis is performed in order to evaluate the weld penetration (minimum leak path) and length of the weld leg in tube-to-tubesheet joints. The results obtained show important variations in those parameters when the parallelism deviations are equal to or greater than −1 mm over the theoretical distance as well as when the distance approaches +1 mm or more. Finally, the incorporation of dimensional controls prior to the welding process is discussed and the implementation of improvements in orbital GTAW equipment is recommended as an optimal solution for this kind of heat exchangers.

Experimental study on the heat transfer performance of a stainless-steel heat pipe with sintered fiber wick

A kind of stainless-steel heat pipe with sintered fiber wick is investigated with the aim to improve the heat dissipation when it is used in spent fuel pool in nuclear power plant. The effects of test angle, porosity and the filling rate on the heat transfer performance of the heat pipe are studied. At test angle 90°, the permeability plays an important role on the power limit since gravity can provide the necessary driving force. Larger porosity involves with poor heat conductivity although it results in better permeability. When test angle is zero gravity is no longer the driving force. In this case, the evaporation section can still avoid dry burning because part of the evaporation section is dipped in the deionized water. Therefore, permeability and filling ratio are two important factors influencing the power limit. Filling rate determines the vapor flowing space. When test angle is smaller than zero, gravity becomes resistance force. Then the lag tension and the filling rate exert greatest influence on the performance of the heat pipe. Smaller porosity corresponds to smaller contact angle.

Evaluation of the Possibility of Using 1.4462 and 1.4501 Steel as a Construction Material for Apparatus Operating at an Increased Temperature and with Corrosive Factors

The objective of this study was to determine the requirements for steels used as construction materials for chemical apparatus operating at an elevated temperature and to correlate them with the properties of the tested steels. The experimental part examined the influence of the annealing process on the structure and properties of X2CrNiMoN22-5-3 (1.4462) and X2CrNiMoCuWN25-7-4 (1.4501) steel. Heat treatment was carried out on the tested samples at a temperature of 600 °C and 800 °C. Changes were observed after the indicated time intervals of 250 and 500 h. In order to determine the differences between the initial state and after individual annealing stages, metallographic specimens were performed, the structure was analyzed using an optical microscope and the micro-hardness was measured using the Vickers method. Potentiostatic tests of the samples were carried out to assess the influence of thermal process parameters on the electrochemical properties of the passive layer. An increase in the hardness of the samples was observed with increasing temperature and annealing time, the disappearance of magnetic properties for both samples after annealing at the temperature of 800 °C, as well as a significant deterioration in corrosion resistance in the case of treatment at a higher temperature.

Microstructural Changes During Short-Term Heat Treatment of Martensitic Stainless Steel—Simulation and Experimental Verification

Short-term heat treatments of steels are used for tools and cutlery but also for the surface treatment of a variety of other workpieces. If corrosion resistance is required, martensitic stainless steels like AISI 420L or AISI 420MoV are typically used. The influence of short-term heat treatment on the different metastable states of the AISI 420L steel was examined and reported in this article. Starting from a defined microstructural state, the influence of a short-term heat treatment is investigated experimentally with the help of a quenching dilatometer and computer assisted simulations are carried out. With the results obtained, a simulation model is built up which allows to compute the microstructural changes during a short-term heat treatment to be evaluated without the need for an experiment. As an indicator, the value of the martensite start temperature is calculated as a function of different holding times at austenitizing temperature. The martensite start temperature is measured by dilatometry and compared to calculated values. Validation of simulated results reveals the potential of optimizing steel heat treatment processes and provides a reliable approach to save time, resources and energy.

Effect of Differential Hardness on Static Load Capacity of AISI 52100 Bearing Steel

Static Load Capacity as defined by Palmgren is the load (stress) applied to a bearing that results in an indentation greater than 0.0001 times the diameter of the rolling element. The effect of hardness on the Static Load Capacity of AISI 52100 bearing steel heat treated to six different hardnesses was investigated. Indentation, depth, diameter, volume, and surface area were measured by the white light interferometer. A total of 468 hardness ball–plate combination tests were conducted. For a given plate (race) hardness, the Static Load Capacity was dependent on plate (race) hardness and independent of mating ball hardness from Rockwell C 56 to 66. For plate (race) hardness between Rockwell C 56 and 60, the Static Load Capacity was relatively constant. At Rockwell C hardness between 60 and 61, the Static Load Capacity increased and then rapidly decreased at a plate hardness of Rockwell C 66, below that value obtained at Rockwell C 56. Experimental results obtained for Static Load Capacity using the Palmgren criteria correlated with the finite element analysis for ball-on-plate indentation but not with Hertz theory. The Static Load Capacity based on Yhland for ball bearings was equal to a maximum Hertz stress of 3.71 GPa (538 ksi) at a ball-race conformity of 52%. This value is 12% lower than that specified in the ISO and ANSI/ABMA Bearing Standards. The manufacturers’ Static Load Rating can be reduced from 4% to 7% for ball bearings and from 8% to 25% for roller bearings.