Abstract
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.
Highlights
Heat exchangers are a key component in several industries
One of the greatest challenges with heat exchangers is to achieve a high reliability during service because they are exposed to important variations in operational parameters and severe conditions related to the fluids they are in contact with
The most common type of heat exchanger used in the oil and petrochemical industries is the shell and tube heat exchanger (Figure 1) [24], a challenging task in the field of mechanized welding is to perform tube-to-tubesheet welds in the closed header box of an air-cooled heat exchanger [1], which is what this work focuses on
Summary
Heat exchangers are a key component in several industries. They can be found in petrochemical plants; chemical and pharmaceutical industries; steam power plants; nuclear reactors; and water power plants amongst other industries [1]. Otegui et al [5] analyzed and discussed the causes of multiple cracks found in a heat exchanger tubesheet at a petrochemical plant, which had been repaired several times The analysis they performed showed embrittlement of the heat affected zone (HAZ) of the welds, and a lack of penetration and fusion at the weld roots. The most common type of heat exchanger used in the oil and petrochemical industries is the shell and tube heat exchanger (Figure 1) [24], a challenging task in the field of mechanized welding is to perform tube-to-tubesheet welds in the closed header box of an air-cooled heat exchanger [1], which is what this work focuses on. The maximum parallelism deviation of double plate header boxes for the petrochemical industry is quantified and its influence on the quality of the welded tube-to-tubesheet joints is evaluated; practical solutions are proposed. All the welded joints of the mockups where made according to a standard procedure for the petrochemical industry [6], using two preheating temperatures for each case
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