Optimization of the SMAW Welding Process in Carbon Steel Pipes for District Heating Systems

The use of pre-insulated carbon steel pipes in district heating systems (DHS) has been widely adopted due to their high mechanical strength, ability to transport hot water or steam over long distances with minimal thermal losses, and durability under various environmental conditions. One of the most commonly used methods for joining these pipes is Shielded Metal Arc Welding (SMAW), as it can be performed on-site, allowing installation over extensive terrains and under variable conditions. Given that the pipelines in these systems can extend over several kilometers, it is essential to optimize the thermal performance of the welding process to minimize electrical consumption during DHS installation, thereby reducing energy costs without compromising the quality of the joints. In this regard, Finite Element Method (FEM) numerical simulations can serve as an effective tool to predict two key aspects: (1) the thermal performance of the weld, aiming to maximize the efficiency of the fusion process while minimizing energy consumption, and (2) the mechanical strength and durability of the welded joints by modeling real service pressure and temperature conditions, enabling the evaluation of behavior under cyclic loads and assessing fatigue resistance. In this study, FEM was used to analyze the thermo-mechanical behavior of SMAW-welded joints in carbon steel pipes intended for installation in DHS systems. The objective was to identify the optimal configuration of SMAW welding parameters, focusing on current intensity in a range of 70 to 80 amperes. The aim was to maximize thermal performance during the fabrication of the welds while reducing energy consumption during the assembly of DHS pipelines. Moreover, the study ensured the structural integrity and durability of the welds, in compliance with the real service pressure and temperature conditions established by EN 13941-1:2019. The research focused on 1.0503 carbon steel pipe, each 100 mm in length, with an outer diameter of 48.3 mm and a wall thickness of 2.6 mm. Welding was carried out using rutile E6013 electrodes with a diameter of 3.2 mm. Both the groove angle and the welding speed were kept constant at 0° and 5 mm/s, respectively. The results obtained demonstrated a maximum thermal efficiency of 76% when applying a current intensity of 73 amperes. For this same value, the fatigue analysis confirmed that the welded joint was capable of withstanding more than 250 load cycles, exceeding the minimum fatigue life requirements established by the UNE-EN 13941-1:2019 standard.