Simulação numérica e experimentação da soldagem em operação de aços inoxidáveis austeníticos nos regimes de escoamento laminar e turbulento

Abstract

Welding in service is defined as the technique in which equipment, pipes and ducts are welded that contain any product or its waste pressurized or not, with or without flow, without the need for operational stops. Pipe welding in service is a technique used in several areas of industry. In this type of welding, the operator’s safety and the environmental and human damages resulting from the perforation of the wall are the main concerns of this type of operation. The concern about drilling during the welding process is due to the high density of energy deposited locally, which can cause melting of a large part of the thickness which combined with the internal pressure of the fluid, can generate perforation in the pipe. Another concern is the high cooling rate of the weld caused by the forced convection of the flow through the pipe. The high cooling rate, in materials susceptible to martensite formation, can promote the formation of a microstructure with high hardness in the Heat Affected Zone (ZAC), enhancing the formation of zones prone to crack formation. The objective of this work is to develop a numerical model with experimental validation for GTAW, SMAW and GMAW welding in AISI 304L and AISI 321 austenitic stainless tube. The numerical model was developed using finite volumes in a commercial simulation program. To validate the model, two welding benches were used in operation and the welding conditions were close to those adopted by the industry. The two benches were instrumented in order to collect the temperatures on the inner surfaces of the tube, fluid flow, current and welding voltage. In the welding in service of AISI 304L tubes, the internal flow was maintained in a laminar regime and the welding energy was equal to 0.63kJ/mm. In AISI 321 tubes, the flow was varied between the laminar and turbulent regimes and the welding energy was changed according to conditions used in the industry. Based on the information obtained from the benches and on microscopic analysis, simulations were developed involving the laminar and turbulent regimes using the finite volume method to predict the welding thermal cycle and the thermally affected zones. Welding energy was modeled as a moving Gaussian surface on an ellipse. The results obtained from the simulations showed good agreement with those obtained on the benches, demonstrating that the simulations can be used as reliable tools for predicting the welding in service process for flows in both laminar and turbulent flow.