The main characteristic of duplex stainless steels is the balance between ferrite and austenite phases, wich ensures to such material the best levels of corrosion and mechanical resistance. However, during the welding process, structural modifications occur, especially with regard to the balance of these phases. This imbalance, depending on the levels of mechanical stress, may lead welded regions to collapse. In order to minimize the imbalance of the phases in the welded steel, several techniques are used, such as the insertion of filler metal with austenite formers, the use of shielding gas with nitrogen or, in other cases, the post weld control. It was tried to identify the true effect of welding parameters and heat treatment specified by the literature in field situations. Through an temporal evaluation, watching a production line of flexible pipes of UNS 32304 duplex stainless steel during three years, using conventional welding procedures with and without the use of heat treatment, failures were observed by a fracture in the heat affected zone (HZA). It was used a local inductor to the heat treatment, generating an intense heat flow that caused temperatures of about 1000 °C at very high rate of ascent and descent, as set for some literatures.
Welding; duplex stainless steel; flexible pipe
