Análise de falha em uma série de ligações soldadas de um trecho de tubulação de utilidades para condução de vapor superaquecido

Abstract

Process pipes for conducting superheated steam in sugar and energy power plants demand high mechanical strength at high temperatures. The joints between the pipe rod and the connection of this system are mostly satisfied by the welding process, particularized for being single v-groove. Although the performance of the welded connection guarantees mechanical resistance equivalent to the entire tube, a joint is defined as a stress concentrator. Therefore, due to the thermal loads request by the continuous transient regime required by the manufacturing process, the circumferential region that includes weld, Heat Affected Zone (HAZ) and edge metal base is a critical candidate volume to determine the allowable loading and service life of the system. Therefore, this project performs a pragmatic failure analysis in a series of welded connections in a stretch of superheated steam pipe, which suffered longitudinal cracks along the joints. The objective is to identify the mechanisms causing the failures. The results obtained indicated that the thermal expansion of the pipe provided by the operation above the limits adopted in the project can generate stress fields at the material's rupture limit. It was also possible to conclude that the presence of heterogeneities in the weld metal or in the coarse-grained HAZ arising from the manufacturing process can cause nuclear cracks from the deformations generated by thermal loading. Despite the inconclusiveness regarding the mechanism causing the failure, it is possible to say that the results of the study are significant. Furthermore, guidelines were established to perform a second iteration of the failure analysis process aiming at more effective results in future works.