Efeitos da incrustação de macroorganismos na corrosão de painéis de aço carbono

Abstract

Seawater is a complex corrosive system, where the biofouling is one of the aspects that influence the corrosion process. The first detailed description about the influence of fouling community at a macrolevel in corrosive process was done in the 50 th , and until now, some studies were done, although they don’t concern about the accuracy of ecological results. The present study aimed to verify the change in corrosion tendency, corrosion intensity and the percent of localised attacks in carbon steel panels associated with the macrofouling and barnacles, in comparison to the results obtained in the control panels, along 6 months. In this way, an experimental design were created exclusively to this study, that was developed near the Cabo Frio Island. Forty eight (48) carbon steel API 5L X-65 panels (150x200x20mm), were distributed in eight aluminium structures. In each structure were placed 6 panels with electric contact, and the structures were suspended in four rafts. Different treatment were provided for the panels. Three of them were included in this study: the control treatment, in which the panels were covered with nylon screens; the community treatment, in which the fouling community were analysed and the barnacle treatment, were other organisms were excluded with brushes and pincers. Weekly, the cover of the organisms in the community and barnacle treatment was estimated using a 10x10 cm quadrat with 30 intersection point, and the corrosion potential was monitored with a multimeter and a electrode Ag/AgCl. After twenty four weeks the structures were taken and brought to laboratory to calculate the uniform corrosion rate and to do visual observation of the localised attacks in each treatment. Variance analysis were applied in all data obtained. During the study were registered 28 taxa, 17 of macroalgae and 11 of macrofauna, classified in 7 functional groups. In the community treatment the dominant were filamentous macroalgae (23,73%), barnacles (17,51%), hydrozoans (16,96%) and incrusting bryozoans (9,58%). In the barnacle treatment, the cover ranged between 39,38% and 62,50%. The corrosion potential ranged to –665,75 mV(Ag/AgCl) to –517, 50 mV (Ag/ AgCl), thus any changes in the potential could be related to the fouling community development. The highest corrosion rate were found in the control treatment and this can suggest that biofouling provide a protection against mass loss. The highest percent of localised attack were found in the community treatment. This may indicate that other organisms induces localised corrosion, and not only barnacles, how is reported in the literature. The methodology utilised in this study and the observation period were appropriated and answered the questions proposed at first.