Failure of an autotank repaired by welding

The aim of this work is to show that welded vessels, which have been coated by a polymer for overcoming the pneumatic test are susceptible to failure. This is so, because the cyclic load, which are applied in the vessel during its work. This aim was reached by applying different inspections and tests to a vessel manufactured with aluminium plates, which was used to freight. The vessel had to be repaired by welding, but it failed after few cycles of loading/unloading in the repaired weld. The specimen under study was inspected visually and by non-destructive tests. In this sense, the plate with fracture was tested by mechanical stress test, optical emission spectrometry, and metallographic analysis. The fracture surface was inspected by scanning electron microscopy. The results of all the techniques showed that the failure occurred due to coalesce of multiple cracks that grew by the mechanism of fatigue from welding defects. On the fracture surfaces was found evidence of sealing polymer used for the pneumatic pressure test. This work demonstrates that in welding repairing, the metallurgy and the welding engineering are critical to avoid premature failures of welded components.