The service environment of the slide gates may cause localized corrosion at welds. In this work, a failure analysis was conducted to determine the causes of the prematurecorrosion of the fillet welds before the commissioning. According to the contractor, the slide gates were manufactured in ASTM A240 Type 316L stainless steel and welded with GMAW using an ER316LSi filler metal. Test samples of the fillet weld metals were extracted from gates after a preliminary visual inspection. The samples were analyzed using ferrite number measurements, Optical Emission Spectrometry, chemical analysis, metallographic examination and Scanning Electron Microscopy with microanalysis. The analysis of results using the Schaeffler and WRC-92 constitution diagrams showed that the estimatedchemical composition of the filler metal differs with the filler metal specified in the WPS suggesting that an incorrect carbon steel filler metal was used during the construction of the gates