Análise do fundo do tanque de diesel S500 de uma base de distribuição de combustíveis

Abstract

Fuel storage tanks are commonly made from carbon steel (ASTM A-283 Gr. C). These tanks can be vertical, with either a floating or fixed roof. The bottom of the tank is designed in a conical shape and is made up of welded plates, which can be annular or cut. The welding used on the tank bottom is performed using the shielded metal arc welding process. To ensure greater ductility, it is recommended that the welding of the tank bottom be performed in at least two passes. Among the fuels stored, Diesel S500 is widely used as an energy source for vehicles and machinery, making it essential for the functioning of the industry and transportation. However, the quality of the tank bottom can be compromised due to factors such as sediment accumulation, water, and fuels. This work aimed to conduct a failure analysis of the Diesel S500 tank bottom, which was condemned after failing company tests due to leakage. The following methods were applied: visual inspection with a stereoscope, metallography, and optical microscopy to analyze the weld area and the base metal. Technical reports and assessments provided by the company were also considered for the discussion. The results obtained concluded that the failure of the tank bottom, which led to the fuel leakage, was due to severe pitting corrosion exacerbated by water, induced by microorganisms, and the incorrect assembly pattern of the plates concentrating stress in the weld area.