LOCALIZED CORROSION IN FLOATS OF THE TANK MEMBRANE SYSTEM USED FOR AVIATION GASOLINE STORAGE

Abstract

Introduction:
A tank used for the storage of aviation gasoline, equipped with a geodesic dome with a floating internal membrane system, reported serious corrosion damage to its floats, which caused them to be replaced in a short period of time.
Objective:
To analyze aluminum floats deterioration causes.
Materials and Methods:
During a visual inspection, corrosion products were collected and analyzed by IR spectrometry. Residual water samples were taken from the tank bottom for physicochemical analysis. Float component materials structural study was carried out,
using a digital multichannel spectrometer and a metallographic microscope.
Results and Discussion:
Float failures occurred in cylindrical body in contact with the fuel, such as localized corrosion. The corroded material corresponded to the aluminum manganese alloy 3004, which was characterized by an important content of iron in its chemical composition and a microstructure with high density of intermetallic particles, in some micro locations forming clusters. Cavities were observed around some particles, and evidence of dissolution of the alloy matrix in a medium in which chloride ions were present.
Conclusions:
The results obtained indicated that in a medium with the presence of chloride ions, the formation of galvanic microcells between cathodic intermetallic particles of important dimensions and the alloy matrix was caused, which led to the formation of deep pits.