In case of liquid storage tank has been designed regardless of international standards and there is
little interest with its operating conditions, it may lead to fully or partially failure. This paper has
studied a failure of Toluene storage tanks with different capacities. Toluene is a liquid aromatic
hydrocarbon C7H8 which is toxic, flammable and may cause boiled liquid expanded vapor
explosions (BLEVE). Failure analysis was performed to determine the root causes of toluene
storage tank failure as well as corrosion influence. Axisymmetric finite Element analysis
(FEA) was performed for fillet welding of tank roof and top shell zone to develop a relation
between weld electrode size and tank diameter at each type of weld electrode to determine the
main framework of roof to top shell welding process. Also, to develop a relation between tank
diameter and maximum stresses that resulted at every amount of vapor pressure according to
maximum von-Mises stress theory. The optimum roof to top shell welding size is obtained through
the circumference welding path. The results of analysis allowed us to redesign the tank according
to API 650 and to express the recommendations for toluene storage tanks operation.