Hydrostatic tests with water are used to evaluate leaks in welds and possible cracks and failures that may have occurred during construction in petroleum storage tanks and derivatives. Defects and cracks in the concrete foundations that support the tank on the ground are also observed in these tests. The use of seawater as a fluid for hydrostatic testing of petroleum storage tanks and derivatives can be a good option in areas lacking fresh water, especially when these tanks are near the sea. The use of seawater is economically attractive; on the other hand, corrosion by seawater is much more aggressive toward carbon steel than corrosion by treated fresh water. The potential advantages of the use of a mixture of silicates and zinc sulphate as a corrosion inhibitor are the effective protection of carbon steel, especially in saline fluids, low cost, and non-aggressive behaviour toward the environment. Gravimetric and electrochemical laboratory tests were carried out using synthetic seawater with the addition of a mixture of sodium silicate (Na2SiO3) and zinc sulphate (ZnSO4.7H2O). Gravimetric testing with an immersion time of 40 days using 1000 and 2000 mg/L of Na2SiO3 and 150 mg/L of ZnSO4.7H2O gave a good performance and can be used for hydrostatic testing with seawater.