Corrosion of Alloy Steels In Hot Concentrated Metal Salt Solutions

The packer and completion fluids used in oil well operation are concentrated metal salt solutions of high density. During the earliest days of oil drilling, sea water and sodium chloride brines were used, but only in low pressure wells because of the low densities of such fluids. Nitrate solutions of high density and low cost were tried but were found to be active promoters of stress-corrosion cracking of well tubing. With low corrosion rate mandatory in packer and completion fluids, high-density solutions of metal chlorides, chromates and phosphates have been tested for corrosivity to various types of steel employed in oil well tubing and casing. Tests reported in this article were conducted in the temperature range 80-150 C. Concentrated sodium chloride, calcium chloride and sodium phosphate solutions were found mildly corrosive to steel. Calcium chloride-zinc chloride solutions were more corrosive, but corrosion rate was reduced by inhibitors containing arsenic. Dipotassium hydrogen phosphate solutions were severely corrosive at 150 C. Sodium chloride-disodium hydrogen phosphate solutions and sodium dichromate solutions were not corrosive. 8.4.3