Use of iron-containing glass enamels for protecting petroleum-grade water lines

Iron oxides increase the water resistance of sodium borosilicate glasses, the base for most enamels, and thus iron-containing vitreous enamels are used for protecting water lines which transport and pump petroleum-accompanying media into oil pools to increase the pressure. However, the compositions of the oil-associated waters differ significantly from ordinary water. As a function of the glass composition, iron oxides can cause both an increase and a decrease in the acid resistance of the glasses. In addition, iron oxides dissolve in the melt during annealing when the slip or frit melts. Hence the iron oxide concentration can substantially increase, affecting the acid resistance of the enamel. The dissolution of iron oxides in sodium borosilicate glass was studied by continuously measuring the increase in the weight of the glass during holding of a steel plate under a layer of melt of this glass at 900 C. It was found that the rate of dissolution of iron oxides in the coating during annealing varies and, for this reason, both the initial amount of FexOy in glass and the increase in its concentration during annealing should be taken into account in using iron-containing vitreous enamels for protecting petroleum-grade water lines from corrosion. 6 refs.