Static corrosion of construction materials exposed to superphosphoric acid made from various sources of phosphate rock

摘要

Corrosion tests were performed with various construction materials, such as carbon steel, cast iron, stainless steels, nickel and nickel-based alloys, copper and its alloys, aluminum alloy, zirconium alloy, and tantalum, exposed to wet-process superphosphoric acids approximately 70% P(sub 2)O(sub 5) from all the suppliers in the United States and to a technical-grade (55% P(sub 2)O(sub 5)) acid made by the electric furnace process. The study was conducted in response to reports from pipe-reactor users of excessive corrosion by superphosphoric acids and electric furnace acid. Test temperatures were ambient approximately (21 C or 70 F), 66 C (150 F), and 93 C (200 F). Test results showed that temperature was a significant factor in acid corrosivity. Electric furnace acid was more corrosive than the superphosphoric acids. Carbon steel, cast iron, and aluminum alloy were not resistant to either the superphosphoric acids or the electric furnace acid. Nickel-chromium (Ni-Cr) and nickel-molybdenum (Ni-Mo) based alloys and tantalum exhibited adequate corrosion resistance in the superphosphoric acids and the electric furnace acid. Stainless steels performed well in all test acids at all test temperatures with some exceptions in the electric furnace acid at 93 C. Zirconium alloy, copper and its alloys, pure nickel, and Monel 400 provided adequate corrosion resistance to all test acids at ambient temperature only.