Anomalous corrosion of Zr in boiling hydrochloric acid solutions

The pitting corrosion and hydrogen embrittlement of a Zr fractionating tower holding a HCl solution are discussed. The corrosion rate in boiling 20% HCl tended to increase with the addition of a trace of HF (1 ppm). The corrosion is attributable to the presence of F in this solution. Carbon was also used in this plant for heat exchanger tube, and local corrosion of Zr was accelerated by galvanic action when it was in contact with carbon chips. The thermally oxidized film of Zr acted as a protection against corrosion, but when it broke locally, the corrosion rate in the broken areas increased in the presence of HF.