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6759824 
Journal Article 
Effect of nitric acid contamination on mild steel corrosion in hydrofluoric acid at 25 degrees C 
van Der Merwe, R; van Der Merwe, JW; Cornish, LA; , 
2020 
Yes 
Corrosion Engineering, Science and Technology
ISSN: 1478-422X
EISSN: 1743-2782 
TAYLOR & FRANCIS LTD 
ABINGDON 
349-359 
WOS:000518444900001 
HNO3 contamination increased the corrosion rates of mild steel storage tanks at an HF plant containing 70% HF acid from 0.5 to nearly 30 mm/year. The steel had been pre-treated by exposure to 70% HF for up to 24 h, to form a protective scale, which restricted the corrosion rate (CR) to <1 mm/year. This study simulated the corrosion effects on a laboratory scale, to determine the corrosion rates and mechanisms of 0.1% <= HNO3 <= 1% (mass per volume), after the nitric acid had been consumed. Mass loss, apparent corrosion rates, acid consumption, scale formation, pit corrosion and depth profiles were measured. The HNO3 selectively dissolved the protective oxide-fluoride scale, which then allowed HF access to the underlying metal and continuously corroded the exposed steel until failure occurred by perforation.