Comparison of Zirconium 705 and Zirconium 702 in Sulfuric Acid

Zirconium is one of a very few materials of construction suitable for processes involving high concentrations of sulfuric acid at temperatures above the atmospheric boiling point.  In this severe environment only zirconium or tantalum can be used with any reliability.  Most corrosion data for zirconium has been developed using welded wrought material as test coupons. Most of this information is related to the corrosion resistance of Zr 702 with very little information available for Zr 705.   In addition, almost no information is available as to the corrosion resistance of the cast forms of either alloy. This paper presents laboratory data comparing the corrosion resistance of Zr 702 and Zr 705 in the welded and wrought forms and in the cast form.  A newly expanded iso-corrosion diagram is presented for both wrought and cast Zr 702 and Zr 705 in sulfuric acid. Zr 705 is a zirconium alloy containing 2.5% Niobium.  Because of the possibility of hydrogen absorption by the Niobium phase during the corrosion process, hydrogen absorption data is also presented for Zr 705.  This hydrogen absorption data is compared with similar data for Zr 702.