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FIGURE 2: ISO-CORROSION DIAGRAM FOR Zr 702 IN SULFURIC
ACID
Figure 2 also
shows that Zirconium resists attack up to 70%. At low concentrations,
< 20%, Zirconium resists attack to temperatures well above
boiling >200 C. The prime advantage of Zirconium over other
metals is in the low concentration / high temperature region
and the 40 to 65% concentration. Weld areas exhibit higher
corrosion rates as shown by the Weld Limit Line. Heat treatment
of the weld will eliminate the weld affect and corrosion of
the weld area will be the same as the unwelded surface. Heat
treatment should be at 775 15° C for one hour per inch (25.4
mm) of thickness. Zirconium is produced as two major alloys
for chemical processing applications; grade 702 is "pure"
zirconium, while grade 705 is zirconium alloyed with 2.0 Ð
3.0% niobium. Figure 3 compares the iso-corrosion curves of
the two different grades. While Zr 702 has better corrosion
resistance than Zr 705, Zr 705 has better strength properties
due to the addition of niobium.
FIGURE 3: COMPARISON OF Zr 702 AND Zr 705 ISO-CORROSION
CURVES
(5 MPY)
Three of Six 1
2 3 4
5 6
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