Hydrofluoric acid, environment-alloy

The higher nickel content of alloy 825 compared to alloy 800 makes it resistant to chloride SCC. Addition of molybdenum and copper gives resistance to pitting and to corrosion in reducing acid environments, such as sulfuric and phosphoric acid solutions. Alloy 825 is resistant to pure sulfuric acid solutions up to 40% by weight at boiling temperatures and at all concentrations at a maximum temperature of 150°F (60°C). In dilute solutions, the presence of oxidizing salts such as cupric or ferric actually reduces the corrosion rates. It has limited use in hydrochloric or hydrofluoric acids. 

Aluminum - non-staining atmospheric exposure Chromium-containing alloys - oxidizing solutions Copper and alloys - reducing and non-oxidizing environments Hastelloys (chlorimets) - hot hydrochloric acid Lead - dilute sulfuric acid Monel - hydrofluoric acid... 

Klarstrom, 1993). Besides HCl solutions, B-2 and B-3 alloys are also used in the handling of other corrosive reducing environments such as sulfuric, acetic, formic, hydrofluoric, and phosphoric acids. The major shortcoming of B-type alloys is their poor resistance to oxidizing environments. 

When 4.5% chromium is added to the alloy, it becomes resistant to severe chloride-containing solutions and other strongly oxidizing environments. The chromium-bearing grade (Durichlor) will handle hydrochloric acid up to 80°F (27°C). Hydrofluoric add causes rapid attack. Table 4.5 lists the compatibility of high-silicon iron with selected corrodents. 

ILLIUM 98 and ILLIUM B perform very well in processes which involve the use of sulfuric, phosphoric, hydrofluoric, nitric, acetic and fluosilicic acids as well as sodium chloride brine, They resist erosion to abrasion in corroding environment. These alloys have high mechanical rigidity. The 98 alloy is nonhardenable while the B alloy is hard-enable. 

---