Sulfuric acid stainless steels corroded

RG. 4—Comparison of Intergranular corrosion in various acid solutions. Measurement of weight-loss and change in electrical resistance on sensitized stainless steel corroding in boiling 65 % nitric acid, and boiling sulfuric acid solutions containing cupric or ferric sulfate. Specimen 0.15 by 0.60 cm In cross section. 

Although hydrogen cyanide is a weak acid and is normally not corrosive, it has a corrosive effect under two special conditions (/) water solutions of hydrogen cyanide cause transcrystalline stress cracking of carbon steels under stress even at room temperature and in dilute solution and (2) water solutions of hydrogen cyanide containing sulfuric acid as a stabilizer severely corrode steel (qv) above 40°C and stainless steels above 80°C. 

For applications requiring corrosion-resistant alloys, either low-carbon or stabilized stainless steels such as Type 321 SS are normally selected. Sensitization-induced polythionic acid corrosion is a concern in such applications. High-nickel alloys and copper-based alloys often corrode rapidly in the presence of high-temperature sulfur compounds. 

BENZENE PHOSPHORUS DICHLORIDE (644-97-3) Reacts with water, steam, forming hydrochloric. Contact with acids or acid fumes produces highly toxic chloride fumes. Aqueous solution incompatible with sulfuric acid, alkalis, ammonia, aliphatic amines, alka-nolamines, alkylene oxides, amides, epichlorohydrin, organic anhydrides, isocyanates, vinyl acetate. Corrodes most metals in the presence of moisture except 316 stainless steel, nickel, and Hastelloy . 

The acid pulping process uses sodium bisulfite or magnesium bisulfite in a pulp digester at a pH of 3. Type 316 stainless steel is normally used as a minimum alloy because the sulfur dioxide can be converted into sulfuric acid. Sulfuric acid can corrode the stainless steel depending on the pH, temperatiire, and pressure of the system. SCC has been observed in the HAZ of weldments in the pulp digesters in the presence of sodium hydroxide. Because of SCC susceptibility of the austenitic stainless steels, duplex stainless steel 2205 is often used in pressure vessels and tanks. 

Storage tanks for oleums of various strengths should be provided with vent scrubbers having continuous irrigation by sulfuric acid. The scrubbers should be fabricated from stainless steel 316 instead of mild steel or cast iron (fhese can become corroded since both acid and oleum can be present). 

The chloride pitting resistance of this alloy is similar to that of type 316 stainless steel and superior to that of types 430 and 439L. Like all ferritic stainless steels, t)/pe 444 relies on a passive film to resist corrosion, but exhibits rather high corrosion rates when activated. This characteristic explains the abrupt transition in corrosion rates that occur at particular acid concentrations. For example, it is resistant to very dilute solutions of sulfuric acid at boiling temperature, but corrodes rapidly at higher concentrations. 

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