Nickel sulfuric acid corrosion

Materials of Construction. Resistance of alloys to concentrated sulfuric acid corrosion iacreases with increasing chromium, molybdenum, copper, and siUcon content. The corrosiveness of sulfuric acid solutions is highly dependent on concentration, temperature, acid velocity, and acid impurities. An excellent summary is available (114). Good general discussions of materials of constmction used ia modem sulfuric acid plants may be found ia References 115 and 116. More detailed discussions are also available (117—121). For nickel-containing alloys Reference 122 is appropriate. An excellent compilation of the relatively scarce Hterature data on corrosion of alloys ia Hquid sulfur trioxide and oleum may be found ia Reference 122. 

F.G. Hodge and B.E. Wilde, Effect of Chloride Ion on the Anodic Dissolution Kinetics of Chromium-Nickel Binary Alloys in Dilute Sulfuric Acid, Corrosion, Vol 26, 1970, p 146-150... 

Corrosion resistance of nickel allovs is superior to that of cast irons but less than that of pure nickel. There is uttle attack from neutral or alkaline solutions. Oxidizing acids such as nitric are highly detrimental. Cold, concentrated sulfuric acid can be handled. 

These alloys have extensive applications in sulfuric acid systems. Because of their increased nickefand molybdenum contents they are more tolerant of chloride-ion contamination than standard stainless steels. The nickel content decreases the risk of stress-corrosion cracking molybdenum improves resistance to crevice corrosion and pitting. 

This alloy has a nominal composition of 65% nickel, 28% molybdenum and 6% iron. It is generally used in reducing conditions. It is intended to work in very severely corrosive situations after post-weld heat treatment to prevent intergranular corrosion. These alloys have outstanding resistance to all concentrations of hydrochloric acid up to boiling-point temperatures and in boiling sulfuric acid solutions up to 60% concentration. 

The composition of this alloy (54% nickel, 15% molybdenum, 15% chromium, 5% tungsten and 5% iron) is less susceptible to intergranular corrosion at welds. The presence of chromium in this alloy gives it better resistance to oxidizing conditions than the nickel/molybdenum alloy, particularly for durability in wet chlorine and concentrated hypochlorite solutions, and has many applications in chlorination processes. In cases in which hydrochloric and sulfuric acid solutions contain oxidizing agents such as ferric and cupric ions, it is better to use the nickel/molybdenum/ chromium alloy than the nickel/molybdenum alloy. 

Nickel/silicon alloy (10% silicon, 3% copper, and 87% nickel) is fabricated only as castings and is rather brittle, although it is superior to the iron/silicon alloy with respect to strength and resistance to thermal and mechanical shock. It is comparable to the iron/silicon alloy in corrosion resistance to boiling sulfuric acid solutions at concentrations above 60%. Therefore, it is chosen for this and other arduous duties where its resistance to thermal shock justifies its much higher price compared with iron/silicon alloys. 

Replacing some of the nickel with iron produces a family of alltws with intermediate corrosion resistance between stainless steels and the Ni-Cr-Mo alloys. Alloys such as Incoloy 825 and Hastelloy G-3 and G-30 are in this family. Incoloy 825 has 40 percent Ni, 21 percent Cr, 3 percent Mo, and 2.25 percent Cu. Hastelloy G-3 contains 44 percent Ni, 22 percent Cr, 6.5 percent Mo, and 0.05 percent C maximum. These alloys have extensive applications in sulfuric acid systems. Because of their increased nickel and molybdenum contents they are more tolerant of chloride-ion contamination than are standard stainless steels. The nickel content decreases the risk of stress-corrosion cracking molybdenum improves resistance to crevice corrosion and pitting. Many of the nickel-based alloys are proprietary and are coverecf by the following specifications ... 

Nickel was first isolated in 1751, and a relatively pure metal was prepared in 1804. In nature, nickel is found primarily as oxide and sulfide ores (USPHS 1977). It has high electrical and thermal conductivities and is resistant to corrosion at environmental temperatures between -20°C and +30°C (Chau and Kulikovsky-Cordeiro 1995). Nickel, also known as carbonyl nickel powder or C.I. No. 77775, has a CAS number of 7440-02-0. Metallic nickel is a hard, lustrous, silvery white metal with a specific gravity of 8.9, a melting point of about 1455°C, and a boiling point at about 2732°C. It is insoluble in water and ammonium hydroxide, soluble in dilute nitric acid or aqua regia, and slightly soluble in hydrochloric and sulfuric acid. Nickel has an atomic weight of 58.71. Nickel is... 

Nickel is added to improve resistance to environmental and stress cracking corrosion. Molybdenum provides even greater resistance to corrosion and improves mechanical strength. Copper increases resistance to sulfuric acid attack. 

INCO Corrosion Engineering Bulletin CEB-1. Resistance of Nickel and High Nickel alloys to Corrosion by Sulfuric Acid." New York, NY International Nickel Company, 1983. 

P3-4 Corrosion of high-nickel stainless steel plates was found to occur in a distillation column used at DuPont to separate HCN and water. Sulfuric acid is always added at the top of the column to prevent polymerization of HCN. Water collects at the bottom cf the column and HCN at the top. The amount of corrosion on each tray is shown in Figure P3-4 as a function of plate location in the column. 

For many of the metallic constituents, the product form in the SCWO liquid effluent is dependent to some degree on pH. As the liquid effluent is near ambient temperature, general chemistry rules may be applied. Acidic conditions can lead to higher dissolved levels of certain metals. A common example is provided by nickel, which forms nickel oxide in the SCWO reactor due to feed oxidation or corrosion. When excess hydrochloric or sulfuric acid is present in the SCWO effluent, some of the nickel oxide dissolves to yield dissolved nickel. Many of the entries in Table 14 have not been reported in the literature, but are based on unpublished observations by MODAR and General Atomics. 

Although substitution was motivated by the availability at that time of propylene and lower cost of the process, it was also a significant improvement in terms of safety, because acetylene is flammable and extremely reactive, carbon monoxide is also toxic and flammable, nickel carbonyl catalysts are toxic, environmentally hazardous (heavy metals), and carcinogenic, and anhydrous HCl (used in the reaction) is toxic and corrosive. However, the new process from propylene carmot be considered inherently safer. Hazards are primarily due to the flammability of reactants, corrosivity of the sulfuric acid catalyst for the esterification step (new solid acids have eliminated this hazard, as discussed in subsequent chapters), small amounts of acrolein as a transient intermediate in the oxidation step, and reactivity hazard for the monomer product. 

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. 

On the other hand, it is possible to observe two current peaks in the anodic region in the current-potential curves of pure nickel in H2SO4 [167]. Most of the amino acids also gave the two peaks in the sulfuric acid solutions, but for some amino acids, the first peak or even both of the peaks are not visible due to corrosion inhibition. In the case of leucine, glutamic acid, and lysine, good inhibition results are obtained and for the lysine the highest efficiency of all the compounds can be obtained. When the pH increases the inhibition effect is decreased, however, the results showed that the amino acids are effective in acidic media. When the pH value increases, the passivation peaks become smaller and the corrosion rates increase. 

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