Monel, corrosion resistance

It is extensively used for making stainless steel and other corrosion-resistant alloys such as Invar(R), Monel(R), Inconel(R), and the Hastelloys(R). Tubing made of copper-nickel alloy is extensively used in making desalination plants for converting sea water into fresh water. 

Stainless steel alloys show exceUent corrosion resistance to HCl gas up to a temperature of 400°C. However, these are normally not recommended for process equipment owing to stress corrosion cracking during periods of cooling and shut down. The corrosion rate of Monel is similar to that of mild steel. Pure (99.6%) nickel and high nickel alloys such as Inconel 600 can be used for operation at temperatures up to 525°C where the corrosion rate is reported to be about 0.08 cm/yr (see Nickel and nickel alloys). 

Chemical-Process Vessels. Explosion-bonded products are used in the manufacture of process equipment for the chemical, petrochemical, and petroleum industries where the corrosion resistance of an expensive metal is combined with the strength and economy of another metal. AppHcations include explosion cladding of titanium tubesheet to Monel, hot fabrication of an explosion clad to form an elbow for pipes in nuclear power plants, and explosion cladding titanium and steel for use in a vessel intended for terephthaHc acid manufacture. 

Copper—Nickels. The copper—nickel alloy system is essentially single phase across its entire range. Alloys made from this system are easily fabricated by casting, forming, and welding. They are noted for excellent tarnishing and corrosion resistance. Commercial copper alloys extend from 5 to 40 wt % nickel. Monel is a nickel—copper alloy that is outside of this range and contains 29—53 wt % of copper. 

The reaction mixture is filtered. The soHds containing K MnO are leached, filtered, and the filtrate composition adjusted for electrolysis. The soHds are gangue. The Cams Chemical Co. electrolyzes a solution containing 120—150 g/L KOH and 50—60 g/L K MnO. The cells are bipolar (68). The anode side is monel and the cathode mild steel. The cathode consists of small protmsions from the bipolar unit. The base of the cathode is coated with a corrosion-resistant plastic such that the ratio of active cathode area to anode area is about 1 to 140. Cells operate at 1.2—1.4 kA. Anode and cathode current densities are about 85—100 A/m and 13—15 kA/m, respectively. The small cathode areas and large anode areas are used to minimize the reduction of permanganate at the cathode (69). Potassium permanganate is continuously crystallized from cell Hquors. The caustic mother Hquors are evaporated and returned to the cell feed preparation system. 

Monel 1500 High corrosion resistance. Good against most acids and alkalies, but attacked by strong hydrochloric and strong oxidizing acids. 

Nickel additions reduce corrosion due to both caustic solutions and ammonia. Monel is resistant to attack in ammonia-containing waters and vapors. Reactions with ammonia are as follows ... 

Nickel and its alloys form another important class of non-ferrous metals (Table 1.3). The superb creep resistance of the nickel-based superalloys is a key factor in designing the modern gas-turbine aero-engine. But nickel alloys even appear in a model steam engine. The flat plates in the firebox must be stayed together to resist the internal steam pressure (see Fig. 1.3). Some model-builders make these stays from pieces of monel rod because it is much stronger than copper, takes threads much better and is very corrosion resistant. 

Monels Superalloys Ni -r 30 Cu 1 Fe 1 Mn Ni -r 30 Cr 30 Fe 0.5 Ti 0.5 Al Ni -r 10 Co 10 W 9 Cr 5 A1 2 Ti Strong, corrosion resistant heat-exchanger tubes. Creep and oxidation resistant furnace ports. Highly creep resistant turbine blades and discs. 

Monel, galvanized or other corrosion resistant metals... 

They must be readily accessible for cleaning, which should be carried out as frequently as necessary to ensure that pressure drop across the filter does not affect normal oil flow rates. The filtering medium should be of corrosion-resistant material such as Monel metal, phosphor-bronze or stainless steel. All first-stage filters should be provided with isolating valves. 

Nickel alloys which rely on nobility for their corrosion resistance, viz. Ni-Cu and Ni-Mo alloys in acidic solution, do not usually pit in these circumstances. It should be noted, however, that the Ni-Cu alloy Monel 400 normally forms a protective oxide film in neutral and alkaline solutions, and this is of particular significance with regard to its corrosion resistance to... 

The substitution of a more corrosion-resistant material, e.g. Monel metal or stainless steel, is often advocated but this is not necessarily a solution a 15% chromium steel, for instance, is prone to failure in corrosion fatigue because of the disruption of the normally protective surface film although as noted earlier some other materials are effective, e.g. Ti-6A1-4V alloys... 

Studies performed so far using Monel (nickel-copper alloys) have shown its low corrosion-resistance due to problems associated to selective leaching in the SCWO processes. Normally it is not to be considered in the materials selection. 

Metals that are almost completely corrosion resistant, as for instance stainless steel uf the 18/8 type, chromium plate products, monel, and gold. 

Monel is a type of alloy containing about 70% nickel, with the remainder mainly copper. Except for susceptibility to nitric acid, Monel is generally superior to stainless steel in corrosion resistance. Monel is similar to stainless steel in machinability and is welded like pure nickel. 

A large number of copper-base and nickel-base alloys (such as cupro-nickels, Monel, and aluminum brass) have been used in sea-water service with success. Special materials such as Hastelloy C, Illium, and titanium are available for extremely corrosive situations. The evidence, so far, indicates titanium to be outstanding and to rank above other commercially available metals in corrosion resistance under conditions involving high temperature, velocity, and other adverse environmental conditions. 

Alloy 400 is known as Monel and its age-hardenable version is K-500. The corrosion resistance of alloy 400 is better than pure nickel in nonoxidizing mineral acids. The alloy shows poor corrosion resistance in HNO3, FeCl3, CuCl2, moist Cl2, chromic acid, S02 and NH3 shows corrosion resistance to HF in the absence of air at all temperatures and is susceptible to SCC in moist aerated HF and H2SiF6. Alloy 400 is unaffected by alkaline salt solutions such as chlorides, carbonates, sulfates and acetates. 

Monel, an alloy of nickel containing 67 percent nickel and 30 percent copper, is often used in the food industries. This alloy is stronger than nickel and has better corrosion-resistance properties than either copper or nickel. Another important nickel alloy is Inconel (77 percent nickel and 15 percent chromium). The presence of chromium in this alloy increases its resistance to oxidizing conditions. 

---