Corrosion resistance of Ni200 and Ni20

In the indoor atmosphere, Ni200 and Ni201 generally maintain a bright metallic luster. In the outdoor atmosphere, corrosion is slow due to a thin protective film on the surface. However, in the S02 industrial atmosphere, the corrosion rate increases with the increase of S02 content, and their corrosion rate is very slow in the ocean and rural atmosphere.
Atmosphere
In flowing seawater, Ni200 has excellent corrosion resistance even in high flow seawater, but in stationary or low-velocity seawater, severe pitting corrosion can occur under the dirt or sediment in the steam heat. In the water system, the initial corrosion rate of Ni200 is very high. As the time lengthens, because the water contains a certain proportion of CO: and air, Ni200 will produce a protective film and the corrosion rate will decrease.
Acid medium AH2S04
Ni200 has acceptable corrosion resistance in low temperature and medium temperature unvented H2S04. Some laboratory test data are shown in Table 3-15. As the temperature increases, the corrosion of Ni200 will intensify. It is mainly used to block air at room temperature. In the sulfuric acid solution, the oxidizing medium in the sulfuric acid will accelerate its corrosion.
BHCl acid
The corrosion behavior of Ni200 in hydrochloric acid is shown in Figure 3-9. At room temperature and at a mass fraction up to 30010 HCI acid, Ni200 is available. The corrosion resistance of Ni200 is due to the fact that Ni200, the corrosion product of nickel chloride, has a very low solubility in this mass fraction. This reason reminds the user of the high flow rate of HC1 acid. The selection must be careful. According to the corrosion condition of Ni200, in the air-fluid hydrochloric acid used above room temperature, the concentration of HC1 acid should be limited to 3 010 – 4070 or less. In the medium, if there is an oxidant, even a small amount will accelerate the corrosion of Ni200. In the HCI acid concentration is less than o. At 5%, used at 150 – 205°C, Ni200 exhibited satisfactory results.
HF acid
Ni200 has excellent corrosion resistance in high temperature anhydrous HF. However, its service temperature in aqueous solution is limited to 80 true c. Ni200 has been found to be heavily corrosive in 60% to 65,010 technical grade HF acid at room temperature.
Salt

In any chloride, Ni200 does not suffer from stress corrosion problems. It has excellent corrosion resistance in non-oxidizing halogen compounds, in oxidizing chloride salts such as Fe, Cu, Hg chloride, Ni200 Severely corroded. Neutral and alkaline salts, Ni200 has good corrosion resistance. In acid salts, the corrosion performance data has a large variation.
Fluorine and gas
In room temperature fluorine gas, Ni200 will produce a protective fluoride film, which can be used to treat low-temperature fluorine, and can achieve satisfactory results. In the high temperature Ni201 is more ideal.
In low temperature dry chlorine, Ni200 has an effective corrosion resistance. In wet chlorine and wet hydrogen chloride, the corrosion behavior of Ni200 is similar to that in hydrochloric acid. It has been found that in 0.25% wet HC1 dry chlorine and wet chlorine, the corrosion rate of Ni200 (o.008 mm/a) is not affected at 205°C.
Bromine is another halogen element, in the room temperature in the commercial bromine dried with sulfuric acid, Ni200 corrosion rate is o. OOlmm/a, in water-saturated bromine, its corrosion rate is o. 064mm/a, Ni200 is a good structural material for the treatment of low temperature bromine.
Ni201 has the same corrosion resistance as Ni200, some of the corrosion data can refer to the data of Ni200. The difference between Ni201 and Ni200 is that Ni201 has a very low carbon content, so there is no brittleness caused by carbon or graphite precipitation at high temperature. This is Ni201. Outstanding advantages.
Ni201 is widely used in the treatment of caustic soda media environments. Figure 3-10 shows the iso-etching of Ni201 in NaOH. In caustic soda only above 75% concentration, the corrosion rate begins to exceed o when the temperature is close to the boiling point. 025mn/a, reaching 0.13 mm/a. In caustic soda, the corrosion rate of Ni201 is very low, which can be attributed to the formation of an oxide protective film on the metal surface. The corrosion of Ni201 in different concentrations of NaOH is shown in Figure 3-11. At the boiling temperature, a thin layer of black oxide film is formed on the metal surface. Chlorides and oxidized sulfides in the base will accelerate the corrosion of Ni201. In high temperature sulfur-containing caustic media, Inconel 600 (OC, l5Ni75Fe) alloy should be used. Ni201 should not be used.
In fluorine gas, Ni201 has excellent corrosion resistance compared with other commercial metals and alloys. Below 450-C, the corrosion rate is below 0.58 m/a.
Among the high temperature chlorine and hydrogen chloride, Ni201 and Inconel 600 alloys are the most valuable structural materials. Typical corrosion data is shown in Table 3-22. The upper limit of the use temperature in kilo chlorine and dry hydrogen chloride is 540°C and 510°C, respectively.
In moisture-containing hydrogen chloride, Ni201 also has good corrosion resistance and the corrosion rate decreases with the test time. After the 20h test, the corrosion rate in wet HC1 is consistent with that in HC1.
In stationary HF, Ni201 has a corrosion resistance, and the presence of aeration or oxidant will accelerate the corrosion of Ni201. In the anhydrous hydrogen fluoride gas, the corrosion rate of Ni201 at 500-595° C. is 0.91 mm/a.