Iron continued corrosion mechanism

In plain tinplate cans for acid foods, tin provides cathodic protection to steel (3,4). The slow dissolution of tin prevents steel corrosion. Many investigators (5-1I) have defined this mechanism in detail and have shown that the tin dissolution rate is a function of the cathodic activity of the base steel, the steel area exposed through the tin and the tin-iron alloy layers, and the stannous ion concentration. Kamm et al. showed that control of the growth of the tin—iron alloy layer provides a nearly continuous tin-iron alloy layer and improves the corrosion resistance of heavily coated (over 45 X 10"6 in. tin) ETP for mildly acid food products in which tin provides cathodic protection to steel (12). The controlled tin-iron alloy layer reduces the area of steel exposed to the product. ETP with the controlled alloy is designated type K, and since 1964, 75 type K ETP has been used to provide the same protection as 100 ETP provided previously (13). 

Even if the mechanisms or the extent of passivation of iron by mineral reactions are still unknown in detail the inorganic reactions most probably effect the degradation behaviour of CHC. A simplified model is capable of simulating the effects of these reactions on CHC reduction at different flow velocities on the assumption that mineral precipitation as well as continuous anaerobic corrosion decrease the reactive iron surface. PHREEQC (Parkhurst and Apello, 1999) can be used for qualitative simulation after modification of the data set integrating ethene and chlorinated ethene species as well as some iron minerals. Figure 13.6 shows the results of two simulations at five times different pore velocities and the model assumptions in Table 13.1. 

Cast iron is the standard material used to construct the cylindrical housing, but other materials may be used if corrosive conditions exist. The rotor is usually a continuous piece of steel that Includes the shaft and is made from bar stock. Special materials can be selected for corrosive applications. Occasionally, the rotor may be a separate iron casting keyed to a shaft. On most standard air compressors, the rotor-shaft seals are semimetallic packing in a stuffing box. Commercial mechanical rotary seals can be supplied... 

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