Corrosion prevention chlorine system

Third Preventative paint Oil corrosion Preventative paint Oil corrosion System primer Chlorinated rubber... 

Nature of the environment This is usually water, an aqueous solution or a two- (or more) component system in which water is one component. Inhibitors are, however, sometimes required for non-aqueous liquid systems. These include pure organic liquids (Al in chlorinated hydrocarbons) various oils and greases and liquid metals (Mg, Zr and Ti have been added to liquid Bi to prevent mild steel corrosion by the latter ). An unusual case of inhibition is the addition of NO to N2O4 to prevent the stress-corrosion cracking of Ti-6A1-4V fuel tanks when the N2O4 is pressurised... 

Chlorination to a residual of 0.5 p.p.m. is widely used. It is required to prevent fouling of the Monel or bronze intake screens, the ducts, pipes, etc., throughout the system. Experience has shown that chlorination, unless carefully controlled to low residuals, tends to increase the corrosivity of saline waters. 

The oxidizer, chlorine, may in larger concentrations lead to breakdown of the passive oxide on stainless steels and cause heavy corrosion. This has happened around swimming pools, where evaporation has led to enrichment of CI2 in water films. In smaller concentrations it is beneficial, preventing organic growth, and chlorination (addition of sodium hypochlorite) is used for this purpose in seawater pipe systems. 

For pipe systems of stainless steel carrying chlorinated seawater, internal localized corrosion can be very efficiently prevented by the application of Resistance-controlled Cathodic Protection (RCP). A resistance is simply inserted between the sacrificial anode and the pipeline, and this makes a system that is particularly suitable when there is a low diffusion-limiting cathodic current in the critical potential range [10.29]. Typical of the method is that the current output from the anode is kept low, which has the consequence that the voltage drops are low and the protected pipe length from each anode is long. 

Oxidizing agents (III. 19) are recommended, too, for slime prevention as far as the oxidizing properties of these agents can be tolerated. Using chlorine, hypochlorites or chlorine dioxide problems may arise by the enrichment of corrosion causing chloride ions in the system. 

Traces of chlorine that remain at the svuface of the silicon wafers after the etching process, when exposed to ambient air, are the major source of corrosion. This typically leads to bubble-type outgrowths on aluminum conductors (Figure 10.132). With an increased copper content in aluminum, this problem is aggravated because this system then acts like a galvanic cell, which is characterized by HCl-catalyzed chemical reactions. Two different strategies are feasible to prevent these corrosion phenomena the silicon wafers are not to be exposed to... 

In offshore applications, in particular, duplex steels, superduplex steels (PRE>40) and superaustenite with >6% Mo are widely used because of their good resistance against localized corrosive attack, as shown in Table 1-16. The maximum temperature with residual chlorine (chlorinating to prevent fouling) in the range of 1 - 2 ppm is limited to 30 °C. Above this temperature only materials with a higher molybdenum content, e.g. 654 SMO, titanium or Cu-Ni alloys, are possible materials for seawaterhandling system (Johnsen, 1987). 

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