Oxygen corrosion agent

For the most common series of corrosive agents, water, steam, acids, alkalis and salts, the hydrolytic processes peculiar to each determine the mechanism of attack. Thus, under the right circumstances, hydrolytic attack on the bridging oxygens can occur in the following way ... 

Azole compounds such as benzotriazole, benzimidazole, indazole and imidazoles are efficient anti-corrosion agents for copper and copper-base alloys [1-10]. Many experimental techniques [11-15] have been used to study the corrosion inhibition mechanisms, however, the mechanisms are still not well understood. It is believed that the complex formation between copper and nitrogen atoms would inhibit oxygen adsorption on copper surface [16-20]. 

Taking into consideration the relative order of corrodibility, it is preferable to describe corrosive damage as attributable to certain agents rather than to the indefinite characterization smoke. Corrosive agents can be placed into four major groups, namely, oxygen and oxidants, acidic materials, salts, and alkalis. 

Dead spots and crevices - where equipment parts are not continuously wetted by oxygen-containing liquids - are prone to severe corrosion. Therefore, fabrication of this equipment should be done to avoid such vulnerable spots. An effort should also be made to reduce the potential for process contamination by corrosive agents such as sulfur (through oil in liquid NH3), H2S (along with C02) and chlorides (from cooling water)88. 

In general corrosion is accelerated by an increase in temperature with the exception when dissolved oxygen is the corrosive agent. Careful control of temperature in corrosion testing is mandatory. Sometimes high temperatures are used in accelerated corrosion tests. 

In general, titanium tends to be quite unreactive. It does not combine with oxygen at room temperature. It also resists attack by acids, chlorine, and other corrosive agents. A corrosive agent is a material that tends to react vigorously with other substances. 

Aluminum, a very active metal, reacts rapidly with O2 from the air to form a surface layer of aluminum oxide, AI2O3, that is so thin that it is transparent. This very tough, hard substance is inert to oxygen, water, and most other corrosive agents in the environment. In this way, objects made of aluminum form their own protective layers and need not be treated further to inhibit corrosion. 

In steam condensers, such as may be found on power stations, the reduced pressure may induce air ingress into the condenser. The oxygen present in the air may represent a corrosion agent. Filming amines may be necessary to control corrosion under these circumstances. Alternatively hydrazine or another volatile oxygen scavenger may be used for oxygen and pH control. 

Surface Barriers The application of an overlay of low-slump concrete, latex-modified concrete (EMC), high-density concrete, polymer concrete, or bituminous concrete with membrane on the existing concrete provides a barrier that impedes continued intrusion of chloride anions, moisture, and oxygen that are necessary for continued corrosion. These barrier systems may be used only after decontamination because corrosive agents get trapped in the concrete, leading to loss in its capacity to function properly. 

Gaseous environments include the open atmosphere, the vapor phase in tanks, natural gas in wells, and the empty space in packaging containers. Here again, water and oxygen are the principal corrosive agents, but the main problem in providing inhibition is to transport the inhibitor from a source to the sites where corrosion may occur (Faessler et al. 1989). 

In the absence of humidity, gaseous oxygen is a corrosive agent only at elevated temperatures (at several hundred degrees Celsius). For this reason, a distinction is made between wet corrosion, or corrosion at ambient temperatures, and dry corrosion,... 

Polymer films form a barrier between the metal substrate and the environment. This protects the metal provided that the barrier is impermeable to corrosive agents and remains free of defects. Paint films rarely fulfill these conditions. Firstly, they may contain defects such as pores and scratches that perforate the barrier. Secondly, even intact paint films are permeable to oxygen and water to an extent that varies with their structure, thickness and chemical composition. 

Extending beyond the aforementioned active removal of oxygen, biofihns may protect materials against a variety of other corrosive agents such as acidic compounds or chloride ions. In contrast to oxygen consumption, living cells are not always necessary their metabohc products such as extracellular polymeric substances (EPS) alone may already be sufficient to exert protective effects in some cases. 

Nitric oxide is an oxidizer and will support combustion. It will react with oxygen, oxidizing agents, halides, and hydrocarbons. Nitric oxide is noncorrosive, and most structural materials are unaffected. However, in the presence of moisture, corrosion can develop with the formation of nitrous and nitric acids. 

In stable passive metals, for instance stainless steels, the weak oxidant water is sufficient to effect the transition to the passive range. The presence of oxygen in the water is not required for this purpose. The passivating oxide layer is quickly replaced following a mechanical rupture (repassivation). As a rule, the balance potential of the existing redox system, i.e. the redox potential of the corrosive agent, is established within a brief period. Stainless steels are therefore preferred for use in mediums the redox potential of which passivates them. In these mediums, the uniform surface corrosion levels are so small with free corrosion that the structural element can be expected to have a technically acceptable service life. 

In the case of surface corrosion or pitting corrosion not microcolonies but biofilms are involved (Kunzel, 1991). Under oxygen deprivation in the biofilm, fermentative processes take place and carbonic acids (also complexing agents) are formed. Also, sulfate reduction occurs (H2S evolution). These processes cause acid corrosion as well as attack by hydrogen sulfide. In the reaction of HjS with iron(II) ions, iron sulfide is formed, and this speeds up/accelerates the oxygen corrosion (cathodic reaction) Cough-ton et al., 1988). These processes are presented in Fig. 4-6. 

What are the two most powerful corrosive agents in a process plant Not acids or sulfur, or caustic or salt. Neither cyanides nor carbonates nor chlorides. The most aggressive corrosive agents are air and water. Nitrogen is inert. It is oxygen in an aqueous environment that is the main cause of many corrosion problems. 

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