The Effects of Corrosion on the Environment
The Effects of Corrosion on the Environment – Corrosion implies “rusting”. The term corrosion is defined as a gradual destruction of material (metals) by chemical reaction with its surroundings. Corrosion in other words is the disintegration of an engineering material into its constituent atoms due to chemical reactions with its environment. (kotz and Treidel, 1997). To order the Complete Project Material, Pay thr Sum of N3,000 to: BANK NAME: FIRST BANK PLC ACCOUNT NAME: CHIBUZOR TOCHI ONYEMENAM ACCOUNT NUMBER: 3066880122 Then send the Project Topic, Your Email Address and Full Name to 07033378184.
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The Effects of Corrosion on the Environment – Types of Corrosion
Corrosion can be considered in terms of chemical and electro-chemical processes. We also have aqueous and dry corrosion.
In electro-chemical processes, the deterioration usually involves metal loss to a solution in some form by a product favored oxidation-reduction reaction. This is a diffusion favored/controlled process. A good example is the rusting of iron, where on exposure to moist atmosphere, forms oxides (i.e. iron III oxide)[Fe2O3. H2O].
Aqueous ———- Water.
Environment ——— Surrounding.
By definition: Aqueous environment is any solution in which water (H2O) is the solvent. It’s just a watery place e.g. sea water, salt water, rain etc
(Shamay, et al ,2011). Aqueous is usually shown in a chemical equation by appending (aq) to the related formula, such as Nacl(aq) which means Nacl dissolved in water. (Zumdahl, 1997).
CORROSIVE AGENTS: This are substances that are capable of causing a corrosive reaction to occur. The common corrosive agents are acids, alkalies and salts . The atmosphere and water which are the two common media for this agents, most times act as corrosive agents too.
In anode reactions, metal loss at anodic sites in an electrochemical cell occurs when the metal atom give up one or more electrons and move into electrolyte as positively charged ions.
The Effects of Corrosion on the Environment – Chemistry of Corrosion
Corrosion is a chemical reaction between metals and corrosive agents. In aqueous corrosion, common corrosive agents which are O2, acid, alkali or salts can react in an anode and cathode reaction that produces dissolved ionic product, like iron metal is,
Anodic reaction : Fe Fe2+ +2e —– (1)
Cathodic reduction involved in corrosion process are:
Neutral medium:O2+2H20+4e– ———- 40H–‑— (2)
Acidic medium:02+4H++4e– ———— 2H20 —- (3)
2H++2e– ————- H2 —- (4)
The cathodic reaction represented by equation (2) exemplifies corrosion in natural pH values. Equation (3)&(4) represents corrosion process taking place in the acidic environment encountered in industrial process or for the confined volume (pit, crevices) where the pH can reach acidic value because of hydrolysis reaction such as,
Fe2+ +2H20 ———– Fe(OH)2+2H+.
This reaction produces H+ ions, the concentration of which under certain conditions can become large if the H+ ions cannot readily move out from a confined volume.
The overall corrosion reactions is the sum of the cathodic and anodic partial reactions for instance, a reaction producing dissolved ions (i.e., sum of reaction (1) &(4) becomes): Fe+2H+ ———– Fe2++H2 or, for a reaction producing insoluble hydroxide (sum of the reaction (1)&(2):
2Fe +02 +2H20 ———- 2Fe(OH)2
The Effects of Corrosion on the Environment
Perhaps the most dangerous of all is corrosion that occurs in major industrial plants, such as electrical power or chemical processing plant shutdown can occur as a result of corrosion. This is just one of its many direct and indirect consequences Some consequences of corrosion are economic, and cause the following;
(i) LOSS OF EFFICIENCY: Such as when overdesign and forming pits on the material constructed. If it is a corrosive material /product it will decrease the heat –transfer rate; this could leads to short down of equipment due to corrosion failure.
(ii) CONTAMINATION OF A PRODUCT: Example in pipes made with lead (Pb) which is very toxic &dangerous to health. As the lead molecules dissolve in water, thereby contaminating the water that passes through it. E.g. fluid, beer goes cloudy when small quantity of heavy metal is released.
(iii) Damage of equipment adjacent to that in which corrosion failure occurs.
(iv) In ability to use desirable materials due to corrosion.
(v) It could also lead to loss of valuable material which also include mechanical damage to values, pumps, etc or blockage of pipes by solid corrosion products.
(iv) Hazard or injures to people arising from structural failure or beaked down (e.g. bridges, cars, aircraft etc).
Some consequences could be social:
SAFETY: for example, fire explosion, release of toxic product, and construction collapse.
HEALTH: pollution due to escaping products from corroded equipment or due to a corrosion product itself.
DEPLETION OF NATURAL RESOURCES: Metal and the fuels used to manufacture them, even the appearance as when corroded material is unpleasing to the eye of course; all the preceding social items have economic aspects also.
This also could lead to single catastrophic failures, for example a corrosion as mentioned in contamination above induced leak in an oil pipe line, with resulting loss of product and environmental contamination can result, in costly damage that is difficult to either assess or repair as well as massive legal penalties as ‘‘punitive damage Perforation of vessels and pipes allowing escape of their contents and possible harm to the surroundings. For instance, a leaky domestic radiator can cause expensive damage to carpet and decorations. Due to this hazards some methods have been designed to control corrosion.
METHODS OF CONTROLLING CORROSION IN AN AQUEOUS ENVIRONMENT.
Some metals are more intrinsically resistant to corrosion than others, either due to the fundamental nature of the electrochemical processes involved or due to the details of how reaction products form. Materials must be matched to the environment that they will encounter in service in selection of materials because each metal and alloy has unique and inherent corrosion behavior that can range from the high resistance of noble metals e.g. gold to the most economical solution for the particular service. (Pierre, 2006).
For instance, in galvanic series in which a metal is used to plate another metal due to its oxidizing power, proper selection of the right grade of material for the specific environment is important for the long-lasting performance of this group of materials (since corrosion can’t just take place without some properties like oxygen, hydrogen and SO2 etc being present in the area).(Danny,1996).
Some specific materials like stainless steel, nickel etc. are corrosion resistant by nature, which might suggest that passivating them would be unnecessary. Passivation here is the shielding of outer layer of material which can be demonstrated with a micro coating or found occurring spontaneously in nature, (i.e. using a very light coat of materials such as metal oxide to create a shell against corrosion) is the technique in passivation. (Perry, 1997/2005).
However, stainless steel are not completely impervious to rusting due to roughing. Also gold is a stable and most strongly reducing acids, where as iron corrodes rapidly, yet finely divided gold can be quickly dissolved in oxygenated cyanide solution that may be contained in steel tanks.(Kotz and Treichel, 1996). So when gold or platinum is used as a choice metal/material for construction, the problem of corrosion will be a forgone issue because they will only tend to decompose spontaneously into pure metal .(Ojovan and Lee, 2007).
The application of design principles can eliminate many corrosion problems and greatly reduce the time and cost associated with corrosion maintenance and repair. One often overlooked in designing manufactured products is drainage. The corrosion of automobile side panel have been minimized by providing drainage to allow any water and debris to fall off of the car instead of collecting and causing corrosion from the far side of the panel. Corrosion often occurs in dead space or crevices, where corrosion medium becomes more corrosive. Where stress-corrosion cracking is possible, the components can be designed to operate at stress levels below the threshold stress for cracking, thus if the material is designed in a flat or table manner/form, such that there will be no pit or crevices on the material constructed, corrosion problem will be minimized.(Ehrlich and Turnbull,1959).
Electroplating (often called “plating”) is the deposition of a metal coating into an object by putting a negative charge on it and putting it into a solution which contains a metal salt. It is the method of coating the surface of one metal with another metal, usually copper, silver, chromium, nickel or gold by means of electrolysis for the decoration or protection of other metals against corrosion. Articles which are usually plated include Cutlery, jewellery, table ware, and iron or steel objects such as the metallic parts of motor-cars .In terms of putting the metal in a solution that contains a salt of the metal, the metal salt will contain positively charged metal ions which are attracted to the natively charged object and are “reduced” to metallic form upon it . How it works
Most times, the salt (Nickel chloride in the example) is simply dissolved in water and may be a little acid. The NaCl2 salt ionizes in the water into Na+ ions and two parts of Cl– ions. (Pierce, 2008).
However ,electroplating as a plating process in which metal ions in a solution are moved by an electric field to coat an electrode, this process uses an electric current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material ,such as a metal.
Electroplating is primarily used for depositing a layer of material to bestow a desired property (e.g., abrasion and wear resistance, corrosion protection, lubricating etc) to a surface that otherwise lacks that property .Another application uses electroplating to build up thickness on undersized parts of a material .(Stetter ,2004). The process used in electroplating is called electrode position.
ORGANIC COATING (POLYMERIC COATING)
Organic Coating are materials that applied to protect or beautify a surface. Coating materials which are polymer coatings include paints, vanishes, stains, industrial maintenance coatings and they can applied to stationary and /or mobile surfaces/objects. (cassoux, 2001). Some other products whose primary aim/function is to protect the surface of an object from the environment can be used example drying oils.(Castle and Watts, 1981). Another way is by “thermal spraying” in which metals are melted and sprayed on a surface to form a coating.(Marie, 2012).It can also be called flame- spraying/metallizing . The metal that are sprayed can be pure metals or alloys that are generally in form of powders, wires or rods.(Funke,1979).
Anode protection is a technique to control the corrosion of a metal surface by making it the anode of an electrochemical cell and controlling the electrode potential in a zone where the metal is passive. It is achieved by impressing upon the metal an anodic current a sufficient magnitude to cause the formation of a passive film. It is used to protect metal that exhibit passivation in environments..(Perry,2005). Anodic protection is used for carbon steel storage tanks containing extreme pH environment.ery high current requirement. (Nester, 2004). We have sacrificial anode just like sacrificial cathode where a more easily corroded metal is connected to the metal to be protected, which is called a sacrificial metal.
A well known example is the reaction between zinc and iron, zinc atoms ionize as it is more electropositive and is oxidized and corrodes. Zn(s) Zn2+(aq) +2e–
Example most of the food can is coated with a layer of metal that is more electropositive than the metal (mostly iron) inside the food can, preventing the iron from contaminating the food with Fe2+ ions, careful design & control is required when using anodic protection for several reasons, including excessive current when passivation is lost or unstable which could lead to accelerated corrosion.(Olen, et-al, 1981).
PASSIVATION: This is using a light coat of material such as metal oxide to create a shell against corrosion. Passivation is used in strengthening and preserving the appearance of metallic .It is an example of anodic control process in which the material reacting anodic ally does not go in solution but forms a layer of oxide or OH over the surface of the metal .This introduces a form of resistance over potential to the metal by limiting access of electrolyte to the metal surface.
This is a technical used to control corrosion of a metal by making it the cathode of an electrochemical cell
since corrosion of metallic stricture a rises when an electric current flows from the metal into the electrolyte .The principle of cathodic protection is in connecting an external anode to the metal to be protected and the passing of an electrical direct current so that all areas of the metal surface become cathodic and therefore do not corrode .(Peabody,2001). The simplest method to apply cathodic protection is by connecting the metal called “sacrificial metal” to act as the anode of the electrochemical cell. Another way by impressed current system e.g. mixed metal oxides or platinum coated with titanium. Cathodic protection is often used to protect buried fuel tanks, structures (metallic), and pipelines.(Brichau,1996). Example of an active metal such as magnesium is connected by a wire to the pipeline or tank to be protected.
Because, the magnesium is a better reducing agent than iron, electrons are furnished by the magnesium, thereby keeping the iron from being oxidizing as oxidation occurs Mg (anode) dissolves, and so it must be replaced periodically (Steven, 2002).
Again the cathodic protection of an iron-containing object, is coated with a film of zinc, a metal more easily oxidized than iron. Therefore, the zinc acts as an anode and force the iron to become the cathode, thereby preventing the corrosion of the iron. Thus, cathodic protection is exhibited by forcing the metal to become the anode instead of the cathode, in an electrochemical cell. Example is galvanized iron, iron that has been coated with a thin film of zinc.
Zinc oxidation has a high standard electrode potential (E) than iron oxidation ,so zinc forms the sacrificial anode. Another reason is that when zinc is corroded, Zn(OH)2 forms on the surface .this hydroxide is even less soluble them Fe(OH)2,thus the insoluble hydroxide film further show corrosion .(kotz and Treichel, 1997).
USE OF CHEMICAL ADDITIVES
The use of chemical additives to control corrosion in construction material is done by adding some chemical products that are specially designed to shield and control corrosion in clear brine fluids. Some of the products include:
OXBAN OXYGEN SCAVENGER:
This oxygen scavenger consists of a specially formulated concentrated liquid inorganic sulfite .The scavenging is by limiting the reaction of O2 at the cathode, less oxygen, less reaction. It eliminates the oxygen as a corrosion promoter in fresh water and low density oil field completion and work over fluids .also used in brine fluid but this one contains a monovalent ions, such as sodium, and potassium.(Steven,2002).
TETRAHIB-CORROSION INHIBITOR: This water soluble, multi component inorganic, film forming corrosion inhibitor it is designed for use in low density clear brine fluids such as potassium chloride (kCl), NaCl, and CaCl. This product is particularly effective in environment where hydrogen and carbon dioxide are present.(Varshneya,2006).
CT 200 FR FRICTION REDUCER: This is a friction reducing additive, used in coiled tubing operation of material construction(s).(varshneya,2006).
ADJUSTING PROCESS CONDITION (TEMPERATURE AND pH).
Adjusting the process condition in terms of temperature and pH of the system in other words the effect of temperature and pH condition in corrosion (particularly in aqueous environment), most chemical reaction rates increases with increase in temperature. Temperature affects the rate of metal in electrolytes primarily through its effect on factors which control the diffusion rate of oxygen. The corrosion of iron and steel is an example of this because temperature affects the corrosion rate by virtue of its effect on the oxygen solubility and oxygen diffusion coefficient.
However as temperature is increased oxygen solubility in aqueous solution decreases until at the boiling point all oxygen is removed, this tends to decrease the corrosion rate. While in a closed system ,where oxygen cannot escape, the corrosion rate continues to increase until all oxygen is consumed .While pH which is the power of hydrogen on corrosion or –log10(aH+).low pH acid water clearly accelerate corrosion by producing a plentiful supply of hydrogenions .Although, even absolutely pure water contains some free hydrogenions, so, free carbon dioxide dissolved in water can multiply the hydrogenion concentration many times .This is because when carbon dioxide dissolves in water it reacts with water molecules to from carbonic acid.
CO2+H2 ———– H2CO3 carbonic acid (Breakell, et-al., 2002).
The Effects of Corrosion on the Environment – Conclusion
In conclusion, corrosion is so disastrous and non visible reaction, therefore considering the effect on the environment needs to be controlled/prevented to retain a long lasting structures and reduce cost. Thus, Corrosion is controlled by variety of ways. However, the effectiveness of a method is dependent on cost and efficiency.
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