Analysis of Materials: Corrosion and its Associated Effects - Term Paper Example

Analysis of Materials: Corrosion and its Associated Effects Prepared and Submitted by [Client’s Name] Submitted to [Professor’s Name] [Subject] Modern society depends too much on metals. It is very hard to picture a successful and progressive society without the aid of metals – buildings would not be constructed, machines and equipments would not be running, cars, ships, and airplanes would not be operational, and strong structural foundation would not have been possible elsewhere. Most of the major uses of metals are confined to structural support. Buildings are erected with a considerable amount of metals for support. At least 95% of the vehicles are made up of strong metals and metal sheets. These few examples stress the relevance of metals in various applications. Although metals are very important in today’s modern world, their importance is not necessarily visible to those who use them. The invisibility of metals in its various applications makes it very prone to performance issues. In most cases, the performance of these metals is only as good as its ability to fend off corrosion. Every year, billions of dollars are lost by companies from various industries from corrosion (Bertolotti & Hurst, 1978). As metals such as iron and steel are exposed to the environment, they are prone to combine with oxygen and such oxidation process form rusts. Rusts corrodes the surface of the metals and such corrosion would eventually introduce structural damages (Yang et al, 2007). These structural damages jeopardize the ability of metals and metals sheet to provide strong support to structural applications, or to create an optimal performance for its intended function because of the high probability of having long-term issues at the granular level. When the smallest unit of a material does not provide strength and support, then the material in itself will eventually fail to provide strength and support to the structure where it is used. With this, the need to understand corrosion, types of corrosion, and agents that influence the rate of corrosion becomes very important. Understanding the factors that contribute to the corrosiveness of materials equips companies of the possible ways to avert the negative effects of corrosion through the application of the appropriate chemicals or curing materials. Generally speaking, there are four kinds of corrosion, depending on the cause and the propagation of corrosion on the material. These are oxygen cell corrosion, chemical corrosion, electrochemical corrosion, and microbiologically influenced corrosion (Abolikhina & Molyar, 2003). Oxygen cell corrosions are commonly referred to as rusts and occur when metals are in direct contact with oxygen in the atmosphere. Chemical corrosion on the other hand occurs when metals are exposed (to some degree) to chemical agents, leading to the corrosion on the exposed areas and its subsequent spreading on other locations of the metal. Chemical corrosions typically include the substitution of one or more element present in the metal compound with another element present on the chemical reactants (Bogart & Vande, 1939). Electrochemical corrosion, as the name suggests, involves the displacement of an element from one phase with another element from another phase, creating an electric potential in the process that tends to corrode the metal. Electrochemical corrosion is also called galvanic corrosion. Microbiologically influenced corrosion is any corrosion that is prompted by the presence of microbial life-forms that alter the composition of the metal thus introducing corrosion in the process. Stress corrosion cracking       Stress corrosion cracking is a type of mechanical corrosion where the grain boundary of the material fails due to the application of stress. Stress corrosion cracking (SCC) is characterized by growth of cracks in areas where there is interaction between conjoint corrosion and the presence of residual or applied stress (Fritz & Gerlock, 2001). There are three general mechanisms that cause the cracking of materials. These are the dissolution of the active part of the metal, hydrogen (or oxygen) embrittlement, and film-induced cleaving. The first of the mechanisms that cause the cracking of a material is the dissolution of its active path. The active path of the material is the location within the microscopic level of the material that receives the largest amount of stress and strain. Active path dissolution accelerates corrosion because it is the path where stress is the highest. The stress experienced by this path is higher than normal and because of the failure in the grain boundary, propagation is hastened. The corrosion involves corrosion along a path with the largest volume of material naturally acted upon external stress. Normally, corrosion can occur along the inter-granular portion of a material and the applied stress is probably the cause for the material to crack giving more room for corrosion to diffuse inside and within (Newman & Procter, 1990).            On the same manner, Hydrogen embrittlement will corrode metals but the effects are chronic. Hydrogen is very small atoms that can dissolves and diffuse in metals by fitting itself to the lattice of metals in a very small extent. So thus it can diffuse rapidly than larger atoms. Metals that have small lattice distances like that of BCC structures do not allow hydrogen atoms to seep through its crystal lattices and corrode the material from within. Consequently, metals whose atomic distance in a crystal lattice is large enough to support the flow of hydrogen atoms like that of the FCC crystal lattice are more prone to corrosion. Hydrogen atom tends to be more attracted in the dilated regions of the crystal where there is tensile stress and the hydrogen in further draws to region ahead of cracks. The dissolve hydrogen then facilitates the fracture of the metals thus making cleavages (Staehle et al, 1977). These will effect to embrittlement of the metal and cracking may then be possible and stress will facilitate the cracking.        The third mechanism in stress induced corrosion cracking is film-induced cleavage. When a metal is coated with a thin-brittle film and if the film is corroded, the corrosion can propagate in the metal for some distance and when pressure is applied to the coated material, the thin film could crack. The crack again will initiate the propagation of corrosion and the process can be repeated. Stress corrosion cracking is a dangerous form of corrosion for it will mark the deterioration of mechanical strength by losing the metal slowly. The impairment of stress corrosion cracking is not obvious upon regular inspections of the materials being corroded however its effect can cause a major catastrophe and mechanical disasters. There are records of disasters in industries where boilers explode, high pressure gas pipes ruptured, and destructions of power stations and gas refineries due to cracking. SCC can be very dangerous in metallic structures that constantly receive loads of stress. If SCC occurs without the knowledge of the engineers, then it is likely that the strength of the structure supported by the metal will be jeopardized. If the metal is a part of the building, then there will be a high probability of a cave-in if the metal can no longer bear the stress of the load. Steel wires used for support in bridges as well as those metal rods used for structural support are prone to acquire stress induced corrosion. Building materials that involve metals whose stress tolerance is inappropriate for the stress received are more likely to collapse than materials whose stress capacity is calibrated to the load requirement. Crevice corrosion       Crevice corrosion can be a combination of mechanical corrosion and chemical corrosion. In most metal works; from small jointing of two metals to large infrastructures, junctions are always present. In these junctions, the space or gaps between the contact point is called a crevice. Inside of cracks, under gaskets, space filled with deposits and under sludge files are also examples of crevices. These narrow spaces, inside cracks, gaps between junctions provoke the formation corrosion localized in areas above mentioned in the presence of stagnant liquid. Unlike stress corrosion cracking, crevice corrosion is facilitated by oxidation-reduction of metals. In this process, metals oxidized by losing electrons in the environment and at the same time oxygen from the environment reduce by gaining electrons released by the metal material (Mueller, 1980). The build up of M+ in the crevice must be balance by e- charge that diffuses inside. However, OH- diffuses faster, resulting to the formation of MOH and e- transfer from the anode to cathode which in this case the outer surface is the cathode and crevices serves as the anode. MOH or Metal Hydroxides formed as precipitates (Frankel, 1998). These precipitates are brittle and commonly known as rust-also used interchangeably with corrosion. And so, the process continues if the precipitate is removed and fresh metal surface is again exposed to environment where reduced oxygen is readily available.  Crevice corrosion is extremely dangerous for metal supports that are constantly exposed to loads of stress and strain as well as with liquid chemicals. Droplets and precipitates of liquid chemicals that can lodge on the stress induced crevices will eventually eat up the metal and thus weaken the integrity of the metal and its functions. A good example of crevice corrosion is the corrosion that occurs on screws and bolts used as fasteners. Chemical compounds can easily seep through the natural crevice provided by the contour of the object, hence making it easy for the corrosion to eat up the metal from within. Accelerated low water corrosion (ALWC) Accelerated low water corrosion is also known as microbiologically induced corrosion (MIC). ALWC occurs only in submerged metals where microbes like the orange soft bacteria helps propagate oxidation of iron and steel into Ferric 3+ oxides along with a layer of black ferric sulphide as the by-product of the reaction of the steel with the waste products of these microbes. When microbes attach themselves to the wall of the submerged metal, their need to clamp their way on the minute rough areas eventually leads to a much larger issue in the long run. As microbes attach themselves to the wall and as their interaction with the environment allows them to exchange oxygen in the air, such interaction can cause corrosion along the rough areas of the metal. More often than not, these rough areas happen to be where the microbes attach themselves. AWLC is extremely dangerous in metals submerged for a long time as the integrity of its strength is jeopardized by the presence of microbes in water whose small damages can result to larger problems when the long-term is considered. Case Analysis One of the most relevant issue pertaining corrosion is that strong presence of AWLC in ports all over the world. Port authorities are becoming more concerned with the expanse of the surface area of the port covered by AWL corrosions as this imply that if they could not slow down or stop the rate of corrosion, they will need to replace all the steel beams and supports submerged in port areas. This also means that port operation needs to stop in order to accommodate the repair and renovation to be done because of the damage caused by AWLC. In Beech & Campbell (2008), an issue with ALWC was investigated and appropriate action through electrolysis was performed in order to slow down the progress of corrosion. The authors were commissioned by the Southern England government to inspect the AWLC that builds up in one of the harbour of Southern England. The researchers were able to observe the presence of poorly adherent, thick corrosive materials whose morphology varies significantly. Majority of the morphology of these materials are exhibited as large blisters located randomly on shallow exposed pits. The researchers subjected the representative samples from these corrosion materials to microbiological, microscopy, and chemical testing. The collected samples were cultured and populated in order to detect significant levels of sulphur-oxidizing bacteria (SOB) and sulphate-reducing bacteria (SRB). These bacteria were collected from samples grown and cultured in biofilm under static condition in the presence of electrodes. Measurements using the linear polarization resistance (LPR) suggest that the corrosion rate on the steel is higher compared to the available government data. This implies that the presence of microbes in the area has reached an alarming rate for metal supports as these unusually large population can eat up steel and other metals in no time, leaving the port area susceptible to integrity loss of metal supports. Images from scanning electron microscope (SEM) show that pitting was also present which further asserts the corrosive attack as a characteristic of ALWC. The authors identified the use of coating the metal piles in ports with high quality flake glass and some sort of cathodic protection to discourage bacteria form thriving in metal piles submerged in the water. Conclusion Corrosion is a serious problem but there is no definite technology that could counter the effects of corrosion. Existing technology only slows down the rate of corrosion in metals by sheathing the surface of the metal with protective coating that enhances the hardness of the material as well as its resistance to oxidation. However, such methods just delay the inevitable. Beech and Campbell’s research is important in one way or the other because of its ability to identify the microbes present in the corrosive materials. Such identification can lead to the proper coating materials that would inhibit the corrosive activity of the microbes attaching themselves to the metal plates. This case study also asserts the goal of the research which is to identify the factors that contribute to the corrosion in metals in order to prepare the necessary steps to prevent the metals from corroding further. References Abolikhina, E & Molyar, A. (2003). Corrosion of Aircraft Structures made of Aluminium Alloy. 39(6). 889-894 Beech, I & Campbell, S. (2008). Accelerated low water corrosion of carbon steel in the presence of a biofilm harbouring sulphate-reducing and sulphur-oxidising bacteria recovered from a marine sediment. Electrochemica Acta. 54(1). 14-21. Bertolotti, R & Hurst, V. (1978). Inhibition of Corrosion during Autoclave Sterilization of Carbon Steel Dental Instruments. Journal of American Dental Association. 97(4). 628-32 Bogart, L. & Vande, G. (1939). Kinds of Corrosion. Retrieved online http://www.corrosion-doctors.org/Corrosion-History/Kinds.htm Frankel, G. (1998). “Pitting Corrosion of Metals, A Review of the Critical Factors.” Journal of the Electrochemical Society, 145(6),186-198 Fritz, J & Gerlock, R. (2001). Chloride stress corrosion cracking resistance of 6% Mo stainless steel alloy. Desalination. 135(1). 93-97 Mueller, R. (1980). Pitting and crevice corrosion in ERW carbon steel heat exchanger tubes. Journal of Materials for Energy Systems. 2(2). Pp 60-64 Newman, RC & Procter, RPM. (1990). Stress Corrosion Cracking: 1965-1990, British Corrosion Journal, vol. 25, no. 4, pp. 259-269 Staehle, RW et al (ed). 1977. Stress–Corrosion Cracking and Hydrogen Embrittlement of Iron Base Alloys, NACE Yang, C., Liang, C. & Liu, X. (2007). Tarnishing of silver in environments with sulphur contamination. Anti-Corrosion Methods and Materials. 57(1). 232 -254 Read More