Materials and Process: Welding - Coursework Example

Microscopic view at the point of weld showing the grain size change Friction weld in carbon steel Friction weld in carbon steel was preceded by making one end of the one part in contact with the face of the other and in contact phase of friction and fusion to give up a single piece(Duffin and Bahrani, 1973, Kumar et al., 2012). All the images below show that the this type of weld result in excess material to left over without welding. The joint is formed only at the point of friction around the rotating piece and the rest of the surface which is flat is left over. Conclusion Welding is done by making use of fusion techniques in which one metal is fused into the other to give the essence of being essentially a single element whereas non-fusion processes do not make use of welding techniques and are carried out without making use of filler material as in case of soldering and brazing. Solid phase welding is the type of fusion process that essentially makes use of welding techniques without incorporating heat, for example, friction welding. Poor welds result in early failure of mechanical structures and can result in much serious consequences. Chapter 3: Defects and Failure Defects and failures are observed in mechanical systems and components ass a result of excessive wear or loading of the component. Here is the exhaustive list of some of the most commonly used components in important mechanical systems with their associated defects and failures. 1. Cast aluminum collet for attached to a steel rope immersed in seawater. Below is the image of aluminum collet used to get attached to steel rope. These specifically made of molten aluminium, casted to get the desired shape. Casting gives good strength and durability to the final products. Casted equipment is then precision machined with CNC machining tools to give better accuracy to the collets. It is used under water due to corrosion resistant property of aluminum. Aluminum gets oxidized quickly and its oxide is hard and ductile in nature which really protects the ships and other underwater substances from corrosion. 2. Stabilized Stainless Steel pipe carried Chlorine at 120oC. Failure occurred in 9 months. Stabilized stainless steel is specifically used to prevent inter-granular corrosion instances. In such cases corrosion directly attacks the boundaries of the crystallites within the crystalline materials. In stabilized stainless steel, these crystalline boundaries are protected by introducing other elements like chromium which make a layer of their carbides over the crystals thus making the surfaces corrosion resistant (Erve et al., 1997). Therefore, it is less prone to corrosion at temperatures below 50ͦ C in chlorine environment. The image shown below is the specific example of stainless steel pipe being used in chlorine carrying applications. In the industrial unit, this pipe was under the effect of extensive strass which ruptured the carbide bindings of the crystal. Also the pipe section shown was being used at elevated temperatures of 120 degree Celsius which increased the corrosion rate within the pipe thus resulting in its failure. 3. Titanium hip joint (femoral) failed in situ. This is the titanium hip joint which failed while being in the human body. Titanium metal is used in all applications regarding knee replacement and other fixture applications in orthopedics and is considered to work throughout the life span of the patient(HJ et al., 1988). The reason behind the failure of this knee replacement instrument was the weight and fatigue applied by the patient on the prosthesis. 4. Lifting lug made of low carbon steel plate. This lifting lug was made of low carbon steel which is the most durable steel because of its ductile nature. This product is usually manufactured by casting the molten steel into the required shape which adds more strength to the product. Afterwards this product is machined to give resulting shape to the metal piece. Lifting lug is specifically used for lifting heavy loads with cranes and other equipment. It is specially designed to work for larger loads but the loads should fall into the load carrying ability of the lug. This failure of low carbon steel lifting lug occurred due to the application of force beyond the level of shear stress bearable for the lug(WorkSafe, 2008). 5. Cast cam shaft. This casted cam failed as a result of least ductile material used for the manufacturing of cam and also casting procedure followed was not durable. These resulted in the failure of the cam shaft due to incorrect pressures applied and break in procedures(Wanjari and Parshiwanikar, 2013). 6. Mazak torque test specimen. Aluminum/Zinc alloy This test specimen is made up of zinc aluminum alloy under torsional stress(Crossland, 1954). The purpose of the test specimen is to check the quality, durability and working limits of a specific metal or metal alloy before being used as a part of any sophisticated instrument’s part. This test is done prior to the implementation f the equipment to just to know whether or not that specific material is capable of performing required tasks. During test this Aluminum-Zinc alloy was tested for a range of shear stresses. This torsional stress resulted in the failure of Mazak at the angle of 45 degrees. 7. Slave spring for refuse vehicle Although the material of the slave spring is good to be used for refuse vehicle but it failed due to excess stress applied beyond the limit of yield stress of the material. Slave spring is used in the clutch master slave system of the refuse vehicles. In these vehicles, clutches behave differently than brakes which are having dual system. Clutch system is usually having a component which is apparently like a valve but not a valve exactly. These valve shaped slave springs are used to hold the seal tightly against the surface to avoid leakages. Here is also the example of a slave spring which failed as pressure was exerted beyond the shear stress limit of the spring. 8. Shear pin for forging press While observing the failure in the shear pin of forging press one can easily observe the grey bits with few tracks of corrosion. Therefore this is the case of stress corrosion. 9. Sheared stainless steel bolt Corrosion of a stainless steel bolt is the specific case of stress and crevice corrosion which took place due to excessive stress applied on the head of the bolt and shear stress applied at the shank followed by corrosion. 9. Splined vehicle drive shaft This casted drive shaft is made up of low carbon steel which resulted in more ductility of the material and hence application of force caused failure of the shaft. This failure occurred due to excess shear stress beyond the limit of yield stress applied on the shaft(Singhal and Mandloi, 2013). Chapter 4: A Research on Corrosion and Prevention Methods Corrosion Corrosion is the destruction of materials specifically metals, with the passage of time due to chemical reactions taking place in the environment. In case of iron, the process of corrosion is regarded as rusting which takes place when iron reacts with oxygen in the presence of water. Types of Corrosion (Two and explain) Exhaustive list of different types of corrosion is given below(EngineeringToolbox): Uniform Corrosion Localized corrosion (pitting corrosion) Wide pitting corrosion Inter-granular corrosion Trans-granular or intra-granular corrosion Galvanic corrosion Selective corrosion Exfoliation corrosion Interfacial corrosion Most common and destructive forms of corrosion are pitting and galvanic corrosion. Pitting(gewater) is most commonly observed when metal surfaces are in contact with low velocity or stagnant fluids. This result in the corrosion of metal but metal is not affected in a uniform manner rather the pattern of corrosion follows a pit configuration as shown in the figure below(TIS). Galvanic corrosion(Miller et al., 2007) is the corrosion which is observed between cracked surfaces or between the surfaces of contact of two metals. This type of corrosion usually takes place when both the metals and metal pieces are at different potentials and placed in electrolytic environment which is capable of eroding the metals. Galvanic Corrosion Prevention methods Metal corrosion is usually prevented by keeping the exposed metal surfaces clean and dry. Sometimes the exposed surfaces are also covered by making use of grease and paints to avoid contact of metals with fluids(TIS). On large scale most commonly used preventive methods from corrosion are: Active corrosion protection Passive corrosion protection In active corrosion methods, anti-corrosion alloys and materials are developed which are capable of influencing the corrosion reactions. This method changes the nature of metal in contact with the moisturizing fluid and hence avoids corrosion, whereas, passive corrosion protection is associated with the introduction of an anti-corrosion material which is applied on the surface of the metal. This does not change the chemical properties of the metal therefore; any damage to the protective layer at any point may result in the corrosion of metal from that place. Cathodic Protection Method This method of protection is specifically used for the protection of metal surfaces in constant contact of fluid or moisturizing medium like bridges, pipelines, ships etc. In such situations corrosion occurs when the subjected body acts as an anode(Bell). Therefore cathodic protection method the submerged body is made cathode by applying a very small voltage but larger than the one required during oxidization(David). This applied voltage applies positive charge on the body thus resulting in preventing electron loss from the surface of the body and hence corrosion. Stress Corrosion Stress corrosion is defined as the combined effect of corrosion and stress which produce destruction in the object under consideration. This is usually observed in pressure vessel, highly stressed components as in naval ships and submarines or in pipework with high speed turbulent flows(NPL). This type of corrosion is really dangerous as it results in tremendous loss of equipment and hence system. The components which are capable of generating stress corrosion are continuously monitored and maintained but they suddenly undergo fractures due to dual destruction processes. Here is the pictorial view of the result of stress corrosion in a pipework: Two new methods which are most commonly being used for the prevention of corrosion are listed below: Sacrificial protection electroplating Cathodic protection method(Britton and Baxter, 2003) First method makes use of electroplating process which is used to deposit a layer of metal which is least suspected to corrosion over the entire surface of the subject. The other method is cathodic protection method. Both the methods are permanent anti corrosion methods rather than temporary ones like paints and grease which result in excessive corrosion if the layer of paint or grease is removed from any place(Langill, 2006). References BELL, T. Corrosion Prevention [Online]. Available: http://metals.about.com/od/metallurgy/a/Corrosion-Prevention.htm. BRITTON, J. N. & BAXTER, R. E. 2003. Corrosion Control Methods for Deep Water Floating Production Equipment. CROSSLAND, B. 1954. The Effect of Fluid Pressure on the Shear Properties of Metals. Proceedings of the Institution of Mechanical Engineers. DAVID. Cathodic Protection [Online]. Available: http://www.daviddarling.info/encyclopedia/C/AE_cathodic_protection.html. DUFFIN, F. D. & BAHRANI, A. S. 1973. Frictional behaviour of mild steel in friction welding. Elsevier. DUPONT, J. N. & MARDER, A. R. 1996. Dilution in Single Pass Arc Welds. Metallurgical and Materials Transactions. EBERT, H. W. & F.WINSOR 1980. Carbon Steel Submerged Arc Welds - Tensile Strength vs. Corrosion Resistance. Welding Research Supplement. ENCOCAM. Available: http://www.encocam.com/. ENGINEERINGTOOLBOX. Types of Corrosion [Online]. Available: http://www.engineeringtoolbox.com/corrosion-d_986.html. ERVE, M., WESSELINGA, U., KILIANA, R., HARDTA, R., BRÜMMERB, G., MAIERC, V. & ILGD, U. 1997. Cracking in stabilized austenitic stainless steel piping of German boiling water reactors—characteristic features and root cause. Nuclear Engineering and Design FULLSUPPLY. 2014. EFW Electric Fusionn Welded Pipe [Online]. Available: http://www.fullsupply.co.uk/efwpipe.php. GEWATER. Corrosion COntrol Systems [Online]. Available: http://www.gewater.com/handbook/cooling_water_systems/ch_24_corrosion.jsp. HJ, A., NW, A., M, B., EA, S., JR, W. P., PM, P. & PG, B. 1988. Metallic wear in failed titanium-alloy total hip replacements. A histological and quantitative analysis. Journal of Bone Joint Surgery. INGHAM, E. 2014. The Benefits of Fusion Welding of Polyethylene Pipes in the Water Industry - An Interview with Edward Ingham [Online]. Available: http://www.azom.com/article.aspx?ArticleID=10647. JESSEMAN & SCHMID, G. C. Submerged Arc Welding a Low-Carbon, Copper-Strengthened Alloy Steel. Welding Research Supplement. KUMAR, S., KUMAR, R. & SINGLA, Y. K. 2012. TO STUDY THE MECHANICAL BEHAVIOUR OF FRICTION WELDING OF ALUMINIUM ALLOY AND MILD STEEL. International Journal of mechanical Engineering and Robotics Research. LANCASTER, J. Handbook of Structural Welding. LANGILL, D. T. J. 2006. Corrosion Protection: Basic corrosion theory and protection methods. MILLER, D. C., HUGHES, W. L., WANG, Z.-L., GALL, K. & STOLDT, C. R. 2007. Mechanical Effects of Galvanic Corrosion on Structural Polysilicon. Journal of Microelectromechanical Systems, 16. MUGGYWELD. 2013. Brass, Bronze and Copper Welding [Online]. MURUGANA, S., RAIA, S. K., KUMARA, P. V., JAYAKUMARA, T., RAJA, B. & BOSEB, M. S. C. 2001. Temperature distribution and residual stresses due to multipass welding in type 304 stainless steel and low carbon steel weld pads. International Journal of Pressure Vessels and Piping. NPL. Stress Corrosion Cracking [Online]. Available: http://www.npl.co.uk/upload/pdf/stress_corrosion_cracking_basics.pdf. SIFTIPS 1932. opper and Brass: A Guide to Successful Welding. Sif Tips. SINGHAL, A. & MANDLOI, R. K. 2013. Failure Analysis of Automotive FWD Flexible Drive Shaft - A review International Journal of Engineering Research and Applications TIS. Classification of Corrosion Protection Methods [Online]. Available: http://www.tis-gdv.de/tis_e/verpack/korrosio/schutz/schutz.htm. TIS. Types of Corrosion [Online]. Available: http://www.tis-gdv.de/tis_e/misc/korro.htm. TOOLINGUNIVERSITY 2013. Welding Trainning. TRUCK-LITE. Available: http://www.truck-lite.eu.com/. WANJARI, R. V. & PARSHIWANIKAR, T. C. 2013. Failure of Camshaft International Journal of Innovative Technology and Exploring Engineering (IJITEE) WORKSAFE 2008. Lifting lug fails on crusher liner. Victorian WorkCover Authority. Read More