PSI - Issue 34

Ramesh Babu et al. / Procedia Structural Integrity 34 (2021) 20–25 Ramesh babu/ Structural Integrity Procedia 00 (2019) 000 – 000

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1.1 INTRODUCTION A benchmark research project by DNV, HHI, KITECH, SYMETAL, of a Wire Arc Additive Manufactured (WAAM) defined in Ding et al. (2016), propeller ’s structural integrity toward a conventional cast Ni-Al bronze marine propeller as stated in DNV Pt.4 Ch.5 Sec.1 (2021) has been carried out for the sake of increased understanding of physical property differences. WAAM is an Additive Manufacturing (AM) technology belonging to the Direct Energy Deposition-Arc (DED-Arc) defined in ISO/ASTM52900 (2015) which deposits metallic materials layer by layer onto a high-quality metallic base material with optimal chemical composition and microstructure for its specific purpose; by the use of a strict controlled i.e. automated electric arc welding process quoted by Ding et al. (2016) for the purpose of manufacturing a part to its near net shape. AM of marine machinery components by arc welding processes has been carried out for several decades, namely clad welded propeller and rudder shafts, cylinder heads, piston crowns, exhaust gas valves and ship hull structures given by Lindstrom (2002), ISO15614-7 (2019) DNVGL-CG-0044 (2015). The very first arc welding processes were invented and patented in 1881quote by Gibson(1994), 1887 Benardos- et al.(2006) and 1890 Car et al.(2004). In 1907, the Swedish marine engineer Oscar Kjellberg patented flux-coated electrodes; the prerequisites for Shield Metal Arc Welding (SMAW). Since 1907, arc welding technology has been further developed and improved, becoming an established process for repair, maintenance, and construction of metallic marine structures which can be seen in vessel Esab IV it is world first welded ship hull. Today, it is understood that the ultimate mechanical properties of weld metals depend upon an intricate relationship between several contributing factors, see Figure 1 given by Lindström (2015). Over time, in pace with the arc welding technology’s progress, arc welding-based AM has been known and/or branded under various names e.g., ‘ s hape welding’, ‘rapid prototyping’, ‘structural overlay welding’, ‘metallic 3D printing’ , LAZER- printed’ and WAAM. The very first arc welding manufactured component reported in the literature is a MMA constructed goblet, year 1936 given in German Safety Standard, (1998). In the 1970 successfully qualified a mechanised Submerged Arc Welding (SAW) manufactured ‘Steam Generator fee d water nozzle’ for the European Nuclear Power indust ry given by Karl et al. (2016). In 2002 a scientific paper by one of the authors Lindstrom (2002) build up hull plates, entire frame and tank top sections during sea going operation on three DNV classed ships; by mechanised Metal Cored Arc Welding (MCAW). Since 1980 a fairly large number of nuclear reactor and pressuriser nozzles been reconstructed by remote controlled semi-automatic mechanised Gas Tungsten Arc Welding (GTAW) Robert Engel (2013), Rishel et al.(2007)and westhouse electric(2018). The seaworthiness of ship propulsion and rudder systems is of the outmost importance as failure or loss thereof can result in fatal consequences. Furthermore, design of the marine propulsion systems is directly related to the fuel consumption efficiency given by Klass et al. (2008). Where the propeller material requirements are a function of its design lifetime and service condition. The general technical requirements are good repair characteristics, excellent sea water fatigue crack resistance and high resistance to galvanic, cavitation, erosion, and crevice corrosion, and impingement attack. The maximum stress and strain magnitudes are normally incurred in the way of propeller blades connection to the propeller hub as detailed by Carlton (2007). According to IACS W24 (2020) there are three severity zones (A – C) on each propeller blades; where A = areas subjected to high operation stress magnitudes; B = moderate; and C = low, see Figure 2. The most common marine propeller material is Nickel Aluminium Bronze, Grade CU3 given in DNV Pt. 2, Ch. 2, Sec. 11; equivalent to EN 1982 (2017) casting and material group as 35 ISO 15608 (2017). The phase transformations of aluminum – bronze have been the subject of many studies due to the formations of intermetallic components promoted by the casting process’ slow cooling rate given by Shakil et al. (2020). An issue that should be able to avoided by WAAM; where the cooling rate can be strictly controlled by the weld heat input explained by Kou (2002) to achieve the required metallurgical and mechanical properties given by Carlton et al. (2007).

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