ANALYSIS METALLOGRAPHY AND CORROSION RATE PREDICTION ON ASTM A36 STEEL FROM SMAW UNDERWATER WELDING

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 12, December 2018, pp , Article ID: IJCIET_09_12_107 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed ANALYSIS METALLOGRAPHY AND CORROSION RATE PREDICTION ON ASTM A36 STEEL FROM SMAW UNDERWATER WELDING Herman Pratikno, Wimala Lalitya Dhanistha Lecturer, Ocean Engineering Department, Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia Achmad Rifqy Ramadhan Bachelor, Ocean Engineering Department, Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia ABSTRACT Underwater welding is a commonly used welding method for dealing with damages to marine building infrastructure such as ships, offshore platforms, or pipelines. These damages occur due to environmental cyclical loads, accident loads, and corrosion effects. Slow reparation handling will result in enlargement of crack propagation that occurs, this can lead to leakage or failure. This research focuses on underwater SMAW wet welding ASTM A36 steel with variation of electrode and heat input to mechanical properties, metallography, and corrosion rate prediction. The electrode used is AWS E6013 and AWS E6019 with variation of heat input 0.65 kj / mm and 1 kj / mm. Based on the result of research, it is concluded that welding using AWS E6019 electrode with heat input 1 kj / mm get best result with 338 MPa (yield strength) and 448 MPa (ultimate strength) tensile strength, HAZ macro structure width 3.2 mm, ferrite percentage in weld metal structure of 51%, and the corrosion rate prediction of mmpy. Keywords: Underwater Welding, Heat Input, Tensile Strength, Metallography, Corrosion Rate Cite this Article: Herman Pratikno, Wimala Lalitya Dhanistha and Achmad Rifqy Ramadhan, Analysis Metallography and Corrosion Rate Prediction on Astm A36 Steel From Smaw Underwater Welding, International Journal of Civil Engineering and Technology, 9(12), 2018, pp editor@iaeme.com

2 Herman Pratikno, Wimala Lalitya Dhanistha and Achmad Rifqy Ramadhan 1. INTRODUCTION During the operation of marine building infrastructure cannot be separated from the damage in it. These damages arise due to several causes such as cyclic loads such as waves, currents, and winds, as well as accidental loads such as collisions, material fall, and anchor collisions, as well as damage caused by corrosion. Handling damages such as cracks on ships, offshore platforms, and subsea pipes can be prevented and handled by welding methods, and one of the methods used is underwater welding. Underwater welding allows for easy and does not require a long time, which has the purpose of preventing the propagation of crack into larger ones which will result in leakage or failure [1]. The most common type of welding is Shielded Metal Arc Welding (SMAW). SMAW is chosen because the equipment used is simple, cheap, and easy to move. This welding method has a high cooling rate resulting in mechanical properties such as more brittle weld metal and Heat Affected Zone (HAZ), reduced ductility, and increased porosity [2]. Research on underwater welding has been carried out by previous researchers, such as Nizar's research on the variations of AWS E6013, AWS E6019, and AWS E7018 electrodes which can be concluded that the AWS E6013 and AWS E6019 electrode types meet the tensile testing standards. The Hadiwianata research [1], on the variation of three different heat inputs with the conclusion of greater heat input in the underwater welding process, will result in specimens having higher hardness and corrosion rate. Electrode selection and precise heat input are taken into account in order to provide maximum results from welding. With that, the author tries to provide more complex problems with variations of electrodes and heat input. Variations of electrodes used are based on the conclusion [3] ie AWS E6013 and AWS E6019. In addition, there are variations of heat input of 0.65 kj/mm and 1 kj/mm. Tests conducted on this research are testing of tensile strength, metallography and corrosion rate prediction. 2. BASIC THEORY 2.1. SMAW Wet Welding SMAW welding is commonly referred to as arc welding or sticks welding [4]. In SMAW wet welding, there are some modifications in the welding equipment. Among them the power supply is placed on the surface of water where power is channeled through cables and hoses. The power supply should be grounded on the ship. The current used is DC current with the -ve polarity. Knife switches on the electrode circuit should be able to disconnect any power supply at any time if needed. Welding machine generator is welding machine most often used in wet welding. Holding electrode is also designed with additional protection in this welding process [5]. Figure 1. SMAW Wet Welding Scheme [6] editor@iaeme.com

3 Analysis Metallography and Corrosion Rate Prediction on Astm A36 Steel From Smaw Underwater Welding 2.2. Tensile Strength Testing Tensile Testing is a method used to test the strength of a material by providing an axial force or voltage load [9]. The mathematical testing of tensile stress can be written as follows [7]. = Where: σ = stress (N/mm 2 ) P = load (N) A0 = First cross sectional area (mm 2 ) (2) 2.3. Metallography Testing Metallography is the study of physical structures and metal components to know the approximate physical properties by recognizing the special features of its microstructure or the characterization of the material [10]. The microstructural characteristics of a metal and its alloys are closely related to the mechanical properties they possess. Based on the observation of this microstructure will be known morphology and phases formed on a metal and alloys. There are several methods used in metallographic testing such as: diffraction (X-ray, electron, and neuron), microscope (optical or electron), analysis (X-ray fluorescence and electron microprobe), and also streometric metallography Corrosion Rate Prediction The predicted rate of corrosion rate can be calculated by using Faraday equation as follows: = Where: CPR = corrosion rate (mmpy) K = value constants ( for mmpy) A = the atomic weight of corroded metal (gr/mol) I = current density (µa/cm 2 ) D = the density of corroded metal (gram/cm 3 ) N = the number of valence metal electrons is corroded The most commonly used method for knowing fast corrosion rate prediction is using the three-electrode cell method. The cell of three electrodes is based on the theory of Voltametri, Voltametri included in the category of electroanalysis methods used in the field of chemistry that is analytical and various processes in industrial activities. In Voltametri, information about an analysis component is obtained by measuring the current as a diverse potential [12]. Most of these methods control the potential (Volt) of the electrode in contact with the current measurement analysis component (Ampere) produced [13]. The method requiresthe following equipment 1. Working Electrode 2. Auxiliary/Counter Electrode 3. Reference Electrode 4. Potential Source 5. NOVA s Software (3) editor@iaeme.com

4 Herman Pratikno, Wimala Lalitya Dhanistha and Achmad Rifqy Ramadhan 3. RESULTS AND ANALYSIS 3.1. Tensile Strength Testing Testing of tensile strength in welding using AWS E6013 and AWS E6019 electrodes at 0.65 kj / mm heat input having success value of 243 MPa and 256 MPa, respectively, and 337 MPa and 373 MPa ultimate strength values concluded that the welding did not meet the criteria because its tensile strength is smaller than the minimum tensile strength of ASTM A36 steel material of 250 MPa for yield strength and 400 MPa for ultimate strength. The yield strength and ultimate strength tensile strength criteria both must meet from the minimum tensile strength of ASTM A36 steel, if only one of the criteria meets the result of tensile strength is considered not to meet the criteria. As an example of this research on welding electrode AWS 6019 heat input 0.65 kj/mm, although yield strength criteria are met while ultimate strength does not meet the result of tensile strength does not meet the criteria. In addition, welding using AWS E6013 and AWS E6019 electrodes at 0.65 kj/mm heat input both have a breaking point area in weld metal, this means that they do not meet the criteria given, since the acceptable breaking point area must be in the base metal area. On the other hand, welding using AWS E6013 and AWS E6019 electrodes at 1 kj/mm heat input concluded to meet the criteria because they have a yield strength strength & ultimate strength greater than 5% of the minimum tensile strength of ASTM A36 steel having a successive yield strength value 325 MPa and 338 MPa and the ultimate strength value of 443 MPa and 448 MPa. In addition, the breaking point area of the heat input occurs on the base metal. Tensile strength of underwater welding using AWS E6013 electrode obtained in this study is smaller when compared with AWS E6019 electrode. This is because the welding results of AWS E6019 electrode has a good penetration when compared with AWS E6013. On the other hand, the influence of heat input also greatly influence from the results of this study which where the greater heat input will result in greater tensile strength as well. The variation of heat input obtained in this research is more emphasis on the size of the selected electric current, the variations of 60 A and 90 A. The use of large electrical currents then the molten metal carries will be fine, while the use of electric current is small then the metal grain will be the greater it is. The smoother grain of metal that is carried away will give the value of greater tensile strength as well. Figure 2. Tensile Strength Result of Electrode and Heat Input Variations editor@iaeme.com

5 Analysis Metallography and Corrosion Rate Prediction on Astm A36 Steel From Smaw Underwater Welding 3.2. Metallography Testing Macro Structure In the photo of the macro structural specimen the highest HAZ area is obtained by welding using AWS E6019 with 1 kj/mm heat input of 3.22 mm. while other welding with AWS E6013 heat input 1 kj/mm electrode AWS E6019 heat input 0.65 kj/mm, AWS E6013 heat input 0.65 kj/mm AWS 0.75 mm, 1.62 mm, and 1.42 mm respectively. Giving a larger heat input, it will result in smoother metal granules obtained from the electrode. Smooth metal granules will be easier to provide significant heat disorders in the weld metal region so that the HAZ area obtained will give greater results as well. Table 1. Length of HAZ Region Information Length of HAZ Region (mm) AWS E6013 Heat Input 0.65 kj/mm 1.42 AWS E6013 Heat Input 1 kj/mm 1.75 AWS E6019 Heat Input 0.65 kj/mm 1.62 AWS E6019 Heat Input 1 kj/mm Micro Structure In welding using AWS E6013 and AWS E6019, it was found that the larger heat input given was directly proportional to the decrease in ferrite composition and increased pearlite composition in the microstructure. Based on the Continuous Cooling Transformation (CCT) Diagram, the welding microstructure occurs due to the change of cooling rate, which means the cooling time of the austenite temperature decreases, the final structure changes from the ferrite-perlite mixture to the martensite-ferrite-biteite-ferrite, ferrite-bainite-martensite, bainite-martensite and finally at a very high speed then the final structure is mantensit. Underwater welding will form a martensite phase in the HAZ area. This can happen because in the weld metal region there is a phase change from austenite to ferrite and pearlite whereas in HAZ area there is austenite phase change to martensite. At the phase change in the weld metal region, hydrogen moves toward the HAZ region because in the weld metal region the austenite phase cannot absorb hydrogen and hydrolyzed solvents in the ferrite phase [20]. In the results of this study, the microstructure of the base metal region consists of ferrite and slightly pearlite so that it can be said that this area has soft characteristics, easy bending, high ductility, but its tensile strength is relatively low. In the HAZ region, the microstructure held consists of ferrite, martensite and pearlite are balanced. So the characteristic obtained is that its tensile strength is lower than the base metal area, but has a brittle nature. While in the weld metal region, the micro structure consists of ferrite and pearlite are almost the same. So the characteristics possessed are among those having the strongest tensile strength but lesser opacity than HAZ. In micro welding structure AWS E6019 heat input 1 kj/mm has the smallest percentage of ferrite weld metal by 51%. With this result, it is concluded that this weld has the strongest tensile strength when compared with other welds. Judging from the sequence of ferrite percentage decrease on base metal to weld metal region are AWS E6013 heat input 1 kj/mm, AWS E6019 heat input 0.65 kj/mm, and AWS E6013 heat input 0.65 kj/mm, respectively. The results of microstructure to electrode and heat input can be seen the figure and table below editor@iaeme.com

6 Herman Pratikno, Wimala Lalitya Dhanistha and Achmad Rifqy Ramadhan Figure 3. AWS E6013 Heat Input 0.65 kj/mm Figure 4. AWS E6013 Heat Input 1 kj/mm Figure 5. AWS E6019 Heat Input 0.65 kj/mm AWS E6013 Heat Input 0.65 KJ/mm AWS E6013 Heat Input 1 KJ/mm AWS E6019 Heat Input 0.65 KJ/mm AWS E6019 Heat Input 1 KJ/mm Figure 6. AWS E6019 Heat Input 1 kj/mm Table 2. Percentage of Micro Structure Base Metal HAZ WM PearliteFerritePearliteMartensiteFerrite PearliteFerrite 24 % 76 % 31 % 36 % 33 % 45 % 56 % 25 % 75 % 30 % 34 % 36 % 48 % 52 % 27 % 73 % 31 % 35 % 34 % 46 % 54 % 26 % 74 % 32 % 33 % 35 % 49 % 51 % 3.3. Corrosion Rate Prediction In the calculation of the predicted corrosion rate based on Equation (3) which states that the current density (icorr) is directly proportional to the predicted rate of corrosion rate that will be obtained. The smaller the corrosion rate value of a material, the better the corrosion resistance properties [21]. The classification of corrosion resistance properties found in this study can be seen in Table editor@iaeme.com

7 Analysis Metallography and Corrosion Rate Prediction on Astm A36 Steel From Smaw Underwater Welding Tabel 3. Corrosion Resistance Value [21] Relative Approximate Metric Equivalent Corrosion Resistence mpy mm/year µm/year nm/year pm/sec Outstranding < 1 < 0.02 < 25 < 2 < 1 Excellent Good Fair Poor Unacceptable > 200 > 5 > 5000 > 500 > 200 Based on Table 3, it was concluded that the welding result using AWS E6019 electrode with 1 kj / mm heat input having a good value of mmpy. AWS E6019 heat input 0.65 kj / mm and AWS E6013 heat input 0.65 kj / mm has a value of mmpy and mmpy respectively with fair (fair) katerogi. Meanwhile, welding with AWS E6019 electrode with 1 kj / mm heat input has a value of mmpy with poor category which in this category should be avoided in SMAW underwater wet welding welding. The corrosion rate of AWS E6019 electrode has a low value when compared with AWS E6013 electrode. This is because the flux content of the electrode owned AWS E6019 is a kind of Iron oxide titania potassium, while the AWS E6013 electrode is a kind of high titania potassium. Iron oxide titania potassium is a potassium titania mixed with iron oxide content, where iron oxide is a compound that has a stable bond so it is not easily corroded. Basically, metal-oxide bonds are formed by the electronegativity of oxygen which is very easy to bind metals such as iron, resulting in a strong and stable bond. Iron oxide layer in iron oxide titania potassium is what increases the resistance of the weld area due to corrosion. The effect of heat input on corrosion rate prediction is found to be inversely related. On the use of electrode AWS E6013 the greater the given heat input, it will increase the value of its corrosion rate. This is shown from the potential value (Ecorr) obtained. The more negative the potential value (Ecorr) of metal, the metal will become increasingly strong reducing agents or the more susceptible to oxidation reactions. Thus, the easier the metal undergoes an oxidation reaction the easier it is to corrode. In other results, with the use of electrode AWS E6019 concluded that the greater heat input given it will reduce the value of corrosion rate obtained. This is because, the potential value (Ecorr) obtained tends to decrease when the heat input is added. When compared with AWS E6013 electrode welding, the potential value (Ecorr) on AWS E6019 tends to have a larger value but has a smaller current density value (icorr). The current density (icorr) which tends to be small in AWS E6019 is caused because the flux layer on this electrode has a corrosion-resistant iron oxide coating editor@iaeme.com

8 Herman Pratikno, Wimala Lalitya Dhanistha and Achmad Rifqy Ramadhan Table 4. Corrosion Rate Predictions Information AWS E6013 Heat Input 0.65 kj/mm AWS E6013 Heat Input 1 kj/mm AWS E6019 Heat Input 0.65 kj/mm AWS E6019 Heat Input 1 kj/mm E corr (mv) i corr (µa/cm²) Corrosion rate (mmpy) CONCLUSIONS Tensile strength test on welding using AWS E6013 and AWS E6019 electrodes at heat input 0.65 kj / mm successively has yield strength value 243 MPa and 256 MPa and ultimate strength 337 MPa and 373 Mpa. On the other hand, Welding uses AWS E6013 and AWS E6019 electrodes at 1 kj / mm heat input respectively 325 MPa and 338 MPa and 443 MPa and 448 MPa ultimate strength values. In metallography testing, photographs of the highest macro-structural specimens of the highest HAZ areas obtained were on welding using AWS E6019 with 1 kj / mm heat input of 3.22 mm. while other welding electrodes AWS E6013 heat input 1 kj / mm, AWS electrode E6019 heat input 0.65 kj / mm, AWS E6013 heat input 0.65 kj / mm console 1.75 mm, 1.62 mm, and 1.42 mm respectively. While the photo of AWS E6019 microstructure specimen with 1 kj / mm heat input has the smallest ferrite percentage and the largest pearlite which has the strongest tensile strength characteristic. In the prediction of corrosion rate, welding results using AWS E6019 electrode with 1 kj / mm heat input which has a value of mmpy is categorized good. AWS E6019 heat input 0.65 kj / mm and AWS E6013 heat input 0.65 kj / mm has a value of mmpy and mmpy respectively with fair. Meanwhile, welding with AWS E6019 electrodes with 1 kj / mm heat input has a value of mmpy with poor category. REFERENCES [1] Hadiwianata, A. Y.: Analysis of mechanical properties and corrosion resistance in marine environment Of Material Carbon Steel ASTM A131 Grade AH 36 At Underwater Welding. Final Project. Departement of Ocean Engineering, ITS, Surabaya, Indonesia, 2017 [2] Khotasa, M. S. A. : Analysis of Influence of Flow Variation and camp shapes on SMAW Welding on Impact Strength of Butt Joint Connection On A36 Steel Plate Final Project. Departement of Ocean Engineering, ITS, Surabaya, Indonesia, 2016 [3] Nizar, H. : Analysis of Mechanical Properties and Micro Structures of Underwater Welding Results with Variations of Electrode Type on ASTM Material A36. Final Project. Departement of Ocean Engineering, ITS, Surabaya, Indonesia, editor@iaeme.com

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