The Effect of Welding Pre Heating of SMAW and GTAW on Mechanical Properties of SA .106 Gr. B Pipe of Energi Sengkang Co.Ltd

This research aimed to analyze the differences in mechanical properties, such as tensile strength and hardness of the materials of SA.106 Gr B. experiencing SMAW and GTAW welding with preheat treatment. The research activities were conducted in the Laboratory of Materials Science of the Department of Mechanical Engineering, Faculty of Engineering, Indonesia Christian University of Paulus, Makassar. The material Preheating was done in the workshop of PT. Energi Sengkang. The method used was to create a specimen of the SA.106 Gr.B material experiencing the SMAW and GTAW welding with the preheat condition of 0°C, 110°C and 125°C. In order to determine the strength of the material, the mechanical test, i.e. the tensile test (ASTM E 8M), Hardness test (Brinneil), and microstructure observation were done. The research results indicated that preheat process had an influence on the mechanical properties of the material before welding. In the process of SMAW and GTAW welding, the increase of preheat temperature had an impact on the increase of the value of the tensile test of preheat temperature of 125°C. In the GTAW welding, it was found that σu = 54.51 kgf/mm, while in SMAW welding, it was found that σu = 53.26 kgf/mm 2 . In hardness test, it was found that the increase of the preheat temperature had an effect on the hardness in the welding area was 43.22 HB while in the GTAW welding it was 43.32 HB.


I. INTRUDUCTION
Welding is the process of switching metallic or nonmetallic performed by heating the material which combined to a temperature welding is performed with or without using pressure, with pressure or not with charger (filter). Conventional Welding divided into working groups, namely by way of welding : Liquid welding, press welding, solder welding and by source of energy used : Chemistry welding, electrical welding for example SMAW and GMAW, SMAW welding ( Shilel metal Arc Welding) or arc welding electrodes encased often called Electrical Welding. SMAW welding is the process of switching two metallic similar or more by using an electric heat source using electrodes that will make a fixed connection.
The Working principle is the current SMAW welding electrode tip is brought near the work piece heat is electric (arc) is made between the work piece with the electrode tip covered melt simultaneously. According to AWS (American Welding society) principle from SMAW is using heat from the arc to melt the base metals and the end of a consumable electrode covered with a voltage of electricity used 23-45 used, for melting up to 500 amperes of electric current that is commonly used ranged from 80-200 ampere. In the SMAW process of oxidation can occur, this need to be prevented due to the oxidation of metal is a compound that does not have the mechanical strength. As to prevent that the material is protected with a layer enhancer welding protective substance called flux or slag which participated melt when welding. However, the density is lighter than metal melted, the liquid flux will float in the liquid metal, and isolate the metal so that it does not oxidize with the outside air. When frozen, the flux will also freeze and still protect the metal from oxidation. The series begins with a power source and cables including welding, electrode holders, connection of the work piece, the work piece (well-meant), and welding electrodes. Advantages of arc welding processes SMAW is the simplest and most versatile, because it is simple and easy to transport tools and equipment to make this SMAW process has broad application, Las SMAW can be done at various positions or locations that can be reached with a piece of electrode.
Location of weld joints with limited eyesight area can still be welded by means of bending the electrode. SMAW welding is used for welding a wide range of ferrous metals. Disadvantages SMAW rate Charging more low than the process of welding semi-automatic, Long electrodes differences despite welding Stop ON welding SMAW taxable income Sycamore electrode Burned Out electrode The wasted Remaining And Time Also wasted to review replace the electrode, slag OR crust Yang formed must be removed from the skin thick layer of thick layers of weld skin BEFORE the next, Singer Steps Up Reduce welding coefficient Approximately 50%.
Preheat or pre-heating is done to prevent the occurrence of weld cracks, eliminating residual stress (residual stress), increased toughness and control of the metallurgical properties in the HAZ ( Heat Affected Zone). Preheating can be done with gas-Oksy flame, forging kitchen and oven. Preheating 274 temperature is determined by the carbon content of the parent metal and has developed a tool to measure temperature first heating by Lincoln Electric. Welding methods can also affect the quality of the weld. The method used must be in accordance with the needs of the construction. One method is welding Gas Tungsten Arc Welding (GTAW) or also called Tungsten Inert Gas (TIG). Welding is commonly used to connect carbon steel, stailess steel, copper and aluminum.
According Sudibyo and Purboputro (2013: 42), using the GTAW welding used to weld stainless steel. This is due to tungsten gas will displace the oxygen that would cause the metal oxide that results are very loud. This is due to tungsten gas will displace the oxygen that would cause the metal oxide that results are very loud. With GTAW, the metal oxide formation can be avoided. Metal welding methods which include welding procedures, heat treatment procedures, joint design and welding techniques adapted to the type of material, equipment and welding position when welding connection is made. Aspects of effectiveness, process efficiency, and economic considerations are closely related to the selection of welding equipment. Metal welding to connect materials of carbon steel, stainless steel, copper and aluminum will be good quality when using GTAW welding.

II. EXPERIMENT
Material The material used in this study is the carbon steel pipe steel (SA-106 GR.B) Outside shaped pipes with a diameter of 3.5 inch and Nominal Sch-80S. Materials cut using saws and grinding to form a V seam connection using Standard ASTM E 8M. Material before welded using GTAW and SMAW welding in hot beriperlakuan beginning first with the flame oksy-gas temperature 110ºC and 125ºC. Material that has been welded and then do day penetrant tested for surface defects of material that has been welded. Material that has been welded and then cut using saws and milling to form the test specimen according to standard ASTM E 8M.
The specimens used in this study, based on the following table:  Tensile test specimens refers to the size of the specimen square berpenampang using the standard ASTM E 8M. Based on these standards, the material forms a test for tensile testing must be adapted to the testing standards as shown below :

Analysis Testing of Tensile
Based on calculations that have been done, graphically results preheat treatment of SMAW welding is known as the graph in Figure 3.1. In the condition known that the process of increase the maximum preheat temperature result in increased tensile strength test specimens. On specimens without preheat treatment, known maximum tensile strength (σu) = 47.57 kgf/mm 2 , the specimen preheat 110 o C maximum strength of 49.02 kgf/mm 2 and at 125 o C preheat obtained the maximum strength of 53.26 kgf/mm 2 .

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In GTAW welding similar conditions showed that the preheat process resulted in the increased value of the tensile strength of the material. as in Figure 3.2 below.     Under the conditions of the test results table with 12 times the emphasis each specimen decreased hardness can be illustrated in the graph in Figure 3.3 below:

Welding GTAW
In GTAW welding preheat effect also impacts on the declining value of the material hardness in the weld metal, the HAZ area, while the value of hardness in the raw material tends to remain, as in the following tebel.  In both SMAW and GTAW welding process both decreased in terms of violence. The condition is caused by a slow cooling rate. The higher the temperature treatment is given, then the cooling process will be slower.

Analysis of Micro Structure
Based on observations on the microstructure known process changes that occur as a result of the welding preheat treatment SMAW is as follows.
By observe microstructure strength increase of the tensile strength and a decrease in the level of violence caused by the change in microstructure.

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In SMAW welding between the specimen without preheat the specimens preheat 125 o C as follows. From the results of the above observations (Fig 3.5), it appears that the composition of the ferrite on specimens without preheat treatment more and distributed in the appeal at 125 o C fewer specimens Preheat these conditions allows the hardness value decreases or lower at a higher preheat temperature. The condition is also greatly influenced by the amount of pearlite is more dominant with larger grains at 125 o C preheat treatment, in which the ferrite hardness values higher than pearlite.
In GTAW welding changes the microstructure in the weld metal can be observed as follows. Based on the observations above photo, from specimen to specimen without preheat to preheat at 125 o C temperature differences after the change. Ferrite composition of the specimen without preheat less. Compared with preheat specimens, while the composition is inversely proportional pearlite.
Changes in the microstructure because of a preheat temperature adjustment of the steel material SA 106 Gr. B to the welding temperature. At a constant temperature welding on the welding current 100 A specimen with a preheat of 125 °C will be more quickly adapted to the welding temperature. Such conditions affect the microstructure affects the mechanical properties of the steel SA 106 Gr. B

IV. CONCLUSION
From the research and analysis of testing and discussion of the data, it can be concluded preheat process influence on the mechanical properties of the material before welding. In the process SMAW and GTAW welding preheat temperature increase impact on the rising value of the tensile test at a temperature of 125 o C preheat. In GTAW welding obtained σu = 54.51 kgf/mm 2 , whereas the SMAW welding σu = 53.26 kgf/mm 2 . In testing the hardness increasing effect on the preheat temperature hardness value. The maximum value of hardness in the welding area of 43.22 HBN whereas GTAW welding of 43.32 HBN.