An Experimental Investigation of Welding Defects in Shielded Metal Arc Welding

Transcription

1 An Experimental Investigation of Welding Defects in Shielded Metal Arc Welding Prakash.M *, Parameshwaran.k, Robert Hentry.A, Prithivraj.T, Abstract: Modern welding technology started just before the end of the 19th century. There are several types of welding methods are possible to perform the operation such as Flux cored arc welding, shielded metal arc welding, submerged arc welding, Gas metal arc wel ding, electro slag welding, electron beam welding, and Gas Tungsten arc welding methods. The option of the welding depends upon various factors. In this present work, when using the SMAW by the electrode E6018 having more defects in the existing welded product. The defects are concluded by the NDT test methods. These major defects are coming from unmatched welding components and its composition. So that changing some components and it s specification we may reduce major defects in welding. That component and specifications are such as electrode, electrode size, current and voltage. In this way we use correct specifications in welding for using that work piece material (carbon steel). Keywords: SMAW, Defects, NDT & Carbon steel. S 1.0 INTRODUCTION hielded metal arc welding was introduced in Russia in Shielded metal arc welding is one of the famous welding process dominates other welding processes. The another name of the Shielded metal arc welding (SMAW) is also known as flux shielded arc welding or manual metal arc welding. An electric current from a welding power supply is used to provide an electric arc between electrode and the metalwork piece to be joined. The shielded metal arc welding consists of welding power supply and an electrode with an electrode holder, a ground clamp, welding cables. The SMAW process use different types of polarity, which depends primarily upon the electrode being used, and the desired properties of the weld. Direct current with a negatively charged electrode causes heat produced on the electrode. It will increase the electrodemelting rate and decreasing the depth of the weld. When reversing the polarity the electrode is positively charged (DCEP) and the work piece is a negatively charged increase the weld penetration. The shielded metal arc welding process consists of a stepdown transformer to reduce the voltage and increase the current and for direct current models a rectifier used which converts alternating current into direct current. 1.1 NonDestructive Testing Methods NDT used to reveal defects that would be difficult or impossible to detect by visual examination. The NDT techniques are used as a quality control tool to determine the quality of the work piece. NDT must take if disruption of production and delays to the program are to be avoided. It is important for NDT to be included in the planning of the fabrication process as it can require substantial time and resources Radiographic Examination In this present work, we have to use Radiographic examination method. Here Electromagnetic radiation has properties that are * Corresponding Author

2 useful for industrial radiography purposes. The radiographic rays are passed in straight lines and it should not be deflected or reflected by mirrors. The radiation, either Xrays from a suitable source or gamma rays from a radioactive isotope, is absorbed as it passes through the material. This absorption increases as the density of the material increases so that if a photographic film is placed on the side opposite the radiation source, any less dense areas will appear as darker areas on the film to give a shadow picture of the internal features of the test sample once the film has been processed. Thus, voids, porosity, slag, cracks and defects of geometry can identified, although planar defects normal to the beam may not be detected. To radiograph a welded joint a suitable source of radiation, a film in a lightproof cassette and some method of processing the film are required. This latter generally requires a dark room where the film can be developed, fixed, washed, dried and viewed. The radiation can be produced from an X ray tube, the energy generally being described by the voltage and current at which the tube is operated. These may vary from 20kV to 30MV and 10 to 30mA, although the normal limit for the commonly available industrial units is around 400kV. A 400kV unit is capable of penetrating up to 100mm of steel and 200mm of aluminium. Gamma radiation is produced by the decay of a naturally occurring or manufactured radioactive isotope. 2.0 EXPERIMENTAL SETUP 2.1 Specifications of Welding Material: Lowalloy steels behave essentially as plain carbon steels. Low carbon steels with less than 30% carbon. For carbon steel, designed area 3.3 to 4 kg/cm2 of the welding, including as much of the flash as is crushed. This margin must be increased to 4.2 kg/cm2 for 20% carbon steel. Good mechanical properties and weld performance for general fabrications. Electrode pass Single pass and high permissiveness to corrode and mill scale. Wire feed, Welding speed, Frequency, Heat input, Number of pass, Position are denoted in following table, Table 1: Weld pad designation before Modifications Name of the welding Shielded metal arc welding Carbon steel dimension in mm Electrode E6018 Filler wire dia in mm 3 Voltage in Volt 30 Mean current in Amp Electrode extension length in mm 15(constant) Wire feed in m/min 4.5 Welding speed in mm/sec 1.74 Back ground current Time sec 5 Frequency in Hz 60 Heat input in J/mm Number of pass 3 Position 2G Method Manual 3.0 FINISHED PRODUCT Fig.1: Experimental Setup Fig.2: finished product of before modification

3 4.0 AFTER CHANGING SMAW SPECIFICATIONS Table 2: Weld Pad Designations after Modifications Name of the welding dimension in mm Electrode Shielded metal arc welding Carbon steel E7018 Filler wire dia in mm 4 Voltage in Volt 25 Mean current in Amp Electrode extension length in mm 15(constant) Wire feed in m/min 4.0 Welding speed in mm/sec Back ground current Time sec 1.74 Frequency in Hz 60 Heat input in J/mm Number of pass 2 Position Method 5 5G Manual 4.1 Finished Product Of Modifications 5.0 TESTING RESULTS 5.1 Radiographic Examination Defect Name (Defects analysis) 1. Lack of side wall fusion 2. Lack of penetration 3. Burnthrough 4. Porosity 5. Crater 6. Crater cracking 7. Spatter 8. Under flushing 9. Solidification cracking 10.Incomplete fill concavity 5.2 Toughness Test SAMPLE (in joules) Changes Welded product I Welded product II Changes Corrosion Rate Measurement Slightly occur Table 3: Comparisons of Tafel Plot to and Changes for Weld Metal. For Weld Metal Cathodic Tafel slope Anodic Tafel slope Fig 3: Finished product of after modification Linear polarization,r Corrosion current(a) Corrosion rate (mil/year) Corrosion rate(angs/min)

4 5.4 Micro Hardness Survey Table 4: Micro Hardness Values S.No Change Change Rockwell Hardness Testing Minor Load : 10 kg Major Load : 150 kg Intender : Diamond Brahl Intender Table 5: Rockwell Hardness of Varies Regions in Weld Pad 8. Finishing product contains more time and cost. 6.2 Advantages of Modifications 1. Increase the tensile strength of the weld component. 2. Avoid unwanted defects. 3. Remove the major defects of before in welding processes. 4. Decrease the time of work. 5. Welding process timing also decreases. 6. E7018 electrode is used to 5G position 7. Low amount of slag is produce. 8. No, need extra process to get the existing product. 9. No need grinding process for surface finishing. Parameters 10. Increase the profit and decrease the power consumption. Weld metal center RC 16 RC 16 Fusion boundary RC 20 RC 23 HAZ RC 14 RC 11 Parent metal RC 12 RC DISCUSSIONS 6.1 Drawbacks of the Finished Component (Welded Component I): 1. Finished component has Low tensile strength, toughness and hardness. 2. Finished product contains more defects such as porosity and crack. 3. In E6018 electrode using only 2G positions. So that welding position also difficult. 4. Finishing work need for grinding process. 5. Slag removal also manual and difficult (Grinding). 6. So extra timing and money also need for grinding process, 7. Not easy to get finished product. 7.0 CONCLUSION 1. In some specifications of the Shielded Metal Arc Welding Process having more defects. 2. In this experimental analysis gives brief details about Shielded metal arc Welding Defects & analyzing the defects in different factors. 3. The Welded product I is using the electrode E6018 and various power source ranges. In this process is having causes many defects. 4. In order to minimize these defects, we have used to the electrode E7018 and changing the parameters. References [1] S.K.Albert, T.P.S. Gill, A.K.Tyagi, S.Dkulakrni and P.Rodriguez., 1997 weld.j, 135S142S. [2] A.Barens, 1995 'the influence of composition on micro structural development and toughness of modified 9cr1mo weld metals', REPORT 509/1995. [3] Gurpreet Singh Sidhu1, Sukhpal Singh Chatha2, (ISSN ) 2012 "Role of

5 Shielded Metal Arc Welding Consumables On Pipe Weld Joint". [4] Carl D.Lundin, Peng Liu And Yan Cui: a literature review on characteristics of high temperature ferritic crmo steels and weldments, WRC BULLETIN 454. [5] S.J.Sanderson, USA, , "mechanical properties and metallurgy of 9%cr 1%mo steel". [6] P.J.Ennis, ,1998, London, A.ZienlinskaLipiec And A.Czyrska Filemomowicz:"quantitative comparison of the microstructures of high chromium steels for advances power stations", [7] EvaLena Bergquist:'consumables and welding modified 9 cr1 mo steel'. ESAB AB, GOTEBORG, SWEDEN.