Welding Quality And Sustainability Of Alternative LPG .

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Songklanakarin J. Sci. Technol.41 (5), 1146-1153, Sep. – Oct. 2019Original ArticleWelding quality and sustainability of alternativeLPG valve boss welding processesThiensak Chucheep1, 2*, Noppadol Thangwichien3, Narissara Mahathaninwong1, 2,Somjai Janudom2, 4, and Chaowana Yirong11 Facultyof Science and Industrial Technology,Prince of Songkla University, Surat Thani Campus, Mueang, Surat Thani, 84000 Thailand2 Centerof Excellence in Materials Engineering, Faculty of Engineering,Prince of Songkla University, Hat Yai, Songkhla, 90112 Thailand3 Facultyof Science and Industrial Technology,Prince of Songkla University, Surat Thani Campus, Mueang, Surat Thani, 84000 Thailand4 Departmentof Mining and Materials Engineering, Faculty of Engineering,Prince of Songkla University, Hat Yai, Songkhla, 90112 ThailandReceived: 18 January 2018; Revised: 24 May 2018; Accepted: 16 June 2018AbstractThis work aimed to evaluate the welding quality and the sustainability of an automatic metal active gas with mixinggases (MAG-M) process for welding the valve boss on liquefied petroleum gas (LPG) upper cylinder half, in comparison to thepresently used automatic submerged arc welding (SAW) process. The weld quality of MAG-M welding samples met the ASMEstandards, comparably to the SAW welding samples. In addition, the MAG-M welding process for welding LPG valve bosses ispreferable over the SAW welding process on the condition that 73,339 pieces are processed. However, the welding fumes andnoises from this process have stronger environmental and social effects than those from SAW welding. Besides, the SAWprocess is preferable in LPG valve boss production up to 73,339 pieces. The solid waste or slag generated in this welding processshould be managed.Keywords: LPG valve boss, welding quality, MAG-M, SAW, sustainability1. IntroductionLiquefied petroleum gas (LPG) cylinder productionis composed of several sheet metal forming, surface treatmentand testing processes, and the processing starts with blanking,deep drawing and piercing, trimming and joggling. Thewelding is next operation for the valve boss, valve guard ring,*Corresponding authorEmail address: thiensak.c@psu.ac.thfoot ring and the two halves. The finished cylinder is then heattreated, tested, shot blasted, and painted. The valve boss isattached before final testing (Repkon Company, 2017).Normally, submerged arc welding and Metal Inert Gas (MIG)/Metal Active Gas (MAG) welding techniques are applied forjoining the parts of LPG cylinders (Repkon Company, 2017;Sahamitr Pressure Container Public Company Limited[SMPCPLC], 2017).Submerged arc welding (SAW) is a process thatmelts and joins metals by heating with an arc establishedbetween a consumable wire electrode and the metals (Kou,2002). It is a fusion welding process in which heat is produced

T. Chucheep et al. / Songklanakarin J. Sci. Technol. 41 (5), 1146-1153, 2019by maintaining an arc between the workpiece and thecontinuously fed filler wire electrode. SAW process employs acontinuous bare electrode wire in solid form and a blanket ofpowder flux. The flux amount is of sufficient depth tosubmerge completely the arc column, so that there is nospatter or smoke and the weld is shielded from theatmospheric gases (Rajput, 2007). However, the quantity ofslag produced during the SAW process is very high. It is nonbiodegradable, thus causing environmental pollution. Treatingwaste slags may be done with a novel technology forrecycling, as reported by Garg and Singh (2016). In the LPGcylinder production, the SAW welding process is applied towelding the body halves on the seam welding machine, andgenerally to welding of the valve boss to the upper cylinderhalf (Repkon Company, 2017; SMPCPLC, 2017), with slagwaste as a crucial problem that demands solutions.MIG welding is an alternative welding processwithout slag waste. The MIG process melts and joins metalsby heating them with an established arc between acontinuously fed filler wire electrode and the metals, with theshielding provided externally by flow of an inert gas (Argon).When an active gas is used this is known as MAG welding. Asa further distinct alternative, MAG-M welding uses argonbased gas mixed with active gases such as CO2 or O2. Inaddition, the MIG welding process has been conventionallyapplied to welding the foot rings and valve guard rings withthe body halves, in gas container manufacturing (RepkonCompany, 2017). It was also recommended for welding thevalve bosses (World LP Gas Association [WLPGA], 2013).Therefore, workers are familiar with this welding process.Nowadays all commercial metals and alloys can be welded inall positions with the MIG welding process by choosingappropriate process parameters for the particular joint designand process variables. However, MIG welding may producespatter and fumes.Typically, the weld quality of welded specimens hasbeen primarily assessed to help select a welding process.Macrostructures, microstructures and mechanical properties ofwelding joints are characterized (Fang et al., 2013). Holuba,Dunovskýb, Kovandac and Kolaříkd (2015) assess thewelding quality based on EN ISO 5817 in the quality level"B".Nevertheless, sustainable manufacturing hasglobally become a goal for governments and industries. Changet al. (2015) stated that sustainability is composed ofeconomic, environmental, and social dimensions. The miningand minerals industry is primary interested in threedimensions of sustainability issues (Azapagic, 2004). In thepast, technologic and economic indicators were thedominating criteria for process selection, while environmentalor social issues were mostly neglected in decisions. Sproesseret al. (2016) considered sustainable welding with regard toeconomic and environmental dimensions. Choi, Kaebernickand Lai (1997) also considered the environmental impactassessment of toy train manufacturing. Regarding the socialdimension, Chang et al. (2015) focused on two critical socialconditions, namely ‘fair salary’ and ‘health and safety’ forwelders as the stakeholders, and compared manual andautomatic MIG welding processes. Alkahla and Pervaiz(2017) characterize three dimensions of sustainability for theSMAW process. They found that 80 – 85% of the overall costin welding operation is related to labor and other overhead,1147while fume inhalation by the welder is among the major healthhazards present in the SMAW operation. The environmentalaspects focused on energy consumption.The SAW process has been conventional in weldingthe LPG valve boss to the upper cylinder half. This processgenerates slag, which negatively impacts the environment.The alternative MAG-M welding process is interestingbecause the workers are familiar with it; it is already used toweld the LPG valve guard and the foot ring. However, acomparison between MAG-M and SAW welding processesfor the welding of LPG valve boss has not been performed sofar, for sustainable process selection. Therefore, this studyevaluates the MAG-M process in a case study (welding thevalve boss to the upper cylinder half) in comparison totraditional SAW welding. The weld quality of welded piecesis the first priority. Sustainability in terms of cost,environmental, and social dimensions is also considered.2. Experimental Procedure2.1. Weld qualityFillet welding of the valve boss to the upper cylinderhaft is investigated, and the welding parameters in both MAGM and SAW welding processes are shown in Table 1. Bothwelding processes are automated.Visual inspection, microstructure, hardness test, andradiographic test are used to assess the weld quality of weldedspecimens. Micro-hardness test was conducted with a Vickersmicro-hardness tester (Eseway 400D series), which used 2 kgfload for 10 s loading time.Iridium 192 source was used in radiography. Thedistance between the X-ray emitter of radiographic testing(RT) and weld sample was maintained at 1 m. The exposuretime was 30 min and the resonance signal was 740 mR/hour.2.2 Sustainability considerationsSustainability was considered in three dimensions,namely cost, environmental, and social. Welding costs foreach welding process included fixed and variable costs. Fixescosts were composed of annual welding equipment costs, andvariable costs were the operating costs. In this work, the weldcircumferential length was 138 mm per valve boss piece. Theoperating costs were calculated by a simple approach, usingtraditional formulae:Electric power (THB.) : (I V Pe t N)/(103 3,600)(1)Wire Electrode (THB.) : t N Fw Ww Pw(2)Flux. (THB.) : t N Ff Wf Pf(3)Shielding gas. (THB.) : t N Vg Pg(4)Slag Elimination (THB): Sl El(5)Spatter Elimination(THB): Sp Ep(6)Total operating cost (mp) : (1) (2) (3) (4) (5) (6)where np is equipment cost (THB), ts is service life (10 years),CRF is capital recovery fund (0.1457 for the interest of 7.5%

T. Chucheep et al. / Songklanakarin J. Sci. Technol. 41 (5), 1146-1153, 20191148Table 1.Welding parametersMAG-MBasic DataFillet weldBase materialWire electrode typeType of shielding gas and Flow rates (L/Min.)Type of FluxChemical composition of flux(%wt)Process ParameterAverage welding speed (cm/min)Number of passesAngle of welding (Degrees)VoltsAmperesPolarityWire electrode dimension (mm.)Wire electrode speed (m/min)Valve boss to the upper cylinder haft- SG 295 JIS G3116 Gas Cylinder HotRolled 2.00-2.20 mm. Thick- S20C JIS G4051 Carbon steels for machinestructural use.AWS. A 5.18 ER 70-S660 % Ar : 40 % CO2 (20)-Valve boss to the upper cylinder haft- SG 295 JIS G3116 Gas Cylinder HotRolled 2.00-2.20 mm. Thick- S20C JIS G4051 Carbon steels formachine structural use.AWS. A 5.18 ER 70-S6AWS A 5.17 F7A2-EM12K24(Al2O3 MnO2), 32(CaO MgO), 25(SiO2 TiO2)3814026185DCEP.1.285624528200DCEP.1.24and service life of 10 years), Fw is feed rate of wire electrode(mm/s), Ww is mass per length of wire electrode (kg/mm), Ffis feed rate of flux (mm/s), Wf is mass per length of flux(kg/mm), Pg is gas cost (THB/m3), t is welding time (s/pass),N is number of welding passes (pass/piece), Vg is gas flow(l/min), I is welding current (A), V is welding voltage (V), Pwis wire electrode cost (THB/kg); Pf is flux cost (THB/kg), andPe is electric power cost (THB/kWh), Sl is the quantity of slag(kg/piece), Sp is the quantity of sputtering (kg/piece), El is slagelimination cost (THB/kg), and Ep is spattering eliminationcost (THB/kg). The weld circumferential length was 138 mmper valve boss piece.The total annual cost with respect to weldingprocess p and welding quantity q is given by equation.Total annual cost (p) mpq npSAW(7)The intercept np represents annual equipment cost(fixed cost) of the considered welding process p. The slope mpcorresponds to total operating cost (variable cost). Thebreakeven point is at the intersection of such straight lines forthe two welding processes compared.Environmental issues are considered as in Choi etal. (1997). The energy consumption, solid waste (slag), and airemissions (fumes) generated by each welding process arecalculated with the formula (8) for energy consumption (kWhper day), (9) for solid waste (kg per day), and (10) for airemissions (mg per day);IV (kW/machine) t Nm(8)S P(9)targets are 5 and 6 for MAG-M and SAW welding processes,respectively. The energy consumption is only calculated fromwelding operation, excluding warm-up of welding machine.Solid waste (S) focuses on slag generated in kg per piece. Inaddition, air emissions (A) generated in the form of fumes areset at 13.5 mg/s and 0.5 mg/s for MAG-M and SAW weldingprocesses (Spiegel-Ciobanu, 2012), respectively. The noiseestimate is obtained by reference to the data of Čudina,Prezelj, and Polajnar, (2008), Horvat, Prezelj, Polajnar, andČudina, (2011), and Smagowska, (2013).The social dimension is considered in terms of thehealth risk (GZ) from welding fumes to welders for the MAGM and SAW welding processes, based on literature references(Chang et al., 2015; Spiegel-Cibanu, 2012). The followingequation is used for assessment of the potential health risk(GZ) (Chang et al., 2015).GZ (EpxWp)xLxRxKb(11)where Ep means emission of specific substance per functionalunit, Wp is potential effect for specific substances in fume, Lis ventilation factor (based on sufficient ventilation or not), Ris spatial factor (outside or in rooms) and Kb is the factor ofrelative distance of head/body and fume source.The current study did not measure fume and noise inthe factory, instead prior reports are referred to as regardsthese. This is a scope limitation of the current study.3. Results and Discussion3.1 Weld quality3.1.1 Weld bead inspectionsA t x60x60 Nm(10)The calculation is based on targeted production P 10,500 pieces/day and Operating time t 22 hr/day. Thenumbers of welding machines (Nm) based on the productionFigure 1 shows the appearances of representativebeads. The regular bead form the MAG-M welding process isshown in Figure 1(a). The SAW process also produced asmooth, regular, and well-formed bead, shown in Figure 1(b).

T. Chucheep et al. / Songklanakarin J. Sci. Technol. 41 (5), 1146-1153, 2019Table 3.Figure 1. Bead appearances of (a) MAG-M (b) SAW weldingsamples, and cross-sections of fillet welding by (c) MAGM (d) SAW.There were no cracks on the bead surfaces in either case, butspatters were seen on MAG-M welding samples. Thesubjective appearance of the weld bead made with the SAWprocess is better than from the MAG-M process. The macrocross-sections in Figure 1(c)-(d) provide a clearer direct viewof the shapes of weld beads. The surfaces of the beads areslightly concave in the MAG-M welded sample (Figure 1(c))and clearly concave in the SAW sample (Figure 1(d)). Thethroat and leg sizes of the weld beads are shown in Table 2,and they comply with the ASME standards (The AmericanSociety of Mechanical Engineers [ASME], 2010).Table 2.Leg and throat sizes of weld beadsWelding processLeg 1 (mm)Leg 2 (mm)Throat (mm)MAG-MSAW7.44 0.227.50 0.207.28 0.337.33 0.295.57 0.404.84 0.32From inspections of the visual and macro-crosssection we can evaluate the quality of each weld bead, usingthe checklist of Table 3.By this examination, the weld quality of testsamples on using the SAW welding process is better than thatfrom the MAG-M process. However, the welded samplesfrom the MAG-M process are acceptable by the ASMEstandards (ASME, 2010). The acceptance criteria of thestandard are complete fusion and freedom from cracks inHAZ, with linear indentations at the root not exceeding 1/32in (0.8 mm). The concavity or convexity should not exceed1/16 in (1.5 mm) and the difference in the lengths of the legsof the fillet should not exceed 1/8 in (3 mm).On the other hand, metal spatter was generated by the MAGM welding on the joint surfaces (pointed out by a blackarrow), as shown in Figure 1(a). Welding technicians of thefactory had accepted these metal spatters because these couldbe scraped off. If the metal spatters would require cleaning offwith a grinder, the welding technicians would not accept thewelding method. Welding spatters deteriorated the weldbead appearance when the CO2 content was higher than1149Inspection checklistDefect typeSAW1. Cracks (Longitudinal or Transverse)2. Incomplete Fusion3. Incomplete Joint Penetration4. Irregular bead profile5. Overlap (Roll Over/Cold Roll)6. Slag Inclusion7. Surface Porosity8. Undercut9. Spatter10. Fillet Weld Leg is Undersized11. Fillet Welds oAcceptedNoYes20% (Zong, Chen, Wu, & Kumar, 2016). Carbon and lowalloy steels are often welded with CO2 as the shielding gas,the advantages being high welding speed, good penetration,and low cost. However, CO2 shielding produces a high levelof spatter, so a relatively low voltage is used to maintain ashort buried arc to minimize spatter (Kou, 2002).3.1.2 MicrostructuresThe locations of microstructure examination areshown in Figure 2(a). The microstructure examinations ofbase meatal (BM) for upper cylinder haft and valve boss basemetals are at locations number 1 and 10, respectively. Thelocations 5 and 8 are for heat affected zone (HAZ), and weldmetal (WM) examinations, respectively. Various micro-phasesare observed in the different zones. The BM is characterizedto be ferrite phase in the light areas and pearlite (P) in the darkareas, as shown in Figure 2(b)-(c).The HAZ of MAG-M welded samples was mainlycomposed of bainite (B), acicular ferrite (AF), and grainboundary ferrite (GBF), seen in Figures 2(d). Small amountsof widmanstatten ferrite (WF) were also observed in the HAZ.It is rather difficult to specify regarding these morphologies,which of the AF, B, and WF structures would be similar tothose in the reports of Ghomashchi, Costin and Kurji (2015)and Zhang et al. (2016). The microstructure in the HAZ ofSAW welded specimens (Figures 2(e)) was different from thatin MAG-M welded specimens. The microstructure in HAZ ofSAW welded samples was mainly composed of coarserwidmanstatten ferrite (WF) and pearlite. The WM of bothwelded samples contains polygonal ferrite (PF), grainboundary ferrite (GBF), widmanstatten ferrite (WF), andacicular ferrite (AF), as shown in Figure 2(f) and 2(g). Inaddition, AF and GBF of SAW welded specimens were alsocoarser than in the MAG-M welded specimens, which isrelated to the high heat input according to Liu et al. (2017).Microstructure transformations normally caused byelevated temperature depend also on exposure time, coolingrate, and chemical composition. Welding parameters are veryimportant to control the obtained microstructures. In thepresent work, welding parameters used in the SAW processare different from those in the MAG-M welding process,particularly as regards welding current, voltage, speed, andpass. These parameters affected the heat transfer to thewelding samples. Liu et al. (2017) showed that the high heatinput of vertical electro-gas welding (VEGW) produced

1150T. Chucheep et al. / Songklanakarin J. Sci. Technol. 41 (5), 1146-1153, 2019Figure 2. (a) locations of microstructure examination and hardness test, BM of (b) valve boss, and (c) upper cylinder half, HAZ of (d) MAG-M(e) SAW, and WM of (f) MAG-M (g) SAW.coarser microstructure than that in a SAW joint. Zhang et al.(2016) also reported that the size of GBF and WF increasedwith temperature. Moreover, heat input increases when thenumber of welding passes is increased. If the SAW joint weldsin one pass, the heat input to the SAW joint will be lower thanthat in one welding pass of MAG-M joint. However, thehigher heat input of SAW joint with two passes implies thatSAW welded samples had higher temperatures during weldingthan those in MAG-M joints with only one pass, leading tocoarser microstructure in the HAZ zone.In addition, the SAW weld is shielded by flux, whilethe MAG-M process is operated under shielding gas. The fluxacts as a thermal insulator and promotes deep penetration ofthe heat, preventing spatter and sparks. Besides, the chemicalcomposition of flux affects microstructures of weldingsamples. An increase in weld Mn content from the fluxpromotes the formation of fine-grained structure (Singh,Khan, Siddiquee, & Maheshwari, 2016). Ti content in flux ofSAW joint plays a very important role for the heterogeneousnucleation of acicular ferrite (Paniagua-Mercadoa, LopezHirataa, Dorantes-Rosalesa, Diazb, & Valdez, 2009). In thecase of MAG-M process, shielding gases are primarily utilizedfor molten pool protection against atmospheric gas and playan important role in determining weld penetration profiles,helping to maintain arc stability.3.1.3 Hardness testThe locations of hardness test profiles are shown inFigure 2(a). Typical micro-hardness profiles of MAG-M andSAW welding samples are shown in Figure 3. The averagehardness of HAZ and WM zones are very closely similar forthe two types of weld joints. This result does not agree withthe previous study of Gowrisankar, Bhaduri, Seetharaman,Verma and Achar (1987). They found that hardness of thewelds increased with the n

Welding quality and sustainability of alternative . between a consumable wire electrode and the metals (Kou, 2002). It is a fusion welding process in which heat is produced . The energy consumption is only calculated from welding operation, excluding warm-up of welding machine. Solid waste (S) focuses on slag generated in kg per piece. .

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