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ScienceDirect Procedia CIRP 48 (2016) 62 – 67
23rd CIRP Conference on Life Cycle Engineering
Life Cycle Assessment of Arc Welding and Gas Welding Processes K S Sangwan1*, Christoph Herrmann2 , Patricia Egede2, Vikrant Bhakar1, Jakob Singer2 2
1 Department of Mechanical Engineering, Birla institute of technology and science, Pilani, Rajasthan, India Institute for Machine Tools and Manufacturing Technology, Technical University of Braunschweig, Germany
* Corresponding author. Tel.: +911596515205; fax: +0-000-000-0000. E-mail address:
[email protected] i.ac.in
Abstract Welding is one of the important processes in most of the manufacturing process chains. In term of material and energy consumption, every welding process is different from each other and thus has different environmental impact. It is estimated that 0.5-1% of the consumables in arc welding are converted into particulate matter, gases and emissions. On global level, the pollutants relea sed through welding process are in tons and a large amount of energy is consumed for the same. This study attempts to evaluate the environmental impact generated due to welding for training purpose. Material and energy flow modeling is carried out using software Umberto NXT universal with database Eco-invent version 3.0. Impact assessment has been carried out using midpoint (CML 2001) and end-point (Impact 2002+) assessment methods. It has been found that in the production of machine/equipment (manufacturing phase) copper and mild steel are major polluter; mild steel is dominant polluter in the use phase; and copper is the major contributor in the end of life phase. This study recommends use of simulation during training for advanced learning technologies for different welding processes © 2016 The Authors. Published by Elsevier B.V. © 2016 The Authors. Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the scientific committee of the scientific committee of the 23rd CIRP Conference on Life Cycle (http://creativecommons.org/licenses/by-nc-nd/4.0/). Engineering. Peer-review under responsibility of the scientific committee of the 23rd CIRP Conference on Life Cycle Engineering Keywords: Welding process; Life cycle assessment; Environ ment impact; Energy consumption
1. Introduction Increasing environmental concerns has got the priority in process development and these practices are gaining priority in present era of environmental consciousness. Green product and process development is a step towards the sustainability and life cycle assessment (LCA) is a useful tool to assess the environmental impact of products and processes. LCA helps the decision makers to identify the hotspots and take appropriate steps. In the past, the term sustainability was mainly environmentally oriented, i.e. sustainability as the quality to sustain the environment. However, in current literature, sustainability is defined with three dimensions: environmental, social and economical sometimes adding a fourth one, technology. LCA studies for various products and processes have been carried out nowadays to achieve the goal of green and sustainable production [1][2][3]. Welding is a process that can be carried out both indoors and outdoors. Whenever welding is carried out, ultimately the dust, fumes and pollutant gases will be emitted into the
external environment. Several researchers and organizations have focused on the environmental consideration of welding emissions and their effect on the environment and workers who are involved in it [4] [5]. Three important factors in term of welding emission are – the volume of emission, the composition and the particle size. The fume emission during welding is commonly less and the symphony is normally nontoxic[6]. The size of particles that are formed due to welding varies from the nanometer scale to hundreds of micrometers with a mode diameter in the interval 0.1– 1.0μm[4]. These particles have high chances of deposition in alveolar region of the lungs. Bureau of Labour Statistics approximates in 2008 shows that the number of welding workers are 369,610 [7]. In India, there are 1634596 engineering students intake seats for different streams of engineering at undergraduate level [8]. All the students undergo the basic training of welding in their first year of education. It shows the importance of the welding process in manufacturing sector and its environmental hazards and hence the motivation for this study. LCA can be utilized to visualize
2212-8271 © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 23rd CIRP Conference on Life Cycle Engineering doi:10.1016/j.procir.2016.03.096
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the environmental impact of product and process involved in welding process.
series standards, LCA studies comprise of four phases. Figure 1 depicts the relationship between these phases of the life cycle.
2. Welding and environmental impact In last few of years some research on environmental impact assessment of welding processes has been carried out by some researchers. Finkbeiner et al. [9] presented a study of LCA of manual metal arc welding (MMAW), laser archybrid welding (LAHW), gas metal arc welding (GMAW), and modified GMAW. The results of the study show that MMAW has the highest effect on global warming, acidification, eutrophication, and photochemical ozone depletion. LAHW has minimum environmental impact and the effect of modified GMAW is between MMAW and LAHW. Chang et al. [10] presented a study incorporating environmental and social LCA of different welding technologies. It is found in this study that the manual welding process brings higher risk of welders to health over the automatic processes. The cause identified for the same are low productivity and speed of manual welding. Sproesser et al. [11] presented a study to evaluate the energy efficiency of the gas metal arc welding (GMAW) by using a Tandem GMAW (TGMAW). It is found in the study that the high power TGMAW process decreased the electricity consumption and time required for welding by 23% and 55% respectively. Vimal et al. [12] presented a study on sustainable SMAW (shielded metal arc welding) process. The research work addressed five important sustainable manufacturing strategies – energy modeling and optimization studies, waste minimization and disposal studies, process parametric optimization, process emission studies, and Employee skill training (green strategies) and involvement program – to study their effect on SMAW. Various disposal scenarios have been assessed using LCA. Sproesser et al. [13] presented a research article for selection of sustainable welding process on the basis of weight space partitions. This study evaluates the two welding processes – manual and automatic GMAW) – on the basis of environmental and economical criteria. The weight space partitions approach used in the study provides opportunity to decision maker for assessment of sensitivity of selection problem. However, the motivation of this study is to show the environmental impact of simple arc welding and gas welding processes carried out by a large number of students in large parts of Asia and particularly in India. 3. Materials and Method 3.1. Life Cycle assessment LCA is a tool that can be used to model the life cycle; and calculate, analyze and evaluate at every step in the life cycle various parameters in term of environmental impact [14]. It includes but not restricted to flow analysis, material and energy flows, cost accounting, outflows and inflows, and environmental impact. Regulated by the ISO 14040 [15]
Fig. 1 Framework of LCA (Source: [15])
In this study life cycle assessment (LCA) methodology has been used to quantify the environmental impacts caused by training of a student in welding section of an Indian university's workshop per year. LCA has been performed from cradle to grave considering production of various raw materials starting from extraction till production of various tools/machines required for welding shop, their use phase and the end of useful life. Transportation of raw material, and processes for production of various tools and equipments have not been included in the LCA. The analysis was conducted using Umberto NXT universal software and Eco-invent v3.0 dataset [16]. In this study CML 2001 and Impact 2002+ valuation standards have been utilized to determine the environmental impacts. Attention has been focused on the calculation of masses of GHG expressed as CO2 Kg equivalent emitted during entire life cycle. Hot spots have been identified and discussed in detail in results and discussions section of study. 3.2. Goal and Scope Definition Every year 850 undergraduate students get training in different engineering shops and perform the respective practical and make demonstrable job for the purpose of learning and evaluation. Welding shop is one of the shops where student practice and make job using both gas and arc welding processes. Our goal is to assess impact on environment due these processes for training of one student per year at welding shop in the workshop. Product systems under the scope definition are gas welding and arc welding. The reference flow of the study is the arc welding and gas welding performed per student per year during training in the welding shop. The purpose of the study is to determine the impacts associated with this flow 0.5m arc welding and 0.5m gas welding per student per year. 3.3. System Boundary
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Fig. 2 Basic flow model for LCA of weld ing training process
System boundary selected for this study considers procurement of material (for equipments, work piece and tools), use of equipment in training process and practical work, and end-of-life phase of the equipments and material used. As compared to the other phases of the life cycle, transportation of material and equipment are negligible in terms of environmental impact. The analysis of the manpower and other energies is not a part of the system boundary. In terms of electricity mix used for the study, it is prudent to mention here that in the use phase Indian electricity mix has been used to assess the impacts more preciously. It also reflects that in Indian electricity mix, approximately 60% of the total electricity is generated by coal based power plants. Figure 2 shows the basic Umberto model of material and energy flow in the welding training process. 3.4. Life cycle Inventory The primary data for the study was estimated by closely observing the training process. For quantification of the materials and weights, measurement was done by actual dimensions or weight measurement, whenever possible, the equipment brochures or internet database have been used for reconfirming the data collected. Rest of process related data was collected by conducting the time study during the running training sessions at the workshop. Primary and secondary data have been combined to create the energy and material flow model of the study. Dataset available in the Eco-invent v3.0 database does not exactly match with defined process in some cases. Thus, a few assumptions have been made throughout the study: • Machines are assumed to be made of steel and cast iron, and hand tools are assumed to be of either hardwood or steel. • For the motors in the equipments, only copper winding has been explicitly considered. • Disposal of refractory bricks isn't considered due to its negligible impact on environment.
3.5. Impact assessment Life cycle Impact assessment is carried out using the CML 2001 and Impact 2002+ valuation standards. Midpoint assessment of the welding training process is carried out using CML 2001 valuation standard and for end-point assessment impact 2002+ has been used. In the end-point assessment, environmental load of a product has to be expressed in a single score. The impact 2002+ end-point assessment is designed around four damage categories of climate change, human health, ecosystem quality and resources. In life cycle impact assessment, we have to deal with three fields of scientific knowledge and reasoning. We refer to these fields as “spheres” [17]: • Technosphere: the description of the life cycle, the emissions from processes, the allocation procedures are based on causal relations. • Ecosphere, the modelling of changes (damages) is inflicted on the “environment”. • Valuesphere: the modelling of the perceived seriousness of such changes (damages), as well as the management of modelling choices that are made in Techno- and Ecosphere. Life cycle model is constructed in technosphere resulting in inventory table, whereas modelling in ecosphere is used to link the inventory table with above mentioned damage categories and finally valuesphere modelling is used to weight the three endpoints to a single indicator [1]. However, CML is a midpoint assessment method. The categories under the midpoint and end-point assessments are mentioned below. Midpoint categories: Acidification Potential (AP), Climate Change (CC), Eutrophication Potential (EP), Freshwater Aquatic Eco-Toxicity Potential (FAETP), Freshwater Sediment Eco-Toxicity Potential (FSETP), Human Toxicity Potential (HTP), Ionizing Radiation (IR), Marine Aquatic Eco-Toxicity Potential (MAETP), Marine Sediment EcoToxicity Potential (MSETP), Photochemical Ox (Summer Smog), Abiotic Depletion Potential (ADP), Ozone Depletion Potential (ODP), and Terrestrial Eco-Toxicity Potential
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(TETP). End-point categories: climate change, ecosystem quality, human health, and resources. 3.5.1. Midpoint Assessment Results Arc Welding Electricity consumption Job material
Gas welding Lubricating oil
100%
copper used for motor winding. In some categories like IR, ADP, ODP, CC etc. the wire housing used for equipments has an impact varying from 1% to 10%. Refractory bricks, eyewear, plastic parts cast iron has almost zero or negligible impact in this phase. Treatment of waste mineral oil
Treatment of waste rubber
Treatment of waste glass
Treatment of scrap steel
Treatment of scrap copper
Treatment of waste PVC
100%
90%
90% 80%
80% 70%
70% 60%
60% 50%
50%
40%
40%
30%
30%
20% 20%
10% 10%
0% 0% AP
Eyewear Copper
Steel for equipments Cast iron
Pla stic pa rts Bra ss
90%
80%
70%
60%
50%
EP
FAETP
FSETP
HTP
IR
MAETP MSETP
SMOG
ADP
ODP
TAETP
Fig. 5 M idpoint assessment of recycling phase
Fig. 3 M idpoint assessment of raw material phase Refractory Bricks Wire housing 100%
CC
In midpoint assessment of consumer use phase (as shown in fig. 4) job piece material has dominant impact in all of the categories mentioned above. Electricity consumption of arc welding process is second most impact in all the categories beside the HTP, ODP and TAETP categories. Lubricating oil use for the transformers and rectifier for arc welding process has lease impact in all the categories beside the ODP, IR, and ADP categories. Effect of gas welding process and arc welding process input is more or less similar in all the midpoint categories.
40%
Table 1 midpoint results with phase wise distribution (CM L 2001) 30%
Raw Consumer Recycling Material Use (%) (%) category (%) AP 44.39 43.09 12.52
Total impact (actual) 6.31E-03
CC
36.25
42.81
20.94
1.11E+00 kg CO2-Eq
EP
55.44
33.67
10.89
2.70E-03
FAETP
1.84
1.01
97.15
3.20E+01 kg 1,4-DCB-Eq
FSETP
1.59
0.90
97.51
8.03E+01 kg 1,4-DCB-Eq
HTP
52.58
31.52
15.90
3.50E+00 kg 1,4-DCB-Eq
46.44
32.28
21.29
1.40E-03
MEATP
2.12
1.24
96.64
1.01E+02 kg 1,4-DCB-Eq
MSETP
1.65
0.98
97.37
1.40E+02 kg 1,4-DCB-Eq
IR
21.45
29.36
49.19
2.77E-09
DALYs
SMOG
47.96
39.19
12.85
4.64E-04
kg ethylene-Eq
ADP
34.67
52.29
13.04
7.23E-03
kg antimony-Eq
ODP
30.66
34.25
35.09
6.09E-08
kg CFC-11-Eq
Impact 20%
10%
Unit kg SO2-Eq
0%
Fig. 4 M idpoint assessment of consumer use phase
To understand the environmental impact of the training process in various categories, midpoint assessment for all three phases is carried out separately for raw materials, consumer use and recycling as shown in table 1. It is found in the raw material phase that steel used to manufacture the equipments and machines is impacting more in all of the categories beside ADP category as shown in fig. 3. After steel, brass used for the small equipments like pressure outlet valves is second most impact in all categories followed by
TAETP
kg PO4-Eq
kg 1,4-DCB-Eq
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In the recycling phase (as shown in fig. 5) of midpoint assessment treatment of waste steel has more impact more in AP, EP, HTP, IR, SMOG, ADP, ODP, TAETP, and it makes it most impacting in overall impacts. Treatment of scrap copper is impacting more in all type of eco-toxicity viz FAETP, FSETP, HTP, MAETP, MSETP varying from 10% to 70%. Treatment of waste mineral oil used for the transformer and rectifiers is having more impact in CC and EP categories. Treatment of rubber is having only one significant impact in CC category, treatment of glass, and PVC is having approx. negligible impact in all the categories. To analyze the impacts of these phases and materials; process specific operational LCA is required. In figure 6 one category, climate change is elaborated in terms of each transition and found that material for job pieces and electricity mix impact more over others. In the figure the global warming potential is shown in an incremental manner to better understand the scenario. Table 2 End-point results with phase wise distribution (Impact 2002+) Total Raw Distribution Consumer Recycling Impact in Impact Material Use category Points (%) (%) (%) (%) (actual)
table 2 and the graphical results are shown in figure 7. It is found that consumer use phase is dominating in all the impact categories followed by the raw material phase. But in case of human health impact category recycling phase break the trend of raw material phase to follow consumer use in impacts. Clima te cha nge
Ecosystem quality
Huma n hea lth
Resources
45.00
40.00
35.00
30.00
Percentage %
66
25.00
20.00
15.00
10.00
5.00
Climate change
36.07
8.19
34.36
21.38
1.05E-04
Ecosystem quality
38.57
15.10
28.43
17.90
5.46E-05
Hu man health 24.51
24.82
19.56
31.11
3.79E-04
Resources
8.12
42.03
15.93
9.33E-05
0.00 Raw Material
33.91
3.5.2. End-point assessment Results CML 2001 - Climate change, GWP 0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
Fig. 6 Climate change impact in a incremental way
The well known impact 2002+ valuation standard is utilized to assess the end-point impacts. The end-point assessment in carried out for all four categories (climate change, ecosystem quality, human health, and resources) of impacts in raw materials, consumer use, and recycling phases. The tabulated results of end-point assessment are shown in
Distribution
Consumer Use
Recycling
Fig. 7 End-point assessment phase wise
4. Conclusions The raw material phase of the welding operation training process is most impacting phase in all of the damage categories because of steel used to manufacture the equipments and machines. The use phase is second most impacting and which is due to the significant amount of electricity consumed in the arc welding process and fumes generated in the process of both arc and gas welding operation. Further from the life cycle impact assessment, it has been observed that impact due to the procurement, use and end-of-life of low alloyed steel (hot spot) is the most harmful to environment in welding operation training process. Second most impacting material is copper used in the transformer, silicon rectifier and filler rods for gas welding. It is recommended that the width of job pieces given to the students can be reduced. Non copper coated wire i.e. SE wire [18][19], with the omission of the copper coating treatment process, has less impact upon the environment than conventional wires in every aspect of energy consumption, CO2 emission and solid waste, during each manufacturing process from raw material procurement to use. Low fume type covered electrode/ZERODE Series [20] can be used with reduced fume generation of 30–50% compared with conventional electrodes. This type of electrode has no burnt slag deposit on the bead surface and a lustrous bead appearance can be obtained. Furthermore, with this covered electrode the amount of spatter is reduced by slightly softening (widening) the arc and also fume generation is reduced by approximately 10% compared with the conventional electrodes.
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Acknowledgements The authors wish to express their gratitude to the program “A New Passage to India” (reference 50744785) funded by the ‘German Academic Exchange Service’ (DAAD). References [1] V. Bhakar, V. V. K. Uppala, a. K. Digalwar, and K. S. Sangwan, “Life cycle assessment of smithy training processes,” Procedia Eng., vol. 64, pp. 1267–1275, 2013. [2] K. S. Sangwan, V. Bhakar, S. Naik, and S. N. Andrat, “Life cycle assessment of incandescent, fluorescent, compact fluorescent and light emitting diode lamps in an Indian scenario,” Procedia CIRP, vol. 15, pp. 467–472, 2014. [3] S. Ibbotson, T. Dett mer, S. Kara, and C. Herrmann, “Eco-efficiency of disposable and reusable surgical instruments - A scissors case,” Int. J. Life Cycle Assess., vol. 18, no. 5, pp. 1137– 1148, 2013. [4] J. M. Antonini, S. Stone, J. R. Roberts, B. Chen, D. Schwegler-Berry, A. a. Afshari, and D. G. Frazer, “Effect of short-term stainless steel welding fume inhalation exposure on lung in flammation, in jury, and defense responses in rats,” Toxicol. Appl. Pharmacol., vol. 223, no. 3, pp. 234– 245, 2007. [5] K. M. Yu, N. Topham, J. Wang, M . Kalivoda, Y. Tseng, C. Y. Wu, W. J. Lee, and K. Cho, “Decreasing biotoxicity of fume particles produced in weld ing process,” J. Hazard. Mater., vol. 185, no. 2– 3, pp. 1587–1591, 2011. [6] S. H. Yeo and K. G. Neo, “Inclusion of environmental perfo rmance for decision making of weld ing processes,” J. Mater. Process. Technol., vol. 82, no. 1–3, pp. 78–88, 1998. [7] S. Bureau of Labour, “Occupational Emp loyment Statistics,” 51-4121 Welders, Cutters, Solderers, and Brazers , 2014. [Online]. Available: http://www.bls.gov/oes/current/oes514121.htm. [Accessed: 10-Oct-2015]. [8] AICTE, “Statistics of Intakes seat in Engineering and Technology,” All India Council of Technical Education, New Delhi, 2014. [On line]. Available: http://www.aicteindia.org/downloads/Growth_Technical_Institutions_310514.pdf#toolbar =0. [Accessed: 23-Oct-2015]. [9] M. Finkbeiner, M. Reth meier, Y.-J. Chang, A. Pittner, and G. Sproesser,
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