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The Effect of Materials on Radiation Exposure during the GTAW Process The study clearly exhibited the effects of materials on the arc light and electric current on photon energy
BY A. GURSEL AND A. KURT
ABSTRACT In this study, the gas tungsten arc welding (GTAW) technique was used to weld samples of three materials: SS304type stainless steel, A36 lowcarbon steel, and T6061 aluminum. The welding was applied at 200 A, and the radiation types and lu minosities were measured for each material. During the welding processes, UV radia tion was the most frequently observed in all parameters; in addition, visible light and IR radiation, 200–1000 nm on an optical scale, were recorded. The effects of electric currents on the photon energy rates were clearly exhibited. The production and type of radiation (photon energy and highfrequency energy) were affected by the GTAW applications using tungsten electrodes containing 2% thorium, thus corroborating previous findings in the literature.
KEYWORDS • Radiation • Arc Welding • Gas Tungsten Arc Welding (GTAW)
Introduction Research has shown that welding arcs produce radiation; however, not enough detailed studies have been carried out based on parameters such as welding techniques, welded materials, and welding currents (Refs. 1–3). Radiation from welding arcs has direct adverse effects, including eye and skin damage, on operators and nearby workers (Refs. 4–6). This is due to the fact that arc welding produces optical radiation in the 200–1400 nanometer (nm) wavelength band as ultraviolet (UV), visible light (VIS), and infrared (IR). Ultraviolet radiation, with a 200–400 nm wavelength, is the most effectual among them. Consequently,
welders have a higher than average risk of developing biologically effective skin cancer and cataracts. Although it is known that welding arcs produce radiation, sufficiently detailed research has not been done on radiation from welding parameters (Ref. 1). Recent studies on welding radiation have provided data covering some welding parameters by measuring the energy, radiation dose, and limitations for health institutes (Refs. 1, 6). Only a few have analyzed the light produced by welding arcs. As a welding arc is not a steady source of radiation, this results in calibration difficulties. Future welding radiation studies are needed in order to accurately cover all welding parameters, including materials and welding techniques (Ref. 2). The pres-
ent study focused only on GTAW and three materials commonly used in industry: aluminum, stainless steel, and low-carbon steel. The materials, SS30-type stainless steel, A36 low-carbon steel, and T6061 aluminum, were prepared as 5 × 50 × 200 millimeter (mm) samples, and GTAW was applied using a 200-A electric current. During the welding process, the different radiation types were measured in terms of their wavelengths. A high amount of UV exposure was detected. Optical radiation covering the entire ultraviolet band (UV-A, UV-B, and UV-C), visible light (VIS), and infrared (high-energy IR-A) were observed for each sample material. Most arc welding and cutting processes, laser and torch welding, cutting, brazing, and soldering produce quantities of radiation requiring precautionary measures. Some processes, such as resistance welding and cold pressure welding, ordinarily produce negligible quantities of radiant energy (Refs. 3, 4). Both ionizing radiation and nonionizing radiation are produced by welding arcs (Ref. 4). Ionizing radiation: • Produced by the electron beam welding process. • Controlled within acceptable limits by using suitable shielding around the electron beam welding area. • Produced during grinding (pointing) of thoriated-tungsten electrodes for the GTAW process, where the grind-
A. GURSEL (
[email protected]) is with Duzce University Faculty of Engineering, Mechanical Engineering Dept., Düzce, Turkey. A. KURT (
[email protected]) is with Gazi University Faculty of Technology, Materials and Metallurgy Dept., Ankara, Turkey.
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Fig. 1 — View of the screen showing measured values as recorded by the software.
Fig. 2 — Optical radiation values for A36 lowcarbon steel at a 200A electric current.
Table 1 — Chemical Composition of SS304 Stainless Steel Element
Cr
Ni
Mn
Si
C
P
S
Fe
%
18.0–20.0
8.0–10.50
2.0 max
1.0 max
0.08 max
0.045 max
0.030 max
Remainder
Table 2 — Chemical Composition of A36 (ATSM) LowCarbon Steel Element
Mn
Si
C
Cu
S
P
Fe
%
1.03 max
0.280 max
0.25–0.290
0.20 max
0.050 max
0.040 max
Remainder
Table 3 — Chemical Composition of T6061 Aluminum Element
Ma
Fe
Si
Zn
Cu
Mn
Ti
Cr
Other
Al
%
0.8–1.2
0.7 max
0.4–0.8
0.25 max
0.15–0.4
0.15 max
0.15 max
0.04–0.35
0.15 max
Remainder
ing dust is radioactive. • Controlled by using local exhaust and, if necessary, an approved respirator (Ref. 4). Nonionizing radiation: • The intensity and wavelength of the energy produced depend on the process, welding parameters, electrode and base metal composition, fluxes, and any coatings or plating on the base material. • Ultraviolet radiation increases approximately as the square of the welding current. • Visible brightness (luminance) of the arc increases at a much lower rate (Refs. 1, 4). The welding arc is a significant artificial source of radiation, mainly producing optical radiation (Ref. 7). Welding arcs generate radiation over a broad range, 200–1400 nm (0.2–1.4 micrometers (μm)), of wavelengths.
These include UV radiation (200–400 nm), VIS (400–700 nm), and IR radiation (700–1400 nm). There are three types of UV radiation: UV-A (400–315 nm), UV-B (315–280 nm), and UV-C (280–100 nm) (Ref. 8). Radiation given off by the arc or flame is electromagnetic energy that may damage eyes and burn skin (Refs. 4, 5). Broad-spectrum UVR is known to be a human carcinogen (Ref. 9). UVC radiation from welding arcs can cause ocular cancer and skin cancer as well as chromosomal and DNA damage (Refs. 10–12). An operator sees visible light radiation. However, he does not see ultraviolet or infrared radiation. UV-A, VIS, and IR radiation may reach the retina and can cause ocular injury (Refs. 13, 14). UV radiation also targets anterior parts of the eye and may be associated with the development of acute and chronic effects.
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The previously mentioned information is discussed in many scientific articles, but without providing detailed classification based on welding parameters. In this study, analysis of radiation type and range was carried out for GTAW applications on stainless steel, low-carbon steel, and aluminum samples.
Experimental Procedure — Materials and Equipment Sample materials of SS304-type stainless steel, A36 low-carbon steel, and T6061 aluminum were used in this study; their chemical compositions are given in Tables 1–3. The test materials were prepared as 5 × 50 × 200-mm samples and welded using the GTAW method. A WT20 tungsten electrode (with 2% thorium)
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Fig. 3 — Optical radiation values for T6061 aluminum at a 200A electric current.
Fig. 4 — Optical radiation values for SS304 stainless steel at a 200A electric current.
Fig. 5 — Comparison of values for the three sample materials.
Fig. 6 — The radiation values of the SS304 sample at a 2m distance and a 200A electric current.
and having dimensions of 0.40 × 0.187 × 7 in. was employed for welding. As added metal, wires with a thickness of 1 ⁄16 in. were used: Lincoln ER 4043L for the aluminum and Lincoln ER 308L for the stainless steel. The samples were welded using a Miller Millermatic 250X welding machine with an argon gas shield. During the welding process, the light values were measured using a ZEISS MCS 501 UV-NIR spectrometer, the features of which are given in Table 4. In this study, the UV source was the welding arc; therefore, the photometer and spectrometer parts of the ZEISS MCS 501 UV-NIR, which sense and analyze the light, were used. For measuring the 200–1000 nm wavelengths, a 1⁄3-s integration period was determined. The probe was positioned at a distance of 1 m from the arc and was connected to the spectrometer by fiber-optic cable. The spectral irradiance from the welding arc were observed and record-
Table 4 — ZEISS MCS 501 UVNIR Spectrometer Type
Resolution
Accurancy
Pixel No.
λ Range
MCS 501 UVNIR
2.4 nm
0.3 nm
512/1024
190–1015 nm
ed by means of AspectPlus, ZEISS MCS 501 UV-NIR software. The screen view showing measured and recorded data can be seen in Fig. 1. The luminosity is seen on the vertical line as lumen (lm) and the wavelength is seen on the horizontal line as nanometer (nm). Three lines are seen in Fig. 1. The observed maximum and minimum optic radiation rates are indicated by the two green lines, and the average rate, which is taken into consideration, is shown by the red line.
Results and Discussion In this study, radiation values were obtained from GTAW applications on three types of test materials. These
values are seen in Figs. 2–5 as diagrams based on the materials and the electric current values. The light was converted to an optical scale; the intensity, which was measurable in this study, was in a wavelength range of 200–400 nm. It was assumed that GTAW produces lower-wavelength light. The UV band is known to be 200–400 nm and is shown in Fig. 2. The highest intensity of light was 200–300 nm, which is the UV-C, the highest energy of the UV band, and some of the UV-B band. The VIS and IR, at 750–840 nm, were above the measurable 400-nm value. As seen in Fig. 3, the optical radiation values for Al are very different from those of the low-carbon steel NOVEMBER 2014 / WELDING JOURNAL 441-s
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WELDING RESEARCH GTAW applications. The light is dispersed over the 200–900 nm wavelength range. These scattered wave ranges cover UV-A, UV-B, UV-C, visible light, and IR radiation. The luminosity reached 25,000 lm on the Al sample. During electron beam welding and when grinding GTAW thoriated tungsten electrodes, ionized radiation may be generated (Ref. 4). As seen in Fig. 4, the highest energy level of radiation was observed on the stainless steel samples. The highest intensity of radiation was 200–300 nm, which is in the UV-B and UV-C bands; the luminosity reached more than 25,000 lm. Figure 5 shows that the highest energy was obtained from the stainless steel sample as luminosity and frequency. The lowest rates were obtained from the low-carbon A36 steel sample. The energy rates from the aluminum sample were dispersed all over the optical scale, but mostly concentrated in the UV and IR bands. The calibration of the ZEISS MCS 501 UV-NIR spectrometer is not very sensitive over 25,000 lm. Therefore, the position of the probe was changed to a distance of 2 m to accommodate the role of distance on radiation with values of more than 25,000 lm — Fig. 6. According to the Inverse-Square Law (radiation intensity with distance), the radiation intensity decreases with the inverse square of the distance. This relationship indicates that doubling the distance from a radiation source decreases the radiation level by a factor of four. With the increasing distance, the emission diverges to an area four times the original area. The measuring of 27,000 lm at a 2m distance means that the optic radiation luminosity is approximately four times more at the 1-m distance, i.e., 108,000 lm. For this study, the distance of the probe from the welding arc was 1 m, whereas an operator is only a few centimeters away from the welding arc. Therefore, the influence of radiation energy for an operator and his/her skin is much higher than that measured here. This measurement was applied for comparing and analyzing the radiation level of stainless steel and the other materials. All three materials
were welded with the GTAW process, at the same electric current, and using an argon gas shield. However, the resulting types and amounts of radiation for each sample differed significantly. The stainless steel sample caused much more radiation energy to be produced.
Conclusions This study has attempted to determine the radiation emissions from welding arcs on test materials. From the values obtained for each of the parameters, the following results and conclusions were observed: 1. Optical radiation, including UVA, UV-B, UV-C, visible light, and IR, is produced by GTAW arcs. 2. Energy input, which is based on the thermal conduction and fusion levels of the materials, also affects the radiation emissions. So long as the energy input increases, the photon intensity and radiation emissions also increase (Ref. 15). Higher light intensity was observed with the increase in the electric current. 3. Since the chemical composition of the welded materials was seen to affect the production and emission of radiation, further research, including studies of other welding techniques, is needed to investigate this aspect. 4. During welding on the stainless steel sample, a high intensity of radiation was observed over a wide area of the electromagnetic spectrum. 5. Obtained values from GTAW on Al ranged throughout the entire optical scale. The highest graphic peaks were seen in the UV and IR bands. Additionally, the form of the Al graphic exhibited a different pattern from those of the values for the other materials. 6. High optical radiation energy levels were displayed with low-carbon steel, stainless steel, and aluminum samples welded using the GTAW process. With the aluminum and stainless steel samples, the intensity was higher than with the low-carbon steel. However, the highest optical radiation energy (108,000 lm at 200–300 nm) was obtained from stainless steel in the form of high-frequency and photon energy.
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References 1. Gursel, A. 2010. Analysis of optical radiation emitted from electric arc welding. PhD thesis. Gazi University Institute of Science and Technology, Ankara, Turkey. 2. Gursel, A., and Kurt, A. 2009. Value in emerging electric arc welding of ultraviolet radiation effects on human and environmental health. International Conference on Welding Technology, Ankara, Turkey. 3. ANSI Z49.1-1999, Safety in Welding, Cutting, and Allied Processes. Miami, Fla.: American Welding Society. 4. AWS Safety and Health Fact Sheet No. 2. 2003. Miami, Fla.: American Welding Society. www.aws.org/technical/facts/ fact-02.pdf. 5. Dixon, A. J., and Dixon, B. F. 2004. Ultraviolet radiation from welding and possible risk of skin and ocular malignancy. The Medical Journal of Australia 181(3): 155–157. 6. Emission of UV radiation during arc welding. 2011. IFA-Institutfür Arbeitsschutz der Deutschen Gesetzlichen Unfallversicherung. 7. Assessment of and Protection from Welding Arc Radiant Hazards. 2006. Jefferson Lab, ESH&Q Manual, Rev. 8.7–7. 8. Repacholi, M. H. 1996. Introduction to Non-Ionizing Radiations. ICNIRP Third International Non-Ionizing Radiation Workshop, pp. 3–12. Beden, Austria. 9. Report on Carcinogens, Twelfth Edition. 2011. U.S. National Toxicology Program, pp. 1–5. 10. Cieminis, K., Ranceliene, V., Slekyte, K., and Tiunaitiene, N. 2001. Industion of DNA and chromosomal damages by UV-C and solar and its photoreactivation in crepis calpillaris cells. 2001. Lab. of Cell Engineering, Institute of Botany. ISNN 1392-0146. Biologia, Nr. 1. 11. Lyon, T. L. 2002. Knowing the dangers of actinic ultraviolet emissions. Welding Journal 2(12): 28–30. 12. IARC Monographs on the Evaluation of Carcinogenic Risk to Humans, Chromium, Nickel and Welding. 1990. World Health Organization — International Agency for Research on Cancer. Volume 49. IARC, Lyon, France. 13. Radiation and the Effects on Eyes and Skin. 2001. Canadian Centre for Occupational Health and Safety (CCOHS). 14. Ultraviolet Radiation, Environmental Health Criteria 160. 1994. World Health Organization. pp. 1–263. 15. AWS Safety and Health Fact Sheet No. 26. 2004. Miami, Fla.: American Welding Society. www.aws.org/technical/facts/ FACT-26_2014.pdf.