10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Link the Oxidation Level between Gaseous and Particulates Compounds: A Study on Nitrogen-enriched Stainless Steel Welding and Cutting
JUN WANG, Marcio Bezerra, Jhy-Charm Soo, Shizhen He, Jacob Bartels, University of Oklahoma
Abstract Number: 1546 Working Group: Workplace Aerosol
Abstract Welding is a metal fabrication process commonly seen in different industries. The process relies on using high-temperature arcs to melt metals and hence either join or cut workpieces. Workers dealing with welding and cutting are exposed to highly oxidized metal particles and other gaseous pollutants emitted during the welding process. The most toxic oxidized metal in welding fume is hexavalent chromium (Cr6+) which is a carcinogen with very low permissible exposure level. Nitrogen (Ni) in the surrounding air can also be oxidized to nitrogen oxides (NOX) and present a potential health hazard. Our previous study showed there was a relatively strong correlation between the oxidation of nitrogen and chromium, which can lead to a potential low-cost and fast solution to detect Cr6+ level in the workplace by ubiquitous NOx sensor. In addition, nitrogen-enriched welding which employs nitrogen in the alloy to enhance resistance to sensitization, provide solid solution hardening, raise yield strength compared to non-nitrogen-enriched stainless steel. Nitrogen-enriched welding is growing in the nuclear industry when building structural material for reactors, as well as in cryogenic and biomedical applications. However, the extra nitrogen in the alloy coupled with nitrogen in shielding gases and surrounding atmosphere will create additional emission of nitric oxide (NO), nitrogen dioxides (NO2), and potentially nitrous oxide (N2O). The objective of this study is to investigate emission of NOX and Cr6+ from nitrogen-enriched welding and to speculate if there is any correlation between them. A conical American Welding Society (AWS) fume chamber and high-volume air sampling pumps were used to collect welding fume. Nitrogen-enriched stainless steel metal plates (316LN) were welded and cut using a pulsed metal inert gas welder and a plasma cutter, respectively. Cr6+ in the fume was analyzed using an ion chromatograph following NIOSH 7604 method. NO, NO2, and ozone were monitored by a GrayWolf air quality monitor with a toxic gas probe in both real-time reading in ppm and integrated total emission. N2O was measured through a passive dosimeter. The results showed plasma cutting generally created more NO, NO2, and Cr6+ than welding. Nitrogen-enriched stainless steel welding and cutting did not emit significant more NOx comparing to regular stainless steel. The NO and NO2 concentration only showed a slight increase while welding with nitrogen-contained shielding gas. N2O was detected during welding for the first time when welding under certain conditions. NO2 was proved to have the best correlation with Cr6+ level (r=0.81). The results show a potentially promising technique to quickly respond to overexpose to Cr6+ by deploying NO2 sensors. However, more field studies are needed before this technique can be widely adopted.