Selecting Processes to Minimize Hexavalent Chromium from Stainless Steel Welding: Eight welding processes/shielding gas combinations were assessed for generation of hexavalent chromium in stainless steel welding fumes

Abstract

Eight welding processes/shielding gas combinations were assessed for generation of hexavalent chromium (Cr⁶⁺) in stainless steel welding fumes. The processes examined were gas metal arc welding (GMAW) (axial spray, short circuit, and pulsed spray modes), flux cored arc welding (FCAW), and shielded metal arc welding (SMAW). The Cr⁶⁺ fractions were measured in the fumes; fume generation rates, Cr⁶⁺ generation rates, and Cr⁶⁺ generation rates per unit mass of welding wire were determined. A limited controlled comparison study was done in a welding shop including SMAW, FCAW, and three GMAW methods. The processes studied were compared for costs, including relative labor costs. Results indicate the Cr⁶⁺ in the fume varied widely, from a low of 2800 to a high of 34,000 ppm. Generation rates of Cr⁶⁺ ranged from 69 to 7800 μg/min, and Cr⁶⁺ generation rates per unit of wire ranged from 1 to 270 μg/g. The results of field study were similar to the findings in the laboratory. The Cr⁶⁺ (ppm) in the fume did not necessarily correlate with the Cr⁶⁺ generation rate. Physical properties were similar for the processes, with mass median aerodynamic diameters ranging from 250 to 336 nm, while the FCAW and SMAW fumes were larger (360 and 670 nm, respectively).

Conclusion: The pulsed axial spray method was the best choice of the processes studied based on minimal fume generation, minimal Cr⁶⁺ generation, and cost per weld. This method is usable in any position, has a high metal deposition rate, and is relatively simple to learn and use.

Keywords: Flux Cored Arc Welding (FCAW); Gas Metal Arc Welding (GMAW); Hexavalent Chromium; Shielded Metal Arc Welding (SMAW); Stainless Steel; Welding Fume.

Fig. 1

American Welding Society-type welding chamber in use.

Fig. 2

Welding fume-generation rates for eight welding processes, in mg/min.

Fig. 3

Hexavalent chromium content in welding fumes from eight processes, in mg/kg.

Fig. 4

Hexavalent chromium generation rates for eight welding processes, in μg Cr⁶⁺/min.

Fig. 5

Hexavalent chromium generation rates for eight welding processes, in μg Cr⁶⁺/g of welding wire consumed.

Fig. 6

Hexavalent chromium exposures inside welder’s helmets in μg Cr6+/m³ for five welding processes.

Fig. 7

Particle size distribution of a typical welding fume in this study using a MOUDI device.