Profiling stainless steel welding processes to reduce fume emissions, hexavalent chromium emissions and operating costs in the workplace

ABSTRACT

Nine gas metal arc welding (GMAW) processes for stainless steel were assessed for fume generation rates, fume generation rates per g of electrode consumed, and emission rates for hexavalent chromium (Cr⁶⁺). Elemental manganese, nickel, chromium, iron emissions per unit length of weld, and labor plus consumables costs were similarly measured. Flux-cored arc welding and shielded metal arc (SMAW) processes were also studied. The objective was to identify the best welding processes for reducing workplace exposures, and estimate costs for all processes. Using a conical chamber, fumes were collected, weighed, recovered, and analyzed by inductively coupled atomic emission spectroscopy for metals, and by ion chromatography for Cr⁶⁺. GMAW processes used were Surface Tension Transfer, Regulated Metal Deposition, Cold Metal Transfer, short-circuit, axial spray, and pulsed spray modes. Flux-cored welding used gas shielding; SMAW used E308 rods. Costs were estimated as dollars per m length of a ¼ in (6.3 mm) thick horizontal butt weld; equipment costs were estimated as ratios of new equipment costs to a 250 ampere capacity SMAW welding machine. Results indicate a broad range of fume emission factors for the processes studied. Fume emission rates per g of electrode were lowest for GMAW processes such as pulsed-spray mode (0.2 mg/g), and highest for SMAW (8 mg fume/g electrode). Emission rates of Cr⁶⁺ ranged from 50–7800 µg/min, and Cr⁶⁺ generation rates per g electrode ranged from 1–270 µg/g. Elemental Cr generation rates spanned 13–330 µg/g. Manganese emission rates ranged from 50–300 µg/g. Nickel emission rates ranged from 4–140 µg/g.

Labor and consumables costs ranged from $3.15 (GMAW pulsed spray) to $7.40 (SMAW) per meter of finished weld, and were measured or estimated for all 11 processes tested. Equipment costs for some processes may be as much as five times the cost of a typical SMAW welding machine.

The results show that all of the GMAW processes in this study can substantially reduce fume, Cr⁶⁺, manganese and costs relative to SMAW, the most commonly used welding process, and several have exceptional capabilities for reducing emissions.

KEYWORDS:

• Flux-cored arc welding
• fume emission factors
• fume generation rates, gas metal arc welding
• hexavalent chromium
• manganese generation rates
• nickel generation rates
• welding costs
• welding fumes

Acknowledgments

The authors would like to thank Wesley Doneth and Mike Ludwig from Fronius USA for the generous loan of the CMT welder, and Doug Dunbar and colleagues at Lincoln Electric for arranging background information and brief training for STT welding.

Disclaimer

The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health. The mention of any company names or products does not imply an endorsement by NIOSH or the Centers for Disease Control and Prevention, nor does it imply that alternative products are unavailable, or unable to be substituted after an appropriate evaluation.