Welding Processes

Information about Welding Processes

Published on January 22, 2008

Author: Riccardino

Source: authorstream.com

Content

Welding Processes and Exposure Assessment Stephanie R. Carter, CIH University of Washington/Central Washington University CIHC 16th Annual Conference December 4, 2006 San Diego, CA:  Welding Processes and Exposure Assessment Stephanie R. Carter, CIH University of Washington/Central Washington University CIHC 16th Annual Conference December 4, 2006 San Diego, CA Introduction:  Introduction Need for welders “Where have All the Welders Gone, As Manufacturing and Repair Boom?” Average age of welders = 54 10% decline in number of welders since 2004 By 2010, demand for welders may outweigh supply by 200,000 Need more trained welders Wall Street Journal 8/15/2006 Introduction:  Introduction In 2020, welding will continue to be the preferred method of joining…. Increases in Plastics, composites, new alloys Aluminum Robotic welding FCAW, GMAW R&D challenges (heavy industry) Make the workplace more attractive by eliminating fumes, noise, and radiation Materials to replace Cr and Ni (Mn?) Welding Technology Roadmap: Vision, AWS/EWI (2000) Introduction:  Introduction Consumable electrodes purchased in 1991: SMAW – 45% GMAW – 34% FCAW – 17% SAW – 4% One California shipyard SMAW – 50% GMAW/GTAW – 5% FCAW – 20% SAW – 25% Development of Particulate and Hazardous Emission Factors for Electric Arc Welding (AP-42,Section 12.19), 1994 Introduction:  Introduction Emerging Issues Health Effects Sampling/Analysis Process Determinants of Exposure Controls Health Effects:  Health Effects Pulmonary Decreased lung function Asthma Lung cancer Increase in infections Other Metal fume fever Conjunctivitis Nervous system Ocular Melanoma/skin cancer Fatality Health Effects:  Health Effects Exposure fatality 2003 fatality in WA/Oregon Oregon sales rep Applied chromium and nickel based thermal sprays for 2 days in WA Health Effects:  Health Effects UV and welding Case-control studies link ocular malignancy with welding Arc welding produces full spectrum of UVR Short distances from source Controls Clothing and sunscreen Aluminum welders need highest protection Dixon, A., B. Dixon. MJA 2004; 181:155-157 Health Effects:  Health Effects UV and welding Welding helmet allows UV in from sides and top, problem for Highly reflective areas, multiple welders Exposure assessment (compared to ACGIH MPE) Tenkata,T. Collins, M. AIHAJ 58(1)33-38 Slide10:  Tenkata,T. Collins, M. AIHAJ 58(1)33-38 Sampling and Analysis:  Sampling and Analysis Questions of old Placement of sampler Grinding influence Analysis Gravimetric Elemental As Pb Co Etc… Newer questions Hexavalent chromium Particle size Analysis Radiation Sampling and Analysis:  Sampling and Analysis Evaluation of the allowed samplers and procedures (ISO 10882-1:2001) Different samplers UK, German, HSE French, Danish (similar to U.S.) Left or right side positioning Lapel vs helmet sampling Grinding effects Surrogate measures of fume composition Chung, et al., Applied Occupational and Environmental Hygiene, 14((107-118), 1999. Sampling and Analysis:  Sampling and Analysis Sampling and Analysis:  Sampling and Analysis Results (Chung, et al) Little difference between samplers Variable effect from right vs. left All collected grinding dust Percent of individual contaminants in fume different than MSDS Lapel sampling Larger ratios than in helmet sampling Collected more grinding dust Except for HSE Slide15:  Comparison of Air Samplers to Dummy Sampling and Analysis:  Sampling and Analysis Hexavalent Chromium OSHA-215 Revision 2 Cr(VI) samples collected on PVC filters from welding operations must be analyzed within 8 days of sampling NIOSH Methods (7605 and 7703) Higher recoveries of CrVI compared to OSHA-215 although not statistically significant NIOSH 7703 Chromium, Hexavalent, by Field-Portable Spectrophotometry No evidence of CrVI reduction to CrIII perhaps related to ultrasonic extraction QA/QC Sampling and Analysis:  Sampling and Analysis Nanoparticles or ultrafine particles <100 nm Arise in workplace through Nucleation Combustion Saturated vapors Mechanical processes Nanophase technology Deposition and alveolar clearance differences Negligible in terms of mass concentration Better to look at surface area or number No personal monitoring devices available Estimation of SSA by respirable sampling Sampling and Analysis:  Sampling and Analysis Particle size Number or surface area of particles vs. mass Ultrafine particles may have greater biological effect than an equivalent mass of larger particles Count median diameter of SMAW = 120 nm Mass median diameter of SMAW = 590 nm Clusters behavior determined by AED, but Primary particles more surface area Hewitt,P. AIHAJ,56(2)128-143 Sampling and Analysis:  Sampling and Analysis Total lung deposition of GMAW estimated to be 60% greater than for SMAW GMAW deliver 3 times the particle surface area to lungs Particle surface chemistry and lung clearance rates vary as well Hewitt,P. AIHAJ,56(2)128-143 Sampling and Analysis:  Sampling and Analysis Analysis questions On-site analysis Portable micro-balances (0.1 mg possible) Portable XRF Non-destructive, filters, wipes, bulks Acceptable LOD except for Cobalt and Arsenic with TWA samples (400 L) No speciation Analysis questions Laboratory analysis PIXE analysis ICP-AES/MS Digestion protocol Nygren,O. JEM,2002, 4,623-627 Sampling and Analysis:  Sampling and Analysis Thorium and GTAW Tungsten electrodes can contain 1-4% Thorium 2% most common (WT-20) 232Th, 228Th, 230Th Alpha emitter Exposure potential “Vapors” during welding Grinding to shape tip Gafvert,T. et.al, RPD,103(4),349-257(2003) Sampling and Analysis:  Sampling and Analysis Welding DC < 3mBq/m3 AC < 10 mBq/m3 Up to 141 mBq/m3 for inexperienced Total dust, outside helmet Grinding 5 mBq/m3 Respirable dust Dose estimates Welding 0.3 to 1 mSv Grinding 10 µSv to 63 µSv Gafvert, et al. Radiation Protection Dosimeter, 103(4)pp.349-357 (2003) Sampling and Analysis:  Sampling and Analysis TIG welding and Thorium Controls LEV No contact with open cuts or wounds Clean-up No eating, drinking, smoking Thorium-free tungsten electrode CeO2 (2%) or La2O3 (1-2%), Zr (1%), Pure Tungsten The Proper Selection and Preparation of Tungsten Electrodes for Arc Welding, www.diamondground.com Quantity and particle size of emissions depends:  Quantity and particle size of emissions depends Welding process itself plus other variables Flux Gas Composition Operating conditions Travel speed Voltage Current Arc length Polarity Welding position Electrode angle Deposition rate Slide25:  By Electrode/Process Development of Particulate and Hazardous Emission Factors for Electric Arc Welding (AP-42,Section 12.19), 1994 Emissions by Current:  Emissions by Current Development of Particulate and Hazardous Emission Factors for Electric Arc Welding (AP-42,Section 12.19), 1994 Emissions by Shielding Gas:  Emissions by Shielding Gas 2001 Ship Production Symposium, EWI Effects on Particle Size:  Effects on Particle Size Zimmer,A. JEM, 2002(4),628-632 Welding Emissions Control:  Welding Emissions Control Process Selection from SMAW to GMAW Fume extraction welding gun Engineering controls Local exhaust Dilution Process modification Power variation (GMAW) Low-fume electrodes Composition changes to minimize spatter or to shift metals to slag Controls – Process Selection:  Controls – Process Selection Fume Generation Rate (g/min) Fiore,S. Welding Journal, 2006, August, 38-42. Controls – Fume Extractions Guns:  Controls – Fume Extractions Guns Wallace, M., et al Applied OEH (2001), 16(8),771-779 Effects of Ventilation:  Effects of Ventilation Elemental with ventilation Arsenic – 2 of 16 exceeded OSHA PEL Hexavalent chromium – Reduced exposures, but still above 50 µg/m3 Wallace, M., et al(2002), Applied OHE 17(3),145-151 Effect of Ventilation – Confined Spaces:  Effect of Ventilation – Confined Spaces Success of either ventilation depends on Work practices backing out backing in Equipment maintenance Wurzelbacher,S. Applied OEH, 17(11):735-740(2002) Welding Processes and Exposure:  Welding Processes and Exposure Effect of pulsed power Wallace, et. Al Applied OEH,16(2), 93-97, 2001 Slide35:  Hex chromium formation (in MIG welding) Courtesty John Dennis Controls:  Controls Process modification Various strategies explored over 10 years 1. Adding some substance to: a) the consumable to react with O3 before it reacts with Cr b) increase the O3 destroying wavelengths of UV c) reduce the O3 forming wavelengths of UV 2. Using a first or second shield gas or a gas in the macro environment of the arc to a) absorb O3 forming wavelengths b) react rapidly with O3. 3. Use a suitable ‘shroud’ to block UV transmission 4. Engineering modification of welding equipment and welding parameters to produce weld conditions which emit little Cr (VI). Courtesty John Dennis Slide37:  Courtesty John Dennis Slide38:  Courtesty John Dennis Slide39:  Dennis JH et al. Control of Exposure to Hexavalent Chromium and Ozone in Gas Metal Arc Welding of Stainless Steels by use of a Secondary Shield Gas. Annals of Occupational Hygiene 46:1, 43-48. 2002. Slide40:  Dennis JH et al. Control of Occupational Exposure to Hexavalent Chromium and Ozone in Tubular Wire Arc-welding Processes by Replacement of Potassium by Lithium or by Addition of Zinc. Annals of Occupational Hygiene 46:1, 33-42. 2002 Controls:  Controls Practical Issues Creativity/ownership Skills To modify Persistence “not sufficiently applicable to moving work” The future Thinking outside the box Light Sensing Self-Adjusting Hood:  Light Sensing Self-Adjusting Hood Ojima, J. JOH,45(2):125-126 (2003) Turkem et. al, AWS, 2005:  Turkem et. al, AWS, 2005 Turkem et. al, AWS, 2005:  Turkem et. al, AWS, 2005

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