New Data on Welding Fume Focus on Controls

Transcription

1 1 New Data on Welding Fume Focus on Controls Presented to: EEI Fall Health and Safety Meeting Presented by: Jeff Hicks, Principal Scientist, Exponent

2 2 Highlights of What We Currently Know Different forms of welding produce different levels l of fume exposures Emphasis of exposure parameters is on Manganese and Hexavalent Chromium Metals in consumables often dictates the composition and concentration of fumes Cr and Mn have no substitutes The hierachery of fume production is SMAW>FCAW>GMAW>GTAW Shielded Metal Arc Welding (SMAW) is the most popular type of welding it is relatively simple, it requires less skill and experience as compared to other types of welding, it has a short set-up time, and the equipment is relatively inexpensive It is one of the most portable types of welding

3 3 Highlights of What We Currently Know SMAW on metals tl containing tii chromium (e.g. above 1%) will result in exposures above the PEL under many circumstances There are many variables that affect fume exposures Indoor work results in higher fume levels as compared to outdoor work GMAW welding can result in overexposures to CrVI but to a lesser extent t as compared to SMAW Exposures to Mn are generally below the current PEL and TLV there is a proposal to lower the TLV, in which case many typical exposures will be above the TLVs

4 4 Highlights of What We currently Know Gas Tungsten Arc Welding (GTAW or TIG) results in the lowest fume exposures, but this welding process is considerably slower as compared to other types of welding, like SMAW or GMAW GTAW rarely results in exposures to Mn and CrVI above the PEL Carbon arc gouging gives rise to very high fume concentrations, including high levels of CrVI on chromium containing alloys, and Mn on all types of steel

5 5 Highlights of What We Currently Know The use of controls on fume exposures is evolving and becoming more commonplace - more and more welders (individuals and contractors) are beginning to use some form of fume exposure control Respirators are the most common method of control The use of local exhaust ventilation (fume extractors) can be very effective at controlling exposures The use of LEV systems is time consuming, the inlet must be positioned very carefully, our field observations show that it is rarely used properly or in a highly efficient way Many contractors do not even try to use LEV they claim that it is too costly and slow, and that t they will use respirators

6 6 How Close Does the Exhaust Hood dneed to Be? (Data from NIOSH) Table 2: Capture Velocities for the Local Exhaust Ventilation Units Distance from Hood Unit 1 (fpm) Unit 2 (fpm) (in)

7 Portable LEV (Fume Extractors) 7

8 Air Velocity at the Weld Site Compared to CrVI Concentration ti Inside the Welding Helmet During SMAW on 308 Stainless Steel

9 Air Velocity (at inlet centerline) Compared to Distance from Exhaust Inlet 140 Air Velocity (fp pm) High Volume LEV Distance from Inlet (inches) 160 Air Velocity (fpm) Low Volume LEV Distance from Inlet (inches)

10 10 Optimizing i i the Use of ffume Extractors t The cross draft exhaust air velocity at the weld site should be greater than 50 feet per minute, ideally near 100 fpm. High volume fume extractors should be kept within 18 inches of the weld site. Low volume fume extractors should be kept within 6 inches of the weld site. If these parameters cannot be achieved, appropriate respiratory protection should be worn when conducting SMAW on stainless steels. Train workers in these procedures.

11 11 Welding Fume Trends over Time Michael Flynn and Pam Susi studied d OSHA welding fume data base information and examined it for exposure trends. They also examined how total fume exposures related to specific metals, like manganese.

12 Flynn, M, and P. Susi, 2010, Manganese, Iron, and total Particulate Exposures to Welders, J. Occ. y,,,, g,, p, Env. Hyg. 7:

13 13 Fume Control Options What About the Welding Process Modifying i the welding fume process should be considered in the options for fume control. OSHA has indicated that welding on high chromium alloys may need to be done with GTAW Given what is known about fume generation by different processes, other alternatives should be considered

14 Cost and Feasibility Analysis of Welding Processes focus on fume exposures, technical and financial feasibility Xcel Energy has been examining i the cost and technical feasibility of using welding processes other than SMAW An initial study has been conducted by Jerome Spear, CIH, (Spear Consulting, LP Magnolia, Texas) and Arlen Siert, PhD, CIH (Xcel Energy, Denver, Colorado) the information contained in the following slides were provided by these individuals id They have examined issues such as technical feasibility, production rate, quality, cost and fume exposures levels emphasis has been on CrVI SMAW FCAW GMAW (two different processes spray, pulse) 14

15 15 15 Welding Process Controlled Comparison Study Power Electric Generation Maintenance Welding SMAW, FCAW, and GMAW Production Rate (or Travel Speed), and Fumes (NOS) Quality Cost 316L Stainless Steel (19% Cr) Horizontal/Vert. Butt Welding Cr(VI), Mn, and Fumes (NOS)

16 16 16 Boiler Bottom Stainless Steel Repair Welding Project 150 MW front wall coal-fired high pressure steam boiler Replacement of boiler wet bottom ash drip plates Stainless steel fillet welding mostly horizontal position, some vertical Divided into four portions to compare SMAW, FCAW, GMAW-spray mode, GMAWpulsed mode

17 Cost Comparison SMAW, FCAW, GMAW-S, GMAW-P stainless steel butt welds 50% horizontal / 50% vertical position - based on travel speed only 17 Consumables 44.7% Labor 55.3% SMAW Labor $1.25/LF Consumable $1.01/LF $2.26/LF26/LF Gas 9.1% Labor 24.5% Consumables 66.4% FCAW Labor $0.27/LF Consumable $0.73/LF Shielding Gas$0.10/LF $1.10/LF10/LF Gas 12.9% Labor 29% Consumables 58.1% GMAW-S Labor $0.31/LF Consumable $0.58/LF Shielding Gas$0.13/LF $1.05/LF Gas 12.6% Labor 28.2% Consumables 59.2% 17 GMAW-P Labor $0.29/LF Consumable $0.61/LF Shielding Gas $0.13/LF $1.03/LF

18 18 Welding 316 (19% Cr) Stainless Steel Exposure Level and Travel Speed by Process Ex xposure Leve el Times the PEL / TLV IPM 30 IPM 40 IPM 28 IPM 44 IPM Expected 32 IPM 24 IPM Lower than normal due to stitch welding Mn 0.32 mg/m mg/m 3 8 IPM 0.2 mg/m mg/m Minute (IPM M) Inches / Hexavalent Chromium PEL 5 ug/m3 Manganese TLV 0.2 mg/m3 Respirable Fume* TLV 3 mg/m3 IPM vertical IPM horizontal Expected IPM horizontal 0 GMAW-P GMAW-S FCAW SMAW 0 *Respirable Particulates Not Otherwise Classified Insoluble or Poorly Soluble

19 19 45 Welding 316 (19% Cr) Stainless Steel (50/50% horizontal/vertical) Exposure Level and Cost by Process -based on travel speed only Hexavalent Chromium PEL 5 ug/m3 Level Times the PEL / TLV $1.03 $1.05 $ $ Per Li inear Foot (L LF) Manganese TLV 0.2 mg/m3 Respirable Fume* TLV 3 mg/m3 Exposure µg/m 20 µg/m µg/m GMAW-P GMAW-S FCAW SMAW 0.5 $ Per LF Process *Respirable Particulates Not Otherwise Classified Insoluble or Poorly Soluble

20 20 20 Welding Process Controlled Comparison Study Power Plant Coal Bunkers Wear Plate Installation Project SMAW, FCAW, and GMAW Production Rate 309L (24% Cr) Stainless Steel (or Travel Speed) Horizontal Welds Quality Cost

21 21 21 Power Plant Coal Bunkers Wear Plate Installation Project 400 LF of 0.25 SS horizontal butt welds on walls Carbon steel wear plates on 60º sloping walls inside large coal bunkers Carbon steel joined to 304 (18% Cr) stainless steel plates below 309L (24% Cr) consumables for dissimilar welds retain Cr with dilution

22 22 22 Power Plant Coal Bunkers Wear Plate Installation Project 4 experienced welders selected for proficiency Fastest production rate possible with acceptable quality Almost equal amounts of FCAW and GMAW with a small amount of SMAW Half-mask P100 respirators or single-use disposables Samples collected inside welding hood

23 Quality Problems: GMAW dripping in spray mode used for penetration too high deposition rate out of position need to slow down wire feed speed 23

24 Quality: better quality later, but some spatter need to fine tune voltage 24

25 309 (24% Cr) Stainless Coal Bunkers Horizontal Welds Exposure Level and Production Rate by Process 25 Exp posure Leve el Times the PEL / TLV µg/m 3.51 mg/m 3 26 mg/m IPM 50% arc-on 100% arc-on 100% arc-on 3.3 IPM 6.3 IPM 19.5 µg/m mg/m 3 mg/m 3 11 µg/m mg/m 3 mg/m Prod duction Rat te Inches / Minute (IPM) Hexavalent Chromium PEL 5 ug/m3 Manganese TLV 0.2 mg/m3 Respirable Fume* TLV 3 mg/m3 IPM 0 CrVI Mn Fume SMAW-S309 GMAW 309 FCAW 309 (n=1) Process (n=2) (n=3) 0 *Respirable Particulates Not Otherwise Classified Insoluble or Poorly Soluble

26 26 26 Welding Process Controlled Comparison Study Coal Fired Boiler Bottom Submerged Flight Conveyor Expansion Project SMAW vs FCAW Production Rate (or Travel Speed) 308L (20% Cr) Stainless Steel Quality Vertical Welds Cost

27 27 27 SMAW vs FCAW (308L, 20% Cr, Vertical Position) SMAW (50% Arc Time) FCAW (100% Arc Time) 1.23 IPM IPM

28 308 Stainless (20% Cr) Vertical Butt Welds on 1/4" Plate 1/8" Gap Exposure Level and Production Rate by Process 79 µg/m IPM Exposure Le evel Times the PEL / TLV % arc-on 100% arc-on 36 µg/m 3 17 mg/m 0.15 mg/m mg/m IPM Production Rate Inches / Minute (IPM) Hexavalent Chromium PEL 5 ug/m3 Manganese TLV 0.2 mg/m3 Respirable Fume* PEL 5 mg/m3 IPM mg/m SMAW 308 FCAW 308 (n=1) Process (median n=3) 0 *Respirable Particulates Not Otherwise Classified Insoluble or Poorly Soluble

29 29 29 Welding Process Controlled Comparison Study WldSh Weld Shop Comparison 316L (20% Cr) Stainless Steel Fillet Welds in Down-Flat Position SMAW (50% Arc Time) FCAW (100% Arc Time) Production Rate (or Travel Speed) Quality Cost

30 30 30 Weld Shop SMAW vs FCAW (316L, 19% Cr, Down-Flat) SMAW (50% Arc Time) FCAW (100% Arc Time) n=3 N= IPM 12.7 IPM

31 316 Stainless (19% Cr) Fillet Welds in Shop Flat Position Median Exposure Level and Mean Production Rate by Process µg/m IPM 12 the PEL / evel Times t TLV Exposure Le IPM CrVI 50% 100% arc-on arc-on.35 mg/m 3 13 mg/m 3 Mn Fume 73.7 µg/m 3 CrVI.79 mg/m mg/m 3 Mn Fume Production Rate Inches / Minute (IPM) Hexavalent Chromium PEL 5 ug/m3 Manganese TLV 0.2 mg/m3 Respirable Fume* TLV 3 mg/m3 IPM 0 SMAW 316 FCAW 316 (n=3) Process (n=4) 0 *Respirable Particulates Not Otherwise Classified Insoluble or Poorly Soluble

32 32 32 Welding Process Controlled Comparison Study Lime Clarifier Tank Project 309L (24% Cr) Stainless Steel Butt Welds in Horizontal (2/3) and Vertical (1/3) Positions FCAW versus GMAW (Short-Circuit) Production Rate (or Travel Speed) Quality Cost

33 309 Stainless (24% Cr) Horizontal Welds on 2 Lime ClarifierTanks 33 4 Exposure Level and Production Rate by Process 16 the PEL / evel Times t TLV Exposure Le µg/m 3 14 IPM 14 IPM 50% arc-on 60% arc-on 44mg/m µg/m 3.22 mg/m mg/m 3.11 mg/m s / Minute Rate Inches (IPM) Production R Hexavalent Chromium PEL 5 ug/m3 Manganese TLV 0.2 mg/m3 Respirable Fume* TLV 3 mg/m3 IPM CrVI Mn Fume CrVI Mn Fume FCAW 309 GMAW 309 (n=1) Process (n=1) 0 *Respirable Particulates Not Otherwise Classified Insoluble or Poorly Soluble

34 34 34 Conclusions/Recommendations This limited study indicates that SMAW does result in high fume exposures, but it can be a more costly process as compared to procedures like GMAW and FCAW Labor is likely the largest cost of welding. SMAW$ >> FCAW$ and GMAW$ This current study is strongly suggestive, but may not consider all of the direct and indirect costs associated with labor and consumables Four different welding projects were examined, additional projects need to be studied to ensure the data are valid This type of analysis can be very useful (and necessary) to push a large scale change in the selection of welding processes

35 35 35 Conclusions/Recommendations Minimize SMAW stainless steel. Air currents have an effect on exposure that are difficult to control. LEV likely needed for SMAW, GMAW, and FCAW on Cr containing alloys Additional research is needed to demonstrate the efficacy of the welding methods, and the positive attributes EPRI is considering such a study