manufacture, processing and use of stainless steel - International ...

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• slag formers (titania, silica flour, fluospar, feldspar) • gas-forming material (carbonates, limestone) • deoxidisers (ferrosilicon, ferromanganese) • binding agents (sodium silicate, potassium silicate, or lithium silicate) • slipping agents (kaolin clay, talc, bentonite clay) Electrode coatings fall into two types: (i) lime type (containing large amounts of limestone and fluospar and producing globular transfer of metal); (ii) titania type (containing rutile (titania), medium amounts of limestone and limited quantities of fluospar, and producing spray-like transfer of metal). Sodium or potassium silicates, which are commonly used as binding agents in the electrode coating, are the main source of alkali ions and can lead to the formation of soluble hexavalent chromium compounds (sodium or potassium dichromate) in SMAW fume. Some electrodes have been developed using lithium silicate as an alternative binding agent; such electrodes have been shown to generate fume with a lower hexavalent chromium content than those containing sodium or potassium silicate binders (Soudure Autogéne Francaise 1997). Flux-cored arc welding (FCAW) FCAW is an arc welding process that uses an arc between a continuous filler electrode and the weld pool. Shielding gas is provided by flux contained within the tubular electrode; additional shielding may be provided by an external supply. The flux contains deoxidisers, slag formers, arc stabilisers and alloying materials. Small diameter flux-cored wires using an argon-based shielding gas can involve either short circuit metal transfer or spray transfer. Submerged arc welding (SAW) The SAW process is completely shielded by a layer of loose granules of flux. Fluxes used in this process generally contain a mixture of slag-forming, deoxidising and alloying ingredients, bonded together by a silicate binder. The process uses a consumable solid wire electrode which is continuously fed from a spool. Plasma arc welding (PAW) The PAW process uses an open, unrestricted gas tungsten arc that is squeezed through a copper nozzle, resulting in an arc that is longer, thinner and more focused. The tungsten electrode is non-consumable. Two gases are supplied by the welding torch, a shielding gas that shields the weld and a plasma or orifice gas that controls the arc characteristics and shields the electrode. Shielding may also be supplemented by an external gas supply. 45
3.1.2 Information on exposure Welding of stainless steel results in the formation of fume containing particles and gases. As the particulate is mostly respirable, welding operations present the potential for inhalation exposure in the occupational setting. Published exposure data for the welding of stainless steel come from field studies and laboratory-based studies. The data from these studies are summarised in Table 3.1. Information on the elemental composition of MMA/SS and MIG/SS welding fume is presented in Table 3.2. Only a few studies are available which have investigated workplace exposure to stainless steel welding fumes using well-designed sampling strategies. In a number of studies, the use and effectiveness of controls have not been assessed and relatively small sample sizes have been used. Overall, the published data on exposure indicate that daily personal TWA concentrations for total fume are in the range 0.1-40 mg/m 3 (range of mean values 1.3-3.1 mg/m 3 ). In confined spaces, mean personal exposure levels up to 37.2 mg/m 3 have been reported. Comparison of total fume concentrations for the different welding methods shows that the highest levels occur with MMA welding compared to MIG or TIG welding. Fume concentrations measured in static samples constitute about one tenth of those found in personal samples. Laboratory-based studies on welding of stainless steel have provided useful data on the composition of fume associated with the different welding methods, the effect of welding parameters on fume composition, and the physical and chemical properties of welding fume. The available data show that MIG/SS welding produces higher total chromium concentrations than MMA/SS welding, although only a negligible proportion of this occurs as Cr VI (see Table 3.1). In contrast, MMA/SS welding generates a higher concentration of Cr VI in the fume compared to MIG and TIG welding; this is due to the presence of alkaline metals in the flux coating. Cr VI in MMA/SS welding fume occurs as sodium or potassium dichromate. The percentage of total chromium which exists as Cr VI in MMA/SS welding fume has been reported to range from 30 to 100% (see Table 3.1), and Cr VI concentrations of up to 1.5 mg/m 3 have been reported with MMA/SS welding operations (van der Wal 1985). The nickel content of fume from welding of stainless steel has been reported to be between 0.2 and 4.9% of the total fume. Nickel in welding fume occurs as oxides, predominantly in the insoluble form. 46
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MANUFACTURE, PROCESSING AND USE OF
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3.2 GRINDING OF STAINLESS STEEL ...
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Within the review, each section is
Page 7 and 8: Results from a single intra-muscula
Page 9 and 10: studies are often based on small nu
Page 11 and 12: The toxicological database for fume
Page 13 and 14: PEFR peak expiratory flow rate PSD
Page 15 and 16: Table 1.1 Identity of stainless ste
Page 17 and 18: There are several different systems
Page 19 and 20: method have been used in some of th
Page 21 and 22: grade was tested, an austenitic sta
Page 23 and 24: pick-up of nickel and chromium when
Page 25 and 26: Human data Patch-testing studies Se
Page 27 and 28: does not allow any conclusions to b
Page 29 and 30: Schriver et al. (1976) reported a c
Page 31 and 32: Other studies reviewed in this sect
Page 33 and 34: Human data on the effects of prolon
Page 35 and 36: Exposure to stainless steel powder
Page 37 and 38: Prolonged exposure Information on t
Page 39 and 40: In view of the chemical/physical pr
Page 41 and 42: Figure 2.1 Production of stainless
Page 43 and 44: Table 2.1 Manufacture of stainless
Page 45 and 46: 2.3 Toxicokinetics Toxicokinetics i
Page 47 and 48: survey, there was no evidence of an
Page 49 and 50: The "exposure" variable used by the
Page 51 and 52: Table 2.2 Epidemiological studies o
Page 53 and 54: Consideration against classificatio
Page 55 and 56: 3 STAINLESS STEEL PROCESSING This s
Page 57: Arc voltage or arc length Arc volta
Page 61 and 62: Reference Akesson & Skerfving (1985
Page 63 and 64: Table 3.2 Elemental composition of
Page 65 and 66: These levels decreased, although ch
Page 67 and 68: treatment group and no effects were
Page 69 and 70: esponses in terms of irritancy, fib
Page 71 and 72: MMA/SS) at approximately 400 mg/m 3
Page 73 and 74: Exposure measure 60 Welders a (n=52
Page 75 and 76: was relatively heterogeneous. No de
Page 77 and 78: used included respiratory symptoms,
Page 79 and 80: Keskinen et al. (1980) reported on
Page 81 and 82: Positive results were reported with
Page 83 and 84: Welding method Electrode Base metal
Page 85 and 86: A significant increase in chromatid
Page 87 and 88: treated with MIG/SS fume. One lung
Page 89 and 90: The mortality experiences of the tw
Page 91 and 92: Moulin et al. 1993b Mortality was s
Page 93 and 94: Moulin 1997 A meta-analysis involvi
Page 95 and 96: Table 3.3. Epidemiological studies
Page 97 and 98: “are known, and in this study too
Page 99 and 100: Bonde et al. (1990) investigated fe
Page 101 and 102: out stainless steel welding in the
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Page 105 and 106: Effects on reproduction No studies
Page 107 and 108: Table 3.4 Grinding of stainless ste
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Reference Process Work piece materi
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No deaths occurred in any treatment
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Human data No studies are available
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mg of dust per animal. In another t
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(Observed 8, Expected 4.7, SMR 170,
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Table 3.5 Epidemiological studies o
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Carcinogenicity The carcinogenicity
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Toxicokinetics and toxicity Informa
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112 APPENDIX 1 22.7.94 Official Jou
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Escales F, Galante J, Rostoker W. B
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IARC. Monographs on the evaluation
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Malmqvist KG, Johansson GI, Bohgard
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Simonato L, Fletcher AC, Andersen A
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Bondemark L, Kurol J, Wennberg A. O
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Furon D, Hilderbrand HF. Research i
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Hooftman RN, Arkesteyn CW, Roza P.
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Koshi K, Yagami T. Chromosomes of c
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Merritt K, Brown SA. Release of hex
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Pereira ML. Studies on the permeabi
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Stern RM . Detecting a possible inc
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Toyoshima M, Sato A, Taniguchi M, I
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