Investigations on Chromium in Stainless Steel Welding Fumes

Investigations on Chromium in Stainless Steel W e l d i n g Fumes Reducing the Na20 + K-,0 content of electrode coverings is described as leading to sufficiently reduced hexavalent Cr in welding fumes

BY S. KIMURA, M. KOBAYASHI, T. G O D A I A N D S. M I N A T O

ABSTRACT. The chemical composition, especially the chemical state of chromium, of lainless steel welding fumes has been investigated. In studying the fractional analysis of chromium w i t h regard to its valence and water solubility, the infrared spectrometry was f o u n d to be useful for the detection of hexavalent chromium in solid fume samples. Shielded metal arc welding fumes generally contain 3 to 7% chromium, 60 to 90% of which is water-soluble. All of the soluble chromium is hexavalent and is present in the form of K.Cr0 4 or Na.CrO,. Gas metal arc welding fume contains approximately 15% chromium in w h i c h a very little fraction is soluble and hexavalent. There is some possibility that the fume contains a small amount of insoluble hexavalent chromium, but this is not regarded as serious. The TLV's of stainless steel welding fumes and low alloy steel welding fumes have been considered. If the alkaline content of the covering calculated as (Na,,0 + K,0) is decreased to less than 0.5%, hexavalent chromium in the fume can be sufficiently reduced. Improved electrodes have been developed and proved to be less hazardous than conventional ones by means of an animal test.

ated during welding of stainless steels, by reason of their high percentage of hexavalent chromium (Cr(VI)) and nickel which are considered to be carcinogenic. Urgent investigations are being made in the United States on this substantial problem. 1 Particularly regarding chromium, it occupies a higher percentage in the stainless steel welding fume and has some analytical difficulties. It is, therefore, necessary to solve the problem of chromium as soon as possible. Even in the I950's Cr(VI) was known to be present in stainless steel welding fumes; Fregert et air confirmed its presence by experimentation in 1963. After that, several reports were presented with similar results, and attention has been drawn lo them since Virtamo et a/.3 showed in the document of the International Institute of Welding that stainless steel welders have been exposed to Cr(VI) of the concentration above its Threshold Limit Value (TLV). In 1977, Maxild et al.' presented some experimental results which revealed intense mutagenicity (i.e., the tendency to produce mutations) of the shielded metal arc welding (SMAW) fumes of stainless steels. This presentation seemed to direct world-wide attention to the Cr(VI) problem.

Introduction Particulate fumes are the most important pollutant in the welding environment. Protective measures against the fumes have been progressively brought into practice, and numerous scientific researches on the fumes have been made extending over a wide range of fields. Recently, attention was directed to the fumes gener-

Paper presented at the AWS 60th Annual Meeting held in Detroit, Michigan, during April 2-6, 1979. The authors are associated with the Technical Center, Welding Division, oi Kobe Steel, Ltd.; 100, Miyamae, Fujisawa, japan, as follows: S. KIMURA—General Manager; T. GODAI-Manager of Technical Department; M. KOBAYASHI and S. MINATO-Senior Researchers, Technical Department.

Meanwhile, the National Institute for Occupational Safety and Health (NIOSH) has proposed to decrease the TLV of Cr(VI) to a great extent. 3 According to the proposal, the TLV, 50 jitg/m 3 so far, should be divided into t w o classes; 25 jug/m 3 for water soluble Cr(VI) and 1 jug/m 3 for water insoluble Cr(VI). It is based on the reason that the insoluble Cr(VI) is carcinogenic. If these TLV's are applied on the welding fumes, the environmental control of fume concentration will greatly depend on the presence of Cr(VI). However, the fractional analysis of Cr(VI) into soluble and insoluble forms has not yet been achieved. Investigations are therefore needed to search for some analytical method. This paper describes the results of the investigation on the chemical compositions of stainless steel welding fumes, especially on the chemical state of chromium in the fumes. In the course of studying the analytical method, it was found that the infrared spectrometry is useful for the detection of Cr(VI) in a solid sample. W i t h the application of this method and X-ray diffractometry in addition to the general wet chemical analysis, the chemical state of chromium was practically ascertained. One purpose of this investigation was to find some ways to decrease the Cr(VI) content of stainless steel w e l d ing fumes as low as possible through knowledge of the essential characteristics of the fumes. A way was found as a result of the research on the effect of covering constituents on the chemical state of chromium. The process and the finally developed electrodes w i t h less hazardous fumes are also described.

W E L D I N G RESEARCH S U P P L E M E N T I 195-s

A remaining problem out of the fractional determination of chromium is how to determine insoluble Cr(VI). Stainless steel welding fumes have a complex chemical composition as shown in Table 1. It seems inevitable that chromium may change its valence in the process of dissolution o w i n g to oxidation (Cr(lll) to Cr(VI)) or reduction (Cr(VI) to Cr(lll)) by reaction w i t h iron or manganese, w h i c h contains both valence of (II) and (III). Moreover, as stainless steel welding fumes cannot easily be dissolved into a clear solution, it is difficult to select an adequate dissolving medium.

authors' laboratory. The infrared spectrometry was, therefore, considered as a substitute for the ESCA method. The principle of the infrared spectrometry may be summarized as follows. When a substance is irradiated w i t h an infrared ray, certain wave lengths out of the ray are absorbed corresponding to the molecular vibration energy. The absorption spectrum has a fine structure, which is characteristic to each substance. Accordingly, infrared spectrometry is useful for identification of a substance. Although major objects are organic materials, inorganic materials can also be identified by taking notice of the characteristic absorption by anion atom groups. In case of Cr(VI), it generally forms an atom group coordinated by oxygen atoms and shows a specific infrared absorption spectrum. Possible Cr(VI) compounds in the stainless steel w e l d ing fumes are CrO,, chromates, and dichromates. As shown in Fig. 2, chromates have a characteristic absorption at nearly 900 cm ', CrO ; , and dichromates have one at nearly 950 cm ' It was expected that Cr(VI) in solid fume samples can be detected based on these absorption peaks; analytical results on the fumes were successful as described later. The potassium iodide pellet technique was used for sample preparation. The total weight of the pellet was 200 mg, of which 3 mg was the fume sample.

After several trials, the determination of insoluble Cr(VI) by means of wet procedure was abandoned.

Fume Analysis of Conventional W e l d i n g Materials

Soluble Cr(VI)

. Soluble Cr Soluble Cr(III)

Total Cr Insoluble Cr(VI) I n s o l u b l e Cr Insoluble Cr(III) Fig. I—Classification of chromium tion described above, Cr(VI) is extracted w i t h methylisobutyl ketone solution of trioctyl-amine. Cr is then determined by atomic absoptiometry. Cr(VI) can also be determined accurately by the s-diphenyl carbazide procedure which is most commonly used. The above described procedure is adopted, however, because of detectability and rapidity.

Studies on Analytical M e t h o d s Wet Chemical Procedures In order to know the chemical state of chromium in stainless steel welding fumes, it is necessary to classify chromium as indicated in Fig. 1. Among these, Total Cr, Soluble Cr, and Soluble Cr(VI) can be determined by means of general wet chemical procedures, and Insoluble Cr and Soluble Cr(III) can be calculated from these results. After some studies, the procedures described in the following summaries were found to be appropriate to determine Total Cr, Soluble Cr, and Soluble Cr(VI).

Consideration on Wet Chemical Determination of Insoluble Cr(VI)

Determination of Total Chromium. The sample is fused w i t h sodium peroxide and sodium hydroxide in a nickel crucible. The melt is extracted by hot water and acidified with sulfuric acid. All Cr is oxidized to Cr(VI) by adding ammonium persulfate. After decomposition of oxidized Mn w i t h hydrochloric acid, Cr(VI) is reduced by adding excess standard solution of ferrous ammonium sulfate. The excess Fe(ll) is titrated w i t h potassium permanganate standard solution. The alkaline fusion technique is used because a considerable amount of undissolved residue remains when dissolved w i t h acids. Determination of Soluble Chromium. 0.2 g sample is transferred in 100 ml water, and boiled for five minutes. The residue is filtered out by a paper filter after cooling, and washed sufficiently with water. The filtrate is diluted to 200 ml, and Cr is determined by the same procedure as the total chromium. Determination of Soluble Cr(VI). From the filtrate of the water extrac-

Table 1 - Chemical Composition of Fumes, Welding material

Cr,Oa

NiO

Total Analysis Study on Infrared Spectrometry It was then necessary to determine Cr(VI) and Cr(III) fractionally in a solid state fume sample w i t h o u t changing their valence during the determination. Electron Spectroscopy for Chemical Analysis (ESCA) has been reported to be applicable for this purpose. 6 Unfortunately, however, the ESCA apparatus was not available in the

Sampling Technique. Fume collection was carried out according to the Japanese Industrial Standard (JIS) Z3920 " M e t h o d of Measuring Total Amount of W e l d Fumes Generated by Covered Electrode." The summary is as follows. By means of manual (semiautomatic in case of gas metal arc welding (GMAW)) bead-on-plate welding in a

% Fe,0 : ,

MnO

SiO,

TiO,

ALO : ;

CaO

MgO

Na..O

K,0

F

E 308

Total Soluble

7.26 5.44

0.59 0.02

6.89 0.14

9.04 0.59

6.67 4.66

8.57 0.28

0.98 0.74

4.23 0.14

0.12 0.02

2.87 2.80

22.14 22.04

17.66 17.5

E 310

Total Soluble

9.34 5.85

1.69 0.06

6.81 0.17

10.46 0.74

5.80 5.36

5.35 0.38

0.83 0.77

3.88 0.08

0.09 0.02

5.90 5.66

23.49 23.01

18.63 15.1

E 430

Total Soluble

4.85 4.41

0.03 0.5%: Dimethylglyoxime separation and EDTA titration method Total: Ascorbic acid reduction and iodine titration method Soluble: Thiocyanic acid absorptiometry Total: Sodium bismuthate oxidation and potassium permanganate titration method Soluble: A m m o n i u m persulfate oxidation absorptiometry M o l y b d e n u m blue absorptiometry < 1 % : Absorptiometry > 1 % : A l u m i n u m reduction and ferric chloride titration m e t h o d Total: Atomic absorption spectrometry Soluble: EDTA titration method EDTA titration m e t h o d Atomic absorption spectrometry Atomic absorption spectrometry Atomic absorption spectrometry Total: Pyrohydrolysis and titration method Soluble: Absorptiometry

Ni Fe Mn

Si Ti Al Ca Mg Na K F

Table 4—Fractional Determination of C h r o m i u m in Fumes, %

1600

1400

1200

1000

800

600

400

ota I Cr

Cr

Cr (VI)

Insoluble Cr

E 308

4.92 5.01

3.83 3.70

3.80 3.79

1.29 1.34

E 310

6.46 6.31

3.97 4.03

4.10 4.04

2.11 2.06

E 430

3.30 3.34

3.00 3.04

3.00 3.0?

0.17 0.21

15.89 16.01

tr. tr.

—

15.93 15.97

Wave N u m b e r ( C m ~ l )

Fig. 2~lnfrared absorption ous Cr(VI) compounds

spectra of vari-

Soluble Cr

Welding material

E R 308

WELDING

R E S E A R C H S U P P L E M E N T I 197-s

High Volume Air Sampler

Fig. 3—Welding chamber for fume collection (dimensions in mm)

Therefore, manganese and chromium contents become higher in the fume compared w i t h the electrode composition, which is 20% Cr, 10% Ni, 1.7% M n , 0.4% Si, and 67% Fe. Fractional Analysis of Chromium, and Infrared Spectrometry Total chromium, soluble and insoluble c h r o m i u m , and soluble Cr(VI) were determined on the four fume samples. Dual determinations were carried out for every fraction. The results are shown in Table 4. The sum of the soluble and insoluble chromium is almost equal to the total c h r o m i u m , indicating that each determination is correct. In other words, insoluble chromium can be calculated by subtracting the soluble from the total. The most important result is that all of the soluble chromium is Cr(VI)-that is, soluble Cr(VI) can be estimated by determining soluble chromium. From those results stainless steel SMAW fumes are regarded to contain 3 to 7?b chromium, 60 to 90% 1 9 8 - s l JULY 1979

of which is soluble Cr(VI). The G M A W fume has a higher chromium content than the SMAW fumes due to absence of flux materials. Almost all of the chromium is insoluble. Paralleling the chemical analysis, infrared spectrometry was applied on the original four fume samples and on the respective residues after extraction of the soluble fraction. The absorption spectral patterns are shown in Fig. 4. In the original SMAW fumes, the absorption peak at 900 cm ' is clearly observed, which almost disappears ir: the pattern of the residues. The peak is assumed to correspond to K-CrOj (E 308 and E 310), or to Na,Cr0 4 (E 430) by referring to the total analysis shown in Table 1. The absorption spectral pattern of the G M A W fume indicates that the small peak at 900 cm ' does not change between the original and the residue. Although chromate may not be formed because of absence of alkalines and alkaline earths, it is

possible that the small peak corresponds to some atom group consisting of Cr(VI) and oxygen. Consequently, very small amounts of insoluble Cr(VI) should be considered. The amount of insoluble Cr(VI), if il is present, in the residues of the SMAW fumes is almost as much as the G M A W fume according to the infrared absorption. Maxild ef a/.4 has reported that G M A W fumes do not have mutagenicity on Salmonella typhimurium,* while SMAW fumes have. The mutagenicity of SMAW fumes is, therefore, not regarded to be caused by the insoluble Cr(VI) in the fumes. Crystal Identification by Means of X-Ray Diffractometry X-ray diffractometry was applied to identify crystals on the original four samples and on the three residues of SMAW fumes. The diffraction patterns

'Bacteria used in a screening test to study the effects oi fume.

1600

1200

800

400

1200

800

400

1200

800

400

1200

800

400

Wave Number (Cm"1) A: Original Fume B: Residues after Extraction of Soluble Fraction Fig. 4—Infrared absorption spectra of stainless steel welding fumes

are shown in Fig. 5. The principal parameters of the X-ray were as follows: target—copper; monochromat o r - g r a p h i t e (002); voltage-50 kV; current—160 mA. In the G M A W fume, only Fe.,0, can be detected. M u c h of other metallic constituents is considered to replace Fe(ll) or Fe(lll) in the Fe ; ,0 4 , and the remainder is amorphous. Fe :! 0 4 has the spinel type crystal structure. It is an interesting fact that spinel type crystal is preferentially formed in welding fume as shown in other reports. In the fume of E 308 and E 310, almost the same patterns are observed. They are also the same in infrared absorption patterns, indicating that chromium content of the deposited metal within a range from 18 to 25% does not affect the chemical and crystalline structure of the fume. A considerable amount of Fe 3 0 4 can be detected in the same way as the G M A W fume. The presence of K,Cr0 4 is the most noteworthy, and here it is confirmed that Cr(VI) is present in the form of K,Cr0 4 . In the insoluble residue, K 2 Cr0 4 disappears, F e , 0 , becomes clearer, and CaF, can be detected. The peaks of Fe.,04 are comparatively weak in the E 430 fume, and NaF and CaF, are remarkable. This pattern is generally observed in SMAW fumes w i t h high content of Na, Ca, and F. Cr(VI) is identified as in the form of Na.CrO,, and here again it is confirmed that Cr(VI) in the stainless steel SMAW fumes exists in the form of

chromate. CaF, and Fe,0 4 remain in the residue. The SMAW fumes easily absorb moisture. Therefore, the diffraction pattern easily changes due to deliquescence or to taking crystal water. For this reason the samples were preserved in polyethylene bags containing silica-gel immediately after the collection. The TLV of Stainless Steel Welding Fumes The TLV for chromic acid and chromates (soluble Cr(VI)) is 0.05 m g / m 3 as Cr according to the most recent recommendation by the American Conference of Governmental Industrial Hygienists (ACGIH). Considering that 5% soluble Cr(VI) at the highest is contained in stainless steel SMAW fumes, total fume concentration has to be controlled to lower than 1 m g / m 3 in order that Cr(VI) concentration should not reach the TLV. This is one fifth of the TLV, 5 m g / m 3 , recommended by ACGIH for general welding fume, and suggests that a stronger control is needed in the stainless steel welding environment. If the NIOSH proposal, 25 ,ug/m 3 for soluble Cr(VI), is put into effect, the TLV of the stainless steel welding fumes becomes as low as 0.5 m g / m 3 . At this concentration, insoluble Cr(VI) does not exceed its proposed TLV, 1 jug/m 3 , if its content in the fume is less than 0.2%. In other words, provided that insoluble Cr(VI) is less than 0.2%, it does not exceed the proposed TLV if

soluble Cr(VI) is controlled below its proposed TLV. Fractional Analysis of Chromium in Low-Alloy Steel Welding Fumes In SMAW, the problem of TLV may arise even w h e n chromium content in the electrode is lower. In order to clarify the problem, total chromium and soluble Cr(VI) were determined on the SMAW fumes given off by electrodes ranging from 13% chromium steel to mild steel. The results are shown in Table 5. All of the coverings were lime-type. If Cr(VI) concentration does not exceed its TLV when total fume concentration reaches 5 m g / m 3 , working environment can be controlled by monitoring the total fume. In this respect, the limit value of Cr(VI) content in the fume is 1%. Consequently, the TLV of total fume concentration, 5 m g / m 1 , can be applied only in welding steels w i t h 5% chromium or lower, or w i t h 3% chromium or lower when the NIOSH proposal w o u l d be put into effect. Effect of Covering Constituents on the Valence of C h r o m i u m in Fumes Experiment on Electrodes Without Covering From the facts that Cr(VI) is not formed in the G M A W fume and that Cr(VI) in the SMAW fume is present in the form of Na.CrO, or K,CrO,, it is assumed that sodium and potassium


200-s I JULY 1979

Table 5—Total Chromium and Cr(VI) in Low-Alloy Steel Welding Fumes, % Cr in deposited metal

Total Cr

Cr(VI)

13 9 7 5 3 2.3 1.3 0.5 0.2 0.02

2.44 2.25 1.78 1.39 0.60 0.66 0.33 0.17 0.07 0.02

2.25 1.56 1.22 0.68 0.37 0.26 0.23 0.125 0.045 0.005

8

Fume

Cr Content of Covered Electrode (%)

19.0

15

15Cr

40Cr

7

R SS £ LL

play some role in the formation of Cr(VI). W i t h this assumption, Cr(VI) in the fume was analyzed using a core wire of 20% chromium w i t h o u t any covering, and the same wire w i t h sodiumpotassium water glass applied on it and dried. Cr(VI) was 0.0013% in the former and 2.75% in the latter. The extreme difference explains that sodium and potassium are probably the main cause of Cr(VI) formation in fume.

Cr Content of Core Wire (%|

5

>

The Effects of Sodium, Potassium, and Lithium Content in the Covering Sodium and potassium content in the covering was varied stepwise, and Cr(VI) in the fume was determined. The tested electrodes have various chromium content in the 5 mm diameter core wire and in the lime-titania covering as shown in Fig. 6. The sodium and potassium content was varied by varying the feldspar content in the covering. Silica-sol, which is free from sodium and potassium, was used as a binding agent. The results are shown in Fig. 6. Sodium and potassium content in the covering is shown as ( N a , 0 + K,0). As (Na.O + K,0) decreases, Cr(VI) in the fume also decreases. The decrease is especially remarkable in the range less than 1 % of ( N a , 0 4- K,0) even in the case of higher chromium content. The range lower than 0.5% of (Na.O + K,0) is the most desirable. These findings are extremely significant from the viewpoint that sufficiently low Cr(VI) fume

Table 6—The Effect of Lithium Content of Covering on Cr(VI) Content of Fume Alkaline in covering,

%

Cr in f u m e , %

LiX>

Na.O

K..O

Total Cr

Cr(VI)

1.36 2.22 3.75

0.09 0.09 0.09

0.04 0.04 0.04

8.01 7.50 6.68

0.65 0.78 0.98

6

4 (Na20 + K20) Content of Covering (%)

Fig. 6—The effect of (Na.20 + K20) content of covering on Cr(VI) content of fume

can be obtained even by a SMAW electrode. Another experiment was carried out to examine the effect of lithium which belongs to the same alkaline family as sodium and potassium. Experimental electrodes w i t h various levels of lithium and low ( N a , 0 4- K,0) level were welded. Total chromium and Cr(VI) in the fumes are shown in Table 6. Additional significant information obtained is that lithium does not form Cr(VI) in the fume, unlike sodium and potassium.

Further experiments to examine the effect of calcium indicated that calcium also had some effect to form Cr(VI), though not so much as sodium and potassium. Other alkaline earths seem to have some effect to various extents. It was also indicated that chromium in the covering had almost the same effect as that in the core wire. This behavior can be explained from the fact that a covering and a core wire have almost the same contribution to the fume formation."

Table 7—Fume Emission Rate, Chromium in Fumes, and Cr(Vl) Emission Rate of the Improved Electrodes Cr in umes, %

AWS specification

Fume emission rate, mg/min

Total C

CR(VI)

Cr(VI) emission rate, mg/min

Conventional E 308 E 308 E 308 L E 309 E 316 E 316L E 347

210 165 170 166 162 145 158

5.38 8.10 8.01 8.09 7.67 7.65 6.94

4.14 0.45 0.41 0.35 0.35 0.39 0.31

8.69 0.74 0.70 0.58 0.57 0.57 0.49


Table 8—Chemical Compositions of the Fume of the Improved E 308 Electrode, %

Cr,0. NiO Fe.,0, MnO SiO., TiO, ALO., CaO MgO Na,0 K..O Li.,0 F

Total

Soluble

11.84 0.87 13.70 13.81 6.87 6.19 0.36 6.72 17.64 1.79 0.96 4.73 10.52

0.66 tr. tr. tr. 0.58 tr. tr. 0.50 0.28 0.98 0.66 3.33 3.80

Characteristics of

Improved

Electrodes Fume Emission Rate and Composition As d e s c r i b e d a b o v e , C r ( V I ) in t h e f u m e c a n b e s u f f i c i e n t l y d e c r e a s e d if ( N a , 0 4- K . O ) i n t h e c o v e r i n g is d u l y r e d u c e d . By u t i l i z i n g t h i s p r i n c i p l e , i m p r o v e d stainless steel c o v e r e d e l e c t r o d e s f o r p r a c t i c a l use h a v e b e e n developed. The i m p r o v e d electrodes are o f l i m e - t i t a n i a c o v e r i n g a n d c o r r e s p o n d t o A W S EXXX-16s. As t h e f u m e e m i s s i o n rate is also d e c r e a s e d b y t h e decrease o f ( N a . O + ECO), i m p r o v e m e n t is a c c o m p l i s h e d s i m u l t a n e o u s l y on b o t h quality and q u a n t i t y of the fume.

Table 7 shows the f u m e emission rates, t o t a l c h r o m i u m a n d C r ( V I ) in t h e f u m e s , a n d C r ( V I ) e m i s s i o n rates o f t h e improved electrodes c o m p a r e d w i t h a c o n v e n t i o n a l E 308 e l e c t r o d e , w h e n 4 m m e l e c t r o d e s are w e l d e d at 140 a m p e r e s a.c. T h e e m i s s i o n rate a t t e n u a t i o n o f t h e t o t a l f u m e a n d C r ( V I ) is 30% a n d 94% r e s p e c t i v e l y . T h e f u m e o f t h e i m p r o v e d E 308 e l e c t r o d e w a s t o t a l l y a n a l y z e d as s h o w n in T a b l e 8. S o l u b l e c o m p o n e n t s are r e m a r k a b l y decreased, and no soluble c o m p o u n d s other than l i t h i u m fluoride can be estimated. The remarkable decrease of a l k a l i n e also seems t o be p r e f e r a b l e from a health hazard v i e w p o i n t . The patterns of the infrared absorpt i o n a n d t h e X-ray d i f f r a c t i o n o f t h e f u m e o f t h e i m p r o v e d E 308 e l e c t r o d e are s h o w n in Figs. 7 a n d 8, r e s p e c t i v e l y . N o c h r o m a t e c a n b e d e t e c t e d b y X-ray diffraction, and a l i m i t e d q u a n t i t y of c h r o m a t e is a s c e r t a i n e d by t h e i n f r a r e d a b s o r p t i o n . T h e p r i n c i p a l crystal c o m p o n e n t is F e , 0 4 , a n d o n e o t h e r d e t e c t a b l e crystal is LiF. T h e f a c t t h a t t h e crystal structure b e c o m e s similar t o t h e G M A W f u m e , o r t o m i l d steel w e l d i n g f u m e s , m a y p o s s i b l y suggest that the effect of the i m p r o v e d f u m e s o n an o r g a n i s m also b e c o m e s s i m i l a r to those fumes. T h e m e l t i n g rates a n d t h e f u m e e m i s s i o n rates b y e v e r y g r a m o f d e p o s i t e d m e t a l are s h o w n in T a b l e 9. T h e results i n d i c a t e t h a t w e l d i n g e f f i c i e n c y

1600 1400

1200 1000

800

Wave Number (cm

26

202-s j JULY 1979

pattern of the fume from the improved

(deg.) E 308

electrode

600

400

)

Fig. 7—Infrared absorption spectra of the fume from the improved E 308 electrode

is n o t l o w e r e d by t h e d e c r e a s e o f f u m e emission. The c o m p o s i t i o n , mechanical properties, c o r r o s i o n resistance, a n d o t h e r p r o p e r t i e s o f w e l d m e t a l s f u l l y satisfy the requirements of the respective AWS specifications.

Original

Fig. 8—X-ray diffraction

-1

Improved lime-type electrodes have also been achieved, although the attenuation of Cr(VI) is a little lower due to high calcium content.

Table 9-Melting Rate and Fume Emission Rate by Every Gram of Deposited Metal of the Improved Electrode

Animal Test White male guinea pigs, weighing 250 to 300 grams each, were exposed to the fumes periodically in the chamber shown schematically in Fig. 9. W e l d i n g and exposure for 30 min each time were carried out twice a week for 3 months. Clinical observation, histological inspection of the lung, and other examinations were carried out on the animals during and after 213 days. The improved E 308 electrode was used for the subject group, and the conventional one for the contrast group. Each group consisted of eight animals. Four of the contrast group died during the test period, and the average lifetime was 122 days. On the other hand, none of the subject group died throughout the test period. Dissection revealed that congestion of blood had. occurred in all the animals, although the subject group suffered to a lesser extent. The fumes of the improved electrodes were thus proved to be less hazardous than conventional ones insofar as acute effects were concerned. Conclusion The chemical composition, especially the chemical state of c h r o m i u m , of fumes generated in welding of stainless steels has been investigated. During the fractional analysis of chromium w i t h regard to its valence and water solubility, it was f o u n d that infrared spectrometry can be a useful

Weld ng current, A

M e l t i n g rate, g/min

Fume emission rate (melting rate), mg/g

140 140 140 140 140

23.7 23.8 24.3 23.6 23.5

9.70 6.93 6.83 6.86 6.72

Commercial E 308 E 308 E 309 E 316 E 347

guideline for the detection of Cr(VI) in solid fume samples. Insoluble Cr(VI) cannot be determined by any wet chemical procedures. The SMAW fumes consist of approximately 60% water soluble fraction in which alkaline, fluorine, and chromium are the main ingredients. Alkaline content is very high. Stainless steel SMAW fumes can be considered as containing 3 to 7% chromium, 60 to 90% of which is soluble. All of the soluble chromium is Cr(VI) , and is present in the form of K.CrO., or Na.CrO,. The G M A W fume contains approximately 15% chromium in which very little fraction is water soluble and hexavalent. There is some possibility that a small amount of insoluble Cr(VI) is contained both in SMAW and G M A W fumes. However, this is not regarded to be the cause of the reported mutagenicity. The TLV of stainless steel welding fumes should be considered to be 1 mg/m 3 . Provided that insoluble Cr(Vl) is less than 0.2% in the fume, it does not exceed the proposed TLV by NIOSH if soluble Cr(VI) is controlled below its proposed TLV. The TLV of the general fumes, 5 mg/m 3 , can be applied only in the case of welding

Impinger

140/

steels with 5% chromium or less. Alkaline content in the covering greatly affects the formation of Cr(VI) in the fumes. If (Na.O + K.O) in the covering is less than 1%, desirably less than 0.5%, Cr(VI) in the fumes can be sufficiently reduced. The fume emission rate can also be decreased. Improved electrodes for practical use attenuate the emission of the total fume and Cr(VI) by as far as 30% and 94% respectively. The animal test has proved that the fumes of the improved electrodes are less hazardous than conventional ones. Acfenow/edgment The authors wish to express their appreciation to K. Kawada, M.D., T. Matsumoto, M.D., Y. Tanabe, T. Adachi, and Y. Nagasaki of Kobe Steel, for giving the animal test and for helpful advice. Appreciation is also expressed to Dr. A. Nakaue of the Asada Research Laboratory, Kobe Steel, for the X-ray diffraction. Significant contributions to the work by a large number of researchers of the authors' Department is gratefully acknowledged. References 1. DeLong, W. T., "OSHA Regulatory

Flow Meter

Suction Pump

JV —\S

Exhaust

480

Dimensions in mm 480 Fume Generation Chamber

Exposure Chamber (Volume : 10.6 6) Fig. 9—Schematic diagram of the fume exposure apparatus for an animal test


Proposals and Philosophies Pertaining to W e l d i n g Fumes," Welding lournal, 57 (7), luly 1978, pp. 15 to 23. 2. Fregert, S., and O v r u m , P., "Chromate in Welding Fumes w i t h Special Reference to Contact Dermatitis," Acta Dermato Venercologica, 43, 1963, pp. 119 to 124. 3. Virtamo, M., and Tuomola, S., "Hexavalent Chromium Compounds in W e l d i n g Fumes," Document VIII-584-74, International Institute of W e l d i n g , 1974. 4. M a x i l d , )., Andersen, M., Kiel, P., and Stern, R.M., "Mutagenicity of Fume Particles from Metal Arc Welding on Stainless

Steel in the Salmonella/Microsome Test," Document VIII-728-77, International Institute of W e l d i n g , 1977. 5. National Institute for Occupational Safety and Health, "Criteria for a Recommended Standard-Occupational Exposure to C h r o m i u m (VI)," HEW Publication No. (NIOSH) 76-129, 1975, Superintendent of Documents, U. S. Government Printing Office, Washington, D. C. 6. Launter, G. M., Carver, ). C , and Konzen, R. B., "Measurement of Chromium VI and Chromium III in Stainless Steel W e l d -

ing Fumes w i t h Electron Spectroscopy for Chemical Analysis and Neutron Activation Analysis," American Industrial Hygienist Association lournal, 39 (8), 1978 pp. 651 to 660. 7. Heile, R. F., and Hill, D. C , "Particulate Fume Generation in Arc W e l d i n g Processes," Welding lournal, 54 (7), July 1975, Research Suppl., pp. 201-s to 210-s. 8. Kobayashi, M., M a k i , S., Hashimoto, Y., and Suga, T., "Some Considerations About Formation Mechanism of W e l d i n g Fumes," Document VIII-715-77, International Institute of W e l d i n g , 1977.

A Reminder to Authors— If you plan to present a paper at the AWS 61st Annual Meeting April 14-18, 1980, be sure to mail your abstract with the Author Application Form (page 49 May issue) no later than August 15, 1979. For papers to be presented at the 11th AWS-WRC International Brazing Conference, April 15, 17, 1980, the Author Application Form (page 85 April issue) and abstract must be mailed no later than September 15, 1979.

204-s MULY 1979