Transcript The Effect of Welding Parameters on the Chemical Composition

Assessment of exposure to chemical
agents in welding fume
Alan Howe, Stephen Bradley, Ken Chung
and Monica Martinez (HSL), Graham
Carter (TWI), and Christine Northage and
Roger Sykes (HSE)
Overview

Background

Aims and objectives

Experimental work

Results

Recommendations
Background (1)

Welding fume
– large number of workers exposed in many industries
– wide range of processes and materials
– 5 mg m-3 limit value for welding fume

Welding fume containing hazardous substances
– measurement of exposure to individual components of
the fume
– EH 54 method of applying a control limit based on the
chemical composition of the fume
Background (2)
For each substance, the fume concentration (mg m-3)
below which its limit value is not exceeded is given by:
100 x LV
c
where LV is the limit value for the substance (mg m-3) and c is its
concentration in the fume (% m/m) from MSDS data
The control limit is lowest value unless this is above the
welding fume limit value (5 mg m-3)
Background (3)
For the EH54 method to work:

Welding fume composition must not be
significantly influenced by welding parameters
(current, voltage etc)

MSDS data must be both accurate and complete

Other airborne particles must not interfere
Aims and objectives (1)

To investigate the effect of welding parameters
on the chemical composition of welding fume
and define test conditions for generating future
MSDS data

To assess the reliability of current MSDS
data on the chemical composition of welding
fume
Aims and objectives (2)

To determine whether dust from welding-related
operations can significantly influence the
chemical composition of airborne particles to
which a welder is exposed

To generate the information necessary to
develop a European and International Standard
on fume data sheets
Experimental

Fume samples generated by mechanised welding:
– semi-mechanised rig used for MMA welding
– Kat Gulley GK 171-90 traverse used for MAG and FCAW

Analysis
– X-ray fluorescence spectrometry (XRFS) and/or inductively
coupled plasma atomic emission spectrometry (ICP-AES) for
metal content
– spectrophotometry for hexavalent chromium
– ion selective electrode (ISE) for fluoride
Welding parameter tests for stainless steel welding
Process
Voltage
Current
Diameter
MMA
Reproducibility




Traverse
speed

MAG









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Mode of
transfer
Gas type
Gas flow
Stick out
Welding
set


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
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

Gas-shielded
FCAW
Self-shielded
FCAW
Process
Test piece
MMA

MAG

Gas-shielded
FCAW
Self-shielded
FCAW


Polarity

Mean results from welding parameter tests
MMA
Mean
SD
% RSD
%Cr
4.42
0.57
12.9
%Cr(VI)
2.45
0.11
4.6
%F7.86
0.34
4.4
%Fe
4.75
1.07
22.6
%K
31.8
3
9.4
%Mn
2.85
0.25
8.8
%Na
4.4
0.54
12.3
%Ni
0.46
0.14
29.9
%Si
8.95
0.98
11
MAG
Mean
SD
% RSD
%Cr
15
1.5
10
Mean
SD
% RSD
%Cr
6.06
0.8
13.2
Mean
SD
% RSD
%Cr
7.1
0.8
11.3
%F4.64
0.31
6.6
%Cr (VI)
2.31
0.09
3.8
%F6.12
0.69
11.3
%Fe
39.6
2.33
5.9
Gas shielded FCAW
%Fe
%K
11.54
13.02
1.75
1.01
15.2
7.8
Self shielded FCAW
%Fe
%K
11.5
13.5
1.5
1.8
13
13.6
%Mn
10.4
2.89
27.7
%Ni
4.8
1.3
27.1
%Mn
8.05
0.63
7.9
%Na
7.73
0.56
7.2
%Ni
1.17
0.27
22.9
%Si
5.05
0.67
13.3
%Mn
4.73
0.38
8
%Na
1.88
0.71
37.8
%Ni
1.71
0.36
20.8
%Si
3.25
0.19
6
Effect of voltage on fume composition for different
wire diameters in MAG welding of stainless steel
32
28
% Element in fume / voltage
24
Voltage
20
16
Chromium
12
Manganese
8
Nickel
4
Silicon
0
0.6
0.8
1
1.2
Wire diam eter (m m )
1.4
1.6
1.8
Welding parameter test results

Repeatability and reproducibility of measurements
were typically better than ± 5 %
 Voltage was the parameter exerting the greatest
effect on welding fume composition

Variation in fume composition with welding
parameters was fairly small, typically < 20 % overall

Results were used to make preliminary
recommendations for future generation of welding
fume composition data
Audit of current MSDS data

Test samples were produced by MMA, MAG and
FCAW welding using stainless steel, nickel alloy,
mild steel, cast iron, hardfacing alloy, copper alloy,
nickel alloy and aluminium alloy consumables

Measured values were compared with MSDS data
for each constituent of the welding fume

The % measured values v MSDS data were
typically in the range 70 % to 140 %, with an
average of around 100 % and an average relative
standard deviation of around 30 %
MSDS audit findings

Fume composition data given on MSDSs does not
exhibit an overall bias %

The average RSD for % measured values v MSDS
data was considerably higher (30 %) than variability
in fume composition found in the welding parameters
study (15 %)

Reproducibility of MSDS fume composition data
could be greatly improved (perhaps to ± 10 %)
Field tests

Dust from welding-related operations, e.g. grinding,
can cause the chemical composition of airborne
particles to which a welder is exposed to vary from
that of the welding fume

Field tests were carried out to assess the
magnitude of this effect and its significance for the
application of the EH 54 procedure
Effect of dust on Cr content of welding fume
14
Sample % (w/w)
12
10
y = 0.4461x
8
6
4
2
0
0
5
10
15
MSDS % (w/w)
20
25
Effect of dust on fume composition
concentration/constituent OEL
Maximum constituent
3.50
3.00
y = 0.3314x + 0.0883
2.50
2.00
1.50
1.00
0.50
0.00
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
Welding fume concentration/welding fume limit value
8.00
Recommendations

Fume composition data on MSDSs should
– be determined by analysing fume collected under the test
conditions recommended in the proposed European and
International Standard EN ISO 15011-4
– should include all components of industrial hygiene
significance
– should give full details of the test conditions

The EH 54 method should be retained, but the
findings of this work should be taken into account
when the it is revised
EN ISO 15011-4 recommendations for MIG/MAG
welding
Parameter
Test requirements
Diameter
most commonly used diameter (e.g. 1.2 mm)
Gas type
as recommended by the manufacturer, or if more than one gas is recommended, the most oxidising mixture given
by the formula:
(1 x CO2) + (2 x O2)
Gas flow
10 x wire diameter (mm) l/min
Contact tip as recommended by the manufacturer, or the maximum of a CTWD range, if given; or as specified in Table B2 in the
to workpiece absence of any recommendation by the manufacturer
distance
(CTWD)
Current
75 % of the maximum of the current range given by the manufacturer
Voltage
minimum voltage for spray transfer, as determined by an experienced welder (defined as an arc with a small amount
of audible crackle)
Polarity
dc+
Traverse
speed
optimum traverse speed, as determined by an experienced welder
Test piece
size: commercial bar stock (e.g. 50 mm width x 10 mm thickness), cut to a suitable length (e.g. 250 mm)
composition: unalloyed steel for unalloyed steel, low alloy steel, cast iron, and surfacing consumables; stainless
steel (e.g. 316) for high alloy steel consumables; composition equal that of the weld, as far as possible, for nickel
alloy, aluminium alloy and copper alloy consumables
configuration: bead on plate
Acknowledgements
Thanks to:

Bohler, Corewire, Elga, ESAB, Lincoln, Metrode,
Murex, Oerlikon, Rigby Maryland and SAF and UTP
for providing the welding consumables for the tests

Graham Carter, TWI, for his invaluable technical input

Colleagues at HSL

Chris Northage and Roger Sykes, HSE, for funding
the work