Journal of Power and Energy Engineering, 2013, 1, 1-5
http://dx.doi.org/10.4236/jpee.2013.17001 Published Online December 2013 (http://www.scirp.org/journal/jpee)
1
Evaluation of Ge om etri c Qu alit y of Wel d Beads in the
Joining of Carbon Steel Pipelines with Single Pass
José Eduardo Silveira Leal, Thonson Ferreira Costa, Rosenda Valdés Arencibia
Federal Universityo f Uberlândia, Avenida João Naves de Ávila, 2121, Cam pus Santa Mônica, Bloco 5F, CEP 38 400-902, Uberlândia-
MG, Brazil.
Received August 2013
ABSTRACT
This work presents the uncertainty evaluation associated with the measurement of linear parameters that define the weld
geometry, specifically the width, using a profile projector, in order to meet the current technical standards. The follow-
ing steps were proposed and implemented : identification of linear parameters that defin e the weld geometry; identific a-
tion and study of variables that affect the measurement of these parameters; the adoption of the mathematical model to
estimate the uncertainty; planning and execution of experiments for data collection, calculation of uncertainty and, fi-
nally, analysis and discussion of the results. Through the results analysis it was concluded that the weld in overhead
position produces the lowest front bead width values and the vertical weld produces the largest width values. The ex-
panded uncertainty values were between 0.016 mm and 0.075 mm for all measurements, and the overhead position
showed, on average, the highest values.
Keywords: Welding; Weld Bead Geometry; Profile Projector; Uncertainty
1. Introduction
Welding is undoubtedly the cheapest, most efficient and
versatile bonding between materials. I ts application is not
restricted to manufacturing and service, but extends to
the maintenance and repair [1]. Welding is the most im-
portant industrial process for metal parts manufacturing
[2].
The scope of the welding is practically unrestricted,
passing from the feasibility of a metal chair to the most
sophisticated spacecraft. The welding is indispensable in
the shipbuilding industry (ships, submarines, etc.), me-
chanical industry (equipment, capital goods, etc.), in the
automotive industry (cars, trucks, tractors, etc.) aerospace
(satellites, aircraft, spaceships, etc.), construction (steel
structures, bridge and buildings), in the nuclear industry
(reactors and cooling systems), in the energy industry
(transmission cables and turbines) in pressure vessels in
petrochemical plants, storage tanks, offshore platforms,
in microelectronics, as well as hundreds of other applica-
tions [1].
The multidisciplinary knowledge is another welding
key feature once the essential requirements are metallurgy,
mechanics, electrotechnology, chemistry, physics, materials,
quality control, safety, and other factors inherent in indus-
trial production.
In any welded joint sizing, several aspects must be
considered, such as: the level of efforts solicitation, the
fixing process, the operation difficulty degree, the geo-
metric ratio between bead and welded components, re-
quired production, the base material composition, the
process automation degree besides the cost involved.
However, an appropriate sizing is not enough to ensure
the final product quality of welding processes and is es-
sential the development of means and methods to verify
the dimensions in order to assess whether they are in
accordance with the specified in the project stage [3].
Therefore, welded joints quality control is critical to
ensure the final product quality of the welding processes,
as well as in the researches developed in the subject.
However, for the results of measurements that underlie
the mare traceable, measurement systems and calibrated
equipment must be used and measurement uncertainty
most be evaluated and declared [4].
During the quality control parameters that define the
weld bead geometry, templates and gauges are used. Some
authors use calipers to measure the weld bead linear pa-
rameters [5], while others use the profile projector [6].
Image capture systems are often used associated with
computer programs [3] especially in research develop-
ment.
These measurement systems have operating principles
and different constructive characteristics, therefore the

Evaluation of Geometric Quality of Weld Beads in the Joining of Carbon Steel Pipelines with Single Pass
2
sources of errors also differ, as well as the necessary
mathematical models for measurement uncertainty eval-
uation [3,5,7].
For these reasons, this article aims to assess the weld
beads geometric quality obtained with MIG/MAG deriv-
ative short-circuit process (STT—Surface Tension Trans-
fer) in the carbon steel pip elines welding with s ingle pass.
For the three forward different conditions: flat (F), ver-
tical (V) a n d overhea d pos i tion (OH) (Figure 1).
Further, the measurement of uncertainty evaluation as-
sociated with the linear parameters which define the weld
bead geometry is shown, specifically the width, using a
profile projector. It also presents an analysis of the in-
fluence factors which affect the overall un certain ty .
This analysis has the expectation of emphasizing the
operator training importance during the measurement
process.
2. Testes Experimentais
Weld beads were obtained using the MIG/MAG deriva-
tive process with short circuit (STT—Surface Tension
Transfer) the welding of carbon steel pipelines with sin-
gle pass. The carbon steel pipes have nominal internal
diameter 2½”(63 mm) and a thickness of 5.5 mm. In this
study, experiment was carried out on the base materials
plates with 75˚ groove, 2.0 mm root-gap and root-face.
The contact-tip to workpiece distance (CTWD) was 12
mm and the electrode wire was used ER 70S-6 with 1.2
mm diameter and Ar + 25% CO2 as shielding gas.
In addition, the weld beads were done in downward
progression, with torch oscillation. The travel speed was
set to maintain about the same amount of weld material
deposited per unit length of weld (WFS/TS constant).
As specific parameters were varied in three levels, the
wire f eed sp eed “W FS” in (2.3 m/min, 2.8 m/min and 3.3
m/min), maintaining constants the peak current “IP” (300
A), the background current “IB” (80 A) and Tail-out (5).
Figure 1. Schematic of pipe weld experiment with different
welding position [8].
Table 1 shows the setting parameters and the meas-
ured values for average curr ent ( IA), av erag e vol tage ( UA)
and welding energy input (EW).
After the welding, specimens were prepared and as-
sembled as shown in Figure 2. These specimens have
been previously identified as SD10, SD11 and SD18 and
each contains three weld beads, one obtained in the flat
(F), vertical (V) and in overhead position (OH).
The front width of each weld bead (Figure 3) was
measured three times using a profile projector, model
PJ-A3000, manufac tured by MI TU TOYO (Figu re 4) and
a 10× magnifying lens.
Table 1. Measured values for electric current and voltage in
the desce ndi ng pr ocess STT.
Test 1(SD10) 2(SD11) 3(SD18)
WFS [m/min] 2.3 3.3 2.8
IB [A] 80 80 80
IP [A] 300 300 300
Tail-out 5 5 5
IA [A] 120.4 146.8 133.7
UA [V] 17.2 15.4 15.2
EW [J/cm] 172.57 125.60 135.48
Figure 2. Specimens SD10, SD11 an d SD18.
Figure 3. Weld bead linear geometric parameters.
Figure 4. Specimens on measurement table of profile pro-
jector.
Flat position
Vertical position
Overheadposition
Front width
Front height
Back height

Evaluation of Geometric Quality of Weld Beads in the Joining of Carbon Steel Pipelines with Single Pass
3
This equipment allows measuring linear dimensions
with a 0.001 mm resolution and angles with 1 minute
resolution. The nominal range for linear dimensions is
defined by the capacities of the axes X and Y, as they are
50 mm, while it is 360 degrees the measurement of an-
gles.
The profile projector used, has a calibration certificate
N. 12137/12 issued by the Mitutoyo Metrology Labora-
tory of South American. The expanded uncertainty asso-
ciated with the magnifying lens calibr ation is 0.01% for k
equals to 2.00 and infinite effective degrees of freedom.
While the expanded uncertainty for length measurement
is 0.002 mm for both axes, with k equal to 2.03 and 99
effective degrees of freedom.
During measurement, the samples were placed on the
coordinates table as s hown in Figure 3.
The measurements were carried out at a controlled
room tempe r ature of (
20 1±
)˚C [9]. A thermo-hygrometer
with a digital increment of 0.1˚C and measurement range
of (−20 to 60)˚C was used to monitor the temperature.This
equipment has a calibration certificate N. R4996/13 is-
sued by Elus Instrumentação Temperature and Humidity
Laboratory. For temperature, the expanded uncertainty is
0.3˚C for k equal to 2.00 and infinite degrees of freedom.
All the instruments and parts used in the measurement
tests were exposed to this temperature for approximately
12 h before the measurements. In order to remove dust or
other dirt particles that could interfere with the meas-
urement results, all the instruments and parts were cleaned
using isopropyl alcohol, gloves, cotton buds and dry
cloths.
The uncertainty evaluation associated with the front
width measurement was performed as recommended by
[10].
The influence factors considered for uncertainty eval-
uation were: variability of the readings indicated by pro-
file projector; profile projector resolution; standard un-
certainty associated with the profile projector calibration;
uncertainty associated with lens increase; temperature
variation during the measurements and the distance from
the environment temperature to the reference temperature
(20˚C).
Thus, the mathematical model is expressed according
to Equation (1).
00
() () ()
PP P
Pe PPe P
M sLRIA
LTLT αα δαα
=∆+∆+∆ +∆
+⋅∆⋅ ++⋅⋅+
(1)
Wherein:
M: the measurement (front b e a d wi dt h );
()sL∆
: correction due to standard deviation of the
values indicated by the projector;
P
R∆
: correction due to the projector resolution;
P
I∆
: correction associated to the standard uncertainty
of the projector calibration;
P
A∆
: correction associated to the projector lens in-
crease;
T δ
: temperature variation during measurements;
T∆
: distance from the environment temperature to the
reference (20˚C);
P
α
: linear thermal expansion coefficient of micrometer
heads material (for linear dimensions);
Pe
α
: linear thermal expansion coefficient of the part
material;
0
L
: average value of the measurement.
Therefore, the law of propagation of uncertainty must
be applied to express the combined standard uncertainty
as:
2
2
22 2
22
22
22
22
22
2
()( )()
()()
()()
()
cP
P
PP
PP
Pe
Pe P
MM
uMusL uR
sL R
MM
uI uA
IA
MM
uTuT
TT
MM
u
δ
δ
α
αα

∂∂

= ⋅∆+⋅∆


∂∆ ∂∆
 
 
∂∂
+ ⋅∆+⋅∆
 
∂∆ ∂∆
 
∂∂
 
+⋅ ∆+⋅
 
∂∆ ∂
 
 
∂∂
+⋅+ ⋅
 
∂∂


2()
P
u α
(2)
The standard uncertainty related to s(L) can be calcu-
lated as shown in Equation (3).
( )
()
s
u sLn ∆=
(3)
Where s is the standard deviation of the measurement
and n is the total number of measurement.
The correction due to the projector resolution is given
by Equation (4).
()23
R
uR∆=
⋅
(4)
The correction associated to the projector lens increase
is given by Equation (5).
0
0.01%( )
()
p
L
uA k ∆=
(5)
The correction due to the uncertainty associated with
the projector indication system is given by Equation (6).
()
p
U
uI k ∆=
(6)
The correction due to difference between coefficients
of thermal expansion of the scale and work piece is given
by Equation (7).
Where
p
α
is the coefficient of thermal expansion of
the scale of projector and αpe is the coefficient of thermal
expansion of the wo rk piece.
0.01()
() 3
PE
u
αα
α
−
∆=
(7 )

Evaluation of Geometric Quality of Weld Beads in the Joining of Carbon Steel Pipelines with Single Pass
4
Both variables related to room temperature variation
were measured using the same measurement system.
Therefore, they were treated as correlated. The correction
due to the distancin g of the tem perature in re lation to 2 0˚C
(ΔT20) is determined using Equation (8).
2
22
TT
20
() 3 23
T
RI T
uT k
 ∆∆
∆  
∆= ++

 
⋅
 
(8)
Where ΔT is the difference between the room tem-
perature and 20˚C; ΔRT is the correction in relation to the
thermometer resolution and ΔIT is the uncertainty asso ci-
ated with the thermometer indication system.
The uncertainty due to temperature variation during
measurement is given by Equation (9).
2
22
TT
()
() 323 T
RI
Var T
uT k δ

∆∆
 
∆=+ +

 
⋅
 

(9)
3. Results and Discussion
Table 2 displays the mean (
x
) and stan da rd deviat ion (s)
from the readings obtained while measuring front width
with the profile projector for all weld beads.
Observing the measurement results shown in Table 2
and comparing each sample separately it may be noted
that the overhead (OH) produces the smallest front bead
width. And, except for SD10 sample, the largest width is
from vertical welding position (V). So, with a smaller
width, the thermal deformation is smaller due to the re-
duced heat affected area and it consumes a smaller elec-
trode qua ntity and weld volu me.
Comparing the average result of the three samples
(Table 3) it is concluded that the OH welding showed,
under the conditions of this study, the smaller bead width
(8.055 mm). And th e vertical welding showed the largest
width (8.732 mm). There was a lower repeatability of
bead width in OH, this can be due to the fact that in this
position it is more difficult to do the welding.
Taking the average width for position V welding as
reference, it can be said that the average width obtained
Table 2. Front width values for each we ld bead.
Front width for each weld bead (mm)
Weld bead Mean(
x
) Standard deviation (s)
SD10-OH 8.866 0.006
SD11-OH 7.607 0.030
SD18-OH 7.693 0.010
SD10-V 9.230 0.017
SD11-V 8.382 0.015
SD18-V 8.584 0.012
SD10-F 10.062 0.006
SD11-F 7.635 0.019
SD18-F 7.609 0.010
in SC position is 7.75% lower, while in F position it wa s
3.40% lower.
The uncertainty associated to the measurement of the
front width in overhead position to the specimen SD10 is
displayed in Table 4. In this table E represents the esti-
mated value of the input variable considered; TI, the type
of standard uncertainty evaluation; DP, the probability
distribution adopted and DF the number of degrees of
freedom.
In Table 4 were added two significant figures to stan-
dard uncertainty values (u), to combined standard uncer-
tainty (uc) and to expanded uncertainty (U) in order to
reduce errors due to rounding. In all cases the sensitivity
coefficient is equal to 1.
It is observed in Table 4 that expanded uncertainty
associated to the front width measurement obtained in
overhead position for specimen SD10 is 0.016mm for k
equal to 4.30% and 95% coverage probability. Thus the
values, which may be attributed to the measure and in
this case, are in the range [8.866 mm ± 0.016 mm].
The variable that most contributed to final uncertainty
was the variability of readings, with a contribution of
approximately 89.86%, followed by the uncertainty asso-
ciated with the profile projector calibration, with 7.35%.
The contribution of the variables, profile projector res-
olution and uncertainty associated to the magnifying lens,
was very small, assuming values of 2.52% and 0.24%,
respectively.
Table 5 displays the results obtained during the evalu-
ation of the uncertainty associated to the width mea-
surement for all weld beads. This table shows the values
of the effective degrees of freedom (νeff), the coverage
factor (k) and the expanded uncertainty (U) in mm. In all
cases the probability of coverage was 9 5% .
Table 3. Average results between the three samples by weld
type.
Type Mean(
x
) Standard deviation (s)
OH 8.055 0.013
V 8.732 0.003
F 8.435 0.007
Table 4. Uncertainty components to the SD10-OH speci-
men.
Uncertainty components
Quantity E (mm) TI DP DF u (mm)
Δs(Lpr) 0.006 A N 2 0.00346
ΔRPr 0.001 B R ∞ 0.00058
ΔAPr 0.00044 B N ∞ 0.00018
ΔIPr 0.0009 B N 99 0.00099
Combined standard uncertainty (uc) [mm] 0.00365
Effective degrees of freedom (νeff) 2.47
Coverage factor (k) 4.30
Expanded uncertainty (U)[mm] 0.01571

Evaluation of Geometric Quality of Weld Beads in the Joining of Carbon Steel Pipelines with Single Pass
5
Table 5. Uncertainty for all weld beads.
Uncertainty for all weld beads
Weld Bead νeff k U (mm)
SD10-OH 2.47 4.30 0.016
SD11-OH 2.01 4.30 0.075
SD18-OH 2.16 4.30 0.026
SD10-V 2.06 4.30 0.043
SD11-V 2.07 4.30 0.038
SD18-V 2.11 4.30 0.031
SD10-F 2.47 4.30 0.016
SD11-F 2.04 4.30 0.048
SD18-F 2.16 4.30 0.026
From Table 5 it fo llows that the expanded uncertainty
values range between 0.016 mm and 0.075 mm for all
measurements, indicating that the results are adequate
considering the required accuracy for measuring the front
bead width. The results obtained are suitable considering
the required accuracy for measuring the front width.
The weld beads obtained at OH position have showed
the highest values of expanded uncertainty, as well as the
higher dispersion between them.
In all cases the variable that most contributed to the
final uncertainty was th e variability of the readings. This
can be explained by the difficulties that the operator finds
when setting the reference points for measuring the front
width. Thus, the operator may be a significant source of
error in this measurement. To minimize this effect, in-
vestments on the operator training must be done.
4. Acknowledgements
The authors are grateful to FAPEMIG/Brazil and CAPES/
PROEX for financia l s upport.
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