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IJMET
© I A E M E
RESEARCH ON THE INFLUENCE OF SAGGING AND CONTINUOUS
UNDERCUT ON THE CAPACITY OF BUTT-WELDED JOINT
Vladimir Stojmanovski1, Zoran Bogatinoski2, Viktor Stojmanovski3
1(Centre for Research, Development and Continuous Education – CIRKO, Inspection Body for
Pressure Vessels, Metal Structures and Cableways, Skopje, Macedonia)
2(Professor, Ss. Cyril and Methodius University in Skopje, Faculty of Mechanical Engineering,
Skopje, Macedonia)
3(Associate Professor, Ss. Cyril and Methodius University in Skopje, Faculty of Mechanical
Engineering, Skopje, Macedonia)
7
ABSTRACT
The behavior of butt-welded joint with imperfection of the outer contour due to sagging and
continuous undercut has been analyzed in this paper. The analysis was done by testing and numerical
investigation using Finite Element Analysis.
For the testing, the standard probes have been made from material S235JR that is mostly used
for the production of welded structures. Sagging and continuous undercut on both sides of the testing
plates have been simulated in the welded joint in order to evaluate the imperfection.
Research presented in this paper is directed in gaining acknowledgement and experience for
analysis of the welded structures and their usage in design, construction, production and testing. In
that manner the real picture of stress distribution is going to be acquired and this will contribute in
the design of structures with decreased factor of safety leading to less expensive and yet safe
structures which is the common interest of the companies that construct, produce and assemble
welded structures.
The purpose of this paper is to endorse the influence of the sagging and continuous undercut
on the capacity of the welded joint in order to make appropriate judgment for the safety.
Keywords: Butt-Weld, Continuous Undercut, FEA, Imperfection, Material Testing, Sagging.
I. INTRODUCTION
Due to discontinuities from various imperfections found on the outer contour of the welded
joint (such as sagging and continuous undercut), there is irregular stress distribution at the joint with
2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 8, August (2014), pp. 07-19 © IAEME
elevated stress peaks. The influence of these peaks cannot be precisely estimated during the
calculation of the joint. In practice, the solution of the problem, in order to prevent the existence of
such imperfections, lays in establishment of rigorous criteria prescribed by the regulation.
Sometimes there is a question whether these rigorous criteria are reasonable due to the fact that they
directly influent the costs of the welded structure. On the other side, in some separate cases as far as
there is discontinuity, it is very likely that during the reparation the situation might worsen,
particularly if there is a location where the reparation is hard to be made. Considering these facts, in
some cases, it is necessary to make judgment whether there is need to make reparation on the
discontinuities found on the outer contour during the examination.
In this paper has been analyzed the behavior of butt-welded joint with imperfection of the
outer contour due to sagging and continuous undercut.
The probes used for the tensile, bending and toughness tests are standard and they are
produced from the plates [2] made from material S235JR that is mostly used for the production of
welded structures. Chemical composition and mechanical properties have been obtained by
analyzing the material. Appropriate welding technology for the probes has been adopted according to
EN499 and E7018 according to AWSA 5.2. the technology has been verified and appropriate WPQR
certificate has been issued.
Sagging and continuous undercut on both sides of the testing plates (probes) were simulated
at the welded joint. Static examination of the basic material S235JR and the welded joint are made.
The joints are analyzed by FEA in their real dimensions of the model and the imperfections with the
ALGOR software [4]. Such analysis has shown the stress distribution of the joint.
Research presented in this paper is directed in gaining acknowledgements and experience for
analysis of the welded structures and their usage in design, construction, production and testing. In
that manner is going to be acquired the real picture of stress distribution that will contribute in the
design of structures with decreased factor of safety leading to less expensive and yet safe structures
that are the common interest of the companies which project, produce and assemble welded
structures.
8
II. BASIC MATERIAL
Models (probes) analyzed in this paper are produced from material S235JR. The material has
been tested in the laboratory and properties of material gained from the test are presented in Table 1
and Table 2.
Table 1: Chemical Composition of the material
Chemical element (%)
C Si Mn P S Cr Ni Al Cu Nb Ti Mo V B Cekv
0,11 0,08 0,58 0,013 0,012 0,03 0,02 0,043 0,03 0,02 0,01 0,01 0,01 0,0 0,213
Table 2: Mechanical Properties of the material
Dimensions
Fm
(N)
Tension Bending Toughness
Reh
(Mpa)
Rm
(MPa)
A5
(%)
Reh/Rm
(mm)
(0)
(J)
9,5x24,6 L=118 L0=90 120980 366 517 31,5 0,71 Ø40 180
112
t= + 200C
3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976
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Tension test graph is presented on Figure 1.
07-19 © IAEME
Fig. 1: Tension test graph for material S235JR
From the performed tests, it can be concluded that chemical composit
properties, the elongation, bending and toughness meet the requirements of the standard EN 10025
for the quality of the material S235JR.
III. WELDING TECHNOLOGY
Welding of the plates was performed with TIG welding procedure (141) for the root
ARC welding procedure for filling and finish. ARC welding was performed with basic electrode type
E424 32 X5 according to EN499 and E7018 according to AWSA 5.2 [3].
Fig. 2: Welding order: 1. Root
-TIG (141), 2. Filling -ARC (111), 3. Finish -
Professionally qualified welder who possesses valid certificates performed the welding. The
prescribed welding technology was verified and the WPQR certificate has been issued
IV. THE PROBES FOR THE TESTING
From the Basic material using the presc
prescribed welding technology appropriate plates are
created for the purpose of the test. The characteristic imperfections (sagging and continuous
9
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composition, mechanical
weld and
ARC (111)
ribed 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 8, August (2014), pp. 07-19 © IAEME
undercut) are simulated at the joint. The imperfection models used in the further tests are presented
in Table 3
Table 3: The Models (probes) used for the tests
10
Probe mark
1. Welded joint with grinded face and root
2.1
2. Weld with significant sagging on one side
2.6.
3. Weld with continuous undercut on both sides
2.7.
IV.1. PERMITTED DEVIATION OF THE IMPERFECTIONS
The characteristic imperfections according to ISO 6520, depending on the level of quality of
the weld are presented in Table 4.
Table 4: Permitted deviation of the imperfections according to ISO 6520
Appearance of the
imperfection
t (mm)
Boundary values of the imperfection for the level of quality
D C B
2.6.
3
Small sizes
h0,25 t
no max 2 mm
for probe 2.6
h2,375 mm
Small sizes
h0,1 t
no max 1 mm
for probe 2.6
h0,95 mm
Small sizes
h0,05 t
no max 0,5 mm
for probe 2.6
h0,475 mm
2.7.
3
h0,2 t
no max 1 mm
for probe 2.7
h1,9 mm
h0,1 t
no max 0,5 mm
for probe 2.7
h0,95 mm
h0,05 t
no max 0,5 mm
for probe 2.7
h0,475 mm
IV.2. VISUAL EXAMINATION OF THE WELDED JOINTS
Visual examination and dimensional control of the welded joints are performed in order to
evaluate the imperfections. The results from the dimensional control of the imperfections are
presented in Table 5.
Table 5: Results from the dimensional control
Joint with significant sagging
2.6.
a1
(mm)
b1
(mm)
a
(mm)
b
(mm)
c
(mm)
7,6 2 14 1 1
Joint with continuous undercut
2.7.
a1
(mm)
b1
(mm)
a
(mm)
b
(mm)
c
(mm)
c1
(mm)
6,4 2 16,4 2 2 2
t
h
t
h
5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 8, August (2014), pp. 07-19 © IAEME
IV.3. RADIOGRAPHIC CONTROL OF THE JOINTS
Welded probes – plates are radiography tested. The radiograms are presented in Table 6
Table 6: Radiograms
Welded joint with grinded surfaces
Mark Model Radiogram
11
2.1.
Grinded face and
grinded root
2.6.
Significant sagging
2.7.
Continuous undercut
The defects are clearly recognizable on the radiogram.
V. TESTING OF THE WELDED JOINTS
Tensile, bending and toughness tests are performed in order to examine the effect of the
imperfection
V.1 TENSILE TEST
The tensile test was performed on both the basic material and the samples without (2.1) and
with imperfections (2.6 and 2.7). The tensile test graph for the basic material is presented on figure 2.
The results from the tensile tests for the models 2.1, 2.6 and 2.7 and for the basic material marked
with 2. are presented in Table 7.
Table 7: The results from the tensile test
Test
probe
Probe
dimension
A0
(mm2)
Rp0,2
(N/mm2)
Breaking
force
Fm(N)
Rupture
stress
Rm (N/mm2)
Location of rupture
2. 9,5 x 24,6 233,70 366 120980 517 5=31,5%
2.1 9,2 x 24,2 220,80 386 123290 558 Basic material
2.6 8,8 x 24,2 212,96 393 126580 594 Basic material
Zone of the
2.7 8,8 x 24,5 215,60 355 119520 554
temperature influence
6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
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All of the welded plates have equal nominal thickness. Therefore, at the location of the joint,
the widths of the probes are approximately equal. The cross sectional area at the location of the
rupture changes due to the different size (depth of the imperfection). At the welded structures where
the joints are butt-welded the area of the cross-section has to be constant. For the calculation of the
butt-welded joint according to the existing standards, the thickness of the weld is permanently
considered as equal to the thickness of the basic material. Then, for different nominal cross section,
for defining of the capacity, for comparison most relevant element is the breaking force Fm (N)
acquired from the test. The intensity of the breaking force is presented on Figure 3.
Fig. 3: The breaking force Fm(N)
12
V.2 BENDING TEST
The results from the bending test of the basic material (signed with 2.), the welded joint with
no imperfection (signed with 2.1) and welded joints with appropriate imperfections (signed with 2.6
and 2.7) are presented in Table 8
Table 8: Results from the bending test
Test
probe
Type of
test
Dimension
(mm)
Diameter of
bend former
(mm)
Shoulders
distance
(mm)
Bending angle
(0)
2. RBB/FBB 10x30 Ø40 70 180
2.1 RBB/FBB 10x30 Ø40 70 180 / 180
2.6 RBB/FBB 10x30 Ø40 70 180 / 180
2.7 RBB/FBB 10x30 Ø40 70 180 / 180
V.3. TOUGHNESS TEST
The results from the toughness test of the basic material (signed with 2.), the welded joint
with no imperfection (signed with 2.1) and welded joints with appropriate imperfections (signed with
2.6 and 2.7) are presented in Table 9. The test was performed according to EN875
7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 8, August (2014), pp. 07-19 © IAEME
Table 9: Results from the toughness test
13
Probe mark
Dimension
of the probe
a x10 x 55
Temperature
(0C)
A0
(cm2)
Deformation energy
(J)
Calculated toughness
(J/cm2)
Location
of the
groove
Type
of
1 2 3 Sr. 1 2 3 Sr. groove
2. V 9,2x10x55 +20 0,74 78 138 120 112 105 187 163 151
Middle
of the
weld
V
2.1 V 9,2x10x55 +20 0,736 144 104 90 112 195 141 122 152
Middle
of the
weld
V
2.6 V 11,0x10x55 +20 0,88 191 294 207 230 217 334 235 262
Middle
of the
weld
V
2.7 V 12,5x10x55 +20 1,0 262 294 295 283 262 294 295 283
Middle
of the
weld
V
According to the analysis of the results of the toughness test it can be concluded:
- Obtained values of the toughness material meet the requirements for the toughness of the
material S235JR at the temperature of +200C. Minimum required is 27 J
- Since the groove of the probe is located in the middle of the joint, discontinuities 2.1, 2.6 and
2.7 do not influence the toughness.
VI. FINITE ELEMENT ANALYSIS OF THE IMPERFECTIONS
Plane strain models for the analysis of the considered cases were used. The analysis was
performed with ALGOR software. The models are loaded with Fsr=65KN, force that delivers stress
condition close to the yielding.
The Yield stress measured from the tensile test is used as load criteria in the Finite Element
Model. For the material S235JR the load is Rp=366 N/mm. According to EN 10025, the material has
minimum yield stress Reh=235 N/mm2. In such case the proper value is the one measured from the
tensile test Rp(0,2)=366 N/mm2. The Young modulus for all the analyzed cases is 2,1x105 N/mm2. In
the Finite Element Model, at the locations of the imperfections the finer mesh has been used. [4].
VI.1. STRESS DISTRIBUTION DUE TO THE IMPERFECTIONS
VI.1.1. WELDED PLATE WITHOUT IMPERFECTIONS (GRINDED FACE AND ROOT –
MODEL 2.1)
The real model and the Finite Element Model are presented on Figure 4.
Fig. 4: The real model and the Finite Element Model for the case 2.1
8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976
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The stress distribution is presented on Figure 5
07-19 © IAEME
Fig. 5: The stress distribution for the case 2.1 (no imperfection)
VI.1.2. WELDED PLATE WITH SAGGING (MODEL 2.6)
The real model and the Finite Element Model are presented on Fi
Fig. 6: The real model and the Finite Element Model for the case 2.6
14
Figure 6.
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9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 8, August (2014), pp. 07-19 © IAEME
15
The stress distribution is presented on Figure 7
Fig. 7: The stress distribution for the case 2.6 (sagging)
VI.1.3. WELDED PLATE WITH CONTINOUS UNDERCUT (MODEL 2.7)
The real model and the Finite Element Model are presented on Figure 8.
Fig. 8. The real model and the Finite Element Model for the case 2.7
10. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 8, August (2014), pp. 07-19 © IAEME
16
The stress distribution is presented on Figure 9
Fig. 9: The stress distribution for the case 2.7 (continuous undercut)
VI.2. ANALYSIS OF THE RESULTS FROM THE FEA
Stress distribution at the welded joint for different cases (models) is presented on Figures 5, 7
and 9. At sufficient distance from the welded joint there is steady stress condition. If the stress
distribution is analyzed, it may be concluded that at the locations where the continuity is interrupted
(imperfection) there is existence of the stress peak. These peaks are close to the values of the yield
stress of the basic material. Analyzing the results of the FEA, the following may be summarized:
- The Imperfections (defects) have significant influence on the stress distribution,
- When the model is loaded with the force Fsr, near the defects (discontinuities), the stress
achieves the values close or equal to the yield stress of the material,
- The verification of the proper modeling is the fact that far enough from the weld there is
steady stress that in fact is the stress delivered when the force Fsr is divided by the cross-sectional
area of the plate (the probe).
VII. COMPARATIVE ANALYSIS AND THE REVIEW OF THE RESULTS
The results from the tensile test of the basic material S235JR and the welded plates with
various imperfections are presented in table 7. For defining of the capacity of the joint the most
proper element for comparison is the value of the breaking force Fm. The value of the breaking force
graphically is presented in Figure 30. The Material S235JR is characterized by good strength
properties and good weldability.
The results from the tensile test are:
- Yielding stress Rp0,2=366 N/mm2,
- Rupture stress Rm=517 N/mm2,
- Breaking elongation 5=31,5%.
According to the provided strength and deformation properties and the chemical composition
it can be concluded that the material S235JR for the butt-welded profiles (2.1, 2.6 and 2.7),
completely fulfills the requirements of the standard EN 10025.
11. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 8, August (2014), pp. 07-19 © IAEME
The breaking force from the tensile test of the joint with grinded face and root (2.1) is
17
Fm
(2.1)=123290 N. This force is approximately equal with the breaking force of the basic material
Fmom.=120890 N. The variation is within the tolerant limits. The rupture occurred in the basic
material.
From the bending test of the probe 2.1 has been obtained bending angle of 1800. It means that
in both cases the criteria of the used bending test standard has been fulfilled.
The results from the toughness test of the probe 2.1 are presented in the table 14. The measured
values for the toughness fulfill the requirements for the material S235JR at the temperature of +200C.
Minimum required value is 27J
Permitted depth of the sagging depending on the level of quality is presented in Table 10 and
the measured dimensions of the weld with sagging are presented in Table 11.
Table 10: Permitted values of the sagging
Level of quality
D C B
Depth of the sagging h (mm) 2,375 0,95 0,475
Depth of the sagging h (mm) - maximum allowed 2,00 1,00 0,50
Table 11: Measured dimensions of the sagging
Probe Depth of the sagging h (mm)
2.6 1,00
From the visual examination and dimension control can be concluded that welded probe 2.6
does not fulfill the criteria for the level of quality C and B.
From the tensile test of the welded probe 2.6, the measured breaking force is Fm
(2.6)=126580
N. By comparing the results from the basic material (probe 2.) and the weld without imperfections
(grinded face and root - probe 2.1) can be summarized:
- The breaking force Fm
(2.6) is superior than breaking forces of the basic material and the probe
2.1
- The rupture occurred at the basic material
- The stress concentration due to imperfection of the outer contour (Figure 7) does not
influence the capacity of the joint in the static loading condition. This is due to superior
ductility of the material S235JR.
From the bending test of the probe 2.6 (Table 8) the bending angle of 1800 has been
measured. It proves that in both cases the required criteria from the bending test standard has been
fulfilled.
From the toughness test of the probe 2.6, (Table 9) have been measured toughness values that
fulfill the requirements of the toughness of the material S235JR on +200C (probes 2.6)
Permitted depth of the continuous undercut depending on the level of quality is presented in
Table 12 and the measured dimensions of the excess metal are presented in Table 13.
Table 12: Permitted values of the continuous undercut
Level of quality
D C B
Depth of the root h (mm) 1,90 0,95 0,475
Depth of the root h (mm) - maximum allowed 1,00 0,50 0,50
12. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 8, August (2014), pp. 07-19 © IAEME
Table 13: Measured dimensions
Probe Depth of the root h (mm)
2.7 2,00
From the visual examination and dimension control can be concluded that welded probe 2.7
does not fulfill the criteria for the level of quality D, C and B.
From the tensile test of the welded probe 2.7, the measured breaking force is Fm
(2.7) is superior than capacity of the probe 2.1. This
18
(2.7)=119540
N. By comparing the results from the basic material (probe 2.) and the weld without imperfections
(grinded face and root - probe 2.1) can be summarized:
- The cross sectional area of the probe 2. is A0
(2)=233,70mm2, and of the probe 2.7 is
A0
(2.7)=215,60mm2. It gives A0
(2.7)=0,92A0
(2). After performing the reduction Fm
(2.7)=130000
N. Reduced capacity of the probe 2.7, Fm
proved that the decreasing of the carrying capacity of the model 2.7 Fm
(2.7)=119520 N is result
of decreased cross-sectional area due to the continuous undercut.
- The rupture occurred in the zone of the thermal influence. This is result of the location of the
zone of thermal influence where by undercut the cross-section is decreased.
- The stress concentration due to discontinuity of the outer contour (Figure 9) does not
influence the capacity of the welded joint in the condition of static loading.
From the bending test of the probe 2.7 and both the root in compressed zone and the root in
tension zone the requirements for the bending tests are fulfilled. In both cases the bending angle of
1800 has been achieved.
From the toughness test of the probes 2.7 (table 12) are obtained values for toughness that
meet the requirements for the toughness of the material S235JR at +200C. (Probe 2.7)
VIII. CONCLUSIONS
From the FEA, the experiments and the analysis of the results from the research it may be concluded:
• The material S235JR of the probes with butt-welds (2.1, 2.6 and 2.7) completely fulfills the
requirements of the standard EN10025. The material has good weldability and due to
increased ductility is less sensitive to the stress concentration.
• Superior sagging (probe 2.6) depending on the depth can influence the capacity of the joint in
static (and presumably in dynamic conditions). The depth of the sagging fulfills the permitted
value for class of quality D (h=1 mm 2mm), but does not fulfill the permitted limits for the
class B (h=1mm 0,5 mm) and h=1 mm = 1mm (class C).
• The high continuous undercut (probe 2.7) depending on the depth has influence of the weld
capacity. The depth of the weld with continuous undercut is higher than the permitted value
for D, C and B level of quality.
• In the static loading conditions, during the quality assessment of the welded joints in the
aspect of imperfections that cause discontinuity of the outer contour can be allowed certain
violation of the imperfection dimensions compared to the permitted values of the standard
ISO 6520.
• During the quality assessment of the welded joints it should be considered the level of stress
at the weld, the kind of the stress and the kind of the loading of the structure.
• During the quality assessment of the welded joints, particularly the dynamically loaded
joints, the material of the welded structure must be considered. That is due to the fact that
different materials have different sensibility of the stress concentration.
13. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 8, August (2014), pp. 07-19 © IAEME
• Having in mind the knowledge gained from this paper, in certain cases the certain welds may
be judged positive even when there are present some imperfections, particularly
imperfections in the outer contour. For delivering such judgment, the person must have good
understanding of materials, welding, construction, design, calculation etc.
19
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