IUST
The Biennial International Conference on Experimental Solid Mechanics (X-Mech 2018)
13-14 Feb., 2018, Tehran, Iran
Center of Excellence in Experimental Solid Mechanics and Dynamics, School of Mechanical Engineering, Iran University of Science and Technology
Using the Failure Assessment Diagram Method to Evaluate Fracture Resistance of E7010-P1 Cellulosic Welding Electrodes
1 Kolooshani, S. H., 2*Atrian, A. and 3Mohseni, E.
1 MSc student, Department of Mechanical Engineering, Najafabad branch, Islamic Azad University, Najafabad, Iran
2 Assistant Professor, Department of Mechanical Engineering, Najafabad branch, Islamic Azad University , Najafabad, Iran
3 Industrial Advisor, National Iranian Gas Company, Isfahan, Iran
*(corresponding author: [email protected])
Abstract- In the present research, fracture resistance of three different cellulosic welding electrodes of type E7010 and E7010-P1 with variant chemical compositions have been investigated at temperature of 25oC. The assessment is made based on Failure Assessment Diagram (FAD) method in accordance with BS 7910-2015 standard. The mechanical and fracture toughness properties of weld material have been determined carrying out all weld metal tensile test as well as CTOD fracture toughness test. The results are then used for finite element (FE) simulations in Abaqus commercial software to compute stress intensity factor along the crack front in the weld material.
These results are then used to plot FAD curves and assessment points for each welding electrode to evaluate the existing crack in simulation. The analysis reveals that the presence of different amount of Mn in the weld metal influences directly the resistance to fracture in weld metal at moderate temperature applications.
Keywords - Failure Assessment Diagram (FAD), E7010-P1welding electrode, Fracture toughness, Crack Tip Opening Displacement (CTOD), Stress intensity factor.
I. INTRODUCTION
E7010-P1 and preceding type E7010 Cellulosic welding electrodes are used in shield metal arc welding (SMAW) process mostly for welding crude oil and gas transmission pipelines circumferential joints. According to AWS A5.5, relatively wide range of elements is allowed for chemical composition of these electrodes (Table 1) [1].
TABLE 1.CHEMICAL COMPOSITION REQUIREMENTS FOR UNDILUTED WELD METAL – AWS A5.5
AWS classification
Alloying elements (single values are maximum)
%C %Si %Mn %P %S %Cr %Mo %Ni
E7010-P1 0.2 0.6 1.20 0.03 0.03 0.3 0.5 1.0
Although all of these electrodes are made based on one standard and they all meet the standard minimum requirements, there are notable variation in fracture resistance of similar electrode types made by each manufacturer which
is due to the significant effect of added alloying elements.
Many authors (Mosallaee et al.,2013; Fattahi et al.,2012;
Trindade et al., 2007 ;) [2]–[4] have reported that the amount of alloying elements have significant effect on the microstructure and mechanical properties of deposited weld metal mainly the strength and toughness of weld metals of C- Mn, low-alloy and medium-alloy steels.
In order to assess this fact three different E7010-P1 cellulosic welding electrodes were selected in this research and relation between the electrode chemical composition and weld metal fracture properties were evaluated by conducting crack tip opening displacement (CTOD) fracture test based on BS7448 part 2[5] as well as performing failure assessment analysis of cracked weld structure using Failure analysis diagram method (FAD) based on BS7910-2015 standard [6].
II. METHOD Experimental procedure
Three different cellulosic welding electrodes that all were in the E7010-P1 classification were selected from different manufactures and subjected to shielded metal arc welding (SMAW) on both plate and pipe specimens. Chemical composition, tensile and fracture properties of weld metals were determined by conducting relevant tests. Tables 2 and 3 exhibit the weld metal properties of these electrodes.
TABLE 2.CHEMICAL COMPOSITION AND CODING OF DIFFERENT ELECTRODES USED IN THIS RESEARCH
Welding electrodes
Alloying elements
%C %Si %Mn %P %S %Cr %Mo %Ni
E7010-P1(1) 0.09 0.1 0.3 0.01 0.01 0.03 0.005 0.5 E7010-P1(2) 0.14 0.39 0.88 0.02 0.02 0.02 0.001 0.05 E7010-P1(3) 0.18 0.44 1.37 0.016 0.009 0.099 0.005 0.073
TABLE 3.TENSION AND FRACTURE PROPERTIES OF DIFFERENT ELECTRODES USED IN THIS RESEARCH
Welding electrodes
Yield Strength
(Mpa)
Ultimate Strength (Mpa)
Young’s Modulus(Mpa)
CTOD Ave-mm
E7010-P1(1) 435 524 240179 0.340
E7010-P1(2) 472 558 255913 0.464
E7010-P1(3) 625 726 199446 0.120
Failure Assessment Diagram
In the BS7910 standard, structural integrity assessments are carried out in the context of a FAD approach in which regions of safe and unsafe operation of the structure are defined in a 2D space. The vertical axis is the toughness ratio Kr which indicates the proximity to fracture. Kr is defined as Eq. 4. The abscissa Lr is the load ratio which indicates the proximity to failure by plastic collapse and is defined by Eq. 5. Failure is predicted at its intersection with the failure assessment curve, represented by Eq.6.
(4)
L . (5)
(6) where represents the failure assessment curve. In most low- and medium-strength structural alloys, it is not practical to obtain a KIC value that is valid according to the BS7448-2 procedure. Consequently, fracture toughness is usually characterized by either J integral or CTOD. The conversions to Kmat for these two parameters are as Eq.7 and Eq.8 [7].
!"#$ (7)
%&'
!"#$ (8)
where E is the elastic Modulus, Jmat and ( are fracture toughness in terms of J integral and CTOD, ) is the Poisson’s ratio, *+ is the 0.2% proof or yield strength of the material at temperature for which CTOD had been determined, *, is the tensile strength at temperature for which fracture test has been performed and - is the plastic constraint factor which is an empirical parameter and is defined by BS7910 as Eq.9:
- 1.517 2%%&34"5.6!77
0.3 %%&3 0.98 (9)
In the present research, Option 2 failure assessment curve was used based on Eq.10 because it is suitable for all metals regardless of the stress-strain behavior.
<A=>>?@%& BD =A>C%>?@& E"!/D (10)
εref is the true strain at the true stress of σref=LrσY and σY is the yield strength of each electrode.
III. FEMODELINGOF CENTER-CRACKED WELDED SPECIMEN
In order to compare the resistance behavior of three E7010- P1 electrodes toward failure, centered cracked welded structure panel (Fig. 1) of width 2W=500mm and thickness B=20mm which is pulled normal to the crack length (2a=100mm), with a far field stress σ=350MPa was modeled in ABAQUS and the fracture parameter of KI at crack tip was computed for each E7010-P1 electrode weld metal.
Fig.1. Configuration of centered cracked welded structure panel [8]
(One space)
Table 4 exhibits both the load and fracture ratio of three welding electrodes calculated for through thickness centered crack specimen described on section III.
TABLE 4.LOAD AND TOUGHNESS RATIO ASSESSMENT POINTS
Welding electrodes Load ratio Toughness ratio
Lr Kr
E7010-P1(1) 0.854 0.530
E7010-P1(2) 0.787 0.364
E7010-P1(3) 0.595 0.858
Fig. 2 illustrates the Option 2 FAD curves and the location of three assessment points , for each electrode weld metals according to BS7910 standard.
Fig.2. Failure assessment curves and the locus of assessment points for each welding electrode.
0 0.2 0.4 0.6 0.8 1 1.2
0 0.2 0.4 0.6 0.8 1 1.2
F(lr)
Lr
E7010-P1(1) 1 E7010-P1(2) 2 E7010-P1(3) 3
The locus of assessment point “1” which belongs to E7010- P1(1) electrode weld metal is tangent to FAD which shows occurrence for onset of unstable failure.
The locus of assessment point “2” which belongs to E7010- P1(2) electrode weld metal lies inside FAD which shows safe condition of panel.
The locus of assessment point “3” which belongs to E7010- P1(3) electrode weld metal falls outside of FAD which shows unsafe condition of panel.
(One space)
IV. CONCLUSION
Although the cellulosic E7010-P1 electrodes are made based on one standard and they all meet the standard minimum requirements, there are notable variation in fracture resistance of similar electrode types made by each manufacturer which is due to the significant effect of weld metal composition.
From this work, it is possible to conclude that for moderate temperature applications the optimum chemical content in the weld metal of E7010-P1 cellulosic welding electrodes is around 0.88 wt. % Mn, because this value enables the highest fracture toughness properties of weld metal as well as reasonable resistance toward plastic collapse of welded structure. Moreover, addition of Ni element around 0.5 wt. % did not influence on the weld metals fracture toughness properties for moderate temperature applications.
(One space) ACKNOWLEDGMENT
The authors wish to thank Isfahan Province Gas Company for sponsorship and also Azmouneh Foulad Counsulting Eng.
Co. for the experimental support for this research.
(One space) REFERENCES
[1] AWS A5.5, Specification for Low-Alloy Steel Electrodes for Shielded Metal Arc Welding Low-Alloy Steel Electrodes. American Welding Society, 1996.
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Int. J. Press. Vessel. Pip., vol. 111–112, pp. 75–81, 2013.
[3] M. Fattahi, N. Nabhani, M. Hosseini, N. Arabian, and E. Rahimi,
“Effect of Ti-containing inclusions on the nucleation of acicular ferrite and mechanical properties of multipass weld metals,”
Micron, vol. 45, pp. 107–114, 2013.
[4] V. B. Da Trindade, J. D. C. Payão, L. F. G. Souza, and R. D. R.
Paranhos, “The role of addition of Ni on the microstructure and mechanical behaviour of C-Mn weld metals,” Exacta, vol. 5, no. 1, pp. 177–183, 2007.
[5] BS 7448 part 2, Fracture mechanics toughness tests: Method for determination of KIC, critical CTOD and critical J values of welds in metallic materials. BSI Standards Publication, 1997.
[6] BS 7910, Guide to methods for assessing the acceptability of flaws in metallic structures. BSI Standards Publication, 2015.
[7] T. L. Anderson, Fracture Mechanics Fundamentals and Applications, 3rd ed. Taylor & Francis Group, 2005.
[8] P. Kumar, Elements of Fracture Mechanics, 7th ed. McGraw Hill Education (India) Private Limited, 2014.