A comprehensive methodology is developed to understand and characterize the fracture behavior of circumferentially cracked boiler tubes in this study. Weld overlay is applied on the coal-fired boiler tubes in order to prevent the degradation of corrosive and erosive environment that the boiler tubes are exposed to in the power plants. Finite element modeling and analysis are employed for all of the computations including steady-state and transient stress intensity factor (SIF) calculations in this study. Circumferential cracking has been one of the failure modes in waterwall boiler tubes, which results in high maintenance and replacement costs. Thermomechanical stresses and corrosive environment are basically the two remarkable contributors that bring about this failure mode. The former one is investigated and quantified in this study in order to explain the fracture behavior of weld overlay coatings during the power plant operation. Periodic soot blowing operations cause cyclic transient thermomechanical stresses on the weld overlay coating that results in crack propagation and fatigue failure. Three-dimensional fracture analysis of circumferentially cracked boiler tubes is examined using enriched finite element method in this study. Transient temperatures and thermomechanical stresses are computed using ANSYS for five different periodic crack spacing values (h), which are 2, 4, 6, 10, and 20 mm in the axial direction. 3D fracture analysis was performed, and stress intensity factors were computed using FRAC3D, which is Finite Element Analysis (FEA) software developed at Lehigh University. The maximum stress intensity factor is obtained at the deepest penetration of the crack in the model which has the largest periodic axial crack spacing, h = 20 mm. The stress intensity factors due to welding residuals decrease as the axial crack spacing, h, decreases. The FEA methodology developed in this research would provide the engineers with the ability to understand the fracture problem and predict component life and improve the reliability of the weld overlay coated boiler tubes utilized in the power plants.

References

References
1.
Luer
,
K.
,
DuPont
,
J. N.
,
Marder
,
A. R.
, and
Skelonis
,
C.
, 2001, “
Corrosion Fatigue of Alloy 625 Weld Claddings in Combustion Environments
,”
Mater. High Temp.
,
18
, pp.
11
19
.
2.
Nied
,
H. F.
, and
Erdogan
,
F.
, 1983, “
Transient Thermal Stress Problem for a Circumferentially Cracked Hollow Cylinder
,”
J. Therm. Stresses
,
6
, pp.
1
14
.
3.
Nied
,
H. F.
, 1984, “
Thermal Shock in a Circumferentially Cracked Hollow Cylinder With Cladding
,”
Eng. Fract. Mech.
,
20
(
1
), pp.
113
137
.
4.
Nied
,
H. F.
, 1987, “
Periodic Array of Cracks in a Half-Plane Subjected to Arbitrary Loading
,”
ASME J. Appl. Mech.
,
54
, pp.
642
648
.
5.
Chiew
,
S. P.
,
Lie
,
S. T.
,
Lee
,
C. K.
, and
Huang
,
Z. W.
, 2001, “
Stress Intensity Factors for a Surface Crack in a Tubular T-Joint
,”
Int. J. Pressure Vessels Piping
,
78
, pp.
677
685
.
6.
Cao
,
J. J.
,
Yang
,
G. J.
,
Packer
,
J. A.
, and
Burdekin
,
F. M.
, 1998, “
Crack Modeling in FE Analysis of Circular Tubular Joints
,”
Eng. Fract. Mech.
,
61
, pp.
537
553
.
7.
Taylor
,
D.
, 1996, “
Crack Modeling: A Technique for the Fatigue Design of Components
,”
Eng. Failure Anal.
,
3
(
2
), pp.
129
136
.
8.
Murugan
,
S.
,
Kumar
,
P. V.
,
Raj
,
B.
, and
Bose
,
M. S. C.
, 1998, “
Temperature Distribution During Multipass Welding of Plates
,”
Int. J. Pressure Vessels Piping
,
75
, pp.
891
905
.
9.
Murugan
,
S.
,
Rai
,
S. K.
,
Kumar
,
P. V.
,
Jayakumar
,
T.
,
Raj
,
B.
, and
Bose
,
M. S. C.
, 2001, “
Temperature Distribution and Residual Stresses Due to Multipass Welding in Type 304 Stainless Steel and Low Carbon Steel Weld Pads
,”
Int. J. Pressure Vessels Piping
,
78
, pp.
307
317
.
10.
Sarkani
,
S.
,
Tritchkov
,
V.
, and
Michaelov
,
G.
, 2000, “
An Efficient Approach for Computing Residual Stresses in Welded Joints
,”
Finite Elem. Anal. Design
,
35
, pp.
247
268
.
11.
Fricke
,
S.
,
Keim
,
E.
, and
Schmidt
,
J.
, 2001, “
Numerical Weld Modeling—A Method for Calculating Weld-Induced Residual Stresses
,”
Nucl. Eng. Des.
,
206
, pp.
139
150
.
12.
Ayhan
,
A. O.
, and
Nied
,
H. F.
, 2002, “
Stress Intensity Factors for Three-Dimensional Surface Cracks Using Enriched Finite Elements
,”
Int. J. Numer. Methods Eng.
,
54
, pp.
899
921
.
13.
ANSYS, Inc., 1999, “
Thermal Analysis Guide
,” ANSYS Release 5.6.
14.
Yildirim
,
B.
, 2000, “
Nonlinear Thermal Stress/Fracture Analysis of Multilayer Structures Using Enriched Finite Elements
,” Ph.D. thesis, Lehigh University, Bethlehem.
You do not currently have access to this content.