Engineering, 2013, 5, 66-68
doi:10.4236/eng.2013.51b012 Published Online January 2013 (
Copyright © 2013 SciRes. ENG
Mechanical Stress Analysis of a 600M W Supercritical Boi-
ler Superheater Outlet Header
Dongyi Li, Zhongguang Fu, Qiang Zhang, Ting He
School of Energy,Power and Mechanical Engineering;North China Electric Power University;Beijing,China
Received 2013
The mechanical stre ss distribution and the stress concentrations of the superheater outlet header of a 600MW supercrit-
ical boiler we r e analyzed by the finite element method. The results showed that the stress concentrated at the inside
conjunction area between the pipe and the header cylinder , and the value of the maximum mechanical stress concentra-
tion factor is 2.51.
Keywords: Superheater Outlet header; Finite Element Method; Stress Concentration
1. Introduction
With t he d evel opment of economy and the rapid increase
of electricity demand, large-capacity high-parameter
thermal power generating unit takes part in the peak load
operation. Since the boiler load changes greatly during
the peak load operating process, the stress of the bearing
pressure parts changes rapidly. Because of that, the stress
of the boiler load section changes drastically which
eventually shorten the ori ginal operating time very muc h
1,2]. Therefore, the stress analysis of the bearing com-
ponents becomes essential for operating the power plant
safely and economically.
The total stress is mainly impacted by the internal
pressure on the basis of previous studies[3,4].This paper
takes a superheater outlet header of a 600MW boiler as
the research object to analyze the distribution and varia-
tion law of mechanical stress with the finite element
analysis software-ANSYS. Besides, the pressure data
during the process of load pick-up is passed as boundary
2. Model and Boundary Conditions
2.1. Structure of Header
Figure 1 shows the structure of the superheater outlet
header of a 600MW supercritical boiler.
This research considers the header as a thick walled
cylinder which diameter and wall thickness are 635mm
and 136mm. On the cylinder, 68 rows of nozzles are
evenly distributed with 304.8mm between each two rows.
The diameter and wall thickness for each nozzle are
45mm and 11mm. The metal material of the header is
T92/P92[5,6] .
Three hypotheses are proposed for the following anal-
ysis: (1) all physical parameters of the cylinder are iso-
tropic; (2) a half part of the cylinder and the inserted
nozzles was taken by the model because of the symme-
trical structure of the cylinder; (3) One nozzle was ran-
domly taken by the model because all nozzles are evenly
distributed on the whole cylinder. The model which con-
tains 52994 units and 79843 nods is analyzed by an algo-
rithm of free mesh SOLID98 element in this research.
Check the mod el on F ig ure 2.
2.2. Load and boundary conditions
The right cr oss-section(B-surface) on Y-axi s shifti ng and
the two longitudinal section(A-surface) on X-axis shift-
ing needs to be constrained. At the same time, restrain
the shifting of the Z-axis on a critical point-D. When
load i ng the inte rnal-p re s sur e o n the i nne r wal l, the t e nsi l e
load also needs to be loaded on the left cross-section and
five nozzle cross-section surfaces in the meantime. The
equations to calculate the tensile load are shown below
Figure 1 . The structure of header.
Copyright © 2013 SciRes. ENG
Figure 2. T he model and the grid divis ion.
Where PC=cylinder end cross-section uniform ten-
sion,mm;PD=nozzles end cross-section uniform ten-
sion,mm;Pi=internal pressure,MPa;do=nozzles outer
diameter,mm;di=nozzles inner diameter,mm; Do = cy-
linder outer diameter, mm; Di = cylinder inner diame-
te r ,mm.
The data of load that used for analysis are the actual
ope rat ing da ta in a po wer pl ant . The c hangi ng p ath o f the
inter nal pressure i s shown in Figure 3.
3. Results and Discussion
3.1. Distribution of Mechanical Stress
Figure 4 shows the distribution of mechanical stress.As
shown in Figure 4, mechanical stress changed greatly at
the inside conjunction area between the pipe and the
header cylinder when it changed very little at the area
which far from the intersecting line area. The phenome-
non of stress centralization at the intersecting line area is
in evidence. The stress at the area far from the intersect-
ing line area can be considered as the membrane stress of
the cylinder. It can be calculated with the follow equa-
)( +
where P = internal pressure,MPa; Di = cylinder inner
dia meter, mm; S = wa ll t hic kne ss, mm. Co mpa riso n of the
ANSYS analysis to the theoretic calculation is shown in
Figure 5. Two results are basically the same. According
to the co mparison, the reliab ility of ANSYS is verified.
3.2. Maxi mum Stre ss Poi nt
During the running process, the maximum stress ap-
peared mainly at point-N as shown in Figure 6. The
point is on the intersectin g line.The variation of mechan-
ical stress at point-N sho ws in Figure 7.
Figure 3 . Pressure change curve in pick-up l oa d process .
Figure 4 . Cloud picture of mech anical stress.
Figure 5. Comparison of the ANSYS analysis to the theo-
retic calculat ion.
Figure 6 . Position of p oint-N.
Copyright © 2013 SciRes. ENG
Figure 7. Variat ion of s tres s at point-N.
Figure 8 . Changing c urve of stress concentr ation fact or.
Impacted by the internal pressure, the mechanical
stress and the internal pressure are sharing the similar
changing tendency.The value of mechanical stress is va-
rying from 56.61MPa to 121.01MPa.
3.3. Stress Concent ration Factor
The mechanical stress concentration factor is indepen-
dent of ru nni n g co nd it ion[ 7] . T he str ess o n t he s tudy a re a
is directly proportional to the value of the internal pres-
sure. Define stress concentration factor as follow[9]:
= maximum stress. The changing curve of
the stress concentration factor during the process of load
pick-up at point-N is shown i n Figure 8.
Based on above computations, in the later period of
the load pick-up process, the stress concentration factor
with its value 2.51 can be considered keeping stable dur-
ing the whole process because of the tiny changes on the
amplitude o f the factor.
4. Conclusion
Refers to the computations, the phenomenon of stress
centralization at the inside conjunction area between
the pipe and the header cylinder is obvious. Far from
the intersecting line area changes less in stress; it can
be considered as the membrane stress of the cylinder.
The maximum stress is distributed mainly at point-N
which is focu sed o n the inters ectin g line. Accor din g to
the numerical calculation, the stress concentration
factor of point-N is 2.51.
These analysis results, especially the stress concentra-
tion factor, can be used in life expenditure on-line
monitoring system in following research.
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