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COMPARATION FOR STRESSES VALUES OBTAINED BY FINITE
ELEMENT ANALYIS (ANSYS) AND BY STRAIN-GAGE METHOD
Jairo João Mola, MBA, Msc
Carlos Morais, MBA, PMP
PRESENTATION TOPICS
• Company Overview
• Problem Description
• Finite Element Results
• Strain-gage Results
• Final results
• Conclusion and next steps
ABOUT UNITÉCNICA
• Founded in 1992, UNITÉNICA is a solution provider for Oil & Gas, Chemical & Petro-chemical and Nuclear industries.
• Our specialization involves the analysis of:– Pipes’ flexibility (TRIFLEX, CAESAR and ROHR softwares)– Pumping systems (FLUIDFLOW software)– Vessels, Reactors, Heat Exchangers, Columns (PVELITE software)– Special equipments (ANSYS software)– Finite Element Analysis (ANSYS software)
• Our main clients are:– PETROBRAS’ REFINARIES – REPLAN / RECAP / REVAP / REFAP / REGAP– TRANSPETRO– CBE / FOSFÉRTIL / FAFEN– BRAZILIAN NAVY (CTMSP)– JARAGUÁ / ASVOTEC / BARDELLA / DEDINI / DELP / INTECNIAL– ENGEVIX / PROJECTUS / TECNOMON / SETAL / PROGEN / ANDRADE GUTIERREZ– NUCLEP / INB / ELETRONUCLEAR
PROBLEM DESCRIPTION
FIGURE 01
PROBLEM DESCRIPTION
• During the hydrostatic test of a nuclear steam generator
(figure 01), the main stresses were monitoring thru strain-
gages.
• The strain-gages were positioning on the regions were the
previous finite element analysis showed the maximum
stresses values
• The stresses values obtained by the two different methods
were compared
FINITE ELEMENT RESULTS
• Finite Element 3D Model – figure 02
• Finite Element Axisymmetric Model – figure 03
• Stress Intensity for 3D Model – Design Condition – figure 04
• Stress Intensity for Axisymmetric Model – Design Condition - figure 05
• Stress Intensity for 3D Model – Test Condition (Tube Side) – figure 06
• Stress Intensity for 3D Model – Test Condition (Shell Side) - figure 07
• Stress Intensity for Axisymmetric Model – Test Condition (Tube Side)
– figure 08
• Stress Intensity for Axisymmetric Model – Test Condition (Shell Side)
– Head Detail – figure 09
FINITE ELEMENT 3D MODEL
FIGURE 02
FINITE ELEMENT AXISYMMETRIC MODEL
FIGURE 03
STRESS INTENSITY FOR 3D MODEL - DESIGN CONDITION
FIGURE 04
STRESS INTENSITY FOR AXISYMMETRIC MODEL - DESIGN
CONDITION
FIGURE 05
NOTE:
The stresses values in
this axisymmetric model
are different comparing
with 3D model, because in
this model we do not have
nozzles and other non-
axisymmetric details.
STRESS INTENSITY FOR 3D MODEL - TEST CONDITION
(TUBE SIDE)
FIGURE 06
STRESS INTENSITY FOR 3D MODEL - TEST CONDITION
(SHELL SIDE)
FIGURE 07
STRESS INTENSITY FOR AXISYMMETRIC MODEL - TEST
CONDITION (TUBE SIDE)
FIGURE 08
STRESS INTENSITY FOR AXISYMMETRIC MODEL - TEST
CONDITION (SHELL SIDE) – HEAD DETAIL
FIGURE 09
STRAIN-GAGE RESULTS
FIGURE 10
STRAIN-GAGE METHODOLOGY
• The strain-gage application and interpretation was done by a
special nuclear technology center: CDTN (Centro de
Desenvolvimento de Tecnologia Nuclear; BH / MG)
• The internal strain-gages were immersed in water during the
test; they needed special protections
• The strain-gages had an global uncertainty of the measured
values evaluated in 4% of the read values.
• Pressure and temperature were monitored and registered
during all the test time
• The stresses values were monitored and registered during all
the test time (figure 11 – Smax, Smin, Shear, Angle)
STRAIN-GAGE MEASUREMENT – EXAMPLE (SG-01)
FIGURE 11
FINAL RESULTS
• The figure 12 shows the stress intensity in the secondary man-way / shell
region, obtained thru finite element analysis (test condition)
• The figure 13 shows the stresses obtained in the same region with strain-
gage SG-20 (test condition)
• Table 01 shows the comparative values for stresses obtained by two
methods (in the table, many values were discharged because it will be
necessary to explain each one separately and we do not have time for
this)
• Like a final result, 28 points were really measured (3 strain-gages had
problems during the operation) and 21 showed a difference lesser than
10% comparing with finite element results. Other 5 points had problems
with strain-gage location.
FINAL RESULTS
THE FINITE ELEMENT ANALYSIS
VALUE WAS 560 MPa
FIGURE 12
FINAL RESULTS
SG20
-700
-500
-300
-100
100
300
-2000 3000 8000 13000 18000 23000
Time [s]
Str
es
s [
MP
a]
smax smin tmax
Angle of the maximum principal stress
0,0
50,0
100,0
150,0
-2000 3000 8000 13000 18000 23000
Time [s]
An
gle
[d
eg
ree
s]
THE STRAIN-GAGE VALUE
WAS -570 MPa
FIGURE 13
FINAL RESULTS
PONTO
Sa Sb (Sb/Sa)
SG1 240 232 0,97
SG8 64 65 1,01
SG9 54 51 0,94
SG10 42 43 1,02
SG11 95 97 1,02
SG12 95 88 0,93
SG13 123 123 1,00
SG14 123 130 1,06
SG15 119 110 0,92
SG16 131 133 1,02
SG17 227 237 1,04
SG18 142 167 1,18
SG19 131 108 0,82
SG20 430 436 1,01
SG22 60 55 0,92
SG23 205 200 0,98
SG24 157 146 0,93
SG25 109 98 0,90
SG26 119 123 1,03
SG27 42 41 0,98
SG29 156 165 1,06
SG30 200 205 1,03
TABLE 01
CONDIÇÃO DE PROJETO
Sa – TENSÕES CALCULADAS
Sb – TENSÕES MEDIDAS
CONCLUSION AND NEXT STEPS
• The convergence of FEM stresses results and strain-gage
stresses measurements indicates that the finite element method is
a powerful tool for mechanical analysis.
• UNITÉCNICA adopts a comparative results report to qualify the
ANSYS software when the client’s quality system demands, for
example.
• UNITÉCNICA has already done the analysis of the strain-gage
results for three nuclear equipments; in all cases the results are
very close with that values obtained in finite element analysis.
• In the future, other nuclear equipments that are today in
fabrication, will be tested and the strain-gage and finite element
methods will be applied again.