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.