Fatigue calculations on benchmark tasks according to ASME code, experiences, results

1st Hungarian-Ukrainian Joint Conference on SAFETY-RELIABILITY AND RISK OF ENGINEERING PLANTS AND

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BAY-LOGI

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Fatigue calculations on benchmark tasks according to ASME code,

experiences, results

Bay Zoltán Foundation for Applied ResearchVEIKI Power Research Institute

Szávai SzabolcsPálfi TamásTóth László


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Benchmark tasks for the Paks License Renewal Project

Created by Mechanical Components Scientific Committee

Solution made by different research institutes, solution methodology accepted by MC-SC

Conflict the ASME interpretation of different experts

Compare the result of different solution methods and tools

Develop verification cases for the applied methodologies of the project

Create a general solution method which can also be used for more complicated problems


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Analysis of pipeline and its elements

Evaluation of flange for structural integrity, stiffness, and leak tightness

Structural and fatigue analysis of a thick walled pressure vessel with openings



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Applied codes and regulations

ASME BPV CODE SECTION. III. (2001)

Procedure for actions related to the life

time extension of equipment operating in

nuclear plants

Directives for structural analysis of

pressure vessels. OAH NBI 3.3


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Simple problems require mainly numerical methods (e.g. FEM) however analytical solutions are also acceptable

ASME based, PNAE material properties

Class I. components Design and operational

conditions Coupled thermo-mechanical

static and cyclic analysis



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Benchmark tasks

Task Elements Type


Pipes, welds, elbows, curved pipes, branch connections, welded transitions

StructuralFatigueTightness

Load conditions:Level A Pressure testCyclic loads

Structural and fatigue analysis of a thick walled pressure vessel with openings

Vessel, nozzle, openings

Evaluation of flange for structural integrity, stiffness, and leak tightness

Flange connection, leak tightness, bolts.


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Analysis types

Test problem Structural analysis Fatigue leakage

Pipeline and its elements

Stress indexes Critical point of the pipe elements (branch connections, welds, etc.)

Vessel Membrane and bending stresses Primary, bending and peak stresses

Critical FEM elements

Take into consideration the FSRF of welds

Flange Membrane and bending stresses Primary, bending and peak stresses for bolts

Bolt, thread Seals


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Loadcases

Design Load: p=13,7 MPa T=325ºC

Test pressure: p=16,4 MPa, T=140ºC

Load on the nozzle:N=300kN, M=200kNm T=100kNm

T [˚C] T [˚C]

T [˚C]T [˚C]

p [MPa] p [MPa]

p [MPa]p [MPa]

A. Cycle (1x) B. Cycle (2x)

C. Cycle (5x) D. Cycle (5x)

t [h] t [h]

t [h]t [min]

130 13019,5 16

300 30012 12

60 60

290 60

0,1 0,1

11 0,1

1,4 1,4

10 40 60

0 0

0 0

1,65 3,4 1,65 3,4

1446 1454

2 month

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Cyclic load:


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Structural and fatigue analysis of a pressure vessel

Structural analysis for design conditions

– Critical points (2. and 3.)– Nozzle

Fatigue evaluation at 3.Thermal stress calculation in the cylindrical wall


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Structural analysisof the nozzle

Material properties based on PNAE Analysis of the nozzle based on WRC107


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Axysymmetrical FEM model to get sufficient results for the critical points. Derive the primary, secondary and peak stresses from the calculated stress distribution Determination of the membrane and membrane+bending stressesFatigue evaluation

– Calculation of the stress intensities– Rainflow analysis for determining the stress cycles– FSRF determination for the analyzed points– CUF calculation – Critical point evaluation

Structural analysisof pressure vessel


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Results, Experiences

Calculations were done by 2 independent research institutes

– VEIKI Rt., Budapest– BAY-LOGI and Univ. of Miskolc, Miskolc

Good agreement between the stresses and the location of critical elementsWRC107: COADE interpolated and „manual” diagram reading of the parameters caused different results in the nozzle


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Results, Experiences


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Wall temperature distributions Cycle „A”Cycle „A” Cycle „C”Cycle „C”


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Fatigue analysis

Stress differences were calculated considering varying principal stress directions:

– At the principal stress calculation the difference of each stress components in the two time steps was used


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Structural analysis– Design condition– Level A– Pressure test

Fatigue analyses– Primary, secondary

and thermal stresses


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Material properties – based on PNAE

CAEPIPE model for– Stiffness calculation – Determination of the Moments for each element

ASME Class 1 stress indexes– Pipes, welds, curved pipes, branch connections, welded

transitions

Structural analysisFatigue analysis

– Determination of the stress amplitudes– CUF calculation

Required steps for analysisof pipeline and its elements


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Stresses were calculated also using shell elements in Msc Nastran4W

In each cross-section:– Stress transformations needed to determine stresses in the

local coordinate system– Parametric calculations needed to calculate the highest

bending stress

Finite element solution


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Results using finite element solution was in good agreement with the results using CAEPIPE model and ASME stress indexes

– Large deformation calculation needed, because the pressure caused deformation at the curved sections essentially affects stiffness

– Special spring elements had to be used to model the support

Finite element solution


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Analysis of flange joint for structural integrity, stiffness

and leak tightnessStructural analysis for:

– Level A – Pressure test

Leak tightness evaluation– seating load– stiffness

Fatigue analysis of bolts and threads


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Material properties: – based on PNAE

Elastic model including:– bolts – sealing


and leak tightness


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Required steps of the evaluation

Required bolt area verification

Analysis of bolts for level A condition

Stiffness calculation of the joint

– Determination of the displacements

– Examination of the leak tightness


and leak tightness


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Required steps of the evaluation:

Analysis of the bolts for test pressure

Calculation of the gasket force

Examination of the thread

Fatigue analysis for bolts and threads


and leak tightness


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The finite element model

Spring elements were used to model the seal and the bolts

Rigid elements were used for the washers

The active bolt length=unconstrained length+2x3 threads


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Results

Calculations were done in 2 independent research institutes

– VEIKI Rt., Budapest: • Finite element model including bolts and sealing

– BUTE, Budapest• Finite element model for the flanges + semi analytical model for

stiffness calculations

Good agreement between the stiffness values and the stresses


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Some of the stress calculations were done also by using analytical methods, and got higher stresses then by FEM calculations, because more complex analytical model required

Results


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Check points for future participants

Task Check points


–Stiffness–Moments at different load cases stress indexes–Stresses–Fatigue cycles, CUF

Structural analysis of a nozzle of the pressure vessel

–WRC107 parameters for nozzle analysis, stresses and categorization

–Stresses for the operational conditions, membrane and membrane+bending stresses

–Critical points from the fatigue calculation, fatigue cycles, stress amplitudes, CUF

–Temperature distribution and thermal stresses

Analysis of flange joint for structural integrity, stiffness and leak tightness

–Stress components from the structural analysis, membrane and membrane+bending stresses

–Stiffness of the flange–Bolt loads and gasket seating condition.–Fatigue evaluation, CUF calculation


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Summary and conclusions

The developed benchmark tasks are suitable for:

– Demonstrating the ASME methodology in accordance

with the Hungarian directives

– Comparing the result of different solution methods and tools

– Providing verification points for the applied

methodologies

– Act as a general solution method, can also be used for

more complex problems

Documents

Fatigue calculations on benchmark tasks according to ASME code, experiences, results