Stress and Fatigue Analysis of ASME Pressure Vessels...

Unrestricted © Siemens AG 2014

FEMAP SYMPOSIUM 2014

Discover New Insights Femap Symposium 2014

May 14-16, Atlanta, GA, USA

Stress and Fatigue Analysis of ASME Pressure

Vessels using Femap API and Fatigue Essentials

Adrian Jensen, Predictive Engineering | Brian Reiling, Endeavor Analysis

2014-05-15


Siemens PLM Software



Abstract

The application of the ASME Section VIII, Division 2 pressure vessel code is

becoming increasingly more popular since it facilitates the optimization of

pressure vessels via detailed stress and fatigue analysis.

The basis of this analysis is the creation of a high quality plate and/or solid mesh

followed by accurate load application and then the extraction and classification of

stresses per code.

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Abstract

Much of this work is algebraic in nature

and is well suited for automation.

Through the use of Femap’s Application

Programing Interface (API) and

customized spreadsheets, the analysis

of ASME-type pressure vessels can be

accelerated from days to minutes.

In many cases, once the vessel has

passed its baseline load requirements, a

fatigue analysis is required to address

cyclic mechanical and thermal loads.

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Abstract

To simplify this calculation, the software program Fatigue Essentials is used and

a brief example is presented on how this program automates the fatigue

calculation.

Although fatigue analysis can be

quite basic and almost an

accounting exercise, the more

stringent ASME requirements of

specialized fatigue curves and

stress output as stress intensity

complicates the procedure.

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ASME VIII Pressure Vessels

Modeling, Analysis and Post Processing

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ASME Section VIII Pressure Vessels

• What happened in Massachusetts?

• Pressure Loads (>15 psig)

• Nozzle Loads

• Fluid Dead Weight

• Thermal Loads

• Seismic Loads

• Highly Ductile Stainless Steel

• Stress Analysis Method

• Specialized Post Processing

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What happened in Massachusetts?

On March 10, 1905, a catastrophic boiler explosion occurred in a shoe factory in

Brockton, Massachusetts, that killed 58 and injured 150 people. At about 8:00

AM there were around 400 employees at the R. B. Grover & Company shoe

factory in Campello, when the boiler exploded, shot through the roof, and caused

the building to collapse.

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What happened in Massachusetts?

The boiler traveled several hundred feet, damaging a number of buildings and

coming to rest in the wall of a house. Thirty-six of the victims were never

identified and were buried in a common grave, where a monument to the victims

was later erected by the city.

Balmer, Robert T (2010). Modern Engineering Thermodynamics. 13.10 Modern Steam Power Plants: Academic Press.

This and similar explosions brought

about the development of the ASME

Boiler and Pressure Vessel Code in

1915.

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Stress Analysis Method

• Surface Stress

• Membrane Stress

• Localized Stress

• Thermal Stress

Post Processing

• Stress Intensity Calculator

• Membrane Stress Calculator

• Stress Linearization Tool

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Loading Conditions

• Pressure loads (external or internal) in excess of 15 psig

• Fluid dead weight loads (hydrostatic pressure)

• Thermal loads (hot/cold fluid, cooling jackets, local/general)

• Seismic Loads (requires analysis even if the vessel is Div. 1)

Materials

• Highly ductile stainless steel

• Excellent fatigue properties

• “Allowable Stress” based on σy

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Transient Thermal Analysis

Development and Load Application

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• Transient Temperature Profile

• Transient Boundary Conditions

• Heat Transfer Coefficients

• Modeling Considerations

• Femap API

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• Transient Temperature Profile

• The thick wall vessel has a significant thermal gradient

though wall thickness and along the length of the vessel

• Transient Boundary Conditions

• The vessel is filling throughout the analysis

• Gas, Boiling Liquid and Non-boiling Liquid have different

temperature deltas and heat transfer coefficients

• The inside surface was meshed with membrane elements

• This allows for easy thermal load application

• Also provides better stress recovery

Low ΔT, High h

High ΔT, Low h

Negligible ΔT,

Negligible h

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Fatigue Essentials

Stress Life Made Easy

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Fatigue Analysis Using Fatigue Essentials

Fatigue Essentials is intended to provide a user friendly tool for conducting

Stress-Life analysis either using classical stress calculations or linked with

FEMAP and using the finite element generated stresses.

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More advanced techniques to account for high strain – low cycle (Strain-Life) are

available as well as more advanced models of crack initiation and multi-axial

stress situations but in most cases these are not necessary for the design of

durable structure.


Fatigue Essentials is intended to

provide a user friendly tool for

conducting Stress-Life analysis

either using classical stress

calculations or linked with FEMAP

and using the finite element

generated stresses.

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Fatigue Essentials is set up to guide the

user through the analysis by following a

tree structure.

General analysis options are selected

following loads, materials, and spectrum

branches. Within each branch are

options for analysis variations or input

methods.

When the model solves there are

multiple options for selecting output to

the screen. For large models (usually

FEA based) it is usually best to push a

damage plot back to FEMAP to view.

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• Analysis Options

• Load Cases

• Material Definition

• Mean Stress Correction

• Spectrum Definition

• Fatigue Damage Calculation

• Material Plot

• Report Generation

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Analysis Options

• Scatter Factor

o Easy way to add reliability

• Stress Units

• Rainflow per ASTM E1049

o Rainflow

o Peak Counting

• Stress Modification

o Stress Multipliers

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Load Cases (Details)

• Enter inter-actively within

GUI

`

• Load from CSV file

• Load from FEMAP

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Material Definition

• Choose from existing library

or create new material curve

• Flexible input allows user to

input any curve and account

for confidence and reliability

vs using a mean curve.

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Material Definition

• Curve can be created three

different ways

• Tabulated

o Log-Log interpolation

• Estimated

o Based on percentages of

material ultimate strength

• Walker Equation (MMPDS)

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Mean Stress Correction

Four methods of correcting for mean stress (stress ratio)


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Material Assignment

• Once material is created

and/or selected it is

assigned to the analysis

detail(s)

• Can have multiple details

and multiple materials in

the same analysis if desired

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Spectrum Definition

• Spectrum can either be

entered in using the GUI or

can be read in from CSV

file.

• The number of spectrum

repeats is entered here

• Multiple spectrums can be

used and the damages for

each spectrum are added

together

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Fatigue Damage

• Options for report

generation are entered

here

• For large models it is best

to have minimal reporting

• Small models it can be

useful to view additional

data

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Material Plot

• The material curve is

plotted for reference at

three stress ratios:

o R = -1

o R = 0

o R = 0.5

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Report Generation

• The report can generate

plots and tables of:

o Details and stresses

o Spectra plot

o Spectra table

o Rainflow pairs

o Damage summary

o Margin of safety

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Contact Information

Adrian Jensen

Sr. Staff Engineer

Predictive Engineering, Inc.

Phone: (503) 206-5571

E-mail: [email protected]

Brian Reiling

Partner / Principal Engineer

Endeavor Analysis, LLC

Phone: (206) 805-9030

E-mail: [email protected]

mailto:[email protected]

mailto:[email protected]

Stress and Fatigue Analysis of ASME Pressure Vessels...

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