FEA-Based Acoustic Fatigue Analysis Methodology - SWRI

7/23/2019 FEA-Based Acoustic Fatigue Analysis Methodology - SWRI

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An FEA-Based Acoustic Fatigue Analysis

Methodology

Timothy C. Allison, Ph.D.

Lawrence J. Goland, P.E.

Southwest Research Institute

San Antonio, TX

ANSYS Regional Conference:

Engineering the SystemAugust 31 - September 1, 2011

Houston, TX


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Outline

Introduction and Theory Existing Acoustic Fatigue/AIV Screening

Methods

Carucci-Mueller, Eisinger Energy Institute

SwRI Method

AIV Solutions Conclusions


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Introduction

Acoustically Induced Vibration (AIV) refersto high-frequency vibration (typically 500-1500+ Hz) in piping downstream of apressure-reducing device

E.g. a control valve or pressure relief valve

Can result in high cycle fatigue failures,particularly at branch connections

First identified in 1983 by Carucci andMueller

Often a concern in flare/blowdown pipingwith thin walls and large diameters.

Image Courtesy Tyco Valves & Controls


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Theory Overview

AIV is caused by the following four physicalphenomena:

Excitation from a pressure-reducing valve causes high-frequency pressure fluctuations in downstream piping.

These fluctuations excite higher order acoustic modes inthe pipe with circumferentially varying pressure modeshapes.

The acoustic pulsations couple to shell modes of themain piping.

Branch connections or other welded discontinuities inthe main line serve as stress risers.


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Theory: Acoustic Cross Modes


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Theory: Pipe Shell Modes


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Existing AIV Screening Methods

Carruci-Mueller paper (1983) introduced designlimits based on failure/non-failure experience.

PWL and Pipe Diameter

Eisinger (1997) modified the Carruci-Mueller

limits to include different excitation parameterand wall thickness.

M*P and Pipe D/t Ratio

Eisinger later (1999) used FEA to extend thedesign curve to lower D/t ratios.


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Existing AIV Screening Methods (2)

Carruci-Mueller Design CurveEisinger Design Curve


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Existing AIV Screening Methods (3)

The Energy Institute (2005) introduced a screeningmethodology for AIV: Simple source PWL computation

PWL decay to branch connection and addition of PWLfrom multiple sources at each branch

Estimate of fatigue life from curve-fit data (data from FEmodels calibrated to historical failure/non-failure data)

Fatigue life estimation including reduction due toweldolet fittings and small branch diameter to main line

diameter ratios Likelihood of Failure (LOF) computed from estimatedfatigue life


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SwRI Method Overview

Valve excitation analysis, acoustic analysis andfinite element analysis performed to determinecoincidence of acoustic and pipe shell modes

Forced response analysis of FE model at coincidentmodes performed with shell models to determinestresses at fillet weld and resulting fatigue life. Excitation from valve amplified by acoustic amplification

factor to account for acoustic resonance

Stresses evaluated using mesh-insensitive procedure for

welded joints in accordance with Section 5.5.5 of theASME Boiler and Pressure Vessel Code, Section VIII,Division 2


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SwRI MethodValve Excitation

Valve excitation analysis performedusing control valve noise predictionstandard IEC 60534-8-3 Detailed source PWL prediction

Peak noise frequency from vena

contracta velocity and jet diameter Model PWL decay to branch and

summation of sources at branch insame manner as Energy Institutemethod

Convert PWL to SPL and dynamicpressure

Image Courtesy Floyd Jury, Fisher Controls


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SwRI MethodAcoustic Modes

Closed form solution used tomodel higher-order acousticmodes

Resulting acousticfrequencies and modeshapes validated with ANSYSAcoustic 3D FEA models

Multiply valve excitation byamplification factor to

account for acousticresonance

p1p2

p3

p4

p5

p6

q1


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SwRI MethodPipe Shell Modes

ANSYS APDL scripts constructed to efficientlyconstruct shell element models of piping at

branch connections

Modal analysis performed for each connectionover excitation frequency range

Results postprocessed externally via spatial FFT

to determine dominant nodal diameter patternsin each mode


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SwRI MethodPipe Shell Modes (2)


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SwRI MethodPipe Shell Modes (3)

Circumferential Mode

Shape (n)FFT performed in order to

identify n


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SwRI MethodCoincidence


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SwRI MethodForced Response


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SwRI MethodForced Response (2)

1150 1170 1190 1210 1230 1250 1270 1290

Mesh-SensitivePeakStress

Frequency, Hz

CoincidentMode


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Note: Stresses shown are mesh-sensitive and are not accurate

absolute values. Mesh-insensitive stresses are calculated with

ASME B&PV Code Sec VIII Div 2 procedure


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At Fillet

Weld

Toe

Note: Stresses shown are mesh-sensitive and are not accurate

absolute values. Mesh-insensitive stresses are calculated with

ASME B&PV Code Sec VIII Div 2 procedure


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SwRI MethodFatigue Life

Use relative stressdistribution from mesh-sensitive results to find

location of maximumstress

Use nodal forces andmoments to calculate

bending and membranestresses and assessfatigue life

Images Courtesy ASME Boiler & Pressure Vessel Code, Section VIII, Division 2


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SwRI MethodFatigue Life ASME Div 2 master S-N developed based on a large

amount of welded pipe and plate joint fatigue test data

Fatigue life assessed on -3S-N curve for


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Conclusions

New AIV analysis methodology developed based

on physical principles

Method uses automated implementation of

valve noise prediction standard and exact

acoustic solution for efficient excitation solution

Automated scripting tools applied for efficient

FEA solution of coincident stress at connection

and mesh-independent fatigue life results

FEA-based approach allows for modeling of

various countermeasures


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Method ComparisonCarruci-

Mueller

Eisinger Energy

Institute

SwRI

Method

Calculates PWL X X X X

Includes Pipe Diameter X X X X

Uses historical data X X X See (1)

Includes pipe wall thickness X X X

Includes multiple sources & decay X X X

Includes connection type X X

Includes branch diameter X X

Includes acoustic/structural coincidence X

Includes excitation frequency X

Allows detailed analysis of design

alternatives

X

Fatigue Life Calculation See (2) X

1Future work includes validation of method with test and historical data

2Calculated fatigue life is part of calibrated screening procedure, not end result


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QUESTIONS?

Documents

FEA-Based Acoustic Fatigue Analysis Methodology - SWRI