A Monitoring System for Industrial Piping Systems Based on Guided Elastic Waves and Vibrations

F. Schubert, B. Frankenstein, T. Klesse, M. Küttner, B. LamekFraunhofer Institute for Non-Destructive Testing, Dresden Branch (IZFP-D)

International SeminarLatest Developments for Ultrasonic

Testing – Guided WavesSaarbrücken, April 8, 2008

2

Introduction

Specific targeted research project in the 6th framework programme of the European commissionDuration: September 2005 – August 200812 partners from 6 countries (Austria, Germany, France, Poland, Russia, China)3 end-users: RWE Power, DOW Chemical, EDFMain Objectives:- Permanent monitoring, (partial) replacement of visual inspections - Monitoring on non-accessible parts- Smart sensor/actuator development- Combination of vibration and guided elastic wave monitoring- Integrated decision support system

SAFE PIPESSafety Assessment and Lifetime Management of Industrial Piping Systems

3

Guided wave based SHM

Traditional vibration based monitoring techniques provide globalinformation by identifying and analyzing specific resonance modes of a structure

Due to the low freqencies only large defects can be identifiedFor crucial parts of a structure, vibration monitoring can be supplemented by using guided elastic waves in the kHz frequency regimeThese waves have a shorter range but are more sensitive to smaller defectsThus, guided waves can serve as an early-warning system raising an alarm long before critical damage occurs

Motivation

4

Guided wave based SHM

Point impact

Helical wave propagation

Additional dispersion effects due to the curvature of the pipe

Helical wave propagation after point excitation (different travel paths between

source and receiver exist)

Guided wave propagation in pipes

5

Guided wave based SHM

L(0,3) & F(1-3,5)

L(0,2)

F(1-3,3)

T(0,1)F(1-3,2)

L(0,1) &

F(1-3,1)T(0,2)

& F(1-3,4)

Group velocity dispersion diagram of a free steel pipe

L(0,2) ≅ S0 L(0,1) ≅ A0T(0,1) ≅ SH0

Pipe Plate

„P-S0“„P-A0“„P-SH“

Pipe geometry:∅ = 406 mmd = 9 mm

Traditional naming convention for the existing wave modes:• L(0,m): Axisymmetric longitudinal modes with m = 1,2,… etc.• T(0,m): Axisymmetric torsional modes with m = 1,2,… etc.• F(n,m): Non-axisymmetric flexural modes with n, m = 1,2, etc.

6

Guided wave based SHM

Steel pipe:Length: 3 mDiameter: 406 mmWall thickness: 9 mm

Laboratory measurements of wave propagation

7

ElectrodeStructure

NMWWürzburg

UltrasonicExcitation

Characteristic

Electrode

Piezoelectric Fibres

PZT fibre transducers for low-temperature applications

Guided wave based SHM

Transducer UnitPreamplifier

8

Guided wave based SHM

Experimental results

3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

x 10-4

-200

0

200

rickers 70kHz 50 messungen - 50ms delayB.dat ---> Data1a

3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

x 10-4

-200

0

200

rickers 126kHz 50 messungen - 50ms delayB.dat ---> Data2a

3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

x 10-4

-200

0

200

rickers 240kHz 50 messungen - 50ms delayB.dat ---> Data3a

3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

x 10-4

-200

0

200

rickers 370kHz 50 messungen - 50ms delayB.dat ---> Data4a

fC = 70 kHz

fC = 126 kHz

fC = 240 kHz

fC = 370 kHz

3050 m/s(P-A0)

4880 m/s(P-S0)

3510 m/s(P-S1)

Group velocities:Modes identified:

1st order helical P-S0 1st order

helical P-A0

P-S0 pipeending echo

All waveforms could be clearly identified!

9

Interaction with defects

Measurements at Titanium elbow provided by DOW

Wall thickness = 6 mm

Artificially introduced notch of different size (and depth)

AD1

D2

AD1

D1 A

D2

A

10

⎯⎯ Measurement with notch⎯⎯ Measurement without notch

Short propagation path A-D1

Long propagation path A-D1

Measurements at Titanium elbow

Interaction with defects

1mm deep notch 3.5mm deep notch

11

Pipe mock-up

12

Crack

Pipe mock-up

⎯⎯ before crack enlargement⎯⎯ after crack enlargement

13

End-user plantHot steam pipe at RWE Neurath

14

- 4 analogue input channels per module - Bandwidth 1: 10 mHz – 10 kHz - Bandwidth 2: 20 – 1000 kHz- Sampling up to 18 MS/s- 32 Bit fix point DSP- Arbitrary waveform generator- Power amplifier- Hardware trigger and synchronization- CAN-Bus-Interface, Bluetooth, ZigBee- Power Supply 24V DC- Movable memory cards and USB-Port

Concept of SHM system

Multi-Channel Acoustic System (MAS-2)

• 4-channel sensor/actuator nodes for SHM applications • Various nodes can be combined to a multi-channel measuring system • It can be used for both active and passive monitoring• High-frequency nodes for guided wave monitoring (10 - 500 kHz)• Low-frequency nodes for vibration monitoring (0.1 - 500 Hz)

MAS-2

15

Concept of SHM system

Modular transducer system

Piezoelectric Langasite single crystal transducers for high-frequency and high-temperature applications (direct couplingvia glas solders)

(Fraunhofer-ISC)

Piezo stack transducers for high-frequencyand high-temperature applications (indirectcoupling via acoustic waveguides)

Piezo fiber and piezo ceramic transducersfor high-frequency and low-temperatureapplications (direct coupling to the pipe)

(NMW & IZFP-D)

Acceleration sensors for low-frequency aswell as low- and high-temperatureapplications (direct or indirect coupling)

(Monitran) (NMW & IZFP-D)

IZFP-D

LaGaSiGlas solder

Steel pipe

16

Concept of SHM system

DecisionSupport System(DSS)

1

2

4

Crucial error-pronepart of the pipe

Piezo arrays for guided wave monitoring (local information)

Acceleration sensors 1-4for vibration monitoring

(global information)

3

Low-frequency node (passive)

High-frequency nodes (active)

High-frequency nodes (active)

Key concept: Combination of low- and high-frequency monitoring

17

Conclusions

Guided elastic waves in the frequency range between 80 and 200 kHz are well-suited for determination of pipe defects having dimensions as specified by the industrial partners. It can therefore be expected that a guided wave based SHM system is able to efficiently close the gap between high-frequency NDE in the MHz frequency regime on the one hand and low-frequency vibration analysis on the other hand.A key concept for an overall SHM system is the combination of low- and high-frequency data providing global as well as local information on the structure.The final goals are:

- Identification of defects: Raise an alarm if a defect is present- Localization of defects: If a defect is present, determine its (approximate) position

- Relevance of defects: State if the defect is relevant for the structural integrity- Residual lifetime: Try to estimate the remaining lifetime of the structure

18

Acknowledgement

The present work was supported by the Commission of the EuropeanCommunities in the framework of the specific targeted research project SAFE PIPES (Safety Assessment and Lifetime Management of Industrial Piping Systems) under the 6th framework program (NMP2-CT-2005-013898). This support is gratefully acknowledged. We also thank all our partners in the SAFE PIPES consortium, especially NMW Würzburg and DOW Stade for providing us with the PZT fibre transducers and the Titanium Elbow, respectively, as well as MPA Stuttgart for inserting the elbow notches and producing the mock-up movie.