Monitoring of pipes by ultrasonic techniques

© Fraunhofer IZFP-D

Monitoring of pipes by ultrasonic techniques

Andreas Schnabel, Bernd Frankenstein, Bianca Weihnacht

Fraunhofer IZFP-DMaria-Reiche-Strasse 2D-01109 DresdenGermany

+49 (0) 3 51/888 [email protected]

mailto:[email protected]

http://www.izfp-d.fraunhofer.de


Content

n Theoretical background

n Propagation of guided waves

n Dispersion of guided waves

n Monitoring of pipes

n Corrosion monitoring (CoMoRanger)

n Crack detection

n Monitoring of pipes in the high frequency range (up to 400°C)

n Wave guides as actuator/sensor

n Langasite transducers glued with glass soldiers as actuator/sensors

n Sapphire fibres as sensors


Actuator

SensorsCrack

Differences in the time signal of a monitored titan pipe: undamaged condition (blue) and introduced damage of a 3.5 mm long crack at a welded seam (red)

Propagation of guided waves – acousto ultrasonics


Reference statewithout defect

(baseline)

Actual statewith defect

Difference betweenactual state andreference state

Unrolled 2d piperepresentation ofwave propagationF. Schubert, IZFP-D

– =

Propagation of guided wavesMonitoring of pipes – Differential concept


(L0,1)

(L0,2)

f [MHz] x d [cm]

Gro

up V

eloc

ity [m

/ms]

(L0,2)

(L0,1)

(L0,3)

L(0,2) ≅ S0 L(0,1) ≅ A0T(0,1) ≅ SH0

Pipe Plate

actuator

sensor

Signal travel path

Dispersion of guided wavesGroup velocity dispersion diagram of a free steel pipe


Decision Support

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)

• For crucial parts of a structure, vibration monitoring can be supplemented by using guided elastic waves in the kHz frequency regime

• Can serve as an early-warning system raising an alarm long before critical damage occurs

Monitoring of pipes – General concept


Corrosion monitoring of pipes in power plants and chemical industry

Operating parameters:• Temperature: 50°C• Pressure: 1 bar

Abrasion

n Two dimensional wall reduction by corrosion

Cause

n Transport media: NH3 (ammoniac)

H2S (hydrogen sulfide)

Result

n Wall reduction of approx. 0.5 - 0.8mm / year


Corrosion monitoring of pipes - Instrumentation

n Monitoring interval: more than 1 year

n Parallel monitoring of two simular pipes in the same plant

1. Actor/Sensor

Sensor for vibration measurement

2. Aktor/sensor in the distance of 70 cm (not shown)

Casing

Casing

Pre-amplifier

CablePiezoelement


P-S0

P-A1

P-A0

Wide-band excitation with sinc-

signal

Received signal

actuator

sensor

Signal travel path

Signal processing:

à measure signal transfer function between actuator and sensor by wide-band excitationà matching scales of dispersion curves and spectrogramà superposition of spectrogram and dispersion curves

Corrosion monitoring – Detection of pipe wall abrasion


Superposition of calculated dispersion curves and the spectrogram for different wall thicknesses

Frequency shift of the inflection point for different wall thicknesses by wide-band excitation (sinc 600kHz)

Initial condition Abrasion 0.5mm Abrasion 1.5mm

P-S0

P-S0 P-S0

Wide-band

excitation with

sinc-signal



n Amplitude increase as a result ofthe mode interference

n Reduction of the wall thicknessleads to increased amplitudes

Dec. 2008 Reference

Oct. 2009

Apr. 2009

Ein

hülle

nden

[mV

]

Zeit [µs]



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


.dat ---> Data2a

3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

x 10-4

-200

0

200


.dat ---> Data3a

3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

x 10-4

-200

0

200


.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

Crack monitoring – Laboratory steel pipe


Crack monitoring - Interaction with introduced defects

#2#3

#4#5

#11

250mm 300mm

160mm

400mm

#1

9,5mm

3mm

Artificially introduced notches of different size

Actuator/sensor array

Sensor array


Crack monitoring - Interaction with introduced defects

0 1 2 3 4

x 10-4

-4000

-3000

-2000

-1000

0

1000

2000

3000

4000

RC4_130k_gut_20xm1_Sender#02_400V_Empf#04_(A-4)_A.dat ---> Data1a (blau) RC4_130k_nut_9,5x3_20xm1_Sender#02_400V_Empf#04_(A-4)_A.dat ---> Data2a (rot)

Direct P-S0wave

Electricalcrosstalk

(t = 0)

Direct P-A0wave

9.5 mm notch

Results

0 1 2 3 4

x 10-4

-4000

-3000

-2000

-1000

0

1000

2000

3000

4000

RC4_130k_gut_20xm1_Sender#02_400V_Empf#04_(A-4)_A.dat ---> Data1a (blau) RC4_130k_nut_19x3_20xm1_Sender#02_400V_Empf#04_(A-4)_A.dat ---> Data2a (rot)

19 mm notch

P-A0 notchreflection

Mode-convertednotch reflectionP-A0 ↔ P-S0

P-S0 notchreflection

0 1 2 3 4

x 10-4

-3000

-2000

-1000

0

1000

2000

3000

RC4_130k_gut_20xm1_Sender#02_400V_Empf#04_(A-4)_A.dat ---> Data1a (blau) RC4_130k_nut_27x3_20xm1_Sender#02_400V_Empf#04_(A-4)_A.dat ---> Data2a (rot)

27 mm notch

Transducer #2: ActuatorTransducer #4: Sensor

Reference measurement(baseline without notch)

Measurement with notch


Interaction with defectsPhase 2: Titanium elbow with artificial weld defects

Artificially introduced notch of variable size (and depth)

1 mm deep notch3.5 mm deep notch

Measurement without notch Measurement with notch

Damage indicator

Damage size


source: Fraunhofer ISC

communication bus

distance: up to 5 meters

MAS - System

sensors on waveguides

data acquisition

integrated tri-axial accelerometer (MEMs)

combination of piezo stack Actuator and piezo sensor for Acousto Ultrasonic

High temperature application – Wave guides



acoustic wave guides bypass isolation


Developed complete high frequency measurement System for hot pipes consist of:

• MAS measurement system (data acquisition) for high and low frequency range

• amplifier and filter unit for high frequency acousto ultrasonic• piezoelectric sensors for waveguides with integrated accelerometer

amplifier MAS

sensors



Transmitting the signals with piezo-stack actuators in distances of 1 and 3 m from the Langasite sensors

Application of two Langasite high-temperature piezo sensors (Fraunhofer ISC) as sensors with a distance of 2 m on the steel tube

Test with high temperature Langasite transducers on a steel tube

High temperature application – Glass soldiers


Application of the Langasite transducer by melting of a special

glass solder adapted for a permanent use at 400°C with a new

designed mobile furnace

20 mm

source: Fraunhofer ISC

sensing element

glass solder

high temperature wire

High temperature application – Glass soldiers


1520 1540 1560 1580 1600 16200.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

nm

High temperature application – Sapphire fibres

Schematic drawing of optical attenuation measurement

Optical output

Optical input

Multimode fiber spool

(50m)Multimode fiber

Au-coating

Multimode fiber standard coating

Prototype sensor

FurnaceOptical spectrum analyzer (OSA)


n Sapphire fiber Bragg-Grating for measurement of temperatures up to 1745°C

Wavelength [nm]

Rel

ativ

e In

tens

ity

Source: M. Busch, W. Ecke, I. Latka, D. Fischer; “Inscription and characterization of Bragg gratings in single-crystal sapphire optical fibres for high-temperature sensor applications”; Meas. Sci. Technol. 20 (2009) 115301 (6pp)

Temperature characteristic of sensorReflection spectra of FBG at different temperatures

High temperature application – Sapphire fibres


High temperature application – Sapphire fibresPrototype

Steel substrate (AISI 304)

Stripped and embedded silica fiber

Embedded sapphire fiberGold coated

silica fiber


Outlook

n Guided waves are well suited to detect cracks and corrosion processes.

n The method was approved by industrial applications at a power plant and at a chemical plant.

n Next steps:

n Establishment of a certified measurement technique

n Development of autarc sensors (wireless)

n Realisation of explosion proof techniques for application in chemical an oil industry

n Cooperation partners are very welcome to join us in our future projects. Some applications are readily available for use.


Thank you for your attention!

Fraunhofer IZFP-DMaria-Reiche-Strasse 2D-01109 DresdenGermany

+49 (0) 3 51/888 [email protected]

mailto:[email protected]

http://www.izfp-d.fraunhofer.de

Monitoring of pipes by ultrasonic techniques

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