Ultrasonic Pig Detection at Pipelines - PPSA, the Pigging Products ...

Ultrasonic Pig Detection at 

Pipelines 

or 

The Power of Acoustic Methods 

Peter Holstein 

Prof. Dr. Peter Holstein 

SONOTEC Ultraschallsensorik Halle GmbH www.sonotec.de

SONOTEC – The Ultrasound Specialist 

SONOTEC Ultraschallsensorik 

Halle GmbH 

Nauendorfer Straße 2 

D-06112 Halle 

Deutschland 

Tel.: +49 (0) 3 45-1 33 17-0 

Fax.: +49 (0) 3 45-1 33 17-99 

Email: sonotec@sonotec.de 

www: http://www.sonotec.de 



Fundamentals 

Frequencies for acoustic and ultrasonic engineering solutions 

Technical 

acoustics 

& vibrations 

Sound emission 

(„passive“) 

NDT 

non-destructive 

testing 

& “active” US 



Basic Effects 

Propagation / Sound fields 

→ estimation of travel times 

→ attenuation 

Sound speed depends on material 



Basic Effects 

→ Diffraction 

→ Reflection 

→ propagation of waves 

→ material properties 

→ surfaces / geometry 

sinα1 

c 

= 

sinα 

c 

2 

→ (Back- )Scattering e.g. 

Doppler-Effect in Fluids 

→ Refraction 

1 

2 



important formula 

(simplified) 

material dependent ! 

Source: Helke, Piezoelektrische Keramiken, TAE 2008, page 21 

material density (kgm -3 ) sound velocity (ms -1 ) impedance (kgm -2 s -1 ) 

steel 7850 5920 3.92·10 7 

water 1000 1484 1.48·10 6 

air (1 bar) 1.04 343 4.13·10 2 



Applications for Ultrasonic Probes 

→ Non-intrusive material testing 

→ Automation 

→ Process measurement techniques 

→ Medical technologies 

→ Consumer techniques 



Requirements for Ultrasonic Probes 

→ Acoustic parameters 

→ Constructive parameters 

→ Electric parameters 

→ Application specific parameters 

→ Economic parameters 

→ Design 

- Sound field characteristic 

- Operating frequency 

- Sensitivity 

- Signal-to-noise ratio 

- Acoustic impedance 

- Pulse shape 

- Focusing 

- Material resistance 

- Pressure resistance 

- Radiation resistance 

- Explosion-proof version 



Selection of Industrial Ultrasonic Probes 

from left: 

contact technique, immersion, miniatur, multi-channel, low frequency, 

phased-array, angle transmitter-receiver 



Applications 

limit switch 

object detection 

(e.g. pigs) 



Applications in Pipeline Industry and Service (selection) 

Active pulse methods 

→ Liquid level estimation 

→ Recognition of different liquids 

→ Measurement of wall thickness 

→ Level limits 

→ Inspection and monitoring of sedimentation and deposits 

→ Measurement of the accumulation of sand, debris, 

incrustation in tanks, pipelines, barrels 

→ Advanced NDT-tasks (e.g. „intelligent“ pigging, material 

testing) 



Passive Sound Emission Methods 

→ Acoustic detection of moving sand in pipelines 

→ Amount of debris 

→ Condensate inspection (e.g. in valves and traps) 

→ Detection of leakages 

→ Flowing sand and debris in pipelines 

→ Monitoring of materials and constructions 



Typical Industrial Applications 

Measurement through the wall 

left: level control of liquids (travel time and intensity are used for the 

estimation of filling heights or for the control of defined filling levels) 

right: measurement of wall thickness (travel time of the echo(s)) 



Pig Detection in Oil Pipelines 

Standard configuration of a transmitting ultrasonic probe for the 

application at crude oil pipelines 



… in Gas Pipelines 

Active Ultrasonics 

Principle of pig signalling by means of an attenuation technique 

1 2 

→ The probes are radially arranged on the circumference 

→ Ultrasonic pulses via probe 1 (→ multi-reflections) 

→ Enhanced attenuation (probe 2) in the moment of pig passing 

right: lab exp. (intensity of echo vs. time) 



Active Ultrasonic Detection 

Field experiment (cleaning pig run) 

peak-to-peak voltage (V) 

0.3 

0.28 

0.26 

0.24 

0.22 

0.2 

0.18 

0.16 

0.14 

0.12 

0.1 

0 500 1000 

time (s) 

1500 2000 

The baseline is also affected since the inner side of the wall has been 

influenced by residual oil collected by the pig in that pipeline. 



Passive Acoustics 

Sound Emission as Pig Signalling Tool 

Typical sensor installations 

(for permanent operation 

or for temporary service) 

Schematic sketch of a typical situation at pig receiver trap of a gas pipeline. The 

sensors are axially arranged (in contrast to the „active“ method ). 



Real-time 

Correlation of 

an acoustic signal 

voltage (V) 

0.08 

0.06 

0.04 

0.02 

0 

-0.02 

-0.04 

-0.06 

-0.08 

2.7 2.75 2.8 2.85 2.9 2.95 3 

time (s ) 

1.5 

correlation 1 (S1,S2) 

sensor 1 

0.08 

0.06 

0.04 sensor 2 

2.7 2.75 2.8 2.85 2.9 2.95 3 

time (s ) 

(Excitation by means of a (low intensity) hammer pulse at sensor 1, 

sensor 2 in a distance of about 10 m). 

The dashed line illustrates the lag of the shift. 

voltage (V) 

2 

0.5 

0 

-0.5 

-1 

-1.5 

-2 

voltage (V) 


SONOTEC Ultraschallsensorik Halle GmbH www.sonotec.de 

0.02 

0 

-0.02 

-0.04 

-0.06 

-0.08 

-0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 

time (s)

Spectral Behaviour of Pipeline Noise 

a m p litu d e (V) 

10 -1 

10 -2 

10 -3 

10 -4 

10 -5 

10 -6 

10 -7 

10 -8 

gas flow only 

0 2 4 6 8 10 12 

x 10 4 

frequency (Hz) 

a m p litu d e (V) 

10 -1 

10 -2 

10 -3 

10 -4 

10 -5 

10 -6 

10 -7 

10 -8 

additional 

unknown mechanical 

sources 

of noise 

0 2 4 6 8 10 12 

x 10 4 


a m plitude (V) 

10 -1 

10 -2 

10 -3 

10 -4 

10 -5 

10 -6 

10 -7 

friction noise 

of a passing pig 

0 2 4 6 8 10 12 

x 10 4 


Frequency characteristics (5 s intervals) of noise during a pig run in a (gas 

transportation) pipeline 

The clearly enhanced signal part at ultrasonic frequencies is obvious 

when a moving pig passes the sensor position. 



A Complete Scenario 

vo lta g e (V) 

0.35 

0.3 

0.25 

0.2 

0.15 

0.1 

0.05 

0 

0 500 1000 1500 2000 2500 3000 

time (s) 


x 10-3 

20 

18 

16 

14 

12 

10 

8 

6 

4 

2 

0 

0 500 1000 1500 2000 2500 3000 

Long time recording of the acoustic signals (cleaning pig, 900 mm pipeline diameter, uncoated) received 

at the sensors 1 and 2 – left: r.m.s. (root mean square) signal without filtering, 

middle: the pig passage (unfiltered) at sensor 1. This signal in the proximity of the pig receiver results from a 

fairly complicated motion. There is no smooth travel of the pig. It moves rather in a stick-slip-procedure 

which makes it impossible to use a „simple“ level indicator as an alarm for a passage. 

right: the same recording but re-calculated with a filter for ultrasonic frequencies. Consequently, the 

intensity is drastically reduced but still sufficient. Furthermore, „longe range“ distortions can be eliminated 

more effectively. 

time (s) 



Ultrasonic Signal during Passage of a Pig 

v o lta g e (V ) 

x 10-3 

20 

18 

16 

14 

12 

10 

8 

6 

4 

2 

0 

2500 2520 2540 2560 2580 2600 

time (s) 

v o lta g e (V) 

x 10-3 

20 

18 

16 

14 

12 

10 

8 

6 

4 

2 

0 

2500 2520 2540 2560 2580 2600 

time (s) 

v o lta g e (V ) 

8 

6 

4 

2 

0 

-2 

-4 

-6 

x 10 -3 

2500 2520 2540 2560 2580 2600 

time (s) 

The digitally r.m.s. filtered signals (20 ...60 kHz) of the 

passing pig at sensor 1 (left) and 2 (middle). The difference (right) signal 

(which is the source for the alarm) is fed into an integration algorithm. 



voltage (V) 

voltage (V) 

0.2 

0.18 

0.16 

0.14 

0.12 

0.1 

0.08 

0.06 

0.04 

0.02 

0 

0 

0.05 

200 400 600 800 

time (s) 

1000 1200 1400 

0.045 

0.04 

0.035 

0.03 

0.025 

0.02 

0.015 

0.01 

0.005 

0 

0 200 400 600 

time (s) 

800 1000 1200 

voltage (V) 

volta g e (V) 

0.05 

0.045 

0.04 

0.035 

0.03 

0.025 

0.02 

0.015 

0.01 

0.005 

0 

1088 1088.5 1089 1089.5 

time (s) 

1090 1090.5 1091 

0.2 

0.18 

0.16 

0.14 

0.12 

0.1 

0.08 

0.06 

0.04 

0.02 

0 

968 969 970 971 

time (s) 

972 973 

volta ge (V) 

voltage (V) 

0.2 

0.18 

0.16 

0.14 

0.12 

0.1 

0.08 

0.06 

0.04 

0.02 

0.05 

0.045 

0.04 

0.035 

0.03 

0.025 

0.02 

0.015 

0.01 

0.005 

0 

1088 1088.5 1089 1089.5 

time (s) 

1090 1090.5 1091 

0 

968 969 970 971 

time (s) 

972 973 

1088 1088.5 1089 1089.5 1090 1090.5 1091 

time (s) 


SONOTEC Ultraschallsensorik Halle GmbH www.sonotec.de 

volta ge (V) 

0.08 

0.06 

0.04 

0.02 

0 

-0.02 

-0.04 

-0.06 

-0.08 


x 10-3 

14 

12 

10 

8 

6 

4 

2 

0 

-2 

-4 

-6 

-8 

968 969 970 971 972 973 

time (s) 

Two further examples of caliper and cleaning pig runs (in the same 

campaign / identical sensor positions) 

The ultrasonic signal is given only.

Elimination of distortions 

v o lt a g e ( V ) 

x 10-3 

20 

18 

16 

14 

12 

10 

8 

6 

4 

2 

0 

1120 1122 1124 1126 1128 1130 

time (s) 


x 10-3 

20 

18 

16 

14 

12 

10 

8 

6 

-1 

4 

-2 

2 

0 

-3 

1120 1122 1124 1126 

time (s) 

1128 

-4 

1130 1120 1122 1124 1126 

time (s) 

1128 1130 

Calibration of probes and choosing the „right“ integration time - 

Signals from distant sources (even with complicate signal patterns) can be “easily” removed by suitable 

filters or algorithms. The distortions of other noisy sources such as rain can be suppressed, too. 


x 10-3 

6 

5 

4 

3 

2 

1 

0 



A Complete Example 

voltage (V) 

0.12 

0.1 

0.08 

0.06 

0.04 

0.02 

0 

0 200 400 600 800 1000 1200 

time (s) 



Passage vs. Distortions 

voltage (V) voltage (V) voltage (V) 

0.1 

0.05 

0.05 

0 

818 820 822 824 826 828 830 

0.1 

time (s) 

0 

818 

0.04 

820 822 824 826 828 830 

0.02 

0 

-0.02 

time (s) 

-0.04 

818 820 822 824 826 828 830 

time (s) 



Combination of Methods 

Highly flexible data processing tools and alarm functions! 



Conclusions 

→ acoustical technologies are powerful and versatile for the application 

in pig detection and signalling 

→ new applications of ultrasonic methods for pig detection purposes 

→ no a priori knowledge about the type of the pig and the operational 

conditions is necessary 

→ improvement of reliability by a combination of different acoustical 

techniques 

→ increased onboard calculation power and new algorithms 

→ the method carries the potential to be extended to pig localization 

We believe, that the potential of the use of ultrasonic techniques 

is still underestimated in the pipeline and pigging sector as well. 



Acknowledgements 

For financial support, the Ministry of Employment and Economic Affairs of the Federal State 

Saxony-Anhalt (Germany) is gratefully acknowledged (grant 0804/0009; 2007-2010). We 

thank VNG (Verbundgas AG Leipzig, Germany) for the support to enable the experimental 

work to continue. 

My special thank goes to the co-authors H.-J.Münch, S. zur Horst-Meyer, SONOTEC, A. 

Tharandt, University of Applied Sciences Leipzig, U. Bauerschäfer, L. Ledig, S. Gai, GMBU 

e.V. Halle. 

Thank you for your attention!

Ultrasonic Pig Detection at Pipelines - PPSA, the Pigging Products ...

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