ultrasonic 180311 revision2

8/13/2019 Ultrasonic 180311 Revision2

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Measurementand Testing

Ultrasonic


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Is the railroad still safe?

Could a small crack grow?

Has the pipeline been checked?

Wherever human or environmental safety is a risk, components are measured and checked ultrasonically. The method is similar

to echo-sounding: Sound pulses of high-frequency are sent through the material and reflected back from edges, cracks or defects.

Sound speed:

in air 330 m/s

in water 1500 m/s

in steel ~6000 m/s

The picture shows measurement of the thickness of a plastic tube wall. The transit time of a

short ultrasonic pulse is measured. Combined with the information about the speed of sound

in the material the wall thickness can be easily calculated.

Ultrasonic Measurement and Testing


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Ultrasound is sound of such high frequencymore than 20 kHz, which means more than20000 oscillations per second - that it is no longer audible.

Technically, ultrasound is produced by means of a vibrating crystal in the

ultrasonic sensor, also called probe or transducer. Using the piezo-electric

effect, electric impulses are converted into mechanical waves - in this case

sound waves. The ultrasonic test equipment used for crack detection is

called ultrasonic flaw detector,normally generates ultrasound with a frequency of several MHz.

In many cases, so-called longitudinal waves are used for crack

detection. They form a pull-push sequence, causing rapid expansion

and compression of the material as the waves pass through it.

Because air is a poor conductor of ultrasonic waves, a film of water or oil is

spread on the material to create direct contact with the ultrasonic sensor.

In the picture this film appears in green. The fluid is called coupling medium.

Ultrasound



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The sensoremits a short ultrasonic pulse which passes through the component being tested and is reflected

from the far end. The sensor acts first as a transmitterand then as a receiver.

A test instrument not only produces the electrical impulses to set the crystal in motion, but also possesses a

monitor screen that displays the ultrasonic signals as they travel through the material.

The ultrasonic pulses are periodically produced. The pulse repitition frequency is so high (around 1 kHz) that

the operator sees a static image.

As the pulse returns from the material, the sensor works as a receiver. The initial pulse and the

reflection from the back-wall are clearly seen on the screen.

The total travel time corresponds to twice the length of the piece.

transmitter andreceiver

This elegantly simple principle is called the

Impuls-echo-method.

Ultrasonic Test Equipment



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This particular type of measurement does

not really require a monitor screen:

all it needs is a digital display to show the reading.

Ultrasonic measurement of the pipe wall thickness in

petrochemical plants not only provides safety, but also saves

time and costs. For instance, pipes carrying hot or agressive

chemicals must be regularly checked for internal corrosion.

A shut-down of the production would call high costs.

Nevertheless ultrasound can be applied since only one side

of the pipe must be accessible.

Wall thickness measurement



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no defect detected

defectdefect

Test

material

initialpulse (IP) back-wallecho (BWE)

defect without BWE

defect without BWE

different

defect depths

defect with BWE

defect with BWE

different

defect depths

different

defect sizes

Ultrasonic reflections from internal cracks and pores arrive earlier than reflections from the back wall of the

component. This phenomenon has been used for the detection and subsequent evaluation of internal defects.

The illustration shows various types of defects and how they are displayed on the screen:

Checking for internal defects



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Weld inspection

initia

lpulse

notv

isible

lack of fusion

crack

Checking welds for defects is a

demanding task for the workers.



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Automatic testing of pipes, bars and rails



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60 Years KARL DEUTSCH

Definitely Tested !

Presented by Instruments, Sensors & Systems for NDT, Germany.

Authors: Dr.(USA) WolframA. Karl Deutsch c/o KARL DEUTSCHProf.Dr.Helmut Richter c/o University of Wuppertal

Websites: www.karldeutsch.de and www.wissensfloater.de

ultrasonic 180311 revision2

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