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Inline Inspection

There are various methods to identify defects in oil and gas pipelines. Pipeline operators choose a method or a combination of the according to the several parameters included:

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    capabilities of these methods

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    pipeline conditions

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    costs

According to the experiences of large pipeline operators, various criteria for selecting these methods can be enumerated. Each smart pig has the ability to detect a wide range of defects.



Types of smart pigs are:

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EGP (Electronic Geometry Pig)

It is used to check the roundness of the pipe cross section and is available in both mechanical and electronic forms.

egp pig
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MFL (Magnetic Flux Leakage)

This tool uses the principles of magnetic flux leakage. The magnetic flux density in a metal leak, where its thickness has decreased due to corrosion. By measuring this magnetic leakage by Hall sensors that directly measure the magnetic flux, the location of the corrosion is detected.

mfl pig

Of course, this device has disadvantages, including the similar effect of different phenomena, because the sensors measure and record any kind of flux change, and the difference between them must be determined by the interpreter.

Other disadvantages of this tool include the inability to detect SCC in the early stages of its development. While using this method is more expensive than other methods.

Axial magnetization

axial magnetization

MFL are intended to detect, locate and size general corrosion, pitting corrosion, circumferential cracks, grith weld anomalies, pipeline construction features, other anomalies of circumferential orientation.

Transverse magnetization

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TFI tools are intended to detect, locate and size all anomalies of axial orientation, including stress corrosion cracking, axial cracks, longitudinal weld anomalies, pipeline construction features, etc..

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TFI (Transverse Field Inspection)

This tool uses the principles of magnetic flux leakage. The magnetic flux density in a metal leak, where its thickness has decreased due to corrosion. By measuring this magnetic leakage by Hall sensors that directly measure the magnetic flux, the location of the corrosion is detected.

tfi pig

Transverse magnetization

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TFI tools are intended to detect, locate and size all anomalies of axial orientation, including stress corrosion cracking, axial cracks, longitudinal weld anomalies, pipeline construction features, etc..

According to a 10-year study of smart pigging reports by Russian Gazprom, only 1% of the defects are cracks that MFL pigs are not able to detect, but in terms of the high risk of these defects (the effect of pipe stress on rupture), operating companies also put TFI pigs on their scope of work In addition, driving the TFI pig with MFL creates a more accurate combination report. On the other hand, the increase in the cost of adding a TFI pig compared to the whole project is acceptable and justifiable.

defect chart
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General corrosion

53%

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Grooves

31%

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Girth weld anomalies

6%

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Pitting

6%

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SCC and Cracks

1%

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Mill defects

2%

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Dents

1%

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UT (Ultrasonic tool)

It is used to check the roundness of the pipe cross section and is available in both mechanical and electronic forms.

ut pig
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Advantages

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Accurate and reliable measurement of pipe wall thickness

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No restrictions on measuring high thicknesses

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In conditions which there are many defects,Ut is more sensitive than mfl

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Lamination detection

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Disadvantages

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Due to the need for liquid fluid to transmit and receive sound waves, this pig has only the ability to inspect the lines carrying liquid fluid and can not be used in gas transmission lines.

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EMAT (Electromagnetic Acoustic Transducer)

Whenever a conductive material conducting electricity is near the surface of a metal, and is placed in a magnetic field, electromagnetic force enters the metal surface according to Laurentz's law. This induced force on the metal, depending on the direction of the magnetic field as well as the electric current of the wire, can cause shear, longitudinal or surface waves in the metal. This method eliminates the need for an intermediate material to create an ultrasonic wave, and lines containing gas can also be inspected by this method.

emat

In this method, the coil and the permanent magnet are located near the metal surface. forced by radio waves (RF) and produce eddy currents. These waves are in constant magnetic contact.

They cause mechanical strain, so they emit sound waves in the pipe.

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