Intelligent Pigging

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INTELLIGENT PIGGING.DOC

E N G I N E E R I N G C O N S U L T A N T S

26 CAMDEN ROAD, TUNBRIDGE WELLS, KENT TN1 2PT

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OFFSHORE OPERATIONS

OVERVIEW OF PIPELINE ENGINEERING


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TABLE OF CONTENTS

TABLE OF CONTENTS .................................................................................................2

INTELLIGENT PIGGING................................................................................................3

Trevor Jee Associates 2002

All information contained in this document has been prepared solely to illustrate engineering principles for a training

course, and is not suitable for use for engineering purposes. Use for any purpose other than general engineeringdesign training constitutes infringement of copyright and is strictly forbidden. No liability can be accepted for any

loss or damage of whatever nature, for whatever reason, arising from use of this information for purposes other than

general engineering design training.


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INTELLIGENT PIGGING.DOC 3/9

INTELLIGENT PIGGING

l Internal survey for corrosion and cracks

l Typically every 5 or 10 years

WHAT IS INTELLIGENT PIGGING?

In addition to external inspection, there are internal inspection techniques availablefor pipelines. These range from the simple gauge plate check for dents and debris,through to sophisticated pig checks for corrosion.

In this section, we will look at three types of intelligent pigs - the magnetic flux,ultrasonic and eddy current pigs, describing their function and their uses.

Before an intelligent pig is sent down the line, a full pig cleaning operation wouldnormally be carried out to ensure the intelligent pig remains undamaged.


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INSPECTION TECHNOLOGIES

l Magnetic flux

leakage

l Transverse

MFL

l Ultrasonic

thickness

l Elastic wave

UT

l Eddy current

There are two main technologies: magnetic flux leakage (MFL) and ultrasonic

thickness measurement (UT). Each has started by finding wall thickness loss (generalcorrosion defects, both inside and outside), and has then been rotated into the hoopdirection to find axial cracks.

A third technology, that of eddy current, is being developed for the inspection offlexibles.

The following slides contain examples of each of these pigs.


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MAGNETIC FLUX PIGS

The picture above shows the PII magnetic flux pig. In the picture, you can see the

magnetic brushes and the finger-like arrays of magnetic flux detectors. The rest ofthe pig contains power and data storage facilities. It is used to detect internal andexternal corrosion defects in oil and gas pipelines.

Typical speeds of intelligent pigs are from 0.3 to 5 m/s (1ft/s to 16 ft/s). If theproduct flow is faster than this, it is normal to include a bypass system to permit thepig to travel slower than the oil. Head losses for pigs are typically less than 1 bar (15psi).


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FLUX LEAKAGE DETECTION

Brush

MagnetSensor

Brush

Magnet

Brush

MagnetSensor

Brush

Magnet

No defect present

Defect presentDEFECT

LEAKAGE FIELD

N

N S

S

PIPEWALL

SECTION

The above diagram illustrates how the pig detects corrosion defects. In the non-

corroded condition, the two brushes form a magnetic circuit and the flux passesthrough the pipeline wall with little passing either side. However, in the lowerdiagram with the defect present, there is less metal through which the flux can pass,

and some of it leaks outside the pipe wall and is detected by the sensor.


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ASSESSMENT OF DATA

Reported axial length (mm)

Reported

peakdepth(%wt)

Courtesy of PII Group

The above diagram shows an example of results obtained from an MFL pig. It shows

over 450,000 internal metal loss features, and there were also over 3,500 externalmetal loss features identified. This analysis looks for any defects where thedimensions exceed those tolerable at 1.5 x MAOP, or where the peak depth exceeds

80%. In this case there were 19 defects identified as needing repair. A detailedassessment was also carried out in this case, measuring the effective depth and lengthof defects, which reduced the number of defects down to just one repair required.


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PIGGING IN REALITY

Here is the pig at the end of the run in an oil line. You can see that some of the

sensors have been slightly damaged and that the magnetic brushes are caked in tarand wax. So there is a deal of refurbishment and cleaning to do at the end of eachrun.

TRANSVERSE SCANNING PIG

l Uses magnetic flux leakage technology

l Rotated 90 to pick up axial cracks and

seam weld defects


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Note the different orientation of the brushes and sensors to pick up axial defects and

cracks.

ULTRASONIC PIG

The ultrasonic pig is used to detect corrosion defects in liquid lines. The liquid iscrucial in acting as a couplant for the sound emitted by the ultrasonic probes. Forthese pigs to function in a gas line, they must be run within a slug of liquid.

Intelligent Pigging

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