A brief article on Pigging: Part 2 of 2

Continuing from Part 1 of 2. Click here to refer part 1 of 2.

Inline Inspection PIGs:

  • In-line inspection tools are used to carry out various types of tasks including:
    • Measuring pipe diameter/geometry
    • Monitoring pipeline curvature
    • Determining pipeline profile
    • Recording temperature/pressure
    • Measuring bend
    • Detecting metal loss/corrosion
    • Performing photographic inspection
    • Detecting crack
    • Measuring wax deposition
    • Detecting leak
    • Taking product samples, and
    • Mapping
  • Types of Defects:
    • Metal Loss
    • Gouging
    • Cracks
    • Dents and Buckles
  • Metal Loss (Fig. 3):
    • Pipeline operators typically use MFL to find metal loss due to corrosion or gouging.
    • Metal loss is found when an MFL tool measures a local change in the magnetic field.
  • Gouging (Fig. 3):
    • Gouging is the mechanical removal of metal from a local area on the surface of pipe.
    • gouged area may contain shallow cracks, which further reduce the pressure-carrying capability of the pipe
  • Dents and Buckles (Fig. 3):
    • Dents are depressions in the pipe surface, and buckles are a partial collapse of the pipe due to excessive bending or compression.
    • MFL tools detects dents and buckles when the sensors lose contact with the wall.
  • Crack (Fig. 3) :
    • Cracks are in pipelines are due to fatigue, stress corrosion, and weld defects.
    • Cracks can sometimes be found when they are oriented in a direction that significantly affects the magnetic field around the defect.
Fig. 3: Various Types of Defects

Magnetic Flux Pigging:

  • History
    • Flux leakage techniques were used as early as 1868 by the Institute of Naval Architects in England.
    • In 1918, magnetic particle inspection was accidentally discovered magnetic particles
    • The first MFL in-line inspection tool for pipelines was introduced in 1965 by Tub scope.

Working Principal of MFL IN-LINE INSPECTION PIG (Fig. 4):

Fig. 4: Flux Leakage Technique

Ultrasonic Intelligent Pig:

  • History
    • The first in-line inspection                            – 1980.
    • Crack inspection tools                                    – 1990.
    • A new generation of ultrasonic tools       – 2002
  • They work in a pulse-echo mode with a rather high repetition frequency.
  • Straight incidence of the ultrasonic pulses is used to measure the wall thickness and 45º incidence is used for the detection of cracks.

Working principal of Ultrasonic Inline inspection Pig (Fig. 5):

Fig. 5: Ultrasonic inline inspection

GEL PIGs: Types of Gel Pigs

  • High-viscosity sealing gels
    • Commissioning cleaning gel systems
    • Polymer Gel Pig
    • Debris pickup gel.
    • Batching or separator gel.
    • Hydrocarbon gel.
    • Dehydrating gel.

The Principal Pipeline applications for gel pigs are as follows:

  • Product separation.
    • Debris removal.
    • Line filling/ hydrotesting.
    • Dewatering and drying.
    • Condensate removal from gas lines.
    • Inhibitor and biocide laydown.
    • Special chemical treatment.
    • Removal of stuck pigs.

Pigging Pressure:


  • During pipeline construction, pigging is used for debris removing, gauging, cleaning, flooding, and dewatering.
  • During fluid production operations, pigging is utilized for removing wax in oil pipelines, removing liquids in gas pipelines.
  • pigging is widely employed for pipeline inspection purposes such as wall thickness measurement and detection of spanning and burial.
  • Pigging is also run for coating the inside surface of pipeline with inhibitor and providing pressure resistance during other pipeline maintenance operations.



Conclusions: Pigging is a vital tool which helps to achieve Pipeline integrity.

  • Safety and product delivery at economical cost.
  • Reduces the failure
  • Overall pressure drop.
  • Pipeline flow efficiency. To go to part 1 click here

Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

Leave a Reply

Your email address will not be published. Required fields are marked *


Recent Content

Subscribe For Latest Updates

Signup for our newsletter and get notified when we publish new articles for free!