Internal Inspections of Pipelines

Method of Pipeline Inspection using Intelligent Pig

Internal inspections of pipelines are carried out using a device called intelligent pig. The intelligent pig is a combined mechanical and electronic device carried by the flow of the transported medium through the pipes. It is comprised of a complex of modules connected by flexible joints and carrying a recording unit, sources, sensors and a transmitter. The sleeves fixed to the pig body seal the device and make the whole device float in the pipeline. The electronic unit works based on variable speed of ultrasonic signal in different environments (media). As the pig passes through the pipes, data is collected, stored and partly processed in the device processor.

The device is equipped with an odometer measuring the distance (the pipeline length). The sensor determines location of a defect in azimuth positions within 360o. The accuracy of collected data with regard to the distance is determined by stationary transmitters, when a receiver in the intelligent pig receives an exact time signal from the transmitter – marker whose position is located with high fidelity. The exact location data is then used for further evaluations if the distance measured by the intelligent pig doesn’t correspond to geodetic findings.

What can be found using the method of the internal pipeline inspection?

The method of internal inspection of pipeline serves to determine the pipeline condition. It identifies abnormalities over 3 x 3 mm located outside and inside the pipes. Let’s imagine a carpet 1.6m wide laid from Hodonín to Litvínov. If we have a record of the inspection run we know what has happened at any point of this imaginary carpet, from above and from below, with resolution of 3 x 3 mm. In addition to the main route corresponding to this example, we have another 300 km of pipelines which are also scanned and may be “read” in this way.

By “abnormalities”, we mean deviations from the ideal dimension with certain allowance, e.g. dimensions of a pipe with wall thickness 9.6 mm may vary from 9.4 mm to 9.8 mm (this allowance would not be noted). Abnormalities may be divided in two basic groups: installations and defects.

Installations include: T-joint, gate valve, pipe bend, flange, circumferential weld, manways, sampling inlet, pig indicator (“pig-sig”), pipe length, and defects being already repaired. Installations concern construction matters and they are always invasive.

Defects include:

• defects on the pipe inner wall over 9 mm² (material lost)
• defects on the pipe outer wall over 9 mm² (material lost, scratch)
• laminations, mill defects
• buckling, dents, wrinkles

Defects may occur during production or may be caused by operation.

Characteristics of Individual Defects

Material lost - thinning of the pipe wall due to corrosion loss (internal/external) or so called out-of-production material. Following the location of the corrosion loss, it is possible to determine with a high degree of certainty if the defect has been caused by an insulation failure. If the corrosion loss is located on the bottom part of the pipeline and is linear, i.e. situated in the direction of the medium flow, it has probably been caused by the insulation failure. These defects are easy to interpret.

Laminations - defect occurring during production, mill defects, inclusions, integrity losses. Laminations may be in contact with the outer or inner surface. They are difficult to interpret; thorough local measurement during exposure is necessary.

Buckling - dented pipe, irregular pipe ruptures occurred during handling, dents (e.g. pipe laid on untreated hard bed – stone – during shrinkage of the surrounding backfilling), cold bending. They are easy to interpret.

Scratch - a production defect when mill defects have been cut off the pipe surface. They are easy to interpret. They are dangerous as they may cause cracks, which the intelligent pig is unable to detect. Significant attention is therefore paid to this during exposures and repairs.

See the presentation of Enbridge Inc.

Inspection Runs in 2005

Almost immediately after the accident at the Družba crude oil pipeline on Feb 9, 2005 in Čáslav, the ultrasound pig from the German company NDT was employed in the pipeline between Velká Bíteš and Nové Město. This pig comprised three sections: the first section including sources, the second one compressing and storing raw data and the last one carrying a set of ultrasonic sensors. The entire device was 2.7 m long.

On March 31, 2005 another special pig was applied. This pig was also manufactured by NDT and its sensors were modified in order to detect cracks. The sensors (153 in total) were located in three groups with sensors overlapping each other. It was a reference run of this type of pig in the Czech pipelines.

The last pig used for the Družba pipeline was Geo-pig produced by Tuboscope. This device used the method of a gyroscope when all deviations of the tool in three axes were recorded and evaluated subsequently in order to get the picture of the pipeline trajectory. The pig was used on July 26, 2005.

The team supervising all these inspections consisted of experts from MERO ČR, a. s. and from specialized international companies.

Inspection Runs

MERO ČR, a. s. considers protection of the environment as a natural part of its activities. The EMS has been introduced as a part of the company management system according to ISO 14 001. MERO ČR, a. s. strives for operating the pipelines free of risk factors.

There are several methods for monitoring the pipeline condition. The ways of monitoring the pipeline condition from the inside are based on the methods used in the material crack detection.