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How Inspection and Detection Protects Your Pipes

February 23, 2016

Pipelines are subjected to a lot of abuse. Deformations, cracks, erosion of the pipe walls and corrosion all wreck havoc on a pipe and can cause catastrophic failure. One way to protect your pipeline is to regularly inspect it, detecting where these problems might be gaining a foothold.

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A pipeline inspection gauge, or "pig," is used to inspect and clean a pipeline without interupting the flow of product.

Pipelines are one of the most common and safest methods of transportation for liquids and gases across long distances. However, the constant exposure of the exterior, in combination with the corrosive, high pressure interior, creates a vulnerable system. Pipelines require regular observation and inspection to prevent both exterior and interior corrosion.

Pipes Take A Lot of Abuse

Pipelines are subject to a number of defects, usually resulting from manufacturing or application. One form of defect is deformations, such as dents in the metal, which cause both mechanical stress and an area of chemical build-up in the interior. More defects come from cracks, where concentrated stress causes the material to fracture. Continued stress encourages the cracks to propagate, causing severe mechanical failure. The last major form of defects in pipelines comes from metal loss on both the interior and the exterior of the pipe wall. This can be caused by erosion on the exterior due to corrosive soil. On the interior, high temperature fluids hitting a wall too directly can cause the wall to thin, which promotes corrosion even further. Any combination of these factors can cause catastrophic failure, which may have drastic environmental consequences.

Pigging

To prevent sudden pipeline failure, regular analyses must be performed to detect defects. This is usually done via Pipeline Inspection Gauges, large mechanical tools that travel in the system to perform maintenance and analysis of the interior of the piping. These “pigs” inspect the interior via non-destructive tests, such as scanning for magnetic flux leakage to check for metal loss. The “pigs” scan for cracks using an ultrasonic tool. The pig is almost the exact same diameter of the interior of pipeline, allowing for careful inspection as close as possible. The pigs are introduced into the pipe at special entry points and travel with the fluid in the pipeline. The data collected by the pigs is used to determine if any sections of the pipeline are at risk or if more inspection is required.

Underground Piping

For underground pipes, an external pipeline review is conducted primarily through testing the pH levels of the soil as unearthing pipeline is both costly and time consuming. Pipeline surrounded by soil is potentially subjected to both continuous moisture and a corrosive environment. By measuring the pH of the soil and the specimen, the electrochemical potential can be measured. Electronegative potential is ideal, as it makes the corrosion reaction not favorable and thus not likely to occur. At sections where the pipeline is exposed, coupon samples are collected and tested to assess any defects.

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