Assess Pipeline Stress

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How to Assess Pipeline Stress and Why This Is Important

Whether they are installed in a power station, a chemical plant, or another type of engineering environment, pipes are subjected to a variety of physical strains and stresses as a consequence of their day-to-day operation and the nature of the environment in which they are required to operate. In order to ensure that this does not result in damage that could lead to a loss of containment or the failure of a pipework installation, steps should be taken to assess any possible pipeline stress.

Often, when liquids and gases are transferred via pipes, they are heated to high temperatures, pumped at high pressures, or both. It is not hard to imagine the consequences of a sudden release of hot gas or liquid under pressure if a portion of the pipework were to fail as a result of accumulated wear and tear. Even plain water at 70 °C is sufficiently hot to cause severe scalding, but what if the escaping liquid should prove to be corrosive or inflammable? Such prospects underline why it is so important to assess pipeline stress at set intervals. So, what kind of anomalies can occur in pipework and how is an assessment conducted?

Pipes often suffer unnoticed or unreported mechanical damage resulting from contact with construction equipment. Any inclusions present in a weld at the time of installation could eventually lead to a crack in its seam, while corrosion can cause thinning of the metal, often in the vicinity of welds. All of these can be remedied and a pipe rendered safe but they must be detected first. To assess pipeline stress, there are a number of possible approaches.

Often, it is not possible to inspect the outside surface of a pipe because it is buried and to overcome this problem, there are a number of specialised tools that can be used to inspect it from within. These are designed to measure the geometric characteristics of a pipe, to detect cracks, and to reveal evidence of metal loss. A typical in-line inspection (ILI) will employ a number of these tools in succession to assess pipeline stress.

The tools form part of a specialised inspection device termed a “pig”, which is designed to fit snugly into a pipe and to travel through it, taking measurements along the way. Geometric tools include callipers to measure the internal diameter, as well as others designed to record curvature, position, and to detect any evidence of gouging or deformation. To check for evidence of metal loss, several types of technology are available to those employed to assess pipeline stress.

The first of these generates a magnetic flux and checks for any point along a pipe at which flux leakage occurs due to thinning of its walls – a clear indication of metal loss. MFL tools can vary in their operation but all employ the same principle and can be used in either liquid or gas lines. Ultrasonic tools employ a principle similar to sonar to detect variations in metal thickness and work best in liquid media. An invaluable means to assess pipeline stress, both tools can be adapted to detect cracks, together with the more basic option of hydrostatic pressure testing.

Contact Oleum Process & Pipeline Services for more information today.

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