Effective prevention of pipeline strain and failures

Pipeline movement poses a potential threat to pipeline integrity as it can lead to excessive strain in the pipe, severe pipe wall deformations and fatigue that can cause pipe rupture. Pipeline movement is caused by a variety of sources including landslides, earthquakes, overburden, field subsidence, permafrost thaw or heave, riverbed erosion, seabed scouring, fishing trawlers, ship anchors, construction in the pipeline right of way, temperature and pressure increase or cycles.

In-line inspections detect potential problems

To maintain pipeline integrity, it is important to monitor both the pipeline's movement and the deformations caused by it. This can be accurately and efficiently achieved by performing in-line inspections.

The inertial navigation system on board the tool allows for accurate 3D measurement of the pipe's centerline position and curvature. This information is used to calculate the bending strain and provides high accuracy pipeline geometry data. Comparison of two surveys at different times is used for precise monitoring of the pipeline movement and bending strain changes between the runs.

The caliper tool also records caliper measurements of the pipe wall shape, which allows for detection of wrinkles and other pipe anomalies that develop as the result of the pipeline displacement.

Strain case study: successful testing

Pipelines can be deformed by flash flooding. Deformation is an integrity threat because it can wrinkle or buckle the pipe, causing enormous local stress.

A major European pipeline operator turned to GE Oil & Gas, PII Pipeline Solutions for a demonstration of our IMU's ability to monitor bending deformation during a blind test in one of its pipelines in 1994. The test was successful and the operator has requested that we continue to monitor bending with IMU run comparisons. This was an excellent opportunity for us to assess our strain spec and prove the capability of our system in an important market.

Client's requirements

• Run-to-run repeatability of 0.02% strain = 2500 D bend or better.
• Reporting to client's spec, including viewer software.
• Repeatability between PII and existing data.

Blind test

GE inspected a pipeline (36” x 29.5 km) with an MFL/IMU pig in February and March 2005. Between runs, the operator excavated a 60m section of pipe and deformed the mid point by 200mm. Accuracy was assessed on repeatability between the runs and accurate location and sizing of the imposed deformation. The operator examined all raw and processed data, comparing with previous data from the same line.

Strain test

The first run is intended primarily as a baseline, but very large environmental deformations (0.125% strain = 400 D bend) can be identified. Comparing curvature data between IMU runs can identify very small deformations. For example, the 0.02% strain spec is equivalent to a 2500 D bend, which for a 36” x 12m pipe joint corresponds to a displacement of just 8mm at the center.

Bending strain is proportional to change in curvature. Note other factors can cause additional strain (e.g. internal or thermal loading).

Analysis and software

Curvature data generation follows the same process as mapping analysis, with an additional step of generating curvature data from the free route. This whole process is handled by version 1.2 of the existing PipeLocator mapping software. New software called StrainCom was written for curvature data display and run comparisons. It is being modified to display mapping data as well as strain.

Results

We successfully identified and sized the deformation. We proved the accuracy of the data collected and the reliability of our system. Similar blind tests have been conducted on another two lines in North America with positive results. Based on customer feedback, development and process improvements continue.

For more information, please contact:

Samia Atif
samia.atif@ge.com

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