A large majority of urban gas distribution pipelines are designed to accommodate future inspection surveys with in-line inspections tools. While this remains true, even with typical inspection design parameters considered, many pipelines end up on a “difficult-to-inspect” list and fall into a “gray” zone.

Much of this can be due to operational parameters, which may have adverse effects on how in-line inspection technologies perform. One of these effects may be stop-start behaviors of the tool itself. Although technically piggable, vintage pipeline design practices such as numerous 1.5D bends, multiple heavy wall transitions, and narrow ID fittings have continually shown to be an ongoing issue when running ILI tools in gas distribution lines. The first assessment characteristically indicates that standard inspection tools can be used for this type of pipeline, but results from previous inspections have shown or show, after the first inspection of the pipeline, that regular technologies cannot be applied, or rather, do not deliver satisfactory results. New methodologies and technologies are required to reduce the incidents of stationary tools, reduce, if not eliminate, potential areas of degraded data and improve overall data quality.

In the end, operators consider these lines a critically important component of their entire system and are keen to gain a clear picture of the assets’ integrity. Suitable in-line inspection solutions are therefore in demand to instill confidence in the assets safe and efficient operation  

 

This paper outlines several elements (including technologies, procedures, or mechanical adaptations) that can be overlooked when selecting and applying inspection and cleaning technologies to these gray-zone pipelines. Applying these elements may allow for the inspection tool to traverse various obstacles and often debris while still providing a high-resolution data set.

 

A detailed case study of a NPS 08” pipeline will be used to support the content. This pipeline did not provide the required operational parameters to gather acceptable data when utilizing standard ILI technologies.

 

This NPS 08” line contained various challenges, such as:

·                     Unknown or unreliable pipeline information, specifically bend radii and wall thicknesses.

·                     No previous cleaning and inspection records.

·                     Low operational pressures of 1000 to 2100 kPa.

·                     Pipeline length over 100 km.

·                     MOP restrictions did not allow for higher pressures.

·                     Flow rate only available in limited windows.

·                     Cleanliness is unknown, assumed to be a concern.

·                     Pipe grade verification

 

Many technical issues initially affected the project, one of which resulted in a stationary cleaning tool. The lessons learned will also be discussed and outlined to better support the approach chosen. In the end, tailored geometry and low-friction MFL technologies, capable of safely traversing the pipeline and gathering high-quality data, were utilized for the inspection. This case study will provide other operators valuable insights into how to inspect similar assets while also outlining specialized technologies suited to support the inspection.


Improving Data Collection With In-Line Inspection in Low-Pressure Gas Distribution Networks

Division / Sponsors: 
Pipeline Systems Division

Paper Proceedings: https://asmedigitalcollection.asme.org/IPC/IPC2020/volume/84447

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