A large majority of urban gas distribution pipelines are designed to accommodate future integrity management surveys with in-line inspection (ILI) tools. However, even with typical inspection design parameters considered, many pipelines end up on a “difficult-to-inspect” list and/or fall into a “gray” zone. Often this is due to operational parameters, which may have adverse effects on how in-line inspection technologies perform during a survey. One of these effects may be stop-start behaviors of the tool itself. Although most segments meet minimum technical specifications to conduct ILI surveys, vintage pipeline design practices, such as numerous 1.5D bends, multiple heavy wall transitions, and narrow ID fittings, consistently present ongoing issues when running ILI tools in gas distribution lines. The first assessment characteristically indicates that standard inspection tools are viable solutions for these types of pipelines, but results from previous inspections typically indicate, after the first inspection of the pipeline, that standard technologies should not be applied, or rather, do not deliver satisfactory results. New methodologies and technologies are required to reduce, if not eliminate, the incidents of stationary tools and the resultant areas of degraded data while improving 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 are often overlooked when selecting and applying inspection and/or cleaning technologies to these gray-zone pipelines. Applying these elements may allow for inspection tools to traverse various obstacles and debris fields encountered while still providing high-resolution data sets.
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 for 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 was only available within limited windows
• Cleanliness was unknown and assumed to be a concern
• Pipe grade documentation required verification
Many technical challenges were encountered in the initial stages of the project. The lessons learned will 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.