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Analysing ILI tools

Published by , Editorial Assistant
World Pipelines,


Lance Wethey, Technical Solutions Specialist, ROSEN, USA, explores facilitating engineering critical assessments of challenging pipelines with ILI.

The Pipeline and Hazardous Materials Safety Administration (PHMSA) introduced a new rule in 2019 that required natural gas transmission operators to reconfirm maximum allowable operating pressures (MAOP) of certain pipelines located in Class 3 or 4 locations, high consequence areas (HCA), or moderate consequence areas (MCA). To address this requirement, PHMSA outlined six separate methods operators may pursue:

  • 1. Pressure test.
  • 2. Pressure reductions.
  • 3. Engineering critical assessment (ECA).
  • 4. Pipe replacement.
  • 5. Pressure reductions for segments with small potential impact radius.
  • 6. Alternative technology.

To minimise the impact on operations, pipeline operators may opt to conduct an ECA. This procedure can allow the avoidance of hydrostatic pressure tests and pressure reductions that interrupt product delivery. An ECA is essentially a fitness for service analysis of material properties, historical data, survey reports, and threat assessments. The result determines a predicted failure pressure thereby reconfirming or re-establishing the pipeline’s MAOP. A key component of an ECA is determining the defects remaining in the pipe which can be efficiently performed with inline inspection (ILI). Potential threats such as geometric anomalies, metal loss, and crack-like defects can be detected utilising various technologies deployed via ILI tools propelled by product flow with minimal interruption to pipeline operations.

Louisville Gas and Electric (LG&E) owns and operates a vast network of natural gas pipelines throughout the greater Louisville, Kentucky (USA). Many of these pipelines are operating at pressures less than 250 psi and consist of varying diameters. In addition, a considerable number of these pipelines were built in the 1950’s utilising construction standards that have since become outdated. From the perspective of ILI, these pipelines are considered challenging due to the combination of operating pressures and pipeline geometry. Three of these pipelines are requiring MAOP reconfirmations and LG&E has opted to pursue ECA’s to satisfy PHMSA requirements and avoid the costly shutdowns associated with hydrostatic pressure tests or operating pressure reductions. To facilitate the ECA’s, numerous ILI technologies are required; the suitable inspection methods include calliper-based, inertial measurement (IMU), magnetic flux leakage (MFL), and electromagnetic acoustic transducer (EMAT) technologies.

Historically, LG&E has worked with ROSEN’s ILI solutions extensively for integrity management purposes in pursuit of safe and efficient system operation, as well as compliance with associated regulatory demands. The relationship would continue with this effort in determining the appropriate ILI solutions.

The first step is to examine the pipelines in detail. LG&E wishes to inspect three 16 x 20 in. multi-diameter natural gas pipelines operating at pressures less than 250 psi. These pipelines include 1.5 dia. 90° bends with a considerable number involving spacing less than 3 ft. Restrictive fittings such as these occurring in a low-pressure gaseous environment challenge data capture due to the expected ILI tool run behaviour. This is a consequence of the compressibility of the natural gas. ILI tools will often slow or stop during traversal of tight bends and diameter reductions as the differential pressure (ΔP) required to maintain momentum increases …

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Read the article online at: https://www.worldpipelines.com/equipment-and-safety/17042023/analysing-ili-tools/

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US pipeline news Pigging and inspection news