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At the bottom of the deep blue sea - Part 2

Published by
World Pipelines,

Gulf of Mexico

In an ideal world, many of these problems could be avoided if ILI experts are consulted when pipelines are designed. In other words, if ILI experts – with their knowledge of the kinds of issues that disrupt or prevent pigging – are invited to contribute directly to the design of the pipeline, costly inspection problems can be avoided. Considering the complexity of these systems, tackling pigging challenges early on significantly reduces risk probability and the potential impact on project schedules and costs.

The importance of early consultation and co-operation has been demonstrated by NDT Global’s experience in the Gulf of Mexico, offshore West Africa and the North Sea, where the company has used its UT tools to inspect approximately 20 difficult-to-pig deepwater pipelines.

In the Gulf of Mexico, NDT Global is in the final stages of adapting a UT tool to requirements specific to a pipeline that is part of a project to extend an existing 12 in. deepwater oil production pipeline with a new 10 in. line to tie-back a new field to the host platform.

Previously, NDT Global supplied a customised high pressure metal loss UT tool for the 12 in. pipeline. The changes to the pipeline required the design of the ILI tool be reviewed. The operator’s project team approached NDT Global during the design phase of the pipeline extension to seek advice on specific design options, and how these would affect the piggability and inspection of the new system.

Following completion of the design work, NDT Global then created a specialised solution for the existing 12 in. UT tool. The new metal loss UT tool is now capable of measuring the entire 10 - 12 in. diameter range with the same accuracy as the previous 12 in. tool, making it possible to determine corrosion growth by comparing data from current inspection runs with previous inspection runs.

West Africa

Another example of how early co-operation delivers benefits is a recent project in West Africa. A major operator developed a new field offshore at a water depth of 2200 m (6900 ft). In conjunction with the pre-FEED phase for the subsea systems, a series of workshops and feasibility studies were conducted with the pipeline design team and pigging experts from NDT Global. The objective was to produce pipeline piggability design guidelines and examine possible ILI tool layouts.

Subsequently, NDT Global was retained to provide a metal loss UT tool tailored to this specific pipeline. The first run with the ILI tool took place in 2012, and delivered high resolution metal loss data. Several anomalies were found in the CRA cladded pipe sections. The most severe metal loss perforated the internal CRA layer completely, reducing the wall thickness of the carbon steel base pipe by an additional 7 mm (0.28 in.). The finding was later verified and confirmed by external inspection.

Clearly, involving ILI specialists in the pipeline design phase and using high resolution UT tools is highly beneficial. It’s essential to use these specialist inspection tools during commissioning because they provide accurate data that pipeline integrity managers rely upon when formulating effective inspection plans. By analysing optimum data well before production commences, the potential for disrupting production to carry out inspections can be greatly reduced, saving time and money.

Paving the way for trouble-free inspections

In light of the current downturn in the oil and gas industry and the technical challenges posed by servicing deepwater networks, a paradigm shift in the client-vendor relationship is required to deliver the best solution. Instead of ‘outsourcing the problem’ to an ILI tool vendor, close co-operation between pipeline operator, pipeline engineering contractor and ILI tool vendor is the key to success. As operators navigate these uncertain times, it’s critical that they consider the serious economic ramifications of effective long-term pipeline inspection and maintenance planning. As demonstrated by the examples above in the Gulf of Mexico and West Africa, one way to control costs is to maintain close co-operation with ILI experts at the design stage. By doing so, the complexity of inspection can be greatly minimised. As a direct result, the costs of inspecting, gauging and cleaning the line are dramatically reduced, and pipeline integrity can be maintained throughout its lifetime. It’s that simple.

Edited from published article by Stephanie Roker

To read the full version of this article, please download a copy of the July 2016 issue of World Pipelines.

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