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From Design to Deployment: A subsea slimline custom crawler case study

The field of asset inspection is varied and complex. It’s also an area ripe to take advantage of robotic technology. The following depicts a real-life case study by Nexxis to overcome a complex inspection of a Sea Cooling Water (SCW) network that didn’t lend itself to any off-the-shelf-solution currently available.

The Challenge

A critical element of an underground section of a SCW network needed to be inspected to identify any cracking within the internal surface. The asset construction is glass reinforced plastic with an interior epoxy coating. It has multiple branch connections to the main header, each of which are under considerable stress. The operator needed to achieve excellent quality images to assess any damage to the integrity of the pipework.

Access to the pipe system was limited and required the removal of a section of piping through which the inspection tool would be inserted. The diameter of this entry point was only 150mm.

The tool needed to negotiate two vertical sections and have the ability to pause as required in a vertical orientation at the branch connections. The task needed to be carried out with some urgency, and a window of only four weeks was given from initial enquiry to completion.


Fast deployment was necessary, yet no ready-made inspection tools were in existence. The main issues were the high quality of the imaging needed in a submerged environment and the dimensions in which the inspection tool had to work. The only equipment available that was up to the task needed a minimum of 200mm to work within. This scenario only had 150mm, so it was immediately apparent that a bespoke solution was needed.

Due to risks identified during the inspection (carried out by a service provider trained and supported by Nexxis) and the complexity of the task, it was necessary to include robust contingency plans for deployment and retrieval.

The Solution

Following the inspection, Nexxis proposed a custom-made, remotely operated, slimline subsea crawler.  Designed by their manufacturing team and manufactured in cooperation with SixDe, the crawler was formed from Acetal, a type of plastic. The choice of material was pivotal to the success of the mission, with both the crawler and internal surface of the pipe having similar hardness values. This meant that if there was any contact between them during the inspection that there was no risk of accidental damage.

The choice of Acetal was also a considered one, as it provided the strength needed to mount the imaging and lighting equipment needed to gain the quality of images required. Its superior mechanical properties allowed for strong magnetic tracks, flood lighting and a superior and large optical zoom camera to be fitted. These were essential to provide the high definition images necessary for an adequate inspection.

The system allowed for the necessary vertical orientation and the ability to stop at the branch connections for clear images to be gathered as required.

As per the Nexxis methodology, the creation of such an RVI system comes with full critical planning, documentation and training for all parties involved, with the latter carried out by the robotic training arm of the company, Lab61. This ensured that everyone involved in the inspection understood each aspect and that there was full mitigation for any delays, incidents or loss of data. It also guaranteed that the short window for deployment was achieved, and that the client had total support and confidence in a successful implementation.

The Verdict

The high quality of the images collected provided the asset owner with two inspection elements:

  1. The identification of few minor damage mechanisms, mainly at points of concentrated stress at the branch connections.
  2. The collection of multiple data that could be stored and used for future inspections

The customer was highly impressed by the quality of the images achieved – far superior to any that might have been taken by a standard crawler. This was especially relevant as the inspection was carried out in a submerged environment.

Nexxis is a global leader in the field of robotic and remote inspection tools. With a unique model that excels in determining novel solutions for the most complex of inspection challenges, they’ve fast become the go-to provider for enlightened organisations that want to take advantage of the cost-effective end-to-end solution blueprint that’s made them so successful.

Discover more about this refreshing approach to robotic inspection or contact us today for a no-obligation chat.

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