Published on 01-Nov-2023

Case Study: Custom Slimline Subsea Crawler

Case Study: Custom Slimline Subsea Crawler


Nexxis was approached by the projects and technology arm of a major Oil and Gas group and tasked with finding a suitable vendor for a complex inspection scope for one of their petrochemical plants.  The asset to be inspected was the underground section of a Sea Cooling Water (SCW) network, an integral system to the plant’s functionality. Certain constraints of this specific SCW system meant that an off-the-shelf solution was not readily available. Nexxis, in collaboration with their engineering capabilities at SixDe, designed, manufactured, and deployed a custom slimline robotic crawler to the operator. Nexxis also provided online training and inspection support, through Lab61, to the local service provider contracted to carry out the inspection works.


The critical asset inspected is constructed of glass reinforced plastic (GRP) with the internal surface finished with an epoxy coating. The aim of the inspection was to identify mechanisms of damage, specifically cracking within the pipe’s internal surface. The inspection was to focus on the multiple branch connections that are made with the main header, as these were recognised to be a point of concentrated stress.

Access into these type of piping systems is ideally done via the removal of a spool, which involves removing a section of piping that grants the full diameter of the pipe to insert the inspection tool. In this instance, the access available was through the removal of a butterfly valve, providing only a 150mm opening. With the only suitable system to carry out this inspection having a minimum height of 200mm, a bespoke solution was required, so a custom slimline subsea crawler was proposed to the operator. To add to the complexity of the scope, the crawler had to negotiate two vertical sections, stopping in a vertical orientation at the branch connection, enabling the required images to be taken, as per the operator’s request.

The operator engaged a service provider to carry out the inspection that were fully supported and trained by Nexxis to deploy the customer crawler. Due to the identified risks of the inspection, Nexxis provided comprehensive inspection methodology documents along with contingency plans for deployment and retrieval. This ensured the inspection was completed successfully.

The operator had a narrow window of opportunity to conduct the inspection during the upcoming turn-around, giving Nexxis a four-week period to design, manufacture, train and deliver a solution.


Nexxis designed a custom slimline subsea crawler aimed solely to meet the objectives of the inspection. The chassis was designed by the Nexxis engineering team and manufactured in collaboration with SixDe. It was manufactured from a form of plastic, Acetal, to ensure no damage could occur if the crawler came into contact with the internal surfaces, due to their similar hardness values. All other exposed metallic surfaces had a protective coating applied to further mitigate any potential damages. Acetal offers excellent mechanical properties, which allowed the system to be heavily equipped with strong magnetic tracks, a large optical zoom equipped camera as well as additional flood lighting, to provide the best image results in large diameter pipes and subsea applications.

It was imperative that this inspection ran according to plan, as the window of opportunity was minimal before this critical asset needed to be brought back online and not delay the turnaround.  The training and inspection methodology documentation provided to the service provider was the result of critical planning, aiming to mitigate any delays, incidents, and lost data. A clear and concise work procedure developed by Nexxis covering from the mobilisation all the way to the demobilisation of the crawler, ensuring that confidence was instilled in the service provider, and the operator.


The successful planning and training that was provided by Nexxis and Lab61, ensured all parties involved were able to complete a successful remote visual inspection of the asset. The asset owner was able to identify a few damage mechanisms that were not major but assisted them in collecting valuable data for future inspections. The visual quality of the inspection, especially submerged, impressed both the operator and service provider. If a smaller standard crawler were used instead of the custom crawler, it never would have achieved the same level of image quality.

Going above and beyond and delivering solutions with the operator’s outcomes in mind are why Nexxis stands out from regular equipment providers. Examples like this only enhance their unrivalled reputation as the go-to robotics provider.

If you have a complex scope that you need an experienced technology advisor to assist with, then get in contact with Nexxis today or visit

Tree PNG back


Tree PNG back




Tree PNG back


Application Notes