Case Study

A New Range of Subsea Remote Cutting Technology

Case Study: A New Range of Subsea Remote Cutting Technology


Oil States Industries was developing an External Cutting Manipulator (ECM) that allows for remotely controlled cutting of subsea steel structures for offshore decommissioning. In order to effectively utilize this abrasive water jet cutting technology, Oil States needed to develop a Rotary Docking Module (RDM) that mounts to a Remotely Operated Vehicle (ROV) to allow proper installation.

The ECM tool can then be deployed subsea in a tool basket for collection and installation by a work class ROV fitted with the Oil States RDM. The RDM required (6) independent hydraulic lines to function with ability to rotate - this design would require a custom rotary union assembly.

The specialized rotary union needed to have a compact design to fit within the available space on the ROV. Additionally, the union's bearing system needed to maintain shaft alignment and support the weight of the RDM. This design would need to operate reliably at subsea depths up to 300 meters within a temperature range of -40° C to 120° C.


DSTI partnered with Oil States' engineering team to develop a custom 6 passage rotary union design that included an integrated, sealed bearing system to protect from sea water contamination.


Working directly with Oil States, DSTI was able to provide a custom and reliable solution that integrated directly into their equipment while meeting strict specification requirements. The rotary unions operated successfully in the application's working environment, validating the quality and performance of the resulting design.

As an offshore service provider specializing in structural decommissioning, construction and maintenance projects, our operations require some of the most demanding specifications. We partnered with DSTI to design a specialized rotary union to directly integrate into our Rotary Docking Module (RDM) for Remotely Operated Vehicles (ROVs). The RDM units provide a quick interchanging interface from a working class ROV to a range of subsea cutting tools and provide the means by which the tools can be freely rotated continuously. The rotary unions we received have been used extensively subsea working to depths of 145 meters in the North Sea for 120+ days. I am excited to report that these units have performed outstandingly in their working environment. I would highly recommend DSTI for their expertise and extensive knowledge in rotary union applications. Mark Riley Oil States MCS Ltd.

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