Yet, at modest depths, of only minus a few meters just below sea level, operators and service companies still struggle to undertake work in the splash zone. Wave action, wind, and tidal forces can make splash zone intervention, where it is difficult to deploy divers or ROV equipment, one of the most challenging areas to perform routine maintenance, mechanical work, and inspection.
OceanTech, a technology-based service company based in Trondheim in Norway, uses innovative robotic equipment, ROV tools, tooling, and techniques, to perform high quality solutions for splash zone interventions.
The key to deploying the OceanTech tools is to fix them to the structure above and below sea level. Whether that structure is a platform jacket leg, a tubular, a riser, or a conductor pipe, giving a stable fixed platform, from which to operate OceanTech’s modified robotic arms and tooling, is the key to successful operations. A lot of the equipment used can be standard ROV tools and tooling.
However, the methods used to access and fix the equipment in the splash zone are generally set up for each application. For example, for the side of a platform jacket, OceanTech would deploy a vertical access tool (VAT) mounted on a rail that is fixed to the platform jacket, along which you can run the robotic arm and tooling into the splash zone.
A similar system is used for risers or conductors where the vertical rail clamps around the riser, conductor, or tubular. In addition, a clamp tool can be used around a riser or conductor, to descend into the splash zone, up and down the riser or conductor itself.
One novel approach even used the rig anchor chains to deploy the robotic arm down the side of the drilling rig into the splash zone for work replacing 600 kg of anodes. This was performed above the anchor chain fairlead wheels at minus 15 meters below sea level. Previous attempts by both divers and ROVs had failed to successfully replace the anodes.
The access systems and equipment to do this are generally lightweight and are deployed from the platform using special rigging techniques and skilled OceanTech rope access technicians. This means that small crews of four to six platform-based personnel can do the work which expensive dive or ROV vessels often struggle to do. Once deployed into the splash zone, OceanTech operations can continue in up to three meters Hs wave height.
Most OceanTech work scopes commonly start with some type of cleaning, to remove marine growth from platform legs, risers, and conductors or – more and more these days – wind turbine foundations. OceanTech robotic tools are controlled from a purpose built control cabin on the platform or where space is at a premium, by compact laptop computer operating modular systems.
High-pressure water jetting techniques give excellent surface cleaning to allow for a wide range of inspections:
GVI – General visual inspection
CVI – Close visual inspection
CP – Cathodic protection measurements and replacement of anodes
UT – Ultrasonic thickness measurements
PEC – Pulse eddy current thickness measurements (note: there is no need for cleaning using this method)
FGI – Field gradient imaging – crack detection (alternating current field measurement)
Other cleaning methods are used too where these and beneficial, like brushes, scrapes or similar.
One of OceanTech’s newest systems, designed for a Norwegian operator, is an inspection robot. The robot can track and follow 360-degree circular nodal welds, where the structural cross tubular meets the platform legs. This is a unique solution developed by OceanTech to detect cracks and measure their length and depth using the alternating current field measurement (ACFM) technique. The inspection robot can be deployed, like all other OceanTech tools, through the splash zone. However, the inspection robot can also be picked up by an ROV and “piggybacked” or deployed to much lower depths using an ROV as the “mother” vehicle.
Splash zone work is not just all about the inspection. OceanTech has completed large mechanical scopes of work ranging from riser repair and anode replacement to the installation of large new I and J tubes on a platform jacket. This work included the design, construction, and installation of large subsea clamps to fix the bottom of the I and J tubes to the platform jacket, at minus 23 meters below sea level. All this work was accomplished independently, by a platform-based OceanTech team, without any support from dive or ROV vessels, resulting in big savings for the operator, on the Northwest Continental shelf of Australia.
Finally, for such an innovative modern technology-based service company, OceanTech’s roots in Trondheim, are closely linked by heritage to a bygone period of history, dating from World War II. Based at Dora II in Trondheim, OceanTech’s current Subsea/Splash Zone Test Center and workshops are housed in a large dry dock which historically was an old submarine pen leftover from another era. These days, the dry dock is a magnificent facility that allows full scale mock-up and testing of OceanTech’s splash zone engineering solutions – wet and dry! Full scale testing and operations are rehearsed many times over, long before the engineering is deployed offshore in the splash zone.