A remotely operated subsea weld inspection tool developed by Norway’s OceanTech aims to remove the need for human diver inspections by sending a 'bot' into and beneath the splash zones of fixed offshore platform and structures. The ‘Roboticised Inspection Tool’ (RIT) is currently in its final development phase, following two years of sea trials. Bernt Schjetne, OceanTech CEO, tells Offshore Marine Technology that the most recent tests were conducted in the North Sea this summer, wherein the customer, a major oil company, described the RIT as constituting “a step change for the inspection of jacket nodes under water”.
Keeping tabs on weld cracking is critical. Cracks can compromise the integrity of the entire structure, putting lives at risk, necessitating exorbitant repair costs and delaying or cancelling projects. Once the operator is aware of the presence of a crack, a clamp can be placed over the affected weld to bolster structural integrity.
The RIT can be deployed in one of two ways. For inspections around and above the splash zone, the bot descends the jacket via a vertical access tool (VAT) built to a patented OceanTech design. The VAT eliminates the need to deploy a separate support boat or send a dive team into the water. Also, transporting the robot to the splash zone via ROV would be impractical given the tight spots and restricted spaces typical of jackets, and would incur a “high risk of damaging the RIT”, he adds.
For deeper subsea inspections, however, an ROV would be the best means of deploying the RIT. The ROV and RIT can be operated from a control room on the platform or from another vessel.
The beetle-like RIT has a dry weight of approximately 70kg and can operate in 3m significant wave heights at the splash zone, giving it a fairly wide deployment window in rough sea states. It would be unsafe for a human dive squad to operate within the splash zone in these conditions. The RIT can currently operate at a maximum depth of 100m, though future modifications will see the robot capable of descending deeper subsea.
Once the VAT has placed the RIT at the weld under survey, the bot relies on six degrees of freedom and machine vision to analyse the weld, mere millimetres from the surface. A front-facing sensor scans the surface and utilises AC field measurement to check for cracks. The RIT can also add various non-destructive evaluation (NDE) sensors and composite video interface (CVI) cameras to its payload.
The RIT is linked by umbilical to a control unit on the topside of the platform – or, for subsea inspections, through the ROV and its umbilical. If a crack is detected, the control unit personnel will be able to assess its length and depth. Schjetne says: “We normally also connect the control unit to the internet, so it can be run from our HQ; this creates a huge saving possibility with regards to persons on board and cost.” However, he adds, it is necessary to maintain the presence of an on-site technician, should the high-tech RIT require maintenance.
Following the recent North Sea trial, OceanTech expects to have commercial versions of the RIT ready before summer 2021. Looking beyond the bot’s current remit of jacket weld inspections, OceanTech believes it could be used for a variety of tasks, including wall thickness measurements and flooded member detection – in fact, anything concerning integrity analysis, across the offshore oil and gas, renewable energy and aquaculture sectors. “Offshore wind jackets are also part of the market, as well as other underwater structures,” Schjetne adds.