Divers have been the only way to do underwater work for many years.
It was always a dangerous occupation, and many sponge divers and pearl divers died bringing back the treasures of the deep – in those days ‘deep’ was a few hundred feet at the most. With the invention of Cousteau’s aqualung, diving became popular as a sporting activity. Many things were learned the hard way; decompression, nitrogen narcosis, the bends were all part of the risk.
As the need for underwater work and exploration increased into deeper waters, divers donned metal suits and tried new types of ‘air’, basically gas mixes that were safe to breathe at the higher pressures needed for deep diving.
Eventually, it became clear that there had to be a move towards underwater vehicles, at first manned but soon to become unmanned…. Remotely Operated Vehicles or ROVs. These ‘work class’ ROVs were complex, expensive to buy and operate, but essential to industry and especially offshore exploration for hydrocarbons and other valuable minerals.
Designed for deepwater and heavy weight tasks they were generally launched off a Dive Support Vessel (DSV), and because of their cost, were only used where absolutely necessary, leaving shallow water work to the divers.
But shallow water is still dangerous - swell, current, rapid changes in pressure all added to the risk and there were still many lives lost. Technology moved on and much smaller ROVs were developed that could carry cameras and work at shallow depths, light enough to be hand launched and useful for observation in calm and clear waters.. but if any work needed to be done the divers were called in.
So, over many years innovations had disrupted the way we did things underwater and the innovations and disruptions continue as we now look at a further ‘diverless’ evolution – the Integrity Class ROV and the world of ODIN®.
In 2016 EM&I started to develop diverless methods – not by using ROVs but instead by doing work that normally needed divers or a work class ROVs, with methods that did not even involve getting wet!
ODIN – the Norse god of wisdom and learning?
Danny Constantinis (Executive Chairman) of the EM&I Group – the international asset integrity specialists - tells the story: ”When operators started asking if it was possible to carry out the class requirement for Underwater Inspections in Lieu of Drydocking (UWILDs) without divers; I asked them why this was important and a senior manager famously said: “we spend millions of dollars and all we see are bubbles and weeds”, so the idea of an alternative method for UWILDs was born.’
EM&I studied the class requirements and realised that the inspections were complex and vital to the safety of the vessel, especially Floating Production units such as Floating Production, Storage and Offloading vessels (FPSOs) that could not easily go to drydock. Isolation valves that controlled vital water flows in and out of the vessel, had to be reliable. Crucial structural elements such as bilge keels, critical welds, mooring systems and, in the case of disconnectable units, steering and propulsion equipment also had to be regularly checked.
It became clear that the task at hand needed several tools in the toolbox; devices that could inspect (and maintain) critical valves as well as a highly capable ROV which could clean, inspect, and help maintain the underwater hull and moorings.
ODIN was conceived and developed…. first a ‘cold tap’ device that allowed cameras and tools to be inserted from the ‘dry’ space into piping adjacent to isolation valves, sea chests and through hull plating so that critical components could be inspected and maintained, without taking the systems off-line and without putting people at risk.
These tasks were traditionally the realm of divers and observation class ROVs, but they were unable to carry out a proper detailed inspection, safely.
ODIN proved to be highly successful and soon many hundreds of ODIN access ports were installed creating a track record over the last 5-years carrying out inspection and replacing valves, replacing side shell plating and cleaning mooring chains and piping and sea chest inlet grids blocked with marine growth (Figure 1).
Figure 1. Examples of ODIN ROV activities.
However, ODIN access ports could not solve all of the challenges and so the task of evolving high performance Integrity Class ROVs began. The specification started with cleaning sea chests, measuring anchor chain links and angles, and taking thickness measurements and cathodic protection readings.
These ROVs had to be light enough to launch from an FPSO deck yet powerful enough to deal with big swells and high currents while remaining stable enough to operate measurement callipers and use cavitation cleaners…a real challenge but one which was met (Figure 2).
Figure 2. Integrity Class ROV.
This was the first part of a two-part article. The second part is available to read here: https://bit.ly/3r4AwSF.
Read the article online at: https://www.oilfieldtechnology.com/offshore-and-subsea/18032021/not-all-rovs-are-equal--part-one/