Not all ROVs are equal - part two

Are Integrity Class ROVs (ICRs) equivalent to divers and work class ROVs?

Divers and work class ROVs have special capabilities that are still required in our industry but the drivers for change are relentless.

Why? Because our industry and society demand that we minimise risk to human lives and that we continue to produce vital energy from the sea at reduced cost, as we transition from fossil fuels to renewable floating wind.

Diving spreads can need ten or more people to operate safely, and even then, are restricted by sea and weather conditions. Integrity Class ROVs need a team of three and can already operate in sea and weather conditions nearly double the safe limits for divers (Table 1).

Table 1. Effects of current conditions on diving operations.

Integrity Class ROVs carry cameras, NDT (Non-Destructive Test) equipment and tools. They can be launched and retrieved from the deck of an FPSO or a support vessel using lightweight Launch and Recovery Systems (LARS).

Figure 3. Lightweight Launch and Recovery System (LARS).

These systems enable the ROV to get past the dangerous ‘splash zone’ before being launched in calmer waters at the correct depth.

Ongoing developments mean greater power and more efficiency

ICRs can also cope with the power required to operate a wide range of tools with power provided by specialised tether systems. They can be provided with stabilised power units with back up UPS (Uninterruptible Power Supply) and do not depend on the reliability and stability of mother vessel power supplies.

Standard tethers are 200 m long, which is usually sufficient for most FPSO UWILDs and mooring chain inspections, etc., but 400 m tethers can also be provided if required.

Long line tethers up to 1000 m are also available using high voltage and transformers to accommodate voltage drops over long distances and thus deliver adequate power at the ROV.

ICRs can be equipped with vectored thrusters which enable an additional capability to rotate on the roll and pitch axes and hold position. This enables tasks needing an awkward orientation such as mooring chain angle measurements and efficient cleaning of sea chest inlet grids or bilge keel ends.

Cleaning sea chest inlet grids and mooring chains is time consuming and to do so efficiently and without damaging coatings needs specialised tools, so EM&I has tested, proved, and introduced cavitation cleaning.

Working limited to daylight hours and good visibility can reduce productivity…

Working limited to daylight hours and good visibility can reduce productivity so EM&I’s integrity class ROVs are equipped with a new sonar system to enable work to continue in poor visibility. This is particularly important for floating assets such as Floating Storage and Regasification Units (FSRUs) which are often moored in river estuaries with strong currents and poor water clarity.

‘IGLOO’ habitats for all the associated topside control equipment can also help to reduce humidity and protect equipment, increasing reliability and productivity. An independent stabilised UPS also reduces site dependency and increases reliability. It also ensures that if the primary power system fails for any reason the ROV can safely return to a safe location.

Skid mounted Deep Water Deployment (DWD) ROVs can be used for depth ranges in excess of 2000 m…

Skid mounted ‘DWDs’ (Deep Water Deployment) ROVs can be used for depth ranges up to 3000 m for inspecting mooring chains and risers which, at that depth, will not require much if any, cleaning (Figure 4).

Figure 4. Deep Water Deployment ROV.

The skid mounted DWD ROVs have a launch garage and a tether management system (TMS) and integral pressurised control cabin which increases their capability for deep water operations at a much lower cost than work class units. They are generally designed for operation from a support vessel, so can be used for mooring chain, riser and pipeline inspections at a distance from the FPSO.

The scope of diverless repairs on FPSOs is rapidly increasing…

The scope of diverless repairs on FPSOs is rapidly increasing, with sea valve isolation, repair or replacement, side shell and caisson repairs, sea chest cleaning, etc., with much more to come as both diverless and robotic technologies develop.

Underwater services have become a key part of the asset integrity industry which is why EM&I pioneered the use of integrity class ROVs for UWILDS and developed cleaning and measuring tools for the hull and moorings over the last 8 years since our first pilot project in Brazil in 2013.

“There’s a lot of technology evolving in working underwater safely and efficiently”, according to Danny Constantinis. “Increasing capability of smaller, more capable and lower cost ROVs is helping achieve the key targets of increasing safety and reducing cost with the added benefit of fewer POB, lower carbon footprint and applications to renewable energy such as floating wind,” he concluded.

This was the second part of a two-part article. The first part is available to read here: https://bit.ly/3eVRgJu.

Read the article online at: https://www.oilfieldtechnology.com/offshore-and-subsea/19032021/not-all-rovs-are-equal--part-two/