ROVs for FPSO Inspections

According to 2015 reports, roughly 20% of global crude oil, and 30% of gas production occurs offshore. With 57% of the world’s energy coming from oil and gas, maintaining the critical structures for these energy methods is vital. Not only would downtime resulting in energy shortages have profound implications around the world, but any undetected degradation of the offshore structures could lead to an environmental disaster. The routine inspection of offshore drilling and storage structures, as well as flexible risers, production, support and gas inject pipelines is the best defense against downtime or spills.

So what does the future of offshore oil and gas look like?

FPSOs, FSOs, and FLNGs

A Floating Production Storage and Offloading (FPSO) vessel is a topside ship that floats near an offshore oil field to store and process crude oil until it can be transferred for refining. If the vessel was constructed without the ability to process oil or gas, it is referred to simply as a Floating Storage and Offloading (FSO) vessel. These vehicles are mainly repurposed tankers, and are desirable as a transportation method without pipeline installation. The equivalent for natural gas is referred to as a Floating Liquid Natural Gas (FLNG) vessel.

Benefits of Remote FPSO Inspections

1. Mobility Launching a vessel rather than platform provides owners the flexibility to relocate once the source of hydrocarbons is depleted or plateaued. Additionally, this mobility can aid in prolonging asset life, since they can change locations to avoid severe weather conditions.

2. Deep Ocean Capabilities The installation of subsurface pipelines becomes more complex as ocean depths increase. Since oil/gas can be stored, processed, and offloaded directly to the vessel, FPSOs are ideal for drilling operations in deep sea environments, a scenario seen each day more commonly in South America and Asia.

3. Minimize Abandonment Costs Requiring minimal infrastructure to transfer oil from offshore sites to refineries, utilizing an FPSO reduces the economic and environmental impact, as well as time commitment when a site becomes decommissioned.

What are the Submerged Components of a FPSO?

While FPSOs are complex vessels with countless features and components for oil/gas production and offloading, for the sake of this article, the focus will be on subsurface assets. So let’s get started

Hull

Similarly to any offshore vessel, the hull refers to the exterior of a FPSO. While a portion of the hull will always remain above surface, the entire underside and lower sections of the sides will consistently be below the water level.

Mooring System

The mooring system will generally consist of a variety of anchors, lines, and connectors. These serve the purpose of holding the FPSO’s station at sea in order to safely and effectively produce and store oil/gas.

Risers

Risers refer to pipelines that connect the FPSO to subsea equipment. ‘Flexible risers’ are the multipurpose pipelines that connect the vessel to the production structures (such as Plets and Plems) or the rigid pipelines at sea bottom level. They are constructed of flexible materials which allow for the FPSO to move without damaging or disconnecting the risers.

How Are Subsea FPSO Assets Inspected?

As identified in the 2013 paper ‘Offshore Dry-Docking of FPSOs: A Response to Industry Needs’, FPSOs are generally designed for continuous usage over 25 years, however reality has shown that although designed to strict criteria, structural and hull maintenance shortcomings have become apparent after prolonged periods, subsequently prompting remedial actions or extensive offshore maintenance campaigns.

Traditional inspection methods of drydocking FPSOs not only come at extensive costs, but pull the vessel out of service during the inspection. Methods of offshore drydocking are being developed, and while these would allow for the FPSO to remain connected to a drill or production site, the cost and scheduling complications of recruiting a heavy transport vessel are substantial. Alternatively, underwater inspections in lieu of drydocking (UWILD) can be performed while the FPSO is underway. This method of inspection keeps the FPSO on site, and is done either via commercial dive teams, ROVs, or a combination of both. As ROVs become more adept at performing in offshore conditions, it is becoming increasingly common for observation class units to be purchased and kept on site for rapid inspections or damage assessment.

ROVs and Drones for Simple and Rapid Inspections

As an alternative to divers, ROVs are a recognized method of performing UWILD inspections. Traditionally, work class ROVs would be required to perform these inspections, due to the harsh conditions of open water environments. These units are extremely large pieces of equipment, requiring a crane to lower, extensive training to operate, might have difficulties working on shallow water, and can cost hundreds of thousands of dollars. This solves concerns over scheduling conflicts and the safety of commercial dive teams, however owning and deploying these large ROVs is still complex and costly.

Observation class ROVs are much smaller than their work class counterparts, and oftentimes are single operator deployable. Advancements in power delivery and station holding via addons like USBL and DVL sensors have enabled these smaller ROVs to deliver high quality visual inspections in a much more manageable package. Additionally, modern observation class ROVs are capable of integrating with tools like thickness probes, imaging sonars, and physical manipulators to provide work capabilities beyond inspection.

Case Study: FPSO Inspection

*For privacy concerns, we can not disclose the company name or location of this particular inspection*

The Scenario

Recently, Deep Trekker ROVs were purchased to conduct inspections of Floating production storage and offloading vessels (FPSO) in the oil and gas industry. Traditionally, this company utilized commercial dive teams to inspect, clean, and perform work on their flexible risers. While effective at performing maintenance tasks while keeping the vessel in service, the customer was seeking alternative methods to conduct safe, fast, and economical inspections.

Equipment Used

Deep Trekker was identified as a desirable manufacturer thanks to their commercial-grade designs in a truly portable form factor. In order to perform inspections in harsh offshore conditions, the team decided to move forward with the PIVOT ROV, the more compact option of Deep Trekker’s six thruster options. Since water clarity was not a concern, they were able to utilize the main camera system as the primary inspection tool rather than 2D imaging sonar.

The Results

Using the PIVOT, workers on the FPSO were able to verify the structural integrity of all the desired assets of each riser (connectors, bend stiffeners, tension lines, and anodes) through harsh water conditions and depths of up to 150 feet. During the inspection, they identified concerning levels of marine growth, including ‘Sun Coral’; an invasive species of coral from Asia, that feeds on native seaweed populations. One of the main stated successes was the speed at which the inspection took place. “A diver takes 3 days to conduct a full scope of work on a single flexible riser, but with the ROV we were able to inspect several flexible risers in a single day”. Although divers are more capable at performing cleaning or maintenance tasks, utilizing an ROV for fast, safe and effective inspections allows for insights into asset health. This allows for dive teams to only be recruited when necessary, and have more targeted goals/appropriate tools to work on identified issues.

Choosing Deep Trekker ROVs for FPSO Inspections

Portability

Deep Trekker’s ROVs and controller systems operate via lithium ion batteries rather than direct topside power. This method of power delivery allows for a much smaller footprint and enhanced remote work capabilities, since no generator is required for operation. “99% of offshore locations are accessed by Helicopter. Being able to fly with the vehicles saves a lot of time rather than shipping the unit” stated one of the staff involved.

Rotating Camera Heads and Tool Platforms

Many ROVs in this size class operate via fixed camera systems. The PIVOT ROV utilizes a 220 degree rotating camera, which provides optimal viewing angles in nearly any scenario. This is extremely useful for inspecting FPSOs and other offshore assets where pilots will be navigating through complex environments and may be difficult to maintain a fixed position. Additionally, the tool platform can rotate over 90 degrees, and operates separately from the camera module for more control flexibility.

Offshore Capabilities in a Compact Package

Six powerful thrusters and a rugged yet hydrodynamic design, alongside intelligent integrations with our in-house BRIDGE software allow the PIVOT ROV to battle substantial current. This provides a stable platform for smooth recordings even through harsh conditions. “Cheaper/lighter ROVs couldn’t get through first layer of swell and heave on similar situations, you need to have a more robust system” explained one of the staff, “The worst we experienced was a 3 meter heave with 3.5 knot current according to the support ship readings, and we were able to inspect in these conditions”. The PIVOT’s ability to automatically combat both vertical and horizontal current allows for less operator input and smoother video in turbulent conditions.

Easy to Use

Deep Trekker ROVs all operate via handheld controllers using BRIDGE. These controllers look and feel very similar in the hands to a video game controller, offering pilots a short learning curve. The 7 inch screen is integrated to display visual, sonar, and GPS location information, either as a picture-in-picture setup, or alternating between full screen viewing. Additionally, if operators can connect to monitors or laptops for larger displays, or to their included microphone to narrate inspections. Deep Trekker controllers also have a variety of custom settings for control inputs, camera/display settings, job data, and more.