Offshore Steel Structures: A Complete Overview

What is an Offshore Steel Structure?

Offshore steel structures serve as essential infrastructures for the exploration and extraction of offshore oil and natural gas reserves. The surge in global oil prices in 2008 prompted a rise in offshore structure projects. An offshore structure is a hybrid of steel structure design, harbor design, and construction.

The initial offshore structures were constructed using wood, with the earliest known offshore oil drilling structure established in 1887 near Santa Barbara, California. This structure was a basic wooden wharf equipped with a drilling ring for vertical wells into the seabed. Subsequent developments included more complex projects supported by timber piers, such as those in Caddo Lake, Louisiana (1911), and Maracaibo, Venezuela (1927). Eventually, researchers realized that the lifetime of these early projects in lakes and oceans was limited due to the attack of marine organisms.

There are various applications of offshore structures such as Offshore Vessels, Drilling Platforms (bridges, booms, decks, living quarters, process skids), Ro-ro Ramps, Headstocks, Pontoon, Dolphin, Gangway, and Subsea Structures.

The offshore vessel serves operational purposes such as oil exploration and construction work on the high seas. It provides not only exploration and drilling of oil but also the provision of necessary supplies to excavation and construction units located on the high seas.

There are four main groups of offshore vessels:

1. Oil exploration and drilling vessels.

2. Offshore support vessels

3. Offshore production vessels

4. Construction/special purpose vessels.

Historically, the offshore vessel was specifically designed to support the offshore oil and gas industry back in the 1950s. This marked the creation of the “Workboat” Industry. Over the years, there have been various advanced innovations in offshore vessels. There are various factors involved in the construction of offshore vessels. First is the primary material used, which is steel. Second is the consideration in the design, as the design depends on where it will be used, for example, if it is an oil exploration vessel that includes drill ships, jack-up vessels, semi-submersible vessels, offshore barges, and floating platforms.

Each vessel has a specific design that suits operational demands. Next are the mathematical computations specialized by engineers to determine the optimal fleet size and mix of vessels, even the weekly routes and schedules for servicing offshore installations. These are just some of the descriptions of the construction then, of course, there are more detailed and complex steps that require expertise in naval architecture and marine engineering.

In offshore structures, there are complex installations used in the extraction of oil and gas from the earth’s crust.

Some of the components are:

• Bridges - these are the pathways of personnel and equipment for transferring materials and facilitating communication between different parts of the offshore installation. There are interfaces such as electrical, instrumentation, and piping interfaces from one platform to another

• Booms - these are used for oil spill response operations to contain and deflect oil away from sensitive areas. It can also be part of lifting and handling systems

• Decks - this is the flat surface area at the top of the structure where most of the facilities are located. Here is the drilling area, processing facilities, and living quarters.

• Living quarters - this is where the crew lives. There are sleeping quarters, dining areas, recreational facilities, and sometimes there are also medical facilities.

• Process skids - these are pre-assembled units that have a process system or part of a process system. They are often used in the oil and gas industry for easier and lighter installation and operation. It can include systems for oil-gas separation, water treatment, chemical injection, etc.

  
  

The RoRo, short for roll-on/roll-off - are the vessels used to carry wheeled cargo such as cars, trucks, and heavy machinery that are taken out and put in using their own wheels or platform vehicle. The RoRo ship, often called RoRo ramps, is designed to accommodate the weight and dimension of the various vehicles.

The design of RoRo ramps follows a specific code of practice such as the British Standard BS 6349-8:2007, which provides guidelines for RoRo ramps. It generally consists of a metal gangway with dimensions suitable for each case. It is joined to the ground and driven by a mechanism that allows it to reach a suitable contact position with the boat. Some challenges faced by engineers in making this are the harsh marine environment, so regular maintenance of these and corrosion-resistant materials is needed to ensure the longevity of the ramps.

Headstocks refer to the concrete structure at the top of a set of sheet piles that hold them together. They must be robust enough to withstand the harsh marine environment and dynamic loads imposed by waves, wind, and currents.

The pontoon-type offshore structures, also known as Very Large Floating Surfaces (VLFSs), are artificial islands used for multiple purposes, including floating airports, bridges, breakwaters, piers and docks, storage facilities (oil and natural gas), wind and solar power plants, and even habitation. Its basic element is a box structure, resting on the water surface intended for deployment in calm waters such as a cove, lagoon, or harbor. It is supported by buoyancy on the sea surface. Steel-concrete composite materials can be used to build this floating structure. Safety and strength requirements, operating conditions, etc. must be considered. The pontoon offshore structure uses a mooring system to keep it in position. These systems use a combination of heavy anchor chains and wire ropes attached to anchors at the seabed.

In the context of offshore structures, the dolphin is a group of pilings arrayed together to serve various purposes. It acts as a protective hardpoint along the dock, waterway, or shore, as it is the point of stabilization of the dock, bridge, or similar structures, as a mooring point and base of navigational aids. It usually contains several piles driven into the seabed or riverbed, connected above the water level to provide a platform or fixing point. Dolphins are also used to protect against possible ship impacts. One notable example of the use of a dolphin is to protect the Sunshine Skyway Bridge across the mouth of Tampa Bay.

The gangway is a specially designed access system that can provide workers with safe and stable access to offshore installations. It connects the vessel or platform to the shore or another vessel, allowing safe access for personnel, equipment, and supplies. They are designed to counteract the ship’s multidimensional swing motions and keep the transfer object steady. One of the successful projects was the dynamic model of an offshore gangway under dynamic load presented in the Journal of Marine Science and Engineering. There was a thorough examination of the equation to carry out the mathematical model that was verified by joint simulation.

Subsea structures are underwater constructions installed on the seabed for the foundation, support, and protection of subsea oil and gas processing equipment. The design and analysis of these involve structural analysis, piping, and finite element analysis. In a case study, inventors used remotely operated vehicles (ROVs) to retrofit subsea infrastructure in 450-foot water depths offshore Trinidad and Tobago. All installations have complicated computations documented for analysis.

All of these have a history or origin that has now led to various innovations. ESC Steel Structure is one of the companies that make it possible to create such projects that can withstand the harsh marine environment. In fact, we are both ready and experienced in compliance with international standards such as DNV, NACE, ISO, ANSI, ASME, BS, ASTM, and AWS standards. They also have various projects that prove the robust materials and installation they have completed.

ESC Steel Structures is a global leader specializing in heavy offshore structure fabrication, serving various industries including general marine, offshore renewables, and oil & gas. The company's core group of engineers collectively offers a wealth of knowledge and experience, delivering high-value steel structures with excellent and professional service. Their applications span offshore vessels, drilling platforms, Ro-ro ramps, and subsea structures, showcasing their versatility and adaptability.

Using ESC Steel Structures' materials in offshore structure fabrication offers several benefits. Their materials are known for their high strength and durability, making them ideal for offshore structures that need to endure harsh environments. ESC Steel Structures' materials are corrosion-resistant, which is crucial considering offshore structures are constantly exposed to saltwater. Using their materials can lead to significant cost savings in terms of maintenance and repair costs, contributing to the economic viability of offshore structures.

To learn more about ESC Steel Structures, visit our website at escsteelstructures.com. We offer a wide range of products and services, including Bailey Bridge, Bridge Structures, Pre-engineered Buildings, Port & Offshore Structures, Offshore Platforms, Pressure Vessels, Steel Bridges, Mining Excavation, Steel Towers, Rail Infrastructures, and others.

For consultation and project discussion, you can reach us at 📞 (980) 689 4389 or via email at info@escsteel.com