Stainless steels, including duplex and super duplex, bring significant economic benefits to the offshore oil and gas industry. Compared with other materials, it is lighter, stronger, more resistant to corrosion, and lower life cycle cost.
Offshore projects are extremely important to the production and processing of hydrocarbons worldwide. In some of the most extreme environments, offshore extraction accounts for nearly 30 percent of global crude oil production. However, the salinized marine environment requires high safety and longevity standards for offshore platforms. Infrastructure for marine and offshore applications is often susceptible to high levels of air- and water-borne salt, and common carbon steel structures are often subject to corrosion and require regular maintenance and maintenance.
Stainless steel, on the other hand, is a solid guarantee of robust material choice for heavy offshore installations. The metal's inherent corrosion resistance provides infrastructure with a high strength-to-weight ratio, even in marine and coastal environmental conditions. Stainless steel also ensures a long design life and impressive resistance to extreme pressure and high temperatures. Remarkably, by using stainless steel, the expected service life of offshore structures can be increased by almost five times compared to its competitors.
life cycle cost
In addition to a longer service life, stainless steel is more qualified for offshore applications due to the growing emphasis on lowest life cycle cost (LCC) in building and construction. This concept underscores the strong need to develop new types of infrastructure that are highly durable and do not require extensive maintenance or repair.
Weight reduction is also a major driving force behind the installation of offshore structures. The reduced weight means the structure is cheaper to build, while allowing for the addition of drill pipe and production equipment for oil and gas production and exploration.
Types of steel used in offshore installations
SS316L is the main austenitic stainless steel grade used in offshore installations to enhance strength at high temperatures and protect structures from severe acidic environments. Austenitic grades containing 6% molybdenum are typically used for permanent immersion in seawater. However, due to fluctuations in global nickel prices over the past few years, duplex stainless steels have widely replaced austenitic grades. Duplex stainless steels offer an excellent combination of mechanical properties and resistance to stress corrosion cracking, making them ideal for offshore applications. UNS S32205 steel is the most commonly used duplex grade for offshore installations.
Although duplex stainless steels are outstanding in offshore heavy installations, the new generation super duplex stainless steels are comparable to austenitic stainless steels in seawater corrosion resistance. In addition, the mechanical properties of these steel grades are significantly improved compared to duplex steels. These super duplex steels feature higher nitrogen, chromium, molybdenum, and nickel contents, which contribute to their resistance to pitting and crevice corrosion. Steel grades such as UNS S32750 and UNS S32760 are used for underwater components of more aggressive offshore installations.
While we note that stainless steel is a better substitute for carbon steel, the key is to understand that selecting the best stainless steel grade for a particular need is critical to the cost-effectiveness and durability of offshore installations.
Applications of stainless steel at sea
Subsea components: pipelines and gratings for oil transfer, sewage discharge and drainage, risers for oil transfer platforms, heat exchangers for ships and coastal power plants, equipment installed on the hull.
Platform structural components: pumps, winches, storage tanks, process vessels, blast doors, umbilicals, steel bars, cable trays, stairs, treads, walkways, gas coolers, gravity separators, etc.
Ship deck components, such as ship deck eyelets, anchor cable brackets, shackles, etc.
Coastal (on land) handrails, ladders, lampposts, etc.
