Marine conditions with salt, sand and water of an offshore oil rig create a very harsh environment and corrosion. Regular steel will rust and corrode. Luckily, there is a solution!
Carbon steel is susceptible to corrosion in any environment but much more so in exposed marine environments. In the early days, oil rig equipment and structures were composed mainly of carbon steel. They quickly discovered that the structures would not last long and that pitting and crevice corrosion were major issues. To combat this, many manufacturers starting using 316 stainless. While 316 stainless holds up much longer than regular steel, in such a harsh environment, it also has issues with surface rust, pitting, and crevice corrosion. These issues caused both suppliers and producers to look at other stainless alloys for a solution. Designers have now started to replace 316 with duplex and super-austenitic grades like 2507 Super Duplex, 904L, or 254SMO.
2507 “Super Duplex”
In recent years, Duplex grade 2507 is becoming the most popular alloy for offshore oil rigs and structures. There are many benefits to using this alloy. These benefits include exceptional strength and corrosion resistance, as well as excellent resistance to chloride stress corrosion cracking. Furthermore, there are high thermal conductivity and a low coefficient of thermal expansion. Specific to offshore structures, the biggest benefit of 2507 is that it has a high nickel, chromium, and molybdenum content that provides excellent resistance to pitting and crevice corrosion.
Another benefit of all duplex stainless steels is the high yield strength. Duplex stainless has a much higher yield strength than the standard austenitic stainless steels. This added strength alloys engineers to design with a smaller shapes or thinner sections creating weight reductions and cost benefits. The other benefit of using 2507 is the lifecycle cost reductions. Studies show that duplex structures can last in a marine environment for over 50 years.
Applications and Availability
Stainless Structurals can produce beams, channels, angles, tees and custom shapes from our laser fusion method in both 2507 duplex and the super-austenitic alloys. We also stock and can produce all of these shapes in various sizes in 316L stainless. Our products are being used today on many offshore oil rigs for things like platforms, catwalks, pipe racks and supports, framing and skids. Let us help you with your next offshore structure. Give us a call or contact us here.