In the oil and gas industry, stainless steel has become necessary for machinery subjected to extreme temperatures and toxic materials. ‘Stainless’ is an umbrella term for numerous types of steel developed for corrosion-resistant applications, including pipelines, heat exchangers and connectors.
Stainless steels are iron-based alloys containing a minimum of 10.5% chromium but can also consist of nickel, titanium, or carbon, depending on their intended purpose.
What types of steel are used in the gas and oil industry?
There are five types of stainless steel available, categorised by their composition and their wide range of uses. The steel types are austenitic, martensitic, ferritic, duplex, and precipitation Hardened.
Austenitic
Austenitic stainless steels contain large amounts of chromium and nickel and are incredibly resistant to corrosion. They are not magnetic and can be hardened via exposure to cold temperatures but not through heat treatment.
Martensitic
Martensitic stainless steels are designed for corrosion resistance and can be hardened via heat treatment. Martensitic stainless steels are magnetic and are used when strength and durability are necessary.
Ferritic
Ferritic stainless steels are used when corrosion resistance is paramount. They are also resistant to stress and cracking and are made without nickel.
Duplex
Duplex stainless steels are also known as ferritic-austenitic types as they are comprised of components from both ferritic and austenitic steels. These are tough, durable steels and have a high level of corrosion resistance. However, they are not as tough as austenitic steels alone.
Precipitation Hardened
These steels can be hardened through heat treatment, enabling a combination of strength, corrosion resistance, and ease of treatment that cannot be found in any other stainless grade.
Duplex stainless steel and precipitation hardened steel are predominantly used in the gas and oil industry because of their high yield strength and high resistance to stress corrosion cracking.
Although ferritic and austenitic stainless steels have their limitations, when 50% of each is combined to produce duplex stainless, it becomes immensely versatile. It can endure high temperatures for an extended period. Additionally, its low nickel count makes it a cost-effective option.
Each type of stainless steel is given a grade, with the most popular being 304, 316 or 316L. These grades are not about the quality of the steel but the specific purpose for which they are needed. The ‘L’ denotes a lower carbon content, meaning it is easily welded to other steels or metals or into shape without cracking.
What Kind of Steel is Used in Oil Pipelines?
Duplex or super duplex steels are frequently used in the main pipes of the offshore oil and gas industry because of their high corrosion resistance, unlike other materials such as carbon steel. Standard carbon steel is prone to corrosion, as it will rust when exposed to air and moisture.
Super duplex steel is commonly used in offshore oil rig heat exchangers, storage tanks, pumps, and flowlines. As crude oil is corrosive, a highly durable and corrosion-resistant material like stainless steel is required to hold it.
The benefits of super duplex steel are:
- High yield strength
- Good weldability
- Maintenance-free (mostly)
- High resistance to corrosion
If you would like more information about our stainless steel solutions for the oil and gas industry, contact us today.