England – 16/10/2011 – The use of duplex stainless steel in the gas and oil extraction industry is set to stay.
For several decades the oil and gas exploration and extraction industry has relied on duplex stainless steel to allow them to drill in deep water.
Duplex stainless steel is made from a combination of austenite and ferrite, which makes it twice as strong as regular stainless steel. The fact that it is a combination of two components is what gives it the name duplex. Its high chromium and low nickel content ensures that it does not corrode, even in salt water.
The evolution of Duplex Stainless Steel
To begin with the mix of austenite and ferrite was 50/50 in duplex stainless steel now it is more likely to be 40/60. The level of chromium is the main and probably the most important variation in the different types of duplex stainless steel.
Standard duplex contains 22% chromium, super duplex contains 25% and, the new, hyper duplex contains up to 33% chromium. The mix of chromium in all duplex stainless steel depends on who makes it. Each manufacturer has a different mix. The development of mixes has to some extent been led by the needs of the industries that use the material. The petro chemical industry has been the main client, so initially development of duplex steel concentrated mainly on improving the ability of the metal to withstand pressure and not to corrode.
Lately, the focus has gone from stopping it from corroding under salt water to enabling it to withstand an acid environment. This is because another big client for duplex steel is the chemical industry.
Another major client, the nuclear power industry has also had a big influence on how duplex steel has been developed. For this industry the ability for the steel not to corrode in water is important, but so is the strength of the material and its ability to withstand extreme heat. For example the new hyper duplex steel is mainly used in heat exchangers.
SPM, a major distributor of duplex stainless steel pipes, has seen demand for duplex pipes grow over the past decade. They expect this growth to accelerate in the near future.
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