In recent years, duplex stainless steel has not only been widely used in major oil companies, the main pipeline system development, and is the main material for offshore oil production and transportation. Standard duplex stainless steel in the sweet, wet, acid service environment performed well. While ordinary carbon steel due to high internal corrosion rate, although the use of preservatives can be used to prevent external corrosion, but can not effectively prevent internal corrosion. Not only that, at 50 ℃ above the ambient temperature, but also may lead to stress corrosion cracking (SCC), so duplex stainless steel also gradually replaced the 300 series stainless steel. With the increase in the concentration of H2S in the transport of oil and gas, along with the gas temperature, pressure and pipe temperature increases, super duplex stainless steel began to use for piping systems, valves, heat exchangers, pressure vessel oil and gas equipment. When the oil industry gradually turned to high temperature, high pressure engineering, super duplex stainless steel will be more used. The general pipeline treatment system, will use 200 ~ 1 000 t super duplex stainless steel. In addition, the super duplex stainless steel can also be used for low pressure conveying system, submarine conveying pipeline. However, due to the higher price of duplex stainless steel, the promotion of its products affected. The advantages of duplex stainless steel are the following:
· Yield strength is greater than the general austenitic stainless steel l times, and a good shape plastic toughness, the same design stress can reduce the wall thickness of 30% to 50%;
· Excellent resistance to stress corrosion, in the chloride ion environment, it can solve the salient stainless steel difficult to solve the outstanding problem;
The most commonly used 2205 duplex stainless steel corrosion resistance is better than 316L austenitic stainless steel, super duplex stainless steel in acetic acid, formic acid and other media can replace high alloy austenitic stainless steel;
· Good resistance to localized corrosion, wear corrosion and corrosion fatigue resistance. Better than the alloy content of austenitic stainless steel;
* Linear expansion is low, close to carbon steel, suitable for connection or composite with carbon steel.
The typical duplex stainless steel is 2205 (22Cr-5Ni-3Mo) and 2507 (25Cr-7Ni-4Mo) type, the most widely used 2205, the oil and gas industry has been laying the length of oil and gas pipeline has more than 850 km, of which about 400 km belong to offshore oil field, the vast majority of 2205. Ferritic – austenitic duplex stainless steel (DSS) has a high strength and good resistance to chloride localized corrosion and stress corrosion. However, it should be noted that duplex stainless steel in the acidic environment, there are still some restrictions. Because the experimental study shows that it is more sensitive to the SSCC, the actual use should pay attention to the environment pH and stress levels.
Source: China Duplex Stainless Steel Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)