The development of duplex stainless steel pipe

In the past ten years, relevant countries such as the United States and South Africa have studied the development of manganese instead of nickel duplex stainless steel. However, in addition to castings, most of the new steels developed have metastable austenite, which is transformed by martensite after cold deformation. To increase the strength, it is difficult to use as welding parts, and it is also difficult to adapt to certain environments, such as stress corrosion environments, which are very limited in use. In recent years, the low-manganese and low-nickel duplex stainless steel developed in Sweden is relatively mature and has a clear goal. In order to save nickel, it can replace the widely used 304, and may even replace the price of 304. The currently not widely used 2304 duplex stainless steel has practical The value of promotion is worth noting. Universal testing machine
The LDX 2101 duplex stainless steel tube (21.5%Cr, 5%Mn, 1.5%Ni, 0.22%N) developed by Avesta Polarit AB in Sweden has obtained stable austenite due to the increased nitrogen in the steel. The phase balance is The structure stability is good, and it is not sensitive to the precipitation of the intermetallic phase. At the most sensitive temperature of 650℃, the impact value drops to 50J after holding for 10 hours. The structure stability is better than that of 2205 steel. The steel has high strength, corrosion resistance equivalent to 304, weldable, and its life cycle cost is lower than that of austenitic stainless steel.

LDX 2101 steel has undergone industrial trial production. After refining in the AOD/CLU furnace, it is continuously casted to produce long steel casting blanks and slab blanks. However, it has not yet been widely promoted and applied. In view of its good comprehensive performance, it has a wide range of potential applications. , Especially for structural parts, it is very promising. For example, it can replace 2205 duplex stainless steel as a bridge structure. It can also be used to make steel bars in concrete to solve the corrosion problem of materials in an environment polluted by chloride ions. In addition, it can also replace 304 and 316 steel manufacturing vessels, towers, hot water storage tanks and heaters, etc.

Judging from the consumption of stainless steel in the world, duplex stainless steel only accounts for a small share, and its price is still relatively high. From the perspective of price ratio: if 304, 304L is 1, then 316L is 1.3, and 2205 is 1.6 , It means that if you want to increase the market share of duplex stainless steel, there should be cheaper new steel grades that can compete with the most commonly used 304 (304L) steel. Of course, there is still much work to be done in this regard.

It is worth mentioning that the development of manganese-containing super duplex stainless steel pipes has been developed in Germany containing 25% Cr, 6% Mn, 6% Ni, 3% Mo, 2% W and ~0.5% N, and Cu High-alloy cast steel, which is solid-solution strengthened, can reach 550 MPa at 0.2, which is nearly 70 MPa higher than similar steels containing 0.15% N. The critical pitting temperature (CPT) reaches 70 ℃, and it has good wear and corrosion resistance. In Austria, BO A920 (26%Cr, 7%Ni, 3%Mn, 4%Mo, 0.35%N) super duplex stainless steel was also developed in Austria. The PREN value is 45, 0.2 is ~600MPa, and AK is 100 ~ 200J, suitable for Use small size high-speed running parts. These two steels are still in the laboratory stage.

One: Chemical and petrochemical processing industry:

This field involves a wide range, complex working conditions, and diverse media. It is also an area where duplex stainless steel is used earlier and more. At present, the catalyst tubes of the large and medium-sized methanol synthesis reactors with a capacity of 200,000 tons and less than 100,000 tons are all made of duplex stainless steel. The large and medium-sized devices use 2205 steel pipes, and more imported pipes are used. Small devices mostly use 18- 5Mo type domestic steel pipe. The medium conditions (HCI, water vapor) of the cooling coil in the oxychlorination reactor of the Qilu Petrochemical Company’s vinyl chloride plant are harsh. Imported 2205 duplex stainless steel pipes have been used, and the results of use remain to be seen. The catalyst regeneration cooler of the ethylene plant adopts domestically made 00C25Ni7Mo3WCuN duplex stainless steel similar to DP3 steel as the seawater cooler tube, and the seawater outlet temperature is 40t. It has been used intermittently for 15 years and the effect is very good. Several coolers of the pulverized coal gasification unit of the Henan Coal Chemical Plant are made of imported 2205 steel pipes. In the next 5 years, China’s petrochemical industry will develop rapidly, with large petrochemical projects under construction and proposed to be spread all over the country. According to the current construction in progress and planned projects, the petrochemical industry’s annual demand for stainless steel pipes in 2005 was about 16,000 tons. . With the improvement of the quality of domestic stainless steel products and the development of special brand products, the application of stainless steel in China’s domestic petrochemical industry will continue to increase in the next five years.

Two: Oil and gas industry:

This is one of the main areas where duplex stainless steel is applied abroad. Currently, there are 1,000km oil and gas pipelines laid. Only the South China Sea Oilfield is used in a small amount in China, and all are imported. In addition, the gas gathering pipeline of the West-East Gas Pipeline Project from the Tarim Basin in the west is considered to use duplex stainless steel welded pipes, which are already produced and manufactured in China. The oil refining industry is the first department to use domestic duplex stainless steel. In Nanjing, Zhenhai, Tianjin, Jinan and other refineries, it is mostly used in the top lining (or composite plate), tower internals, air coolers and The longest water cooler has been used for 20 years. The production of small-size duplex stainless steel seamless pipes is relatively mature in China. The current urgent need to solve is the production of larger-size seamless pipes and welded pipes, and the production process needs to be developed. In addition, how to lower the price of duplex stainless steel products is also related to the development of domestic duplex stainless steel. Although it is important to expand production and produce marketable products, it is important to adopt new technologies and new processes, using molybdenum oxide balls instead of metal molybdenum, nickel oxide instead of metal nickel, reducing smelting costs, and promoting the use of duplex stainless steel continuous casting technology. Improve the yield rate and so on.

Three: Application in the fertilizer industry:

The fertilizer industry adopts domestically-made 0Cr25Ni6Mo3CuN aging-strengthened duplex stainless steel, which uses its wear and corrosion resistance to be used for the internal parts of various specifications of high-pressure shut-off valves in the main process pipeline of the urea plant. The effect is good. At present, the CO2 stripping method and NH3 stripping method for the production of urea mostly use high-alloy austenitic stainless steel or even titanium. The country has begun to use high-chromium duplex stainless steel for the pump body of the large-scale urea plant. 316L (urea grade) steel. Since the 1980s, the three high-pressure equipment of the stripping tower, carbamate condenser and high-pressure decomposition tower in the new ACES urea process developed by Japan’s Toyo Engineering Company have adopted DP-12 (25Cr-7Ni-3Mo containing trace tungsten and copper). -N steel) and R-5 (00Cr25Ni6.5Mo1.5N) duplex stainless steel. The former is used to make gas stripping pipes, condensers, decomposition pipes and conveying pipes, while the latter is used for high-pressure equipment shells. In 2005, the annual demand for stainless steel pipes in the petrochemical industry was about 7,800 tons, and it is expected to increase to 9,600 tons in 2010. The national standard of stainless steel has not been revised for more than ten years. The acceptance and revision of duplex stainless steel must be considered when revising the national standard.

For the 2205 grade, which accounts for 80% of the output, the user acceptance standards for product factory inspection have been specially formulated in foreign countries. We should also consider introducing and absorbing to fulfill the existing inspection methods and standards to promote the production and ordering of duplex stainless steel. In addition, vigorously develop the potential markets for industrial and civil use of duplex stainless steel (such as construction industry structures, bridges, concrete steel bars; such as manufacturing containers, storage tanks, chemical tankers, speedboats, tank trucks; and high-level domestic facilities Water tanks, electric water heaters, housing steam pipes, etc.), and develop, test and promote some new varieties developed abroad that are suitable for China’s national conditions (nickel and chromium deficiency) (such as low-nickel-saving duplex stainless steel). I believe that China will promote duplex Stainless steel has very broad application prospects.