Duplex stainless steel was developed because strong acids and alkalis in petrochemicals produce local pitting, stress corrosion and cavitation corrosion, and ordinary stainless steel is not competent. Because duplex stainless steel has very strong corrosion resistance, high strength and toughness, it is now widely used in civil engineering and energy transportation, such as aircraft, ships, automobiles and chemical materials in coastal areas.
Large duplex stainless steel high-pressure heat exchanger
Among them, the oil and gas industry is one of the main areas of foreign duplex stainless steel, and it is less used in China. The oil refining industry first used domestic duplex stainless steel, mostly used in the top lining (or composite plate) of the atmospheric and vacuum distillation tower, tower internals, air coolers and water coolers, etc. The longest has been used for 20 years. Zhenhai Refining and Chemical Company is the largest oil refining base in my country, with a processing capacity of 16 million tons, and is one of the top 100 in the world. The material used for many sets of equipment in the condensation cooling system is duplex stainless steel.
This field has a wide range, complex working conditions, and a variety of environmental media. It is also an early and extensive field for the application of duplex stainless steel.
Fertilizer industry
The urea industry is one of the earliest industries to use domestic duplex stainless steel. The heat exchange equipment containing chloride ion water in its equipment is widely used. For example, the three-stage cooler of the CO2 compressor in the urea unit originally used 304L austenitic stainless steel tube bundles. After one month, it leaked due to stress corrosion cracking. Duplex stainless steel can be used for more than 5 years. Subsequently, the first and second stage coolers were also replaced with 18-5Mo or 2205 duplex stainless steel.
Because duplex stainless steel has very good corrosion fatigue resistance in urea medium, it is very suitable for manufacturing the key equipment of urea production-the pump body of the A-type pump. The domestic 00Cr25Ni6MO2N steel can pass the intergranular corrosion tendency test of the Huey method and has been used in some large fertilizer plants. The pump bodies of the A-type pumps in small and medium-sized fertilizer plants in China are basically made of 18-5Mo stainless steel, and dozens of them use high-chromium lead-containing duplex stainless steel.
In addition, domestic OCr25Ni6Mo3CuN aging-strengthened duplex stainless steel is used for its wear and corrosion resistance, and is used for the internal parts of various specifications of high-pressure stop valves in the main process pipelines of the urea plant, with very good results.
Transportation Industry
Now the offshore chemical tanker industry has become the largest foreign user of duplex stainless steel, and its consumption accounts for about half of hot-rolled stainless steel plates. Chemical tankers carry a variety of liquid cargoes, including chemical and petrochemical products, food, etc., which requires that the cabin materials must not only be corrosion-resistant but also have high strength. Now 2205 duplex stainless steel has replaced 316L and 317L austenitic stainless steels and become the standard material for offshore chemical tankers.
Papermaking and salt-making light industry
Because duplex stainless steel has better resistance to pitting and crevice corrosion in neutral chloride solutions, this feature has been used to develop the application of duplex stainless steel in vacuum salt production and salt and salt co-production units. The large brine and mirabilite evaporation tanks of 200,000-300,000-ton salt plants all use duplex stainless steel linings and composite plates, which solves the problem of salt scaling and corrosion of equipment. Domestic duplex stainless steel has mature experience in large vacuum salt production units.
In the field of pulp and paper industry, China lacks relevant experience. The sulfate cooking method still mostly uses low-carbon steel cooking pots, while foreign countries have long popularized the use of duplex stainless steel cooking, bleaching and other equipment, and China has introduced less.
It can be seen that the use of duplex stainless steel in China has limitations. Similar to the large-scale use of duplex stainless steel abroad, such as pulp and paper industry, oil and gas industry, transportation industry, and even construction industry, several major fields are still in the development stage in China. By using the performance advantages of duplex stainless steel, in addition to continuing to expand its application in chemical and petrochemical fields in the future, combined with the technical transformation of the pulp and paper industry, it needs to develop applications in this field, but the promotion of oil and gas pipelines is still relatively difficult because the price of duplex stainless steel is relatively expensive.
