Stainless Steel Tubes

We are currently the second largest consumer of electricity in the world, with the installed capacity of electricity increasing from 520 million kilowatts in 2005 to 1,144 million kilowatts in 2012, with an average annual growth rate of 11.97%. As a country with more coal and less gas and oil, coal-fired power generation still dominates our total power generation capacity. According to BP’s World Energy Statistics Yearbook 2012, coal accounts for 70.39% of the primary energy consumption structure.

Currently, the installed thermal power generation capacity accounts for 71.59% of the total installed power generation capacity, and the installed thermal power generation capacity increased from 390 million kilowatts in 2005 to 819 million kilowatts in 2012, with an average annual growth rate of 11.18%.

Thermal power generation is a form of power generation that uses the thermal energy generated by burning coal to heat water, turning it into high-pressure water vapor, which then drives a generator to generate electricity. Thermal power plant mainly consists of three major parts: power generation boiler, steam turbine and generator, in which the steam and water pipes in power generation boiler include reheater pipe, superheater pipe, water cooling wall pipe, coal saver pipe, air preheating pipe, heat conduction pipe, descending pipe and various joint box pipes. Due to the use of the above-mentioned pipeline in high temperature and high pressure conditions for a long time, the pipeline will be oxidation and corrosion under the action of high-temperature flue gas and water vapor, so the requirements of steel pipe with high lasting strength, high oxidation resistance corrosion performance and good organizational stability. To meet the above requirements, stainless steel tubes are used in large numbers in thermal power boilers. China’s thermal power unit investment has driven the development of stainless steel tubes for the power equipment manufacturing industry.

At present, with the development of the chemical industry, the application of duplex stainless steel is becoming more and more widespread, and the domestic duplex stainless steel pipe is growing at a rate of 10% per year, and has a great future in the petroleum, urea and other industries.

The outstanding performance of duplex stainless steel pipe is high yield strength and stress corrosion resistance, with good weldability, welding cold cracking and hot cracking sensitivity are less. In Japan, austenitic and ferritic stainless steel welded pipe in the petrochemical industry in the pipeline system accounted for 54% of the market share.  Stainless steel welded pipe is mainly used in the decorative field, the use of corrosion-resistant welded pipe in the petrochemical field is still basically blank.

Stainless steel national standards have not been revised for more than a decade, in the revision of the national standard must be considered duplex stainless steel standard and revision. Foreign for 80% of the production of 2205 grade specifically developed the product factory inspection of the user acceptance criteria, we should also consider the introduction and absorption, enriching the existing inspection methods and standards to promote the production and ordering of duplex stainless steel.

In addition, the duplex stainless steel to develop the potential market for industrial and civil use (such as construction – structures, bridges, concrete reinforcement; such as manufacturing – containers, storage tanks, chemical carriers, speedboats, tankers; and household facilities – high water tanks, electric water heaters, housing water and steam pipes, etc.), and development, trial, promotion of foreign development and suitable for our national conditions (lack of nickel and chromium) of some new varieties (such as low nickel saving duplex stainless steel), I believe that China’s promotion of duplex stainless steel has a very broad application prospects.

Stainless steel is a recognized health material that can be implanted in the human body and is used in almost all areas involving human health. It has been widely used. Stainless steel plumbing is an environmentally friendly material that meets health requirements, can be 100% recycled, saves water, reduces transmission costs, reduces heat loss, avoids sanitary ware pollution and other advantages. The details are shown as follows.

1.Life span
Stainless steel pipe has ^ long service life. Analysis of the use of stainless steel from abroad, the life of stainless steel water pipes can reach 100 years, or at least 70 years, as long as the life of the building.

2. Corrosion resistance
One of the outstanding advantages of stainless steel pipe ^ is its excellent corrosion resistance, which is ^ good in various pipes. Because stainless steel can be passivated with oxidizing agents, forming a layer of tough and dense chromium-rich oxide protective film Dr2O3 on the surface, effectively preventing further oxidation reactions. Other metal pipes, such as galvanized water pipes, copper pipes passivation ability is very small, which is the galvanized copper pipe corrosion resistance is far less than the key reason for stainless steel pipe. Stainless steel does not occur as uniform corrosion of carbon steel, the use of protective coating is not required; the use of stainless steel water pipe, there is no restriction on the chemical composition of the water, because stainless steel in a variety of oxygen content, temperature, PH and hardness of the water have very good corrosion resistance; stainless steel water pipe can withstand very high flow rate, even if the flow rate is greater than 40 m / s, still maintain a very low corrosion rate, not more than 0.003 mm / year Especially suitable for high-rise water supply. Stainless steel generally does not occur in local corrosion, 304 stainless steel can withstand the chloride content of 200ppm, 316 stainless steel can withstand the chloride content of up to 1000ppm, this conclusion is based on exposure test data and has been confirmed by the use of experience. Stainless steel tube thermal expansion coefficient and copper tube is about the same, is 1.5 times the ordinary steel pipe, compared to the stainless steel tube has the characteristics of slow thermal expansion and contraction.

3. Heat resistance and insulation
The thermal conductivity of stainless steel pipe is 1/25 of copper pipe, is 1/4 of ordinary steel pipe, especially suitable for hot water transmission. Water industry ^ often use stainless steel is 316 and 304 stainless steel, they can meet the majority of water treatment and transmission off conditions.

4. Strength
The tensile strength of 304 stainless steel pipe is 2 times that of steel pipe and 8 to 10 times that of plastic pipe. The strength of the material determines whether the water pipe is strong and resistant to impact, safe and reliable. And safety and reliability is the building water ^ important requirements. In the case of impact by external forces, the possibility of leakage of stainless steel water pipes is very small. High building water supply system working pressure is generally greater than 0.6Mpa; the pipe pressure requirements are high. Thin-walled stainless steel pipe due to the excellent mechanical properties, can withstand very high water pressure, up to 10Mpa or more, especially suitable for high-rise water supply.

Many fickle factors indicate the characteristics of corrosive media, namely chemicals and their concentration, atmospheric conditions, temperature, time, so if you do not know the correct nature of the medium, to use the material, the choice of materials is difficult. However, the following can be used as a guide for selection.

Type 304 widely used materials. It can withstand general rust and corrosion in construction, resist food processing media leaching (but corrosion may occur at high temperature states containing concentrated acid and chloride components), and resist organic compounds, dyes, and a wide variety of inorganic compounds.

Type 304L (low carbon), good resistance to nitric acid, and durable medium temperature and concentration of sulfuric acid, widely used as liquid gas storage tanks, used as low temperature equipment (304N), appliances other consumer products, kitchen equipment, hospital equipment, transportation, wastewater treatment devices.

Type 316 contains slightly more nickel than type 304 and contains 2%─3% molybdenum, corrosion resistance is better than type 304, especially in chloride media that tend to cause pitting corrosion. type 316 has been developed for use as sulfite pulpers because it is durable sulfuric acid compounds. Moreover, its use has been expanded to handle many chemicals in the processing industry.

Type 317 contains 3%-4% molybdenum (also the higher level obtained in this series) and contains more chromium than Type 316, providing higher resistance to pitting and crevice corrosion.

Type 430 is lower in alloy than Type 304 and is used for highly polished decorative applications in mild atmospheres, as well as in nitric acid and food processing equipment.

Type 410 has the lower alloy content of the three general-purpose stainless steels and is selected for high strength parts requiring a combination of strength and corrosion resistance, such as strong parts. 410 is resistant to corrosion in mild atmospheres, water vapors, and many mild chemical product media.

Type 2205 is superior to Types 304 and 316 because he has high resistance to chloride stress corrosion cracking and has approximately twice the strength.