Performance Analysis and Application of Domestic P9 Seamless Steel Tube

P9 ferritic alloy seamless steel pipes for petroleum cracking , normalizing + tempering and isothermal annealing are used to evaluate the room temperature properties , transient high temperature tensile properties , high temperature durable creep properties and microstructure of P9 products. shape analysis . And compared the test data , main chemical composition control level , high temperature durability and application performance with the quality of imported pipes, the results show that the domestic P9 ferritic alloy seamless steel pipe products can meet the requirements of the American Society for Testing and Materials standard ASTM A335 , The product quality has reached the foreign advanced level and can replace imported products .
Keywords :petroleum cracking, P9 ferritic steel, seamless tube, alloy

With the gradual development of large-scale high-temperature cracking equipment in China's petrochemical industry and the gradual increase in imported high-sulfur crude oil, the corrosion problem of petrochemical equipment has become increasingly serious . Therefore, it is urgent to develop better high-temperature - resistant and corrosion-resistant materials to meet the needs of the rapid development of petroleum cracking equipment . In order to meet this demand, Baosteel launched the development of P9 ferritic alloy seamless steel pipe for petroleum cracking in 2005. The product performance meets the requirements of the American Society for Testing and Materials standard ASTMA335 and can replace imported products .
1 P9 steel chemical composition and alloying principle
P9 steel is compared with traditional seamless steel pipes for petroleum cracking (such as P11, P12, P22, P5 ) , the mass fraction of Cr element in P9 is higher, reaching an average of 9.0% ; the average mass fraction of Mo element reaches 1.0 % , see Table 1 for specific parameters . A high Cr content is beneficial to improve the high temperature oxidation corrosion resistance and thermal strength of the material, and the mechanism is mainly due to the formation of denser Fe s O on the surface . • 2 hearts . 3 film or dense Cr 2 O 3 film in Table 1 to slow down the rate of continued oxidation of steel [ 1 ] . Mo element is the main element that increases the recrystallization temperature of the solid solution matrix and improves the thermal strength. After being dissolved in the solid solution, it will cause strong lattice distortion, increase the attraction of the lattice atomic bonds, and increase the recrystallization temperature of the a - ridge matrix [ 2 ] , It is beneficial to enhance the thermal strength of steel . The mass fraction of C element is less than 0.15% , which is beneficial to welding . When the mass fraction of Mn element is 0. 30% - 0. 60% , it has a good deoxidation and desulfurization effect, which is beneficial to improve the steel quality . When the mass fraction of Si element is 0.25% - 1.00 % , it has good deoxidation ability. At the same time, a dense and protective oxide film will be formed on the surface of heat-resistant steel containing silicon at high temperature, which is beneficial to improve the oxidation resistance of steel . Lower S , P content helps to resist hydrogen sulfide stress corrosion . Therefore, compared with P11 , P12 , P22 , and P5, P9 has better resistance to high temperature oxidation , hydrogen sulfide stress corrosion resistance, and higher thermal strength, and can be popularized and used in large petrochemical plants .

ASTM A335M	C	Si	Mn	P	S	Cr	Mo
P11	0. 05-0. 15	0. 50-1. 00	0. 30-0. 60	W0. 025	W0. 025	1. 00-1. 50	0. 44-0. 65
P12	0. 05-0. 15	W0. 50	0. 30-0. 61	W0. 025	W0. 025	0. 80-1. 25	0. 44-0. 65
P22	0. 05-0. 15	W 0. 50	0. 30-0. 60	W 0.025	W 0.025	1. 90-2. 60	0.87-1. 13
P5	W 0.15	W 0. 50	0. 30-0. 60	W 0.025	W 0.025	4. 00-6. 00	0.45-0. 65
P9	W 0.15	0. 25-1. 00	0. 30-0. 60	W 0.025	W 0.025	8.00-10. 00	0.90-1. ten

2.1 Tensile properties at room temperature
Due to the different application conditions of users, the finished product of P9 seamless steel pipe

 

Supplier organization status also has different requirements . One of the commonly used delivery states is normalizing + tempering, and the other is isothermal annealing . The room temperature tensile properties of the two heat-treated steel pipes are required to meet the requirements of the ASTM A335M standard, that is: the yield strength is greater than 205 MPa, the tensile strength is greater than 415 MPa, and the elongation is greater than 30% .

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