What kind of low-temperature steel bars are used in LNG storage tanks? What are the characteristics?

LNG is usually stored in slightly positive pressure low-temperature storage tanks below -162 ℃ with a pressure of 25 to 29k Pa. The storage tank capacity is generally 40,000 to 200,000 m3. LNG storage tanks can be divided into four types according to their structure: single-containment tanks, double-containment tanks, full-containment tanks and membrane tanks. At present, the LNG storage tanks built and under construction in my country are all 160,000 m3 full-containment LNG storage tanks. Full-containment storage tanks usually consist of prestressed concrete outer tanks and 9% nickel (Ni) steel inner tanks. The main purpose of the concrete outer tank is to contain the LNG working fluid vapor (BOG gas) during normal operation of the LNG storage tank, and to hold the LNG liquid and maintain the evaporation gas seal when the LNG storage tank leaks. When the LNG full-capacity tank causes overflow or sudden accident (earthquake, inner tank rupture, etc.) during normal operation (overfilling), the LNG liquid will leak from the 9% Ni steel inner tank into the annular space and come into direct contact with the tank bottom and tank wall. This requires additional cold insulation measures and low-temperature resistance for the concrete outer tank. Both concrete and structural steel bars should have good low-temperature resistance. The extreme working conditions of this type of steel bars are below -20°C and -29°C. They are suitable for the main properties of low-temperature steel and can be called low-temperature steel bars. At present, there are no production standards for low-temperature steel bars in China. Foreign steel bar manufacturers generally adopt standards such as B S4449, B S7777 and E N14620. You can also refer to E N1992-1-1 and E N10080. : 2005 and other relevant standards. Below is the grade 500B steel bar produced by Arcelor Mittal International. ① The chemical composition of low-temperature steel bars is low carbon alloy structural steel. ②On the one hand, the yield strength of low-temperature steel bars is ≥ 500MPa, while the ferrite + pearlite structure is difficult to meet the yield strength Rp0.2 ≥ 500MPa. The sorbite structure can meet the yield strength but must undergo quenching and tempering treatment (quenching + high temperature tempering). The quenching and tempering treatment production process is complicated. The bainite structure is obtained by air cooling or controlling the cooling rate, and the yield strength can reach 530 ~ 1 500MPa. a, so there are only two types of metallographic structures to choose from for low-temperature steel bars, non-quenched and tempered steel or low-carbon bainitic steel. On the other hand, from the perspective of preventing crack propagation, the lath structure is more advantageous. Therefore, the metallographic structure of low-temperature steel bars should be low-carbon bainite structure, and the low-carbon bainite structure is a medium-temperature transformation structure. Hot rolling can directly form materials without heat treatment. ③ From the NSR analysis, the larger the NSR value, the smaller the notch sensitivity. Materials with NSR>1 are plastic materials. The material transforms to a brittle state at low temperatures. The yield strength and tensile strength of low-temperature steel bars in the notched state at low temperatures are very close. That is, under stress, the material may have fractured before the notched sample has 0.2% residual deformation. Therefore, in order to ensure the normal use and plasticity of low-temperature steel bars at low temperatures, the tensile strength with notches must be greater than the yield strength without notches.

Mix it together :) The liquid oxygen and liquid nitrogen storage tank foundation uses pearlescent sand concrete as the foundation insulation layer. Are there any special requirements for steel bars? :)

;P Maybe its danger level is too high. The foundation of the air separation tower is to use stainless steel as a barrier to prevent groundwater, and a certain thickness of concrete mixed with pearlescent sand and cement as an insulation layer. The steel bars are made of ordinary secondary rebar.

The steel bars used should refer to full-capacity tanks, that is, the outer tank is reinforced concrete, the inner tank is low-temperature steel, there is cold insulation material between the inner and outer tanks, and the bottom of the tank is foam glass bricks, which also keep cold.； There are no low temperature requirements for steel bars, only strength requirements for concrete.