A350 LF2 Blind Flange Forged ASME B16.5 Class 300

Ferritic low temperature steels generally have obvious toughness-brittleness transition temperatures, and when the temperature drops to a certain critical value (or range), there will be a sudden drop in toughness. The attached figure shows the relationship between the impact value and temperature of 0.2% carbon steel containing carbon, and its transition temperature is around -20°C. Therefore, ferritic steel should not be used below its transformation temperature. Generally, alloying elements such as Mn and Ni need to be added to reduce interstitial impurities, refine grains, and control the size, shape and distribution of the second phase in the steel. The ductile-brittle transition temperature of the bulk steel is reduced (see Strengthening of metals).

Ferritic low temperature steel is divided into three categories according to the composition

Low carbon manganese steel
Low-alloy steel
Medium (high) alloy steel
Low-temperature steel in LPG cryogenic separation equipment, most of the minimum operating temperature is -110 ℃, and some equipment can reach -150 ℃. Low alloy steel, 3~6% nickel steel or 9% nickel steel can be used respectively. In the air separation equipment, the minimum working temperature is -196℃, and 9% nickel steel or austenitic low temperature steel is generally used. Liquid hydrogen production, storage and transportation equipment with a working temperature of -253 °C, and liquid helium equipment with a working temperature of -269 °C should use austenitic low-temperature steel with stable microstructure. For some special equipment, such as superconducting magnets or superconducting motors, it is advisable to use steel that can maintain extremely low magnetic permeability (μ) ≤ 1.01 or lower in addition to stable austenite structure below the working temperature. kind.

Some iron-nickel-based and nickel-based superalloys with higher low temperature toughness, such as A-286, Inconel718, InconelX-750, etc., are also commonly used in low-temperature equipment requiring high strength.

Blind flange is also called blind. It is a flange without a hole in the middle for sealing the pipe plug. There are many types of sealing surfaces, including flat surface, convex surface, concave-convex surface, tongue and groove surface, and ring connection surface.
Production Process
The production process is mainly divided into three types: forging, casting and cutting.
Cast and forged flanges
For the cast flange, the shape and size of the blank are accurate, the processing volume is small, and the cost is low, but there are casting defects (pores, cracks, inclusions); the internal organization of the casting is less streamlined (if it is a cutting part, the streamlined shape is even worse);
Forged flanges generally have lower carbon content than cast flanges and are not easy to rust, the forgings are streamlined, the structure is relatively dense, and the mechanical properties are better than those of cast flanges;
Improper forging process will also cause large or uneven grains, hardening cracks, and forging costs are higher than casting flanges.
Forgings can withstand higher shear and tensile forces than castings.
The advantage of casting is that it can make a more complex shape and the cost is relatively low;
The advantage of forgings is that the internal structure is uniform, and there are no harmful defects such as pores and inclusions in the casting;
The difference between cast flanges and forged flanges is distinguished from the production process. For example, centrifugal flanges are a type of cast flanges.
Centrifugal flanges belong to the precision casting method to produce flanges. Compared with ordinary sand castings, this type of casting has a much finer structure and improved quality, and is not prone to problems such as loose organization, pores, and trachoma.