ASTM A182 / ASME SA182 F321H Stainless Steel Flange for Chemical Industry

ASTM A182/ASME SA182 standard specifies the requirements for pipeline flanges, forged fittings, valves, and parts used for high temperature (and generally also applicable to low temperature or corrosive environments) services, covering various grades of austenitic stainless steel such as F304H, F316H, F321H, etc.

F321H is the material grade code specified in the ASTM A182 standard. The "H" suffix stands for High Temperature Service, which means it is designed for high temperature applications. UNS S32109 is its corresponding unified numbering system code (H type usually corresponds to this UNS), which belongs to high carbon titanium stabilized austenitic stainless steel, non-magnetic, with good face-centered cubic crystal structure, toughness, formability, weldability and corrosion resistance.

In terms of chemical elements, the carbon content range of F321H is higher than that of ordinary F321, which helps it maintain strength at high temperatures. The core value of F321H stainless steel flange lies in the addition of a certain amount of titanium. The affinity between titanium and carbon is much higher than that of chromium, and it can preferentially combine with carbon to form stable titanium carbide and prevent the precipitation of chromium carbide.

Comparison between ASTM A182 F321H and other related austenitic stainless steel materials

• Vs. F321 (non-H type): The upper limit of carbon content for non-H F321 is lower (≤ 0.08%), and high-temperature yield strength is not mandatory. F321H is designed specifically for applications that require higher high-temperature strength.

• Vs. F304/F304H: F304 belongs to low-carbon stainless steel and has better corrosion resistance at room temperature due to less carbide precipitation. However, its strength in high-temperature environments is significantly lower than that of F304H and F321H. F304H and F321H are both high carbon austenitic stainless steels with good high-temperature strength. However, due to their absence of titanium, intergranular corrosion is prone to occur during welding or exposure to sensitization temperature ranges. F321H addresses this issue by adding titanium, making it safer and more stable during welding and sensitization conditions.

• Vs. F347/F347H: F347/F347H material is stabilized with niobium instead of titanium, and its performance is very similar to F321H. The selection is sometimes based on subtle differences in cost, welding process habits, or specific corrosive environments. The strength at extremely high temperatures may be slightly better than F321H.