ASTM A182 F321H Stainless Steel Flanges for High Temperature Service

ASTM A182 F321H Stainless Steel Flange for Chemical Industry

ASTM A182 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.

ASTM A182 F321H Stainless Steel Flange Main Features

• Excellent resistance to intergranular corrosion: This is the most prominent characteristic of the 321 series stainless steel. Due to the addition of titanium, even when exposed within the sensitization temperature range (450°C - 850°C), it effectively avoids the tendency for intergranular corrosion caused by chromium carbide precipitation. This makes the 321 series stainless steel particularly suitable for welded components and equipment operating at high temperatures for extended periods.
• Good high-temperature performance and oxidation resistance: The "H" grade ensures that 321H stainless steel exhibits better creep resistance and endurance strength than ordinary 321 at temperatures above 525°C. Simultaneously, it maintains good oxidation resistance and anti-scaling properties under cyclic use at approximately 800°C and continuous use at approximately 925°C.
• Good overall mechanical properties: It possesses good strength, plasticity, and toughness at room temperature, making it easy to machine and form.

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.