Good Mid-Range Corrosion Resistant Alloy
- Mid-range corrosion resistant alloy
- Decent mechanical strength to 1000°F
- Alloy 20 chemistry and specifications
- Alloy 20 sulfric acid performance
- Lap joint flange features and benefits
Also known as Carpenter 20 and 20CB-3, Alloy 20 lap joint flanges offer users a combination of nickel, chromium, molybdenum, and copper which provides good general corrosion resistance. Alloy 20 lap joint flanges are best suited for mid-range corrosion use – better than steel alloys but not at the level of high performance nickel based alloys like Hastelloy C276. Alloy 20 is a nickel alloy that was initially designed to withstand the harsh environment of hot sulfuric acid but also performs well in a variety of other acids. Alloy 20 lap joint flanges are an ideal choice when you don’t need the corrosion resistance power and price-tag of high performance nickel alloys like Hastelloy C276; but you need something that will give you more protection than 316 stainless steel or even a Super Duplex 2507 stainless steel.
Alloy 20 lap joint flanges provide good performance in hot sulfuric acid, specifically they offer good resistance to stress-corrosion cracking in boiling sulfuric acid at specific range of 20% to 40% concentration, as well as general sulfuric acid resistance. Alloy 20 offers solid acid protection and will perform better than Duplex or even Monel, but for high temperature and high concentration acids, you may need to look to Inconel or Hastelloy fasteners. In addition, Alloy 20 lap joint flanges also show useful resistance to phosphoric acid and nitric acid.
Key Corrosion Resistant Features:
- Good sulfuric acid protection at 20% - 40%
- Decent stress corrosion cracking, pitting and crevice corrosion resistance in chloride
- Resonable general corrosion protection
- Good intergranular corrosion resistance in the as-welded condition
In addition to their corrosion resistance, Alloy 20 lap joint flanges also perform well at moderately high temperatures, with the ability to maintain their mechanical strength up to 1000°F.
Alloy 20 lap joint flanges are stabilized with Columbium to minimize carbide precipitation during welding. In addition it offers intergranular corrosion resistance in the as-welded condition.
• Power plants rely on alloy 20 lap joint flanges for flue-gas desulfurization
• Alloy 20 lap joint flanges are used to connect heat exchangers, mixing tanks, metal cleaning equipment, pickling tanks and racks, and piping in mid-range corrosive chemcial processing environments.
• Alloy 20 lap joint flanges help solve corrosion issues in food and dye production.
• Manufacturers of plastics and synthetic rubber also utilize alloy 20 fasteners.
Alloy 20 Specifications: UNS N08020, ASME SA240, , ASME SB366, ASME SB462, ASME SB463, ASME SB464, ASME SB473, ASME SB729, ASTM A240, ASTM B366, ASTM B463, ASTM B464, ASTM B473, ASTM B729, ASTM BB462, ANSI/ASTM A555-79, EN 2.4660, , Werkstoff 2.4660, CN7M, DIN 2.4660
Alloy 20 Sulfuric Acid Comparison
Lap joint flanges are unique in that they are made of two pieces, the flange itself and the stub end.
- The backside, has a slight shoulder that is square cut at the center or pipe hole
- The front side has a flat face with a filleted (rounded) center hole to match the filleted back face of the stub end. Here the stub end will wrap tightly around the center hole of the flange.
- Shaped like a short piece of pipe with a weld bevel on one. This portion of the stub end is also called the sleeve.
- Narrow shoulder on the flange facing end called is the hub. The back face of the hub has a rounded transition (or inside fillet) that joins the hub to the sleeve
Because a lap joint flange has a two piece configuration, it offers a way to cut cost when piping systems requires
- For high cost alloys the only "wetted" part is the stub end. In this situation, it is only required for the stub-end to be made of the higher cost corrosion-resistant material, where the flange itself can be the produced from lower cost steel.
- Ease of Work
By using lap joint flanges, work can be simplified in situations that require frequent and rapid disassemble and assembly during the operation of a plant. The ability to spin that backing flange compensates for misalignment of the bolt holes during assembly.