Carbon Steel Flange: Types and Specification
Carbon Steel Flange and end flange connectors are basically made of carbon steel. Common standards include ASTM A694, ASTM A105N (SA105N), MSS SP-44, DIN 2533. Accompanying pressure ratings are from class 150 to 2500.
Carbon Steel Flange
Carbon Steel Flange and end flange connectors are basically made of carbon steel. Common standards include ASTM A694, ASTM A105N (SA105N), MSS SP-44, DIN 2533. Accompanying pressure ratings are from class 150 to 2500.
Carbon steel is a steel with carbon content up to 2.1% by weight. According to AISI, carbon steel is defined as having:
- No minimum required content of alloying elements such as chromium (Cr), molybdenum (Mo), nickel (Ni), titanium (Ti), vanadium (Va), etc.
- A specified minimum copper (Cu) content not exceeding 0.04%.
- A maximum of 1.65% manganese (Mn) and 0.06% silicon (Si).
As carbon content increases, the steel becomes harder and stronger when heat treated, but its ductility decreases. Without heat treatment, higher carbon content also reduces weldability.
Carbon steels may include alloy steels, provided they are not classified as stainless steel.
Mild Steel or Low Carbon Steel Pipe Flanges
Carbon steel pipe flanges are commonly made from mild or low carbon steel, which contains a small percentage of carbon. This material is strong and tough, though not easily tempered, making it a cost-effective option suitable for a wide range of applications.
Carbon content classifications:
- Low carbon steel: 0.005% – 0.3%
- Medium carbon steel: 0.3% – 0.8%
- High carbon steel: 0.8% – 2.0%
- Ultra-high carbon steel: 1.25% – 2.0%
ASTM A105N (SA105N) Carbon Steel Pipe Flanges
ASTM A105 is a widely used mild carbon steel grade for forged carbon steel flanges, suitable for ambient and high-temperature service in pressure systems. It offers durability, cost efficiency, and resistance to fracture. When used in stainless steel piping systems, it must be paired with a lap joint stub end to prevent galvanic corrosion.
Chemical composition of A105 carbon steel pipe flanges
|
Element |
Composition, % |
|
Carbon |
0.35 max |
|
Manganese |
0.60-1.05 |
|
Phosphorus |
0.035 max |
|
Sulfur |
0.040 max |
|
Silicon |
0.10-0.35 |
|
Copper |
0.40 max A |
|
Nickel |
0.40 max A |
|
Chromium |
0.30 max A,B |
|
Molybdenum |
0.12 max A,B |
|
Vanadium |
0.08 max |
ASTM A350 (SA350) LF2 – Low Temperature Use
ASTM A350 LF2 is a carbon steel grade designed for low-temperature applications, closely related to ASTM A105N. It requires notch toughness testing and is widely used across various industries, including low-temperature fittings.
ASTM A694 – High-Strength Carbon Steel Flange Material
ASTM A694 sets stricter standards than A105N and A350, targeting high-pressure fluid transmission in oil and gas pipelines. This grade demands enhanced strength for both low and high-temperature conditions, with a specified minimum yield strength for all its grades.
Manufacturing Types and Standards
Carbon steel flanges are produced by forging or casting methods.
Differences Between Forged Steel and Cast Iron Flanges
- Forging is more costly than casting.
- Cast iron allows complex shapes; forging does not produce large or uneven pieces.
- Cast iron flanges are limited to non-pressure pipelines; forged steel flanges are used in high-pressure systems.
- Centrifugal casting yields higher precision cast iron flanges than standard casting.
- Forged steel flanges are easier to machine and have higher tensile strength.
- Overall, forged steel flanges outperform cast iron in durability, shape accuracy, and corrosion resistance due to lower carbon content.
Relevant Standards
- ASTM B16.5: Dimensions for steel pipe flanges and fittings
- ASTM B16.34: Flanged, threaded, and welding end valves
- ASTM B16.47: Large diameter steel flanges
- API 605: Large diameter carbon steel flanges
- API SP44: Steel pipeline flanges
Coating Types
Common coatings for corrosion protection include:
- Anti-rust painting
- Oil varnish
- Electro-galvanized zinc (white or yellow)
- Alloy coatings (lined or clad)
Common Carbon Steel Flange Types
- Weld Neck Flange
- Slip-On Flange
- Blind Flange
- Socket Weld Flange
- Threaded Flange
- Reducing Flange