📘 What Is a Flange?
A flange is a mechanical connector used to join pipes, valves, pumps, or other equipment, forming a leak-proof and detachable joint. Flanges allow for easy assembly, disassembly, and system maintenance.
📏 Flange Dimensions
Flange dimensions are determined by international standards and include several key aspects:
🔹 Key Flange Dimensions:
| Term | Description |
|---|---|
| NPS / DN | Nominal Pipe Size (inch or mm) |
| OD | Outside Diameter of the flange |
| Bolt Circle | Diameter of the circle where bolt holes are located |
| Bolt Hole Size | Diameter of each bolt hole |
| Thickness | Thickness of the flange body |
| Raised Face (RF) | Height of the raised face for gasket seating |
| Hub Height | For weld neck and long weld neck flanges |
📘 Dimensions vary by standard (e.g., ASME B16.5, EN 1092-1, JIS B2220, DIN 2633).
🧪 Pressure Ratings (Classes)
Flanges are rated by the maximum pressure they can withstand, categorized into pressure classes:
🔹 ASME Pressure Classes:
Class 150
Class 300
Class 600
Class 900
Class 1500
Class 2500
💡 Higher class = thicker flange + more bolts = greater pressure tolerance.
🔹 PN Ratings (European/ISO):
PN 10 / PN 16 / PN 25 / PN 40 / PN 63 / PN 100 (Pressure Nominale in bar)
🧱 Common Flange Materials
| Material | Features | Applications |
|---|---|---|
| Carbon Steel | Cost-effective, high strength | General industry, water/oil pipelines |
| Stainless Steel | Corrosion-resistant, durable (e.g., 304, 316) | Food, pharma, marine, chemical plants |
| Alloy Steel | Higher strength and corrosion resistance (e.g., A182 F11) | High-temp, pressure systems |
| Duplex Stainless | High strength + better corrosion resistance | Oil & gas, seawater systems |
| Nickel Alloys | Exceptional corrosion & heat resistance (e.g., Inconel, Hastelloy, Monel, Incoloy) | Aggressive environments |
| Aluminum / Bronze | Lightweight, corrosion-resistant | Marine, specialized water systems |
| Plastic (PVC, HDPE) | Lightweight, low-pressure use | Water distribution, drainage |
🧰 Flange Types (Brief Recap)
| Flange Type | Best for... |
|---|---|
| Weld Neck | High pressure & temperature |
| Slip-On | Easy installation, moderate pressure |
| Socket Weld | Small-diameter pipes, smooth bore |
| Threaded | No welding, low-pressure |
| Lap Joint | Frequent dismantling, misalignment tolerance |
| Blind | Seal ends of pipe or nozzles |
| Long Weld Neck | Pressure vessels, special applications |
🛠️ Choosing the Right Flange
Consider these factors:
Pipe Size (NPS or DN)
Pressure Class or PN
Material compatibility
Environment (corrosive, high-temp, seawater?)
Flange Type based on use case
Standard required by project (ASME, EN, DIN, JIS, etc.)
