What is flange

A flange (Flange) is a disk-shaped mechanical component with bolt holes, typically used in pairs with gaskets and fastened by bolts to connect pipelines, valves, or equipment. Its structure includes three critical elements:

1. ‌Sealing surface‌: Flat or raised designs (e.g., Raised Face RF, Flat Face FF) ensure tight contact with gaskets.
2. ‌Bolt holes‌: Uniformly distributed along the circumference (commonly 4, 8, or more holes) for secure fastening.
3. ‌Materials‌: Carbon steel, stainless steel, alloy steel, etc., selected based on media and pressure requirements.
   Example: DN150 (150mm diameter) flanges are widely used in chemical pipelines, typically featuring 8 bolt holes and pressure ratings up to PN16 (16 bar).

II. Five Core Functions of Flanges

1. ‌Pipeline system connection‌:
   Enables rapid joining of pipe segments, especially in long-distance transport lines (e.g., oil pipelines connected via flanges for modular installation).

2. ‌Facilitated maintenance and disassembly‌:
   Compared to welding, flange connections allow on-demand disassembly for cleaning or part replacement, reducing maintenance time by over 90% in chemical plants.

3. ‌High-pressure and extreme environment adaptability‌:
   High-pressure flanges (e.g., Class 600) withstand pressures exceeding 60MPa, applied in power plant boilers/gas pipelines. Corrosion-resistant materials (e.g., 316L stainless steel) enhance durability.

4. ‌Media isolation and diversion‌:
   Blind flanges temporarily seal pipelines, while flange tees enable fluid diversion.

5. ‌Vibration damping and misalignment compensation‌:
   Lap Joint Flanges accommodate minor pipe offsets, mitigating stress from thermal expansion or vibration.

III. Flange Selection and Common Issues

• ‌Selection criteria‌:
  • ‌Pressure rating‌: PN10 (low), PN40 (medium), Class 900 (high).
  • ‌Sealing face type‌: RF for most scenarios; Ring Joint (RTJ) for ultra-high pressure.
  • ‌Standard systems‌: GB/T (China), ANSI (US), EN (EU)—must match pipeline specifications.
• ‌Common pitfalls‌:
  1. Neglecting gasket material compatibility (e.g., asbestos gaskets fail in acidic media).
  2. Mixing flange standards causing leaks (e.g., ANSI vs. JIS bolt hole spacing differences)