A flange is a protruding flat rim or disc-shaped profile element used to mechanically join two parts. Flanges occur on pipes, steel sections and plate structures and provide a strong, often demountable connection. In construction, flanges play a central role in both installation engineering and structural steelwork.
Types of flanges
Depending on application, three main groups are distinguished:
Pipe flanges
In water, gas and heating lines, flanges are used to make pipes joinable:
| Flange type | Application |
|---|---|
| Weld neck flange | Welded to the pipe, for process technology |
| Threaded flange | Screwed onto the pipe |
| Blind flange | Closes a line at the end |
| Slip-on flange | Slides over a flared end |
Steel sections
In H, I, U and T sections, the horizontal edges are called flanges; the vertical connection is the web:
- Top flange — takes compression
- Bottom flange — takes tension
- Web — connects the flanges, takes shear
Floor and wall flanges
In precast floors or plate material, an upstanding rim can also be called a flange, especially in hollow-core slabs, TT slabs and sheet piling.
Application
Flanges are found in almost every modern construction:
- Heating systems — pumps, boilers, expansion vessels
- Water supply — connection to mains
- Sewerage — coupling with manholes
- Fire-fighting mains — dry and wet risers
- Steel structures — bolting columns to bases
- Bridge building — coupling between girders
Advantages
- Demountable — parts can be unbolted
- Strong and reliable — bolted connection takes high loads
- Standard sizes — DIN, EN or ANSI standards
- Medium-tight — gaskets ensure sealing
- Inspectable — accessible for maintenance
Gasket and fixing
In pipe flanges a gasket is placed between the two faces:
- Rubber — for low-pressure water
- Klingerit — fibre-rubber, higher temperatures
- PTFE / Teflon — aggressive media
- Spiral-wound — high pressure and temperature
Bolts are usually grade 8.8 steel or stainless, with lock and spring washers for sustained clamping.
Related terms
- I-section
- H-section
- Pipework
- Construction metal
- Steel connection
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