Gaskets selected for different flange types
The core of the flange gasket is determined by the sealing surface type, which determines the gasket structure, and the pressure and temperature determine the material; Below are matching and recommendations based on the most commonly used sealing surfaces
1, FF flat face flange
Features: The sealing surface is fully flat, with a large area and low surface pressure. It is commonly used in low-pressure, cast iron/enamel equipment.
Gasket selection:
Full plane perforated soft gaskets (with the same outer diameter as the flange and bolt holes) must be used.
Recommendation: Rubber, asbestos free fiber, PTFE cushion; Pressure ≤ PN16, temperature ≤ 200 ℃.
Strictly prohibit: metal wrapping pads, metal ring pads (not tightly pressed, prone to leakage).
2, RF raised face flange
Features: Raised sealing surface, medium area, high surface pressure, most commonly used (PN10-PN100).
Gasket selection (preferably with inner and outer wrapped gaskets):
Low voltage (PN10 – PN25): graphite winding pad (basic type/inner ring), graphite composite pad, PTFE pad.
Medium and high voltage (PN40-PN100): equipped with inner and outer metal wrapped pads (304/316+graphite) and corrugated composite pads.
Temperature: -200~650 ℃ (graphite); ≤ 260 ℃ (PTFE).
3, MFM concave convex flange (Male/Female)
Features: Convex surface embedded in concave surface, well positioned, anti blowing, medium high pressure (PN16-PN160).
Gasket selection:
Only narrow face gaskets (outer diameter ≤ convex diameter) can be used.
Recommendations: Metal wrapped pad (inner ring), metal wrapped pad, toothed pad, flexible graphite pad.
Not recommended: Full flat cushion (easy to extrude).
4, TG tenon groove flange (Tongue/Groove)
Features: The tenon is embedded in the groove, the sealing surface is narrow, the surface pressure is extremely high, and high-pressure/highly toxic media (PN63-PN250) are used.
Gasket selection:
Narrow strip gaskets (size matching groove) must be used.
Recommendations: Metal wrap pad (without outer ring), metal solid pad, graphite pad, PTFE pad.
Advantage: The gasket is not blown out, suitable for hydrogen, chlorine, liquefied gas, etc.
5, RTJ Ring Joint flange
Features: Trapezoidal groove, equipped with metal ring gasket, high temperature and high pressure (PN100-PN420, -200~800 ℃), commonly used in petroleum/natural gas.
Gasket selection:
Special metal ring gasket (oval/octagonal), material: soft iron, carbon steel, 304/316, Monel, titanium.
Matching: The groove type (R/G) is consistent with the ring gasket model; Hardness lower than flange HB30-50.
