Flange Face Finish and Gasket Selection: Raised Face, Flat Face, and RTJ Sealing Guide
Short answer: flange leakage is usually not caused by the flange alone. It is the result of the complete bolted joint: flange facing, gasket type, surface finish, bolt material, lubricant, alignment, tightening sequence, and operating temperature. Selecting the correct raised face flange, flat face flange, or RTJ flange is one of the most effective ways to improve sealing reliability.
For engineering buyers, a flange quotation should define the sealing face as clearly as size and pressure class. SongHai manufactures ASME, EN, JIS, GOST, and project-specific flanges with controlled face finish, bolt-hole accuracy, and inspection records for industrial piping and equipment.
Flange facing types and when to use them
| Facing | Common use | Key consideration |
|---|---|---|
| Raised face flange | General process piping, water, steam, oil, gas | Requires correct gasket width and serrated finish |
| Flat face flange | Cast iron equipment, low-pressure utility systems | Full-face gasket helps avoid bending brittle mating parts |
| Ring type joint flange | High pressure and severe service | Groove accuracy and metal ring compatibility are critical |
| Tongue and groove flange | Controlled gasket confinement | Mating geometry must be supplied as a matched pair |
| Male and female flange | Equipment joints and selected process systems | Alignment and gasket compression need close control |
Why face finish matters
The gasket needs enough surface roughness to grip, but not so much that it creates leak paths. A typical serrated raised face is suitable for many soft and semi-metallic gaskets. RTJ grooves require precise geometry and a smooth controlled surface because the metal ring seals by high local contact stress.
Useful RFQ keywords include flange face finish, serrated flange face, smooth finish flange, and RTJ groove machining. These details help the manufacturer select the proper tooling, inspection method, and surface roughness report.
Gasket compatibility
A spiral wound gasket flange arrangement is common in refineries, chemical plants, power systems, and high-temperature service. PTFE gaskets are often chosen for chemical resistance, while graphite gaskets handle higher temperature. Metal ring gaskets are used with RTJ flanges. The gasket material should be checked against fluid, temperature, pressure, flange rating, and bolt load.
If gasket data is available, include gasket style, material, thickness, inner and outer diameter, and required seating stress. This prevents a mismatch between flange geometry and gasket sealing range.
Bolt loading and assembly
Even a correctly machined flange can leak if bolt load is uneven. A good assembly procedure defines bolt grade, nut grade, washer use, lubricant, tightening pattern, torque or tensioning method, and final verification. For larger sizes, hydraulic tensioning or controlled torque may be required.
- Check that flanges are parallel before installing the gasket.
- Clean sealing surfaces and bolt threads.
- Use the specified lubricant and tightening sequence.
- Increase load in multiple passes instead of one full-torque pass.
- Do not use flange bolts to force severe pipe misalignment.
Manufacturing controls for sealing faces
SongHai controls sealing performance through CNC machining, facing roughness inspection, flatness checks, bolt-hole position measurement, and protective packing. For RTJ flanges, groove angle, depth, width, radius, and surface finish should be inspected. For raised face flanges, raised-face height, finish pattern, and gasket contact width should be confirmed.
الأسئلة الشائعة
What information should be given for flange sealing surface quotation?
Provide standard, size, pressure class, material, facing type, gasket type, surface finish requirement, bolt standard, operating conditions, and inspection requirements.
Is a smooth flange face always better?
No. Many gasket materials need a controlled serrated finish to grip and seal correctly. The best finish depends on gasket design and service conditions.
Can SongHai machine RTJ flanges?
Yes. SongHai can manufacture RTJ flanges and project-specific sealing grooves according to drawings and applicable standards.
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