What is an RTJ flange
author: www.qishine.com
2026-04-08
An RTJ (Ring Type Joint) flange is a type of flange sealing design specifically used for high-pressure, high-temperature, or flammable/explosive media.
Key features:
1. Different sealing principle:
- Ordinary flanges (e.g., Raised Face RF) rely on bolting down a flat gasket to seal.
- An RTJ flange has a precision-machined groove on its face. During assembly, an oval or octagonal metal ring gasket is placed into the groove. When bolts are tightened, the flange groove "bites" into the metal ring gasket, achieving a line-contact seal through slight metal deformation. The higher the pressure, the tighter the seal becomes.
1. Different sealing principle:
- Ordinary flanges (e.g., Raised Face RF) rely on bolting down a flat gasket to seal.
- An RTJ flange has a precision-machined groove on its face. During assembly, an oval or octagonal metal ring gasket is placed into the groove. When bolts are tightened, the flange groove "bites" into the metal ring gasket, achieving a line-contact seal through slight metal deformation. The higher the pressure, the tighter the seal becomes.
Ring Type Joint Flange vs Raise Face Flange
2. Main advantages:
- High-pressure resistance: Commonly used from Class 600 (PN110) to Class 2500 (PN420) and even higher.
- High-temperature resistance: Metal ring gaskets withstand higher temperatures than non-metallic gaskets.
- Reliable sealing: Extremely low leakage rate, ideal for natural gas, hydrogen, toxic, or high-temperature steam pipelines.
- High-pressure resistance: Commonly used from Class 600 (PN110) to Class 2500 (PN420) and even higher.
- High-temperature resistance: Metal ring gaskets withstand higher temperatures than non-metallic gaskets.
- Reliable sealing: Extremely low leakage rate, ideal for natural gas, hydrogen, toxic, or high-temperature steam pipelines.
3. Disadvantages:
- High cost: The flange itself requires high machining precision, and metal ring gaskets are expensive (non-reusable).
- Strict installation requirements: High bolt preload is needed, and the groove must not be damaged, as it is difficult to repair.
- High cost: The flange itself requires high machining precision, and metal ring gaskets are expensive (non-reusable).
- Strict installation requirements: High bolt preload is needed, and the groove must not be damaged, as it is difficult to repair.
4. How to identify:
- Look at the flange sealing face: It is not flat but has a circular trapezoidal groove.
- Look at the gasket: A metal ring is used, not a flat gasket.
- Look at the flange sealing face: It is not flat but has a circular trapezoidal groove.
- Look at the gasket: A metal ring is used, not a flat gasket.
How do you install an RTJ Flange ?
How do you install an RTJ flange?
1. Preparation and cleaning
- Inspect: Carefully check the flange ring groove for scratches, dents, rust, or other defects.
- Clean: Ensure no foreign matter remains in the ring groove.
- Inspect: Carefully check the flange ring groove for scratches, dents, rust, or other defects.
- Clean: Ensure no foreign matter remains in the ring groove.
2. Metal ring gasket selection and placement
- Use a new gasket: Metal ring gaskets must never be reused because they undergo permanent deformation after installation.
- Material matching: The ring gasket material should be softer than the flange material.
- Place into the groove: Gently lower the metal ring gasket into the flange ring groove, ensuring it is centered, level, and not caught on the groove edge.
- Use a new gasket: Metal ring gaskets must never be reused because they undergo permanent deformation after installation.
- Material matching: The ring gasket material should be softer than the flange material.
- Place into the groove: Gently lower the metal ring gasket into the flange ring groove, ensuring it is centered, level, and not caught on the groove edge.
3. Flange alignment
- Bring the two flanges together carefully without knocking the ring gasket out of place.
- Allowable misalignment: Parallelism deviation ≤ 1.5 mm, bolt hole misalignment ≤ 3 mm. Never use bolts to forcibly pull severely misaligned flanges into alignment.
- Bring the two flanges together carefully without knocking the ring gasket out of place.
- Allowable misalignment: Parallelism deviation ≤ 1.5 mm, bolt hole misalignment ≤ 3 mm. Never use bolts to forcibly pull severely misaligned flanges into alignment.
4. Bolt and nut preparation
- Lubrication: Bolt threads, nut bearing surfaces, and washers must be coated with high-temperature anti-seize lubricant (e.g., molybdenum disulfide, graphite paste). Dry tightening is wrong — it can waste over 70% of torque on friction, resulting in insufficient clamping force.
- Inspection: Bolts and nuts should be free of damage, with intact threads.
- Lubrication: Bolt threads, nut bearing surfaces, and washers must be coated with high-temperature anti-seize lubricant (e.g., molybdenum disulfide, graphite paste). Dry tightening is wrong — it can waste over 70% of torque on friction, resulting in insufficient clamping force.
- Inspection: Bolts and nuts should be free of damage, with intact threads.
5. Stepwise, symmetrical tightening (most critical step)
Use a calibrated torque wrench or hydraulic torque wrench. Tighten in stages and in the correct sequence:
Use a calibrated torque wrench or hydraulic torque wrench. Tighten in stages and in the correct sequence:
| Pass | Torque value | Tightening sequence |
| 1st pass | 30% of final torque | Cross pattern |
| 2nd pass | 60% of final torque | Cross pattern |
| 3rd pass | 100% of final torque | Cross pattern |
| Final supplement | 100% of final torque | Clockwise (circumferential) pattern |
Torquing Sequence
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Website: www.qishine.com
Email: qishine@qishine.com
Tel: 0592-5225595
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+86 15985833169
Website: www.qishine.com
Email: qishine@qishine.com
Tel: 0592-5225595
WhatsApp: +86 15960259563
+86 15985833169
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