High-Pressure Quartz Tube Sealing Guide

Technical Guide for Sealing Quartz Tubes in High-Pressure Conditions (≥10MPa)
Selection, Installation & Verification Procedures for Quartz, Alumina, and Sapphire Tubes

1. Seal Type Comparison Table

Seal Type	Max Pressure	Temp Range	Reusable	Tube Diameter Range	Recommended Use Case
Metal Flange + Conical Seal	≤30 MPa	-200 ~ 500 °C	✓	5–100 mm	High-pressure reactors requiring frequent access
Glass Fusion Seal	≤15 MPa	≤450 °C	✗	3–50 mm	Permanent sensor encapsulation
Hydraulic Cold Compression	≤100 MPa	-273 ~ 1000 °C	✗	3–20 mm (thick wall)	Extreme pressure/cryogenic applications
Metallized Brazing	≤50 MPa	≤1000 °C	✗	3–20 mm	Aerospace and defense-grade reliability

2. Metal Flange with Conical Seal (Recommended Method)

1. Required Components

• Flange Material: Inconel 718 (corrosion-resistant nickel alloy)
• Seal Gasket: Annealed copper (1 mm thick, HV50 hardness)
• Conical Angle: 20° ± 0.5° (must match tube precision-ground taper)

2. Installation Procedure

① Preparation

• Flame polish quartz tube ends to eliminate microcracks
• Mirror-polish flange taper surface (Ra ≤ 0.8 μm)

② Assembly

1. Place the copper gasket on the flange cone
2. Apply high-temp vacuum grease (e.g., Apiezon N) to the tube’s taper
3. Tighten bolts progressively using a hydraulic torque wrench

Bolt Torque Schedule (for M6 bolts):

Stage	Torque (N·m)	Dwell Time
Preload	10	5 min
Mid	20	10 min
Final	30	30 min

3. Leak Testing Criteria

• Helium Leak Rate: ≤ 1×10⁻⁸ mbar·L/s
• Pressure Hold Test: 15 MPa for 1 hour, pressure drop <1%

3. Safety Precautions

1. Explosion Protection

• 6 mm polycarbonate blast shield around the tube (with IR camera window optional)
• Install mechanical pressure relief valve (setpoint = 12 MPa)

2. Operational Guidelines

Do Not:

• ✗ Rapid pressurization (use ≤ 1 MPa/min pressure ramp)
• ✗ Overpressure at ambient temperature (preheat to ≥ 100 °C before pressurizing)

4. Failure Case Studies

Case 1: Flange Seal Leak (POSTECH Case)

• Issue: Helium leak rate surged at 8 MPa
• Root Cause: Gasket was not annealed; high hardness prevented proper deformation
• Solution: Switched to HV50 soft copper; leak reduced by 100×

Case 2: Tube Fracture (NIMS Japan Lab)

• Issue: Longitudinal cracking at 12 MPa
• Root Cause: Subsurface flaw from laser cutting went undetected
• Improvement: Supplier now must provide fluorescent penetrant inspection report

5. Technical Support

Quartz Tube Supplier | Customizable Tubes & Heaters | GlobalQT
For further consultation based on specific test parameters (e.g., CO₂ phase, ramp rate, etc.), please бидэнтэй холбоо барина уу.

This document should be revised by the experimenter based on specific experimental parameters (e.g., CO₂ phase state, heating rate, etc.).