Can a Quartz Tube Withstand 10 MPa Pressure? (Part 1 of 6)

Customer Background

The customer requires a customized quartz tube with high precision (inner diameter 7.75 mm ± tolerance to be confirmed), high pressure resistance (10 MPa), and high temperature resistance (500 °C). The tube will be used to contain high-pressure CO₂ fluid (approximately 10 MPa). They are inquiring whether a suitable customized solution can be provided.

1. Analysis of Quartz Tube Pressure Resistance

The pressure resistance of a quartz tube (fused silica) depends on several factors, including:

Material purity (higher purity quartz has greater strength)
Wall thickness (thicker walls offer higher pressure resistance)
Manufacturing process (seamless tube vs. welded tube)
Temperature effects (high temperatures reduce mechanical strength)

Typical pressure resistance range for quartz tubes:

Standard commercial quartz tubes (wall thickness 1–2 mm): typically withstand 1–3 MPa (10–30 bar) static pressure.
High-pressure quartz tubes (wall thickness 3–5 mm, special annealing process): can withstand 5–10 MPa or more (custom production required).

A pressure of 10 MPa (~100 bar) is considered high pressure. Standard quartz tubes cannot usually meet this requirement directly — thick-walled or specially reinforced tubes are necessary.

2. Key Considerations for 10 MPa Applications

(1) Wall Thickness Calculation (Estimation)
Using the thin-walled cylindrical pressure vessel formula:

σ: tensile strength of quartz (~50 MPa, decreases at high temperature)
P: internal pressure (10 MPa)
r: inner radius (7.75 mm → radius 3.875 mm)
t: required minimum wall thickness

In practice, the following must be considered:

Safety factor (at least 3–5×, recommended wall thickness ≥3 mm)
High-temperature strength reduction (at 500 °C, strength may decrease by 30–50%)

Conclusion:
A high-purity quartz tube with wall thickness of at least 3–5 mm is needed to safely withstand 10 MPa pressure.

(2) Other Critical Factors

End sealing: High pressure requires special flanges or metal encapsulation to prevent port cracking.
Surface defects: Microcracks or bubbles significantly reduce pressure resistance — optical-grade defect-free quartz is required.
Cyclic pressure testing: If the experiment involves pressure fluctuations, fatigue life assessment is necessary.

3. Recommended Solutions

(1) Custom High-Pressure Quartz Tube

Material: High-purity fused silica (SiO₂ > 99.99%) to minimize impurity-related weakening.
Wall thickness: Recommended ≥3 mm (outer diameter ≈14–15 mm).
Manufacturing process:
- Seamless drawing (avoid welded weak points)
- Annealing (eliminate internal stress)
- Surface polishing (reduce microcracks)

(2) Alternative Solutions

Quartz + metal composite tube: Inner quartz layer (corrosion resistance), outer stainless steel layer (pressure bearing), but may affect IR transmission.
Sapphire tube: Much higher pressure resistance (up to 100 MPa), but cost is extremely high (~10× quartz).

(3) Supplier Communication Points

Clearly specify working conditions: “10 MPa static pressure + 500 °C high temperature”
Request pressure test report (e.g., burst pressure ≥30 MPa)
Confirm end treatment method (threaded, flanged, or O-ring seal)

4. Application Considerations

High-pressure CO₂ fluid: Ensure no chemical reaction between quartz and CO₂ (generally safe).
ITO heater compatibility: The 9.53 mm OD heater must be adapted to the thicker quartz tube (custom OD ≈14–15 mm).
Safety protection: Install safety valves and blast shields to prevent injury from tube rupture.

Conclusion

A standard quartz tube (wall thickness 1–2 mm) cannot meet the 10 MPa high-pressure requirement.

A custom high-pressure quartz tube is required with:

Wall thickness ≥3 mm (outer diameter ≈14–15 mm)
High-purity seamless fused silica
Pressure test certification

It is recommended to contact a specialized quartz manufacturer and specify detailed technical requirements.