Product Overview
Borosilicate sight glass is an engineered glass product (SiO₂–B₂O₃-based). The design allows for direct visual monitoring of process fluids. It is available in three primary formats:
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Rectangular / Long-strip sight glass — flat panels for plate-type sight windows and level gauge plates.
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Round sight glass — circular discs for flanged sight ports and inspection covers.
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Tube sight glass — precision tubes for tube-style level gauges and sight columns.
Common alias: borosilicate gauge glass, sight glass tube, flat sight window, round sight disc.
Key Technical Advantages
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High thermal stability: continuous operating temperature of up to 450 °C, short-term exposure of up to 500 °C.
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Low thermal expansion: ~3.3 × 10⁻⁶ /K, reducing thermal stress and cracking risks.
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Good chemical resistance: resistant to most acids/alkalis (except hydrofluoric acid).
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High optical clarity: visible transmittance > 90%, refractive index ≈ 1.47.
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Reliable mechanical performance: typical bending strength range 40–100 MPa (application dependent).
Material Properties & Specifications (real-world industry values)
| Property | Typical Value |
|---|---|
| Material | Borosilicate glass (e.g., Borosilicate 3.3 family) |
| Density | 2.23 g/cm³ |
| Softening Point | ~820 °C |
| Continuous Working Temp | ≤ 450 °C |
| Short-term Temp | ≤ 500 °C |
| Coefficient of Thermal Expansion | ~3.3 × 10⁻⁶ /K |
| Refractive Index (nD) | ~1.47 |
| Visible Light Transmittance | > 90% |
| Typical Bending Strength | 40 – 100 MPa (depends on annealing & finish) |
📥 Download Technical Datasheet (PDF)
Common Sizes & Typical Thicknesses (realistic, ready-for-order)
Rectangular (Long-strip / Plate) — typical use in flat sight windows and level gauges
| Thickness (mm) | Width (mm) | Length (mm) | Typical use |
|---|---|---|---|
| 5 | 30 | 140 / 165 / 190 | Light-duty indicators |
| 8 | 30 | 220 / 250 | Standard level gauges |
| 10 | 34 | 280 / 320 | Medium-duty / higher pressure |
| 12 | 34 | 340 / 370 | Boiler sight windows |
| 15 | 34 | 400 / 500 | Larger panels / high durability |
Round sight discs
| Diameter (mm) | Thickness (mm) | Typical use |
|---|---|---|
| Ø50 | 8 / 10 | Small flanged ports |
| Ø80 | 10 / 12 | Standard sight windows |
| Ø100 | 12 / 15 | Medium vessels |
| Ø150 | 15 / 19 | Large inspection ports |
| Ø200 | 19 / 25 | Heavy-duty applications |
Tube sight glass (Quartz alternative is common for extreme temp—borosilicate used widely in gauge tubes)
| Outer Diameter (mm) | Wall Thickness (mm) | Typical length (mm) |
|---|---|---|
| Ø10 | 1.5 / 2.0 | 150 / 200 / 250 |
| Ø16 | 1.5 / 2.5 | 200 / 300 / 400 |
| Ø20 | 2.0 / 3.0 | 200 / 500 / 1000 |
| Ø25 | 2.5 / 3.5 | 300 / 500 / 1500 |
| Ø30 | 3.0 / 4.0 | 300 / 2000 |
Custom sizes, drilled holes, chamfered or lapped edges, and through-holes available on request.
Applications & Use Cases
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Industrial boilers & steam drums — reliable water-level indication where thermal cycling occurs.
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Chemical reactors & process vessels — direct visual inspection of liquids and phase boundaries.
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Petrochemical and refinery units — corrosion-resistant windows for hydrocarbon service (note HF exceptions).
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Food & beverage / pharmaceutical — sanitary viewing windows when combined with suitable gasket materials.
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Water & wastewater treatment — visual monitoring of clarifiers, clarifiers and dosing tanks.
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Power generation & utilities — feedwater tanks, deaerators, and condensate systems.
Selection Guidance
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Choose material & thickness by application: for continuous service ≤450 °C and moderate pressure, borosilicate 5–12 mm is typical; for higher mechanical load choose 12–25 mm and confirm frame rating.
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Size vs. pressure trade-off: larger plate/diameter at the same thickness reduces allowable pressure — verify with frame/gasket vendor or request our engineering check.
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Tube selection: pick OD and wall thickness based on measured pressure and length — long unsupported tubes require thicker walls or protective housings.
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Sealing material: use mica, graphite, or PTFE gaskets compatible with your medium and temperature; we supply recommended gasket options.
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Replacement orders: provide exact dimensions, thickness, edge finish, and any hole/slot drawings to ensure drop-in compatibility.
Pressure & Temperature Reference (engineering guidance)
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Temperature: continuous ≤ 450 °C; short-term spikes up to 500 °C may be tolerated depending on configuration.
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Pressure: allowable working pressure is a function of thickness, unsupported span, and mounting flange design. For example, a flat borosilicate plate 10 mm thick in a standard 34 mm-wide plate frame is typically used up to low–medium pressures (consult datasheet and frame supplier). For precise rating, submit drawing/specs for engineering confirmation.
Quality Assurance & E-E-A-T
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Expertise: over 12 years supplying sight glass components to OEMs and power plants.
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Experience: supplied >10,000 sight glass panels and tubes to petrochemical and power clients worldwide.
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Authority: manufacturing under ISO 9001 processes; optical and mechanical inspections performed in-house (flatness, visual clarity, stress birefringence, dimensional).
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Trust: batch traceability, material certificates, and optional 3rd-party testing (pressure/thermal shock) available on request.
Installation & Maintenance Notes
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Install with new gaskets and follow bolt-torque patterns to avoid point loads.
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Avoid iron filings/magnetic debris near tube assemblies.
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Clean with non-abrasive agents; avoid HF-based cleaners.
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Inspect periodically for scratches, pits, or opacity; replace on any damage.
Ordering & Lead Time
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Minimum order: small quantities accepted; discounts for volume purchases.
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Typical lead time: 7–21 business days depending on customization and quantity (confirm at RFQ).
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How to order: supply part drawing or select size from the size sheet and state: material, thickness, finish, quantity, and delivery port.
Downloadable Resources
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Technical Datasheet (PDF):
borosilicate-sight-glass-datasheet.pdf
Why Buy From Us
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Direct industrial supplier with engineering support for selection and replacement.
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Consistent batch quality and delivery for OEM & MRO customers.
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Customization: edge finishes, drilled holes, polished faces, and protective sleeves.
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On-demand testing and certificates (material certificate, visual inspection reports, optional pressure/thermal shock tests).
Contact & Quotation
Email: info@hsahglass.com
WhatsApp: 8618632879676
Website: www.hsahglass.com
To get an accurate quote please provide: product format (rectangular / round / tube), dimensions (thickness × width × length or OD × wall × length), working temperature, working pressure, medium type, quantity, and desired delivery date.
