LUMIGLAS® Type 76 Fused Sight Glass — Metal-Fused Borosilicate Disc for Welding Neck Flanges (DIN 28121)
LUMIGLAS® Type 76 is a metal-fused borosilicate sight glass disc manufactured to DIN 7079 for welding neck flange assemblies to DIN 28121 — also compatible with welding neck flanges with flat or raised faces. Rated −60°C to +300°C, 16 and 40 bar standard pressure classes. Ring materials: S355J2+N, Duplex SS (1.4462), Hastelloy C-22, C-276 and C-4. Direct drop-in replacement for conventional glass discs — no housing modification required.
Description
The LUMIGLAS® Type 76 fused sight glass is a metal-fused borosilicate observation disc. Specifically, Lumiglas manufactures it to DIN 7079 and DIN 7080, engineering it perfectly for welding neck flange assemblies to DIN 28121. During production, Lumistar heats the borosilicate glass insert and the metal ring together until the glass flows against the ring surface. Afterward, the assembly undergoes a controlled precision cooling phase. Consequently, this process holds the glass insert in permanent compressive stress. Ultimately, this mechanical prestress gives the Type 76 its defining safety advantage over conventional thermally toughened sight glass discs.
Therefore, engineers specify the Type 76 as a direct replacement for conventional glass discs in DIN 28121 circular sight ports and welding neck flanges with flat or raised faces. Importantly, you do not require any housing modification — the Type 76 fits as a seamless drop-in replacement. Furthermore, standard pressure ratings of 16 bar and 40 bar cover the vast majority of welding neck flange applications across the chemical, petrochemical, pharmaceutical, and power generation industries.
📋 Installation & Maintenance Manual (PDF)
📐 Selection Guide — Ring Material & Pressure Rating Reference (PDF)
Technical Specifications — LUMIGLAS® Type 76 Fused Sight Glass
| Parameter | Value / Standard |
|---|---|
| Product Type | Type 76 Fused (Metal-Fused) Sight Glass Disc for Welding Neck Flanges |
| Glass Material | Specifically, borosilicate glass fused to metal ring per DIN 7079; base glass per DIN 7080 |
| Operating Temperature | Generally, −60°C to +300°C (ring material dependent) |
| Operating Pressure | Indeed, up to 40 bar (standard) · We provide higher pressures on request |
| Primary Assembly Standard | DIN 28121 circular sight ports · Welding neck flanges with flat or raised faces |
| Ring Materials | S355J2+N (Carbon Steel) · Duplex SS (1.4462) · Hastelloy C-22 (2.4602) · Hastelloy C-276 (2.4605) · Hastelloy C-4 (2.4610) |
| Pressure Equipment Directive | PED 2014/68/EU, Module H/H1 (DIN/EN/ISO 9001) |
| AD Standards | AD-Merkblatt W0/TRD 100 |
| Material Certificates | Furthermore, we supply EN 10204-3.1 or 3.2 Certificate of Conformity as standard |
Ring Materials & Operating Temperature
Fundamentally, the metal ring serves as the primary pressure-bearing component. Therefore, you must select it based on the minimum operating temperature and process medium chemical compatibility. Additionally, please consult Lumistar if the correct material remains uncertain.
| Ring Material | Min. Temp. | Max. Temp. | Typical Application |
|---|---|---|---|
| S355J2+N (Carbon Steel) | −10°C | +300°C | First, General industrial, pressure vessels, boilers |
| Duplex Stainless Steel (1.4462) | −30°C | +280°C | Next, Corrosive service, offshore, chemical processing |
| Hastelloy C-22 (2.4602) | −60°C | +300°C | Furthermore, Aggressive acids, oxidising media, pharmaceutical |
| Hastelloy C-276 (2.4605) | −60°C | +300°C | Additionally, Chloride-rich, halogenated, severe environments |
| Hastelloy C-4 (2.4610) | −60°C | +300°C | Finally, High-temperature corrosive environments |
Standard Dimensions & Pressure Ratings — DIN 28121 Welding Neck Flange
Typically, d1 = outer diameter (mm) · d2 = inner/viewing diameter (mm) · S = required glass thickness (mm) at rated pressure · * indicates approved dimensions
| Nominal Size | 16 bar | 40 bar | ||||
|---|---|---|---|---|---|---|
| d1 | d2 | S | d1 | d2 | S | |
| 25 | 70 | 30 | 10 | 70* | 30 | 15 |
| 32 | 82 | 40 | 12 | 82 | 40 | 15 |
| 40 | 92 | 45 | 15 | 92 | 45 | 20 |
| 50 | 107 | 50 | 15 | 107 | 50 | 20 |
| 65 | 127 | 70 | 15 | 127 | 70 | 25 |
| 80 | 142 | 75 | 20 | 142 | 75 | 25 |
| 100 | 162 | 80 | 20 | 162* | 80 | 25 |
| 125 | 192 | 100 | 20 | 192* | 100 | 30 |
| 150 | 218 | 100 | 25 | 218* | 100 | 35 |
| 200 | 273 | 120 | 30 | 273* | 120 | 40 |
* Specifically, this symbol indicates approved dimensions per applicable approval documentation. Non-standard dimensions and higher pressure ratings remain available on request — simply provide d1, d2, operating pressure and ring material when enquiring.
Why Specify a Type 76 Fused Sight Glass for Welding Neck Flanges?
Generally, conventional thermally toughened sight glass discs can fail suddenly and without warning under pressure surges, thermal cycling or mechanical impact. In contrast, the compressive prestress on the glass insert of the Type 76 ensures that any surface damage remains localised. Thus, it cannot propagate to catastrophic fracture. Indeed, this resilient property, unique to glass-fused-to-metal sight glasses per DIN 7079, makes the Type 76 the preferred specification wherever you require fail-safe visual access on welding neck flange assemblies.
Fail-Safe Performance
The compressive prestress structure effectively eliminates sudden, unexpected rupture — resolving the primary failure mode of conventional glass discs on welding neck flanges.
Over-Tightening Tolerant
High resistance to bending and uneven bolt torque offers simple, safe installation on welding neck flanges with flat or raised faces, completely eliminating the risk of breakage during fitting.
Reusable
Unlike conventional glass discs, operators can remove, clean and refit the Type 76 in the same housing or relocate it to any compatible DIN 28121 assembly — drastically reducing total cost of ownership.
Wide Industry Acceptance
Extreme resistance to impact, pressure and temperature means European and American chemical, petrochemical and process industries widely adopt this design.
Compatible Assemblies & Typical Applications
Therefore, the LUMIGLAS® Type 76 fused sight glass fits directly into the following assemblies as a drop-in replacement for conventional glass discs. Crucially, you do not require any housing modification for any standard DIN 28121 assembly.
- ▸First, DIN 28121 circular sight ports — serves as a direct drop-in replacement fused sight glass disc for welding neck flange circular sight port assemblies.
- ▸Furthermore, Welding neck flanges with flat or raised faces — stays compatible with any assembly sharing the exact d1/d2 dimensions of the standard DIN 28121 size series.
- ▸Additionally, Chemical process vessels and reactors — excels wherever operators must reliably prevent glass rupture on a pressure-bearing vessel.
- ▸Moreover, High-pressure reactors, filtration and mixing vessels — ideal for applications requiring a durable, fail-safe sight window at 16 or 40 bar service pressure.
- ▸Finally, Vacuum & pressure coating systems, pilot plants and laboratory vessels — shines wherever plant safety dictates a reusable sight window with superior safety performance over conventional flat glass.
Technical Documents & Downloads
📄 Technical Datasheet
Full specifications, dimensional table (16 bar & 40 bar), ring material reference and approvals — DIN 7079 / DIN 28121.
📋 Installation & Maintenance Manual
Installation procedure, damage factor analysis, inspection schedule and replacement instructions per DIN 7079.
📐 Selection Guide
6-step selection process, ring material chemical compatibility matrix, pressure/temperature envelope and DIN 28121 dimensional reference.
Frequently Asked Questions
Request a Quote — LUMIGLAS® Type 76 Fused Sight Glass
All nominal sizes DN25–DN200 · All ring materials · DIN 28121 · EN 10204-3.1 cert · OEM & project volumes welcome
