The 81-Type Fused Sight Glass is a high-strength metal-fused borosilicate sight glass disc designed specifically for DIN 11851 threaded sight glass fittings. It features a permanently integrated glass-to-metal construction, making it suitable for visual inspection in compatible pipe connections and industrial process equipment.

During manufacturing, the borosilicate glass and metal ring are heated together under controlled conditions. The glass fuses to the metal ring and is subsequently cooled through a controlled process, creating a compressive stress structure within the glass. This construction helps improve resistance to mechanical stress and thermal shock compared with conventional loose glass discs when correctly selected and installed.

The Type 81 is designed for use with DIN 11851 screwed pipe fittings. Its compact design supports straightforward installation in compatible threaded sight glass assemblies, while the glass surface provides a clear viewing area for observing products and process conditions inside the pipeline or connected equipment.

The sight glass is manufactured using borosilicate glass in accordance with DIN 7080 and the applicable DIN 7079 glass-to-metal fusion design. Operating pressure and temperature depend on the nominal size, metal ring material, and installation conditions. Reference configurations are available with maximum allowable pressures up to 40 bar, while higher-pressure requirements should be evaluated separately.

Available metal ring materials include Duplex stainless steel 1.4462 and selected nickel-based alloys, such as Hastelloy C-22, C-276, C-4, and other suitable grades, depending on the required specification. Reference operating temperature ranges vary by material, from approximately -30°C to +280°C for Duplex stainless steel 1.4462, with selected nickel-based alloy configurations covering lower temperatures down to -80°C and upper temperatures up to +300°C.