DIN 28120 and DIN 28121: construction and connection differences
How weld-in fittings differ from constructions with a load path bypassing the glass, and why replacing one type with the other requires verification.
Short answer
DIN 28120 is a fitting that carries the load through the glass element and is welded into the wall; DIN 28121 carries the effort bypassing the glass (force shunt) and is bolted onto a prepared flange. The types are not interchangeable without verifying the connection.
The comparison is based on standard overviews and manufacturer explanations; the specific version, PN and temperatures are confirmed by the product manufacturer.
Comparison table
| Feature | DIN 28120 | DIN 28121 |
|---|---|---|
| Load path | through the glass element (force-fit) | bypassing the glass plate (force shunt) |
| Mounting | welded into the vessel wall | bolted onto a prepared flange |
| Disc replacement | requires careful disassembly of the pack | without dismantling the load frame |
| Typical use | reactors, jacketed apparatus | vessels with flanged connections, hygienic tasks |
| Replacing one type with the other | not allowed without verifying the vessel construction | not allowed without verifying the flange |
Selection algorithm
Determine what already exists on the vessel: a prepared opening for welding, or a finished flange.
- a flange exists → consider DIN 28121 after verifying dimensions and PN;
- a new penetration is needed → DIN 28120 per the manufacturer documentation;
- doubts about the connection → record the actual dimensions in the RFQ sheet.
Typical mistakes
Three mistakes occur most often:
- substituting the view diameter for DN;
- transferring glass characteristics to the whole assembly;
- mounting a DIN 28121 fitting on a flange without verifying the sealing surface.