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Matching fitting standards
DN50 and 2 inch are not the same thing, and a line with mixed standards is a maintenance problem waiting several years to appear.
Pipe and fitting dimensions are set by standards that developed separately: ANSI and ASTM in North America, DIN in Germany, JIS in Japan, BS in the UK, GB in China, with ISO alongside and SH and HG covering specific Chinese process industries. A nominal size in one is not a nominal size in another.
DN50 and 2 inch are the classic example. They describe roughly the same bore and different outside diameters, flange drillings and sealing faces, which means a fitting from one system may bolt up to the other without actually sealing properly.
Mixed standards work until something has to be replaced. The line runs for years, then a valve fails, and the replacement in the local system does not fit the component installed by whoever was cheapest when the plant was built. At that point the maintenance team is fabricating an adapter under time pressure.
The preventive measure is to state the standard on every enquiry, not just the size. A supplier who covers several standards can match the plant; one who covers one will quietly supply their own and leave the mismatch for later.
Specifications
| Standards | ANSI, ASTM, DIN, JIS, BS, ISO, GB, SH, HG |
|---|---|
| DN50 and 2 inch | Similar bore, different flange and face |
| Mixing | Works until a replacement is needed |
| Always state | The standard, not just the size |
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