There's no material specified for that elbow (other than "steel") and I'm wondering why such an odd-size fitting was created when standard sizes exist.
I seem to recall seeing a 5" connection once on a European-sourced compressor and of course metric DIN and JIS sizes, but like LittleInch, never 7" in petrochem, cryo, pulp and paper or chem.
Maybe the greenhouse industry is somehow special and they need oddball pipe sizes...
Piping Design Central