Pipe in Pipe is the technology that include an inner pipe + insulation + carrier outer pipe.
Inner pipe is for pressure containement and fluid transportation, while insulation and outer pipe are used to reduce heat exchanges for deep water application.
As far as i know, PiP maximum size is 14"OD x 18" OD.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
I've never heard anyone just call it "Pipe in Pipe" in industry, but okay.
One of the main things you need to look at are elbows or changes in direction. For example, while a 4" straight pipe fits nicely inside a 6" straight pipe, a 4" 90 does not fit inside a 6" 90.
If you're trying to provide secondary containment for a large OD pipe, double wall piping probably isn't the most cost effective solution.