can impact test requirement depend only on thickness or design temperature also essential
Impact testing requirement is depends on MDMT of material used for construction or fabrication.
For carbon steels CVN is required when the MDMT lower than -28 C
For low temp carbon steels -46 C
Yes, design engineer will determine Minimum Design Metal Temperatture (MDMT).
Also see ASME B31.3 Para. 323.2 Temperature limitations